diff --git a/RELEASES.md b/RELEASES.md
index 2e9a14e5..ae226bae 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -7,12 +7,26 @@ Version 0.19.9
 This version removes the confusing differences between _packages_ and _modules_
 by unifying the terminology and API under the global umbrella of _modules_.
 
+Bug fixes
+---------
+
+* Property access in 
+
 Breaking changes
 ----------------
 
 * `Engine::load_package` is renamed `Engine::register_global_module` and now must explicitly pass a shared [`Module`].
 * `Engine::register_module` is renamed `Engine::register_static_module` and now must explicitly pass a shared [`Module`].
 * `Package::get` is renamed `Package::as_shared_module`.
+* `Engine::set_module_resolver` now takes a straight module resolver instead of an `Option`. To disable module resolving, use the new `DummyModuleResolver`.
+
+Enhancements
+------------
+
+* `Scope` is now `Clone + Hash`.
+* `Engine::register_static_module` now supports sub-module paths (e.g. `foo::bar::baz`).
+* `Engine::register_custom_operator` now accepts reserved symbols.
+* `Engine::register_custom_operator` now returns an error if given a precedence of zero.
 
 
 Version 0.19.8
diff --git a/codegen/src/attrs.rs b/codegen/src/attrs.rs
index a7986b6b..bd2272a4 100644
--- a/codegen/src/attrs.rs
+++ b/codegen/src/attrs.rs
@@ -3,7 +3,7 @@ use syn::{
     spanned::Spanned,
 };
 
-#[derive(Debug)]
+#[derive(Debug, Clone, Eq, PartialEq, Hash)]
 pub enum ExportScope {
     PubOnly,
     Prefix(String),
@@ -22,12 +22,14 @@ pub trait ExportedParams: Sized {
     fn from_info(info: ExportInfo) -> syn::Result<Self>;
 }
 
+#[derive(Debug, Clone)]
 pub struct AttrItem {
     pub key: proc_macro2::Ident,
     pub value: Option<syn::LitStr>,
     pub span: proc_macro2::Span,
 }
 
+#[derive(Debug, Clone)]
 pub struct ExportInfo {
     pub item_span: proc_macro2::Span,
     pub items: Vec<AttrItem>,
diff --git a/codegen/src/function.rs b/codegen/src/function.rs
index e84232c3..426f4edc 100644
--- a/codegen/src/function.rs
+++ b/codegen/src/function.rs
@@ -22,23 +22,30 @@ use crate::attrs::{ExportInfo, ExportScope, ExportedParams};
 
 #[derive(Clone, Debug, Eq, PartialEq, Copy, Hash)]
 pub enum FnNamespaceAccess {
+    Unset,
     Global,
     Internal,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+impl Default for FnNamespaceAccess {
+    fn default() -> Self {
+        Self::Unset
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq, Copy, Hash)]
 pub enum Index {
     Get,
     Set,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub enum Property {
     Get(syn::Ident),
     Set(syn::Ident),
 }
 
-#[derive(Clone, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq, Hash)]
 pub enum FnSpecialAccess {
     None,
     Index(Index),
@@ -97,11 +104,11 @@ pub(crate) fn print_type(ty: &syn::Type) -> String {
 
 #[derive(Debug, Default)]
 pub(crate) struct ExportedFnParams {
-    pub name: Option<Vec<String>>,
+    pub name: Vec<String>,
     pub return_raw: bool,
     pub skip: bool,
     pub special: FnSpecialAccess,
-    pub namespace: Option<FnNamespaceAccess>,
+    pub namespace: FnNamespaceAccess,
     pub span: Option<proc_macro2::Span>,
 }
 
@@ -138,7 +145,7 @@ impl ExportedParams for ExportedFnParams {
         let mut name = Vec::new();
         let mut return_raw = false;
         let mut skip = false;
-        let mut namespace = None;
+        let mut namespace = FnNamespaceAccess::Unset;
         let mut special = FnSpecialAccess::None;
         for attr in attrs {
             let crate::attrs::AttrItem {
@@ -226,22 +233,16 @@ impl ExportedParams for ExportedFnParams {
                 ("global", Some(s)) | ("internal", Some(s)) => {
                     return Err(syn::Error::new(s.span(), "extraneous value"))
                 }
-                ("global", None) => {
-                    if let Some(ns) = namespace {
-                        if ns != FnNamespaceAccess::Global {
-                            return Err(syn::Error::new(key.span(), "conflicting namespace"));
-                        }
-                    }
-                    namespace = Some(FnNamespaceAccess::Global);
-                }
-                ("internal", None) => {
-                    if let Some(ns) = namespace {
-                        if ns != FnNamespaceAccess::Internal {
-                            return Err(syn::Error::new(key.span(), "conflicting namespace"));
-                        }
-                    }
-                    namespace = Some(FnNamespaceAccess::Internal);
-                }
+                ("global", None) => match namespace {
+                    FnNamespaceAccess::Unset => namespace = FnNamespaceAccess::Global,
+                    FnNamespaceAccess::Global => (),
+                    _ => return Err(syn::Error::new(key.span(), "conflicting namespace")),
+                },
+                ("internal", None) => match namespace {
+                    FnNamespaceAccess::Unset => namespace = FnNamespaceAccess::Internal,
+                    FnNamespaceAccess::Internal => (),
+                    _ => return Err(syn::Error::new(key.span(), "conflicting namespace")),
+                },
                 (attr, _) => {
                     return Err(syn::Error::new(
                         key.span(),
@@ -252,7 +253,7 @@ impl ExportedParams for ExportedFnParams {
         }
 
         Ok(ExportedFnParams {
-            name: if name.is_empty() { None } else { Some(name) },
+            name,
             return_raw,
             skip,
             special,
@@ -455,16 +456,12 @@ impl ExportedFn {
     }
 
     pub(crate) fn exported_names(&self) -> Vec<syn::LitStr> {
-        let mut literals = self
+        let mut literals: Vec<_> = self
             .params
             .name
-            .as_ref()
-            .map(|v| {
-                v.iter()
-                    .map(|s| syn::LitStr::new(s, proc_macro2::Span::call_site()))
-                    .collect()
-            })
-            .unwrap_or_else(|| Vec::new());
+            .iter()
+            .map(|s| syn::LitStr::new(s, proc_macro2::Span::call_site()))
+            .collect();
 
         if let Some((s, _, span)) = self.params.special.get_fn_name() {
             literals.push(syn::LitStr::new(&s, span));
@@ -481,11 +478,10 @@ impl ExportedFn {
     }
 
     pub(crate) fn exported_name<'n>(&'n self) -> Cow<'n, str> {
-        if let Some(ref name) = self.params.name {
-            name.last().unwrap().as_str().into()
-        } else {
-            self.signature.ident.to_string().into()
-        }
+        self.params.name.last().map_or_else(
+            || self.signature.ident.to_string().into(),
+            |s| s.as_str().into(),
+        )
     }
 
     pub(crate) fn arg_list(&self) -> impl Iterator<Item = &syn::FnArg> {
@@ -712,10 +708,12 @@ impl ExportedFn {
 
     pub fn generate_impl(&self, on_type_name: &str) -> proc_macro2::TokenStream {
         let sig_name = self.name().clone();
-        let name = self.params.name.as_ref().map_or_else(
-            || self.name().to_string(),
-            |names| names.last().unwrap().clone(),
-        );
+        let name = self
+            .params
+            .name
+            .last()
+            .cloned()
+            .unwrap_or_else(|| self.name().to_string());
 
         let arg_count = self.arg_count();
         let is_method_call = self.mutable_receiver();
diff --git a/codegen/src/lib.rs b/codegen/src/lib.rs
index ea341e1b..d71054a0 100644
--- a/codegen/src/lib.rs
+++ b/codegen/src/lib.rs
@@ -21,7 +21,7 @@
 //! let m = exported_module!(advanced_math);
 //! let mut r = StaticModuleResolver::new();
 //! r.insert("Math::Advanced", m);
-//! engine.set_module_resolver(Some(r));
+//! engine.set_module_resolver(r);
 //!
 //! assert_eq!(engine.eval::<FLOAT>(
 //!     r#"
@@ -51,7 +51,7 @@
 //! set_exported_fn!(m, "euclidean_distance", distance_function);
 //! let mut r = StaticModuleResolver::new();
 //! r.insert("Math::Advanced", m);
-//! engine.set_module_resolver(Some(r));
+//! engine.set_module_resolver(r);
 //!
 //! assert_eq!(engine.eval::<FLOAT>(
 //!     r#"
diff --git a/codegen/src/module.rs b/codegen/src/module.rs
index 283436ab..de6fbd28 100644
--- a/codegen/src/module.rs
+++ b/codegen/src/module.rs
@@ -19,9 +19,9 @@ use std::borrow::Cow;
 use crate::attrs::{AttrItem, ExportInfo, ExportScope, ExportedParams};
 use crate::function::ExportedFnParams;
 
-#[derive(Debug, Default)]
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Default)]
 pub(crate) struct ExportedModParams {
-    pub name: Option<String>,
+    pub name: String,
     skip: bool,
     pub scope: ExportScope,
 }
@@ -49,21 +49,32 @@ impl ExportedParams for ExportedModParams {
 
     fn from_info(info: ExportInfo) -> syn::Result<Self> {
         let ExportInfo { items: attrs, .. } = info;
-        let mut name = None;
+        let mut name = Default::default();
         let mut skip = false;
-        let mut scope = ExportScope::default();
+        let mut scope = None;
         for attr in attrs {
             let AttrItem { key, value, .. } = attr;
             match (key.to_string().as_ref(), value) {
-                ("name", Some(s)) => name = Some(s.value()),
+                ("name", Some(s)) => {
+                    let new_name = s.value();
+                    if name == new_name {
+                        return Err(syn::Error::new(key.span(), "conflicting name"));
+                    }
+                    name = new_name;
+                }
                 ("name", None) => return Err(syn::Error::new(key.span(), "requires value")),
+
                 ("skip", None) => skip = true,
                 ("skip", Some(s)) => return Err(syn::Error::new(s.span(), "extraneous value")),
-                ("export_prefix", Some(s)) => scope = ExportScope::Prefix(s.value()),
+
+                ("export_prefix", Some(_)) | ("export_all", None) if scope.is_some() => {
+                    return Err(syn::Error::new(key.span(), "duplicate export scope"));
+                }
+                ("export_prefix", Some(s)) => scope = Some(ExportScope::Prefix(s.value())),
                 ("export_prefix", None) => {
                     return Err(syn::Error::new(key.span(), "requires value"))
                 }
-                ("export_all", None) => scope = ExportScope::All,
+                ("export_all", None) => scope = Some(ExportScope::All),
                 ("export_all", Some(s)) => {
                     return Err(syn::Error::new(s.span(), "extraneous value"))
                 }
@@ -79,7 +90,7 @@ impl ExportedParams for ExportedModParams {
         Ok(ExportedModParams {
             name,
             skip,
-            scope,
+            scope: scope.unwrap_or_default(),
             ..Default::default()
         })
     }
@@ -87,7 +98,7 @@ impl ExportedParams for ExportedModParams {
 
 #[derive(Debug)]
 pub(crate) struct Module {
-    mod_all: Option<syn::ItemMod>,
+    mod_all: syn::ItemMod,
     fns: Vec<ExportedFn>,
     consts: Vec<ExportedConst>,
     submodules: Vec<Module>,
@@ -183,7 +194,7 @@ impl Parse for Module {
             fns = new_vec![];
         }
         Ok(Module {
-            mod_all: Some(mod_all),
+            mod_all,
             fns,
             consts,
             submodules,
@@ -194,39 +205,27 @@ impl Parse for Module {
 
 #[allow(dead_code)]
 impl Module {
-    pub fn attrs(&self) -> Option<&Vec<syn::Attribute>> {
-        self.mod_all.as_ref().map(|m| &m.attrs)
+    pub fn attrs(&self) -> &Vec<syn::Attribute> {
+        &self.mod_all.attrs
     }
 
-    pub fn module_name(&self) -> Option<&syn::Ident> {
-        self.mod_all.as_ref().map(|m| &m.ident)
+    pub fn module_name(&self) -> &syn::Ident {
+        &self.mod_all.ident
     }
 
-    pub fn exported_name(&self) -> Option<Cow<str>> {
-        if let Some(ref s) = self.params.name {
-            Some(s.into())
+    pub fn exported_name(&self) -> Cow<str> {
+        if !self.params.name.is_empty() {
+            self.params.name.as_str().into()
         } else {
-            self.module_name().map(|m| m.to_string().into())
+            self.module_name().to_string().into()
         }
     }
 
     pub fn update_scope(&mut self, parent_scope: &ExportScope) {
         let keep = match (self.params.skip, parent_scope) {
             (true, _) => false,
-            (_, ExportScope::PubOnly) => {
-                if let Some(ref mod_all) = self.mod_all {
-                    matches!(mod_all.vis, syn::Visibility::Public(_))
-                } else {
-                    false
-                }
-            }
-            (_, ExportScope::Prefix(s)) => {
-                if let Some(ref mod_all) = self.mod_all {
-                    mod_all.ident.to_string().starts_with(s)
-                } else {
-                    false
-                }
-            }
+            (_, ExportScope::PubOnly) => matches!(self.mod_all.vis, syn::Visibility::Public(_)),
+            (_, ExportScope::Prefix(s)) => self.mod_all.ident.to_string().starts_with(s),
             (_, ExportScope::All) => true,
         };
         self.params.skip = !keep;
@@ -249,14 +248,13 @@ impl Module {
 
         // Extract the current structure of the module.
         let Module {
-            mod_all,
+            mut mod_all,
             mut fns,
             consts,
             mut submodules,
             params,
             ..
         } = self;
-        let mut mod_all = mod_all.unwrap();
         let mod_name = mod_all.ident.clone();
         let (_, orig_content) = mod_all.content.take().unwrap();
         let mod_attrs = mem::take(&mut mod_all.attrs);
@@ -299,8 +297,8 @@ impl Module {
         }
     }
 
-    pub fn name(&self) -> Option<&syn::Ident> {
-        self.mod_all.as_ref().map(|m| &m.ident)
+    pub fn name(&self) -> &syn::Ident {
+        &self.mod_all.ident
     }
 
     pub fn consts(&self) -> &[ExportedConst] {
@@ -317,10 +315,10 @@ impl Module {
 
     pub fn content(&self) -> Option<&Vec<syn::Item>> {
         match self.mod_all {
-            Some(syn::ItemMod {
+            syn::ItemMod {
                 content: Some((_, ref vec)),
                 ..
-            }) => Some(vec),
+            } => Some(vec),
             _ => None,
         }
     }
diff --git a/codegen/src/register.rs b/codegen/src/register.rs
index 321769b7..515f13d1 100644
--- a/codegen/src/register.rs
+++ b/codegen/src/register.rs
@@ -18,6 +18,7 @@ pub(crate) fn generated_module_path(
 }
 
 type RegisterMacroInput = (syn::Expr, proc_macro2::TokenStream, syn::Path);
+
 pub fn parse_register_macro(
     args: proc_macro::TokenStream,
 ) -> Result<RegisterMacroInput, syn::Error> {
diff --git a/codegen/src/rhai_module.rs b/codegen/src/rhai_module.rs
index b1e26691..5d9c148f 100644
--- a/codegen/src/rhai_module.rs
+++ b/codegen/src/rhai_module.rs
@@ -40,15 +40,13 @@ pub(crate) fn generate_body(
         if itemmod.skipped() {
             continue;
         }
-        let module_name = itemmod.module_name().unwrap();
-        let exported_name: syn::LitStr = if let Some(name) = itemmod.exported_name() {
-            syn::LitStr::new(&name, proc_macro2::Span::call_site())
-        } else {
-            syn::LitStr::new(&module_name.to_string(), proc_macro2::Span::call_site())
-        };
+        let module_name = itemmod.module_name();
+        let exported_name: syn::LitStr = syn::LitStr::new(
+            itemmod.exported_name().as_ref(),
+            proc_macro2::Span::call_site(),
+        );
         let cfg_attrs: Vec<&syn::Attribute> = itemmod
             .attrs()
-            .unwrap()
             .iter()
             .filter(|&a| a.path.get_ident().map(|i| *i == "cfg").unwrap_or(false))
             .collect();
@@ -158,12 +156,14 @@ pub(crate) fn generate_body(
                 }
             }
 
-            if let Some(ns) = function.params().namespace {
-                namespace = ns;
+            match function.params().namespace {
+                FnNamespaceAccess::Unset => (),
+                ns => namespace = ns,
             }
 
             let ns_str = syn::Ident::new(
                 match namespace {
+                    FnNamespaceAccess::Unset => unreachable!(),
                     FnNamespaceAccess::Global => "Global",
                     FnNamespaceAccess::Internal => "Internal",
                 },
@@ -243,24 +243,24 @@ pub(crate) fn check_rename_collisions(fns: &Vec<ExportedFn>) -> Result<(), syn::
     let mut fn_defs = HashMap::<String, proc_macro2::Span>::new();
 
     for itemfn in fns.iter() {
-        if itemfn.params().name.is_some() || itemfn.params().special != FnSpecialAccess::None {
-            let mut names = itemfn
+        if !itemfn.params().name.is_empty() || itemfn.params().special != FnSpecialAccess::None {
+            let mut names: Vec<_> = itemfn
                 .params()
                 .name
-                .as_ref()
-                .map(|v| v.iter().map(|n| (n.clone(), n.clone())).collect())
-                .unwrap_or_else(|| Vec::new());
+                .iter()
+                .map(|n| (n.clone(), n.clone()))
+                .collect();
 
             if let Some((s, n, _)) = itemfn.params().special.get_fn_name() {
                 names.push((s, n));
             }
 
             for (name, fn_name) in names {
-                let current_span = itemfn.params().span.as_ref().unwrap();
+                let current_span = itemfn.params().span.unwrap();
                 let key = make_key(&name, itemfn);
-                if let Some(other_span) = renames.insert(key, *current_span) {
+                if let Some(other_span) = renames.insert(key, current_span) {
                     let mut err = syn::Error::new(
-                        *current_span,
+                        current_span,
                         format!("duplicate Rhai signature for '{}'", &fn_name),
                     );
                     err.combine(syn::Error::new(
diff --git a/codegen/tests/test_functions.rs b/codegen/tests/test_functions.rs
index 590ac6e9..303076e2 100644
--- a/codegen/tests/test_functions.rs
+++ b/codegen/tests/test_functions.rs
@@ -18,14 +18,11 @@ fn raw_fn_test() -> Result<(), Box<EvalAltResult>> {
     engine.register_fn("get_mystic_number", || 42 as FLOAT);
     let mut m = Module::new();
     rhai::set_exported_fn!(m, "euclidean_distance", raw_fn::distance_function);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
         engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let x = math::euclidean_distance(0.0, 1.0, 0.0, get_mystic_number()); x"#
+            r#"let x = Math::Advanced::euclidean_distance(0.0, 1.0, 0.0, get_mystic_number()); x"#
         )?,
         41.0
     );
@@ -48,16 +45,13 @@ fn raw_fn_mut_test() -> Result<(), Box<EvalAltResult>> {
     engine.register_fn("get_mystic_number", || 42 as FLOAT);
     let mut m = Module::new();
     rhai::set_exported_fn!(m, "add_in_place", raw_fn_mut::add_in_place);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
         engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let x = get_mystic_number();
-           math::add_in_place(x, 1.0);
-           x"#
+            r#"let x = get_mystic_number();
+            Math::Advanced::add_in_place(x, 1.0);
+            x"#
         )?,
         43.0
     );
@@ -80,16 +74,10 @@ fn raw_fn_str_test() -> Result<(), Box<EvalAltResult>> {
     engine.register_fn("get_mystic_number", || 42 as FLOAT);
     let mut m = Module::new();
     rhai::set_exported_fn!(m, "write_out_str", raw_fn_str::write_out_str);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Host::IO", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Host::IO", m.into());
 
     assert_eq!(
-        engine.eval::<bool>(
-            r#"import "Host::IO" as io;
-           let x = io::write_out_str("hello world!");
-           x"#
-        )?,
+        engine.eval::<bool>(r#"let x = Host::IO::write_out_str("hello world!"); x"#)?,
         true
     );
     Ok(())
@@ -138,18 +126,16 @@ fn mut_opaque_ref_test() -> Result<(), Box<EvalAltResult>> {
     rhai::set_exported_fn!(m, "new_message", mut_opaque_ref::new_message);
     rhai::set_exported_fn!(m, "new_os_message", mut_opaque_ref::new_os_message);
     rhai::set_exported_fn!(m, "write_out_message", mut_opaque_ref::write_out_message);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Host::Msg", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Host::Msg", m.into());
 
     assert_eq!(
         engine.eval::<bool>(
-            r#"import "Host::Msg" as msg;
-           let message1 = msg::new_message(true, "it worked");
-           let ok1 = msg::write_out_message(message1);
-           let message2 = msg::new_os_message(true, 0);
-           let ok2 = msg::write_out_message(message2);
-           ok1 && ok2"#
+            r#"
+            let message1 = Host::Msg::new_message(true, "it worked");
+            let ok1 = Host::Msg::write_out_message(message1);
+            let message2 = Host::Msg::new_os_message(true, 0);
+            let ok2 = Host::Msg::write_out_message(message2);
+            ok1 && ok2"#
         )?,
         true
     );
@@ -179,14 +165,11 @@ fn raw_returning_fn_test() -> Result<(), Box<EvalAltResult>> {
     engine.register_fn("get_mystic_number", || 42 as FLOAT);
     let mut m = Module::new();
     rhai::set_exported_fn!(m, "euclidean_distance", raw_returning_fn::distance_function);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
         engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let x = math::euclidean_distance(0.0, 1.0, 0.0, get_mystic_number()); x"#
+            r#"let x = Math::Advanced::euclidean_distance(0.0, 1.0, 0.0, get_mystic_number()); x"#
         )?,
         41.0
     );
diff --git a/codegen/tests/test_modules.rs b/codegen/tests/test_modules.rs
index 878f4fef..4993c5c3 100644
--- a/codegen/tests/test_modules.rs
+++ b/codegen/tests/test_modules.rs
@@ -12,14 +12,8 @@ pub mod empty_module {
 fn empty_module_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::empty_module::EmptyModule);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Module::Empty", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Module::Empty", m.into());
 
-    assert_eq!(
-        engine.eval::<INT>(r#"import "Module::Empty" as m; 42"#)?,
-        42
-    );
     Ok(())
 }
 
@@ -39,16 +33,10 @@ pub mod one_fn_module {
 fn one_fn_module_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::one_fn_module::advanced_math);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
-        engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let m = math::get_mystic_number();
-           m"#
-        )?,
+        engine.eval::<FLOAT>(r#"let m = Math::Advanced::get_mystic_number();m"#)?,
         42.0
     );
     Ok(())
@@ -73,16 +61,14 @@ pub mod one_fn_and_const_module {
 fn one_fn_and_const_module_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::one_fn_and_const_module::advanced_math);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
         engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let m = math::MYSTIC_NUMBER;
-           let x = math::euclidean_distance(0.0, 1.0, 0.0, m);
-           x"#
+            r#"
+            let m = Math::Advanced::MYSTIC_NUMBER;
+            let x = Math::Advanced::euclidean_distance(0.0, 1.0, 0.0, m);
+            x"#
         )?,
         41.0
     );
@@ -105,16 +91,10 @@ pub mod raw_fn_str_module {
 fn raw_fn_str_module_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::raw_fn_str_module::host_io);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Host::IO", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Host::IO", m.into());
 
     assert_eq!(
-        engine.eval::<bool>(
-            r#"import "Host::IO" as io;
-           let x = io::write_out_str("hello world!");
-           x"#
-        )?,
+        engine.eval::<bool>(r#"let x = Host::IO::write_out_str("hello world!"); x"#)?,
         true
     );
     Ok(())
@@ -162,19 +142,17 @@ pub mod mut_opaque_ref_module {
 fn mut_opaque_ref_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::mut_opaque_ref_module::host_msg);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Host::Msg", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Host::Msg", m.into());
 
     assert_eq!(
         engine.eval::<bool>(
-            r#"import "Host::Msg" as msg;
-           let success = "it worked";
-           let message1 = msg::new_message(true, success);
-           let ok1 = msg::write_out_message(message1);
-           let message2 = msg::new_os_message(true, 0);
-           let ok2 = msg::write_out_message(message2);
-           ok1 && ok2"#
+            r#"
+            let success = "it worked";
+            let message1 = Host::Msg::new_message(true, success);
+            let ok1 = Host::Msg::write_out_message(message1);
+            let message2 = Host::Msg::new_os_message(true, 0);
+            let ok2 = Host::Msg::write_out_message(message2);
+            ok1 && ok2"#
         )?,
         true
     );
@@ -204,18 +182,16 @@ fn duplicate_fn_rename_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     engine.register_fn("get_mystic_number", || 42 as FLOAT);
     let m = rhai::exported_module!(crate::duplicate_fn_rename::my_adds);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     let output_array = engine.eval::<Array>(
-        r#"import "Math::Advanced" as math;
-       let fx = get_mystic_number();
-       let fy = math::add(fx, 1.0);
-       let ix = 42;
-       let iy = math::add(ix, 1);
-       [fy, iy]
-       "#,
+        r#"
+        let fx = get_mystic_number();
+        let fy = Math::Advanced::add(fx, 1.0);
+        let ix = 42;
+        let iy = Math::Advanced::add(ix, 1);
+        [fy, iy]
+        "#,
     )?;
     assert_eq!(&output_array[0].as_float().unwrap(), &43.0);
     assert_eq!(&output_array[1].as_int().unwrap(), &43);
@@ -291,6 +267,7 @@ fn multiple_fn_rename_test() -> Result<(), Box<EvalAltResult>> {
 
 mod export_by_prefix {
     use rhai::plugin::*;
+
     #[export_module(export_prefix = "foo_")]
     pub mod my_adds {
         use rhai::{FLOAT, INT};
@@ -328,20 +305,18 @@ mod export_by_prefix {
 fn export_by_prefix_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::export_by_prefix::my_adds);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     let output_array = engine.eval::<Array>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::foo_add_f(ex, 1.0);
-       let gx = math::foo_m(41.0, 1.0);
-       let ei = 41;
-       let fi = math::bar_add_i(ei, 1);
-       let gi = math::foo_n(41, 1);
-       [fx, gx, fi, gi]
-       "#,
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::foo_add_f(ex, 1.0);
+        let gx = Math::Advanced::foo_m(41.0, 1.0);
+        let ei = 41;
+        let fi = Math::Advanced::bar_add_i(ei, 1);
+        let gi = Math::Advanced::foo_n(41, 1);
+        [fx, gx, fi, gi]
+        "#,
     )?;
     assert_eq!(&output_array[0].as_float().unwrap(), &42.0);
     assert_eq!(&output_array[1].as_float().unwrap(), &42.0);
@@ -349,30 +324,31 @@ fn export_by_prefix_test() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(&output_array[3].as_int().unwrap(), &42);
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::foo_add_float2(ex, 1.0);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::foo_add_float2 (f64, f64)"
-            && p == rhai::Position::new(3, 23)));
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::foo_add_float2(ex, 1.0);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::foo_add_float2 (f64, f64)"
+            && p == rhai::Position::new(3, 34)));
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::bar_m(ex, 1.0);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::bar_m (f64, f64)"
-            && p == rhai::Position::new(3, 23)));
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::bar_m(ex, 1.0);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::bar_m (f64, f64)"
+            && p == rhai::Position::new(3, 34)));
 
     Ok(())
 }
 
 mod export_all {
     use rhai::plugin::*;
+
     #[export_module(export_all)]
     pub mod my_adds {
         use rhai::{FLOAT, INT};
@@ -411,20 +387,18 @@ mod export_all {
 fn export_all_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::export_all::my_adds);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     let output_array = engine.eval::<Array>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::foo_add_f(ex, 1.0);
-       let gx = math::foo_m(41.0, 1.0);
-       let ei = 41;
-       let fi = math::foo_add_i(ei, 1);
-       let gi = math::foo_n(41, 1);
-       [fx, gx, fi, gi]
-       "#,
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::foo_add_f(ex, 1.0);
+        let gx = Math::Advanced::foo_m(41.0, 1.0);
+        let ei = 41;
+        let fi = Math::Advanced::foo_add_i(ei, 1);
+        let gi = Math::Advanced::foo_n(41, 1);
+        [fx, gx, fi, gi]
+        "#,
     )?;
     assert_eq!(&output_array[0].as_float().unwrap(), &42.0);
     assert_eq!(&output_array[1].as_float().unwrap(), &42.0);
@@ -432,14 +406,14 @@ fn export_all_test() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(&output_array[3].as_int().unwrap(), &42);
 
     assert!(matches!(*engine.eval::<INT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41;
-       let fx = math::foo_p(ex, 1);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::foo_p (i64, i64)"
-            && p == rhai::Position::new(3, 23)));
+        r#"
+        let ex = 41;
+        let fx = Math::Advanced::foo_p(ex, 1);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::foo_p (i64, i64)"
+            && p == rhai::Position::new(3, 34)));
 
     Ok(())
 }
diff --git a/codegen/tests/test_nested.rs b/codegen/tests/test_nested.rs
index cf2c1a2e..a7f898b5 100644
--- a/codegen/tests/test_nested.rs
+++ b/codegen/tests/test_nested.rs
@@ -20,16 +20,10 @@ pub mod one_fn_module_nested_attr {
 fn one_fn_module_nested_attr_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::one_fn_module_nested_attr::advanced_math);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
-        engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let m = math::get_mystic_number();
-           m"#
-        )?,
+        engine.eval::<FLOAT>(r#"let m = Math::Advanced::get_mystic_number(); m"#)?,
         42.0
     );
     Ok(())
@@ -56,16 +50,10 @@ pub mod one_fn_submodule_nested_attr {
 fn one_fn_submodule_nested_attr_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::one_fn_submodule_nested_attr::advanced_math);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     assert_eq!(
-        engine.eval::<FLOAT>(
-            r#"import "Math::Advanced" as math;
-           let m = math::constants::get_mystic_number();
-           m"#
-        )?,
+        engine.eval::<FLOAT>(r#"let m = Math::Advanced::constants::get_mystic_number(); m"#)?,
         42.0
     );
     Ok(())
@@ -73,8 +61,8 @@ fn one_fn_submodule_nested_attr_test() -> Result<(), Box<EvalAltResult>> {
 
 mod export_nested_by_prefix {
     use rhai::plugin::*;
-    #[export_module(export_prefix = "foo_")]
 
+    #[export_module(export_prefix = "foo_")]
     pub mod my_adds {
         pub mod foo_first_adders {
             use rhai::{FLOAT, INT};
@@ -131,26 +119,24 @@ mod export_nested_by_prefix {
 fn export_nested_by_prefix_test() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
     let m = rhai::exported_module!(crate::export_nested_by_prefix::my_adds);
-    let mut r = StaticModuleResolver::new();
-    r.insert("Math::Advanced", m);
-    engine.set_module_resolver(Some(r));
+    engine.register_static_module("Math::Advanced", m.into());
 
     let output_array = engine.eval::<Array>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::foo_first_adders::add_float(ex, 1.0);
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::foo_first_adders::add_float(ex, 1.0);
 
-       let ei = 41;
-       let fi = math::foo_first_adders::add_int(ei, 1);
+        let ei = 41;
+        let fi = Math::Advanced::foo_first_adders::add_int(ei, 1);
 
-       let gx = 41.0;
-       let hx = math::foo_second_adders::add_float(gx, 1.0);
+        let gx = 41.0;
+        let hx = Math::Advanced::foo_second_adders::add_float(gx, 1.0);
 
-       let gi = 41;
-       let hi = math::foo_second_adders::add_int(gi, 1);
+        let gi = 41;
+        let hi = Math::Advanced::foo_second_adders::add_int(gi, 1);
 
-       [fx, hx, fi, hi]
-       "#,
+        [fx, hx, fi, hi]
+        "#,
     )?;
     assert_eq!(&output_array[0].as_float().unwrap(), &42.0);
     assert_eq!(&output_array[1].as_float().unwrap(), &42.0);
@@ -158,44 +144,44 @@ fn export_nested_by_prefix_test() -> Result<(), Box<EvalAltResult>> {
     assert_eq!(&output_array[3].as_int().unwrap(), &42);
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::foo_third_adders::add_float(ex, 1.0);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::foo_third_adders::add_float (f64, f64)"
-            && p == rhai::Position::new(3, 41)));
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::foo_third_adders::add_float(ex, 1.0);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::foo_third_adders::add_float (f64, f64)"
+            && p == rhai::Position::new(3, 52)));
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41;
-       let fx = math::foo_third_adders::add_int(ex, 1);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::foo_third_adders::add_int (i64, i64)"
-            && p == rhai::Position::new(3, 41)));
+        r#"
+        let ex = 41;
+        let fx = Math::Advanced::foo_third_adders::add_int(ex, 1);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::foo_third_adders::add_int (i64, i64)"
+            && p == rhai::Position::new(3, 52)));
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41;
-       let fx = math::bar_fourth_adders::add_int(ex, 1);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::bar_fourth_adders::add_int (i64, i64)"
-            && p == rhai::Position::new(3, 42)));
+        r#"
+        let ex = 41;
+        let fx = Math::Advanced::bar_fourth_adders::add_int(ex, 1);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::bar_fourth_adders::add_int (i64, i64)"
+            && p == rhai::Position::new(3, 53)));
 
     assert!(matches!(*engine.eval::<FLOAT>(
-        r#"import "Math::Advanced" as math;
-       let ex = 41.0;
-       let fx = math::bar_fourth_adders::add_float(ex, 1.0);
-       fx
-       "#).unwrap_err(),
-       EvalAltResult::ErrorFunctionNotFound(s, p)
-            if s == "math::bar_fourth_adders::add_float (f64, f64)"
-            && p == rhai::Position::new(3, 42)));
+        r#"
+        let ex = 41.0;
+        let fx = Math::Advanced::bar_fourth_adders::add_float(ex, 1.0);
+        fx
+        "#).unwrap_err(),
+        EvalAltResult::ErrorFunctionNotFound(s, p)
+            if s == "Math::Advanced::bar_fourth_adders::add_float (f64, f64)"
+            && p == rhai::Position::new(3, 53)));
 
     Ok(())
 }
diff --git a/doc/src/SUMMARY.md b/doc/src/SUMMARY.md
index 45c199df..4b3e7e30 100644
--- a/doc/src/SUMMARY.md
+++ b/doc/src/SUMMARY.md
@@ -127,19 +127,22 @@ The Rhai Scripting Language
    7. [One Engine Instance Per Call](patterns/parallel.md)
    8. [Scriptable Event Handler with State](patterns/events.md)
    9. [Dynamic Constants Provider](patterns/dynamic-const.md)
-9.  [Advanced Topics](advanced.md)
-   10. [Capture Scope for Function Call](language/fn-capture.md)
-   11. [Low-Level API](rust/register-raw.md)
-   12. [Variable Resolver](engine/var.md)
-   13. [Use as DSL](engine/dsl.md)
+9. [Advanced Topics](advanced.md)
+   1. [Capture Scope for Function Call](language/fn-capture.md)
+   2. [Low-Level API](rust/register-raw.md)
+   3. [Variable Resolver](engine/var.md)
+   4. [Use as DSL](engine/dsl.md)
       1. [Disable Keywords and/or Operators](engine/disable.md)
       2. [Custom Operators](engine/custom-op.md)
       3. [Extending with Custom Syntax](engine/custom-syntax.md)
-   14. [Multiple Instantiation](patterns/multiple.md)
-   15. [Functions Metadata](engine/metadata/index.md)
-      4. [Generate Function Signatures](engine/metadata/gen_fn_sig.md)
-      5. [Export Metadata to JSON](engine/metadata/export_to_json.md)
-10. [Appendix](appendix/index.md)
+   5. [Multiple Instantiation](patterns/multiple.md)
+   6. [Functions Metadata](engine/metadata/index.md)
+      1. [Generate Function Signatures](engine/metadata/gen_fn_sig.md)
+      2. [Export Metadata to JSON](engine/metadata/export_to_json.md)
+10. [External Tools](tools/index.md)
+    1. [Online Playground](tools/playground.md)
+    2. [`rhai-doc`](tools/rhai-doc.md)
+11. [Appendix](appendix/index.md)
     1. [Keywords](appendix/keywords.md)
     2. [Operators and Symbols](appendix/operators.md)
     3. [Literals](appendix/literals.md)
diff --git a/doc/src/about/related.md b/doc/src/about/related.md
index 9b55003b..0f29cb16 100644
--- a/doc/src/about/related.md
+++ b/doc/src/about/related.md
@@ -15,13 +15,19 @@ Online Resources for Rhai
 
 * [`LIB.RS`](https://lib.rs/crates/rhai) - Rhai library info
 
-* [Online Playground][playground] - Run scripts directly from editor
-
 * [Discord Chat](https://discord.gg/HquqbYFcZ9) - Rhai channel
 
 * [Reddit](https://www.reddit.com/r/Rhai) - Rhai community
 
 
+External Tools
+--------------
+
+* [Online Playground][playground] - Run Rhai scripts directly from an editor in the browser
+
+* [`rhai-doc`] - Rhai script documentation tool
+
+
 Other Cool Projects
 -------------------
 
diff --git a/doc/src/engine/call-fn.md b/doc/src/engine/call-fn.md
index a68925ac..466ec1ee 100644
--- a/doc/src/engine/call-fn.md
+++ b/doc/src/engine/call-fn.md
@@ -41,8 +41,8 @@ let mut scope = Scope::new();
 // If arguments of the wrong types are passed, the Engine will not find the function.
 
 let result: i64 = engine.call_fn(&mut scope, &ast, "hello", ( String::from("abc"), 123_i64 ) )?;
-//                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-//                                                          put arguments in a tuple
+//          ^^^                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+//        return type must be specified                          put arguments in a tuple
 
 let result: i64 = engine.call_fn(&mut scope, &ast, "hello", (123_i64,) )?;
 //                                                          ^^^^^^^^^^ tuple of one
diff --git a/doc/src/engine/custom-op.md b/doc/src/engine/custom-op.md
index e2a118e9..3dacfa9d 100644
--- a/doc/src/engine/custom-op.md
+++ b/doc/src/engine/custom-op.md
@@ -6,7 +6,8 @@ Custom Operators
 For use as a DSL (Domain-Specific Languages), it is sometimes more convenient to augment Rhai with
 customized operators performing specific logic.
 
-`Engine::register_custom_operator` registers a keyword as a custom operator.
+`Engine::register_custom_operator` registers a keyword as a custom operator, giving it a particular
+_precedence_ (which cannot be zero).
 
 
 Example
@@ -52,15 +53,23 @@ into a syntax that uses the corresponding function calls.
 Using `Engine::register_custom_operator` merely enables a convenient shortcut.
 
 
-Must Follow Variable Naming
---------------------------
+Must be a Valid Identifier or Reserved Symbol
+--------------------------------------------
 
 All custom operators must be _identifiers_ that follow the same naming rules as [variables].
 
+Alternatively, they can also be [reserved symbols]({{rootUrl}}/appendix/operators.md#symbols),
+[disabled operators or keywords][disable keywords and operators].
+
 ```rust
 engine.register_custom_operator("foo", 20);     // 'foo' is a valid custom operator
 
-engine.register_custom_operator("=>", 30);      // <- error: '=>' is not a valid custom operator
+engine.register_custom_operator("#", 20);       // the reserved symbol '#' is also
+                                                // a valid custom operator
+
+engine.register_custom_operator("+", 30);       // <- error: '+' is an active operator
+
+engine.register_custom_operator("=>", 30);      // <- error: '=>' is an active symbol
 ```
 
 
diff --git a/doc/src/rust/modules/ast.md b/doc/src/rust/modules/ast.md
index 1410fa20..80dd7c5a 100644
--- a/doc/src/rust/modules/ast.md
+++ b/doc/src/rust/modules/ast.md
@@ -7,22 +7,24 @@ Create a Module from an AST
 `Module::eval_ast_as_new`
 ------------------------
 
-A _module_ can be created from a single script (or pre-compiled [`AST`]) containing global variables,
+A [module] can be created from a single script (or pre-compiled [`AST`]) containing global variables,
 functions and sub-modules via the `Module::eval_ast_as_new` method.
 
-See the section on [_Exporting Variables, Functions and Sub-Modules_][`export`] for details on how to prepare
-a Rhai script for this purpose as well as to control which functions/variables to export.
+See the section on [_Exporting Variables, Functions and Sub-Modules_][`export`] for details on how to
+prepare a Rhai script for this purpose as well as to control which functions/variables to export.
 
-When given an [`AST`], it is first evaluated, then the following items are exposed as members of the new module:
+When given an [`AST`], it is first evaluated, then the following items are exposed as members of the
+new [module]:
 
 * Global variables - all variables exported via the `export` statement (those not exported remain hidden).
 
 * Functions not specifically marked `private`.
 
-* Global modules that remain in the [`Scope`] at the end of a script run.
+* Global modules that remain in the [`Scope`] at the end of a script run (become sub-modules).
 
-`Module::eval_ast_as_new` encapsulates the entire `AST` into each function call, merging the module namespace
-with the global namespace.  Therefore, functions defined within the same module script can cross-call each other.
+`Module::eval_ast_as_new` encapsulates the entire `AST` into each function call, merging the
+module namespace with the global namespace.  Therefore, functions defined within the same module
+script can cross-call each other.
 
 
 Examples
diff --git a/doc/src/rust/modules/create.md b/doc/src/rust/modules/create.md
index d31ccf42..d6d3496a 100644
--- a/doc/src/rust/modules/create.md
+++ b/doc/src/rust/modules/create.md
@@ -25,7 +25,6 @@ Use Case 1 - Make the `Module` Globally Available
 `Engine::register_global_module` registers a shared [module] into the _global_ namespace.
 
 All [functions] and [type iterators] can be accessed without _namespace qualifiers_.
-
 Variables and sub-modules are **ignored**.
 
 This is by far the easiest way to expose a module's functionalities to Rhai.
@@ -35,11 +34,11 @@ use rhai::{Engine, Module};
 
 let mut module = Module::new();             // new module
 
-// Use the 'set_fn_XXX' API to add functions.
-let hash = module.set_fn_1("inc", |x: i64| Ok(x+1));
+// Use the 'Module::set_fn_XXX' API to add functions.
+let hash = module.set_fn_1("inc", |x: i64| Ok(x + 1));
 
 // Remember to update the parameter names/types and return type metadata.
-// 'set_fn_XXX' by default does not set function metadata.
+// 'Module::set_fn_XXX' by default does not set function metadata.
 module.update_fn_metadata(hash, ["x: i64", "i64"]);
 
 // Register the module into the global namespace of the Engine.
@@ -49,6 +48,19 @@ engine.register_global_module(module.into());
 engine.eval::<i64>("inc(41)")? == 42;       // no need to import module
 ```
 
+Registering a [module] via `Engine::register_global_module` is essentially the _same_
+as calling `Engine::register_fn` (or any of the `Engine::register_XXX` API) individually
+on each top-level function within that [module].  In fact, the actual implementation of
+`Engine::register_fn` etc. simply adds the function to an internal [module]!
+
+```rust
+// The above is essentially the same as:
+let mut engine = Engine::new();
+
+engine.register_fn("inc", |x: i64| x + 1);
+
+engine.eval::<i64>("inc(41)")? == 42;       // no need to import module
+```
 
 Use Case 2 - Make the `Module` a Static Module
 ---------------------------------------------
@@ -60,25 +72,27 @@ use rhai::{Engine, Module};
 
 let mut module = Module::new();             // new module
 
-// Use the 'set_fn_XXX' API to add functions.
-let hash = module.set_fn_1("inc", |x: i64| Ok(x+1));
+// Use the 'Module::set_fn_XXX' API to add functions.
+let hash = module.set_fn_1("inc", |x: i64| Ok(x + 1));
 
 // Remember to update the parameter names/types and return type metadata.
-// 'set_fn_XXX' by default does not set function metadata.
+// 'Module::set_fn_XXX' by default does not set function metadata.
 module.update_fn_metadata(hash, ["x: i64", "i64"]);
 
-// Register the module into the Engine as a static module namespace 'calc'
+// Register the module into the Engine as the static module namespace path
+// 'services::calc'
 let mut engine = Engine::new();
-engine.register_static_module("calc", module.into());
+engine.register_static_module("services::calc", module.into());
 
-engine.eval::<i64>("calc::inc(41)")? == 42; // refer to the 'Calc' module
+// refer to the 'services::calc' module
+engine.eval::<i64>("services::calc::inc(41)")? == 42;
 ```
 
 ### Expose Functions to the Global Namespace
 
-`Module::set_fn_mut` and `Module::set_fn_XXX_mut` can optionally expose functions (usually _methods_)
-in the module to the _global_ namespace, so [getters/setters] and [indexers] for [custom types]
-can work as expected.
+The `Module::set_fn_XXX_mut` API methods can optionally expose functions in the [module]
+to the _global_ namespace by setting the `namespace` parameter to `FnNamespace::Global`,
+so [getters/setters] and [indexers] for [custom types] can work as expected.
 
 [Type iterators], because of their special nature, are _always_ exposed to the _global_ namespace.
 
@@ -87,19 +101,24 @@ use rhai::{Engine, Module, FnNamespace};
 
 let mut module = Module::new();             // new module
 
-// Expose method 'inc' to the global namespace (default is 'Internal')
-let hash = module.set_fn_1_mut("inc", FnNamespace::Global, |x: &mut i64| Ok(x+1));
+// Expose method 'inc' to the global namespace (default is 'FnNamespace::Internal')
+let hash = module.set_fn_1_mut("inc", FnNamespace::Global, |x: &mut i64| Ok(x + 1));
 
 // Remember to update the parameter names/types and return type metadata.
-// 'set_fn_XXX' by default does not set function metadata.
+// 'Module::set_fn_XXX_mut' by default does not set function metadata.
 module.update_fn_metadata(hash, ["x: &mut i64", "i64"]);
 
 // Register the module into the Engine as a static module namespace 'calc'
 let mut engine = Engine::new();
 engine.register_static_module("calc", module.into());
 
-// The method 'inc' works as expected because it is exposed to the global namespace
+// 'inc' works when qualified by the namespace
+engine.eval::<i64>("calc::inc(41)")? == 42;
+
+// 'inc' also works without a namespace qualifier
+// because it is exposed to the global namespace
 engine.eval::<i64>("let x = 41; x.inc()")? == 42;
+engine.eval::<i64>("let x = 41; inc(x)")? == 42;
 ```
 
 
@@ -118,7 +137,7 @@ use rhai::module_resolvers::StaticModuleResolver;
 
 let mut module = Module::new();             // new module
 module.set_var("answer", 41_i64);           // variable 'answer' under module
-module.set_fn_1("inc", |x: i64| Ok(x+1));   // use the 'set_fn_XXX' API to add functions
+module.set_fn_1("inc", |x: i64| Ok(x + 1)); // use the 'set_fn_XXX' API to add functions
 
 // Create the module resolver
 let mut resolver = StaticModuleResolver::new();
@@ -129,7 +148,7 @@ resolver.insert("question", module);
 
 // Set the module resolver into the 'Engine'
 let mut engine = Engine::new();
-engine.set_module_resolver(Some(resolver));
+engine.set_module_resolver(resolver);
 
 // Use namespace-qualified variables
 engine.eval::<i64>(r#"import "question" as q; q::answer + 1"#)? == 42;
diff --git a/doc/src/rust/modules/imp-resolver.md b/doc/src/rust/modules/imp-resolver.md
index 0b8f789c..1094e208 100644
--- a/doc/src/rust/modules/imp-resolver.md
+++ b/doc/src/rust/modules/imp-resolver.md
@@ -62,7 +62,7 @@ impl ModuleResolver for MyModuleResolver {
 let mut engine = Engine::new();
 
 // Set the custom module resolver into the 'Engine'.
-engine.set_module_resolver(Some(MyModuleResolver {}));
+engine.set_module_resolver(MyModuleResolver {});
 
 engine.consume(r#"
     import "hello" as foo;  // this 'import' statement will call
diff --git a/doc/src/rust/modules/resolvers.md b/doc/src/rust/modules/resolvers.md
index a56b9b14..c7ba3196 100644
--- a/doc/src/rust/modules/resolvers.md
+++ b/doc/src/rust/modules/resolvers.md
@@ -153,13 +153,19 @@ A collection of module resolvers. Modules will be resolved from each resolver in
 This is useful when multiple types of modules are needed simultaneously.
 
 
+`DummyResolversCollection`
+-------------------------
+
+This module resolver acts as a _dummy_ and always fails all module resolution calls.
+
+
 Set into `Engine`
 -----------------
 
 An [`Engine`]'s module resolver is set via a call to `Engine::set_module_resolver`:
 
 ```rust
-use rhai::module_resolvers::StaticModuleResolver;
+use rhai::module_resolvers::{DummyModuleResolver, StaticModuleResolver};
 
 // Create a module resolver
 let resolver = StaticModuleResolver::new();
@@ -167,8 +173,9 @@ let resolver = StaticModuleResolver::new();
 // Register functions into 'resolver'...
 
 // Use the module resolver
-engine.set_module_resolver(Some(resolver));
+engine.set_module_resolver(resolver);
 
-// Effectively disable 'import' statements by setting module resolver to 'None'
-engine.set_module_resolver(None);
+// Effectively disable 'import' statements by setting module resolver to
+// the 'DummyModuleResolver' which acts as... well... a dummy.
+engine.set_module_resolver(DummyModuleResolver::new());
 ```
diff --git a/doc/src/rust/override.md b/doc/src/rust/override.md
index f6d4d656..7620bfd5 100644
--- a/doc/src/rust/override.md
+++ b/doc/src/rust/override.md
@@ -3,18 +3,19 @@ Override a Built-in Function
 
 {{#include ../links.md}}
 
-Any similarly-named function defined in a script overrides any built-in or registered
+Any similarly-named function defined in a script _overrides_ any built-in or registered
 native Rust function of the same name and number of parameters.
 
 ```rust
-// Override the built-in function 'to_int'
-fn to_int(num) {
-    print("Ha! Gotcha! " + num);
+// Override the built-in function 'to_float' when called as a method
+fn to_float() {
+    print("Ha! Gotcha! " + this);
+    42.0
 }
 
-let x = (123).to_int();
+let x = 123.to_float();
 
-print(x);               // what happens?
+print(x);       // what happens?
 ```
 
 A registered native Rust function, in turn, overrides any built-in function of the
diff --git a/doc/src/start/examples/rust.md b/doc/src/start/examples/rust.md
index bd3064c8..0b343a52 100644
--- a/doc/src/start/examples/rust.md
+++ b/doc/src/start/examples/rust.md
@@ -11,13 +11,13 @@ A number of examples can be found in the `examples` directory:
 | [`custom_types_and_methods`]({{repoTree}}/examples/custom_types_and_methods.rs) | shows how to register a custom Rust type and methods for it                                                                                  |
 | [`hello`]({{repoTree}}/examples/hello.rs)                                       | simple example that evaluates an expression and prints the result                                                                            |
 | [`reuse_scope`]({{repoTree}}/examples/reuse_scope.rs)                           | evaluates two pieces of code in separate runs, but using a common [`Scope`]                                                                  |
-| [`rhai_runner`]({{repoTree}}/examples/rhai_runner.rs)                           | runs each filename passed to it as a Rhai script                                                                                             |
+| [`rhai-repl`]({{repoTree}}/examples/rhai-repl.rs)                               | a simple REPL, interactively evaluate statements from stdin                                                                                  |
+| [`rhai-run`]({{repoTree}}/examples/rhai-run.rs)                                 | runs each filename passed to it as a Rhai script                                                                                             |
 | [`serde`]({{repoTree}}/examples/serde.rs)                                       | example to serialize and deserialize Rust types with [`serde`](https://crates.io/crates/serde).<br/>The [`serde`] feature is required to run |
 | [`simple_fn`]({{repoTree}}/examples/simple_fn.rs)                               | shows how to register a simple function                                                                                                      |
 | [`strings`]({{repoTree}}/examples/strings.rs)                                   | shows different ways to register functions taking string arguments                                                                           |
-| [`repl`]({{repoTree}}/examples/repl.rs)                                         | a simple REPL, interactively evaluate statements from stdin                                                                                  |
 
-The `repl` example is a particularly good one as it allows one to interactively try out Rhai's
+The `rhai-repl` example is a particularly good one as it allows one to interactively try out Rhai's
 language features in a standard REPL (**R**ead-**E**val-**P**rint **L**oop).
 
 
diff --git a/doc/src/start/examples/scripts.md b/doc/src/start/examples/scripts.md
index f3167a93..8de664a5 100644
--- a/doc/src/start/examples/scripts.md
+++ b/doc/src/start/examples/scripts.md
@@ -46,8 +46,8 @@ The following scripts are for benchmarking the speed of Rhai:
 Running Example Scripts
 ----------------------
 
-The [`rhai_runner`](../examples/rust.md) example can be used to run the scripts:
+The [`rhai-run`](../examples/rust.md) example can be used to run the scripts:
 
 ```bash
-cargo run --example rhai_runner scripts/any_script.rhai
+cargo run --example rhai-run scripts/any_script.rhai
 ```
diff --git a/doc/src/tools/index.md b/doc/src/tools/index.md
new file mode 100644
index 00000000..9b9eff01
--- /dev/null
+++ b/doc/src/tools/index.md
@@ -0,0 +1,6 @@
+External Tools
+==============
+
+{{#include ../links.md}}
+
+External tools available to work with Rhai.
diff --git a/doc/src/tools/playground.md b/doc/src/tools/playground.md
new file mode 100644
index 00000000..91507a3d
--- /dev/null
+++ b/doc/src/tools/playground.md
@@ -0,0 +1,15 @@
+Online Playground
+=================
+
+{{#include ../links.md}}
+
+
+The Online Playground runs off a [WASM] build of Rhai and allows evaluating
+Rhai scripts directly within a browser editor window.
+
+
+Author : [`@alvinhochun`](https://github.com/alvinhochun)
+
+Repo : [On GitHub](https://github.com/alvinhochun/rhai-playground)
+
+URL : [Link to Online Playground][playground]
diff --git a/doc/src/tools/rhai-doc.md b/doc/src/tools/rhai-doc.md
new file mode 100644
index 00000000..fd32be6a
--- /dev/null
+++ b/doc/src/tools/rhai-doc.md
@@ -0,0 +1,6 @@
+Rhai Script Documentation Tool
+=============================
+
+{{#include ../links.md}}
+
+<< TODO >>
\ No newline at end of file
diff --git a/examples/arrays_and_structs.rs b/examples/arrays_and_structs.rs
index 0ad34051..094a7d08 100644
--- a/examples/arrays_and_structs.rs
+++ b/examples/arrays_and_structs.rs
@@ -1,38 +1,40 @@
-use rhai::{Engine, RegisterFn, INT};
+use rhai::{Engine, EvalAltResult, RegisterFn, INT};
 
-#[derive(Clone, Debug)]
+#[derive(Debug, Clone)]
 struct TestStruct {
     x: INT,
 }
 
 impl TestStruct {
-    fn update(&mut self) {
+    pub fn update(&mut self) {
         self.x += 1000;
     }
 
-    fn new() -> Self {
+    pub fn new() -> Self {
         Self { x: 1 }
     }
 }
 
 #[cfg(not(feature = "no_index"))]
 #[cfg(not(feature = "no_object"))]
-fn main() {
+fn main() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
 
     engine
         .register_type::<TestStruct>()
-        .register_fn("update", TestStruct::update)
-        .register_fn("new_ts", TestStruct::new);
+        .register_fn("new_ts", TestStruct::new)
+        .register_fn("update", TestStruct::update);
 
     println!(
         "{:?}",
-        engine.eval::<TestStruct>("let x = new_ts(); x.update(); x")
+        engine.eval::<TestStruct>("let x = new_ts(); x.update(); x")?
     );
     println!(
         "{:?}",
-        engine.eval::<TestStruct>("let x = [new_ts()]; x[0].update(); x[0]")
+        engine.eval::<TestStruct>("let x = [new_ts()]; x[0].update(); x[0]")?
     );
+
+    Ok(())
 }
 
 #[cfg(any(feature = "no_index", feature = "no_object"))]
diff --git a/examples/custom_types_and_methods.rs b/examples/custom_types_and_methods.rs
index 4b0118fa..c48a7fde 100644
--- a/examples/custom_types_and_methods.rs
+++ b/examples/custom_types_and_methods.rs
@@ -1,16 +1,16 @@
 use rhai::{Engine, EvalAltResult, RegisterFn, INT};
 
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 struct TestStruct {
     x: INT,
 }
 
 impl TestStruct {
-    fn update(&mut self) {
+    pub fn update(&mut self) {
         self.x += 1000;
     }
 
-    fn new() -> Self {
+    pub fn new() -> Self {
         Self { x: 1 }
     }
 }
@@ -21,8 +21,8 @@ fn main() -> Result<(), Box<EvalAltResult>> {
 
     engine
         .register_type::<TestStruct>()
-        .register_fn("update", TestStruct::update)
-        .register_fn("new_ts", TestStruct::new);
+        .register_fn("new_ts", TestStruct::new)
+        .register_fn("update", TestStruct::update);
 
     let result = engine.eval::<TestStruct>("let x = new_ts(); x.update(); x")?;
 
diff --git a/examples/repl.rs b/examples/rhai-repl.rs
similarity index 96%
rename from examples/repl.rs
rename to examples/rhai-repl.rs
index 92e04a71..f60a0a81 100644
--- a/examples/repl.rs
+++ b/examples/rhai-repl.rs
@@ -43,7 +43,7 @@ fn print_help() {
     println!("quit, exit => quit");
     println!("scope      => print all variables in the scope");
     println!("functions  => print all functions defined");
-    println!("ast        => print the last AST");
+    println!("ast        => print the last AST (optimized)");
     println!("astu       => print the last raw, un-optimized AST");
     println!(r"end a line with '\' to continue to the next line.");
     println!();
@@ -67,7 +67,7 @@ fn main() {
     print_help();
 
     'main_loop: loop {
-        print!("rhai> ");
+        print!("rhai-repl> ");
         stdout().flush().expect("couldn't flush stdout");
 
         input.clear();
@@ -126,12 +126,12 @@ fn main() {
             }
             "astu" => {
                 // print the last un-optimized AST
-                println!("{:#?}\n", &ast_u);
+                println!("{:#?}\n", ast_u);
                 continue;
             }
             "ast" => {
                 // print the last AST
-                println!("{:#?}\n", &ast);
+                println!("{:#?}\n", ast);
                 continue;
             }
             "functions" => {
diff --git a/examples/rhai_runner.rs b/examples/rhai-run.rs
similarity index 100%
rename from examples/rhai_runner.rs
rename to examples/rhai-run.rs
diff --git a/examples/serde.rs b/examples/serde.rs
index 1868f44b..eca31453 100644
--- a/examples/serde.rs
+++ b/examples/serde.rs
@@ -17,13 +17,13 @@ mod example {
     use rhai::{Dynamic, Engine, Map};
     use serde::{Deserialize, Serialize};
 
-    #[derive(Debug, Serialize, Deserialize)]
+    #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
     struct Point {
         x: f64,
         y: f64,
     }
 
-    #[derive(Debug, Serialize, Deserialize)]
+    #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
     struct MyStruct {
         a: i64,
         b: Vec<String>,
@@ -71,6 +71,18 @@ mod example {
         // Convert the 'Dynamic' object map into 'MyStruct'
         let x: MyStruct = from_dynamic(&result).unwrap();
 
+        assert_eq!(
+            x,
+            MyStruct {
+                a: 42,
+                b: vec!["hello".into(), "world".into()],
+                c: true,
+                d: Point {
+                    x: 123.456,
+                    y: 999.0,
+                },
+            }
+        );
         println!("Deserialized to struct: {:#?}", x);
     }
 }
diff --git a/examples/strings.rs b/examples/strings.rs
index f24e9545..dc5f76b3 100644
--- a/examples/strings.rs
+++ b/examples/strings.rs
@@ -69,7 +69,7 @@ fn main() -> Result<(), Box<EvalAltResult>> {
                 display("Trimmed", x);
                 display("Trimmed Length", x.len());
                 display("Index of \"!!!\"", x.index_of("!!!"));
-        "#,
+            "#,
         )?;
 
         println!();
diff --git a/scripts/README.md b/scripts/README.md
index ca204dd9..f3bf5b4a 100644
--- a/scripts/README.md
+++ b/scripts/README.md
@@ -7,14 +7,14 @@ Testing scripts written in Rhai.
 How to Run
 ----------
 
-Compile the `rhai_runner` example:
+Compile the `rhai-run` example:
 
 ```bash
-cargo build --example rhai_runner
+cargo build --example rhai-run
 ```
 
 Run it:
 
 ```bash
-./target/debug/examples/rhai_runner ./scripts/test_script_to_run.rhai
+./target/debug/examples/rhai-run ./scripts/test_script_to_run.rhai
 ```
diff --git a/src/ast.rs b/src/ast.rs
index bc801376..b6c211c6 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -9,7 +9,7 @@ use crate::stdlib::{
     collections::HashMap,
     fmt,
     hash::Hash,
-    num::NonZeroUsize,
+    num::{NonZeroU64, NonZeroUsize},
     ops::{Add, AddAssign},
     string::String,
     vec,
@@ -736,7 +736,7 @@ impl Stmt {
             _ => false,
         }
     }
-    /// Get the [position][`Position`] of this statement.
+    /// Get the [position][Position] of this statement.
     pub fn position(&self) -> Position {
         match self {
             Self::Noop(pos)
@@ -765,7 +765,7 @@ impl Stmt {
             Self::Share(x) => x.pos,
         }
     }
-    /// Override the [position][`Position`] of this statement.
+    /// Override the [position][Position] of this statement.
     pub fn set_position(&mut self, new_pos: Position) -> &mut Self {
         match self {
             Self::Noop(pos)
@@ -914,16 +914,14 @@ pub struct BinaryExpr {
 #[derive(Debug, Clone, Default)]
 pub struct FnCallExpr {
     /// Pre-calculated hash for a script-defined function of the same name and number of parameters.
-    pub hash: u64,
-    /// Call native functions only? Set to [`true`] to skip searching for script-defined function overrides
-    /// when it is certain that the function must be native (e.g. an operator).
-    pub native_only: bool,
+    /// None if native Rust only.
+    pub hash_script: Option<NonZeroU64>,
     /// Does this function call capture the parent scope?
     pub capture: bool,
     /// Default value when the function is not found, mostly used to provide a default for comparison functions.
     pub def_value: Option<Dynamic>,
     /// Namespace of the function, if any. Boxed because it occurs rarely.
-    pub namespace: Option<Box<NamespaceRef>>,
+    pub namespace: Option<NamespaceRef>,
     /// Function name.
     /// Use [`Cow<'static, str>`][Cow] because a lot of operators (e.g. `==`, `>=`) are implemented as
     /// function calls and the function names are predictable, so no need to allocate a new [`String`].
@@ -963,13 +961,19 @@ pub enum Expr {
     Map(Box<StaticVec<(Ident, Expr)>>, Position),
     /// ()
     Unit(Position),
-    /// Variable access - (optional index, optional modules, hash, variable name)
-    Variable(Box<(Option<NonZeroUsize>, Option<Box<NamespaceRef>>, u64, Ident)>),
+    /// Variable access - (optional index, optional (hash, modules), variable name)
+    Variable(
+        Box<(
+            Option<NonZeroUsize>,
+            Option<(NonZeroU64, NamespaceRef)>,
+            Ident,
+        )>,
+    ),
     /// Property access - (getter, setter), prop
-    Property(Box<((ImmutableString, ImmutableString), Ident)>),
+    Property(Box<(ImmutableString, ImmutableString, Ident)>),
     /// { [statement][Stmt] }
     Stmt(Box<StaticVec<Stmt>>, Position),
-    /// Wrapped [expression][`Expr`] - should not be optimized away.
+    /// Wrapped [expression][Expr] - should not be optimized away.
     Expr(Box<Expr>),
     /// func `(` expr `,` ... `)`
     FnCall(Box<FnCallExpr>, Position),
@@ -1044,11 +1048,11 @@ impl Expr {
     /// Is the expression a simple variable access?
     pub(crate) fn get_variable_access(&self, non_qualified: bool) -> Option<&str> {
         match self {
-            Self::Variable(x) if !non_qualified || x.1.is_none() => Some((x.3).name.as_str()),
+            Self::Variable(x) if !non_qualified || x.1.is_none() => Some((x.2).name.as_str()),
             _ => None,
         }
     }
-    /// Get the [position][`Position`] of the expression.
+    /// Get the [position][Position] of the expression.
     pub fn position(&self) -> Position {
         match self {
             Self::Expr(x) => x.position(),
@@ -1064,9 +1068,9 @@ impl Expr {
             Self::FnPointer(_, pos) => *pos,
             Self::Array(_, pos) => *pos,
             Self::Map(_, pos) => *pos,
-            Self::Property(x) => (x.1).pos,
+            Self::Property(x) => (x.2).pos,
             Self::Stmt(_, pos) => *pos,
-            Self::Variable(x) => (x.3).pos,
+            Self::Variable(x) => (x.2).pos,
             Self::FnCall(_, pos) => *pos,
 
             Self::And(x, _) | Self::Or(x, _) | Self::In(x, _) => x.lhs.position(),
@@ -1078,7 +1082,7 @@ impl Expr {
             Self::Custom(_, pos) => *pos,
         }
     }
-    /// Override the [position][`Position`] of the expression.
+    /// Override the [position][Position] of the expression.
     pub fn set_position(&mut self, new_pos: Position) -> &mut Self {
         match self {
             Self::Expr(x) => {
@@ -1096,8 +1100,8 @@ impl Expr {
             Self::FnPointer(_, pos) => *pos = new_pos,
             Self::Array(_, pos) => *pos = new_pos,
             Self::Map(_, pos) => *pos = new_pos,
-            Self::Variable(x) => (x.3).pos = new_pos,
-            Self::Property(x) => (x.1).pos = new_pos,
+            Self::Variable(x) => (x.2).pos = new_pos,
+            Self::Property(x) => (x.2).pos = new_pos,
             Self::Stmt(_, pos) => *pos = new_pos,
             Self::FnCall(_, pos) => *pos = new_pos,
             Self::And(_, pos) | Self::Or(_, pos) | Self::In(_, pos) => *pos = new_pos,
@@ -1172,6 +1176,12 @@ impl Expr {
     }
     /// Is a particular [token][Token] allowed as a postfix operator to this expression?
     pub fn is_valid_postfix(&self, token: &Token) -> bool {
+        match token {
+            #[cfg(not(feature = "no_object"))]
+            Token::Period => return true,
+            _ => (),
+        }
+
         match self {
             Self::Expr(x) => x.is_valid_postfix(token),
 
@@ -1189,24 +1199,20 @@ impl Expr {
             | Self::Unit(_) => false,
 
             Self::StringConstant(_, _)
-            | Self::Stmt(_, _)
             | Self::FnCall(_, _)
+            | Self::Stmt(_, _)
             | Self::Dot(_, _)
             | Self::Index(_, _)
             | Self::Array(_, _)
             | Self::Map(_, _) => match token {
                 #[cfg(not(feature = "no_index"))]
                 Token::LeftBracket => true,
-                #[cfg(not(feature = "no_object"))]
-                Token::Period => true,
                 _ => false,
             },
 
             Self::Variable(_) => match token {
                 #[cfg(not(feature = "no_index"))]
                 Token::LeftBracket => true,
-                #[cfg(not(feature = "no_object"))]
-                Token::Period => true,
                 Token::LeftParen => true,
                 Token::Bang => true,
                 Token::DoubleColon => true,
@@ -1216,8 +1222,6 @@ impl Expr {
             Self::Property(_) => match token {
                 #[cfg(not(feature = "no_index"))]
                 Token::LeftBracket => true,
-                #[cfg(not(feature = "no_object"))]
-                Token::Period => true,
                 Token::LeftParen => true,
                 _ => false,
             },
diff --git a/src/dynamic.rs b/src/dynamic.rs
index c6efb8b8..ba4abb5d 100644
--- a/src/dynamic.rs
+++ b/src/dynamic.rs
@@ -748,13 +748,16 @@ impl Dynamic {
 
         Self(Union::Variant(Box::new(boxed), AccessMode::ReadWrite))
     }
-    /// Turn the [`Dynamic`] value into a shared [`Dynamic`] value backed by an [`Rc`][std::rc::Rc]`<`[`RefCell`][std::cell::RefCell]`<`[`Dynamic`]`>>`
-    /// or [`Arc`][std::sync::Arc]`<`[`RwLock`][std::sync::RwLock]`<`[`Dynamic`]`>>` depending on the `sync` feature.
+    /// Turn the [`Dynamic`] value into a shared [`Dynamic`] value backed by an
+    /// [`Rc`][std::rc::Rc]`<`[`RefCell`][std::cell::RefCell]`<`[`Dynamic`]`>>` or
+    /// [`Arc`][std::sync::Arc]`<`[`RwLock`][std::sync::RwLock]`<`[`Dynamic`]`>>`
+    /// depending on the `sync` feature.
     ///
     /// Shared [`Dynamic`] values are relatively cheap to clone as they simply increment the
     /// reference counts.
     ///
-    /// Shared [`Dynamic`] values can be converted seamlessly to and from ordinary [`Dynamic`] values.
+    /// Shared [`Dynamic`] values can be converted seamlessly to and from ordinary [`Dynamic`]
+    /// values.
     ///
     /// If the [`Dynamic`] value is already shared, this method returns itself.
     ///
@@ -970,8 +973,8 @@ impl Dynamic {
     ///
     /// If the [`Dynamic`] is not a shared value, it returns itself.
     ///
-    /// If the [`Dynamic`] is a shared value, it returns the shared value if there are
-    /// no outstanding references, or a cloned copy.
+    /// If the [`Dynamic`] is a shared value, it returns the shared value if there are no
+    /// outstanding references, or a cloned copy.
     #[inline(always)]
     pub fn flatten(self) -> Self {
         match self.0 {
diff --git a/src/engine.rs b/src/engine.rs
index bb6cb872..012578c9 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -18,8 +18,8 @@ use crate::stdlib::{
     collections::{HashMap, HashSet},
     fmt, format,
     hash::{Hash, Hasher},
-    iter::{empty, once},
-    num::NonZeroUsize,
+    iter::{empty, once, FromIterator},
+    num::{NonZeroU64, NonZeroU8, NonZeroUsize},
     ops::DerefMut,
     string::{String, ToString},
 };
@@ -112,23 +112,15 @@ impl Imports {
     }
     /// Does the specified function hash key exist in this stack of imported [modules][Module]?
     #[allow(dead_code)]
-    pub fn contains_fn(&self, hash: u64) -> bool {
-        if hash == 0 {
-            false
-        } else {
-            self.0.iter().any(|(_, m)| m.contains_qualified_fn(hash))
-        }
+    pub fn contains_fn(&self, hash: NonZeroU64) -> bool {
+        self.0.iter().any(|(_, m)| m.contains_qualified_fn(hash))
     }
     /// Get specified function via its hash key.
-    pub fn get_fn(&self, hash: u64) -> Option<&CallableFunction> {
-        if hash == 0 {
-            None
-        } else {
-            self.0
-                .iter()
-                .rev()
-                .find_map(|(_, m)| m.get_qualified_fn(hash))
-        }
+    pub fn get_fn(&self, hash: NonZeroU64) -> Option<&CallableFunction> {
+        self.0
+            .iter()
+            .rev()
+            .find_map(|(_, m)| m.get_qualified_fn(hash))
     }
     /// Does the specified [`TypeId`][std::any::TypeId] iterator exist in this stack of imported [modules][Module]?
     #[allow(dead_code)]
@@ -144,6 +136,22 @@ impl Imports {
     }
 }
 
+impl<'a, T: IntoIterator<Item = (&'a ImmutableString, &'a Shared<Module>)>> From<T> for Imports {
+    fn from(value: T) -> Self {
+        Self(
+            value
+                .into_iter()
+                .map(|(k, v)| (k.clone(), v.clone()))
+                .collect(),
+        )
+    }
+}
+impl FromIterator<(ImmutableString, Shared<Module>)> for Imports {
+    fn from_iter<T: IntoIterator<Item = (ImmutableString, Shared<Module>)>>(iter: T) -> Self {
+        Self(iter.into_iter().collect())
+    }
+}
+
 #[cfg(not(feature = "unchecked"))]
 #[cfg(debug_assertions)]
 pub const MAX_CALL_STACK_DEPTH: usize = 8;
@@ -478,7 +486,7 @@ pub struct State {
     /// Number of modules loaded.
     pub modules: usize,
     /// Cached lookup values for function hashes.
-    pub functions_cache: HashMap<u64, Option<CallableFunction>, StraightHasherBuilder>,
+    pub functions_cache: HashMap<NonZeroU64, Option<CallableFunction>, StraightHasherBuilder>,
 }
 
 impl State {
@@ -616,11 +624,11 @@ pub struct Engine {
     /// A collection of all modules loaded into the global namespace of the Engine.
     pub(crate) global_modules: StaticVec<Shared<Module>>,
     /// A collection of all sub-modules directly loaded into the Engine.
-    pub(crate) global_sub_modules: Imports,
+    pub(crate) global_sub_modules: HashMap<ImmutableString, Shared<Module>>,
 
     /// A module resolution service.
     #[cfg(not(feature = "no_module"))]
-    pub(crate) module_resolver: Option<Box<dyn crate::ModuleResolver>>,
+    pub(crate) module_resolver: Box<dyn crate::ModuleResolver>,
 
     /// A hashmap mapping type names to pretty-print names.
     pub(crate) type_names: HashMap<String, String>,
@@ -628,7 +636,7 @@ pub struct Engine {
     /// A hashset containing symbols to disable.
     pub(crate) disabled_symbols: HashSet<String>,
     /// A hashmap containing custom keywords and precedence to recognize.
-    pub(crate) custom_keywords: HashMap<String, Option<u8>>,
+    pub(crate) custom_keywords: HashMap<String, Option<NonZeroU8>>,
     /// Custom syntax.
     pub(crate) custom_syntax: HashMap<ImmutableString, CustomSyntax>,
     /// Callback closure for resolving variable access.
@@ -752,7 +760,7 @@ impl Engine {
             #[cfg(not(feature = "no_module"))]
             #[cfg(not(feature = "no_std"))]
             #[cfg(not(target_arch = "wasm32"))]
-            module_resolver: Some(Box::new(crate::module::resolvers::FileModuleResolver::new())),
+            module_resolver: Box::new(crate::module::resolvers::FileModuleResolver::new()),
             #[cfg(not(feature = "no_module"))]
             #[cfg(any(feature = "no_std", target_arch = "wasm32",))]
             module_resolver: None,
@@ -815,7 +823,7 @@ impl Engine {
             global_sub_modules: Default::default(),
 
             #[cfg(not(feature = "no_module"))]
-            module_resolver: None,
+            module_resolver: Box::new(crate::module::resolvers::DummyModuleResolver::new()),
 
             type_names: Default::default(),
             disabled_symbols: Default::default(),
@@ -856,19 +864,19 @@ impl Engine {
 
     /// Search for a variable within the scope or within imports,
     /// depending on whether the variable name is namespace-qualified.
-    pub(crate) fn search_namespace<'s, 'a>(
+    pub(crate) fn search_namespace<'s>(
         &self,
         scope: &'s mut Scope,
         mods: &mut Imports,
         state: &mut State,
         lib: &[&Module],
         this_ptr: &'s mut Option<&mut Dynamic>,
-        expr: &'a Expr,
-    ) -> Result<(Target<'s>, &'a str, Position), Box<EvalAltResult>> {
+        expr: &Expr,
+    ) -> Result<(Target<'s>, Position), Box<EvalAltResult>> {
         match expr {
             Expr::Variable(v) => match v.as_ref() {
                 // Qualified variable
-                (_, Some(modules), hash_var, Ident { name, pos }) => {
+                (_, Some((hash_var, modules)), Ident { name, pos }) => {
                     let module = search_imports(mods, state, modules)?;
                     let target = module.get_qualified_var(*hash_var).map_err(|mut err| {
                         match *err {
@@ -883,7 +891,7 @@ impl Engine {
                     // Module variables are constant
                     let mut target = target.clone();
                     target.set_access_mode(AccessMode::ReadOnly);
-                    Ok((target.into(), name, *pos))
+                    Ok((target.into(), *pos))
                 }
                 // Normal variable access
                 _ => self.search_scope_only(scope, mods, state, lib, this_ptr, expr),
@@ -893,16 +901,16 @@ impl Engine {
     }
 
     /// Search for a variable within the scope
-    pub(crate) fn search_scope_only<'s, 'a>(
+    pub(crate) fn search_scope_only<'s>(
         &self,
         scope: &'s mut Scope,
         mods: &mut Imports,
         state: &mut State,
         lib: &[&Module],
         this_ptr: &'s mut Option<&mut Dynamic>,
-        expr: &'a Expr,
-    ) -> Result<(Target<'s>, &'a str, Position), Box<EvalAltResult>> {
-        let (index, _, _, Ident { name, pos }) = match expr {
+        expr: &Expr,
+    ) -> Result<(Target<'s>, Position), Box<EvalAltResult>> {
+        let (index, _, Ident { name, pos }) = match expr {
             Expr::Variable(v) => v.as_ref(),
             _ => unreachable!(),
         };
@@ -910,7 +918,7 @@ impl Engine {
         // Check if the variable is `this`
         if name.as_str() == KEYWORD_THIS {
             if let Some(val) = this_ptr {
-                return Ok(((*val).into(), KEYWORD_THIS, *pos));
+                return Ok(((*val).into(), *pos));
             } else {
                 return EvalAltResult::ErrorUnboundThis(*pos).into();
             }
@@ -938,7 +946,7 @@ impl Engine {
                 resolve_var(name, index, &context).map_err(|err| err.fill_position(*pos))?
             {
                 result.set_access_mode(AccessMode::ReadOnly);
-                return Ok((result.into(), name, *pos));
+                return Ok((result.into(), *pos));
             }
         }
 
@@ -952,7 +960,7 @@ impl Engine {
                 .0
         };
 
-        let val = scope.get_mut(index);
+        let val = scope.get_mut_by_index(index);
 
         // Check for data race - probably not necessary because the only place it should conflict is in a method call
         //                       when the object variable is also used as a parameter.
@@ -960,7 +968,7 @@ impl Engine {
         //     return EvalAltResult::ErrorDataRace(name.into(), *pos).into();
         // }
 
-        Ok((val.into(), name, *pos))
+        Ok((val.into(), *pos))
     }
 
     /// Chain-evaluate a dot/index chain.
@@ -980,7 +988,7 @@ impl Engine {
         new_val: Option<(Dynamic, Position)>,
     ) -> Result<(Dynamic, bool), Box<EvalAltResult>> {
         if chain_type == ChainType::None {
-            panic!();
+            unreachable!();
         }
 
         let is_ref = target.is_ref();
@@ -1047,7 +1055,7 @@ impl Engine {
                             let args = &mut [target_val, &mut idx_val2, &mut new_val.0];
 
                             self.exec_fn_call(
-                                mods, state, lib, FN_IDX_SET, 0, args, is_ref, true, false,
+                                mods, state, lib, FN_IDX_SET, None, args, is_ref, true, false,
                                 new_val.1, None, None, level,
                             )
                             .map_err(|err| match *err {
@@ -1083,23 +1091,22 @@ impl Engine {
                     Expr::FnCall(x, pos) if x.namespace.is_none() => {
                         let FnCallExpr {
                             name,
-                            native_only: native,
-                            hash,
+                            hash_script: hash,
                             def_value,
                             ..
                         } = x.as_ref();
                         let def_value = def_value.as_ref();
                         let args = idx_val.as_fn_call_args();
                         self.make_method_call(
-                            mods, state, lib, name, *hash, target, args, def_value, *native, false,
-                            *pos, level,
+                            mods, state, lib, name, *hash, target, args, def_value, false, *pos,
+                            level,
                         )
                     }
                     // xxx.module::fn_name(...) - syntax error
                     Expr::FnCall(_, _) => unreachable!(),
                     // {xxx:map}.id = ???
                     Expr::Property(x) if target_val.is::<Map>() && new_val.is_some() => {
-                        let Ident { name, pos } = &x.1;
+                        let Ident { name, pos } = &x.2;
                         let index = name.clone().into();
                         let mut val = self.get_indexed_mut(
                             mods, state, lib, target_val, index, *pos, true, is_ref, false, level,
@@ -1112,7 +1119,7 @@ impl Engine {
                     }
                     // {xxx:map}.id
                     Expr::Property(x) if target_val.is::<Map>() => {
-                        let Ident { name, pos } = &x.1;
+                        let Ident { name, pos } = &x.2;
                         let index = name.clone().into();
                         let val = self.get_indexed_mut(
                             mods, state, lib, target_val, index, *pos, false, is_ref, false, level,
@@ -1122,11 +1129,11 @@ impl Engine {
                     }
                     // xxx.id = ???
                     Expr::Property(x) if new_val.is_some() => {
-                        let ((_, setter), Ident { pos, .. }) = x.as_ref();
+                        let (_, setter, Ident { pos, .. }) = x.as_ref();
                         let mut new_val = new_val;
                         let mut args = [target_val, &mut new_val.as_mut().unwrap().0];
                         self.exec_fn_call(
-                            mods, state, lib, setter, 0, &mut args, is_ref, true, false, *pos,
+                            mods, state, lib, setter, None, &mut args, is_ref, true, false, *pos,
                             None, None, level,
                         )
                         .map(|(v, _)| (v, true))
@@ -1134,10 +1141,10 @@ impl Engine {
                     }
                     // xxx.id
                     Expr::Property(x) => {
-                        let ((getter, _), Ident { pos, .. }) = x.as_ref();
+                        let (getter, _, Ident { pos, .. }) = x.as_ref();
                         let mut args = [target_val];
                         self.exec_fn_call(
-                            mods, state, lib, getter, 0, &mut args, is_ref, true, false, *pos,
+                            mods, state, lib, getter, None, &mut args, is_ref, true, false, *pos,
                             None, None, level,
                         )
                         .map(|(v, _)| (v, false))
@@ -1147,7 +1154,7 @@ impl Engine {
                     Expr::Index(x, x_pos) | Expr::Dot(x, x_pos) if target_val.is::<Map>() => {
                         let mut val = match &x.lhs {
                             Expr::Property(p) => {
-                                let Ident { name, pos } = &p.1;
+                                let Ident { name, pos } = &p.2;
                                 let index = name.clone().into();
                                 self.get_indexed_mut(
                                     mods, state, lib, target_val, index, *pos, false, is_ref, true,
@@ -1158,16 +1165,15 @@ impl Engine {
                             Expr::FnCall(x, pos) if x.namespace.is_none() => {
                                 let FnCallExpr {
                                     name,
-                                    native_only: native,
-                                    hash,
+                                    hash_script: hash,
                                     def_value,
                                     ..
                                 } = x.as_ref();
                                 let def_value = def_value.as_ref();
                                 let args = idx_val.as_fn_call_args();
                                 let (val, _) = self.make_method_call(
-                                    mods, state, lib, name, *hash, target, args, def_value,
-                                    *native, false, *pos, level,
+                                    mods, state, lib, name, *hash, target, args, def_value, false,
+                                    *pos, level,
                                 )?;
                                 val.into()
                             }
@@ -1188,12 +1194,12 @@ impl Engine {
                         match &x.lhs {
                             // xxx.prop[expr] | xxx.prop.expr
                             Expr::Property(p) => {
-                                let ((getter, setter), Ident { pos, .. }) = p.as_ref();
+                                let (getter, setter, Ident { pos, .. }) = p.as_ref();
                                 let arg_values = &mut [target_val, &mut Default::default()];
                                 let args = &mut arg_values[..1];
                                 let (mut val, updated) = self
                                     .exec_fn_call(
-                                        mods, state, lib, getter, 0, args, is_ref, true, false,
+                                        mods, state, lib, getter, None, args, is_ref, true, false,
                                         *pos, None, None, level,
                                     )
                                     .map_err(|err| err.fill_position(*pos))?;
@@ -1220,7 +1226,7 @@ impl Engine {
                                     // Re-use args because the first &mut parameter will not be consumed
                                     arg_values[1] = val;
                                     self.exec_fn_call(
-                                        mods, state, lib, setter, 0, arg_values, is_ref, true,
+                                        mods, state, lib, setter, None, arg_values, is_ref, true,
                                         false, *pos, None, None, level,
                                     )
                                     .or_else(
@@ -1240,16 +1246,15 @@ impl Engine {
                             Expr::FnCall(f, pos) if f.namespace.is_none() => {
                                 let FnCallExpr {
                                     name,
-                                    native_only: native,
-                                    hash,
+                                    hash_script: hash,
                                     def_value,
                                     ..
                                 } = f.as_ref();
                                 let def_value = def_value.as_ref();
                                 let args = idx_val.as_fn_call_args();
                                 let (mut val, _) = self.make_method_call(
-                                    mods, state, lib, name, *hash, target, args, def_value,
-                                    *native, false, *pos, level,
+                                    mods, state, lib, name, *hash, target, args, def_value, false,
+                                    *pos, level,
                                 )?;
                                 let val = &mut val;
                                 let target = &mut val.into();
@@ -1306,11 +1311,11 @@ impl Engine {
                 let Ident {
                     name: var_name,
                     pos: var_pos,
-                } = &x.3;
+                } = &x.2;
 
                 self.inc_operations(state, *var_pos)?;
 
-                let (target, _, pos) =
+                let (target, pos) =
                     self.search_namespace(scope, mods, state, lib, this_ptr, lhs)?;
 
                 // Constants cannot be modified
@@ -1501,8 +1506,8 @@ impl Engine {
                 let mut idx = idx;
                 let args = &mut [target, &mut idx];
                 self.exec_fn_call(
-                    _mods, state, _lib, FN_IDX_GET, 0, args, _is_ref, true, false, idx_pos, None,
-                    None, _level,
+                    _mods, state, _lib, FN_IDX_GET, None, args, _is_ref, true, false, idx_pos,
+                    None, None, _level,
                 )
                 .map(|(v, _)| v.into())
                 .map_err(|err| match *err {
@@ -1553,7 +1558,8 @@ impl Engine {
 
                     // Qualifiers (none) + function name + number of arguments + argument `TypeId`'s.
                     let hash =
-                        calc_native_fn_hash(empty(), OP_EQUALS, args.iter().map(|a| a.type_id()));
+                        calc_native_fn_hash(empty(), OP_EQUALS, args.iter().map(|a| a.type_id()))
+                            .unwrap();
 
                     let pos = rhs.position();
 
@@ -1603,7 +1609,7 @@ impl Engine {
         match expr {
             // var - point directly to the value
             Expr::Variable(_) => {
-                let (mut target, _, pos) =
+                let (mut target, pos) =
                     self.search_namespace(scope, mods, state, lib, this_ptr, expr)?;
 
                 // If necessary, constants are cloned
@@ -1659,7 +1665,7 @@ impl Engine {
 
                     if target.is::<Map>() {
                         // map.prop - point directly to the item
-                        let (_, Ident { name, pos }) = p.as_ref();
+                        let (_, _, Ident { name, pos }) = p.as_ref();
                         let idx = name.clone().into();
 
                         if target.is_shared() || target.is_value() {
@@ -1677,10 +1683,10 @@ impl Engine {
                         .map(|v| (v, *pos))
                     } else {
                         // var.prop - call property getter
-                        let ((getter, _), Ident { pos, .. }) = p.as_ref();
+                        let (getter, _, Ident { pos, .. }) = p.as_ref();
                         let mut args = [target.as_mut()];
                         self.exec_fn_call(
-                            mods, state, lib, getter, 0, &mut args, is_ref, true, false, *pos,
+                            mods, state, lib, getter, None, &mut args, is_ref, true, false, *pos,
                             None, None, level,
                         )
                         .map(|(v, _)| (v.into(), *pos))
@@ -1721,15 +1727,15 @@ impl Engine {
             Expr::StringConstant(x, _) => Ok(x.clone().into()),
             Expr::CharConstant(x, _) => Ok((*x).into()),
             Expr::FnPointer(x, _) => Ok(FnPtr::new_unchecked(x.clone(), Default::default()).into()),
-            Expr::Variable(x) if (x.3).name == KEYWORD_THIS => {
+            Expr::Variable(x) if (x.2).name == KEYWORD_THIS => {
                 if let Some(val) = this_ptr {
                     Ok(val.clone())
                 } else {
-                    EvalAltResult::ErrorUnboundThis((x.3).pos).into()
+                    EvalAltResult::ErrorUnboundThis((x.2).pos).into()
                 }
             }
             Expr::Variable(_) => {
-                let (val, _, _) = self.search_namespace(scope, mods, state, lib, this_ptr, expr)?;
+                let (val, _) = self.search_namespace(scope, mods, state, lib, this_ptr, expr)?;
                 Ok(val.take_or_clone())
             }
             Expr::Property(_) => unreachable!(),
@@ -1778,17 +1784,16 @@ impl Engine {
             Expr::FnCall(x, pos) if x.namespace.is_none() => {
                 let FnCallExpr {
                     name,
-                    native_only: native,
                     capture: cap_scope,
-                    hash,
+                    hash_script: hash,
                     args,
                     def_value,
                     ..
                 } = x.as_ref();
                 let def_value = def_value.as_ref();
                 self.make_function_call(
-                    scope, mods, state, lib, this_ptr, name, args, def_value, *hash, *native,
-                    false, *pos, *cap_scope, level,
+                    scope, mods, state, lib, this_ptr, name, args, def_value, *hash, false, *pos,
+                    *cap_scope, level,
                 )
             }
 
@@ -1797,15 +1802,16 @@ impl Engine {
                 let FnCallExpr {
                     name,
                     namespace,
-                    hash,
+                    hash_script: hash,
                     args,
                     def_value,
                     ..
                 } = x.as_ref();
-                let namespace = namespace.as_ref().map(|v| v.as_ref());
+                let namespace = namespace.as_ref();
+                let hash = hash.unwrap();
                 let def_value = def_value.as_ref();
                 self.make_qualified_function_call(
-                    scope, mods, state, lib, this_ptr, namespace, name, args, def_value, *hash,
+                    scope, mods, state, lib, this_ptr, namespace, name, args, def_value, hash,
                     *pos, level,
                 )
             }
@@ -1935,11 +1941,15 @@ impl Engine {
                 let mut rhs_val = self
                     .eval_expr(scope, mods, state, lib, this_ptr, rhs_expr, level)?
                     .flatten();
-                let (mut lhs_ptr, name, pos) =
+                let (mut lhs_ptr, pos) =
                     self.search_namespace(scope, mods, state, lib, this_ptr, lhs_expr)?;
 
                 if !lhs_ptr.is_ref() {
-                    return EvalAltResult::ErrorAssignmentToConstant(name.to_string(), pos).into();
+                    return EvalAltResult::ErrorAssignmentToConstant(
+                        lhs_expr.get_variable_access(false).unwrap().to_string(),
+                        pos,
+                    )
+                    .into();
                 }
 
                 self.inc_operations(state, pos)?;
@@ -1947,7 +1957,7 @@ impl Engine {
                 if lhs_ptr.as_ref().is_read_only() {
                     // Assignment to constant variable
                     Err(Box::new(EvalAltResult::ErrorAssignmentToConstant(
-                        name.to_string(),
+                        lhs_expr.get_variable_access(false).unwrap().to_string(),
                         pos,
                     )))
                 } else if op.is_empty() {
@@ -1966,7 +1976,7 @@ impl Engine {
 
                     // Qualifiers (none) + function name + number of arguments + argument `TypeId`'s.
                     let arg_types = once(lhs_ptr.as_mut().type_id()).chain(once(rhs_val.type_id()));
-                    let hash_fn = calc_native_fn_hash(empty(), op, arg_types);
+                    let hash_fn = calc_native_fn_hash(empty(), op, arg_types).unwrap();
 
                     match self
                         .global_namespace
@@ -2015,8 +2025,8 @@ impl Engine {
 
                             // Run function
                             let (value, _) = self.exec_fn_call(
-                                mods, state, lib, op, 0, args, false, false, false, *op_pos, None,
-                                None, level,
+                                mods, state, lib, op, None, args, false, false, false, *op_pos,
+                                None, None, level,
                             )?;
 
                             let value = value.flatten();
@@ -2051,7 +2061,7 @@ impl Engine {
 
                     let result = self
                         .exec_fn_call(
-                            mods, state, lib, op, 0, args, false, false, false, *op_pos, None,
+                            mods, state, lib, op, None, args, false, false, false, *op_pos, None,
                             None, level,
                         )
                         .map(|(v, _)| v)?;
@@ -2203,7 +2213,7 @@ impl Engine {
                     state.scope_level += 1;
 
                     for iter_value in func(iter_obj) {
-                        let loop_var = scope.get_mut(index);
+                        let loop_var = scope.get_mut_by_index(index);
 
                         let value = iter_value.flatten();
                         if cfg!(not(feature = "no_closure")) && loop_var.is_shared() {
@@ -2369,31 +2379,24 @@ impl Engine {
                     .eval_expr(scope, mods, state, lib, this_ptr, &expr, level)?
                     .try_cast::<ImmutableString>()
                 {
-                    if let Some(resolver) = &self.module_resolver {
-                        let module = resolver.resolve(self, &path, expr.position())?;
+                    let module = self.module_resolver.resolve(self, &path, expr.position())?;
 
-                        if let Some(name_def) = alias {
-                            if !module.is_indexed() {
-                                // Index the module (making a clone copy if necessary) if it is not indexed
-                                let mut module = crate::fn_native::shared_take_or_clone(module);
-                                module.build_index();
-                                mods.push(name_def.name.clone(), module);
-                            } else {
-                                mods.push(name_def.name.clone(), module);
-                            }
-                            // When imports list is modified, clear the functions lookup cache
-                            state.functions_cache.clear();
+                    if let Some(name_def) = alias {
+                        if !module.is_indexed() {
+                            // Index the module (making a clone copy if necessary) if it is not indexed
+                            let mut module = crate::fn_native::shared_take_or_clone(module);
+                            module.build_index();
+                            mods.push(name_def.name.clone(), module);
+                        } else {
+                            mods.push(name_def.name.clone(), module);
                         }
-
-                        state.modules += 1;
-
-                        Ok(Dynamic::UNIT)
-                    } else {
-                        Err(
-                            EvalAltResult::ErrorModuleNotFound(path.to_string(), expr.position())
-                                .into(),
-                        )
+                        // When imports list is modified, clear the functions lookup cache
+                        state.functions_cache.clear();
                     }
+
+                    state.modules += 1;
+
+                    Ok(Dynamic::UNIT)
                 } else {
                     Err(self.make_type_mismatch_err::<ImmutableString>("", expr.position()))
                 }
@@ -2419,7 +2422,7 @@ impl Engine {
             #[cfg(not(feature = "no_closure"))]
             Stmt::Share(x) => {
                 if let Some((index, _)) = scope.get_index(&x.name) {
-                    let val = scope.get_mut(index);
+                    let val = scope.get_mut_by_index(index);
 
                     if !val.is_shared() {
                         // Replace the variable with a shared value.
diff --git a/src/engine_api.rs b/src/engine_api.rs
index 0a38b820..026e0df8 100644
--- a/src/engine_api.rs
+++ b/src/engine_api.rs
@@ -209,9 +209,10 @@ impl Engine {
     pub fn register_get<T: Variant + Clone, U: Variant + Clone>(
         &mut self,
         name: &str,
-        callback: impl Fn(&mut T) -> U + SendSync + 'static,
+        get_fn: impl Fn(&mut T) -> U + SendSync + 'static,
     ) -> &mut Self {
-        crate::RegisterFn::register_fn(self, &crate::engine::make_getter(name), callback)
+        use crate::{engine::make_getter, RegisterFn};
+        self.register_fn(&make_getter(name), get_fn)
     }
     /// Register a getter function for a member of a registered type with the [`Engine`].
     ///
@@ -255,13 +256,10 @@ impl Engine {
     pub fn register_get_result<T: Variant + Clone>(
         &mut self,
         name: &str,
-        callback: impl Fn(&mut T) -> Result<Dynamic, Box<EvalAltResult>> + SendSync + 'static,
+        get_fn: impl Fn(&mut T) -> Result<Dynamic, Box<EvalAltResult>> + SendSync + 'static,
     ) -> &mut Self {
-        crate::RegisterResultFn::register_result_fn(
-            self,
-            &crate::engine::make_getter(name),
-            callback,
-        )
+        use crate::{engine::make_getter, RegisterResultFn};
+        self.register_result_fn(&make_getter(name), get_fn)
     }
     /// Register a setter function for a member of a registered type with the [`Engine`].
     ///
@@ -304,9 +302,10 @@ impl Engine {
     pub fn register_set<T: Variant + Clone, U: Variant + Clone>(
         &mut self,
         name: &str,
-        callback: impl Fn(&mut T, U) + SendSync + 'static,
+        set_fn: impl Fn(&mut T, U) + SendSync + 'static,
     ) -> &mut Self {
-        crate::RegisterFn::register_fn(self, &crate::engine::make_setter(name), callback)
+        use crate::{engine::make_setter, RegisterFn};
+        self.register_fn(&make_setter(name), set_fn)
     }
     /// Register a setter function for a member of a registered type with the [`Engine`].
     ///
@@ -352,13 +351,12 @@ impl Engine {
     pub fn register_set_result<T: Variant + Clone, U: Variant + Clone>(
         &mut self,
         name: &str,
-        callback: impl Fn(&mut T, U) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
+        set_fn: impl Fn(&mut T, U) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
     ) -> &mut Self {
-        crate::RegisterResultFn::register_result_fn(
-            self,
-            &crate::engine::make_setter(name),
-            move |obj: &mut T, value: U| callback(obj, value).map(Into::into),
-        )
+        use crate::{engine::make_setter, RegisterResultFn};
+        self.register_result_fn(&make_setter(name), move |obj: &mut T, value: U| {
+            set_fn(obj, value).map(Into::into)
+        })
     }
     /// Short-hand for registering both getter and setter functions
     /// of a registered type with the [`Engine`].
@@ -453,7 +451,7 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_get<T: Variant + Clone, X: Variant + Clone, U: Variant + Clone>(
         &mut self,
-        callback: impl Fn(&mut T, X) -> U + SendSync + 'static,
+        get_fn: impl Fn(&mut T, X) -> U + SendSync + 'static,
     ) -> &mut Self {
         if TypeId::of::<T>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
@@ -469,7 +467,8 @@ impl Engine {
             panic!("Cannot register indexer for strings.");
         }
 
-        crate::RegisterFn::register_fn(self, crate::engine::FN_IDX_GET, callback)
+        use crate::{engine::FN_IDX_GET, RegisterFn};
+        self.register_fn(FN_IDX_GET, get_fn)
     }
     /// Register an index getter for a custom type with the [`Engine`].
     ///
@@ -518,7 +517,7 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_get_result<T: Variant + Clone, X: Variant + Clone>(
         &mut self,
-        callback: impl Fn(&mut T, X) -> Result<Dynamic, Box<EvalAltResult>> + SendSync + 'static,
+        get_fn: impl Fn(&mut T, X) -> Result<Dynamic, Box<EvalAltResult>> + SendSync + 'static,
     ) -> &mut Self {
         if TypeId::of::<T>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
@@ -534,7 +533,8 @@ impl Engine {
             panic!("Cannot register indexer for strings.");
         }
 
-        crate::RegisterResultFn::register_result_fn(self, crate::engine::FN_IDX_GET, callback)
+        use crate::{engine::FN_IDX_GET, RegisterResultFn};
+        self.register_result_fn(FN_IDX_GET, get_fn)
     }
     /// Register an index setter for a custom type with the [`Engine`].
     ///
@@ -581,7 +581,7 @@ impl Engine {
     #[inline(always)]
     pub fn register_indexer_set<T: Variant + Clone, X: Variant + Clone, U: Variant + Clone>(
         &mut self,
-        callback: impl Fn(&mut T, X, U) + SendSync + 'static,
+        set_fn: impl Fn(&mut T, X, U) + SendSync + 'static,
     ) -> &mut Self {
         if TypeId::of::<T>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
@@ -597,7 +597,8 @@ impl Engine {
             panic!("Cannot register indexer for strings.");
         }
 
-        crate::RegisterFn::register_fn(self, crate::engine::FN_IDX_SET, callback)
+        use crate::{engine::FN_IDX_SET, RegisterFn};
+        self.register_fn(FN_IDX_SET, set_fn)
     }
     /// Register an index setter for a custom type with the [`Engine`].
     ///
@@ -651,7 +652,7 @@ impl Engine {
         U: Variant + Clone,
     >(
         &mut self,
-        callback: impl Fn(&mut T, X, U) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
+        set_fn: impl Fn(&mut T, X, U) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
     ) -> &mut Self {
         if TypeId::of::<T>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
@@ -667,11 +668,10 @@ impl Engine {
             panic!("Cannot register indexer for strings.");
         }
 
-        crate::RegisterResultFn::register_result_fn(
-            self,
-            crate::engine::FN_IDX_SET,
-            move |obj: &mut T, index: X, value: U| callback(obj, index, value).map(Into::into),
-        )
+        use crate::{engine::FN_IDX_SET, RegisterResultFn};
+        self.register_result_fn(FN_IDX_SET, move |obj: &mut T, index: X, value: U| {
+            set_fn(obj, index, value).map(Into::into)
+        })
     }
     /// Short-hand for register both index getter and setter functions for a custom type with the [`Engine`].
     ///
@@ -723,21 +723,22 @@ impl Engine {
         self.register_indexer_get(getter)
             .register_indexer_set(setter)
     }
-    /// Register a shared [`Module`][crate::Module] into the global namespace of [`Engine`].
+    /// Register a shared [`Module`] into the global namespace of [`Engine`].
     ///
-    /// All functions and type iterators are automatically available to scripts without namespace qualifications.
+    /// All functions and type iterators are automatically available to scripts without namespace
+    /// qualifications.
     ///
     /// Sub-modules and variables are **ignored**.
     ///
-    /// When searching for functions, modules loaded later are preferred.
-    /// In other words, loaded modules are searched in reverse order.
+    /// When searching for functions, modules loaded later are preferred. In other words, loaded
+    /// modules are searched in reverse order.
     #[inline(always)]
     pub fn register_global_module(&mut self, module: Shared<Module>) -> &mut Self {
         // Insert the module into the front
         self.global_modules.insert(0, module);
         self
     }
-    /// Register a shared [`Module`][crate::Module] into the global namespace of [`Engine`].
+    /// Register a shared [`Module`] into the global namespace of [`Engine`].
     ///
     /// ## Deprecated
     ///
@@ -747,15 +748,17 @@ impl Engine {
     pub fn load_package(&mut self, module: impl Into<Shared<Module>>) -> &mut Self {
         self.register_global_module(module.into())
     }
-    /// Register a shared [`Module`][crate::Module] as a static module namespace with the [`Engine`].
+    /// Register a shared [`Module`] as a static module namespace with the
+    /// [`Engine`].
     ///
-    /// Functions marked `FnNamespace::Global` and type iterators are exposed to scripts without namespace qualifications.
+    /// Functions marked [`FnNamespace::Global`] and type iterators are exposed to scripts without
+    /// namespace qualifications.
     ///
     /// # Example
     ///
     /// ```
     /// # fn main() -> Result<(), Box<rhai::EvalAltResult>> {
-    /// use rhai::{Engine, Module};
+    /// use rhai::{Engine, Shared, Module};
     ///
     /// let mut engine = Engine::new();
     ///
@@ -763,9 +766,18 @@ impl Engine {
     /// let mut module = Module::new();
     /// module.set_fn_1("calc", |x: i64| Ok(x + 1));
     ///
-    /// // Register the module as a fixed sub-module
-    /// engine.register_static_module("CalcService", module.into());
+    /// let module: Shared<Module> = module.into();
     ///
+    /// // Register the module as a fixed sub-module
+    /// engine.register_static_module("foo::bar::baz", module.clone());
+    ///
+    /// // Multiple registrations to the same partial path is also OK!
+    /// engine.register_static_module("foo::bar::hello", module.clone());
+    ///
+    /// engine.register_static_module("CalcService", module);
+    ///
+    /// assert_eq!(engine.eval::<i64>("foo::bar::baz::calc(41)")?, 42);
+    /// assert_eq!(engine.eval::<i64>("foo::bar::hello::calc(41)")?, 42);
     /// assert_eq!(engine.eval::<i64>("CalcService::calc(41)")?, 42);
     /// # Ok(())
     /// # }
@@ -773,20 +785,50 @@ impl Engine {
     #[cfg(not(feature = "no_module"))]
     pub fn register_static_module(
         &mut self,
-        name: impl Into<crate::ImmutableString>,
+        name: impl AsRef<str>,
         module: Shared<Module>,
     ) -> &mut Self {
-        if !module.is_indexed() {
-            // Index the module (making a clone copy if necessary) if it is not indexed
-            let mut module = crate::fn_native::shared_take_or_clone(module);
-            module.build_index();
-            self.global_sub_modules.push(name, module);
-        } else {
-            self.global_sub_modules.push(name, module);
+        fn register_static_module_raw(
+            root: &mut crate::stdlib::collections::HashMap<crate::ImmutableString, Shared<Module>>,
+            name: impl AsRef<str>,
+            module: Shared<Module>,
+        ) {
+            let separator = crate::token::Token::DoubleColon.syntax();
+
+            if !name.as_ref().contains(separator.as_ref()) {
+                if !module.is_indexed() {
+                    // Index the module (making a clone copy if necessary) if it is not indexed
+                    let mut module = crate::fn_native::shared_take_or_clone(module);
+                    module.build_index();
+                    root.insert(name.as_ref().trim().into(), module.into());
+                } else {
+                    root.insert(name.as_ref().trim().into(), module);
+                }
+            } else {
+                let mut iter = name.as_ref().splitn(2, separator.as_ref());
+                let sub_module = iter.next().unwrap().trim();
+                let remainder = iter.next().unwrap().trim();
+
+                if !root.contains_key(sub_module) {
+                    let mut m: Module = Default::default();
+                    register_static_module_raw(m.sub_modules_mut(), remainder, module);
+                    m.build_index();
+                    root.insert(sub_module.into(), m.into());
+                } else {
+                    let m = root.remove(sub_module).unwrap();
+                    let mut m = crate::fn_native::shared_take_or_clone(m);
+                    register_static_module_raw(m.sub_modules_mut(), remainder, module);
+                    m.build_index();
+                    root.insert(sub_module.into(), m.into());
+                }
+            }
         }
+
+        register_static_module_raw(&mut self.global_sub_modules, name.as_ref(), module);
         self
     }
-    /// Register a shared [`Module`][crate::Module] as a static module namespace with the [`Engine`].
+
+    /// Register a shared [`Module`] as a static module namespace with the [`Engine`].
     ///
     /// ## Deprecated
     ///
@@ -796,7 +838,7 @@ impl Engine {
     #[deprecated = "use `register_static_module` instead"]
     pub fn register_module(
         &mut self,
-        name: impl Into<crate::ImmutableString>,
+        name: impl AsRef<str>,
         module: impl Into<Shared<Module>>,
     ) -> &mut Self {
         self.register_static_module(name, module.into())
@@ -1407,7 +1449,7 @@ impl Engine {
         scope: &mut Scope,
         ast: &AST,
     ) -> Result<T, Box<EvalAltResult>> {
-        let mods = &mut self.global_sub_modules.clone();
+        let mods = &mut (&self.global_sub_modules).into();
 
         let result = self.eval_ast_with_scope_raw(scope, mods, ast)?;
 
@@ -1493,7 +1535,7 @@ impl Engine {
         scope: &mut Scope,
         ast: &AST,
     ) -> Result<(), Box<EvalAltResult>> {
-        let mods = &mut self.global_sub_modules.clone();
+        let mods = &mut (&self.global_sub_modules).into();
         let state = &mut State {
             source: ast.clone_source(),
             ..Default::default()
@@ -1539,12 +1581,12 @@ impl Engine {
     /// ```
     #[cfg(not(feature = "no_function"))]
     #[inline]
-    pub fn call_fn<A: crate::fn_args::FuncArgs, T: Variant + Clone>(
+    pub fn call_fn<T: Variant + Clone>(
         &self,
         scope: &mut Scope,
         ast: &AST,
         name: &str,
-        args: A,
+        args: impl crate::fn_args::FuncArgs,
     ) -> Result<T, Box<EvalAltResult>> {
         let mut arg_values = args.into_vec();
         let mut args: crate::StaticVec<_> = arg_values.as_mut().iter_mut().collect();
@@ -1650,7 +1692,7 @@ impl Engine {
             .ok_or_else(|| EvalAltResult::ErrorFunctionNotFound(name.into(), Position::NONE))?;
 
         let mut state = Default::default();
-        let mut mods = self.global_sub_modules.clone();
+        let mut mods = (&self.global_sub_modules).into();
 
         // Check for data race.
         if cfg!(not(feature = "no_closure")) {
@@ -1680,7 +1722,7 @@ impl Engine {
     /// With this method, it is no longer necessary to recompile a large script.
     /// The script [`AST`] can be compiled just once. Before evaluation,
     /// constants are passed into the [`Engine`] via an external scope
-    /// (i.e. with [`scope.push_constant(...)`][crate::Scope::push_constant]).
+    /// (i.e. with [`Scope::push_constant`]).
     /// Then, the [`AST`] is cloned and the copy re-optimized before running.
     #[cfg(not(feature = "no_optimize"))]
     #[inline]
diff --git a/src/engine_settings.rs b/src/engine_settings.rs
index 7d5d17f4..1a291ccc 100644
--- a/src/engine_settings.rs
+++ b/src/engine_settings.rs
@@ -1,7 +1,7 @@
 //! Configuration settings for [`Engine`].
 
-use crate::stdlib::{format, string::String};
-use crate::token::{is_valid_identifier, Token};
+use crate::stdlib::{format, num::NonZeroU8, string::String};
+use crate::token::Token;
 use crate::Engine;
 
 #[cfg(not(feature = "no_module"))]
@@ -168,9 +168,9 @@ impl Engine {
     #[inline(always)]
     pub fn set_module_resolver(
         &mut self,
-        resolver: Option<impl crate::ModuleResolver + 'static>,
+        resolver: impl crate::ModuleResolver + 'static,
     ) -> &mut Self {
-        self.module_resolver = resolver.map(|f| Box::new(f) as Box<dyn crate::ModuleResolver>);
+        self.module_resolver = Box::new(resolver);
         self
     }
     /// Disable a particular keyword or operator in the language.
@@ -214,10 +214,12 @@ impl Engine {
         self.disabled_symbols.insert(symbol.into());
         self
     }
-    /// Register a custom operator into the language.
+    /// Register a custom operator with a precedence into the language.
     ///
     /// The operator must be a valid identifier (i.e. it cannot be a symbol).
     ///
+    /// The precedence cannot be zero.
+    ///
     /// # Example
     ///
     /// ```rust
@@ -245,22 +247,38 @@ impl Engine {
         keyword: &str,
         precedence: u8,
     ) -> Result<&mut Self, String> {
-        if !is_valid_identifier(keyword.chars()) {
-            return Err(format!("not a valid identifier: '{}'", keyword).into());
+        let precedence = NonZeroU8::new(precedence);
+
+        if precedence.is_none() {
+            return Err("precedence cannot be zero".into());
         }
 
         match Token::lookup_from_syntax(keyword) {
             // Standard identifiers, reserved keywords and custom keywords are OK
             None | Some(Token::Reserved(_)) | Some(Token::Custom(_)) => (),
-            // Disabled keywords are also OK
-            Some(token) if !self.disabled_symbols.contains(token.syntax().as_ref()) => (),
             // Active standard keywords cannot be made custom
-            Some(_) => return Err(format!("'{}' is a reserved keyword", keyword).into()),
+            // Disabled keywords are OK
+            Some(token) if token.is_keyword() => {
+                if !self.disabled_symbols.contains(token.syntax().as_ref()) {
+                    return Err(format!("'{}' is a reserved keyword", keyword).into());
+                }
+            }
+            // Active standard operators cannot be made custom
+            Some(token) if token.is_operator() => {
+                if !self.disabled_symbols.contains(token.syntax().as_ref()) {
+                    return Err(format!("'{}' is a reserved operator", keyword).into());
+                }
+            }
+            // Active standard symbols cannot be made custom
+            Some(token) if !self.disabled_symbols.contains(token.syntax().as_ref()) => {
+                return Err(format!("'{}' is a reserved symbol", keyword).into())
+            }
+            // Disabled symbols are OK
+            Some(_) => (),
         }
 
         // Add to custom keywords
-        self.custom_keywords
-            .insert(keyword.into(), Some(precedence));
+        self.custom_keywords.insert(keyword.into(), precedence);
 
         Ok(self)
     }
diff --git a/src/fn_call.rs b/src/fn_call.rs
index 6d19919d..8b42985f 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -15,10 +15,12 @@ use crate::stdlib::{
     format,
     iter::{empty, once},
     mem,
+    num::NonZeroU64,
     ops::Deref,
     string::ToString,
     vec::Vec,
 };
+use crate::utils::combine_hashes;
 use crate::{
     calc_native_fn_hash, calc_script_fn_hash, Dynamic, Engine, EvalAltResult, FnPtr,
     ImmutableString, Module, ParseErrorType, Position, Scope, StaticVec, INT,
@@ -161,7 +163,7 @@ impl Engine {
         state: &mut State,
         lib: &[&Module],
         fn_name: &str,
-        hash_fn: u64,
+        hash_fn: NonZeroU64,
         args: &mut FnCallArgs,
         is_ref: bool,
         pub_only: bool,
@@ -453,22 +455,22 @@ impl Engine {
         &self,
         mods: Option<&Imports>,
         lib: &[&Module],
-        hash_fn: u64,
-        hash_script: u64,
+        hash_fn: Option<NonZeroU64>,
+        hash_script: Option<NonZeroU64>,
         pub_only: bool,
     ) -> bool {
         // First check script-defined functions
-        (hash_script != 0 && lib.iter().any(|&m| m.contains_fn(hash_script, pub_only)))
-            //|| lib.iter().any(|&m| m.contains_fn(hash_fn, pub_only))
+        hash_script.map(|hash| lib.iter().any(|&m| m.contains_fn(hash, pub_only))).unwrap_or(false)
+            //|| hash_fn.map(|hash| lib.iter().any(|&m| m.contains_fn(hash, pub_only))).unwrap_or(false)
             // Then check registered functions
-            //|| (hash_script != 0 && self.global_namespace.contains_fn(hash_script, pub_only))
-            || self.global_namespace.contains_fn(hash_fn, false)
+            //|| hash_script.map(|hash| self.global_namespace.contains_fn(hash, pub_only)).unwrap_or(false)
+            || hash_fn.map(|hash| self.global_namespace.contains_fn(hash, false)).unwrap_or(false)
             // Then check packages
-            || (hash_script != 0 && self.global_modules.iter().any(|m| m.contains_fn(hash_script, false)))
-            || self.global_modules.iter().any(|m| m.contains_fn(hash_fn, false))
+            || hash_script.map(|hash| self.global_modules.iter().any(|m| m.contains_fn(hash, false))).unwrap_or(false)
+            || hash_fn.map(|hash| self.global_modules.iter().any(|m| m.contains_fn(hash, false))).unwrap_or(false)
             // Then check imported modules
-            || (hash_script != 0 && mods.map(|m| m.contains_fn(hash_script)).unwrap_or(false))
-            || mods.map(|m| m.contains_fn(hash_fn)).unwrap_or(false)
+            || hash_script.map(|hash| mods.map(|m| m.contains_fn(hash)).unwrap_or(false)).unwrap_or(false)
+            || hash_fn.map(|hash| mods.map(|m| m.contains_fn(hash)).unwrap_or(false)).unwrap_or(false)
     }
 
     /// Perform an actual function call, native Rust or scripted, taking care of special functions.
@@ -484,7 +486,7 @@ impl Engine {
         state: &mut State,
         lib: &[&Module],
         fn_name: &str,
-        hash_script: u64,
+        hash_script: Option<NonZeroU64>,
         args: &mut FnCallArgs,
         is_ref: bool,
         _is_method: bool,
@@ -534,9 +536,11 @@ impl Engine {
 
             // Script-like function found
             #[cfg(not(feature = "no_function"))]
-            _ if hash_script != 0
-                && self.has_override(Some(mods), lib, 0, hash_script, pub_only) =>
+            _ if hash_script.is_some()
+                && self.has_override(Some(mods), lib, None, hash_script, pub_only) =>
             {
+                let hash_script = hash_script.unwrap();
+
                 // Get function
                 let (func, mut source) = lib
                     .iter()
@@ -636,7 +640,16 @@ impl Engine {
 
             // Normal native function call
             _ => self.call_native_fn(
-                mods, state, lib, fn_name, hash_fn, args, is_ref, pub_only, pos, def_val,
+                mods,
+                state,
+                lib,
+                fn_name,
+                hash_fn.unwrap(),
+                args,
+                is_ref,
+                pub_only,
+                pos,
+                def_val,
             ),
         }
     }
@@ -723,11 +736,10 @@ impl Engine {
         state: &mut State,
         lib: &[&Module],
         fn_name: &str,
-        hash_script: u64,
+        hash_script: Option<NonZeroU64>,
         target: &mut crate::engine::Target,
         mut call_args: StaticVec<Dynamic>,
         def_val: Option<&Dynamic>,
-        native: bool,
         pub_only: bool,
         pos: Position,
         level: usize,
@@ -745,11 +757,7 @@ impl Engine {
             let fn_name = fn_ptr.fn_name();
             let args_len = call_args.len() + fn_ptr.curry().len();
             // Recalculate hash
-            let hash = if native {
-                0
-            } else {
-                calc_script_fn_hash(empty(), fn_name, args_len)
-            };
+            let hash = hash_script.and_then(|_| calc_script_fn_hash(empty(), fn_name, args_len));
             // Arguments are passed as-is, adding the curried arguments
             let mut curry = fn_ptr.curry().iter().cloned().collect::<StaticVec<_>>();
             let mut arg_values = curry
@@ -773,11 +781,7 @@ impl Engine {
             let fn_name = fn_ptr.fn_name();
             let args_len = call_args.len() + fn_ptr.curry().len();
             // Recalculate hash
-            let hash = if native {
-                0
-            } else {
-                calc_script_fn_hash(empty(), fn_name, args_len)
-            };
+            let hash = hash_script.and_then(|_| calc_script_fn_hash(empty(), fn_name, args_len));
             // Replace the first argument with the object pointer, adding the curried arguments
             let mut curry = fn_ptr.curry().iter().cloned().collect::<StaticVec<_>>();
             let mut arg_values = once(obj)
@@ -837,17 +841,14 @@ impl Engine {
                             .enumerate()
                             .for_each(|(i, v)| call_args.insert(i, v));
                         // Recalculate the hash based on the new function name and new arguments
-                        hash = if native {
-                            0
-                        } else {
-                            calc_script_fn_hash(empty(), fn_name, call_args.len())
-                        };
+                        hash = hash_script
+                            .and_then(|_| calc_script_fn_hash(empty(), fn_name, call_args.len()));
                     }
                 }
             };
 
-            if native {
-                hash = 0;
+            if hash_script.is_none() {
+                hash = None;
             }
 
             // Attached object pointer in front of the arguments
@@ -881,8 +882,7 @@ impl Engine {
         fn_name: &str,
         args_expr: impl AsRef<[Expr]>,
         def_val: Option<&Dynamic>,
-        mut hash_script: u64,
-        native: bool,
+        mut hash_script: Option<NonZeroU64>,
         pub_only: bool,
         pos: Position,
         capture_scope: bool,
@@ -951,7 +951,7 @@ impl Engine {
 
         if name == KEYWORD_FN_PTR_CALL
             && args_expr.len() >= 1
-            && !self.has_override(Some(mods), lib, 0, hash_script, pub_only)
+            && !self.has_override(Some(mods), lib, None, hash_script, pub_only)
         {
             let fn_ptr = self.eval_expr(scope, mods, state, lib, this_ptr, &args_expr[0], level)?;
 
@@ -1041,7 +1041,7 @@ impl Engine {
                     .map(|expr| self.eval_expr(scope, mods, state, lib, this_ptr, expr, level))
                     .collect::<Result<_, _>>()?;
 
-                let (mut target, _, pos) =
+                let (mut target, pos) =
                     self.search_namespace(scope, mods, state, lib, this_ptr, &args_expr[0])?;
 
                 if target.as_ref().is_read_only() {
@@ -1071,11 +1071,21 @@ impl Engine {
             }
         }
 
-        let hash = if native { 0 } else { hash_script };
         let args = args.as_mut();
 
         self.exec_fn_call(
-            mods, state, lib, name, hash, args, is_ref, false, pub_only, pos, capture, def_val,
+            mods,
+            state,
+            lib,
+            name,
+            hash_script,
+            args,
+            is_ref,
+            false,
+            pub_only,
+            pos,
+            capture,
+            def_val,
             level,
         )
         .map(|(v, _)| v)
@@ -1093,7 +1103,7 @@ impl Engine {
         fn_name: &str,
         args_expr: impl AsRef<[Expr]>,
         def_val: Option<&Dynamic>,
-        hash_script: u64,
+        hash_script: NonZeroU64,
         pos: Position,
         level: usize,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
@@ -1127,7 +1137,7 @@ impl Engine {
                     .collect::<Result<_, _>>()?;
 
                 // Get target reference to first argument
-                let (target, _, pos) =
+                let (target, pos) =
                     self.search_scope_only(scope, mods, state, lib, this_ptr, &args_expr[0])?;
 
                 self.inc_operations(state, pos)?;
@@ -1167,9 +1177,9 @@ impl Engine {
                 // 2) Calculate a second hash with no qualifiers, empty function name,
                 //    and the actual list of argument `TypeId`'.s
                 let hash_fn_args =
-                    calc_native_fn_hash(empty(), "", args.iter().map(|a| a.type_id()));
-                // 3) The final hash is the XOR of the two hashes.
-                let hash_qualified_fn = hash_script ^ hash_fn_args;
+                    calc_native_fn_hash(empty(), "", args.iter().map(|a| a.type_id())).unwrap();
+                // 3) The two hashes are combined.
+                let hash_qualified_fn = combine_hashes(hash_script, hash_fn_args);
 
                 module.get_qualified_fn(hash_qualified_fn)
             }
diff --git a/src/fn_func.rs b/src/fn_func.rs
index 94b3cba5..1791c0ba 100644
--- a/src/fn_func.rs
+++ b/src/fn_func.rs
@@ -27,15 +27,15 @@ pub trait Func<ARGS, RET> {
     /// // Func takes two type parameters:
     /// //   1) a tuple made up of the types of the script function's parameters
     /// //   2) the return type of the script function
-    /// //
+    ///
     /// // 'func' will have type Box<dyn Fn(i64, String) -> Result<bool, Box<EvalAltResult>>> and is callable!
     /// let func = Func::<(i64, String), bool>::create_from_ast(
     /// //                ^^^^^^^^^^^^^ function parameter types in tuple
     ///
-    ///                 engine,                         // the 'Engine' is consumed into the closure
-    ///                 ast,                            // the 'AST'
-    ///                 "calc"                          // the entry-point function name
-    /// );
+    ///                                             engine, // the 'Engine' is consumed into the closure
+    ///                                             ast,    // the 'AST'
+    ///                                             "calc"  // the entry-point function name
+    ///                                         );
     ///
     /// func(123, "hello".to_string())? == false;       // call the anonymous function
     /// # Ok(())
@@ -58,15 +58,15 @@ pub trait Func<ARGS, RET> {
     /// // Func takes two type parameters:
     /// //   1) a tuple made up of the types of the script function's parameters
     /// //   2) the return type of the script function
-    /// //
+    ///
     /// // 'func' will have type Box<dyn Fn(i64, String) -> Result<bool, Box<EvalAltResult>>> and is callable!
     /// let func = Func::<(i64, String), bool>::create_from_script(
     /// //                ^^^^^^^^^^^^^ function parameter types in tuple
     ///
-    ///                 engine,                         // the 'Engine' is consumed into the closure
-    ///                 script,                         // the script, notice number of parameters must match
-    ///                 "calc"                          // the entry-point function name
-    /// )?;
+    ///                                             engine, // the 'Engine' is consumed into the closure
+    ///                                             script, // the script, notice number of parameters must match
+    ///                                             "calc"  // the entry-point function name
+    ///                                         )?;
     ///
     /// func(123, "hello".to_string())? == false;       // call the anonymous function
     /// # Ok(())
diff --git a/src/fn_native.rs b/src/fn_native.rs
index 71a3a775..68b5b0ce 100644
--- a/src/fn_native.rs
+++ b/src/fn_native.rs
@@ -3,7 +3,14 @@
 use crate::ast::{FnAccess, ScriptFnDef};
 use crate::engine::Imports;
 use crate::plugin::PluginFunction;
-use crate::stdlib::{boxed::Box, convert::TryFrom, fmt, iter::empty, mem, string::String};
+use crate::stdlib::{
+    boxed::Box,
+    convert::{TryFrom, TryInto},
+    fmt,
+    iter::empty,
+    mem,
+    string::String,
+};
 use crate::token::is_valid_identifier;
 use crate::{
     calc_script_fn_hash, Dynamic, Engine, EvalAltResult, EvalContext, ImmutableString, Module,
@@ -153,25 +160,13 @@ impl<'e, 's, 'a, 'm, 'pm> NativeCallContext<'e, 's, 'a, 'm, 'pm> {
         args: &mut [&mut Dynamic],
         def_value: Option<&Dynamic>,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
-        let mut mods = self.mods.cloned().unwrap_or_default();
-
-        let hash_script = calc_script_fn_hash(
-            empty(),
-            fn_name,
-            if is_method {
-                args.len() - 1
-            } else {
-                args.len()
-            },
-        );
-
         self.engine()
             .exec_fn_call(
-                &mut mods,
+                &mut self.mods.cloned().unwrap_or_default(),
                 &mut Default::default(),
                 self.lib,
                 fn_name,
-                hash_script,
+                calc_script_fn_hash(empty(), fn_name, args.len() - if is_method { 1 } else { 0 }),
                 args,
                 is_method,
                 is_method,
@@ -225,11 +220,15 @@ pub type FnCallArgs<'a> = [&'a mut Dynamic];
 
 /// A general function pointer, which may carry additional (i.e. curried) argument values
 /// to be passed onto a function during a call.
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone)]
 pub struct FnPtr(ImmutableString, StaticVec<Dynamic>);
 
 impl FnPtr {
     /// Create a new function pointer.
+    pub fn new(name: impl Into<ImmutableString>) -> Result<Self, Box<EvalAltResult>> {
+        name.into().try_into()
+    }
+    /// Create a new function pointer without checking its parameters.
     #[inline(always)]
     pub(crate) fn new_unchecked(
         name: impl Into<ImmutableString>,
@@ -257,7 +256,24 @@ impl FnPtr {
     pub fn curry(&self) -> &[Dynamic] {
         self.1.as_ref()
     }
-    /// Does this function pointer refer to an anonymous function?
+    /// Add a new curried argument.
+    #[inline(always)]
+    pub fn add_curry(&mut self, value: Dynamic) -> &mut Self {
+        self.1.push(value);
+        self
+    }
+    /// Set curried arguments to the function pointer.
+    #[inline(always)]
+    pub fn set_curry(&mut self, values: impl IntoIterator<Item = Dynamic>) -> &mut Self {
+        self.1 = values.into_iter().collect();
+        self
+    }
+    /// Is the function pointer curried?
+    #[inline(always)]
+    pub fn is_curried(&self) -> bool {
+        !self.1.is_empty()
+    }
+    /// Does the function pointer refer to an anonymous function?
     #[cfg(not(feature = "no_function"))]
     #[inline(always)]
     pub fn is_anonymous(&self) -> bool {
diff --git a/src/lib.rs b/src/lib.rs
index 00f60db2..9f7a8773 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,14 +1,18 @@
 //! # Rhai - embedded scripting for Rust
 //!
+//! ![Rhai logo](https://schungx.github.io/rhai/images/logo/rhai-banner-transparent-colour.svg)
+//!
 //! Rhai is a tiny, simple and fast embedded scripting language for Rust
 //! that gives you a safe and easy way to add scripting to your applications.
-//! It provides a familiar syntax based on JavaScript and Rust and a simple Rust interface.
-//! Here is a quick example.
 //!
-//! First, the contents of `my_script.rhai`:
+//! It provides a familiar syntax based on JavaScript+Rust and a simple Rust interface.
+//!
+//! # A Quick Example
+//!
+//! ## Contents of `my_script.rhai`
 //!
 //! ```,ignore
-//! // Brute force factorial function
+//! /// Brute force factorial function
 //! fn factorial(x) {
 //!     if x == 1 { return 1; }
 //!     x * factorial(x - 1)
@@ -18,7 +22,7 @@
 //! compute(factorial(10))
 //! ```
 //!
-//! And the Rust part:
+//! ## The Rust part
 //!
 //! ```,no_run
 //! use rhai::{Engine, EvalAltResult, RegisterFn};
diff --git a/src/module/mod.rs b/src/module/mod.rs
index 84862afe..92c7b8fb 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -10,13 +10,14 @@ use crate::stdlib::{
     collections::HashMap,
     fmt, format,
     iter::empty,
+    num::NonZeroU64,
     num::NonZeroUsize,
     ops::{Add, AddAssign, Deref, DerefMut},
     string::{String, ToString},
     vec::Vec,
 };
 use crate::token::Token;
-use crate::utils::StraightHasherBuilder;
+use crate::utils::{combine_hashes, StraightHasherBuilder};
 use crate::{
     Dynamic, EvalAltResult, ImmutableString, NativeCallContext, Position, Shared, StaticVec,
 };
@@ -34,9 +35,9 @@ use crate::Map;
 /// A type representing the namespace of a function.
 #[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
 pub enum FnNamespace {
-    /// Global namespace.
+    /// Expose to global namespace.
     Global,
-    /// Internal only.
+    /// Module namespace only.
     Internal,
 }
 
@@ -79,9 +80,9 @@ pub struct FuncInfo {
     /// Number of parameters.
     pub params: usize,
     /// Parameter types (if applicable).
-    pub param_types: Option<StaticVec<TypeId>>,
+    pub param_types: StaticVec<TypeId>,
     /// Parameter names (if available).
-    pub param_names: Option<StaticVec<ImmutableString>>,
+    pub param_names: StaticVec<ImmutableString>,
 }
 
 impl FuncInfo {
@@ -89,13 +90,19 @@ impl FuncInfo {
     pub fn gen_signature(&self) -> String {
         let mut sig = format!("{}(", self.name);
 
-        if let Some(ref names) = self.param_names {
-            let mut params: Vec<_> = names.iter().map(ImmutableString::to_string).collect();
+        if !self.param_names.is_empty() {
+            let mut params: Vec<_> = self
+                .param_names
+                .iter()
+                .map(ImmutableString::to_string)
+                .collect();
             let return_type = params.pop().unwrap_or_else(|| "()".to_string());
             sig.push_str(&params.join(", "));
             if return_type != "()" {
                 sig.push_str(") -> ");
                 sig.push_str(&return_type);
+            } else if self.func.is_script() {
+                sig.push_str(") -> Dynamic");
             } else {
                 sig.push_str(")");
             }
@@ -106,7 +113,12 @@ impl FuncInfo {
                     sig.push_str(", ");
                 }
             }
-            sig.push_str(") -> Dynamic");
+
+            if self.func.is_script() {
+                sig.push_str(") -> Dynamic");
+            } else {
+                sig.push_str(") -> ?");
+            }
         }
 
         sig
@@ -126,12 +138,12 @@ pub struct Module {
     /// Module variables.
     variables: HashMap<ImmutableString, Dynamic>,
     /// Flattened collection of all module variables, including those in sub-modules.
-    all_variables: HashMap<u64, Dynamic, StraightHasherBuilder>,
+    all_variables: HashMap<NonZeroU64, Dynamic, StraightHasherBuilder>,
     /// External Rust functions.
-    functions: HashMap<u64, FuncInfo, StraightHasherBuilder>,
+    functions: HashMap<NonZeroU64, FuncInfo, StraightHasherBuilder>,
     /// Flattened collection of all external Rust functions, native or scripted.
     /// including those in sub-modules.
-    all_functions: HashMap<u64, CallableFunction, StraightHasherBuilder>,
+    all_functions: HashMap<NonZeroU64, CallableFunction, StraightHasherBuilder>,
     /// Iterator functions, keyed by the type producing the iterator.
     type_iterators: HashMap<TypeId, IteratorFn>,
     /// Flattened collection of iterator functions, including those in sub-modules.
@@ -344,7 +356,7 @@ impl Module {
         self.get_var(name).and_then(Dynamic::try_cast::<T>)
     }
 
-    /// Get a module variable as a [`Dynamic`][crate::Dynamic].
+    /// Get a module variable as a [`Dynamic`].
     ///
     /// # Example
     ///
@@ -387,16 +399,15 @@ impl Module {
     /// Get a reference to a namespace-qualified variable.
     /// Name and Position in `EvalAltResult` are None and must be set afterwards.
     ///
-    /// The [`u64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
+    /// The [`NonZeroU64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
     #[inline(always)]
-    pub(crate) fn get_qualified_var(&self, hash_var: u64) -> Result<&Dynamic, Box<EvalAltResult>> {
-        if hash_var == 0 {
-            Err(EvalAltResult::ErrorVariableNotFound(String::new(), Position::NONE).into())
-        } else {
-            self.all_variables.get(&hash_var).ok_or_else(|| {
-                EvalAltResult::ErrorVariableNotFound(String::new(), Position::NONE).into()
-            })
-        }
+    pub(crate) fn get_qualified_var(
+        &self,
+        hash_var: NonZeroU64,
+    ) -> Result<&Dynamic, Box<EvalAltResult>> {
+        self.all_variables.get(&hash_var).ok_or_else(|| {
+            EvalAltResult::ErrorVariableNotFound(String::new(), Position::NONE).into()
+        })
     }
 
     /// Set a script-defined function into the module.
@@ -404,12 +415,12 @@ impl Module {
     /// If there is an existing function of the same name and number of arguments, it is replaced.
     #[cfg(not(feature = "no_function"))]
     #[inline]
-    pub(crate) fn set_script_fn(&mut self, fn_def: impl Into<Shared<ScriptFnDef>>) -> u64 {
+    pub(crate) fn set_script_fn(&mut self, fn_def: impl Into<Shared<ScriptFnDef>>) -> NonZeroU64 {
         let fn_def = fn_def.into();
 
         // None + function name + number of arguments.
         let num_params = fn_def.params.len();
-        let hash_script = crate::calc_script_fn_hash(empty(), &fn_def.name, num_params);
+        let hash_script = crate::calc_script_fn_hash(empty(), &fn_def.name, num_params).unwrap();
         let mut param_names: StaticVec<_> = fn_def.params.iter().cloned().collect();
         param_names.push("Dynamic".into());
         self.functions.insert(
@@ -419,8 +430,8 @@ impl Module {
                 namespace: FnNamespace::Internal,
                 access: fn_def.access,
                 params: num_params,
-                param_types: None,
-                param_names: Some(param_names),
+                param_types: Default::default(),
+                param_names,
                 func: fn_def.into(),
             },
         );
@@ -454,6 +465,24 @@ impl Module {
             .map(|FuncInfo { func, .. }| func.get_fn_def())
     }
 
+    /// Get a mutable reference to the underlying [`HashMap`] of sub-modules.
+    ///
+    /// ## Warning
+    ///
+    /// By taking a mutable reference, it is assumed that some sub-modules will be modified.
+    /// Thus the module is automatically set to be non-indexed.
+    #[inline(always)]
+    pub(crate) fn sub_modules_mut(&mut self) -> &mut HashMap<ImmutableString, Shared<Module>> {
+        // We must assume that the user has changed the sub-modules
+        // (otherwise why take a mutable reference?)
+        self.all_functions.clear();
+        self.all_variables.clear();
+        self.all_type_iterators.clear();
+        self.indexed = false;
+
+        &mut self.modules
+    }
+
     /// Does a sub-module exist in the module?
     ///
     /// # Example
@@ -515,7 +544,7 @@ impl Module {
 
     /// Does the particular Rust function exist in the module?
     ///
-    /// The [`u64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
+    /// The [`NonZeroU64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
     /// It is also returned by the `set_fn_XXX` calls.
     ///
     /// # Example
@@ -528,10 +557,8 @@ impl Module {
     /// assert!(module.contains_fn(hash, true));
     /// ```
     #[inline]
-    pub fn contains_fn(&self, hash_fn: u64, public_only: bool) -> bool {
-        if hash_fn == 0 {
-            false
-        } else if public_only {
+    pub fn contains_fn(&self, hash_fn: NonZeroU64, public_only: bool) -> bool {
+        if public_only {
             self.functions
                 .get(&hash_fn)
                 .map(|FuncInfo { access, .. }| access.is_public())
@@ -543,7 +570,7 @@ impl Module {
 
     /// Update the metadata (parameter names/types and return type) of a registered function.
     ///
-    /// The [`u64`] hash is calculated either by the function [`crate::calc_native_fn_hash`] or
+    /// The [`NonZeroU64`] hash is calculated either by the function [`crate::calc_native_fn_hash`] or
     /// the function [`crate::calc_script_fn_hash`].
     ///
     /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
@@ -552,20 +579,24 @@ impl Module {
     /// In other words, the number of entries should be one larger than the number of parameters.
     pub fn update_fn_metadata<'a>(
         &mut self,
-        hash_fn: u64,
+        hash_fn: NonZeroU64,
         arg_names: impl AsRef<[&'a str]>,
     ) -> &mut Self {
         if let Some(f) = self.functions.get_mut(&hash_fn) {
-            f.param_names = Some(arg_names.as_ref().iter().map(|&n| n.into()).collect());
+            f.param_names = arg_names.as_ref().iter().map(|&n| n.into()).collect();
         }
         self
     }
 
     /// Update the namespace of a registered function.
     ///
-    /// The [`u64`] hash is calculated either by the function [`crate::calc_native_fn_hash`] or
+    /// The [`NonZeroU64`] hash is calculated either by the function [`crate::calc_native_fn_hash`] or
     /// the function [`crate::calc_script_fn_hash`].
-    pub fn update_fn_namespace(&mut self, hash_fn: u64, namespace: FnNamespace) -> &mut Self {
+    pub fn update_fn_namespace(
+        &mut self,
+        hash_fn: NonZeroU64,
+        namespace: FnNamespace,
+    ) -> &mut Self {
         if let Some(f) = self.functions.get_mut(&hash_fn) {
             f.namespace = namespace;
         }
@@ -588,12 +619,13 @@ impl Module {
         arg_names: Option<&[&str]>,
         arg_types: &[TypeId],
         func: CallableFunction,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let name = name.into();
 
-        let hash_fn = crate::calc_native_fn_hash(empty(), &name, arg_types.iter().cloned());
+        let hash_fn =
+            crate::calc_native_fn_hash(empty(), &name, arg_types.iter().cloned()).unwrap();
 
-        let params = arg_types
+        let param_types = arg_types
             .into_iter()
             .cloned()
             .map(|id| {
@@ -611,9 +643,13 @@ impl Module {
                 name,
                 namespace,
                 access,
-                params: params.len(),
-                param_types: Some(params),
-                param_names: arg_names.map(|p| p.iter().map(|&v| v.into()).collect()),
+                params: param_types.len(),
+                param_types,
+                param_names: if let Some(p) = arg_names {
+                    p.iter().map(|&v| v.into()).collect()
+                } else {
+                    Default::default()
+                },
                 func: func.into(),
             },
         );
@@ -624,7 +660,7 @@ impl Module {
     }
 
     /// Set a Rust function taking a reference to the scripting [`Engine`][crate::Engine],
-    /// the current set of functions, plus a list of mutable [`Dynamic`][crate::Dynamic] references
+    /// the current set of functions, plus a list of mutable [`Dynamic`] references
     /// into the module, returning a hash key.
     ///
     /// Use this to register a built-in function which must reference settings on the scripting
@@ -639,7 +675,7 @@ impl Module {
     ///
     /// A list of [`TypeId`]'s is taken as the argument types.
     ///
-    /// Arguments are simply passed in as a mutable array of [`&mut Dynamic`][crate::Dynamic],
+    /// Arguments are simply passed in as a mutable array of [`&mut Dynamic`],
     /// which is guaranteed to contain enough arguments of the correct types.
     ///
     /// The function is assumed to be a _method_, meaning that the first argument should not be consumed.
@@ -697,7 +733,7 @@ impl Module {
         func: impl Fn(NativeCallContext, &mut FnCallArgs) -> Result<T, Box<EvalAltResult>>
             + SendSync
             + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f =
             move |ctx: NativeCallContext, args: &mut FnCallArgs| func(ctx, args).map(Dynamic::from);
 
@@ -733,7 +769,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn() -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, _: &mut FnCallArgs| func().map(Dynamic::from);
         let arg_types = [];
         self.set_fn(
@@ -768,7 +804,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(A) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             func(cast_arg::<A>(&mut args[0])).map(Dynamic::from)
         };
@@ -808,7 +844,7 @@ impl Module {
         name: impl Into<String>,
         namespace: FnNamespace,
         func: impl Fn(&mut A) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             func(&mut args[0].write_lock::<A>().unwrap()).map(Dynamic::from)
         };
@@ -847,7 +883,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(&mut A) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         self.set_fn_1_mut(
             crate::engine::make_getter(&name.into()),
             FnNamespace::Global,
@@ -879,7 +915,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(A, B) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let a = cast_arg::<A>(&mut args[0]);
             let b = cast_arg::<B>(&mut args[1]);
@@ -926,7 +962,7 @@ impl Module {
         name: impl Into<String>,
         namespace: FnNamespace,
         func: impl Fn(&mut A, B) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let b = cast_arg::<B>(&mut args[1]);
             let a = &mut args[0].write_lock::<A>().unwrap();
@@ -972,7 +1008,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(&mut A, B) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         self.set_fn_2_mut(
             crate::engine::make_setter(&name.into()),
             FnNamespace::Global,
@@ -1011,7 +1047,7 @@ impl Module {
     pub fn set_indexer_get_fn<A: Variant + Clone, B: Variant + Clone, T: Variant + Clone>(
         &mut self,
         func: impl Fn(&mut A, B) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         if TypeId::of::<A>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
         }
@@ -1058,7 +1094,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(A, B, C) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let a = cast_arg::<A>(&mut args[0]);
             let b = cast_arg::<B>(&mut args[1]);
@@ -1111,7 +1147,7 @@ impl Module {
         name: impl Into<String>,
         namespace: FnNamespace,
         func: impl Fn(&mut A, B, C) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let b = cast_arg::<B>(&mut args[2]);
             let c = cast_arg::<C>(&mut args[3]);
@@ -1162,7 +1198,7 @@ impl Module {
     pub fn set_indexer_set_fn<A: Variant + Clone, B: Variant + Clone, C: Variant + Clone>(
         &mut self,
         func: impl Fn(&mut A, B, C) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         if TypeId::of::<A>() == TypeId::of::<Array>() {
             panic!("Cannot register indexer for arrays.");
         }
@@ -1234,7 +1270,7 @@ impl Module {
         &mut self,
         getter: impl Fn(&mut A, B) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
         setter: impl Fn(&mut A, B, T) -> Result<(), Box<EvalAltResult>> + SendSync + 'static,
-    ) -> (u64, u64) {
+    ) -> (NonZeroU64, NonZeroU64) {
         (
             self.set_indexer_get_fn(getter),
             self.set_indexer_set_fn(setter),
@@ -1271,7 +1307,7 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         func: impl Fn(A, B, C, D) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let a = cast_arg::<A>(&mut args[0]);
             let b = cast_arg::<B>(&mut args[1]);
@@ -1331,7 +1367,7 @@ impl Module {
         name: impl Into<String>,
         namespace: FnNamespace,
         func: impl Fn(&mut A, B, C, D) -> Result<T, Box<EvalAltResult>> + SendSync + 'static,
-    ) -> u64 {
+    ) -> NonZeroU64 {
         let f = move |_: NativeCallContext, args: &mut FnCallArgs| {
             let b = cast_arg::<B>(&mut args[1]);
             let c = cast_arg::<C>(&mut args[2]);
@@ -1358,48 +1394,43 @@ impl Module {
 
     /// Get a Rust function.
     ///
-    /// The [`u64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
+    /// The [`NonZeroU64`] hash is calculated by the function [`crate::calc_native_fn_hash`].
     /// It is also returned by the `set_fn_XXX` calls.
     #[inline(always)]
-    pub(crate) fn get_fn(&self, hash_fn: u64, public_only: bool) -> Option<&CallableFunction> {
-        if hash_fn == 0 {
-            None
-        } else {
-            self.functions
-                .get(&hash_fn)
-                .and_then(|FuncInfo { access, func, .. }| match access {
-                    _ if !public_only => Some(func),
-                    FnAccess::Public => Some(func),
-                    FnAccess::Private => None,
-                })
-        }
+    pub(crate) fn get_fn(
+        &self,
+        hash_fn: NonZeroU64,
+        public_only: bool,
+    ) -> Option<&CallableFunction> {
+        self.functions
+            .get(&hash_fn)
+            .and_then(|FuncInfo { access, func, .. }| match access {
+                _ if !public_only => Some(func),
+                FnAccess::Public => Some(func),
+                FnAccess::Private => None,
+            })
     }
 
     /// Does the particular namespace-qualified function exist in the module?
     ///
-    /// The [`u64`] hash is calculated by the function [`crate::calc_native_fn_hash`] and must match
+    /// The [`NonZeroU64`] hash is calculated by the function [`crate::calc_native_fn_hash`] and must match
     /// the hash calculated by [`build_index`][Module::build_index].
-    #[inline]
-    pub fn contains_qualified_fn(&self, hash_fn: u64) -> bool {
-        if hash_fn == 0 {
-            false
-        } else {
-            self.all_functions.contains_key(&hash_fn)
-        }
+    #[inline(always)]
+    pub fn contains_qualified_fn(&self, hash_fn: NonZeroU64) -> bool {
+        self.all_functions.contains_key(&hash_fn)
     }
 
     /// Get a namespace-qualified function.
     /// Name and Position in `EvalAltResult` are None and must be set afterwards.
     ///
-    /// The [`u64`] hash is calculated by the function [`crate::calc_native_fn_hash`] and must match
+    /// The [`NonZeroU64`] hash is calculated by the function [`crate::calc_native_fn_hash`] and must match
     /// the hash calculated by [`build_index`][Module::build_index].
     #[inline(always)]
-    pub(crate) fn get_qualified_fn(&self, hash_qualified_fn: u64) -> Option<&CallableFunction> {
-        if hash_qualified_fn == 0 {
-            None
-        } else {
-            self.all_functions.get(&hash_qualified_fn)
-        }
+    pub(crate) fn get_qualified_fn(
+        &self,
+        hash_qualified_fn: NonZeroU64,
+    ) -> Option<&CallableFunction> {
+        self.all_functions.get(&hash_qualified_fn)
     }
 
     /// Combine another module into this module.
@@ -1686,7 +1717,7 @@ impl Module {
         ast: &crate::AST,
         engine: &crate::Engine,
     ) -> Result<Self, Box<EvalAltResult>> {
-        let mut mods = engine.global_sub_modules.clone();
+        let mut mods: crate::engine::Imports = (&engine.global_sub_modules).into();
         let orig_mods_len = mods.len();
 
         // Run the script
@@ -1745,8 +1776,8 @@ impl Module {
         fn index_module<'a>(
             module: &'a Module,
             qualifiers: &mut Vec<&'a str>,
-            variables: &mut HashMap<u64, Dynamic, StraightHasherBuilder>,
-            functions: &mut HashMap<u64, CallableFunction, StraightHasherBuilder>,
+            variables: &mut HashMap<NonZeroU64, Dynamic, StraightHasherBuilder>,
+            functions: &mut HashMap<NonZeroU64, CallableFunction, StraightHasherBuilder>,
             type_iterators: &mut HashMap<TypeId, IteratorFn>,
         ) {
             module.modules.iter().for_each(|(name, m)| {
@@ -1760,7 +1791,7 @@ impl Module {
             module.variables.iter().for_each(|(var_name, value)| {
                 // Qualifiers + variable name
                 let hash_var =
-                    crate::calc_script_fn_hash(qualifiers.iter().map(|&v| v), var_name, 0);
+                    crate::calc_script_fn_hash(qualifiers.iter().map(|&v| v), var_name, 0).unwrap();
                 variables.insert(hash_var, value.clone());
             });
 
@@ -1781,7 +1812,7 @@ impl Module {
                             name,
                             namespace,
                             params,
-                            param_types: types,
+                            param_types,
                             func,
                             ..
                         },
@@ -1793,9 +1824,10 @@ impl Module {
 
                         // Qualifiers + function name + number of arguments.
                         let hash_qualified_script =
-                            crate::calc_script_fn_hash(qualifiers.iter().cloned(), name, *params);
+                            crate::calc_script_fn_hash(qualifiers.iter().cloned(), name, *params)
+                                .unwrap();
 
-                        if let Some(param_types) = types {
+                        if !func.is_script() {
                             assert_eq!(*params, param_types.len());
 
                             // Namespace-qualified Rust functions are indexed in two steps:
@@ -1807,9 +1839,11 @@ impl Module {
                                 empty(),
                                 "",
                                 param_types.iter().cloned(),
-                            );
-                            // 3) The final hash is the XOR of the two hashes.
-                            let hash_qualified_fn = hash_qualified_script ^ hash_fn_args;
+                            )
+                            .unwrap();
+                            // 3) The two hashes are combined.
+                            let hash_qualified_fn =
+                                combine_hashes(hash_qualified_script, hash_fn_args);
 
                             functions.insert(hash_qualified_fn, func.clone());
                         } else if cfg!(not(feature = "no_function")) {
@@ -1897,7 +1931,7 @@ impl Module {
 /// _(INTERNALS)_ A chain of [module][Module] names to namespace-qualify a variable or function call.
 /// Exported under the `internals` feature only.
 ///
-/// A [`u64`] hash key is cached for quick search purposes.
+/// A [`NonZeroU64`] offset to the current [`Scope`][crate::Scope] is cached for quick search purposes.
 ///
 /// A [`StaticVec`] is used because most namespace-qualified access contains only one level,
 /// and it is wasteful to always allocate a [`Vec`] with one element.
@@ -1906,13 +1940,13 @@ impl Module {
 ///
 /// This type is volatile and may change.
 #[derive(Clone, Eq, PartialEq, Default, Hash)]
-pub struct NamespaceRef(StaticVec<Ident>, Option<NonZeroUsize>);
+pub struct NamespaceRef(Option<NonZeroUsize>, StaticVec<Ident>);
 
 impl fmt::Debug for NamespaceRef {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&self.0, f)?;
+        fmt::Debug::fmt(&self.1, f)?;
 
-        if let Some(index) = self.1 {
+        if let Some(index) = self.0 {
             write!(f, " -> {}", index)
         } else {
             Ok(())
@@ -1924,19 +1958,19 @@ impl Deref for NamespaceRef {
     type Target = StaticVec<Ident>;
 
     fn deref(&self) -> &Self::Target {
-        &self.0
+        &self.1
     }
 }
 
 impl DerefMut for NamespaceRef {
     fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
+        &mut self.1
     }
 }
 
 impl fmt::Display for NamespaceRef {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        for Ident { name, .. } in self.0.iter() {
+        for Ident { name, .. } in self.1.iter() {
             write!(f, "{}{}", name, Token::DoubleColon.syntax())?;
         }
         Ok(())
@@ -1945,7 +1979,7 @@ impl fmt::Display for NamespaceRef {
 
 impl From<StaticVec<Ident>> for NamespaceRef {
     fn from(modules: StaticVec<Ident>) -> Self {
-        Self(modules, None)
+        Self(None, modules)
     }
 }
 
@@ -1975,12 +2009,14 @@ impl<M: Into<Module>> AddAssign<M> for Module {
 }
 
 impl NamespaceRef {
+    /// Get the [`Scope`][crate::Scope] index offset.
     pub(crate) fn index(&self) -> Option<NonZeroUsize> {
-        self.1
+        self.0
     }
+    /// Set the [`Scope`][crate::Scope] index offset.
     #[cfg(not(feature = "no_module"))]
     pub(crate) fn set_index(&mut self, index: Option<NonZeroUsize>) {
-        self.1 = index
+        self.0 = index
     }
 }
 
diff --git a/src/module/resolvers/collection.rs b/src/module/resolvers/collection.rs
index 71c3fe27..30039234 100644
--- a/src/module/resolvers/collection.rs
+++ b/src/module/resolvers/collection.rs
@@ -16,7 +16,7 @@ use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};
 /// collection.push(resolver);
 ///
 /// let mut engine = Engine::new();
-/// engine.set_module_resolver(Some(collection));
+/// engine.set_module_resolver(collection);
 /// ```
 #[derive(Default)]
 pub struct ModuleResolversCollection(Vec<Box<dyn ModuleResolver>>);
@@ -36,16 +36,41 @@ impl ModuleResolversCollection {
     /// collection.push(resolver);
     ///
     /// let mut engine = Engine::new();
-    /// engine.set_module_resolver(Some(collection));
+    /// engine.set_module_resolver(collection);
     /// ```
     #[inline(always)]
     pub fn new() -> Self {
         Default::default()
     }
-    /// Add a module keyed by its path.
+    /// Append a module resolver to the end.
     #[inline(always)]
-    pub fn push(&mut self, resolver: impl ModuleResolver + 'static) {
+    pub fn push(&mut self, resolver: impl ModuleResolver + 'static) -> &mut Self {
         self.0.push(Box::new(resolver));
+        self
+    }
+    /// Insert a module resolver to an offset index.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the index is out of bounds.
+    #[inline(always)]
+    pub fn insert(&mut self, index: usize, resolver: impl ModuleResolver + 'static) -> &mut Self {
+        self.0.insert(index, Box::new(resolver));
+        self
+    }
+    /// Remove the last module resolver from the end, if any.
+    #[inline(always)]
+    pub fn pop(&mut self) -> Option<Box<dyn ModuleResolver>> {
+        self.0.pop()
+    }
+    /// Remove a module resolver at an offset index.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the index is out of bounds.
+    #[inline(always)]
+    pub fn remove(&mut self, index: usize) -> Box<dyn ModuleResolver> {
+        self.0.remove(index)
     }
     /// Get an iterator of all the module resolvers.
     #[inline(always)]
@@ -59,8 +84,9 @@ impl ModuleResolversCollection {
     }
     /// Remove all module resolvers.
     #[inline(always)]
-    pub fn clear(&mut self) {
+    pub fn clear(&mut self) -> &mut Self {
         self.0.clear();
+        self
     }
     /// Is this [`ModuleResolversCollection`] empty?
     #[inline(always)]
@@ -75,8 +101,9 @@ impl ModuleResolversCollection {
     /// Add another [`ModuleResolversCollection`] to the end of this collection.
     /// The other [`ModuleResolversCollection`] is consumed.
     #[inline(always)]
-    pub fn append(&mut self, other: Self) {
+    pub fn append(&mut self, other: Self) -> &mut Self {
         self.0.extend(other.0.into_iter());
+        self
     }
 }
 
diff --git a/src/module/resolvers/dummy.rs b/src/module/resolvers/dummy.rs
new file mode 100644
index 00000000..8ed3b3f0
--- /dev/null
+++ b/src/module/resolvers/dummy.rs
@@ -0,0 +1,48 @@
+use crate::stdlib::boxed::Box;
+use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};
+
+/// Empty/disabled module resolution service that acts as a dummy.
+///
+/// # Example
+///
+/// ```
+/// use rhai::{Engine, Module};
+/// use rhai::module_resolvers::DummyModuleResolver;
+///
+/// let resolver = DummyModuleResolver::new();
+/// let mut engine = Engine::new();
+/// engine.set_module_resolver(resolver);
+/// ```
+#[derive(Debug, Copy, Eq, PartialEq, Clone, Default, Hash)]
+pub struct DummyModuleResolver;
+
+impl DummyModuleResolver {
+    /// Create a new [`DummyModuleResolver`].
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use rhai::{Engine, Module};
+    /// use rhai::module_resolvers::DummyModuleResolver;
+    ///
+    /// let resolver = DummyModuleResolver::new();
+    /// let mut engine = Engine::new();
+    /// engine.set_module_resolver(resolver);
+    /// ```
+    #[inline(always)]
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
+impl ModuleResolver for DummyModuleResolver {
+    #[inline(always)]
+    fn resolve(
+        &self,
+        _: &Engine,
+        path: &str,
+        pos: Position,
+    ) -> Result<Shared<Module>, Box<EvalAltResult>> {
+        EvalAltResult::ErrorModuleNotFound(path.into(), pos).into()
+    }
+}
diff --git a/src/module/resolvers/file.rs b/src/module/resolvers/file.rs
index 0831ff25..b3be9bce 100644
--- a/src/module/resolvers/file.rs
+++ b/src/module/resolvers/file.rs
@@ -1,5 +1,9 @@
 use crate::stdlib::{
-    boxed::Box, collections::HashMap, io::Error as IoError, path::PathBuf, string::String,
+    boxed::Box,
+    collections::HashMap,
+    io::Error as IoError,
+    path::{Path, PathBuf},
+    string::String,
 };
 use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};
 
@@ -31,7 +35,7 @@ use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};
 ///
 /// let mut engine = Engine::new();
 ///
-/// engine.set_module_resolver(Some(resolver));
+/// engine.set_module_resolver(resolver);
 /// ```
 #[derive(Debug)]
 pub struct FileModuleResolver {
@@ -65,10 +69,10 @@ impl FileModuleResolver {
     /// let resolver = FileModuleResolver::new_with_path("./scripts");
     ///
     /// let mut engine = Engine::new();
-    /// engine.set_module_resolver(Some(resolver));
+    /// engine.set_module_resolver(resolver);
     /// ```
     #[inline(always)]
-    pub fn new_with_path<P: Into<PathBuf>>(path: P) -> Self {
+    pub fn new_with_path(path: impl Into<PathBuf>) -> Self {
         Self::new_with_path_and_extension(path, "rhai")
     }
 
@@ -87,12 +91,12 @@ impl FileModuleResolver {
     /// let resolver = FileModuleResolver::new_with_path_and_extension("./scripts", "x");
     ///
     /// let mut engine = Engine::new();
-    /// engine.set_module_resolver(Some(resolver));
+    /// engine.set_module_resolver(resolver);
     /// ```
     #[inline(always)]
-    pub fn new_with_path_and_extension<P: Into<PathBuf>, E: Into<String>>(
-        path: P,
-        extension: E,
+    pub fn new_with_path_and_extension(
+        path: impl Into<PathBuf>,
+        extension: impl Into<String>,
     ) -> Self {
         Self {
             path: path.into(),
@@ -114,12 +118,64 @@ impl FileModuleResolver {
     /// let resolver = FileModuleResolver::new();
     ///
     /// let mut engine = Engine::new();
-    /// engine.set_module_resolver(Some(resolver));
+    /// engine.set_module_resolver(resolver);
     /// ```
     #[inline(always)]
     pub fn new() -> Self {
         Default::default()
     }
+
+    /// Get the base path for script files.
+    #[inline(always)]
+    pub fn path(&self) -> &Path {
+        self.path.as_ref()
+    }
+    /// Set the base path for script files.
+    #[inline(always)]
+    pub fn set_path(&mut self, path: impl Into<PathBuf>) -> &mut Self {
+        self.path = path.into();
+        self
+    }
+
+    /// Get the script file extension.
+    #[inline(always)]
+    pub fn extension(&self) -> &str {
+        &self.extension
+    }
+
+    /// Set the script file extension.
+    #[inline(always)]
+    pub fn set_extension(&mut self, extension: impl Into<String>) -> &mut Self {
+        self.extension = extension.into();
+        self
+    }
+
+    /// Empty the internal cache.
+    #[inline(always)]
+    pub fn clear_cache(&mut self) {
+        #[cfg(not(feature = "sync"))]
+        self.cache.borrow_mut().clear();
+        #[cfg(feature = "sync")]
+        self.cache.write().unwrap().clear();
+    }
+
+    /// Empty the internal cache.
+    #[inline(always)]
+    pub fn clear_cache_for_path(&mut self, path: impl AsRef<Path>) -> Option<Shared<Module>> {
+        #[cfg(not(feature = "sync"))]
+        return self
+            .cache
+            .borrow_mut()
+            .remove_entry(path.as_ref())
+            .map(|(_, v)| v);
+        #[cfg(feature = "sync")]
+        return self
+            .cache
+            .write()
+            .unwrap()
+            .remove_entry(path.as_ref())
+            .map(|(_, v)| v);
+    }
 }
 
 impl ModuleResolver for FileModuleResolver {
diff --git a/src/module/resolvers/mod.rs b/src/module/resolvers/mod.rs
index d131a1d0..f257f0e8 100644
--- a/src/module/resolvers/mod.rs
+++ b/src/module/resolvers/mod.rs
@@ -2,6 +2,9 @@ use crate::fn_native::SendSync;
 use crate::stdlib::boxed::Box;
 use crate::{Engine, EvalAltResult, Module, Position, Shared};
 
+mod dummy;
+pub use dummy::DummyModuleResolver;
+
 mod collection;
 pub use collection::ModuleResolversCollection;
 
diff --git a/src/module/resolvers/stat.rs b/src/module/resolvers/stat.rs
index 553a462f..311d92d0 100644
--- a/src/module/resolvers/stat.rs
+++ b/src/module/resolvers/stat.rs
@@ -16,7 +16,7 @@ use crate::{Engine, EvalAltResult, Module, ModuleResolver, Position, Shared};
 ///
 /// let mut engine = Engine::new();
 ///
-/// engine.set_module_resolver(Some(resolver));
+/// engine.set_module_resolver(resolver);
 /// ```
 #[derive(Debug, Clone, Default)]
 pub struct StaticModuleResolver(HashMap<String, Shared<Module>>);
@@ -36,7 +36,7 @@ impl StaticModuleResolver {
     /// resolver.insert("hello", module);
     ///
     /// let mut engine = Engine::new();
-    /// engine.set_module_resolver(Some(resolver));
+    /// engine.set_module_resolver(resolver);
     /// ```
     #[inline(always)]
     pub fn new() -> Self {
@@ -60,8 +60,13 @@ impl StaticModuleResolver {
     }
     /// Get an iterator of all the modules.
     #[inline(always)]
-    pub fn iter(&self) -> impl Iterator<Item = (&str, Shared<Module>)> {
-        self.0.iter().map(|(k, v)| (k.as_str(), v.clone()))
+    pub fn iter(&self) -> impl Iterator<Item = (&str, &Shared<Module>)> {
+        self.0.iter().map(|(k, v)| (k.as_str(), v))
+    }
+    /// Get a mutable iterator of all the modules.
+    #[inline(always)]
+    pub fn iter_mut(&mut self) -> impl Iterator<Item = (&str, &mut Shared<Module>)> {
+        self.0.iter_mut().map(|(k, v)| (k.as_str(), v))
     }
     /// Get a mutable iterator of all the modules.
     #[inline(always)]
@@ -75,8 +80,8 @@ impl StaticModuleResolver {
     }
     /// Get an iterator of all the modules.
     #[inline(always)]
-    pub fn values<'a>(&'a self) -> impl Iterator<Item = Shared<Module>> + 'a {
-        self.0.values().map(|m| m.clone())
+    pub fn values(&self) -> impl Iterator<Item = &Shared<Module>> {
+        self.0.values().map(|m| m)
     }
     /// Remove all modules.
     #[inline(always)]
@@ -95,6 +100,8 @@ impl StaticModuleResolver {
     }
     /// Merge another [`StaticModuleResolver`] into this.
     /// The other [`StaticModuleResolver`] is consumed.
+    ///
+    /// Existing modules of the same path name are overwritten.
     #[inline(always)]
     pub fn merge(&mut self, other: Self) {
         if !other.is_empty() {
diff --git a/src/optimize.rs b/src/optimize.rs
index 53be762e..07d16642 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -2,7 +2,7 @@
 
 use crate::ast::{Expr, ScriptFnDef, Stmt};
 use crate::dynamic::AccessMode;
-use crate::engine::{KEYWORD_DEBUG, KEYWORD_EVAL, KEYWORD_PRINT, KEYWORD_TYPE_OF};
+use crate::engine::{Imports, KEYWORD_DEBUG, KEYWORD_EVAL, KEYWORD_PRINT, KEYWORD_TYPE_OF};
 use crate::fn_call::run_builtin_binary_op;
 use crate::parser::map_dynamic_to_expr;
 use crate::stdlib::{
@@ -62,6 +62,8 @@ struct State<'a> {
     variables: Vec<(String, AccessMode, Expr)>,
     /// An [`Engine`] instance for eager function evaluation.
     engine: &'a Engine,
+    /// Collection of sub-modules.
+    mods: Imports,
     /// [Module] containing script-defined functions.
     lib: &'a [&'a Module],
     /// Optimization level.
@@ -76,6 +78,7 @@ impl<'a> State<'a> {
             changed: false,
             variables: vec![],
             engine,
+            mods: (&engine.global_sub_modules).into(),
             lib,
             optimization_level: level,
         }
@@ -138,7 +141,7 @@ fn call_fn_with_constant_arguments(
             &mut Default::default(),
             state.lib,
             fn_name,
-            hash_fn,
+            hash_fn.unwrap(),
             arg_values.iter_mut().collect::<StaticVec<_>>().as_mut(),
             false,
             true,
@@ -149,7 +152,7 @@ fn call_fn_with_constant_arguments(
         .map(|(v, _)| v)
 }
 
-/// Optimize a block of [statements][crate::ast::Stmt].
+/// Optimize a block of [statements][Stmt].
 fn optimize_stmt_block(
     mut statements: Vec<Stmt>,
     pos: Position,
@@ -274,7 +277,7 @@ fn optimize_stmt_block(
     }
 }
 
-/// Optimize a [statement][crate::ast::Stmt].
+/// Optimize a [statement][Stmt].
 fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
     match stmt {
         // expr op= expr
@@ -470,7 +473,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut State, preserve_result: bool) {
     }
 }
 
-/// Optimize an [expression][crate::ast::Expr].
+/// Optimize an [expression][Expr].
 fn optimize_expr(expr: &mut Expr, state: &mut State) {
     // These keywords are handled specially
     const DONT_EVAL_KEYWORDS: &[&str] = &[
@@ -501,7 +504,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
         Expr::Dot(x, _) => match (&mut x.lhs, &mut x.rhs) {
             // map.string
             (Expr::Map(m, pos), Expr::Property(p)) if m.iter().all(|(_, x)| x.is_pure()) => {
-                let prop = &p.1.name;
+                let prop = &p.2.name;
                 // Map literal where everything is pure - promote the indexed item.
                 // All other items can be thrown away.
                 state.set_dirty();
@@ -655,7 +658,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
             let arg_types: StaticVec<_> = arg_values.iter().map(Dynamic::type_id).collect();
 
             // Search for overloaded operators (can override built-in).
-            if !state.engine.has_override_by_name_and_arguments(Some(&state.engine.global_sub_modules), state.lib, x.name.as_ref(), arg_types.as_ref(), false) {
+            if !state.engine.has_override_by_name_and_arguments(Some(&state.mods), state.lib, x.name.as_ref(), arg_types.as_ref(), false) {
                 if let Some(result) = run_builtin_binary_op(x.name.as_ref(), &arg_values[0], &arg_values[1])
                                         .ok().flatten()
                                         .and_then(|result| map_dynamic_to_expr(result, *pos))
@@ -717,12 +720,12 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
         Expr::FnCall(x, _) => x.args.iter_mut().for_each(|a| optimize_expr(a, state)),
 
         // constant-name
-        Expr::Variable(x) if x.1.is_none() && state.find_constant(&x.3.name).is_some() => {
+        Expr::Variable(x) if x.1.is_none() && state.find_constant(&x.2.name).is_some() => {
             state.set_dirty();
 
             // Replace constant with value
-            let mut result = state.find_constant(&x.3.name).unwrap().clone();
-            result.set_position(x.3.pos);
+            let mut result = state.find_constant(&x.2.name).unwrap().clone();
+            result.set_position(x.2.pos);
             *expr = result;
         }
 
@@ -734,7 +737,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
     }
 }
 
-/// Optimize a block of [statements][crate::ast::Stmt] at top level.
+/// Optimize a block of [statements][Stmt] at top level.
 fn optimize_top_level(
     mut statements: Vec<Stmt>,
     engine: &Engine,
diff --git a/src/packages/fn_basic.rs b/src/packages/fn_basic.rs
index 4b241f55..ad1586ab 100644
--- a/src/packages/fn_basic.rs
+++ b/src/packages/fn_basic.rs
@@ -32,7 +32,7 @@ mod fn_ptr_functions {
             } else {
                 let hash_script = calc_script_fn_hash(empty(), fn_name, num_params as usize);
                 ctx.engine()
-                    .has_override(ctx.mods, ctx.lib, 0, hash_script, true)
+                    .has_override(ctx.mods, ctx.lib, None, hash_script, true)
             }
         }
     }
diff --git a/src/parse_error.rs b/src/parse_error.rs
index 7419fb98..a9ce4e7f 100644
--- a/src/parse_error.rs
+++ b/src/parse_error.rs
@@ -91,13 +91,16 @@ pub enum ParseErrorType {
     UnknownOperator(String),
     /// Expecting a particular token but not finding one. Wrapped values are the token and description.
     MissingToken(String, String),
-    /// An expression in function call arguments `()` has syntax error. Wrapped value is the error description (if any).
+    /// An expression in function call arguments `()` has syntax error. Wrapped value is the error
+    /// description (if any).
     MalformedCallExpr(String),
-    /// An expression in indexing brackets `[]` has syntax error. Wrapped value is the error description (if any).
+    /// An expression in indexing brackets `[]` has syntax error. Wrapped value is the error
+    /// description (if any).
     ///
     /// Never appears under the `no_index` feature.
     MalformedIndexExpr(String),
-    /// An expression in an `in` expression has syntax error. Wrapped value is the error description (if any).
+    /// An expression in an `in` expression has syntax error. Wrapped value is the error description
+    /// (if any).
     ///
     /// Never appears under the `no_object` and `no_index` features combination.
     MalformedInExpr(String),
@@ -137,7 +140,8 @@ pub enum ParseErrorType {
     ///
     /// Never appears under the `no_function` feature.
     FnMissingParams(String),
-    /// A function definition has duplicated parameters. Wrapped values are the function name and parameter name.
+    /// A function definition has duplicated parameters. Wrapped values are the function name and
+    /// parameter name.
     ///
     /// Never appears under the `no_function` feature.
     FnDuplicatedParam(String, String),
diff --git a/src/parser.rs b/src/parser.rs
index 9a879083..5d22c9dd 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -13,7 +13,7 @@ use crate::stdlib::{
     format,
     hash::{Hash, Hasher},
     iter::empty,
-    num::NonZeroUsize,
+    num::{NonZeroU64, NonZeroUsize},
     string::{String, ToString},
     vec,
     vec::Vec,
@@ -34,7 +34,7 @@ use crate::FnAccess;
 
 type PERR = ParseErrorType;
 
-type FunctionsLib = HashMap<u64, ScriptFnDef, StraightHasherBuilder>;
+type FunctionsLib = HashMap<NonZeroU64, ScriptFnDef, StraightHasherBuilder>;
 
 /// A type that encapsulates the current state of the parser.
 #[derive(Debug)]
@@ -238,10 +238,10 @@ impl Expr {
     fn into_property(self, state: &mut ParseState) -> Self {
         match self {
             Self::Variable(x) if x.1.is_none() => {
-                let ident = x.3;
+                let ident = x.2;
                 let getter = state.get_interned_string(crate::engine::make_getter(&ident.name));
                 let setter = state.get_interned_string(crate::engine::make_setter(&ident.name));
-                Self::Property(Box::new(((getter, setter), ident.into())))
+                Self::Property(Box::new((getter, setter, ident.into())))
             }
             _ => self,
         }
@@ -278,8 +278,11 @@ fn parse_paren_expr(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    settings: ParseSettings,
+    mut settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    // ( ...
+    settings.pos = eat_token(input, Token::LeftParen);
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -310,7 +313,7 @@ fn parse_fn_call(
     lib: &mut FunctionsLib,
     id: ImmutableString,
     capture: bool,
-    mut namespace: Option<Box<NamespaceRef>>,
+    mut namespace: Option<NamespaceRef>,
     settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
     let (token, token_pos) = input.peek().unwrap();
@@ -335,7 +338,7 @@ fn parse_fn_call(
         Token::RightParen => {
             eat_token(input, Token::RightParen);
 
-            let hash_script = if let Some(modules) = namespace.as_mut() {
+            let mut hash_script = if let Some(ref mut modules) = namespace {
                 #[cfg(not(feature = "no_module"))]
                 modules.set_index(state.find_module(&modules[0].name));
 
@@ -352,13 +355,17 @@ fn parse_fn_call(
                 calc_script_fn_hash(empty(), &id, 0)
             };
 
+            // script functions can only be valid identifiers
+            if !is_valid_identifier(id.chars()) {
+                hash_script = None;
+            }
+
             return Ok(Expr::FnCall(
                 Box::new(FnCallExpr {
                     name: id.to_string().into(),
-                    native_only: !is_valid_identifier(id.chars()), // script functions can only be valid identifiers
                     capture,
                     namespace,
-                    hash: hash_script,
+                    hash_script,
                     args,
                     ..Default::default()
                 }),
@@ -383,7 +390,7 @@ fn parse_fn_call(
             (Token::RightParen, _) => {
                 eat_token(input, Token::RightParen);
 
-                let hash_script = if let Some(modules) = namespace.as_mut() {
+                let mut hash_script = if let Some(modules) = namespace.as_mut() {
                     #[cfg(not(feature = "no_module"))]
                     modules.set_index(state.find_module(&modules[0].name));
 
@@ -400,13 +407,17 @@ fn parse_fn_call(
                     calc_script_fn_hash(empty(), &id, args.len())
                 };
 
+                // script functions can only be valid identifiers
+                if !is_valid_identifier(id.chars()) {
+                    hash_script = None;
+                }
+
                 return Ok(Expr::FnCall(
                     Box::new(FnCallExpr {
                         name: id.to_string().into(),
-                        native_only: !is_valid_identifier(id.chars()), // script functions can only be valid identifiers
                         capture,
                         namespace,
-                        hash: hash_script,
+                        hash_script,
                         args,
                         ..Default::default()
                     }),
@@ -629,8 +640,11 @@ fn parse_array_literal(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    settings: ParseSettings,
+    mut settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    // [ ...
+    settings.pos = eat_token(input, Token::LeftBracket);
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -696,8 +710,11 @@ fn parse_map_literal(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    settings: ParseSettings,
+    mut settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    // #{ ...
+    settings.pos = eat_token(input, Token::MapStart);
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -939,105 +956,196 @@ fn parse_primary(
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
-    let (token, _) = match token {
+    let mut root_expr = match token {
+        Token::EOF => return Err(PERR::UnexpectedEOF.into_err(settings.pos)),
+
+        Token::IntegerConstant(_)
+        | Token::CharConstant(_)
+        | Token::StringConstant(_)
+        | Token::True
+        | Token::False => match input.next().unwrap().0 {
+            Token::IntegerConstant(x) => Expr::IntegerConstant(x, settings.pos),
+            Token::CharConstant(c) => Expr::CharConstant(c, settings.pos),
+            Token::StringConstant(s) => {
+                Expr::StringConstant(state.get_interned_string(s), settings.pos)
+            }
+            Token::True => Expr::BoolConstant(true, settings.pos),
+            Token::False => Expr::BoolConstant(false, settings.pos),
+            _ => unreachable!(),
+        },
+        #[cfg(not(feature = "no_float"))]
+        Token::FloatConstant(x) => {
+            let x = *x;
+            input.next().unwrap();
+            Expr::FloatConstant(x, settings.pos)
+        }
+
         // { - block statement as expression
         Token::LeftBrace if settings.allow_stmt_expr => {
-            return parse_block(input, state, lib, settings.level_up()).map(|block| match block {
+            match parse_block(input, state, lib, settings.level_up())? {
                 Stmt::Block(statements, pos) => Expr::Stmt(Box::new(statements.into()), pos),
                 _ => unreachable!(),
-            })
-        }
-        Token::EOF => return Err(PERR::UnexpectedEOF.into_err(settings.pos)),
-        _ => input.next().unwrap(),
-    };
-
-    let (next_token, _) = input.peek().unwrap();
-
-    let mut root_expr = match token {
-        Token::IntegerConstant(x) => Expr::IntegerConstant(x, settings.pos),
-        #[cfg(not(feature = "no_float"))]
-        Token::FloatConstant(x) => Expr::FloatConstant(x, settings.pos),
-        Token::CharConstant(c) => Expr::CharConstant(c, settings.pos),
-        Token::StringConstant(s) => {
-            Expr::StringConstant(state.get_interned_string(s), settings.pos)
-        }
-
-        // Function call
-        Token::Identifier(s) if *next_token == Token::LeftParen || *next_token == Token::Bang => {
-            // Once the identifier consumed we must enable next variables capturing
-            #[cfg(not(feature = "no_closure"))]
-            {
-                state.allow_capture = true;
-            }
-            let var_name_def = Ident {
-                name: state.get_interned_string(s),
-                pos: settings.pos,
-            };
-            Expr::Variable(Box::new((None, None, 0, var_name_def)))
-        }
-        // Namespace qualification
-        #[cfg(not(feature = "no_module"))]
-        Token::Identifier(s) if *next_token == Token::DoubleColon => {
-            // Once the identifier consumed we must enable next variables capturing
-            #[cfg(not(feature = "no_closure"))]
-            {
-                state.allow_capture = true;
-            }
-            let var_name_def = Ident {
-                name: state.get_interned_string(s),
-                pos: settings.pos,
-            };
-            Expr::Variable(Box::new((None, None, 0, var_name_def)))
-        }
-        // Normal variable access
-        Token::Identifier(s) => {
-            let index = state.access_var(&s, settings.pos);
-            let var_name_def = Ident {
-                name: state.get_interned_string(s),
-                pos: settings.pos,
-            };
-            Expr::Variable(Box::new((index, None, 0, var_name_def)))
-        }
-
-        // Function call is allowed to have reserved keyword
-        Token::Reserved(s) if *next_token == Token::LeftParen || *next_token == Token::Bang => {
-            if is_keyword_function(&s) {
-                let var_name_def = Ident {
-                    name: state.get_interned_string(s),
-                    pos: settings.pos,
-                };
-                Expr::Variable(Box::new((None, None, 0, var_name_def)))
-            } else {
-                return Err(PERR::Reserved(s).into_err(settings.pos));
             }
         }
-
-        // Access to `this` as a variable is OK
-        Token::Reserved(s) if s == KEYWORD_THIS && *next_token != Token::LeftParen => {
-            if !settings.is_function_scope {
-                let msg = format!("'{}' can only be used in functions", s);
-                return Err(LexError::ImproperSymbol(s, msg).into_err(settings.pos));
-            } else {
-                let var_name_def = Ident {
-                    name: state.get_interned_string(s),
-                    pos: settings.pos,
-                };
-                Expr::Variable(Box::new((None, None, 0, var_name_def)))
-            }
-        }
-
-        Token::Reserved(s) if is_valid_identifier(s.chars()) => {
-            return Err(PERR::Reserved(s).into_err(settings.pos));
-        }
-
+        // ( - grouped expression
         Token::LeftParen => parse_paren_expr(input, state, lib, settings.level_up())?,
+
+        // If statement is allowed to act as expressions
+        Token::If if settings.allow_if_expr => Expr::Stmt(
+            Box::new(vec![parse_if(input, state, lib, settings.level_up())?].into()),
+            settings.pos,
+        ),
+        // Switch statement is allowed to act as expressions
+        Token::Switch if settings.allow_switch_expr => Expr::Stmt(
+            Box::new(vec![parse_switch(input, state, lib, settings.level_up())?].into()),
+            settings.pos,
+        ),
+        // | ...
+        #[cfg(not(feature = "no_function"))]
+        Token::Pipe | Token::Or if settings.allow_anonymous_fn => {
+            let mut new_state = ParseState::new(
+                state.engine,
+                state.script_hash,
+                #[cfg(not(feature = "unchecked"))]
+                state.max_function_expr_depth,
+                #[cfg(not(feature = "unchecked"))]
+                state.max_function_expr_depth,
+            );
+
+            let settings = ParseSettings {
+                allow_if_expr: true,
+                allow_switch_expr: true,
+                allow_stmt_expr: true,
+                allow_anonymous_fn: true,
+                is_global: false,
+                is_function_scope: true,
+                is_breakable: false,
+                level: 0,
+                pos: settings.pos,
+            };
+
+            let (expr, func) = parse_anon_fn(input, &mut new_state, lib, settings)?;
+
+            #[cfg(not(feature = "no_closure"))]
+            new_state.externals.iter().for_each(|(closure, pos)| {
+                state.access_var(closure, *pos);
+            });
+
+            // Qualifiers (none) + function name + number of arguments.
+            let hash = calc_script_fn_hash(empty(), &func.name, func.params.len()).unwrap();
+
+            lib.insert(hash, func);
+
+            expr
+        }
+
+        // Array literal
         #[cfg(not(feature = "no_index"))]
         Token::LeftBracket => parse_array_literal(input, state, lib, settings.level_up())?,
+
+        // Map literal
         #[cfg(not(feature = "no_object"))]
         Token::MapStart => parse_map_literal(input, state, lib, settings.level_up())?,
-        Token::True => Expr::BoolConstant(true, settings.pos),
-        Token::False => Expr::BoolConstant(false, settings.pos),
-        Token::LexError(err) => return Err(err.into_err(settings.pos)),
+
+        // Identifier
+        Token::Identifier(_) => {
+            let s = match input.next().unwrap().0 {
+                Token::Identifier(s) => s,
+                _ => unreachable!(),
+            };
+
+            match input.peek().unwrap().0 {
+                // Function call
+                Token::LeftParen | Token::Bang => {
+                    // Once the identifier consumed we must enable next variables capturing
+                    #[cfg(not(feature = "no_closure"))]
+                    {
+                        state.allow_capture = true;
+                    }
+                    let var_name_def = Ident {
+                        name: state.get_interned_string(s),
+                        pos: settings.pos,
+                    };
+                    Expr::Variable(Box::new((None, None, var_name_def)))
+                }
+                // Namespace qualification
+                #[cfg(not(feature = "no_module"))]
+                Token::DoubleColon => {
+                    // Once the identifier consumed we must enable next variables capturing
+                    #[cfg(not(feature = "no_closure"))]
+                    {
+                        state.allow_capture = true;
+                    }
+                    let var_name_def = Ident {
+                        name: state.get_interned_string(s),
+                        pos: settings.pos,
+                    };
+                    Expr::Variable(Box::new((None, None, var_name_def)))
+                }
+                // Normal variable access
+                _ => {
+                    let index = state.access_var(&s, settings.pos);
+                    let var_name_def = Ident {
+                        name: state.get_interned_string(s),
+                        pos: settings.pos,
+                    };
+                    Expr::Variable(Box::new((index, None, var_name_def)))
+                }
+            }
+        }
+
+        // Reserved keyword or symbol
+        Token::Reserved(_) => {
+            let s = match input.next().unwrap().0 {
+                Token::Reserved(s) => s,
+                _ => unreachable!(),
+            };
+
+            match input.peek().unwrap().0 {
+                // Function call is allowed to have reserved keyword
+                Token::LeftParen | Token::Bang => {
+                    if s == KEYWORD_THIS {
+                        return Err(PERR::Reserved(s).into_err(settings.pos));
+                    } else if is_keyword_function(&s) {
+                        let var_name_def = Ident {
+                            name: state.get_interned_string(s),
+                            pos: settings.pos,
+                        };
+                        Expr::Variable(Box::new((None, None, var_name_def)))
+                    } else {
+                        return Err(PERR::Reserved(s).into_err(settings.pos));
+                    }
+                }
+                // Access to `this` as a variable is OK
+                _ if s == KEYWORD_THIS => {
+                    if !settings.is_function_scope {
+                        let msg = format!("'{}' can only be used in functions", s);
+                        return Err(LexError::ImproperSymbol(s, msg).into_err(settings.pos));
+                    } else {
+                        let var_name_def = Ident {
+                            name: state.get_interned_string(s),
+                            pos: settings.pos,
+                        };
+                        Expr::Variable(Box::new((None, None, var_name_def)))
+                    }
+                }
+                _ if is_valid_identifier(s.chars()) => {
+                    return Err(PERR::Reserved(s).into_err(settings.pos));
+                }
+                _ => {
+                    return Err(LexError::UnexpectedInput(s).into_err(settings.pos));
+                }
+            }
+        }
+
+        Token::LexError(_) => {
+            let err = match input.next().unwrap().0 {
+                Token::LexError(err) => err,
+                _ => unreachable!(),
+            };
+
+            return Err(err.into_err(settings.pos));
+        }
 
         _ => {
             return Err(
@@ -1048,26 +1156,26 @@ fn parse_primary(
 
     // Tail processing all possible postfix operators
     loop {
-        let (token, _) = input.peek().unwrap();
+        let (tail_token, _) = input.peek().unwrap();
 
-        if !root_expr.is_valid_postfix(token) {
+        if !root_expr.is_valid_postfix(tail_token) {
             break;
         }
 
-        let (token, token_pos) = input.next().unwrap();
-        settings.pos = token_pos;
+        let (tail_token, tail_pos) = input.next().unwrap();
+        settings.pos = tail_pos;
 
-        root_expr = match (root_expr, token) {
+        root_expr = match (root_expr, tail_token) {
             // Qualified function call with !
             (Expr::Variable(x), Token::Bang) if x.1.is_some() => {
                 return Err(if !match_token(input, Token::LeftParen).0 {
-                    LexError::UnexpectedInput(Token::Bang.syntax().to_string()).into_err(token_pos)
+                    LexError::UnexpectedInput(Token::Bang.syntax().to_string()).into_err(tail_pos)
                 } else {
                     LexError::ImproperSymbol(
                         "!".to_string(),
                         "'!' cannot be used to call module functions".to_string(),
                     )
-                    .into_err(token_pos)
+                    .into_err(tail_pos)
                 });
             }
             // Function call with !
@@ -1081,35 +1189,38 @@ fn parse_primary(
                     .into_err(pos));
                 }
 
-                let (_, modules, _, Ident { name, pos }) = *x;
+                let (_, namespace, Ident { name, pos }) = *x;
                 settings.pos = pos;
-                parse_fn_call(input, state, lib, name, true, modules, settings.level_up())?
+                let ns = namespace.map(|(_, ns)| ns);
+                parse_fn_call(input, state, lib, name, true, ns, settings.level_up())?
             }
             // Function call
             (Expr::Variable(x), Token::LeftParen) => {
-                let (_, modules, _, Ident { name, pos }) = *x;
+                let (_, namespace, Ident { name, pos }) = *x;
                 settings.pos = pos;
-                parse_fn_call(input, state, lib, name, false, modules, settings.level_up())?
+                let ns = namespace.map(|(_, ns)| ns);
+                parse_fn_call(input, state, lib, name, false, ns, settings.level_up())?
             }
             (Expr::Property(_), _) => unreachable!(),
             // module access
             (Expr::Variable(x), Token::DoubleColon) => match input.next().unwrap() {
                 (Token::Identifier(id2), pos2) => {
-                    let (index, mut modules, _, var_name_def) = *x;
+                    let (index, mut namespace, var_name_def) = *x;
 
-                    if let Some(ref mut modules) = modules {
-                        modules.push(var_name_def);
+                    if let Some((_, ref mut namespace)) = namespace {
+                        namespace.push(var_name_def);
                     } else {
-                        let mut m: NamespaceRef = Default::default();
-                        m.push(var_name_def);
-                        modules = Some(Box::new(m));
+                        let mut ns: NamespaceRef = Default::default();
+                        ns.push(var_name_def);
+                        let index = NonZeroU64::new(42).unwrap(); // Dummy
+                        namespace = Some((index, ns));
                     }
 
                     let var_name_def = Ident {
                         name: state.get_interned_string(id2),
                         pos: pos2,
                     };
-                    Expr::Variable(Box::new((index, modules, 0, var_name_def)))
+                    Expr::Variable(Box::new((index, namespace, var_name_def)))
                 }
                 (Token::Reserved(id2), pos2) if is_valid_identifier(id2.chars()) => {
                     return Err(PERR::Reserved(id2).into_err(pos2));
@@ -1121,11 +1232,17 @@ fn parse_primary(
             (expr, Token::LeftBracket) => {
                 parse_index_chain(input, state, lib, expr, settings.level_up())?
             }
-            // Method access
+            // Property access
             #[cfg(not(feature = "no_object"))]
             (expr, Token::Period) => {
+                // prevents capturing of the object properties as vars: xxx.<var>
+                #[cfg(not(feature = "no_closure"))]
+                if let (Token::Identifier(_), _) = input.peek().unwrap() {
+                    state.allow_capture = false;
+                }
+
                 let rhs = parse_unary(input, state, lib, settings.level_up())?;
-                make_dot_expr(state, expr, rhs, token_pos)?
+                make_dot_expr(state, expr, rhs, tail_pos)?
             }
             // Unknown postfix operator
             (expr, token) => unreachable!(
@@ -1146,14 +1263,16 @@ fn parse_primary(
         _ => None,
     }
     .map(|x| {
-        let (_, modules, hash, Ident { name, .. }) = x.as_mut();
-        let namespace = modules.as_mut().unwrap();
+        if let (_, Some((ref mut hash, ref mut namespace)), Ident { name, .. }) = x.as_mut() {
+            // Qualifiers + variable name
+            *hash =
+                calc_script_fn_hash(namespace.iter().map(|v| v.name.as_str()), name, 0).unwrap();
 
-        // Qualifiers + variable name
-        *hash = calc_script_fn_hash(namespace.iter().map(|v| v.name.as_str()), name, 0);
-
-        #[cfg(not(feature = "no_module"))]
-        namespace.set_index(state.find_module(&namespace[0].name));
+            #[cfg(not(feature = "no_module"))]
+            namespace.set_index(state.find_module(&namespace[0].name));
+        } else {
+            unreachable!();
+        }
     });
 
     // Make sure identifiers are valid
@@ -1174,16 +1293,6 @@ fn parse_unary(
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
     match token {
-        // If statement is allowed to act as expressions
-        Token::If if settings.allow_if_expr => Ok(Expr::Stmt(
-            Box::new(vec![parse_if(input, state, lib, settings.level_up())?].into()),
-            settings.pos,
-        )),
-        // Switch statement is allowed to act as expressions
-        Token::Switch if settings.allow_switch_expr => Ok(Expr::Stmt(
-            Box::new(vec![parse_switch(input, state, lib, settings.level_up())?].into()),
-            settings.pos,
-        )),
         // -expr
         Token::UnaryMinus => {
             let pos = eat_token(input, Token::UnaryMinus);
@@ -1208,16 +1317,12 @@ fn parse_unary(
                 // Call negative function
                 expr => {
                     let op = "-";
-                    let hash = calc_script_fn_hash(empty(), op, 1);
                     let mut args = StaticVec::new();
                     args.push(expr);
 
                     Ok(Expr::FnCall(
                         Box::new(FnCallExpr {
                             name: op.into(),
-                            native_only: true,
-                            namespace: None,
-                            hash,
                             args,
                             ..Default::default()
                         }),
@@ -1238,16 +1343,12 @@ fn parse_unary(
                 // Call plus function
                 expr => {
                     let op = "+";
-                    let hash = calc_script_fn_hash(empty(), op, 1);
                     let mut args = StaticVec::new();
                     args.push(expr);
 
                     Ok(Expr::FnCall(
                         Box::new(FnCallExpr {
                             name: op.into(),
-                            native_only: true,
-                            namespace: None,
-                            hash,
                             args,
                             ..Default::default()
                         }),
@@ -1264,13 +1365,10 @@ fn parse_unary(
             args.push(expr);
 
             let op = "!";
-            let hash = calc_script_fn_hash(empty(), op, 1);
 
             Ok(Expr::FnCall(
                 Box::new(FnCallExpr {
                     name: op.into(),
-                    native_only: true,
-                    hash,
                     args,
                     def_value: Some(false.into()), // NOT operator, when operating on invalid operand, defaults to false
                     ..Default::default()
@@ -1278,44 +1376,6 @@ fn parse_unary(
                 pos,
             ))
         }
-        // | ...
-        #[cfg(not(feature = "no_function"))]
-        Token::Pipe | Token::Or if settings.allow_anonymous_fn => {
-            let mut new_state = ParseState::new(
-                state.engine,
-                state.script_hash,
-                #[cfg(not(feature = "unchecked"))]
-                state.max_function_expr_depth,
-                #[cfg(not(feature = "unchecked"))]
-                state.max_function_expr_depth,
-            );
-
-            let settings = ParseSettings {
-                allow_if_expr: true,
-                allow_switch_expr: true,
-                allow_stmt_expr: true,
-                allow_anonymous_fn: true,
-                is_global: false,
-                is_function_scope: true,
-                is_breakable: false,
-                level: 0,
-                pos: *token_pos,
-            };
-
-            let (expr, func) = parse_anon_fn(input, &mut new_state, lib, settings)?;
-
-            #[cfg(not(feature = "no_closure"))]
-            new_state.externals.iter().for_each(|(closure, pos)| {
-                state.access_var(closure, *pos);
-            });
-
-            // Qualifiers (none) + function name + number of arguments.
-            let hash = calc_script_fn_hash(empty(), &func.name, func.params.len());
-
-            lib.insert(hash, func);
-
-            Ok(expr)
-        }
         // <EOF>
         Token::EOF => Err(PERR::UnexpectedEOF.into_err(settings.pos)),
         // All other tokens
@@ -1323,6 +1383,7 @@ fn parse_unary(
     }
 }
 
+/// Make an assignment statement.
 fn make_assignment_stmt<'a>(
     fn_name: Cow<'static, str>,
     state: &mut ParseState,
@@ -1338,7 +1399,7 @@ fn make_assignment_stmt<'a>(
         )),
         // var (indexed) = rhs
         Expr::Variable(x) => {
-            let (index, _, _, Ident { name, pos }) = x.as_ref();
+            let (index, _, Ident { name, pos }) = x.as_ref();
             match state.stack[(state.stack.len() - index.unwrap().get())].1 {
                 AccessMode::ReadWrite => Ok(Stmt::Assignment(
                     Box::new((lhs, fn_name.into(), rhs)),
@@ -1359,7 +1420,7 @@ fn make_assignment_stmt<'a>(
             )),
             // var[???] (indexed) = rhs, var.??? (indexed) = rhs
             Expr::Variable(x) => {
-                let (index, _, _, Ident { name, pos }) = x.as_ref();
+                let (index, _, Ident { name, pos }) = x.as_ref();
                 match state.stack[(state.stack.len() - index.unwrap().get())].1 {
                     AccessMode::ReadWrite => Ok(Stmt::Assignment(
                         Box::new((lhs, fn_name.into(), rhs)),
@@ -1443,16 +1504,16 @@ fn make_dot_expr(
         }
         // lhs.id
         (lhs, Expr::Variable(x)) if x.1.is_none() => {
-            let ident = x.3;
+            let ident = x.2;
             let getter = state.get_interned_string(crate::engine::make_getter(&ident.name));
             let setter = state.get_interned_string(crate::engine::make_setter(&ident.name));
-            let rhs = Expr::Property(Box::new(((getter, setter), ident)));
+            let rhs = Expr::Property(Box::new((getter, setter, ident)));
 
             Expr::Dot(Box::new(BinaryExpr { lhs, rhs }), op_pos)
         }
         // lhs.module::id - syntax error
         (_, Expr::Variable(x)) if x.1.is_some() => {
-            return Err(PERR::PropertyExpected.into_err(x.1.unwrap()[0].pos));
+            return Err(PERR::PropertyExpected.into_err(x.1.unwrap().1[0].pos));
         }
         // lhs.prop
         (lhs, prop @ Expr::Property(_)) => {
@@ -1662,15 +1723,24 @@ fn parse_binary_op(
 
     loop {
         let (current_op, current_pos) = input.peek().unwrap();
-        let precedence = if let Token::Custom(c) = current_op {
-            // Custom operators
-            if let Some(Some(p)) = state.engine.custom_keywords.get(c) {
-                *p
-            } else {
-                return Err(PERR::Reserved(c.clone()).into_err(*current_pos));
+        let precedence = match current_op {
+            Token::Custom(c) => {
+                if state
+                    .engine
+                    .custom_keywords
+                    .get(c)
+                    .map(Option::is_some)
+                    .unwrap_or(false)
+                {
+                    state.engine.custom_keywords.get(c).unwrap().unwrap().get()
+                } else {
+                    return Err(PERR::Reserved(c.clone()).into_err(*current_pos));
+                }
             }
-        } else {
-            current_op.precedence()
+            Token::Reserved(c) if !is_valid_identifier(c.chars()) => {
+                return Err(PERR::UnknownOperator(c.into()).into_err(*current_pos))
+            }
+            _ => current_op.precedence(),
         };
         let bind_right = current_op.is_bind_right();
 
@@ -1682,28 +1752,27 @@ fn parse_binary_op(
 
         let (op_token, pos) = input.next().unwrap();
 
-        if cfg!(not(feature = "no_object")) && op_token == Token::Period {
-            if let (Token::Identifier(_), _) = input.peek().unwrap() {
-                // prevents capturing of the object properties as vars: xxx.<var>
-                #[cfg(not(feature = "no_closure"))]
-                {
-                    state.allow_capture = false;
-                }
-            }
-        }
-
         let rhs = parse_unary(input, state, lib, settings)?;
 
         let (next_op, next_pos) = input.peek().unwrap();
-        let next_precedence = if let Token::Custom(c) = next_op {
-            // Custom operators
-            if let Some(Some(p)) = state.engine.custom_keywords.get(c) {
-                *p
-            } else {
-                return Err(PERR::Reserved(c.clone()).into_err(*next_pos));
+        let next_precedence = match next_op {
+            Token::Custom(c) => {
+                if state
+                    .engine
+                    .custom_keywords
+                    .get(c)
+                    .map(Option::is_some)
+                    .unwrap_or(false)
+                {
+                    state.engine.custom_keywords.get(c).unwrap().unwrap().get()
+                } else {
+                    return Err(PERR::Reserved(c.clone()).into_err(*next_pos));
+                }
             }
-        } else {
-            next_op.precedence()
+            Token::Reserved(c) if !is_valid_identifier(c.chars()) => {
+                return Err(PERR::UnknownOperator(c.into()).into_err(*next_pos))
+            }
+            _ => next_op.precedence(),
         };
 
         // Bind to right if the next operator has higher precedence
@@ -1723,11 +1792,9 @@ fn parse_binary_op(
 
         let cmp_def = Some(false.into());
         let op = op_token.syntax();
-        let hash = calc_script_fn_hash(empty(), &op, 2);
 
         let op_base = FnCallExpr {
             name: op,
-            native_only: true,
             capture: false,
             ..Default::default()
         };
@@ -1747,19 +1814,11 @@ fn parse_binary_op(
             | Token::PowerOf
             | Token::Ampersand
             | Token::Pipe
-            | Token::XOr => Expr::FnCall(
-                Box::new(FnCallExpr {
-                    hash,
-                    args,
-                    ..op_base
-                }),
-                pos,
-            ),
+            | Token::XOr => Expr::FnCall(Box::new(FnCallExpr { args, ..op_base }), pos),
 
             // '!=' defaults to true when passed invalid operands
             Token::NotEqualsTo => Expr::FnCall(
                 Box::new(FnCallExpr {
-                    hash,
                     args,
                     def_value: Some(true.into()),
                     ..op_base
@@ -1774,7 +1833,6 @@ fn parse_binary_op(
             | Token::GreaterThan
             | Token::GreaterThanEqualsTo => Expr::FnCall(
                 Box::new(FnCallExpr {
-                    hash,
                     args,
                     def_value: cmp_def,
                     ..op_base
@@ -1810,20 +1868,31 @@ fn parse_binary_op(
                 make_in_expr(current_lhs, rhs, pos)?
             }
 
-            #[cfg(not(feature = "no_object"))]
-            Token::Period => {
-                let rhs = args.pop().unwrap();
-                let current_lhs = args.pop().unwrap();
-                make_dot_expr(state, current_lhs, rhs, pos)?
-            }
+            // #[cfg(not(feature = "no_object"))]
+            // Token::Period => {
+            //     let rhs = args.pop().unwrap();
+            //     let current_lhs = args.pop().unwrap();
+            //     make_dot_expr(state, current_lhs, rhs, pos)?
+            // }
+            Token::Custom(s)
+                if state
+                    .engine
+                    .custom_keywords
+                    .get(&s)
+                    .map(Option::is_some)
+                    .unwrap_or(false) =>
+            {
+                let hash_script = if is_valid_identifier(s.chars()) {
+                    // Accept non-native functions for custom operators
+                    calc_script_fn_hash(empty(), &s, 2)
+                } else {
+                    None
+                };
 
-            Token::Custom(s) if state.engine.custom_keywords.contains_key(&s) => {
-                // Accept non-native functions for custom operators
                 Expr::FnCall(
                     Box::new(FnCallExpr {
-                        hash,
+                        hash_script,
                         args,
-                        native_only: false,
                         ..op_base
                     }),
                     pos,
@@ -1892,7 +1961,7 @@ fn parse_custom_syntax(
                     segments.push(name.clone());
                     tokens.push(state.get_interned_string(MARKER_IDENT));
                     let var_name_def = Ident { name, pos };
-                    keywords.push(Expr::Variable(Box::new((None, None, 0, var_name_def))));
+                    keywords.push(Expr::Variable(Box::new((None, None, var_name_def))));
                 }
                 (Token::Reserved(s), pos) if is_valid_identifier(s.chars()) => {
                     return Err(PERR::Reserved(s).into_err(pos));
@@ -2549,7 +2618,7 @@ fn parse_stmt(
                     let func = parse_fn(input, &mut new_state, lib, access, settings, comments)?;
 
                     // Qualifiers (none) + function name + number of arguments.
-                    let hash = calc_script_fn_hash(empty(), &func.name, func.params.len());
+                    let hash = calc_script_fn_hash(empty(), &func.name, func.params.len()).unwrap();
 
                     lib.insert(hash, func);
 
@@ -2565,6 +2634,7 @@ fn parse_stmt(
         }
 
         Token::If => parse_if(input, state, lib, settings.level_up()).map(Some),
+        Token::Switch => parse_switch(input, state, lib, settings.level_up()).map(Some),
         Token::While | Token::Loop => {
             parse_while_loop(input, state, lib, settings.level_up()).map(Some)
         }
@@ -2812,22 +2882,22 @@ fn make_curry_from_externals(fn_expr: Expr, externals: StaticVec<Ident>, pos: Po
 
     #[cfg(not(feature = "no_closure"))]
     externals.iter().for_each(|x| {
-        args.push(Expr::Variable(Box::new((None, None, 0, x.clone().into()))));
+        args.push(Expr::Variable(Box::new((None, None, x.clone().into()))));
     });
 
     #[cfg(feature = "no_closure")]
     externals.into_iter().for_each(|x| {
-        args.push(Expr::Variable(Box::new((None, None, 0, x.clone().into()))));
+        args.push(Expr::Variable(Box::new((None, None, x.clone().into()))));
     });
 
     let curry_func = crate::engine::KEYWORD_FN_PTR_CURRY;
 
-    let hash = calc_script_fn_hash(empty(), curry_func, num_externals + 1);
+    let hash_script = calc_script_fn_hash(empty(), curry_func, num_externals + 1);
 
     let expr = Expr::FnCall(
         Box::new(FnCallExpr {
             name: curry_func.into(),
-            hash,
+            hash_script,
             args,
             ..Default::default()
         }),
diff --git a/src/plugin.rs b/src/plugin.rs
index d07cc188..9882951f 100644
--- a/src/plugin.rs
+++ b/src/plugin.rs
@@ -13,8 +13,8 @@ pub use rhai_codegen::*;
 pub use rhai_codegen::{export_fn, register_exported_fn};
 
 /// Trait implemented by a _plugin function_.
-/// This trait should not be used directly.
 ///
+/// This trait should not be used directly.
 /// Use the `#[export_module]` and `#[export_fn]` procedural attributes instead.
 pub trait PluginFunction {
     /// Call the plugin function with the arguments provided.
diff --git a/src/result.rs b/src/result.rs
index 7719f225..02a0f5c8 100644
--- a/src/result.rs
+++ b/src/result.rs
@@ -55,8 +55,8 @@ pub enum EvalAltResult {
     /// String indexing out-of-bounds.
     /// Wrapped values are the current number of characters in the string and the index number.
     ErrorStringBounds(usize, INT, Position),
-    /// Trying to index into a type that is not an array, an object map, or a string, and has no indexer function defined.
-    /// Wrapped value is the type name.
+    /// Trying to index into a type that is not an array, an object map, or a string, and has no
+    /// indexer function defined. Wrapped value is the type name.
     ErrorIndexingType(String, Position),
     /// Invalid arguments for `in` operator.
     ErrorInExpr(Position),
diff --git a/src/scope.rs b/src/scope.rs
index 4e5cc08a..3498dce3 100644
--- a/src/scope.rs
+++ b/src/scope.rs
@@ -39,17 +39,18 @@ use crate::{Dynamic, ImmutableString, StaticVec};
 // # Implementation Notes
 //
 // [`Scope`] is implemented as two [`Vec`]'s of exactly the same length.  Variables data (name, type, etc.)
-// is manually split into three equal-length arrays.  That's because variable names take up the most space,
-// with [`Cow<str>`][Cow] being four words long, but in the vast majority of cases the name is NOT used to look up
-// a variable's value.  Variable lookup is usually via direct index, by-passing the name altogether.
+// is manually split into two equal-length arrays.  That's because variable names take up the most space,
+// with [`Cow<str>`][Cow] being four words long, but in the vast majority of cases the name is NOT used to
+// look up a variable.  Variable lookup is usually via direct indexing, by-passing the name altogether.
 //
 // Since [`Dynamic`] is reasonably small, packing it tightly improves cache locality when variables are accessed.
-// The variable type is packed separately into another array because it is even smaller.
-#[derive(Debug)]
+//
+// The alias is `Box`'ed because it occurs infrequently.
+#[derive(Debug, Clone, Hash)]
 pub struct Scope<'a> {
     /// Current value of the entry.
     values: Vec<Dynamic>,
-    /// (Name, aliases) of the entry. The list of aliases is Boxed because it occurs rarely.
+    /// (Name, aliases) of the entry.
     names: Vec<(Cow<'a, str>, Box<StaticVec<ImmutableString>>)>,
 }
 
@@ -357,8 +358,35 @@ impl<'a> Scope<'a> {
         self
     }
     /// Get a mutable reference to an entry in the [`Scope`].
+    ///
+    /// If the entry by the specified name is not found, of if it is read-only,
+    /// [`None`] is returned.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use rhai::Scope;
+    ///
+    /// let mut my_scope = Scope::new();
+    ///
+    /// my_scope.push("x", 42_i64);
+    /// assert_eq!(my_scope.get_value::<i64>("x").unwrap(), 42);
+    ///
+    /// let ptr = my_scope.get_mut("x").unwrap();
+    /// *ptr = 123_i64.into();
+    ///
+    /// assert_eq!(my_scope.get_value::<i64>("x").unwrap(), 123);
+    /// ```
+    pub fn get_mut(&mut self, name: &str) -> Option<&mut Dynamic> {
+        self.get_index(name)
+            .and_then(move |(index, access)| match access {
+                AccessMode::ReadWrite => Some(self.get_mut_by_index(index)),
+                AccessMode::ReadOnly => None,
+            })
+    }
+    /// Get a mutable reference to an entry in the [`Scope`] based on the index.
     #[inline(always)]
-    pub(crate) fn get_mut(&mut self, index: usize) -> &mut Dynamic {
+    pub(crate) fn get_mut_by_index(&mut self, index: usize) -> &mut Dynamic {
         self.values.get_mut(index).expect("invalid index in Scope")
     }
     /// Update the access type of an entry in the [`Scope`].
diff --git a/src/serde_impl/metadata.rs b/src/serde_impl/metadata.rs
index b8bb010b..80a6cd01 100644
--- a/src/serde_impl/metadata.rs
+++ b/src/serde_impl/metadata.rs
@@ -90,7 +90,7 @@ struct FnMetadata {
     pub return_type: Option<String>,
     pub signature: String,
     #[serde(default, skip_serializing_if = "Option::is_none")]
-    pub doc_comments: Option<Vec<String>>,
+    pub doc_comments: Vec<String>,
 }
 
 impl PartialOrd for FnMetadata {
@@ -152,9 +152,9 @@ impl From<&crate::module::FuncInfo> for FnMetadata {
             },
             signature: info.gen_signature(),
             doc_comments: if info.func.is_script() {
-                Some(info.func.get_fn_def().comments.clone())
+                info.func.get_fn_def().comments.clone()
             } else {
-                None
+                Default::default()
             },
         }
     }
diff --git a/src/syntax.rs b/src/syntax.rs
index 4ceec8f9..8ce578fa 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -121,20 +121,26 @@ impl Engine {
                 continue;
             }
 
+            let token = Token::lookup_from_syntax(s);
+
             let seg = match s {
                 // Markers not in first position
                 MARKER_IDENT | MARKER_EXPR | MARKER_BLOCK if !segments.is_empty() => s.into(),
                 // Standard or reserved keyword/symbol not in first position
-                s if !segments.is_empty() && Token::lookup_from_syntax(s).is_some() => {
-                    // Make it a custom keyword/symbol
-                    if !self.custom_keywords.contains_key(s) {
+                s if !segments.is_empty() && token.is_some() => {
+                    // Make it a custom keyword/symbol if it is disabled or reserved
+                    if (self.disabled_symbols.contains(s)
+                        || matches!(token, Some(Token::Reserved(_))))
+                        && !self.custom_keywords.contains_key(s)
+                    {
                         self.custom_keywords.insert(s.into(), None);
                     }
                     s.into()
                 }
                 // Standard keyword in first position
                 s if segments.is_empty()
-                    && Token::lookup_from_syntax(s)
+                    && token
+                        .as_ref()
                         .map(|v| v.is_keyword() || v.is_reserved())
                         .unwrap_or(false) =>
                 {
@@ -151,7 +157,11 @@ impl Engine {
                 }
                 // Identifier in first position
                 s if segments.is_empty() && is_valid_identifier(s.chars()) => {
-                    if !self.custom_keywords.contains_key(s) {
+                    // Make it a custom keyword/symbol if it is disabled or reserved
+                    if (self.disabled_symbols.contains(s)
+                        || matches!(token, Some(Token::Reserved(_))))
+                        && !self.custom_keywords.contains_key(s)
+                    {
                         self.custom_keywords.insert(s.into(), None);
                     }
                     s.into()
@@ -208,7 +218,7 @@ impl Engine {
     /// * `parse` is the parsing function.
     /// * `func` is the implementation function.
     ///
-    /// All custom keywords must be manually registered via [`register_custom_operator`][Engine::register_custom_operator].
+    /// All custom keywords must be manually registered via [`Engine::register_custom_operator`].
     /// Otherwise, custom keywords won't be recognized.
     pub fn register_custom_syntax_raw(
         &mut self,
diff --git a/src/token.rs b/src/token.rs
index ee3febb0..1d3fbead 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -532,10 +532,10 @@ impl Token {
             #[cfg(feature = "no_module")]
             "import" | "export" | "as" => Reserved(syntax.into()),
 
-            "===" | "!==" | "->" | "<-" | ":=" | "::<" | "(*" | "*)" | "#" | "public" | "new"
-            | "use" | "module" | "package" | "var" | "static" | "begin" | "end" | "shared"
-            | "with" | "each" | "then" | "goto" | "unless" | "exit" | "match" | "case"
-            | "default" | "void" | "null" | "nil" | "spawn" | "thread" | "go" | "sync"
+            "===" | "!==" | "->" | "<-" | ":=" | "**" | "::<" | "(*" | "*)" | "#" | "public"
+            | "new" | "use" | "module" | "package" | "var" | "static" | "begin" | "end"
+            | "shared" | "with" | "each" | "then" | "goto" | "unless" | "exit" | "match"
+            | "case" | "default" | "void" | "null" | "nil" | "spawn" | "thread" | "go" | "sync"
             | "async" | "await" | "yield" => Reserved(syntax.into()),
 
             KEYWORD_PRINT | KEYWORD_DEBUG | KEYWORD_TYPE_OF | KEYWORD_EVAL | KEYWORD_FN_PTR
@@ -1742,27 +1742,21 @@ impl<'a> Iterator for TokenIterator<'a, '_> {
             Some((Token::Identifier(s), pos)) if self.engine.custom_keywords.contains_key(&s) => {
                 Some((Token::Custom(s), pos))
             }
-            // Custom standard keyword - must be disabled
-            Some((token, pos)) if token.is_keyword() && self.engine.custom_keywords.contains_key(token.syntax().as_ref()) => {
+            // Custom standard keyword/symbol - must be disabled
+            Some((token, pos)) if self.engine.custom_keywords.contains_key(token.syntax().as_ref()) => {
                 if self.engine.disabled_symbols.contains(token.syntax().as_ref()) {
-                    // Disabled standard keyword
+                    // Disabled standard keyword/symbol
                     Some((Token::Custom(token.syntax().into()), pos))
                 } else {
                     // Active standard keyword - should never be a custom keyword!
-                    unreachable!()
+                    unreachable!("{:?}", token)
                 }
             }
-            // Disabled operator
-            Some((token, pos)) if token.is_operator() && self.engine.disabled_symbols.contains(token.syntax().as_ref()) => {
-                Some((
-                    Token::LexError(LexError::UnexpectedInput(token.syntax().into())),
-                    pos,
-                ))
-            }
-            // Disabled standard keyword
-            Some((token, pos)) if token.is_keyword() && self.engine.disabled_symbols.contains(token.syntax().as_ref()) => {
+            // Disabled symbol
+            Some((token, pos)) if self.engine.disabled_symbols.contains(token.syntax().as_ref()) => {
                 Some((Token::Reserved(token.syntax().into()), pos))
             }
+            // Normal symbol
             r => r,
         };
 
diff --git a/src/utils.rs b/src/utils.rs
index 8513dd6d..52dfda99 100644
--- a/src/utils.rs
+++ b/src/utils.rs
@@ -9,30 +9,34 @@ use crate::stdlib::{
     fmt,
     hash::{BuildHasher, Hash, Hasher},
     iter::{empty, FromIterator},
+    num::NonZeroU64,
     ops::{Add, AddAssign, Deref},
     str::FromStr,
     string::{String, ToString},
 };
 use crate::Shared;
 
-/// A hasher that only takes one single [`u64`] and returns it as a hash key.
+/// A hasher that only takes one single [`NonZeroU64`] and returns it as a hash key.
 ///
 /// # Panics
 ///
-/// Panics when hashing any data type other than a [`u64`].
-#[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash, Default)]
-pub struct StraightHasher(u64);
+/// Panics when hashing any data type other than a [`NonZeroU64`].
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct StraightHasher(NonZeroU64);
 
 impl Hasher for StraightHasher {
     #[inline(always)]
     fn finish(&self) -> u64 {
-        self.0
+        self.0.get()
     }
     #[inline(always)]
     fn write(&mut self, bytes: &[u8]) {
         let mut key = [0_u8; 8];
         key.copy_from_slice(&bytes[..8]); // Panics if fewer than 8 bytes
-        self.0 = u64::from_le_bytes(key);
+
+        // HACK - If it so happens to hash directly to zero (OMG!) then change it to 42...
+        self.0 = NonZeroU64::new(u64::from_le_bytes(key))
+            .unwrap_or_else(|| NonZeroU64::new(42).unwrap());
     }
 }
 
@@ -45,11 +49,22 @@ impl BuildHasher for StraightHasherBuilder {
 
     #[inline(always)]
     fn build_hasher(&self) -> Self::Hasher {
-        Default::default()
+        StraightHasher(NonZeroU64::new(42).unwrap())
     }
 }
 
-/// _(INTERNALS)_ Calculate a [`u64`] hash key from a namespace-qualified function name and parameter types.
+/// Create an instance of the default hasher.
+pub fn get_hasher() -> impl Hasher {
+    #[cfg(feature = "no_std")]
+    let s: ahash::AHasher = Default::default();
+    #[cfg(not(feature = "no_std"))]
+    let s = crate::stdlib::collections::hash_map::DefaultHasher::new();
+
+    s
+}
+
+/// _(INTERNALS)_ Calculate a [`NonZeroU64`] hash key from a namespace-qualified function name and
+/// parameter types.
 /// Exported under the `internals` feature only.
 ///
 /// Module names are passed in via `&str` references from an iterator.
@@ -63,11 +78,11 @@ pub fn calc_native_fn_hash<'a>(
     modules: impl Iterator<Item = &'a str>,
     fn_name: &str,
     params: impl Iterator<Item = TypeId>,
-) -> u64 {
+) -> Option<NonZeroU64> {
     calc_fn_hash(modules, fn_name, None, params)
 }
 
-/// _(INTERNALS)_ Calculate a [`u64`] hash key from a namespace-qualified function name
+/// _(INTERNALS)_ Calculate a [`NonZeroU64`] hash key from a namespace-qualified function name
 /// and the number of parameters, but no parameter types.
 /// Exported under the `internals` feature only.
 ///
@@ -82,21 +97,11 @@ pub fn calc_script_fn_hash<'a>(
     modules: impl Iterator<Item = &'a str>,
     fn_name: &str,
     num: usize,
-) -> u64 {
+) -> Option<NonZeroU64> {
     calc_fn_hash(modules, fn_name, Some(num), empty())
 }
 
-/// Create an instance of the default hasher.
-pub fn get_hasher() -> impl Hasher {
-    #[cfg(feature = "no_std")]
-    let s: ahash::AHasher = Default::default();
-    #[cfg(not(feature = "no_std"))]
-    let s = crate::stdlib::collections::hash_map::DefaultHasher::new();
-
-    s
-}
-
-/// Calculate a [`u64`] hash key from a namespace-qualified function name and parameter types.
+/// Calculate a [`NonZeroU64`] hash key from a namespace-qualified function name and parameter types.
 ///
 /// Module names are passed in via `&str` references from an iterator.
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
@@ -104,12 +109,13 @@ pub fn get_hasher() -> impl Hasher {
 /// # Note
 ///
 /// The first module name is skipped.  Hashing starts from the _second_ module in the chain.
+#[inline(always)]
 fn calc_fn_hash<'a>(
     mut modules: impl Iterator<Item = &'a str>,
     fn_name: &str,
     num: Option<usize>,
     params: impl Iterator<Item = TypeId>,
-) -> u64 {
+) -> Option<NonZeroU64> {
     let s = &mut get_hasher();
 
     // Hash a boolean indicating whether the hash is namespace-qualified.
@@ -122,7 +128,15 @@ fn calc_fn_hash<'a>(
     } else {
         params.for_each(|t| t.hash(s));
     }
-    s.finish()
+    // HACK - If it so happens to hash directly to zero (OMG!) then change it to 42...
+    NonZeroU64::new(s.finish()).or_else(|| NonZeroU64::new(42))
+}
+
+/// Combine two [`NonZeroU64`] hashes by taking the XOR of them.
+#[inline(always)]
+pub(crate) fn combine_hashes(a: NonZeroU64, b: NonZeroU64) -> NonZeroU64 {
+    // HACK - If it so happens to hash directly to zero (OMG!) then change it to 42...
+    NonZeroU64::new(a.get() ^ b.get()).unwrap_or_else(|| NonZeroU64::new(42).unwrap())
 }
 
 /// The system immutable string type.
diff --git a/tests/arrays.rs b/tests/arrays.rs
index 3c1dbff2..78cf30b6 100644
--- a/tests/arrays.rs
+++ b/tests/arrays.rs
@@ -32,7 +32,7 @@ fn test_arrays() -> Result<(), Box<EvalAltResult>> {
                 x.append(y);
 
                 x.len + r
-           "
+            "
         )?,
         14
     );
@@ -42,7 +42,7 @@ fn test_arrays() -> Result<(), Box<EvalAltResult>> {
                 let x = [1, 2, 3];
                 x += [4, 5];
                 len(x)
-           "
+            "
         )?,
         5
     );
@@ -53,7 +53,7 @@ fn test_arrays() -> Result<(), Box<EvalAltResult>> {
                     let x = [1, 2, 3];
                     let y = [4, 5];
                     x + y
-           "
+                "
             )?
             .len(),
         5
diff --git a/tests/call_fn.rs b/tests/call_fn.rs
index 7b959472..c95e2853 100644
--- a/tests/call_fn.rs
+++ b/tests/call_fn.rs
@@ -82,7 +82,7 @@ fn test_call_fn_private() -> Result<(), Box<EvalAltResult>> {
     let ast = engine.compile("private fn add(x, n, ) { x + n }")?;
 
     assert!(matches!(
-        *engine.call_fn::<_, INT>(&mut scope, &ast, "add", (40 as INT, 2 as INT))
+        *(engine.call_fn(&mut scope, &ast, "add", (40 as INT, 2 as INT)) as Result<INT, Box<EvalAltResult>>)
             .expect_err("should error"),
         EvalAltResult::ErrorFunctionNotFound(fn_name, _) if fn_name == "add"
     ));
diff --git a/tests/closures.rs b/tests/closures.rs
index 7c74e9bd..4a0cd74b 100644
--- a/tests/closures.rs
+++ b/tests/closures.rs
@@ -54,6 +54,17 @@ fn test_closures() -> Result<(), Box<EvalAltResult>> {
         ParseErrorType::BadInput(_)
     ));
 
+    assert_eq!(
+        engine.eval::<INT>(
+            r"
+                let foo = #{ x: 42 };
+                let f = || { this.x };
+                foo.call(f)                
+            ",
+        )?,
+        42
+    );
+
     assert_eq!(
         engine.eval::<INT>(
             r#"
@@ -239,7 +250,7 @@ fn test_closures_shared_obj() -> Result<(), Box<EvalAltResult>> {
     let f = move |p1: TestStruct, p2: TestStruct| -> Result<(), Box<EvalAltResult>> {
         let action_ptr = res["action"].clone().cast::<FnPtr>();
         let name = action_ptr.fn_name();
-        engine.call_fn::<_, ()>(&mut Scope::new(), &ast, name, (p1, p2))
+        engine.call_fn(&mut Scope::new(), &ast, name, (p1, p2))
     };
 
     // Test closure
diff --git a/tests/modules.rs b/tests/modules.rs
index b07d4d5d..26c4af8c 100644
--- a/tests/modules.rs
+++ b/tests/modules.rs
@@ -101,7 +101,7 @@ fn test_module_resolver() -> Result<(), Box<EvalAltResult>> {
     resolver.insert("hello", module);
 
     let mut engine = Engine::new();
-    engine.set_module_resolver(Some(resolver));
+    engine.set_module_resolver(resolver);
 
     assert_eq!(
         engine.eval::<INT>(
@@ -295,13 +295,13 @@ fn test_module_from_ast() -> Result<(), Box<EvalAltResult>> {
         "#,
     )?;
 
-    engine.set_module_resolver(Some(resolver1));
+    engine.set_module_resolver(resolver1);
 
     let module = Module::eval_ast_as_new(Scope::new(), &ast, &engine)?;
 
     let mut resolver2 = StaticModuleResolver::new();
     resolver2.insert("testing", module);
-    engine.set_module_resolver(Some(resolver2));
+    engine.set_module_resolver(resolver2);
 
     assert_eq!(
         engine.eval::<INT>(r#"import "testing" as ttt; ttt::abc"#)?,
@@ -384,7 +384,7 @@ fn test_module_str() -> Result<(), Box<EvalAltResult>> {
 
     let mut static_modules = rhai::module_resolvers::StaticModuleResolver::new();
     static_modules.insert("test", module);
-    engine.set_module_resolver(Some(static_modules));
+    engine.set_module_resolver(static_modules);
 
     assert_eq!(
         engine.eval::<INT>(r#"import "test" as test; test::test("test");"#)?,
@@ -418,7 +418,7 @@ fn test_module_ast_namespace() -> Result<(), Box<EvalAltResult>> {
 
     let mut resolver = StaticModuleResolver::new();
     resolver.insert("testing", module);
-    engine.set_module_resolver(Some(resolver));
+    engine.set_module_resolver(resolver);
 
     assert_eq!(
         engine.eval::<INT>(r#"import "testing" as t; t::foo(41)"#)?,
@@ -466,7 +466,7 @@ fn test_module_ast_namespace2() -> Result<(), Box<EvalAltResult>> {
     let module = Module::eval_ast_as_new(Scope::new(), &module_ast, &engine)?;
     let mut static_modules = rhai::module_resolvers::StaticModuleResolver::new();
     static_modules.insert("test_module", module);
-    engine.set_module_resolver(Some(static_modules));
+    engine.set_module_resolver(static_modules);
 
     engine.consume(SCRIPT)?;
 
diff --git a/tests/tokens.rs b/tests/tokens.rs
index 0070c23d..71158313 100644
--- a/tests/tokens.rs
+++ b/tests/tokens.rs
@@ -21,12 +21,17 @@ fn test_tokens_disabled() {
             .compile("let x = 40 + 2; x += 1;")
             .expect_err("should error")
             .0,
-        ParseErrorType::BadInput(LexError::UnexpectedInput("+=".to_string()))
+        ParseErrorType::UnknownOperator("+=".to_string())
     );
+
+    assert!(matches!(
+        *engine.compile("let x = += 0;").expect_err("should error").0,
+        ParseErrorType::BadInput(LexError::UnexpectedInput(err)) if err == "+="
+    ));
 }
 
 #[test]
-fn test_tokens_custom_operator() -> Result<(), Box<EvalAltResult>> {
+fn test_tokens_custom_operator_identifiers() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
 
     // Register a custom operator called `foo` and give it
@@ -55,6 +60,29 @@ fn test_tokens_custom_operator() -> Result<(), Box<EvalAltResult>> {
     Ok(())
 }
 
+#[test]
+fn test_tokens_custom_operator_symbol() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    // Register a custom operator `#` and give it
+    // a precedence of 160 (i.e. between +|- and *|/).
+    engine.register_custom_operator("#", 160).unwrap();
+
+    // Register a binary function named `#`
+    engine.register_fn("#", |x: INT, y: INT| (x * y) - (x + y));
+
+    assert_eq!(engine.eval_expression::<INT>("1 + 2 * 3 # 4 - 5 / 6")?, 15);
+
+    // Register a custom operator named `=>`
+    assert!(engine.register_custom_operator("=>", 160).is_err());
+    engine.disable_symbol("=>");
+    engine.register_custom_operator("=>", 160).unwrap();
+    engine.register_fn("=>", |x: INT, y: INT| (x * y) - (x + y));
+    assert_eq!(engine.eval_expression::<INT>("1 + 2 * 3 => 4 - 5 / 6")?, 15);
+
+    Ok(())
+}
+
 #[test]
 fn test_tokens_unicode_xid_ident() -> Result<(), Box<EvalAltResult>> {
     let engine = Engine::new();