diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4f785f8c..1772d4f1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ Bug fixes
 * `import` statements inside `eval` no longer cause errors in subsequent code.
 * Functions marked `global` in `import`ed modules with no alias names now work properly.
 * Incorrect loop optimizations that are too aggressive (e.g. unrolling a `do { ... } until true` with a `break` statement inside) and cause crashes are removed.
+* `Dynamic::is` now works properly for shared values.
 
 Breaking changes
 ----------------
@@ -25,6 +26,11 @@ Breaking changes
 New features
 ------------
 
+### `Dynamic` detection API
+
+* New methods are added to `Dynamic` in the form of `is_XXX()` where `XXX` is a type (e.g. `is_int`, `is_unit`, `is_bool`, `is_array`).
+* This new API is to make it easier to detect the data type, instead of having to call `is::<XXX>()`.
+
 ### Loop expressions
 
 * Loops (such as `loop`, `do`, `while` and `for`) can now act as _expressions_, with the `break` statement returning an optional value.
@@ -33,13 +39,13 @@ New features
 
 ### Static hashing
 
-* It is now possible to specify a fixed _seed_ for use with the `ahash` hasher, via a static function `rhai::config::hashing::set_ahash_seed` or an environment variable, in order to force static (i.e. deterministic) hashes for function signatures.
+* It is now possible to specify a fixed _seed_ for use with the `ahash` hasher, via a static function `rhai::config::hashing::set_ahash_seed` or an environment variable (`RHAI_AHASH_SEED`), in order to force static (i.e. deterministic) hashes for function signatures.
 * This is necessary when using Rhai across shared-library boundaries.
 * A build script is used to extract the environment variable (`RHAI_AHASH_SEED`, if any) and splice it into the source code before compilation.
 
-### No Timestamps
+### `no_time` for no timestamps
 
-* A new feature, `no_time`, is added to disable support timestamps.
+* A new feature, `no_time`, is added to disable support for timestamps.
 * This may be necessary when building for architectures without time support, such as raw WASM.
 
 ### Serializable `Scope`
diff --git a/Cargo.toml b/Cargo.toml
index 4db19d3b..0efb84c7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,8 +19,7 @@ categories = ["no-std", "embedded", "wasm", "parser-implementations"]
 
 [dependencies]
 smallvec = { version = "1.7", default-features = false, features = ["union", "const_new", "const_generics"] }
-# 0.8.1 pulls in `getrandom/js` which breaks no-std
-ahash = { version = "=0.8.0", default-features = false, features = ["compile-time-rng"] }
+ahash = { version = "0.8.2", default-features = false, features = ["compile-time-rng"] }
 num-traits = { version = "0.2", default-features = false }
 bitflags = { version = "1", default-features = false }
 smartstring = { version = "1", default-features = false }
@@ -28,7 +27,7 @@ rhai_codegen = { version = "1.4.1", path = "codegen", default-features = false }
 
 no-std-compat = { version = "0.4", default-features = false, features = ["alloc"], optional = true }
 libm = { version = "0.2", default-features = false, optional = true }
-hashbrown = { version = "0.12", optional = true }
+hashbrown = { version = "0.13", optional = true }
 core-error = { version = "0.0", default-features = false, features = ["alloc"], optional = true }
 serde = { version = "1.0", default-features = false, features = ["derive", "alloc"], optional = true }
 serde_json = { version = "1.0", default-features = false, features = ["alloc"], optional = true }
diff --git a/src/api/build_type.rs b/src/api/build_type.rs
index 9ce59ba4..2ebab673 100644
--- a/src/api/build_type.rs
+++ b/src/api/build_type.rs
@@ -99,6 +99,10 @@ impl Engine {
 ///
 /// To define a pretty-print name, call [`with_name`][`TypeBuilder::with_name`],
 /// to use [`Engine::register_type_with_name`] instead.
+///
+/// # WARNING - Volatile Type
+///
+/// This type is volatile and may change in the future.
 #[deprecated = "This type is NOT deprecated, but it is considered volatile and may change in the future."]
 pub struct TypeBuilder<'a, T: Variant + Clone> {
     engine: &'a mut Engine,
diff --git a/src/api/call_fn.rs b/src/api/call_fn.rs
index 1a78cae1..335be57d 100644
--- a/src/api/call_fn.rs
+++ b/src/api/call_fn.rs
@@ -3,9 +3,10 @@
 
 use crate::eval::{Caches, GlobalRuntimeState};
 use crate::types::dynamic::Variant;
+use crate::types::RestoreOnDrop;
 use crate::{
-    reify, Dynamic, Engine, FuncArgs, Position, RhaiResult, RhaiResultOf, Scope, SharedModule,
-    StaticVec, AST, ERR,
+    reify, Dynamic, Engine, FuncArgs, Position, RhaiResult, RhaiResultOf, Scope, StaticVec, AST,
+    ERR,
 };
 use std::any::{type_name, TypeId};
 #[cfg(feature = "no_std")]
@@ -248,31 +249,28 @@ impl Engine {
         arg_values: &mut [Dynamic],
     ) -> RhaiResult {
         let statements = ast.statements();
-        let lib = &[AsRef::<SharedModule>::as_ref(ast).clone()];
+
+        let orig_lib_len = global.lib.len();
+
+        #[cfg(not(feature = "no_function"))]
+        global.lib.push(ast.shared_lib().clone());
 
         let mut no_this_ptr = Dynamic::NULL;
         let this_ptr = this_ptr.unwrap_or(&mut no_this_ptr);
 
-        let orig_scope_len = scope.len();
-
         #[cfg(not(feature = "no_module"))]
         let orig_embedded_module_resolver = std::mem::replace(
             &mut global.embedded_module_resolver,
             ast.resolver().cloned(),
         );
-        #[cfg(not(feature = "no_module"))]
-        let global = &mut *crate::types::RestoreOnDrop::lock(global, move |g| {
-            g.embedded_module_resolver = orig_embedded_module_resolver
-        });
 
         let result = if eval_ast && !statements.is_empty() {
-            let r = self.eval_global_statements(global, caches, lib, scope, statements);
+            let orig_scope_len = scope.len();
+            let scope = &mut *RestoreOnDrop::lock_if(rewind_scope, scope, move |s| {
+                s.rewind(orig_scope_len);
+            });
 
-            if rewind_scope {
-                scope.rewind(orig_scope_len);
-            }
-
-            r
+            self.eval_global_statements(global, caches, scope, statements)
         } else {
             Ok(Dynamic::UNIT)
         }
@@ -287,7 +285,6 @@ impl Engine {
                 self.call_script_fn(
                     global,
                     caches,
-                    lib,
                     scope,
                     this_ptr,
                     fn_def,
@@ -298,15 +295,21 @@ impl Engine {
             } else {
                 Err(ERR::ErrorFunctionNotFound(name.into(), Position::NONE).into())
             }
-        })?;
+        });
 
         #[cfg(feature = "debugging")]
         if self.debugger.is_some() {
             global.debugger.status = crate::eval::DebuggerStatus::Terminate;
             let node = &crate::ast::Stmt::Noop(Position::NONE);
-            self.run_debugger(global, caches, lib, scope, this_ptr, node)?;
+            self.run_debugger(global, caches, scope, this_ptr, node)?;
         }
 
-        Ok(result)
+        #[cfg(not(feature = "no_module"))]
+        {
+            global.embedded_module_resolver = orig_embedded_module_resolver;
+        }
+        global.lib.truncate(orig_lib_len);
+
+        result
     }
 }
diff --git a/src/api/custom_syntax.rs b/src/api/custom_syntax.rs
index a12ea593..b884cc24 100644
--- a/src/api/custom_syntax.rs
+++ b/src/api/custom_syntax.rs
@@ -89,6 +89,7 @@ impl Expression<'_> {
     /// # WARNING - Low Level API
     ///
     /// This function is _extremely_ low level.  It evaluates an expression from an [`AST`][crate::AST].
+    #[deprecated = "This API is NOT deprecated, but it is considered volatile and may change in the future."]
     #[inline(always)]
     pub fn eval_with_context_raw(
         &self,
diff --git a/src/api/eval.rs b/src/api/eval.rs
index 10cf9040..2c5ffb70 100644
--- a/src/api/eval.rs
+++ b/src/api/eval.rs
@@ -6,9 +6,9 @@ use crate::types::dynamic::Variant;
 use crate::{
     Dynamic, Engine, OptimizationLevel, Position, RhaiResult, RhaiResultOf, Scope, AST, ERR,
 };
-use std::any::type_name;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
+use std::{any::type_name, mem};
 
 impl Engine {
     /// Evaluate a string as a script, returning the result value or an error.
@@ -190,19 +190,6 @@ impl Engine {
 
         let result = self.eval_ast_with_scope_raw(global, caches, scope, ast)?;
 
-        #[cfg(feature = "debugging")]
-        if self.debugger.is_some() {
-            global.debugger.status = crate::eval::DebuggerStatus::Terminate;
-            let lib = &[
-                #[cfg(not(feature = "no_function"))]
-                AsRef::<crate::SharedModule>::as_ref(ast).clone(),
-            ];
-            let mut this = Dynamic::NULL;
-            let node = &crate::ast::Stmt::Noop(Position::NONE);
-
-            self.run_debugger(global, caches, lib, scope, &mut this, node)?;
-        }
-
         let typ = self.map_type_name(result.type_name());
 
         result.try_cast::<T>().ok_or_else(|| {
@@ -216,21 +203,22 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-
         scope: &mut Scope,
         ast: &'a AST,
     ) -> RhaiResult {
-        global.source = ast.source_raw().cloned();
+        let orig_source = mem::replace(&mut global.source, ast.source_raw().cloned());
+
+        #[cfg(not(feature = "no_function"))]
+        let orig_lib_len = global.lib.len();
+
+        #[cfg(not(feature = "no_function"))]
+        global.lib.push(ast.shared_lib().clone());
 
         #[cfg(not(feature = "no_module"))]
-        let orig_embedded_module_resolver = std::mem::replace(
+        let orig_embedded_module_resolver = mem::replace(
             &mut global.embedded_module_resolver,
             ast.resolver().cloned(),
         );
-        #[cfg(not(feature = "no_module"))]
-        let global = &mut *crate::types::RestoreOnDrop::lock(global, move |g| {
-            g.embedded_module_resolver = orig_embedded_module_resolver
-        });
 
         let statements = ast.statements();
 
@@ -238,12 +226,28 @@ impl Engine {
             return Ok(Dynamic::UNIT);
         }
 
-        let lib = &[
-            #[cfg(not(feature = "no_function"))]
-            AsRef::<crate::SharedModule>::as_ref(ast).clone(),
-        ];
+        let result = self.eval_global_statements(global, caches, scope, statements);
 
-        self.eval_global_statements(global, caches, lib, scope, statements)
+        #[cfg(feature = "debugging")]
+        if self.debugger.is_some() {
+            global.debugger.status = crate::eval::DebuggerStatus::Terminate;
+            let mut this = Dynamic::NULL;
+            let node = &crate::ast::Stmt::Noop(Position::NONE);
+
+            self.run_debugger(global, caches, scope, &mut this, node)?;
+        }
+
+        #[cfg(not(feature = "no_module"))]
+        {
+            global.embedded_module_resolver = orig_embedded_module_resolver;
+        }
+
+        #[cfg(not(feature = "no_function"))]
+        global.lib.truncate(orig_lib_len);
+
+        global.source = orig_source;
+
+        result
     }
     /// _(internals)_ Evaluate a list of statements with no `this` pointer.
     /// Exported under the `internals` feature only.
@@ -259,12 +263,10 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[crate::SharedModule],
-
         scope: &mut Scope,
         statements: &[crate::ast::Stmt],
     ) -> RhaiResult {
-        self.eval_global_statements(global, caches, lib, scope, statements)
+        self.eval_global_statements(global, caches, scope, statements)
     }
 }
 
diff --git a/src/api/json.rs b/src/api/json.rs
index c22d682c..4365a4a8 100644
--- a/src/api/json.rs
+++ b/src/api/json.rs
@@ -166,7 +166,7 @@ pub fn format_map_as_json(map: &Map) -> String {
 
         if let Some(val) = value.read_lock::<Map>() {
             result.push_str(&format_map_as_json(&*val));
-        } else if value.is::<()>() {
+        } else if value.is_unit() {
             result.push_str("null");
         } else {
             write!(result, "{:?}", value).unwrap();
diff --git a/src/api/optimize.rs b/src/api/optimize.rs
index f790a803..0baccba6 100644
--- a/src/api/optimize.rs
+++ b/src/api/optimize.rs
@@ -52,7 +52,7 @@ impl Engine {
         let mut ast = ast;
 
         #[cfg(not(feature = "no_function"))]
-        let lib = ast
+        let functions = ast
             .shared_lib()
             .iter_fn()
             .filter(|f| f.func.is_script())
@@ -64,7 +64,7 @@ impl Engine {
             scope,
             ast.take_statements(),
             #[cfg(not(feature = "no_function"))]
-            lib,
+            functions,
             optimization_level,
         );
 
diff --git a/src/api/run.rs b/src/api/run.rs
index 551b5e98..a83a3a73 100644
--- a/src/api/run.rs
+++ b/src/api/run.rs
@@ -2,7 +2,7 @@
 
 use crate::eval::{Caches, GlobalRuntimeState};
 use crate::parser::ParseState;
-use crate::{Engine, RhaiResultOf, Scope, SharedModule, AST};
+use crate::{Engine, RhaiResultOf, Scope, AST};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
@@ -115,6 +115,9 @@ impl Engine {
         let global = &mut GlobalRuntimeState::new(self);
         global.source = ast.source_raw().cloned();
 
+        #[cfg(not(feature = "no_function"))]
+        global.lib.push(ast.shared_lib().clone());
+
         #[cfg(not(feature = "no_module"))]
         {
             global.embedded_module_resolver = ast.resolver().cloned();
@@ -122,28 +125,15 @@ impl Engine {
 
         let statements = ast.statements();
         if !statements.is_empty() {
-            let lib: &[SharedModule] = &[
-                #[cfg(not(feature = "no_function"))]
-                AsRef::<SharedModule>::as_ref(ast).clone(),
-            ];
-            let lib = if lib.first().map_or(true, |m| m.is_empty()) {
-                &[][..]
-            } else {
-                &lib
-            };
-            self.eval_global_statements(global, caches, lib, scope, statements)?;
+            self.eval_global_statements(global, caches, scope, statements)?;
         }
 
         #[cfg(feature = "debugging")]
         if self.debugger.is_some() {
             global.debugger.status = crate::eval::DebuggerStatus::Terminate;
-            let lib = &[
-                #[cfg(not(feature = "no_function"))]
-                AsRef::<crate::SharedModule>::as_ref(ast).clone(),
-            ];
             let mut this = crate::Dynamic::NULL;
             let node = &crate::ast::Stmt::Noop(crate::Position::NONE);
-            self.run_debugger(global, caches, lib, scope, &mut this, node)?;
+            self.run_debugger(global, caches, scope, &mut this, node)?;
         }
 
         Ok(())
diff --git a/src/ast/ast.rs b/src/ast/ast.rs
index c1cfbaed..71b07669 100644
--- a/src/ast/ast.rs
+++ b/src/ast/ast.rs
@@ -57,12 +57,11 @@ impl fmt::Debug for AST {
         fp.field("body", &self.body.as_slice());
 
         #[cfg(not(feature = "no_function"))]
-        if !self.lib.is_empty() {
-            for (.., fn_def) in self.lib.iter_script_fn() {
-                let sig = fn_def.to_string();
-                fp.field(&sig, &fn_def.body.as_slice());
-            }
+        for (.., fn_def) in self.lib.iter_script_fn() {
+            let sig = fn_def.to_string();
+            fp.field(&sig, &fn_def.body.as_slice());
         }
+
         fp.finish()
     }
 }
@@ -739,7 +738,7 @@ impl AST {
         &mut self,
         filter: impl Fn(FnNamespace, FnAccess, &str, usize) -> bool,
     ) -> &mut Self {
-        if !self.lib.is_empty() {
+        if self.has_functions() {
             crate::func::shared_make_mut(&mut self.lib).retain_script_functions(filter);
         }
         self
diff --git a/src/ast/expr.rs b/src/ast/expr.rs
index 163fdbc9..1d39171d 100644
--- a/src/ast/expr.rs
+++ b/src/ast/expr.rs
@@ -20,16 +20,6 @@ use std::{
     num::{NonZeroU64, NonZeroU8, NonZeroUsize},
 };
 
-#[cfg(not(feature = "no_float"))]
-use std::{
-    hash::Hasher,
-    ops::{Deref, DerefMut},
-    str::FromStr,
-};
-
-#[cfg(not(feature = "no_float"))]
-use num_traits::float::FloatCore as Float;
-
 /// _(internals)_ A binary expression.
 /// Exported under the `internals` feature only.
 #[derive(Debug, Clone, Hash)]
@@ -273,120 +263,6 @@ impl FnCallExpr {
     }
 }
 
-/// A type that wraps a floating-point number and implements [`Hash`].
-///
-/// Not available under `no_float`.
-#[cfg(not(feature = "no_float"))]
-#[derive(Clone, Copy, PartialEq, PartialOrd)]
-pub struct FloatWrapper<F>(F);
-
-#[cfg(not(feature = "no_float"))]
-impl Hash for FloatWrapper<crate::FLOAT> {
-    #[inline]
-    fn hash<H: Hasher>(&self, state: &mut H) {
-        self.0.to_ne_bytes().hash(state);
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> AsRef<F> for FloatWrapper<F> {
-    #[inline(always)]
-    #[must_use]
-    fn as_ref(&self) -> &F {
-        &self.0
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> AsMut<F> for FloatWrapper<F> {
-    #[inline(always)]
-    #[must_use]
-    fn as_mut(&mut self) -> &mut F {
-        &mut self.0
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> Deref for FloatWrapper<F> {
-    type Target = F;
-
-    #[inline(always)]
-    fn deref(&self) -> &Self::Target {
-        &self.0
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> DerefMut for FloatWrapper<F> {
-    #[inline(always)]
-    fn deref_mut(&mut self) -> &mut Self::Target {
-        &mut self.0
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float + fmt::Debug> fmt::Debug for FloatWrapper<F> {
-    #[cold]
-    #[inline(never)]
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        fmt::Debug::fmt(&self.0, f)
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float + fmt::Display + fmt::LowerExp + From<f32>> fmt::Display for FloatWrapper<F> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let abs = self.0.abs();
-        if abs.is_zero() {
-            f.write_str("0.0")
-        } else if abs > Self::MAX_NATURAL_FLOAT_FOR_DISPLAY.into()
-            || abs < Self::MIN_NATURAL_FLOAT_FOR_DISPLAY.into()
-        {
-            write!(f, "{:e}", self.0)
-        } else {
-            fmt::Display::fmt(&self.0, f)?;
-            if abs.fract().is_zero() {
-                f.write_str(".0")?;
-            }
-            Ok(())
-        }
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> From<F> for FloatWrapper<F> {
-    #[inline(always)]
-    fn from(value: F) -> Self {
-        Self::new(value)
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float + FromStr> FromStr for FloatWrapper<F> {
-    type Err = <F as FromStr>::Err;
-
-    #[inline]
-    fn from_str(s: &str) -> Result<Self, Self::Err> {
-        F::from_str(s).map(Into::into)
-    }
-}
-
-#[cfg(not(feature = "no_float"))]
-impl<F: Float> FloatWrapper<F> {
-    /// Maximum floating-point number for natural display before switching to scientific notation.
-    pub const MAX_NATURAL_FLOAT_FOR_DISPLAY: f32 = 10_000_000_000_000.0;
-
-    /// Minimum floating-point number for natural display before switching to scientific notation.
-    pub const MIN_NATURAL_FLOAT_FOR_DISPLAY: f32 = 0.000_000_000_000_1;
-
-    /// Create a new [`FloatWrapper`].
-    #[inline(always)]
-    #[must_use]
-    pub const fn new(value: F) -> Self {
-        Self(value)
-    }
-}
-
 /// _(internals)_ An expression sub-tree.
 /// Exported under the `internals` feature only.
 #[derive(Clone, Hash)]
@@ -405,7 +281,7 @@ pub enum Expr {
     IntegerConstant(INT, Position),
     /// Floating-point constant.
     #[cfg(not(feature = "no_float"))]
-    FloatConstant(FloatWrapper<crate::FLOAT>, Position),
+    FloatConstant(crate::types::FloatWrapper<crate::FLOAT>, Position),
     /// Character constant.
     CharConstant(char, Position),
     /// [String][ImmutableString] constant.
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
index 00719a31..695f0786 100644
--- a/src/ast/mod.rs
+++ b/src/ast/mod.rs
@@ -26,9 +26,6 @@ pub use stmt::{
     SwitchCasesCollection, TryCatchBlock,
 };
 
-#[cfg(not(feature = "no_float"))]
-pub use expr::FloatWrapper;
-
 /// _(internals)_ Placeholder for a script-defined function.
 /// Exported under the `internals` feature only.
 #[cfg(feature = "no_function")]
diff --git a/src/bin/rhai-repl.rs b/src/bin/rhai-repl.rs
index 71801d82..260f7de8 100644
--- a/src/bin/rhai-repl.rs
+++ b/src/bin/rhai-repl.rs
@@ -559,7 +559,7 @@ fn main() {
                 // Evaluate
                 engine.eval_ast_with_scope::<Dynamic>(&mut scope, &main_ast)
             }) {
-            Ok(result) if !result.is::<()>() => {
+            Ok(result) if !result.is_unit() => {
                 println!("=> {result:?}");
                 println!();
             }
diff --git a/src/config/hashing.rs b/src/config/hashing.rs
index dd93e812..671b6664 100644
--- a/src/config/hashing.rs
+++ b/src/config/hashing.rs
@@ -94,7 +94,7 @@ fn hokmalock(address: usize) -> &'static HokmaLock {
     &RECORDS[address % LEN]
 }
 
-// Safety: lol, there is a reason its called "SusLock<T>"
+// Safety: lol, there is a reason its called `SusLock<T>`
 #[must_use]
 struct SusLock<T>
 where
@@ -118,36 +118,39 @@ where
         }
     }
 
+    #[inline(always)]
+    #[must_use]
+    pub fn is_initialized(&self) -> bool {
+        self.initialized.load(Ordering::SeqCst)
+    }
+
     #[must_use]
     pub fn get(&self) -> Option<&'static T> {
         if self.initialized.load(Ordering::SeqCst) {
             let hokma = hokmalock(unsafe { mem::transmute(self.data.get()) });
             // we forgo the optimistic read, because we don't really care
             let guard = hokma.write();
-            let val = {
-                let cast: *const T = self.data.get().cast();
-                unsafe { mem::transmute::<*const T, &'static T>(cast) }
-            };
+            let cast: *const T = self.data.get().cast();
+            let val = unsafe { mem::transmute::<*const T, &'static T>(cast) };
             guard.the_price_of_silence();
             Some(val)
         } else {
-            return None;
+            None
         }
     }
 
     #[must_use]
-    pub fn get_or_init(&self, f: impl FnOnce() -> T) -> Option<&'static T> {
+    pub fn get_or_init(&self, f: impl FnOnce() -> T) -> &'static T {
         if !self.initialized.load(Ordering::SeqCst) {
-            let value = f();
             self.initialized.store(true, Ordering::SeqCst);
             let hokma = hokmalock(unsafe { mem::transmute(self.data.get()) });
             hokma.write();
             unsafe {
-                self.data.get().write(MaybeUninit::new(value));
+                self.data.get().write(MaybeUninit::new(f()));
             }
         }
 
-        self.get()
+        self.get().unwrap()
     }
 
     pub fn set(&self, value: T) -> Result<(), T> {
@@ -217,10 +220,9 @@ pub fn set_ahash_seed(new_seed: Option<[u64; 4]>) -> Result<(), Option<[u64; 4]>
 #[inline]
 #[must_use]
 pub fn get_ahash_seed() -> &'static Option<[u64; 4]> {
-    const NONE: &'static Option<[u64; 4]> = &None;
-
-    match AHASH_SEED.get_or_init(|| hashing_env::AHASH_SEED) {
-        Some(ash) => ash,
-        None => NONE,
+    if !AHASH_SEED.is_initialized() {
+        return &hashing_env::AHASH_SEED;
     }
+
+    AHASH_SEED.get().unwrap_or(&hashing_env::AHASH_SEED)
 }
diff --git a/src/eval/cache.rs b/src/eval/cache.rs
index ee4f07a3..96160d7e 100644
--- a/src/eval/cache.rs
+++ b/src/eval/cache.rs
@@ -44,44 +44,39 @@ impl FnResolutionCache {
 /// The following caches are contained inside this type:
 /// * A stack of [function resolution caches][FnResolutionCache]
 #[derive(Debug, Clone)]
-pub struct Caches {
-    /// Stack of [function resolution caches][FnResolutionCache].
-    stack: StaticVec<FnResolutionCache>,
-}
+pub struct Caches(StaticVec<FnResolutionCache>);
 
 impl Caches {
     /// Create an empty [`Caches`].
     #[inline(always)]
     #[must_use]
     pub const fn new() -> Self {
-        Self {
-            stack: StaticVec::new_const(),
-        }
+        Self(StaticVec::new_const())
     }
     /// Get the number of function resolution cache(s) in the stack.
     #[inline(always)]
     #[must_use]
     pub fn fn_resolution_caches_len(&self) -> usize {
-        self.stack.len()
+        self.0.len()
     }
     /// Get a mutable reference to the current function resolution cache.
     #[inline]
     #[must_use]
     pub fn fn_resolution_cache_mut(&mut self) -> &mut FnResolutionCache {
-        if self.stack.is_empty() {
+        if self.0.is_empty() {
             // Push a new function resolution cache if the stack is empty
             self.push_fn_resolution_cache();
         }
-        self.stack.last_mut().unwrap()
+        self.0.last_mut().unwrap()
     }
     /// Push an empty function resolution cache onto the stack and make it current.
     #[inline(always)]
     pub fn push_fn_resolution_cache(&mut self) {
-        self.stack.push(Default::default());
+        self.0.push(Default::default());
     }
     /// Rewind the function resolution caches stack to a particular size.
     #[inline(always)]
     pub fn rewind_fn_resolution_caches(&mut self, len: usize) {
-        self.stack.truncate(len);
+        self.0.truncate(len);
     }
 }
diff --git a/src/eval/chaining.rs b/src/eval/chaining.rs
index ca813d86..5c3fa792 100644
--- a/src/eval/chaining.rs
+++ b/src/eval/chaining.rs
@@ -5,9 +5,7 @@ use super::{Caches, GlobalRuntimeState, Target};
 use crate::ast::{ASTFlags, Expr, OpAssignment};
 use crate::types::dynamic::Union;
 use crate::types::RestoreOnDrop;
-use crate::{
-    Dynamic, Engine, FnArgsVec, Position, RhaiResult, RhaiResultOf, Scope, SharedModule, ERR,
-};
+use crate::{Dynamic, Engine, FnArgsVec, Position, RhaiResult, RhaiResultOf, Scope, ERR};
 use std::hash::Hash;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -43,7 +41,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         this_ptr: &mut Dynamic,
         target: &mut Target,
         root: (&str, Position),
@@ -63,7 +60,7 @@ impl Engine {
             #[cfg(not(feature = "no_index"))]
             ChainType::Indexing => {
                 // Check for existence with the null conditional operator
-                if parent_options.contains(ASTFlags::NEGATED) && target.is::<()>() {
+                if parent_options.contains(ASTFlags::NEGATED) && target.is_unit() {
                     return Ok((Dynamic::UNIT, false));
                 }
 
@@ -75,7 +72,7 @@ impl Engine {
                         if !parent_options.contains(ASTFlags::BREAK) =>
                     {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, _parent)?;
+                        self.run_debugger(global, caches, scope, this_ptr, _parent)?;
 
                         let idx_val = &mut idx_values.pop().unwrap();
                         let mut idx_val_for_setter = idx_val.clone();
@@ -84,14 +81,14 @@ impl Engine {
 
                         let (try_setter, result) = {
                             let mut obj = self.get_indexed_mut(
-                                global, caches, lib, target, idx_val, idx_pos, false, true,
+                                global, caches, target, idx_val, idx_pos, false, true,
                             )?;
                             let is_obj_temp_val = obj.is_temp_value();
                             let obj_ptr = &mut obj;
 
                             match self.eval_dot_index_chain_helper(
-                                global, caches, lib, this_ptr, obj_ptr, root, rhs, *options,
-                                &x.rhs, idx_values, rhs_chain, new_val,
+                                global, caches, this_ptr, obj_ptr, root, rhs, *options, &x.rhs,
+                                idx_values, rhs_chain, new_val,
                             ) {
                                 Ok((result, true)) if is_obj_temp_val => {
                                     (Some(obj.take_or_clone()), (result, true))
@@ -105,13 +102,11 @@ impl Engine {
                             // Try to call index setter if value is changed
                             let idx = &mut idx_val_for_setter;
                             let new_val = &mut new_val;
-                            self.call_indexer_set(
-                                global, caches, lib, target, idx, new_val, is_ref_mut,
-                            )
-                            .or_else(|e| match *e {
-                                ERR::ErrorIndexingType(..) => Ok((Dynamic::UNIT, false)),
-                                _ => Err(e),
-                            })?;
+                            self.call_indexer_set(global, caches, target, idx, new_val, is_ref_mut)
+                                .or_else(|e| match *e {
+                                    ERR::ErrorIndexingType(..) => Ok((Dynamic::UNIT, false)),
+                                    _ => Err(e),
+                                })?;
                         }
 
                         Ok(result)
@@ -119,19 +114,19 @@ impl Engine {
                     // xxx[rhs] op= new_val
                     _ if new_val.is_some() => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, _parent)?;
+                        self.run_debugger(global, caches, scope, this_ptr, _parent)?;
 
                         let (new_val, op_info) = new_val.take().expect("`Some`");
                         let idx_val = &mut idx_values.pop().unwrap();
                         let idx = &mut idx_val.clone();
 
                         let try_setter = match self
-                            .get_indexed_mut(global, caches, lib, target, idx, pos, true, false)
+                            .get_indexed_mut(global, caches, target, idx, pos, true, false)
                         {
                             // Indexed value is not a temp value - update directly
                             Ok(ref mut obj_ptr) => {
                                 self.eval_op_assignment(
-                                    global, caches, lib, op_info, obj_ptr, root, new_val,
+                                    global, caches, op_info, obj_ptr, root, new_val,
                                 )?;
                                 self.check_data_size(obj_ptr, op_info.pos)?;
                                 None
@@ -149,13 +144,12 @@ impl Engine {
                                 let idx = &mut idx_val.clone();
 
                                 // Call the index getter to get the current value
-                                if let Ok(val) =
-                                    self.call_indexer_get(global, caches, lib, target, idx)
+                                if let Ok(val) = self.call_indexer_get(global, caches, target, idx)
                                 {
                                     let mut val = val.into();
                                     // Run the op-assignment
                                     self.eval_op_assignment(
-                                        global, caches, lib, op_info, &mut val, root, new_val,
+                                        global, caches, op_info, &mut val, root, new_val,
                                     )?;
                                     // Replace new value
                                     new_val = val.take_or_clone();
@@ -167,7 +161,7 @@ impl Engine {
                             let new_val = &mut new_val;
 
                             self.call_indexer_set(
-                                global, caches, lib, target, idx_val, new_val, is_ref_mut,
+                                global, caches, target, idx_val, new_val, is_ref_mut,
                             )?;
                         }
 
@@ -176,11 +170,11 @@ impl Engine {
                     // xxx[rhs]
                     _ => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, _parent)?;
+                        self.run_debugger(global, caches, scope, this_ptr, _parent)?;
 
                         let idx_val = &mut idx_values.pop().unwrap();
 
-                        self.get_indexed_mut(global, caches, lib, target, idx_val, pos, false, true)
+                        self.get_indexed_mut(global, caches, target, idx_val, pos, false, true)
                             .map(|v| (v.take_or_clone(), false))
                     }
                 }
@@ -189,7 +183,7 @@ impl Engine {
             #[cfg(not(feature = "no_object"))]
             ChainType::Dotting => {
                 // Check for existence with the Elvis operator
-                if parent_options.contains(ASTFlags::NEGATED) && target.is::<()>() {
+                if parent_options.contains(ASTFlags::NEGATED) && target.is_unit() {
                     return Ok((Dynamic::UNIT, false));
                 }
 
@@ -197,8 +191,8 @@ impl Engine {
                     // xxx.fn_name(arg_expr_list)
                     Expr::MethodCall(x, pos) if !x.is_qualified() && new_val.is_none() => {
                         #[cfg(feature = "debugging")]
-                        let reset = self
-                            .run_debugger_with_reset(global, caches, lib, scope, this_ptr, rhs)?;
+                        let reset =
+                            self.run_debugger_with_reset(global, caches, scope, this_ptr, rhs)?;
                         #[cfg(feature = "debugging")]
                         let global = &mut *RestoreOnDrop::lock(global, move |g| {
                             g.debugger.reset_status(reset)
@@ -217,7 +211,7 @@ impl Engine {
                         let pos1 = args.get(0).map_or(Position::NONE, Expr::position);
 
                         self.make_method_call(
-                            global, caches, lib, name, *hashes, target, call_args, pos1, *pos,
+                            global, caches, name, *hashes, target, call_args, pos1, *pos,
                         )
                     }
                     // xxx.fn_name(...) = ???
@@ -229,38 +223,37 @@ impl Engine {
                         unreachable!("function call in dot chain should not be namespace-qualified")
                     }
                     // {xxx:map}.id op= ???
-                    Expr::Property(x, pos) if target.is::<crate::Map>() && new_val.is_some() => {
+                    Expr::Property(x, pos) if target.is_map() && new_val.is_some() => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, rhs)?;
+                        self.run_debugger(global, caches, scope, this_ptr, rhs)?;
 
                         let index = &mut x.2.clone().into();
                         let (new_val, op_info) = new_val.take().expect("`Some`");
                         {
                             let val_target = &mut self.get_indexed_mut(
-                                global, caches, lib, target, index, *pos, true, false,
+                                global, caches, target, index, *pos, true, false,
                             )?;
                             self.eval_op_assignment(
-                                global, caches, lib, op_info, val_target, root, new_val,
+                                global, caches, op_info, val_target, root, new_val,
                             )?;
                         }
                         self.check_data_size(target.source(), op_info.pos)?;
                         Ok((Dynamic::UNIT, true))
                     }
                     // {xxx:map}.id
-                    Expr::Property(x, pos) if target.is::<crate::Map>() => {
+                    Expr::Property(x, pos) if target.is_map() => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, rhs)?;
+                        self.run_debugger(global, caches, scope, this_ptr, rhs)?;
 
                         let index = &mut x.2.clone().into();
-                        let val = self.get_indexed_mut(
-                            global, caches, lib, target, index, *pos, false, false,
-                        )?;
+                        let val = self
+                            .get_indexed_mut(global, caches, target, index, *pos, false, false)?;
                         Ok((val.take_or_clone(), false))
                     }
                     // xxx.id op= ???
                     Expr::Property(x, pos) if new_val.is_some() => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, rhs)?;
+                        self.run_debugger(global, caches, scope, this_ptr, rhs)?;
 
                         let ((getter, hash_get), (setter, hash_set), name) = &**x;
                         let (mut new_val, op_info) = new_val.take().expect("`Some`");
@@ -269,23 +262,18 @@ impl Engine {
                             let args = &mut [target.as_mut()];
                             let (mut orig_val, ..) = self
                                 .exec_native_fn_call(
-                                    global, caches, lib, getter, None, *hash_get, args, is_ref_mut,
-                                    *pos,
+                                    global, caches, getter, None, *hash_get, args, is_ref_mut, *pos,
                                 )
                                 .or_else(|err| match *err {
                                     // Try an indexer if property does not exist
                                     ERR::ErrorDotExpr(..) => {
                                         let mut prop = name.into();
-                                        self.call_indexer_get(
-                                            global, caches, lib, target, &mut prop,
-                                        )
-                                        .map(|r| (r, false))
-                                        .map_err(|e| {
-                                            match *e {
+                                        self.call_indexer_get(global, caches, target, &mut prop)
+                                            .map(|r| (r, false))
+                                            .map_err(|e| match *e {
                                                 ERR::ErrorIndexingType(..) => err,
                                                 _ => e,
-                                            }
-                                        })
+                                            })
                                     }
                                     _ => Err(err),
                                 })?;
@@ -294,7 +282,7 @@ impl Engine {
                                 let orig_val = &mut (&mut orig_val).into();
 
                                 self.eval_op_assignment(
-                                    global, caches, lib, op_info, orig_val, root, new_val,
+                                    global, caches, op_info, orig_val, root, new_val,
                                 )?;
                             }
 
@@ -303,7 +291,7 @@ impl Engine {
 
                         let args = &mut [target.as_mut(), &mut new_val];
                         self.exec_native_fn_call(
-                            global, caches, lib, setter, None, *hash_set, args, is_ref_mut, *pos,
+                            global, caches, setter, None, *hash_set, args, is_ref_mut, *pos,
                         )
                         .or_else(|err| match *err {
                             // Try an indexer if property does not exist
@@ -311,7 +299,7 @@ impl Engine {
                                 let idx = &mut name.into();
                                 let new_val = &mut new_val;
                                 self.call_indexer_set(
-                                    global, caches, lib, target, idx, new_val, is_ref_mut,
+                                    global, caches, target, idx, new_val, is_ref_mut,
                                 )
                                 .map_err(|e| match *e {
                                     ERR::ErrorIndexingType(..) => err,
@@ -324,19 +312,19 @@ impl Engine {
                     // xxx.id
                     Expr::Property(x, pos) => {
                         #[cfg(feature = "debugging")]
-                        self.run_debugger(global, caches, lib, scope, this_ptr, rhs)?;
+                        self.run_debugger(global, caches, scope, this_ptr, rhs)?;
 
                         let ((getter, hash_get), _, name) = &**x;
                         let args = &mut [target.as_mut()];
                         self.exec_native_fn_call(
-                            global, caches, lib, getter, None, *hash_get, args, is_ref_mut, *pos,
+                            global, caches, getter, None, *hash_get, args, is_ref_mut, *pos,
                         )
                         .map_or_else(
                             |err| match *err {
                                 // Try an indexer if property does not exist
                                 ERR::ErrorDotExpr(..) => {
                                     let mut prop = name.into();
-                                    self.call_indexer_get(global, caches, lib, target, &mut prop)
+                                    self.call_indexer_get(global, caches, target, &mut prop)
                                         .map(|r| (r, false))
                                         .map_err(|e| match *e {
                                             ERR::ErrorIndexingType(..) => err,
@@ -351,25 +339,25 @@ impl Engine {
                     }
                     // {xxx:map}.sub_lhs[expr] | {xxx:map}.sub_lhs.expr
                     Expr::Index(x, options, x_pos) | Expr::Dot(x, options, x_pos)
-                        if target.is::<crate::Map>() =>
+                        if target.is_map() =>
                     {
                         let _node = &x.lhs;
 
                         let val_target = &mut match x.lhs {
                             Expr::Property(ref p, pos) => {
                                 #[cfg(feature = "debugging")]
-                                self.run_debugger(global, caches, lib, scope, this_ptr, _node)?;
+                                self.run_debugger(global, caches, scope, this_ptr, _node)?;
 
                                 let index = &mut p.2.clone().into();
                                 self.get_indexed_mut(
-                                    global, caches, lib, target, index, pos, false, true,
+                                    global, caches, target, index, pos, false, true,
                                 )?
                             }
                             // {xxx:map}.fn_name(arg_expr_list)[expr] | {xxx:map}.fn_name(arg_expr_list).expr
                             Expr::MethodCall(ref x, pos) if !x.is_qualified() => {
                                 #[cfg(feature = "debugging")]
                                 let reset = self.run_debugger_with_reset(
-                                    global, caches, lib, scope, this_ptr, _node,
+                                    global, caches, scope, this_ptr, _node,
                                 )?;
                                 #[cfg(feature = "debugging")]
                                 let global = &mut *RestoreOnDrop::lock(global, move |g| {
@@ -390,8 +378,7 @@ impl Engine {
                                 let pos1 = args.get(0).map_or(Position::NONE, Expr::position);
 
                                 self.make_method_call(
-                                    global, caches, lib, name, *hashes, target, call_args, pos1,
-                                    pos,
+                                    global, caches, name, *hashes, target, call_args, pos1, pos,
                                 )?
                                 .0
                                 .into()
@@ -406,7 +393,7 @@ impl Engine {
                         let rhs_chain = rhs.into();
 
                         self.eval_dot_index_chain_helper(
-                            global, caches, lib, this_ptr, val_target, root, rhs, *options, &x.rhs,
+                            global, caches, this_ptr, val_target, root, rhs, *options, &x.rhs,
                             idx_values, rhs_chain, new_val,
                         )
                         .map_err(|err| err.fill_position(*x_pos))
@@ -419,7 +406,7 @@ impl Engine {
                             // xxx.prop[expr] | xxx.prop.expr
                             Expr::Property(ref p, pos) => {
                                 #[cfg(feature = "debugging")]
-                                self.run_debugger(global, caches, lib, scope, this_ptr, _node)?;
+                                self.run_debugger(global, caches, scope, this_ptr, _node)?;
 
                                 let ((getter, hash_get), (setter, hash_set), name) = &**p;
                                 let rhs_chain = rhs.into();
@@ -429,23 +416,19 @@ impl Engine {
                                 // Assume getters are always pure
                                 let (mut val, ..) = self
                                     .exec_native_fn_call(
-                                        global, caches, lib, getter, None, *hash_get, args,
-                                        is_ref_mut, pos,
+                                        global, caches, getter, None, *hash_get, args, is_ref_mut,
+                                        pos,
                                     )
                                     .or_else(|err| match *err {
                                         // Try an indexer if property does not exist
                                         ERR::ErrorDotExpr(..) => {
                                             let mut prop = name.into();
-                                            self.call_indexer_get(
-                                                global, caches, lib, target, &mut prop,
-                                            )
-                                            .map(|r| (r, false))
-                                            .map_err(
-                                                |e| match *e {
+                                            self.call_indexer_get(global, caches, target, &mut prop)
+                                                .map(|r| (r, false))
+                                                .map_err(|e| match *e {
                                                     ERR::ErrorIndexingType(..) => err,
                                                     _ => e,
-                                                },
-                                            )
+                                                })
                                         }
                                         _ => Err(err),
                                     })?;
@@ -454,8 +437,8 @@ impl Engine {
 
                                 let (result, may_be_changed) = self
                                     .eval_dot_index_chain_helper(
-                                        global, caches, lib, this_ptr, val, root, rhs, *options,
-                                        &x.rhs, idx_values, rhs_chain, new_val,
+                                        global, caches, this_ptr, val, root, rhs, *options, &x.rhs,
+                                        idx_values, rhs_chain, new_val,
                                     )
                                     .map_err(|err| err.fill_position(*x_pos))?;
 
@@ -465,8 +448,8 @@ impl Engine {
                                     let mut arg_values = [target.as_mut(), val.as_mut()];
                                     let args = &mut arg_values;
                                     self.exec_native_fn_call(
-                                        global, caches, lib, setter, None, *hash_set, args,
-                                        is_ref_mut, pos,
+                                        global, caches, setter, None, *hash_set, args, is_ref_mut,
+                                        pos,
                                     )
                                     .or_else(
                                         |err| match *err {
@@ -475,7 +458,7 @@ impl Engine {
                                                 let idx = &mut name.into();
                                                 let new_val = val;
                                                 self.call_indexer_set(
-                                                    global, caches, lib, target, idx, new_val,
+                                                    global, caches, target, idx, new_val,
                                                     is_ref_mut,
                                                 )
                                                 .or_else(|e| match *e {
@@ -499,7 +482,7 @@ impl Engine {
                                 let val = {
                                     #[cfg(feature = "debugging")]
                                     let reset = self.run_debugger_with_reset(
-                                        global, caches, lib, scope, this_ptr, _node,
+                                        global, caches, scope, this_ptr, _node,
                                     )?;
                                     #[cfg(feature = "debugging")]
                                     let global = &mut *RestoreOnDrop::lock(global, move |g| {
@@ -521,8 +504,7 @@ impl Engine {
                                     let pos1 = args.get(0).map_or(Position::NONE, Expr::position);
 
                                     self.make_method_call(
-                                        global, caches, lib, name, *hashes, target, call_args,
-                                        pos1, pos,
+                                        global, caches, name, *hashes, target, call_args, pos1, pos,
                                     )?
                                     .0
                                 };
@@ -531,8 +513,8 @@ impl Engine {
                                 let rhs_chain = rhs.into();
 
                                 self.eval_dot_index_chain_helper(
-                                    global, caches, lib, this_ptr, val, root, rhs, *options,
-                                    &x.rhs, idx_values, rhs_chain, new_val,
+                                    global, caches, this_ptr, val, root, rhs, *options, &x.rhs,
+                                    idx_values, rhs_chain, new_val,
                                 )
                                 .map_err(|err| err.fill_position(pos))
                             }
@@ -556,7 +538,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         expr: &Expr,
@@ -597,7 +578,7 @@ impl Engine {
             // All other patterns - evaluate the arguments chain
             _ => {
                 self.eval_dot_index_chain_arguments(
-                    global, caches, lib, scope, this_ptr, rhs, options, chain_type, idx_values,
+                    global, caches, scope, this_ptr, rhs, options, chain_type, idx_values,
                 )?;
             }
         }
@@ -606,18 +587,18 @@ impl Engine {
             // id.??? or id[???]
             Expr::Variable(x, .., var_pos) => {
                 #[cfg(feature = "debugging")]
-                self.run_debugger(global, caches, lib, scope, this_ptr, lhs)?;
+                self.run_debugger(global, caches, scope, this_ptr, lhs)?;
                 self.track_operation(global, *var_pos)?;
 
                 let (mut target, ..) =
-                    self.search_namespace(global, caches, lib, scope, this_ptr, lhs)?;
+                    self.search_namespace(global, caches, scope, this_ptr, lhs)?;
 
                 let obj_ptr = &mut target;
                 let root = (x.3.as_str(), *var_pos);
                 let mut this = Dynamic::NULL;
 
                 self.eval_dot_index_chain_helper(
-                    global, caches, lib, &mut this, obj_ptr, root, expr, options, rhs, idx_values,
+                    global, caches, &mut this, obj_ptr, root, expr, options, rhs, idx_values,
                     chain_type, new_val,
                 )
             }
@@ -626,13 +607,13 @@ impl Engine {
             // {expr}.??? or {expr}[???]
             expr => {
                 let value = self
-                    .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                    .eval_expr(global, caches, scope, this_ptr, expr)?
                     .flatten();
                 let obj_ptr = &mut value.into();
                 let root = ("", expr.start_position());
 
                 self.eval_dot_index_chain_helper(
-                    global, caches, lib, this_ptr, obj_ptr, root, expr, options, rhs, idx_values,
+                    global, caches, this_ptr, obj_ptr, root, expr, options, rhs, idx_values,
                     chain_type, new_val,
                 )
             }
@@ -646,7 +627,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         expr: &Expr,
@@ -663,7 +643,7 @@ impl Engine {
             {
                 for arg_expr in &x.args {
                     idx_values.push(
-                        self.get_arg_value(global, caches, lib, scope, this_ptr, arg_expr)?
+                        self.get_arg_value(global, caches, scope, this_ptr, arg_expr)?
                             .0
                             .flatten(),
                     );
@@ -697,7 +677,7 @@ impl Engine {
                     {
                         for arg_expr in &x.args {
                             _arg_values.push(
-                                self.get_arg_value(global, caches, lib, scope, this_ptr, arg_expr)?
+                                self.get_arg_value(global, caches, scope, this_ptr, arg_expr)?
                                     .0
                                     .flatten(),
                             );
@@ -714,7 +694,7 @@ impl Engine {
                     #[cfg(not(feature = "no_index"))]
                     _ if parent_chain_type == ChainType::Indexing => {
                         _arg_values.push(
-                            self.eval_expr(global, caches, lib, scope, this_ptr, lhs)?
+                            self.eval_expr(global, caches, scope, this_ptr, lhs)?
                                 .flatten(),
                         );
                     }
@@ -725,7 +705,7 @@ impl Engine {
                 let chain_type = expr.into();
 
                 self.eval_dot_index_chain_arguments(
-                    global, caches, lib, scope, this_ptr, rhs, *options, chain_type, idx_values,
+                    global, caches, scope, this_ptr, rhs, *options, chain_type, idx_values,
                 )?;
 
                 if !_arg_values.is_empty() {
@@ -739,7 +719,7 @@ impl Engine {
             }
             #[cfg(not(feature = "no_index"))]
             _ if parent_chain_type == ChainType::Indexing => idx_values.push(
-                self.eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                self.eval_expr(global, caches, scope, this_ptr, expr)?
                     .flatten(),
             ),
             _ => unreachable!("unknown chained expression: {:?}", expr),
@@ -754,7 +734,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         target: &mut Dynamic,
         idx: &mut Dynamic,
     ) -> RhaiResultOf<Dynamic> {
@@ -763,10 +742,11 @@ impl Engine {
         let fn_name = crate::engine::FN_IDX_GET;
         let pos = Position::NONE;
 
+        let orig_level = global.level;
         global.level += 1;
-        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level -= 1);
+        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
-        self.exec_native_fn_call(global, caches, lib, fn_name, None, hash, args, true, pos)
+        self.exec_native_fn_call(global, caches, fn_name, None, hash, args, true, pos)
             .map(|(r, ..)| r)
     }
 
@@ -776,7 +756,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         target: &mut Dynamic,
         idx: &mut Dynamic,
         new_val: &mut Dynamic,
@@ -787,12 +766,11 @@ impl Engine {
         let fn_name = crate::engine::FN_IDX_SET;
         let pos = Position::NONE;
 
+        let orig_level = global.level;
         global.level += 1;
-        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level -= 1);
+        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
-        self.exec_native_fn_call(
-            global, caches, lib, fn_name, None, hash, args, is_ref_mut, pos,
-        )
+        self.exec_native_fn_call(global, caches, fn_name, None, hash, args, is_ref_mut, pos)
     }
 
     /// Get the value at the indexed position of a base type.
@@ -801,7 +779,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         target: &'t mut Dynamic,
         idx: &mut Dynamic,
         idx_pos: Position,
@@ -1010,7 +987,7 @@ impl Engine {
             }
 
             _ if use_indexers => self
-                .call_indexer_get(global, caches, lib, target, idx)
+                .call_indexer_get(global, caches, target, idx)
                 .map(Into::into),
 
             _ => Err(ERR::ErrorIndexingType(
diff --git a/src/eval/data_check.rs b/src/eval/data_check.rs
index abda0e45..bce0b87b 100644
--- a/src/eval/data_check.rs
+++ b/src/eval/data_check.rs
@@ -147,15 +147,11 @@ impl Engine {
             return Err(ERR::ErrorTooManyOperations(pos).into());
         }
 
-        // Report progress - only in steps
-        if let Some(ref progress) = self.progress {
-            if let Some(token) = progress(num_operations) {
-                // Terminate script if progress returns a termination token
-                return Err(ERR::ErrorTerminated(token, pos).into());
-            }
-        }
-
-        Ok(())
+        // Report progress
+        self.progress
+            .as_ref()
+            .and_then(|p| p(num_operations))
+            .map_or(Ok(()), |token| Err(ERR::ErrorTerminated(token, pos).into()))
     }
 
     /// Check a result to ensure that it is valid.
diff --git a/src/eval/debugger.rs b/src/eval/debugger.rs
index 6eed7279..bf74af3d 100644
--- a/src/eval/debugger.rs
+++ b/src/eval/debugger.rs
@@ -3,9 +3,7 @@
 
 use super::{Caches, EvalContext, GlobalRuntimeState};
 use crate::ast::{ASTNode, Expr, Stmt};
-use crate::{
-    Dynamic, Engine, EvalAltResult, ImmutableString, Position, RhaiResultOf, Scope, SharedModule,
-};
+use crate::{Dynamic, Engine, EvalAltResult, ImmutableString, Position, RhaiResultOf, Scope};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{fmt, iter::repeat, mem};
@@ -413,14 +411,13 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         node: impl Into<ASTNode<'a>>,
     ) -> RhaiResultOf<()> {
         if self.debugger.is_some() {
             if let Some(cmd) =
-                self.run_debugger_with_reset_raw(global, caches, lib, scope, this_ptr, node)?
+                self.run_debugger_with_reset_raw(global, caches, scope, this_ptr, node)?
             {
                 global.debugger.status = cmd;
             }
@@ -439,13 +436,12 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         node: impl Into<ASTNode<'a>>,
     ) -> RhaiResultOf<Option<DebuggerStatus>> {
         if self.debugger.is_some() {
-            self.run_debugger_with_reset_raw(global, caches, lib, scope, this_ptr, node)
+            self.run_debugger_with_reset_raw(global, caches, scope, this_ptr, node)
         } else {
             Ok(None)
         }
@@ -461,7 +457,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         node: impl Into<ASTNode<'a>>,
@@ -494,7 +489,7 @@ impl Engine {
             },
         };
 
-        self.run_debugger_raw(global, caches, lib, scope, this_ptr, node, event)
+        self.run_debugger_raw(global, caches, scope, this_ptr, node, event)
     }
     /// Run the debugger callback unconditionally.
     ///
@@ -507,7 +502,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         node: ASTNode<'a>,
@@ -515,7 +509,7 @@ impl Engine {
     ) -> Result<Option<DebuggerStatus>, Box<crate::EvalAltResult>> {
         let src = global.source_raw().cloned();
         let src = src.as_ref().map(|s| s.as_str());
-        let context = crate::EvalContext::new(self, global, caches, lib, scope, this_ptr);
+        let context = crate::EvalContext::new(self, global, caches, scope, this_ptr);
 
         if let Some((.., ref on_debugger)) = self.debugger {
             let command = on_debugger(context, event, node, src, node.position())?;
diff --git a/src/eval/eval_context.rs b/src/eval/eval_context.rs
index f8f2fd1a..82b3750b 100644
--- a/src/eval/eval_context.rs
+++ b/src/eval/eval_context.rs
@@ -1,7 +1,7 @@
 //! Evaluation context.
 
 use super::{Caches, GlobalRuntimeState};
-use crate::{Dynamic, Engine, Module, Scope, SharedModule};
+use crate::{Dynamic, Engine, Module, Scope};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 
@@ -11,14 +11,12 @@ use std::prelude::v1::*;
 pub struct EvalContext<'a, 's, 'ps, 'g, 'c, 't> {
     /// The current [`Engine`].
     engine: &'a Engine,
-    /// The current [`Scope`].
-    scope: &'s mut Scope<'ps>,
     /// The current [`GlobalRuntimeState`].
     global: &'g mut GlobalRuntimeState,
     /// The current [caches][Caches], if available.
     caches: &'c mut Caches,
-    /// The current stack of imported [modules][Module].
-    lib: &'a [SharedModule],
+    /// The current [`Scope`].
+    scope: &'s mut Scope<'ps>,
     /// The current bound `this` pointer, if any.
     this_ptr: &'t mut Dynamic,
 }
@@ -31,16 +29,14 @@ impl<'a, 's, 'ps, 'g, 'c, 't> EvalContext<'a, 's, 'ps, 'g, 'c, 't> {
         engine: &'a Engine,
         global: &'g mut GlobalRuntimeState,
         caches: &'c mut Caches,
-        lib: &'a [SharedModule],
         scope: &'s mut Scope<'ps>,
         this_ptr: &'t mut Dynamic,
     ) -> Self {
         Self {
             engine,
-            scope,
             global,
             caches,
-            lib,
+            scope,
             this_ptr,
         }
     }
@@ -104,17 +100,23 @@ impl<'a, 's, 'ps, 'g, 'c, 't> EvalContext<'a, 's, 'ps, 'g, 'c, 't> {
         self.global
     }
     /// Get an iterator over the namespaces containing definition of all script-defined functions.
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[inline]
     pub fn iter_namespaces(&self) -> impl Iterator<Item = &Module> {
-        self.lib.iter().map(|m| m.as_ref())
+        self.global.lib.iter().map(|m| m.as_ref())
     }
     /// _(internals)_ The current set of namespaces containing definitions of all script-defined functions.
     /// Exported under the `internals` feature only.
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[cfg(feature = "internals")]
     #[inline(always)]
     #[must_use]
-    pub const fn namespaces(&self) -> &[SharedModule] {
-        self.lib
+    pub fn namespaces(&self) -> &[crate::SharedModule] {
+        &self.global.lib
     }
     /// The current bound `this` pointer, if any.
     #[inline]
@@ -181,20 +183,14 @@ impl<'a, 's, 'ps, 'g, 'c, 't> EvalContext<'a, 's, 'ps, 'g, 'c, 't> {
             crate::ast::Expr::Stmt(statements) => self.engine.eval_stmt_block(
                 self.global,
                 self.caches,
-                self.lib,
                 self.scope,
                 self.this_ptr,
                 statements,
                 rewind_scope,
             ),
-            _ => self.engine.eval_expr(
-                self.global,
-                self.caches,
-                self.lib,
-                self.scope,
-                self.this_ptr,
-                expr,
-            ),
+            _ => self
+                .engine
+                .eval_expr(self.global, self.caches, self.scope, self.this_ptr, expr),
         }
     }
 }
diff --git a/src/eval/expr.rs b/src/eval/expr.rs
index 0c18772a..58e45d8a 100644
--- a/src/eval/expr.rs
+++ b/src/eval/expr.rs
@@ -51,24 +51,22 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
-
         scope: &'s mut Scope,
         this_ptr: &'s mut Dynamic,
         expr: &Expr,
     ) -> RhaiResultOf<(Target<'s>, Position)> {
         match expr {
             Expr::Variable(_, Some(_), _) => {
-                self.search_scope_only(global, caches, lib, scope, this_ptr, expr)
+                self.search_scope_only(global, caches, scope, this_ptr, expr)
             }
             Expr::Variable(v, None, _var_pos) => match &**v {
                 // Normal variable access
                 #[cfg(not(feature = "no_module"))]
                 (_, ns, ..) if ns.is_empty() => {
-                    self.search_scope_only(global, caches, lib, scope, this_ptr, expr)
+                    self.search_scope_only(global, caches, scope, this_ptr, expr)
                 }
                 #[cfg(feature = "no_module")]
-                (_, (), ..) => self.search_scope_only(global, caches, lib, scope, this_ptr, expr),
+                (_, (), ..) => self.search_scope_only(global, caches, scope, this_ptr, expr),
 
                 // Qualified variable access
                 #[cfg(not(feature = "no_module"))]
@@ -135,8 +133,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
-
         scope: &'s mut Scope,
         this_ptr: &'s mut Dynamic,
         expr: &Expr,
@@ -157,7 +153,8 @@ impl Engine {
             // Scripted function with the same name
             #[cfg(not(feature = "no_function"))]
             Expr::Variable(v, None, pos)
-                if lib
+                if global
+                    .lib
                     .iter()
                     .flat_map(|m| m.iter_script_fn())
                     .any(|(_, _, f, ..)| f == v.3.as_str()) =>
@@ -172,7 +169,7 @@ impl Engine {
 
         // Check the variable resolver, if any
         if let Some(ref resolve_var) = self.resolve_var {
-            let context = EvalContext::new(self, global, caches, lib, scope, this_ptr);
+            let context = EvalContext::new(self, global, caches, scope, this_ptr);
             let var_name = expr.get_variable_name(true).expect("`Expr::Variable`");
             match resolve_var(var_name, index, context) {
                 Ok(Some(mut result)) => {
@@ -220,8 +217,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
-
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         expr: &Expr,
@@ -233,7 +228,7 @@ impl Engine {
         // binary operators are also function calls.
         if let Expr::FnCall(x, pos) = expr {
             #[cfg(feature = "debugging")]
-            let reset = self.run_debugger_with_reset(global, caches, lib, scope, this_ptr, expr)?;
+            let reset = self.run_debugger_with_reset(global, caches, scope, this_ptr, expr)?;
             #[cfg(feature = "debugging")]
             let global = &mut *crate::types::RestoreOnDrop::lock(global, move |g| {
                 g.debugger.reset_status(reset)
@@ -241,7 +236,7 @@ impl Engine {
 
             self.track_operation(global, expr.position())?;
 
-            return self.eval_fn_call_expr(global, caches, lib, scope, this_ptr, x, *pos);
+            return self.eval_fn_call_expr(global, caches, scope, this_ptr, x, *pos);
         }
 
         // Then variable access.
@@ -249,7 +244,7 @@ impl Engine {
         // will cost more than the mis-predicted `match` branch.
         if let Expr::Variable(x, index, var_pos) = expr {
             #[cfg(feature = "debugging")]
-            self.run_debugger(global, caches, lib, scope, this_ptr, expr)?;
+            self.run_debugger(global, caches, scope, this_ptr, expr)?;
 
             self.track_operation(global, expr.position())?;
 
@@ -260,13 +255,13 @@ impl Engine {
                     Ok(this_ptr.clone())
                 }
             } else {
-                self.search_namespace(global, caches, lib, scope, this_ptr, expr)
+                self.search_namespace(global, caches, scope, this_ptr, expr)
                     .map(|(val, ..)| val.take_or_clone())
             };
         }
 
         #[cfg(feature = "debugging")]
-        let reset = self.run_debugger_with_reset(global, caches, lib, scope, this_ptr, expr)?;
+        let reset = self.run_debugger_with_reset(global, caches, scope, this_ptr, expr)?;
         #[cfg(feature = "debugging")]
         let global = &mut *crate::types::RestoreOnDrop::lock(global, move |g| {
             g.debugger.reset_status(reset)
@@ -287,7 +282,7 @@ impl Engine {
 
             // `... ${...} ...`
             Expr::InterpolatedString(x, _) => {
-                let mut concat = self.get_interned_string("").into();
+                let mut concat = self.const_empty_string().into();
                 let target = &mut concat;
 
                 let mut op_info = OpAssignment::new_op_assignment(OP_CONCAT, Position::NONE);
@@ -296,11 +291,13 @@ impl Engine {
                 let result = x
                     .iter()
                     .try_for_each(|expr| {
-                        let item = self.eval_expr(global, caches, lib, scope, this_ptr, expr)?;
+                        let item = self
+                            .eval_expr(global, caches, scope, this_ptr, expr)?
+                            .flatten();
 
                         op_info.pos = expr.start_position();
 
-                        self.eval_op_assignment(global, caches, lib, &op_info, target, root, item)
+                        self.eval_op_assignment(global, caches, &op_info, target, root, item)
                     })
                     .map(|_| concat.take_or_clone());
 
@@ -317,7 +314,7 @@ impl Engine {
                         crate::Array::with_capacity(x.len()),
                         |mut array, item_expr| {
                             let value = self
-                                .eval_expr(global, caches, lib, scope, this_ptr, item_expr)?
+                                .eval_expr(global, caches, scope, this_ptr, item_expr)?
                                 .flatten();
 
                             #[cfg(not(feature = "unchecked"))]
@@ -349,7 +346,7 @@ impl Engine {
                 x.0.iter()
                     .try_fold(x.1.clone(), |mut map, (key, value_expr)| {
                         let value = self
-                            .eval_expr(global, caches, lib, scope, this_ptr, value_expr)?
+                            .eval_expr(global, caches, scope, this_ptr, value_expr)?
                             .flatten();
 
                         #[cfg(not(feature = "unchecked"))]
@@ -372,30 +369,30 @@ impl Engine {
             }
 
             Expr::And(x, ..) => Ok((self
-                .eval_expr(global, caches, lib, scope, this_ptr, &x.lhs)?
+                .eval_expr(global, caches, scope, this_ptr, &x.lhs)?
                 .as_bool()
                 .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.lhs.position()))?
                 && self
-                    .eval_expr(global, caches, lib, scope, this_ptr, &x.rhs)?
+                    .eval_expr(global, caches, scope, this_ptr, &x.rhs)?
                     .as_bool()
                     .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.rhs.position()))?)
             .into()),
 
             Expr::Or(x, ..) => Ok((self
-                .eval_expr(global, caches, lib, scope, this_ptr, &x.lhs)?
+                .eval_expr(global, caches, scope, this_ptr, &x.lhs)?
                 .as_bool()
                 .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.lhs.position()))?
                 || self
-                    .eval_expr(global, caches, lib, scope, this_ptr, &x.rhs)?
+                    .eval_expr(global, caches, scope, this_ptr, &x.rhs)?
                     .as_bool()
                     .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, x.rhs.position()))?)
             .into()),
 
             Expr::Coalesce(x, ..) => {
-                let value = self.eval_expr(global, caches, lib, scope, this_ptr, &x.lhs)?;
+                let value = self.eval_expr(global, caches, scope, this_ptr, &x.lhs)?;
 
-                if value.is::<()>() {
-                    self.eval_expr(global, caches, lib, scope, this_ptr, &x.rhs)
+                if value.is_unit() {
+                    self.eval_expr(global, caches, scope, this_ptr, &x.rhs)
                 } else {
                     Ok(value)
                 }
@@ -415,7 +412,7 @@ impl Engine {
                         *pos,
                     ))
                 })?;
-                let mut context = EvalContext::new(self, global, caches, lib, scope, this_ptr);
+                let mut context = EvalContext::new(self, global, caches, scope, this_ptr);
 
                 let result = (custom_def.func)(&mut context, &expressions, &custom.state);
 
@@ -423,16 +420,16 @@ impl Engine {
             }
 
             Expr::Stmt(x) if x.is_empty() => Ok(Dynamic::UNIT),
-            Expr::Stmt(x) => self.eval_stmt_block(global, caches, lib, scope, this_ptr, x, true),
+            Expr::Stmt(x) => self.eval_stmt_block(global, caches, scope, this_ptr, x, true),
 
             #[cfg(not(feature = "no_index"))]
             Expr::Index(..) => {
-                self.eval_dot_index_chain(global, caches, lib, scope, this_ptr, expr, &mut None)
+                self.eval_dot_index_chain(global, caches, scope, this_ptr, expr, &mut None)
             }
 
             #[cfg(not(feature = "no_object"))]
             Expr::Dot(..) => {
-                self.eval_dot_index_chain(global, caches, lib, scope, this_ptr, expr, &mut None)
+                self.eval_dot_index_chain(global, caches, scope, this_ptr, expr, &mut None)
             }
 
             _ => unreachable!("expression cannot be evaluated: {:?}", expr),
diff --git a/src/eval/global_state.rs b/src/eval/global_state.rs
index 94dcb837..703ae510 100644
--- a/src/eval/global_state.rs
+++ b/src/eval/global_state.rs
@@ -1,6 +1,6 @@
 //! Global runtime state.
 
-use crate::{Dynamic, Engine, ImmutableString};
+use crate::{Dynamic, Engine, ImmutableString, SharedModule, StaticVec};
 use std::fmt;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -25,10 +25,13 @@ pub type GlobalConstants =
 pub struct GlobalRuntimeState {
     /// Names of imported [modules][crate::Module].
     #[cfg(not(feature = "no_module"))]
-    imports: crate::StaticVec<ImmutableString>,
+    imports: StaticVec<ImmutableString>,
     /// Stack of imported [modules][crate::Module].
     #[cfg(not(feature = "no_module"))]
-    modules: crate::StaticVec<crate::SharedModule>,
+    modules: StaticVec<SharedModule>,
+    /// The current stack of loaded [modules][crate::Module] containing script-defined functions.
+    #[cfg(not(feature = "no_function"))]
+    pub lib: StaticVec<SharedModule>,
     /// Source of the current context.
     ///
     /// No source if the string is empty.
@@ -81,9 +84,11 @@ impl GlobalRuntimeState {
     pub fn new(engine: &Engine) -> Self {
         Self {
             #[cfg(not(feature = "no_module"))]
-            imports: crate::StaticVec::new_const(),
+            imports: StaticVec::new_const(),
             #[cfg(not(feature = "no_module"))]
-            modules: crate::StaticVec::new_const(),
+            modules: StaticVec::new_const(),
+            #[cfg(not(feature = "no_function"))]
+            lib: StaticVec::new_const(),
             source: None,
             num_operations: 0,
             #[cfg(not(feature = "no_module"))]
@@ -130,7 +135,7 @@ impl GlobalRuntimeState {
     #[cfg(not(feature = "no_module"))]
     #[inline(always)]
     #[must_use]
-    pub fn get_shared_import(&self, index: usize) -> Option<crate::SharedModule> {
+    pub fn get_shared_import(&self, index: usize) -> Option<SharedModule> {
         self.modules.get(index).cloned()
     }
     /// Get a mutable reference to the globally-imported [module][crate::Module] at a
@@ -141,10 +146,7 @@ impl GlobalRuntimeState {
     #[allow(dead_code)]
     #[inline(always)]
     #[must_use]
-    pub(crate) fn get_shared_import_mut(
-        &mut self,
-        index: usize,
-    ) -> Option<&mut crate::SharedModule> {
+    pub(crate) fn get_shared_import_mut(&mut self, index: usize) -> Option<&mut SharedModule> {
         self.modules.get_mut(index)
     }
     /// Get the index of a globally-imported [module][crate::Module] by name.
@@ -168,7 +170,7 @@ impl GlobalRuntimeState {
     pub fn push_import(
         &mut self,
         name: impl Into<ImmutableString>,
-        module: impl Into<crate::SharedModule>,
+        module: impl Into<SharedModule>,
     ) {
         self.imports.push(name.into());
         self.modules.push(module.into());
@@ -201,7 +203,7 @@ impl GlobalRuntimeState {
     #[inline]
     pub(crate) fn iter_imports_raw(
         &self,
-    ) -> impl Iterator<Item = (&ImmutableString, &crate::SharedModule)> {
+    ) -> impl Iterator<Item = (&ImmutableString, &SharedModule)> {
         self.imports.iter().zip(self.modules.iter()).rev()
     }
     /// Get an iterator to the stack of globally-imported [modules][crate::Module] in forward order.
@@ -209,9 +211,7 @@ impl GlobalRuntimeState {
     /// Not available under `no_module`.
     #[cfg(not(feature = "no_module"))]
     #[inline]
-    pub fn scan_imports_raw(
-        &self,
-    ) -> impl Iterator<Item = (&ImmutableString, &crate::SharedModule)> {
+    pub fn scan_imports_raw(&self) -> impl Iterator<Item = (&ImmutableString, &SharedModule)> {
         self.imports.iter().zip(self.modules.iter())
     }
     /// Can the particular function with [`Dynamic`] parameter(s) exist in the stack of
@@ -318,37 +318,7 @@ impl GlobalRuntimeState {
 }
 
 #[cfg(not(feature = "no_module"))]
-impl IntoIterator for GlobalRuntimeState {
-    type Item = (ImmutableString, crate::SharedModule);
-    type IntoIter = std::iter::Rev<
-        std::iter::Zip<
-            smallvec::IntoIter<[ImmutableString; crate::STATIC_VEC_INLINE_SIZE]>,
-            smallvec::IntoIter<[crate::SharedModule; crate::STATIC_VEC_INLINE_SIZE]>,
-        >,
-    >;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.imports.into_iter().zip(self.modules.into_iter()).rev()
-    }
-}
-
-#[cfg(not(feature = "no_module"))]
-impl<'a> IntoIterator for &'a GlobalRuntimeState {
-    type Item = (&'a ImmutableString, &'a crate::SharedModule);
-    type IntoIter = std::iter::Rev<
-        std::iter::Zip<
-            std::slice::Iter<'a, ImmutableString>,
-            std::slice::Iter<'a, crate::SharedModule>,
-        >,
-    >;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.imports.iter().zip(self.modules.iter()).rev()
-    }
-}
-
-#[cfg(not(feature = "no_module"))]
-impl<K: Into<ImmutableString>, M: Into<crate::SharedModule>> Extend<(K, M)> for GlobalRuntimeState {
+impl<K: Into<ImmutableString>, M: Into<SharedModule>> Extend<(K, M)> for GlobalRuntimeState {
     #[inline]
     fn extend<T: IntoIterator<Item = (K, M)>>(&mut self, iter: T) {
         for (k, m) in iter {
@@ -365,22 +335,31 @@ impl fmt::Debug for GlobalRuntimeState {
         let mut f = f.debug_struct("GlobalRuntimeState");
 
         #[cfg(not(feature = "no_module"))]
-        f.field("imports", &self.scan_imports_raw().collect::<Vec<_>>());
+        f.field("imports", &self.scan_imports_raw().collect::<Vec<_>>())
+            .field("num_modules_loaded", &self.num_modules_loaded)
+            .field("embedded_module_resolver", &self.embedded_module_resolver);
+
+        #[cfg(not(feature = "no_function"))]
+        f.field("lib", &self.lib);
 
         f.field("source", &self.source)
-            .field("num_operations", &self.num_operations);
+            .field("num_operations", &self.num_operations)
+            .field("level", &self.level)
+            .field("scope_level", &self.scope_level)
+            .field("always_search_scope", &self.always_search_scope);
 
         #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
         f.field("fn_hash_indexing", &self.fn_hash_indexing);
 
-        #[cfg(not(feature = "no_module"))]
-        f.field("num_modules_loaded", &self.num_modules_loaded)
-            .field("embedded_module_resolver", &self.embedded_module_resolver);
-
         #[cfg(not(feature = "no_module"))]
         #[cfg(not(feature = "no_function"))]
         f.field("constants", &self.constants);
 
+        f.field("tag", &self.tag);
+
+        #[cfg(feature = "debugging")]
+        f.field("debugger", &self.debugger);
+
         f.finish()
     }
 }
diff --git a/src/eval/stmt.rs b/src/eval/stmt.rs
index 9a086ed9..ae5a7890 100644
--- a/src/eval/stmt.rs
+++ b/src/eval/stmt.rs
@@ -6,9 +6,11 @@ use crate::ast::{
     ASTFlags, BinaryExpr, Expr, Ident, OpAssignment, Stmt, SwitchCasesCollection, TryCatchBlock,
 };
 use crate::func::{get_builtin_op_assignment_fn, get_hasher};
-use crate::types::dynamic::{AccessMode, Union};
+use crate::types::dynamic::AccessMode;
 use crate::types::RestoreOnDrop;
-use crate::{Dynamic, Engine, Position, RhaiResult, RhaiResultOf, Scope, SharedModule, ERR, INT};
+use crate::{
+    Dynamic, Engine, ImmutableString, Position, RhaiResult, RhaiResultOf, Scope, ERR, INT,
+};
 use std::hash::{Hash, Hasher};
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -26,7 +28,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         statements: &[Stmt],
@@ -73,15 +74,8 @@ impl Engine {
             #[cfg(not(feature = "no_module"))]
             let imports_len = global.num_imports();
 
-            let result = self.eval_stmt(
-                global,
-                caches,
-                lib,
-                scope,
-                this_ptr,
-                stmt,
-                restore_orig_state,
-            )?;
+            let result =
+                self.eval_stmt(global, caches, scope, this_ptr, stmt, restore_orig_state)?;
 
             #[cfg(not(feature = "no_module"))]
             if matches!(stmt, Stmt::Import(..)) {
@@ -117,7 +111,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         op_info: &OpAssignment,
         target: &mut Target,
         root: (&str, Position),
@@ -148,10 +141,11 @@ impl Engine {
                     // Built-in found
                     let op = op_assign_token.literal_syntax();
 
+                    let orig_level = global.level;
                     global.level += 1;
-                    let global = &*RestoreOnDrop::lock(global, move |g| g.level -= 1);
+                    let global = &*RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
-                    let context = (self, op, None, global, lib, *op_pos).into();
+                    let context = (self, op, None, global, *op_pos).into();
                     return func(context, args).map(|_| ());
                 }
             }
@@ -160,9 +154,9 @@ impl Engine {
             let op = op_token.literal_syntax();
             let token = Some(op_assign_token);
 
-            match self.exec_native_fn_call(
-                global, caches, lib, op_assign, token, hash, args, true, *op_pos,
-            ) {
+            match self
+                .exec_native_fn_call(global, caches, op_assign, token, hash, args, true, *op_pos)
+            {
                 Ok(_) => (),
                 Err(err) if matches!(*err, ERR::ErrorFunctionNotFound(ref f, ..) if f.starts_with(op_assign)) =>
                 {
@@ -171,11 +165,10 @@ impl Engine {
 
                     *args[0] = self
                         .exec_native_fn_call(
-                            global, caches, lib, op, token, *hash_op, args, true, *op_pos,
+                            global, caches, op, token, *hash_op, args, true, *op_pos,
                         )
                         .map_err(|err| err.fill_position(op_info.pos))?
-                        .0
-                        .flatten();
+                        .0;
                 }
                 Err(err) => return Err(err),
             }
@@ -183,6 +176,13 @@ impl Engine {
             self.check_data_size(args[0], root.1)?;
         } else {
             // Normal assignment
+
+            // If value is a string, intern it
+            if new_val.is_string() {
+                let value = new_val.into_immutable_string().expect("`ImmutableString`");
+                new_val = self.get_interned_string(value).into();
+            }
+
             *target.write_lock::<Dynamic>().unwrap() = new_val;
         }
 
@@ -201,14 +201,13 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         stmt: &Stmt,
         rewind_scope: bool,
     ) -> RhaiResult {
         #[cfg(feature = "debugging")]
-        let reset = self.run_debugger_with_reset(global, caches, lib, scope, this_ptr, stmt)?;
+        let reset = self.run_debugger_with_reset(global, caches, scope, this_ptr, stmt)?;
         #[cfg(feature = "debugging")]
         let global = &mut *RestoreOnDrop::lock(global, move |g| g.debugger.reset_status(reset));
 
@@ -219,7 +218,7 @@ impl Engine {
         if let Stmt::FnCall(x, pos) = stmt {
             self.track_operation(global, stmt.position())?;
 
-            return self.eval_fn_call_expr(global, caches, lib, scope, this_ptr, x, *pos);
+            return self.eval_fn_call_expr(global, caches, scope, this_ptr, x, *pos);
         }
 
         // Then assignments.
@@ -232,11 +231,11 @@ impl Engine {
 
             if let Expr::Variable(x, ..) = lhs {
                 let rhs_val = self
-                    .eval_expr(global, caches, lib, scope, this_ptr, rhs)?
+                    .eval_expr(global, caches, scope, this_ptr, rhs)?
                     .flatten();
 
                 let (mut lhs_ptr, pos) =
-                    self.search_namespace(global, caches, lib, scope, this_ptr, lhs)?;
+                    self.search_namespace(global, caches, scope, this_ptr, lhs)?;
 
                 let var_name = x.3.as_str();
 
@@ -257,49 +256,45 @@ impl Engine {
                 let root = (var_name, pos);
                 let lhs_ptr = &mut lhs_ptr;
 
-                return self
-                    .eval_op_assignment(global, caches, lib, op_info, lhs_ptr, root, rhs_val)
-                    .map(|_| Dynamic::UNIT);
+                self.eval_op_assignment(global, caches, op_info, lhs_ptr, root, rhs_val)?;
+
+                return Ok(Dynamic::UNIT);
             }
 
             #[cfg(any(not(feature = "no_index"), not(feature = "no_object")))]
             {
-                let rhs_val = self.eval_expr(global, caches, lib, scope, this_ptr, rhs)?;
+                let mut rhs_val = self
+                    .eval_expr(global, caches, scope, this_ptr, rhs)?
+                    .flatten();
 
-                // Check if the result is a string. If so, intern it.
-                #[cfg(not(feature = "no_closure"))]
-                let is_string = !rhs_val.is_shared() && rhs_val.is::<crate::ImmutableString>();
-                #[cfg(feature = "no_closure")]
-                let is_string = rhs_val.is::<crate::ImmutableString>();
-
-                let rhs_val = if is_string {
-                    self.get_interned_string(
-                        rhs_val.into_immutable_string().expect("`ImmutableString`"),
-                    )
-                    .into()
-                } else {
-                    rhs_val.flatten()
-                };
+                // If value is a string, intern it
+                if rhs_val.is_string() {
+                    let value = rhs_val.into_immutable_string().expect("`ImmutableString`");
+                    rhs_val = self.get_interned_string(value).into();
+                }
 
                 let _new_val = &mut Some((rhs_val, op_info));
 
                 // Must be either `var[index] op= val` or `var.prop op= val`
-                return match lhs {
+                match lhs {
                     // name op= rhs (handled above)
                     Expr::Variable(..) => {
                         unreachable!("Expr::Variable case is already handled")
                     }
                     // idx_lhs[idx_expr] op= rhs
                     #[cfg(not(feature = "no_index"))]
-                    Expr::Index(..) => self
-                        .eval_dot_index_chain(global, caches, lib, scope, this_ptr, lhs, _new_val),
+                    Expr::Index(..) => {
+                        self.eval_dot_index_chain(global, caches, scope, this_ptr, lhs, _new_val)
+                    }
                     // dot_lhs.dot_rhs op= rhs
                     #[cfg(not(feature = "no_object"))]
-                    Expr::Dot(..) => self
-                        .eval_dot_index_chain(global, caches, lib, scope, this_ptr, lhs, _new_val),
+                    Expr::Dot(..) => {
+                        self.eval_dot_index_chain(global, caches, scope, this_ptr, lhs, _new_val)
+                    }
                     _ => unreachable!("cannot assign to expression: {:?}", lhs),
-                }
-                .map(|_| Dynamic::UNIT);
+                }?;
+
+                return Ok(Dynamic::UNIT);
             }
         }
 
@@ -311,13 +306,13 @@ impl Engine {
 
             // Expression as statement
             Stmt::Expr(expr) => self
-                .eval_expr(global, caches, lib, scope, this_ptr, expr)
+                .eval_expr(global, caches, scope, this_ptr, expr)
                 .map(Dynamic::flatten),
 
             // Block scope
             Stmt::Block(statements, ..) if statements.is_empty() => Ok(Dynamic::UNIT),
             Stmt::Block(statements, ..) => {
-                self.eval_stmt_block(global, caches, lib, scope, this_ptr, statements, true)
+                self.eval_stmt_block(global, caches, scope, this_ptr, statements, true)
             }
 
             // If statement
@@ -325,14 +320,14 @@ impl Engine {
                 let (expr, if_block, else_block) = &**x;
 
                 let guard_val = self
-                    .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                    .eval_expr(global, caches, scope, this_ptr, expr)?
                     .as_bool()
                     .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, expr.position()))?;
 
                 if guard_val && !if_block.is_empty() {
-                    self.eval_stmt_block(global, caches, lib, scope, this_ptr, if_block, true)
+                    self.eval_stmt_block(global, caches, scope, this_ptr, if_block, true)
                 } else if !guard_val && !else_block.is_empty() {
-                    self.eval_stmt_block(global, caches, lib, scope, this_ptr, else_block, true)
+                    self.eval_stmt_block(global, caches, scope, this_ptr, else_block, true)
                 } else {
                     Ok(Dynamic::UNIT)
                 }
@@ -352,7 +347,7 @@ impl Engine {
 
                 let mut result = None;
 
-                let value = self.eval_expr(global, caches, lib, scope, this_ptr, expr)?;
+                let value = self.eval_expr(global, caches, scope, this_ptr, expr)?;
 
                 if value.is_hashable() {
                     let hasher = &mut get_hasher();
@@ -369,7 +364,7 @@ impl Engine {
                             let cond_result = match block.condition {
                                 Expr::BoolConstant(b, ..) => b,
                                 ref c => self
-                                    .eval_expr(global, caches, lib, scope, this_ptr, c)?
+                                    .eval_expr(global, caches, scope, this_ptr, c)?
                                     .as_bool()
                                     .map_err(|typ| {
                                         self.make_type_mismatch_err::<bool>(typ, c.position())
@@ -381,7 +376,7 @@ impl Engine {
                                 break;
                             }
                         }
-                    } else if value.is::<INT>() && !ranges.is_empty() {
+                    } else if value.is_int() && !ranges.is_empty() {
                         // Then check integer ranges
                         let value = value.as_int().expect("`INT`");
 
@@ -391,7 +386,7 @@ impl Engine {
                             let cond_result = match block.condition {
                                 Expr::BoolConstant(b, ..) => b,
                                 ref c => self
-                                    .eval_expr(global, caches, lib, scope, this_ptr, c)?
+                                    .eval_expr(global, caches, scope, this_ptr, c)?
                                     .as_bool()
                                     .map_err(|typ| {
                                         self.make_type_mismatch_err::<bool>(typ, c.position())
@@ -409,7 +404,7 @@ impl Engine {
                 result
                     .or_else(|| def_case.as_ref().map(|&index| &expressions[index].expr))
                     .map_or(Ok(Dynamic::UNIT), |expr| {
-                        self.eval_expr(global, caches, lib, scope, this_ptr, expr)
+                        self.eval_expr(global, caches, scope, this_ptr, expr)
                     })
             }
 
@@ -425,7 +420,7 @@ impl Engine {
 
                 loop {
                     if let Err(err) =
-                        self.eval_stmt_block(global, caches, lib, scope, this_ptr, body, true)
+                        self.eval_stmt_block(global, caches, scope, this_ptr, body, true)
                     {
                         match *err {
                             ERR::LoopBreak(false, ..) => (),
@@ -442,7 +437,7 @@ impl Engine {
 
                 loop {
                     let condition = self
-                        .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                        .eval_expr(global, caches, scope, this_ptr, expr)?
                         .as_bool()
                         .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, expr.position()))?;
 
@@ -455,7 +450,7 @@ impl Engine {
                     }
 
                     if let Err(err) =
-                        self.eval_stmt_block(global, caches, lib, scope, this_ptr, body, true)
+                        self.eval_stmt_block(global, caches, scope, this_ptr, body, true)
                     {
                         match *err {
                             ERR::LoopBreak(false, ..) => (),
@@ -474,7 +469,7 @@ impl Engine {
                 loop {
                     if !body.is_empty() {
                         if let Err(err) =
-                            self.eval_stmt_block(global, caches, lib, scope, this_ptr, body, true)
+                            self.eval_stmt_block(global, caches, scope, this_ptr, body, true)
                         {
                             match *err {
                                 ERR::LoopBreak(false, ..) => continue,
@@ -485,7 +480,7 @@ impl Engine {
                     }
 
                     let condition = self
-                        .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                        .eval_expr(global, caches, scope, this_ptr, expr)?
                         .as_bool()
                         .map_err(|typ| self.make_type_mismatch_err::<bool>(typ, expr.position()))?;
 
@@ -500,7 +495,7 @@ impl Engine {
                 let (var_name, counter, expr, statements) = &**x;
 
                 let iter_obj = self
-                    .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                    .eval_expr(global, caches, scope, this_ptr, expr)?
                     .flatten();
 
                 let iter_type = iter_obj.type_id();
@@ -579,9 +574,7 @@ impl Engine {
                         continue;
                     }
 
-                    match self
-                        .eval_stmt_block(global, caches, lib, scope, this_ptr, statements, true)
-                    {
+                    match self.eval_stmt_block(global, caches, scope, this_ptr, statements, true) {
                         Ok(_) => (),
                         Err(err) => match *err {
                             ERR::LoopBreak(false, ..) => (),
@@ -602,7 +595,7 @@ impl Engine {
                 let is_break = options.contains(ASTFlags::BREAK);
 
                 let value = if let Some(ref expr) = expr {
-                    self.eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                    self.eval_expr(global, caches, scope, this_ptr, expr)?
                 } else {
                     Dynamic::UNIT
                 };
@@ -621,7 +614,7 @@ impl Engine {
                     catch_block,
                 } = &**x;
 
-                match self.eval_stmt_block(global, caches, lib, scope, this_ptr, try_block, true) {
+                match self.eval_stmt_block(global, caches, scope, this_ptr, try_block, true) {
                     r @ Ok(_) => r,
                     Err(err) if err.is_pseudo_error() => Err(err),
                     Err(err) if !err.is_catchable() => Err(err),
@@ -672,31 +665,23 @@ impl Engine {
                             scope.push(catch_var.clone(), err_value);
                         }
 
-                        self.eval_stmt_block(
-                            global,
-                            caches,
-                            lib,
-                            scope,
-                            this_ptr,
-                            catch_block,
-                            true,
-                        )
-                        .map(|_| Dynamic::UNIT)
-                        .map_err(|result_err| match *result_err {
-                            // Re-throw exception
-                            ERR::ErrorRuntime(Dynamic(Union::Unit(..)), pos) => {
-                                err.set_position(pos);
-                                err
-                            }
-                            _ => result_err,
-                        })
+                        self.eval_stmt_block(global, caches, scope, this_ptr, catch_block, true)
+                            .map(|_| Dynamic::UNIT)
+                            .map_err(|result_err| match *result_err {
+                                // Re-throw exception
+                                ERR::ErrorRuntime(v, pos) if v.is_unit() => {
+                                    err.set_position(pos);
+                                    err
+                                }
+                                _ => result_err,
+                            })
                     }
                 }
             }
 
             // Throw value
             Stmt::Return(Some(expr), options, pos) if options.contains(ASTFlags::BREAK) => self
-                .eval_expr(global, caches, lib, scope, this_ptr, expr)
+                .eval_expr(global, caches, scope, this_ptr, expr)
                 .and_then(|v| Err(ERR::ErrorRuntime(v.flatten(), *pos).into())),
 
             // Empty throw
@@ -706,7 +691,7 @@ impl Engine {
 
             // Return value
             Stmt::Return(Some(expr), .., pos) => self
-                .eval_expr(global, caches, lib, scope, this_ptr, expr)
+                .eval_expr(global, caches, scope, this_ptr, expr)
                 .and_then(|v| Err(ERR::Return(v.flatten(), *pos).into())),
 
             // Empty return
@@ -737,7 +722,7 @@ impl Engine {
                         nesting_level: global.scope_level,
                         will_shadow,
                     };
-                    let context = EvalContext::new(self, global, caches, lib, scope, this_ptr);
+                    let context = EvalContext::new(self, global, caches, scope, this_ptr);
 
                     if !filter(true, info, context)? {
                         return Err(ERR::ErrorForbiddenVariable(var_name.to_string(), *pos).into());
@@ -746,7 +731,7 @@ impl Engine {
 
                 // Evaluate initial value
                 let mut value = self
-                    .eval_expr(global, caches, lib, scope, this_ptr, expr)?
+                    .eval_expr(global, caches, scope, this_ptr, expr)?
                     .flatten();
 
                 let _alias = if !rewind_scope {
@@ -755,7 +740,7 @@ impl Engine {
                     #[cfg(not(feature = "no_module"))]
                     if global.scope_level == 0
                         && access == AccessMode::ReadOnly
-                        && lib.iter().any(|m| !m.is_empty())
+                        && global.lib.iter().any(|m| !m.is_empty())
                     {
                         crate::func::locked_write(global.constants.get_or_insert_with(|| {
                             crate::Shared::new(
@@ -801,10 +786,10 @@ impl Engine {
                     return Err(ERR::ErrorTooManyModules(*_pos).into());
                 }
 
-                let v = self.eval_expr(global, caches, lib, scope, this_ptr, expr)?;
+                let v = self.eval_expr(global, caches, scope, this_ptr, expr)?;
                 let typ = v.type_name();
-                let path = v.try_cast::<crate::ImmutableString>().ok_or_else(|| {
-                    self.make_type_mismatch_err::<crate::ImmutableString>(typ, expr.position())
+                let path = v.try_cast::<ImmutableString>().ok_or_else(|| {
+                    self.make_type_mismatch_err::<ImmutableString>(typ, expr.position())
                 })?;
 
                 use crate::ModuleResolver;
@@ -832,7 +817,7 @@ impl Engine {
                 let (export, must_be_indexed) = if !export.is_empty() {
                     (export.name.clone(), true)
                 } else {
-                    (self.get_interned_string(""), false)
+                    (self.const_empty_string(), false)
                 };
 
                 if !must_be_indexed || module.is_indexed() {
@@ -897,13 +882,12 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         statements: &[Stmt],
     ) -> RhaiResult {
         let mut this = Dynamic::NULL;
 
-        self.eval_stmt_block(global, caches, lib, scope, &mut this, statements, false)
+        self.eval_stmt_block(global, caches, scope, &mut this, statements, false)
             .or_else(|err| match *err {
                 ERR::Return(out, ..) => Ok(out),
                 ERR::LoopBreak(..) => {
diff --git a/src/eval/target.rs b/src/eval/target.rs
index c48aa62a..64bfe3b3 100644
--- a/src/eval/target.rs
+++ b/src/eval/target.rs
@@ -9,11 +9,11 @@ use std::{
     ops::{Deref, DerefMut},
 };
 
-// Calculate an offset+len pair given an actual length of the underlying array.
-//
-// Negative starting positions count from the end.
-//
-// Values going over bounds are limited to the actual length.
+/// Calculate an offset+len pair given an actual length of the underlying array.
+///
+/// Negative starting positions count from the end.
+///
+/// Values going over bounds are limited to the actual length.
 #[inline]
 #[allow(dead_code)]
 pub fn calc_offset_len(length: usize, start: crate::INT, len: crate::INT) -> (usize, usize) {
@@ -41,11 +41,11 @@ pub fn calc_offset_len(length: usize, start: crate::INT, len: crate::INT) -> (us
     (start, len)
 }
 
-// Calculate an offset+len pair given an actual length of the underlying array.
-//
-// Negative starting positions count from the end.
-//
-// Values going over bounds call the provided closure to return a default value or an error.
+/// Calculate an offset+len pair given an actual length of the underlying array.
+///
+/// Negative starting positions count from the end.
+///
+/// Values going over bounds call the provided closure to return a default value or an error.
 #[inline]
 #[allow(dead_code)]
 pub fn calc_index<E>(
diff --git a/src/func/builtin.rs b/src/func/builtin.rs
index 8ff37e67..b6461191 100644
--- a/src/func/builtin.rs
+++ b/src/func/builtin.rs
@@ -690,7 +690,7 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
                 PlusAssign => Some(|_ctx, args| {
                     let (first, second) = args.split_first_mut().expect(BUILTIN);
                     let x = &mut *first.write_lock::<ImmutableString>().expect(BUILTIN);
-                    let y = std::mem::take(second[0]).cast::<ImmutableString>();
+                    let y = &*second[0].read_lock::<ImmutableString>().expect(BUILTIN);
 
                     #[cfg(not(feature = "unchecked"))]
                     if !x.is_empty() && !y.is_empty() {
@@ -704,7 +704,7 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
                 MinusAssign => Some(|_, args| {
                     let (first, second) = args.split_first_mut().expect(BUILTIN);
                     let x = &mut *first.write_lock::<ImmutableString>().expect(BUILTIN);
-                    let y = std::mem::take(second[0]).cast::<ImmutableString>();
+                    let y = &*second[0].read_lock::<ImmutableString>().expect(BUILTIN);
                     Ok((*x -= y).into())
                 }),
                 _ => None,
@@ -718,7 +718,7 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
 
             return match op {
                 PlusAssign => Some(|_ctx, args| {
-                    let x = std::mem::take(args[1]).cast::<Array>();
+                    let x = std::mem::take(args[1]).into_array().expect(BUILTIN);
 
                     if x.is_empty() {
                         return Ok(Dynamic::UNIT);
@@ -749,7 +749,7 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
 
             return match op {
                 PlusAssign => Some(|_ctx, args| {
-                    let blob2 = std::mem::take(args[1]).cast::<Blob>();
+                    let blob2 = std::mem::take(args[1]).into_blob().expect(BUILTIN);
                     let blob1 = &mut *args[0].write_lock::<Blob>().expect(BUILTIN);
 
                     #[cfg(not(feature = "unchecked"))]
@@ -951,14 +951,14 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
 
             return match op {
                 PlusAssign => Some(|_ctx, args| {
-                    let s = std::mem::take(args[1]).cast::<ImmutableString>();
+                    let (first, second) = args.split_first_mut().expect(BUILTIN);
+                    let blob = &mut *first.write_lock::<Blob>().expect(BUILTIN);
+                    let s = &*second[0].read_lock::<ImmutableString>().expect(BUILTIN);
 
                     if s.is_empty() {
                         return Ok(Dynamic::UNIT);
                     }
 
-                    let blob = &mut *args[0].write_lock::<Blob>().expect(BUILTIN);
-
                     #[cfg(not(feature = "unchecked"))]
                     _ctx.engine().raise_err_if_over_data_size_limit((
                         blob.len() + s.len(),
@@ -966,7 +966,7 @@ pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Opt
                         0,
                     ))?;
 
-                    Ok(append_str(blob, &s).into())
+                    Ok(append_str(blob, s).into())
                 }),
                 _ => None,
             };
diff --git a/src/func/call.rs b/src/func/call.rs
index 38020404..4dcc7ced 100644
--- a/src/func/call.rs
+++ b/src/func/call.rs
@@ -12,7 +12,7 @@ use crate::tokenizer::{is_valid_function_name, Token};
 use crate::types::RestoreOnDrop;
 use crate::{
     calc_fn_hash, calc_fn_hash_full, Dynamic, Engine, FnArgsVec, FnPtr, ImmutableString,
-    OptimizationLevel, Position, RhaiError, RhaiResult, RhaiResultOf, Scope, SharedModule, ERR,
+    OptimizationLevel, Position, RhaiError, RhaiResult, RhaiResultOf, Scope, ERR,
 };
 #[cfg(feature = "no_std")]
 use hashbrown::hash_map::Entry;
@@ -145,7 +145,7 @@ impl Engine {
         format!(
             "{fn_name} ({})",
             args.iter()
-                .map(|a| if a.is::<ImmutableString>() {
+                .map(|a| if a.is_string() {
                     "&str | ImmutableString | String"
                 } else {
                     self.map_type_name(a.type_name())
@@ -166,10 +166,9 @@ impl Engine {
     #[must_use]
     fn resolve_fn<'s>(
         &self,
-        _global: &GlobalRuntimeState,
+        global: &GlobalRuntimeState,
         caches: &'s mut Caches,
         local_entry: &'s mut Option<FnResolutionCacheEntry>,
-        lib: &[SharedModule],
         op_token: Option<&Token>,
         hash_base: u64,
         args: Option<&mut FnCallArgs>,
@@ -194,17 +193,28 @@ impl Engine {
                 let mut bitmask = 1usize; // Bitmask of which parameter to replace with `Dynamic`
 
                 loop {
-                    let func = lib
+                    #[cfg(not(feature = "no_function"))]
+                    let func = global
+                        .lib
                         .iter()
+                        .rev()
                         .chain(self.global_modules.iter())
                         .find_map(|m| m.get_fn(hash).map(|f| (f, m.id_raw())));
+                    #[cfg(feature = "no_function")]
+                    let func = None;
+
+                    let func = func.or_else(|| {
+                        self.global_modules
+                            .iter()
+                            .find_map(|m| m.get_fn(hash).map(|f| (f, m.id_raw())))
+                    });
 
                     #[cfg(not(feature = "no_module"))]
                     let func = if args.is_none() {
                         // Scripted functions are not exposed globally
                         func
                     } else {
-                        func.or_else(|| _global.get_qualified_fn(hash)).or_else(|| {
+                        func.or_else(|| global.get_qualified_fn(hash)).or_else(|| {
                             self.global_sub_modules
                                 .values()
                                 .find_map(|m| m.get_qualified_fn(hash).map(|f| (f, m.id_raw())))
@@ -229,15 +239,21 @@ impl Engine {
 
                     // Check `Dynamic` parameters for functions with parameters
                     if allow_dynamic && max_bitmask == 0 && num_args > 0 {
-                        let is_dynamic = lib.iter().any(|m| m.may_contain_dynamic_fn(hash_base))
-                            || self
-                                .global_modules
+                        let is_dynamic = self
+                            .global_modules
+                            .iter()
+                            .any(|m| m.may_contain_dynamic_fn(hash_base));
+
+                        #[cfg(not(feature = "no_function"))]
+                        let is_dynamic = is_dynamic
+                            || global
+                                .lib
                                 .iter()
                                 .any(|m| m.may_contain_dynamic_fn(hash_base));
 
                         #[cfg(not(feature = "no_module"))]
                         let is_dynamic = is_dynamic
-                            || _global.may_contain_dynamic_fn(hash_base)
+                            || global.may_contain_dynamic_fn(hash_base)
                             || self
                                 .global_sub_modules
                                 .values()
@@ -325,7 +341,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         name: &str,
         op_token: Option<&Token>,
         hash: u64,
@@ -342,7 +357,6 @@ impl Engine {
             global,
             caches,
             local_entry,
-            lib,
             op_token,
             hash,
             Some(args),
@@ -384,7 +398,7 @@ impl Engine {
 
             // Run external function
             let src = source.as_ref().map(|s| s.as_str());
-            let context = (self, name, src, &*global, lib, pos).into();
+            let context = (self, name, src, &*global, pos).into();
 
             let mut _result = if func.is_plugin_fn() {
                 let f = func.get_plugin_fn().unwrap();
@@ -415,7 +429,7 @@ impl Engine {
                     };
 
                     if let Err(err) =
-                        self.run_debugger_raw(global, caches, lib, scope, &mut this, node, event)
+                        self.run_debugger_raw(global, caches, scope, &mut this, node, event)
                     {
                         _result = Err(err);
                     }
@@ -537,12 +551,11 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         _scope: Option<&mut Scope>,
         fn_name: &str,
         op_token: Option<&Token>,
         hashes: FnCallHashes,
-        mut args: &mut FnCallArgs,
+        mut _args: &mut FnCallArgs,
         is_ref_mut: bool,
         _is_method_call: bool,
         pos: Position,
@@ -557,27 +570,28 @@ impl Engine {
 
         // Check for data race.
         #[cfg(not(feature = "no_closure"))]
-        ensure_no_data_race(fn_name, args, is_ref_mut)?;
+        ensure_no_data_race(fn_name, _args, is_ref_mut)?;
 
+        let orig_level = global.level;
         global.level += 1;
-        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level -= 1);
+        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
         // These may be redirected from method style calls.
         if hashes.is_native_only() {
             match fn_name {
                 // Handle type_of()
-                KEYWORD_TYPE_OF if args.len() == 1 => {
-                    let typ = self.map_type_name(args[0].type_name()).to_string().into();
+                KEYWORD_TYPE_OF if _args.len() == 1 => {
+                    let typ = self.map_type_name(_args[0].type_name()).to_string().into();
                     return Ok((typ, false));
                 }
 
                 // Handle is_def_fn()
                 #[cfg(not(feature = "no_function"))]
                 crate::engine::KEYWORD_IS_DEF_FN
-                    if args.len() == 2 && args[0].is::<FnPtr>() && args[1].is::<crate::INT>() =>
+                    if _args.len() == 2 && _args[0].is_fnptr() && _args[1].is_int() =>
                 {
-                    let fn_name = args[0].read_lock::<ImmutableString>().expect("`FnPtr`");
-                    let num_params = args[1].as_int().expect("`INT`");
+                    let fn_name = _args[0].read_lock::<ImmutableString>().expect("`FnPtr`");
+                    let num_params = _args[1].as_int().expect("`INT`");
 
                     return Ok((
                         if num_params < 0 || num_params > crate::MAX_USIZE_INT {
@@ -585,7 +599,7 @@ impl Engine {
                         } else {
                             let hash_script =
                                 calc_fn_hash(None, fn_name.as_str(), num_params as usize);
-                            self.has_script_fn(global, caches, lib, hash_script)
+                            self.has_script_fn(global, caches, hash_script)
                         }
                         .into(),
                         false,
@@ -594,15 +608,15 @@ impl Engine {
 
                 // Handle is_shared()
                 #[cfg(not(feature = "no_closure"))]
-                crate::engine::KEYWORD_IS_SHARED if args.len() == 1 => {
+                crate::engine::KEYWORD_IS_SHARED if _args.len() == 1 => {
                     return no_method_err(fn_name, pos)
                 }
 
-                KEYWORD_FN_PTR | KEYWORD_EVAL | KEYWORD_IS_DEF_VAR if args.len() == 1 => {
+                KEYWORD_FN_PTR | KEYWORD_EVAL | KEYWORD_IS_DEF_VAR if _args.len() == 1 => {
                     return no_method_err(fn_name, pos)
                 }
 
-                KEYWORD_FN_PTR_CALL | KEYWORD_FN_PTR_CURRY if !args.is_empty() => {
+                KEYWORD_FN_PTR_CALL | KEYWORD_FN_PTR_CURRY if !_args.is_empty() => {
                     return no_method_err(fn_name, pos)
                 }
 
@@ -617,7 +631,7 @@ impl Engine {
             let local_entry = &mut None;
 
             if let Some(FnResolutionCacheEntry { func, ref source }) = self
-                .resolve_fn(global, caches, local_entry, lib, None, hash, None, false)
+                .resolve_fn(global, caches, local_entry, None, hash, None, false)
                 .cloned()
             {
                 // Script function call
@@ -643,31 +657,29 @@ impl Engine {
 
                 return if _is_method_call {
                     // Method call of script function - map first argument to `this`
-                    let (first_arg, rest_args) = args.split_first_mut().unwrap();
+                    let (first_arg, rest_args) = _args.split_first_mut().unwrap();
 
                     self.call_script_fn(
-                        global, caches, lib, scope, first_arg, func, rest_args, true, pos,
+                        global, caches, scope, first_arg, func, rest_args, true, pos,
                     )
                 } else {
                     // Normal call of script function
                     let backup = &mut ArgBackup::new();
 
                     // The first argument is a reference?
-                    let swap = is_ref_mut && !args.is_empty();
+                    let swap = is_ref_mut && !_args.is_empty();
 
                     if swap {
-                        backup.change_first_arg_to_copy(args);
+                        backup.change_first_arg_to_copy(_args);
                     }
 
-                    let args = &mut *RestoreOnDrop::lock_if(swap, &mut args, move |a| {
+                    let args = &mut *RestoreOnDrop::lock_if(swap, &mut _args, move |a| {
                         backup.restore_first_arg(a)
                     });
 
                     let mut this = Dynamic::NULL;
 
-                    self.call_script_fn(
-                        global, caches, lib, scope, &mut this, func, args, true, pos,
-                    )
+                    self.call_script_fn(global, caches, scope, &mut this, func, args, true, pos)
                 }
                 .map(|r| (r, false));
             }
@@ -677,7 +689,7 @@ impl Engine {
         let hash = hashes.native();
 
         self.exec_native_fn_call(
-            global, caches, lib, fn_name, op_token, hash, args, is_ref_mut, pos,
+            global, caches, fn_name, op_token, hash, _args, is_ref_mut, pos,
         )
     }
 
@@ -687,7 +699,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         arg_expr: &Expr,
@@ -697,7 +708,7 @@ impl Engine {
             self.track_operation(global, arg_expr.start_position())?;
 
             #[cfg(feature = "debugging")]
-            self.run_debugger(global, caches, lib, scope, this_ptr, arg_expr)?;
+            self.run_debugger(global, caches, scope, this_ptr, arg_expr)?;
 
             return Ok((value, arg_expr.start_position()));
         }
@@ -710,7 +721,7 @@ impl Engine {
         #[cfg(feature = "debugging")]
         let global = &mut *RestoreOnDrop::lock(global, move |g| g.debugger.reset_status(reset));
 
-        self.eval_expr(global, caches, lib, scope, this_ptr, arg_expr)
+        self.eval_expr(global, caches, scope, this_ptr, arg_expr)
             .map(|r| (r, arg_expr.start_position()))
     }
 
@@ -720,7 +731,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         fn_name: &str,
         mut hash: FnCallHashes,
         target: &mut crate::eval::Target,
@@ -731,7 +741,7 @@ impl Engine {
         let is_ref_mut = target.is_ref();
 
         let (result, updated) = match fn_name {
-            KEYWORD_FN_PTR_CALL if target.is::<FnPtr>() => {
+            KEYWORD_FN_PTR_CALL if target.is_fnptr() => {
                 // FnPtr call
                 let fn_ptr = target.read_lock::<FnPtr>().expect("`FnPtr`");
 
@@ -760,7 +770,6 @@ impl Engine {
                 self.exec_fn_call(
                     global,
                     caches,
-                    lib,
                     None,
                     fn_name,
                     None,
@@ -775,7 +784,7 @@ impl Engine {
                 if call_args.is_empty() {
                     let typ = self.map_type_name(target.type_name());
                     return Err(self.make_type_mismatch_err::<FnPtr>(typ, fn_call_pos));
-                } else if !call_args[0].is::<FnPtr>() {
+                } else if !call_args[0].is_fnptr() {
                     let typ = self.map_type_name(call_args[0].type_name());
                     return Err(self.make_type_mismatch_err::<FnPtr>(typ, first_arg_pos));
                 }
@@ -815,7 +824,6 @@ impl Engine {
                 self.exec_fn_call(
                     global,
                     caches,
-                    lib,
                     None,
                     &fn_name,
                     None,
@@ -827,7 +835,7 @@ impl Engine {
                 )
             }
             KEYWORD_FN_PTR_CURRY => {
-                if !target.is::<FnPtr>() {
+                if !target.is_fnptr() {
                     let typ = self.map_type_name(target.type_name());
                     return Err(self.make_type_mismatch_err::<FnPtr>(typ, fn_call_pos));
                 }
@@ -915,7 +923,6 @@ impl Engine {
                 self.exec_fn_call(
                     global,
                     caches,
-                    lib,
                     None,
                     fn_name,
                     None,
@@ -941,7 +948,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         fn_name: &str,
@@ -967,9 +973,9 @@ impl Engine {
             KEYWORD_FN_PTR_CALL if total_args >= 1 => {
                 let arg = first_arg.unwrap();
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, arg)?;
+                    self.get_arg_value(global, caches, scope, this_ptr, arg)?;
 
-                if !arg_value.is::<FnPtr>() {
+                if !arg_value.is_fnptr() {
                     let typ = self.map_type_name(arg_value.type_name());
                     return Err(self.make_type_mismatch_err::<FnPtr>(typ, arg_pos));
                 }
@@ -1008,7 +1014,7 @@ impl Engine {
             KEYWORD_FN_PTR if total_args == 1 => {
                 let arg = first_arg.unwrap();
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, arg)?;
+                    self.get_arg_value(global, caches, scope, this_ptr, arg)?;
 
                 // Fn - only in function call style
                 return arg_value
@@ -1023,9 +1029,9 @@ impl Engine {
             KEYWORD_FN_PTR_CURRY if total_args > 1 => {
                 let first = first_arg.unwrap();
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, first)?;
+                    self.get_arg_value(global, caches, scope, this_ptr, first)?;
 
-                if !arg_value.is::<FnPtr>() {
+                if !arg_value.is_fnptr() {
                     let typ = self.map_type_name(arg_value.type_name());
                     return Err(self.make_type_mismatch_err::<FnPtr>(typ, arg_pos));
                 }
@@ -1034,8 +1040,7 @@ impl Engine {
 
                 // Append the new curried arguments to the existing list.
                 let fn_curry = a_expr.iter().try_fold(fn_curry, |mut curried, expr| {
-                    let (value, ..) =
-                        self.get_arg_value(global, caches, lib, scope, this_ptr, expr)?;
+                    let (value, ..) = self.get_arg_value(global, caches, scope, this_ptr, expr)?;
                     curried.push(value);
                     Ok::<_, RhaiError>(curried)
                 })?;
@@ -1047,8 +1052,7 @@ impl Engine {
             #[cfg(not(feature = "no_closure"))]
             crate::engine::KEYWORD_IS_SHARED if total_args == 1 => {
                 let arg = first_arg.unwrap();
-                let (arg_value, ..) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, arg)?;
+                let (arg_value, ..) = self.get_arg_value(global, caches, scope, this_ptr, arg)?;
                 return Ok(arg_value.is_shared().into());
             }
 
@@ -1057,14 +1061,14 @@ impl Engine {
             crate::engine::KEYWORD_IS_DEF_FN if total_args == 2 => {
                 let first = first_arg.unwrap();
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, first)?;
+                    self.get_arg_value(global, caches, scope, this_ptr, first)?;
 
                 let fn_name = arg_value
                     .into_immutable_string()
                     .map_err(|typ| self.make_type_mismatch_err::<ImmutableString>(typ, arg_pos))?;
 
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, &a_expr[0])?;
+                    self.get_arg_value(global, caches, scope, this_ptr, &a_expr[0])?;
 
                 let num_params = arg_value
                     .as_int()
@@ -1074,7 +1078,7 @@ impl Engine {
                     false
                 } else {
                     let hash_script = calc_fn_hash(None, &fn_name, num_params as usize);
-                    self.has_script_fn(global, caches, lib, hash_script)
+                    self.has_script_fn(global, caches, hash_script)
                 }
                 .into());
             }
@@ -1083,7 +1087,7 @@ impl Engine {
             KEYWORD_IS_DEF_VAR if total_args == 1 => {
                 let arg = first_arg.unwrap();
                 let (arg_value, arg_pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, arg)?;
+                    self.get_arg_value(global, caches, scope, this_ptr, arg)?;
                 let var_name = arg_value
                     .into_immutable_string()
                     .map_err(|typ| self.make_type_mismatch_err::<ImmutableString>(typ, arg_pos))?;
@@ -1097,16 +1101,15 @@ impl Engine {
                 #[cfg(not(feature = "no_module"))]
                 let orig_imports_len = global.num_imports();
                 let arg = first_arg.unwrap();
-                let (arg_value, pos) =
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, arg)?;
+                let (arg_value, pos) = self.get_arg_value(global, caches, scope, this_ptr, arg)?;
                 let s = &arg_value
                     .into_immutable_string()
                     .map_err(|typ| self.make_type_mismatch_err::<ImmutableString>(typ, pos))?;
 
+                let orig_level = global.level;
                 global.level += 1;
-                let global = &mut *RestoreOnDrop::lock(global, move |g| g.level -= 1);
 
-                let result = self.eval_script_expr_in_place(global, caches, lib, scope, s, pos);
+                let result = self.eval_script_expr_in_place(global, caches, scope, s, pos);
 
                 // IMPORTANT! If the eval defines new variables in the current scope,
                 //            all variable offsets from this point on will be mis-aligned.
@@ -1118,6 +1121,7 @@ impl Engine {
                 if scope_changed {
                     global.always_search_scope = true;
                 }
+                global.level = orig_level;
 
                 return result.map_err(|err| {
                     ERR::ErrorInFunctionCall(
@@ -1148,7 +1152,7 @@ impl Engine {
                 .copied()
                 .chain(a_expr.iter())
                 .try_for_each(|expr| {
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, expr)
+                    self.get_arg_value(global, caches, scope, this_ptr, expr)
                         .map(|(value, ..)| arg_values.push(value.flatten()))
                 })?;
             args.extend(curry.iter_mut());
@@ -1159,8 +1163,8 @@ impl Engine {
 
             return self
                 .exec_fn_call(
-                    global, caches, lib, scope, name, op_token, hashes, &mut args, is_ref_mut,
-                    false, pos,
+                    global, caches, scope, name, op_token, hashes, &mut args, is_ref_mut, false,
+                    pos,
                 )
                 .map(|(v, ..)| v);
         }
@@ -1176,16 +1180,16 @@ impl Engine {
                 let first_expr = first_arg.unwrap();
 
                 #[cfg(feature = "debugging")]
-                self.run_debugger(global, caches, lib, scope, this_ptr, first_expr)?;
+                self.run_debugger(global, caches, scope, this_ptr, first_expr)?;
 
                 // func(x, ...) -> x.func(...)
                 a_expr.iter().try_for_each(|expr| {
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, expr)
+                    self.get_arg_value(global, caches, scope, this_ptr, expr)
                         .map(|(value, ..)| arg_values.push(value.flatten()))
                 })?;
 
                 let (mut target, _pos) =
-                    self.search_namespace(global, caches, lib, scope, this_ptr, first_expr)?;
+                    self.search_namespace(global, caches, scope, this_ptr, first_expr)?;
 
                 if target.is_read_only() {
                     target = target.into_owned();
@@ -1212,7 +1216,7 @@ impl Engine {
                     .into_iter()
                     .chain(a_expr.iter())
                     .try_for_each(|expr| {
-                        self.get_arg_value(global, caches, lib, scope, this_ptr, expr)
+                        self.get_arg_value(global, caches, scope, this_ptr, expr)
                             .map(|(value, ..)| arg_values.push(value.flatten()))
                     })?;
                 args.extend(curry.iter_mut());
@@ -1222,7 +1226,7 @@ impl Engine {
         }
 
         self.exec_fn_call(
-            global, caches, lib, None, name, op_token, hashes, &mut args, is_ref_mut, false, pos,
+            global, caches, None, name, op_token, hashes, &mut args, is_ref_mut, false, pos,
         )
         .map(|(v, ..)| v)
     }
@@ -1233,7 +1237,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         namespace: &crate::ast::Namespace,
@@ -1254,20 +1257,20 @@ impl Engine {
             // and avoid cloning the value
             if !args_expr.is_empty() && args_expr[0].is_variable_access(true) {
                 #[cfg(feature = "debugging")]
-                self.run_debugger(global, caches, lib, scope, this_ptr, &args_expr[0])?;
+                self.run_debugger(global, caches, scope, this_ptr, &args_expr[0])?;
 
                 // func(x, ...) -> x.func(...)
                 arg_values.push(Dynamic::UNIT);
 
                 args_expr.iter().skip(1).try_for_each(|expr| {
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, expr)
+                    self.get_arg_value(global, caches, scope, this_ptr, expr)
                         .map(|(value, ..)| arg_values.push(value.flatten()))
                 })?;
 
                 // Get target reference to first argument
                 let first_arg = &args_expr[0];
                 let (target, _pos) =
-                    self.search_scope_only(global, caches, lib, scope, this_ptr, first_arg)?;
+                    self.search_scope_only(global, caches, scope, this_ptr, first_arg)?;
 
                 self.track_operation(global, _pos)?;
 
@@ -1290,7 +1293,7 @@ impl Engine {
             } else {
                 // func(..., ...) or func(mod::x, ...)
                 args_expr.iter().try_for_each(|expr| {
-                    self.get_arg_value(global, caches, lib, scope, this_ptr, expr)
+                    self.get_arg_value(global, caches, scope, this_ptr, expr)
                         .map(|(value, ..)| arg_values.push(value.flatten()))
                 })?;
                 args.extend(arg_values.iter_mut());
@@ -1357,8 +1360,9 @@ impl Engine {
             }
         }
 
+        let orig_level = global.level;
         global.level += 1;
-        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level -= 1);
+        let global = &mut *RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
         match func {
             #[cfg(not(feature = "no_function"))]
@@ -1371,12 +1375,12 @@ impl Engine {
                 let global = &mut *RestoreOnDrop::lock(global, move |g| g.source = orig_source);
 
                 self.call_script_fn(
-                    global, caches, lib, new_scope, &mut this, fn_def, &mut args, true, pos,
+                    global, caches, new_scope, &mut this, fn_def, &mut args, true, pos,
                 )
             }
 
             Some(f) if f.is_plugin_fn() => {
-                let context = (self, fn_name, module.id(), &*global, lib, pos).into();
+                let context = (self, fn_name, module.id(), &*global, pos).into();
                 let f = f.get_plugin_fn().expect("plugin function");
                 let result = if !f.is_pure() && !args.is_empty() && args[0].is_read_only() {
                     Err(ERR::ErrorNonPureMethodCallOnConstant(fn_name.to_string(), pos).into())
@@ -1388,7 +1392,7 @@ impl Engine {
 
             Some(f) if f.is_native() => {
                 let func = f.get_native_fn().expect("native function");
-                let context = (self, fn_name, module.id(), &*global, lib, pos).into();
+                let context = (self, fn_name, module.id(), &*global, pos).into();
                 let result = func(context, &mut args);
                 self.check_return_value(result, pos)
             }
@@ -1416,7 +1420,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         script: &str,
         _pos: Position,
@@ -1442,7 +1445,7 @@ impl Engine {
 
         // If new functions are defined within the eval string, it is an error
         #[cfg(not(feature = "no_function"))]
-        if !ast.shared_lib().is_empty() {
+        if ast.has_functions() {
             return Err(crate::PERR::WrongFnDefinition.into());
         }
 
@@ -1452,7 +1455,7 @@ impl Engine {
         }
 
         // Evaluate the AST
-        self.eval_global_statements(global, caches, lib, scope, statements)
+        self.eval_global_statements(global, caches, scope, statements)
     }
 
     /// Evaluate a function call expression.
@@ -1460,7 +1463,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         expr: &FnCallExpr,
@@ -1482,12 +1484,12 @@ impl Engine {
         // Short-circuit native binary operator call if under Fast Operators mode
         if op_token.is_some() && self.fast_operators() && args.len() == 2 {
             let mut lhs = self
-                .get_arg_value(global, caches, lib, scope, this_ptr, &args[0])?
+                .get_arg_value(global, caches, scope, this_ptr, &args[0])?
                 .0
                 .flatten();
 
             let mut rhs = self
-                .get_arg_value(global, caches, lib, scope, this_ptr, &args[1])?
+                .get_arg_value(global, caches, scope, this_ptr, &args[1])?
                 .0
                 .flatten();
 
@@ -1497,16 +1499,17 @@ impl Engine {
                 get_builtin_binary_op_fn(op_token.as_ref().unwrap(), operands[0], operands[1])
             {
                 // Built-in found
+                let orig_level = global.level;
                 global.level += 1;
-                let global = &*RestoreOnDrop::lock(global, move |g| g.level -= 1);
+                let global = &*RestoreOnDrop::lock(global, move |g| g.level = orig_level);
 
-                let context = (self, name.as_str(), None, global, lib, pos).into();
+                let context = (self, name.as_str(), None, global, pos).into();
                 return func(context, operands);
             }
 
             return self
                 .exec_fn_call(
-                    global, caches, lib, None, name, op_token, *hashes, operands, false, false, pos,
+                    global, caches, None, name, op_token, *hashes, operands, false, false, pos,
                 )
                 .map(|(v, ..)| v);
         }
@@ -1517,7 +1520,7 @@ impl Engine {
             let hash = hashes.native();
 
             return self.make_qualified_function_call(
-                global, caches, lib, scope, this_ptr, namespace, name, args, hash, pos,
+                global, caches, scope, this_ptr, namespace, name, args, hash, pos,
             );
         }
 
@@ -1528,8 +1531,8 @@ impl Engine {
         );
 
         self.make_function_call(
-            global, caches, lib, scope, this_ptr, name, op_token, first_arg, args, *hashes,
-            *capture, pos,
+            global, caches, scope, this_ptr, name, op_token, first_arg, args, *hashes, *capture,
+            pos,
         )
     }
 }
diff --git a/src/func/hashing.rs b/src/func/hashing.rs
index 83b2fed1..0f5af48f 100644
--- a/src/func/hashing.rs
+++ b/src/func/hashing.rs
@@ -78,7 +78,7 @@ impl BuildHasher for StraightHasherBuilder {
 #[must_use]
 pub fn get_hasher() -> ahash::AHasher {
     match config::hashing::get_ahash_seed() {
-        Some([seed1, seed2, seed3, seed4]) if seed1 | seed2 | seed3 | seed4 != 0 => {
+        Some([seed1, seed2, seed3, seed4]) if (seed1 | seed2 | seed3 | seed4) != 0 => {
             ahash::RandomState::with_seeds(*seed1, *seed2, *seed3, *seed4).build_hasher()
         }
         _ => ahash::AHasher::default(),
diff --git a/src/func/mod.rs b/src/func/mod.rs
index d5659854..0b31f72b 100644
--- a/src/func/mod.rs
+++ b/src/func/mod.rs
@@ -23,6 +23,7 @@ pub use callable_function::CallableFunction;
 pub use func::Func;
 pub use hashing::{calc_fn_hash, calc_fn_hash_full, calc_var_hash, get_hasher, StraightHashMap};
 #[cfg(feature = "internals")]
+#[allow(deprecated)]
 pub use native::NativeCallContextStore;
 pub use native::{
     locked_read, locked_write, shared_get_mut, shared_make_mut, shared_take, shared_take_or_clone,
diff --git a/src/func/native.rs b/src/func/native.rs
index de74f6c6..fd5f1836 100644
--- a/src/func/native.rs
+++ b/src/func/native.rs
@@ -73,14 +73,17 @@ pub struct NativeCallContext<'a> {
     source: Option<&'a str>,
     /// The current [`GlobalRuntimeState`], if any.
     global: &'a GlobalRuntimeState,
-    /// The current stack of loaded [modules][Module].
-    lib: &'a [SharedModule],
     /// [Position] of the function call.
     pos: Position,
 }
 
 /// _(internals)_ Context of a native Rust function call.
 /// Exported under the `internals` feature only.
+///
+/// # WARNING - Volatile Type
+///
+/// This type is volatile and may change in the future.
+#[deprecated = "This type is NOT deprecated, but it is considered volatile and may change in the future."]
 #[cfg(feature = "internals")]
 #[derive(Debug, Clone)]
 pub struct NativeCallContextStore {
@@ -90,15 +93,19 @@ pub struct NativeCallContextStore {
     pub source: Option<String>,
     /// The current [`GlobalRuntimeState`], if any.
     pub global: GlobalRuntimeState,
-    /// The current stack of loaded [modules][Module].
-    pub lib: StaticVec<SharedModule>,
     /// [Position] of the function call.
     pub pos: Position,
 }
 
 #[cfg(feature = "internals")]
+#[allow(deprecated)]
 impl NativeCallContextStore {
     /// Create a [`NativeCallContext`] from a [`NativeCallContextClone`].
+    ///
+    /// # WARNING - Unstable API
+    ///
+    /// This API is volatile and may change in the future.
+    #[deprecated = "This API is NOT deprecated, but it is considered volatile and may change in the future."]
     #[inline(always)]
     #[must_use]
     pub fn create_context<'a>(&'a self, engine: &'a Engine) -> NativeCallContext<'a> {
@@ -112,7 +119,6 @@ impl<'a>
         &'a str,
         Option<&'a str>,
         &'a GlobalRuntimeState,
-        &'a [SharedModule],
         Position,
     )> for NativeCallContext<'a>
 {
@@ -123,7 +129,6 @@ impl<'a>
             &'a str,
             Option<&'a str>,
             &'a GlobalRuntimeState,
-            &'a [SharedModule],
             Position,
         ),
     ) -> Self {
@@ -132,8 +137,7 @@ impl<'a>
             fn_name: value.1,
             source: value.2,
             global: value.3,
-            lib: value.4,
-            pos: value.5,
+            pos: value.4,
         }
     }
 }
@@ -152,7 +156,6 @@ impl<'a> NativeCallContext<'a> {
         fn_name: &'a str,
         source: Option<&'a str>,
         global: &'a GlobalRuntimeState,
-        lib: &'a [SharedModule],
         pos: Position,
     ) -> Self {
         Self {
@@ -160,37 +163,46 @@ impl<'a> NativeCallContext<'a> {
             fn_name,
             source,
             global,
-            lib,
             pos,
         }
     }
 
     /// _(internals)_ Create a [`NativeCallContext`] from a [`NativeCallContextClone`].
     /// Exported under the `internals` feature only.
+    ///
+    /// # WARNING - Unstable API
+    ///
+    /// This API is volatile and may change in the future.
+    #[deprecated = "This API is NOT deprecated, but it is considered volatile and may change in the future."]
     #[cfg(feature = "internals")]
     #[inline]
     #[must_use]
+    #[allow(deprecated)]
     pub fn from_stored_data(engine: &'a Engine, context: &'a NativeCallContextStore) -> Self {
         Self {
             engine,
             fn_name: &context.fn_name,
             source: context.source.as_ref().map(String::as_str),
             global: &context.global,
-            lib: &context.lib,
             pos: context.pos,
         }
     }
     /// _(internals)_ Store this [`NativeCallContext`] into a [`NativeCallContextClone`].
     /// Exported under the `internals` feature only.
+    ///
+    /// # WARNING - Unstable API
+    ///
+    /// This API is volatile and may change in the future.
+    #[deprecated = "This API is NOT deprecated, but it is considered volatile and may change in the future."]
     #[cfg(feature = "internals")]
     #[inline]
     #[must_use]
+    #[allow(deprecated)]
     pub fn store_data(&self) -> NativeCallContextStore {
         NativeCallContextStore {
             fn_name: self.fn_name.to_string(),
             source: self.source.map(|s| s.to_string()),
             global: self.global.clone(),
-            lib: self.lib.iter().cloned().collect(),
             pos: self.pos,
         }
     }
@@ -261,17 +273,23 @@ impl<'a> NativeCallContext<'a> {
     }
     /// Get an iterator over the namespaces containing definitions of all script-defined functions
     /// in reverse order (i.e. parent namespaces are iterated after child namespaces).
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[inline]
     pub fn iter_namespaces(&self) -> impl Iterator<Item = &Module> {
-        self.lib.iter().map(|m| m.as_ref())
+        self.global.lib.iter().map(|m| m.as_ref())
     }
     /// _(internals)_ The current stack of namespaces containing definitions of all script-defined functions.
     /// Exported under the `internals` feature only.
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[cfg(feature = "internals")]
     #[inline(always)]
     #[must_use]
-    pub const fn namespaces(&self) -> &[SharedModule] {
-        self.lib
+    pub fn namespaces(&self) -> &[SharedModule] {
+        &self.global.lib
     }
     /// Call a function inside the call context with the provided arguments.
     #[inline]
@@ -408,7 +426,6 @@ impl<'a> NativeCallContext<'a> {
                 .exec_native_fn_call(
                     global,
                     caches,
-                    self.lib,
                     fn_name,
                     op_token,
                     calc_fn_hash(None, fn_name, args_len),
@@ -435,7 +452,6 @@ impl<'a> NativeCallContext<'a> {
             .exec_fn_call(
                 global,
                 caches,
-                self.lib,
                 None,
                 fn_name,
                 op_token,
@@ -517,14 +533,14 @@ pub fn locked_write<T>(value: &Locked<T>) -> LockGuardMut<T> {
     return value.write().unwrap();
 }
 
-/// General function trail object.
+/// General Rust function trail object.
 #[cfg(not(feature = "sync"))]
 pub type FnAny = dyn Fn(NativeCallContext, &mut FnCallArgs) -> RhaiResult;
-/// General function trail object.
+/// General Rust function trail object.
 #[cfg(feature = "sync")]
 pub type FnAny = dyn Fn(NativeCallContext, &mut FnCallArgs) -> RhaiResult + Send + Sync;
 
-/// Trail object for built-in functions.
+/// Built-in function trait object.
 pub type FnBuiltin = fn(NativeCallContext, &mut FnCallArgs) -> RhaiResult;
 
 /// Function that gets an iterator from a type.
@@ -535,8 +551,10 @@ pub type IteratorFn = dyn Fn(Dynamic) -> Box<dyn Iterator<Item = RhaiResultOf<Dy
 pub type IteratorFn =
     dyn Fn(Dynamic) -> Box<dyn Iterator<Item = RhaiResultOf<Dynamic>>> + Send + Sync;
 
+/// Plugin function trait object.
 #[cfg(not(feature = "sync"))]
 pub type FnPlugin = dyn PluginFunction;
+/// Plugin function trait object.
 #[cfg(feature = "sync")]
 pub type FnPlugin = dyn PluginFunction + Send + Sync;
 
diff --git a/src/func/script.rs b/src/func/script.rs
index db3fa542..55ba1361 100644
--- a/src/func/script.rs
+++ b/src/func/script.rs
@@ -4,7 +4,7 @@
 use super::call::FnCallArgs;
 use crate::ast::ScriptFnDef;
 use crate::eval::{Caches, GlobalRuntimeState};
-use crate::{Dynamic, Engine, Position, RhaiError, RhaiResult, Scope, SharedModule, ERR};
+use crate::{Dynamic, Engine, Position, RhaiError, RhaiResult, Scope, ERR};
 use std::mem;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -26,7 +26,6 @@ impl Engine {
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         scope: &mut Scope,
         this_ptr: &mut Dynamic,
         fn_def: &ScriptFnDef,
@@ -79,6 +78,7 @@ impl Engine {
         }
 
         let orig_scope_len = scope.len();
+        let orig_lib_len = global.lib.len();
         #[cfg(not(feature = "no_module"))]
         let orig_imports_len = global.num_imports();
 
@@ -106,53 +106,34 @@ impl Engine {
         let orig_fn_resolution_caches_len = caches.fn_resolution_caches_len();
 
         #[cfg(not(feature = "no_module"))]
-        let mut lib_merged = crate::StaticVec::with_capacity(lib.len() + 1);
-
-        #[cfg(not(feature = "no_module"))]
-        let (lib, constants) = if let Some(ref environ) = fn_def.environ {
+        let orig_constants = if let Some(ref environ) = fn_def.environ {
             let crate::ast::EncapsulatedEnviron {
-                lib: fn_lib,
-                imports,
-                constants,
-            } = environ.as_ref();
+                ref lib,
+                ref imports,
+                ref constants,
+            } = **environ;
 
             imports
                 .iter()
                 .cloned()
                 .for_each(|(n, m)| global.push_import(n, m));
 
-            (
-                if fn_lib.is_empty() {
-                    lib
-                } else {
-                    caches.push_fn_resolution_cache();
-                    lib_merged.push(fn_lib.clone());
-                    lib_merged.extend(lib.iter().cloned());
-                    &lib_merged
-                },
-                Some(mem::replace(&mut global.constants, constants.clone())),
-            )
+            global.lib.push(lib.clone());
+
+            Some(mem::replace(&mut global.constants, constants.clone()))
         } else {
-            (lib, None)
+            None
         };
 
         #[cfg(feature = "debugging")]
         {
             let node = crate::ast::Stmt::Noop(fn_def.body.position());
-            self.run_debugger(global, caches, lib, scope, this_ptr, &node)?;
+            self.run_debugger(global, caches, scope, this_ptr, &node)?;
         }
 
         // Evaluate the function
         let mut _result = self
-            .eval_stmt_block(
-                global,
-                caches,
-                lib,
-                scope,
-                this_ptr,
-                &fn_def.body,
-                rewind_scope,
-            )
+            .eval_stmt_block(global, caches, scope, this_ptr, &fn_def.body, rewind_scope)
             .or_else(|err| match *err {
                 // Convert return statement to return value
                 ERR::Return(x, ..) => Ok(x),
@@ -188,7 +169,7 @@ impl Engine {
                     Ok(ref r) => crate::eval::DebuggerEvent::FunctionExitWithValue(r),
                     Err(ref err) => crate::eval::DebuggerEvent::FunctionExitWithError(err),
                 };
-                match self.run_debugger_raw(global, caches, lib, scope, this_ptr, node, event) {
+                match self.run_debugger_raw(global, caches, scope, this_ptr, node, event) {
                     Ok(_) => (),
                     Err(err) => _result = Err(err),
                 }
@@ -205,12 +186,13 @@ impl Engine {
             // Remove arguments only, leaving new variables in the scope
             scope.remove_range(orig_scope_len, args.len());
         }
+        global.lib.truncate(orig_lib_len);
         #[cfg(not(feature = "no_module"))]
         global.truncate_imports(orig_imports_len);
 
         // Restore constants
         #[cfg(not(feature = "no_module"))]
-        if let Some(constants) = constants {
+        if let Some(constants) = orig_constants {
             global.constants = constants;
         }
 
@@ -224,9 +206,8 @@ impl Engine {
     #[must_use]
     pub(crate) fn has_script_fn(
         &self,
-        _global: &GlobalRuntimeState,
+        global: &GlobalRuntimeState,
         caches: &mut Caches,
-        lib: &[SharedModule],
         hash_script: u64,
     ) -> bool {
         let cache = caches.fn_resolution_cache_mut();
@@ -236,14 +217,14 @@ impl Engine {
         }
 
         // First check script-defined functions
-        let result = lib.iter().any(|m| m.contains_fn(hash_script))
+        let result = global.lib.iter().any(|m| m.contains_fn(hash_script))
             // Then check the global namespace and packages
             || self.global_modules.iter().any(|m| m.contains_fn(hash_script));
 
         #[cfg(not(feature = "no_module"))]
         let result = result ||
             // Then check imported modules
-            _global.contains_qualified_fn(hash_script)
+            global.contains_qualified_fn(hash_script)
             // Then check sub-modules
             || self.global_sub_modules.values().any(|m| m.contains_qualified_fn(hash_script));
 
diff --git a/src/lib.rs b/src/lib.rs
index 4fdb59f2..7af804f2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -300,17 +300,19 @@ pub type OptimizationLevel = ();
 pub use types::dynamic::{AccessMode, DynamicReadLock, DynamicWriteLock, Variant};
 
 #[cfg(feature = "internals")]
-pub use tokenizer::{get_next_token, parse_string_literal};
-
-#[cfg(feature = "internals")]
-pub use tokenizer::{
-    is_valid_function_name, is_valid_identifier, InputStream, MultiInputsStream, Span, Token,
-    TokenIterator, TokenizeState, TokenizerControl, TokenizerControlBlock,
-};
+#[cfg(not(feature = "no_float"))]
+pub use types::FloatWrapper;
 
 #[cfg(feature = "internals")]
 pub use types::StringsInterner;
 
+#[cfg(feature = "internals")]
+pub use tokenizer::{
+    get_next_token, is_valid_function_name, is_valid_identifier, parse_string_literal, InputStream,
+    MultiInputsStream, Span, Token, TokenIterator, TokenizeState, TokenizerControl,
+    TokenizerControlBlock,
+};
+
 #[cfg(feature = "internals")]
 pub use parser::ParseState;
 
@@ -334,11 +336,11 @@ pub use ast::Namespace;
 pub use ast::EncapsulatedEnviron;
 
 #[cfg(feature = "internals")]
-#[cfg(not(feature = "no_float"))]
-pub use ast::FloatWrapper;
+pub use eval::{Caches, FnResolutionCache, FnResolutionCacheEntry, GlobalRuntimeState};
 
 #[cfg(feature = "internals")]
-pub use eval::{Caches, FnResolutionCache, FnResolutionCacheEntry, GlobalRuntimeState};
+#[allow(deprecated)]
+pub use func::NativeCallContextStore;
 
 #[cfg(feature = "internals")]
 #[cfg(feature = "metadata")]
diff --git a/src/module/mod.rs b/src/module/mod.rs
index a8676655..91be1a53 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -543,14 +543,13 @@ impl Module {
     #[inline]
     #[must_use]
     pub fn is_empty(&self) -> bool {
-        self.indexed
-            && !self.contains_indexed_global_functions
+        !self.contains_indexed_global_functions
             && self.functions.is_empty()
-            && self.all_functions.as_ref().map_or(true, |m| m.is_empty())
             && self.variables.as_ref().map_or(true, |m| m.is_empty())
-            && self.all_variables.as_ref().map_or(true, |m| m.is_empty())
             && self.modules.as_ref().map_or(true, |m| m.is_empty())
             && self.type_iterators.as_ref().map_or(true, |t| t.is_empty())
+            && self.all_functions.as_ref().map_or(true, |m| m.is_empty())
+            && self.all_variables.as_ref().map_or(true, |m| m.is_empty())
             && self
                 .all_type_iterators
                 .as_ref()
@@ -1980,6 +1979,10 @@ impl Module {
         // Save global state
         let orig_imports_len = global.num_imports();
         let orig_source = global.source.clone();
+
+        #[cfg(not(feature = "no_function"))]
+        let orig_lib_len = global.lib.len();
+
         #[cfg(not(feature = "no_function"))]
         let orig_constants = std::mem::take(&mut global.constants);
 
@@ -2007,7 +2010,12 @@ impl Module {
         // Restore global state
         #[cfg(not(feature = "no_function"))]
         let constants = std::mem::replace(&mut global.constants, orig_constants);
+
         global.truncate_imports(orig_imports_len);
+
+        #[cfg(not(feature = "no_function"))]
+        global.lib.truncate(orig_lib_len);
+
         global.source = orig_source;
 
         result?;
diff --git a/src/optimizer.rs b/src/optimizer.rs
index 9bf57005..d903c836 100644
--- a/src/optimizer.rs
+++ b/src/optimizer.rs
@@ -12,7 +12,7 @@ use crate::tokenizer::Token;
 use crate::types::dynamic::AccessMode;
 use crate::{
     calc_fn_hash, calc_fn_hash_full, Dynamic, Engine, FnPtr, Identifier, ImmutableString, Position,
-    Scope, StaticVec, AST, INT,
+    Scope, StaticVec, AST,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -59,9 +59,6 @@ struct OptimizerState<'a> {
     global: GlobalRuntimeState,
     /// Function resolution caches.
     caches: Caches,
-    /// [Module][crate::Module] containing script-defined functions.
-    #[cfg(not(feature = "no_function"))]
-    lib: &'a [crate::SharedModule],
     /// Optimization level.
     optimization_level: OptimizationLevel,
 }
@@ -74,15 +71,20 @@ impl<'a> OptimizerState<'a> {
         #[cfg(not(feature = "no_function"))] lib: &'a [crate::SharedModule],
         optimization_level: OptimizationLevel,
     ) -> Self {
+        let mut _global = GlobalRuntimeState::new(engine);
+
+        #[cfg(not(feature = "no_function"))]
+        {
+            _global.lib = lib.iter().cloned().collect();
+        }
+
         Self {
             changed: false,
             variables: StaticVec::new_const(),
             propagate_constants: true,
             engine,
-            global: GlobalRuntimeState::new(engine),
+            global: _global,
             caches: Caches::new(),
-            #[cfg(not(feature = "no_function"))]
-            lib,
             optimization_level,
         }
     }
@@ -138,16 +140,10 @@ impl<'a> OptimizerState<'a> {
         op_token: Option<&Token>,
         arg_values: &mut [Dynamic],
     ) -> Dynamic {
-        #[cfg(not(feature = "no_function"))]
-        let lib = self.lib;
-        #[cfg(feature = "no_function")]
-        let lib = &[];
-
         self.engine
             .exec_native_fn_call(
                 &mut self.global,
                 &mut self.caches,
-                lib,
                 fn_name,
                 op_token,
                 calc_fn_hash(None, fn_name, arg_values.len()),
@@ -592,7 +588,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
             }
 
             // Then check ranges
-            if value.is::<INT>() && !ranges.is_empty() {
+            if value.is_int() && !ranges.is_empty() {
                 let value = value.as_int().unwrap();
 
                 // Only one range or all ranges without conditions
@@ -1138,12 +1134,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
                 _ if x.args.len() == 2 && x.op_token.is_some() && (state.engine.fast_operators() || !has_native_fn_override(state.engine, x.hashes.native(), &arg_types)) => {
                     if let Some(result) = get_builtin_binary_op_fn(x.op_token.as_ref().unwrap(), &arg_values[0], &arg_values[1])
                         .and_then(|f| {
-                            #[cfg(not(feature = "no_function"))]
-                            let lib = state.lib;
-                            #[cfg(feature = "no_function")]
-                            let lib = &[][..];
-
-                            let context = (state.engine, x.name.as_str(),None, &state.global, lib, *pos).into();
+                            let context = (state.engine, x.name.as_str(),None, &state.global, *pos).into();
                             let (first, second) = arg_values.split_first_mut().unwrap();
                             (f)(context, &mut [ first, &mut second[0] ]).ok()
                         }) {
@@ -1183,7 +1174,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
         => {
             // First search for script-defined functions (can override built-in)
             #[cfg(not(feature = "no_function"))]
-            let has_script_fn = !x.hashes.is_native_only() && state.lib.iter().find_map(|m| m.get_script_fn(&x.name, x.args.len())).is_some();
+            let has_script_fn = !x.hashes.is_native_only() && state.global.lib.iter().find_map(|m| m.get_script_fn(&x.name, x.args.len())).is_some();
             #[cfg(feature = "no_function")]
             let has_script_fn = false;
 
diff --git a/src/packages/string_basic.rs b/src/packages/string_basic.rs
index a0763ada..63218d2b 100644
--- a/src/packages/string_basic.rs
+++ b/src/packages/string_basic.rs
@@ -39,7 +39,7 @@ pub fn print_with_func(
     value: &mut Dynamic,
 ) -> crate::ImmutableString {
     match ctx.call_native_fn_raw(fn_name, true, &mut [value]) {
-        Ok(result) if result.is::<crate::ImmutableString>() => {
+        Ok(result) if result.is_string() => {
             result.into_immutable_string().expect("`ImmutableString`")
         }
         Ok(result) => ctx.engine().map_type_name(result.type_name()).into(),
@@ -75,7 +75,7 @@ mod print_debug_functions {
     /// Return the empty string.
     #[rhai_fn(name = "print", name = "debug")]
     pub fn print_empty_string(ctx: NativeCallContext) -> ImmutableString {
-        ctx.engine().get_interned_string("")
+        ctx.engine().const_empty_string()
     }
 
     /// Return the `string`.
@@ -121,7 +121,7 @@ mod print_debug_functions {
     #[rhai_fn(name = "print", name = "to_string")]
     pub fn print_unit(ctx: NativeCallContext, unit: ()) -> ImmutableString {
         let _ = unit;
-        ctx.engine().get_interned_string("")
+        ctx.engine().const_empty_string()
     }
     /// Convert the unit into a string in debug format.
     #[rhai_fn(name = "debug", name = "to_debug")]
@@ -134,26 +134,26 @@ mod print_debug_functions {
     #[cfg(not(feature = "no_float"))]
     #[rhai_fn(name = "print", name = "to_string")]
     pub fn print_f64(number: f64) -> ImmutableString {
-        crate::ast::FloatWrapper::new(number).to_string().into()
+        crate::types::FloatWrapper::new(number).to_string().into()
     }
     /// Convert the value of `number` into a string.
     #[cfg(not(feature = "no_float"))]
     #[rhai_fn(name = "print", name = "to_string")]
     pub fn print_f32(number: f32) -> ImmutableString {
-        crate::ast::FloatWrapper::new(number).to_string().into()
+        crate::types::FloatWrapper::new(number).to_string().into()
     }
     /// Convert the value of `number` into a string.
     #[cfg(not(feature = "no_float"))]
     #[rhai_fn(name = "debug", name = "to_debug")]
     pub fn debug_f64(number: f64) -> ImmutableString {
-        let number = crate::ast::FloatWrapper::new(number);
+        let number = crate::types::FloatWrapper::new(number);
         format!("{number:?}").into()
     }
     /// Convert the value of `number` into a string.
     #[cfg(not(feature = "no_float"))]
     #[rhai_fn(name = "debug", name = "to_debug")]
     pub fn debug_f32(number: f32) -> ImmutableString {
-        let number = crate::ast::FloatWrapper::new(number);
+        let number = crate::types::FloatWrapper::new(number);
         format!("{number:?}").into()
     }
 
diff --git a/src/packages/string_more.rs b/src/packages/string_more.rs
index 72c4a6ca..bc39f8cb 100644
--- a/src/packages/string_more.rs
+++ b/src/packages/string_more.rs
@@ -348,7 +348,7 @@ mod string_functions {
         len: INT,
     ) -> ImmutableString {
         if string.is_empty() || len <= 0 {
-            return ctx.engine().get_interned_string("");
+            return ctx.engine().const_empty_string();
         }
         let len = len.min(MAX_USIZE_INT) as usize;
 
@@ -896,18 +896,18 @@ mod string_functions {
         len: INT,
     ) -> ImmutableString {
         if string.is_empty() {
-            return ctx.engine().get_interned_string("");
+            return ctx.engine().const_empty_string();
         }
 
         let mut chars = StaticVec::with_capacity(string.len());
 
         let offset = if string.is_empty() || len <= 0 {
-            return ctx.engine().get_interned_string("");
+            return ctx.engine().const_empty_string();
         } else if start < 0 {
             let abs_start = start.unsigned_abs();
 
             if abs_start as u64 > MAX_USIZE_INT as u64 {
-                return ctx.engine().get_interned_string("");
+                return ctx.engine().const_empty_string();
             }
 
             let abs_start = abs_start as usize;
@@ -918,7 +918,7 @@ mod string_functions {
                 chars.len() - abs_start
             }
         } else if start > MAX_USIZE_INT || start as usize >= string.chars().count() {
-            return ctx.engine().get_interned_string("");
+            return ctx.engine().const_empty_string();
         } else {
             start as usize
         };
@@ -964,7 +964,7 @@ mod string_functions {
         start: INT,
     ) -> ImmutableString {
         if string.is_empty() {
-            ctx.engine().get_interned_string("")
+            ctx.engine().const_empty_string()
         } else {
             let len = string.len() as INT;
             sub_string(ctx, string, start, len)
@@ -1348,7 +1348,7 @@ mod string_functions {
 
                 if abs_index as u64 > MAX_USIZE_INT as u64 {
                     return vec![
-                        ctx.engine().get_interned_string("").into(),
+                        ctx.engine().const_empty_string().into(),
                         string.as_str().into(),
                     ];
                 }
@@ -1357,7 +1357,7 @@ mod string_functions {
                 let num_chars = string.chars().count();
                 if abs_index > num_chars {
                     vec![
-                        ctx.engine().get_interned_string("").into(),
+                        ctx.engine().const_empty_string().into(),
                         string.as_str().into(),
                     ]
                 } else {
@@ -1368,7 +1368,7 @@ mod string_functions {
             } else if index > MAX_USIZE_INT {
                 vec![
                     string.as_str().into(),
-                    ctx.engine().get_interned_string("").into(),
+                    ctx.engine().const_empty_string().into(),
                 ]
             } else {
                 let prefix: String = string.chars().take(index as usize).collect();
diff --git a/src/parser.rs b/src/parser.rs
index fed55ac3..38f357bf 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -374,7 +374,7 @@ impl Expr {
     fn ensure_bool_expr(self) -> ParseResult<Expr> {
         let type_name = match self {
             Expr::Unit(..) => "()",
-            Expr::DynamicConstant(ref v, ..) if !v.is::<bool>() => v.type_name(),
+            Expr::DynamicConstant(ref v, ..) if !v.is_bool() => v.type_name(),
             Expr::IntegerConstant(..) => "a number",
             #[cfg(not(feature = "no_float"))]
             Expr::FloatConstant(..) => "a floating-point number",
@@ -1248,7 +1248,7 @@ impl Engine {
                         continue;
                     }
 
-                    if value.is::<INT>() && !ranges.is_empty() {
+                    if value.is_int() && !ranges.is_empty() {
                         return Err(PERR::WrongSwitchIntegerCase.into_err(expr.start_position()));
                     }
 
@@ -2909,14 +2909,8 @@ impl Engine {
             let caches = &mut Caches::new();
             let mut this = Dynamic::NULL;
 
-            let context = EvalContext::new(
-                self,
-                &mut state.global,
-                caches,
-                &[],
-                &mut state.stack,
-                &mut this,
-            );
+            let context =
+                EvalContext::new(self, &mut state.global, caches, &mut state.stack, &mut this);
 
             match filter(false, info, context) {
                 Ok(true) => (),
diff --git a/src/serde/de.rs b/src/serde/de.rs
index 42d4739f..1e3f3664 100644
--- a/src/serde/de.rs
+++ b/src/serde/de.rs
@@ -370,7 +370,7 @@ impl<'de> Deserializer<'de> for DynamicDeserializer<'de> {
     }
 
     fn deserialize_option<V: Visitor<'de>>(self, visitor: V) -> RhaiResultOf<V::Value> {
-        if self.0.is::<()>() {
+        if self.0.is_unit() {
             visitor.visit_none()
         } else {
             visitor.visit_some(self)
diff --git a/src/tests.rs b/src/tests.rs
index 6e36c977..01a0e8e7 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -45,9 +45,9 @@ fn check_struct_sizes() {
         assert_eq!(
             size_of::<NativeCallContext>(),
             if cfg!(feature = "no_position") {
-                64
+                48
             } else {
-                72
+                56
             }
         );
     }
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index 7dea89d9..17f9087e 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -382,7 +382,7 @@ pub enum Token {
     ///
     /// Reserved under the `no_float` feature.
     #[cfg(not(feature = "no_float"))]
-    FloatConstant(crate::ast::FloatWrapper<crate::FLOAT>),
+    FloatConstant(crate::types::FloatWrapper<crate::FLOAT>),
     /// A [`Decimal`][rust_decimal::Decimal] constant.
     ///
     /// Requires the `decimal` feature.
@@ -1682,7 +1682,7 @@ fn get_next_token_inner(
                         // If integer parsing is unnecessary, try float instead
                         #[cfg(not(feature = "no_float"))]
                         let num = num.or_else(|_| {
-                            crate::ast::FloatWrapper::from_str(&result).map(Token::FloatConstant)
+                            crate::types::FloatWrapper::from_str(&result).map(Token::FloatConstant)
                         });
 
                         // Then try decimal
diff --git a/src/types/dynamic.rs b/src/types/dynamic.rs
index eeee966a..3b1a6cee 100644
--- a/src/types/dynamic.rs
+++ b/src/types/dynamic.rs
@@ -70,7 +70,7 @@ pub enum Union {
     Int(INT, Tag, AccessMode),
     /// A floating-point value.
     #[cfg(not(feature = "no_float"))]
-    Float(crate::ast::FloatWrapper<crate::FLOAT>, Tag, AccessMode),
+    Float(super::FloatWrapper<crate::FLOAT>, Tag, AccessMode),
     /// _(decimal)_ A fixed-precision decimal value.
     /// Exported under the `decimal` feature only.
     #[cfg(feature = "decimal")]
@@ -260,10 +260,18 @@ impl Dynamic {
     }
     /// Is the value held by this [`Dynamic`] a particular type?
     ///
-    /// If the [`Dynamic`] is a shared variant checking is performed on top of its internal value.
+    /// # Panics or Deadlocks When Value is Shared
+    ///
+    /// Under the `sync` feature, this call may deadlock, or [panic](https://doc.rust-lang.org/std/sync/struct.RwLock.html#panics-1).
+    /// Otherwise, this call panics if the data is currently borrowed for write.
     #[inline]
     #[must_use]
     pub fn is<T: Any + Clone>(&self) -> bool {
+        #[cfg(not(feature = "no_closure"))]
+        if self.is_shared() {
+            return TypeId::of::<T>() == self.type_id();
+        }
+
         if TypeId::of::<T>() == TypeId::of::<()>() {
             return matches!(self.0, Union::Unit(..));
         }
@@ -867,7 +875,7 @@ impl Dynamic {
     #[must_use]
     pub const fn from_float(value: crate::FLOAT) -> Self {
         Self(Union::Float(
-            crate::ast::FloatWrapper::new(value),
+            super::FloatWrapper::new(value),
             DEFAULT_TAG_VALUE,
             ReadWrite,
         ))
@@ -1626,14 +1634,205 @@ impl Dynamic {
             _ => None,
         }
     }
+
+    /// Return `true` if the [`Dynamic`] holds a `()`.
+    #[inline]
+    #[must_use]
+    pub fn is_unit(&self) -> bool {
+        match self.0 {
+            Union::Unit(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Unit(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds the system integer type [`INT`].
+    #[inline]
+    #[must_use]
+    pub fn is_int(&self) -> bool {
+        match self.0 {
+            Union::Int(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Int(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds the system floating-point type [`FLOAT`][crate::FLOAT].
+    ///
+    /// Not available under `no_float`.
+    #[cfg(not(feature = "no_float"))]
+    #[inline]
+    #[must_use]
+    pub fn is_float(&self) -> bool {
+        match self.0 {
+            Union::Float(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Float(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// _(decimal)_ Return `true` if the [`Dynamic`] holds a [`Decimal`][rust_decimal::Decimal].
+    ///
+    /// Exported under the `decimal` feature only.
+    #[cfg(feature = "decimal")]
+    #[inline]
+    #[must_use]
+    pub fn is_decimal(&self) -> bool {
+        match self.0 {
+            Union::Decimal(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Decimal(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [`bool`].
+    #[inline]
+    #[must_use]
+    pub fn is_bool(&self) -> bool {
+        match self.0 {
+            Union::Bool(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Bool(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [`char`].
+    #[inline]
+    #[must_use]
+    pub fn is_char(&self) -> bool {
+        match self.0 {
+            Union::Char(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Char(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds an [`ImmutableString`].
+    #[inline]
+    #[must_use]
+    pub fn is_string(&self) -> bool {
+        match self.0 {
+            Union::Str(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Str(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds an [`Array`][crate::Array].
+    ///
+    /// Not available under `no_index`.
+    #[cfg(not(feature = "no_index"))]
+    #[inline]
+    #[must_use]
+    pub fn is_array(&self) -> bool {
+        match self.0 {
+            Union::Array(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Array(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [`Blob`][crate::Blob].
+    ///
+    /// Not available under `no_index`.
+    #[cfg(not(feature = "no_index"))]
+    #[inline]
+    #[must_use]
+    pub fn is_blob(&self) -> bool {
+        match self.0 {
+            Union::Blob(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Blob(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [`Map`][crate::Map].
+    ///
+    /// Not available under `no_object`.
+    #[cfg(not(feature = "no_object"))]
+    #[inline]
+    #[must_use]
+    pub fn is_map(&self) -> bool {
+        match self.0 {
+            Union::Map(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Map(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [`FnPtr`].
+    #[inline]
+    #[must_use]
+    pub(crate) fn is_fnptr(&self) -> bool {
+        match self.0 {
+            Union::FnPtr(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::FnPtr(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+    /// Return `true` if the [`Dynamic`] holds a [timestamp][Instant].
+    ///
+    /// Not available under `no_time`.
+    #[cfg(not(feature = "no_time"))]
+    #[inline]
+    #[must_use]
+    pub fn is_timestamp(&self) -> bool {
+        match self.0 {
+            Union::TimeStamp(..) => true,
+            #[cfg(not(feature = "no_closure"))]
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::TimeStamp(..) => true,
+                _ => false,
+            },
+            _ => false,
+        }
+    }
+
     /// Cast the [`Dynamic`] as a unit `()`.
     /// Returns the name of the actual type if the cast fails.
     #[inline]
     pub fn as_unit(&self) -> Result<(), &'static str> {
         match self.0 {
-            Union::Unit(v, ..) => Ok(v),
+            Union::Unit(..) => Ok(()),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Unit(..) => Ok(()),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1644,7 +1843,10 @@ impl Dynamic {
         match self.0 {
             Union::Int(n, ..) => Ok(n),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Int(n, ..) => Ok(n),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1658,7 +1860,10 @@ impl Dynamic {
         match self.0 {
             Union::Float(n, ..) => Ok(*n),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Float(n, ..) => Ok(*n),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1672,7 +1877,10 @@ impl Dynamic {
         match self.0 {
             Union::Decimal(ref n, ..) => Ok(**n),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Decimal(ref n, ..) => Ok(**n),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1683,7 +1891,10 @@ impl Dynamic {
         match self.0 {
             Union::Bool(b, ..) => Ok(b),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Bool(b, ..) => Ok(b),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1692,12 +1903,16 @@ impl Dynamic {
     #[inline]
     pub fn as_char(&self) -> Result<char, &'static str> {
         match self.0 {
-            Union::Char(n, ..) => Ok(n),
+            Union::Char(c, ..) => Ok(c),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(..) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Char(c, ..) => Ok(c),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
+
     /// Cast the [`Dynamic`] as a string slice.
     /// Returns the name of the actual type if the cast fails.
     ///
@@ -1728,38 +1943,34 @@ impl Dynamic {
         match self.0 {
             Union::Str(s, ..) => Ok(s),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => {
-                let value = crate::func::locked_read(cell);
-
-                match value.0 {
-                    Union::Str(ref s, ..) => Ok(s.clone()),
-                    _ => Err((*value).type_name()),
-                }
-            }
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Str(ref s, ..) => Ok(s.clone()),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
     /// Convert the [`Dynamic`] into an [`Array`][crate::Array].
     /// Returns the name of the actual type if the cast fails.
+    ///
+    /// Not available under `no_index`.
     #[cfg(not(feature = "no_index"))]
     #[inline(always)]
     pub fn into_array(self) -> Result<crate::Array, &'static str> {
         match self.0 {
             Union::Array(a, ..) => Ok(*a),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => {
-                let value = crate::func::locked_read(cell);
-
-                match value.0 {
-                    Union::Array(ref a, ..) => Ok(a.as_ref().clone()),
-                    _ => Err((*value).type_name()),
-                }
-            }
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Array(ref a, ..) => Ok(a.as_ref().clone()),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
     /// Convert the [`Dynamic`] into a [`Vec`].
     /// Returns the name of the actual type if any cast fails.
+    ///
+    /// Not available under `no_index`.
     #[cfg(not(feature = "no_index"))]
     #[inline(always)]
     pub fn into_typed_array<T: Variant + Clone>(self) -> Result<Vec<T>, &'static str> {
@@ -1780,12 +1991,12 @@ impl Dynamic {
                     v.try_cast::<T>().ok_or(typ)
                 })
                 .collect(),
-            Union::Blob(..) if TypeId::of::<T>() == TypeId::of::<u8>() => Ok(self.cast::<Vec<T>>()),
+            Union::Blob(b, ..) if TypeId::of::<T>() == TypeId::of::<u8>() => {
+                Ok(reify!(*b => Vec<T>))
+            }
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(ref cell, ..) => {
-                let value = crate::func::locked_read(cell);
-
-                match value.0 {
+                match crate::func::locked_read(cell).0 {
                     Union::Array(ref a, ..) => {
                         a.iter()
                             .map(|v| {
@@ -1803,10 +2014,10 @@ impl Dynamic {
                             })
                             .collect()
                     }
-                    Union::Blob(..) if TypeId::of::<T>() == TypeId::of::<u8>() => {
-                        Ok((*value).clone().cast::<Vec<T>>())
+                    Union::Blob(ref b, ..) if TypeId::of::<T>() == TypeId::of::<u8>() => {
+                        Ok(reify!(b.clone() => Vec<T>))
                     }
-                    _ => Err((*value).type_name()),
+                    _ => Err(cell.type_name()),
                 }
             }
             _ => Err(self.type_name()),
@@ -1814,20 +2025,18 @@ impl Dynamic {
     }
     /// Convert the [`Dynamic`] into a [`Blob`][crate::Blob].
     /// Returns the name of the actual type if the cast fails.
+    ///
+    /// Not available under `no_index`.
     #[cfg(not(feature = "no_index"))]
     #[inline(always)]
     pub fn into_blob(self) -> Result<crate::Blob, &'static str> {
         match self.0 {
-            Union::Blob(a, ..) => Ok(*a),
+            Union::Blob(b, ..) => Ok(*b),
             #[cfg(not(feature = "no_closure"))]
-            Union::Shared(ref cell, ..) => {
-                let value = crate::func::locked_read(cell);
-
-                match value.0 {
-                    Union::Blob(ref a, ..) => Ok(a.as_ref().clone()),
-                    _ => Err((*value).type_name()),
-                }
-            }
+            Union::Shared(ref cell, ..) => match crate::func::locked_read(cell).0 {
+                Union::Blob(ref b, ..) => Ok(b.as_ref().clone()),
+                _ => Err(cell.type_name()),
+            },
             _ => Err(self.type_name()),
         }
     }
@@ -1859,9 +2068,9 @@ impl From<crate::FLOAT> for Dynamic {
     }
 }
 #[cfg(not(feature = "no_float"))]
-impl From<crate::ast::FloatWrapper<crate::FLOAT>> for Dynamic {
+impl From<super::FloatWrapper<crate::FLOAT>> for Dynamic {
     #[inline(always)]
-    fn from(value: crate::ast::FloatWrapper<crate::FLOAT>) -> Self {
+    fn from(value: super::FloatWrapper<crate::FLOAT>) -> Self {
         Self(Union::Float(value, DEFAULT_TAG_VALUE, ReadWrite))
     }
 }
diff --git a/src/types/error.rs b/src/types/error.rs
index 906f32c9..1a8035e5 100644
--- a/src/types/error.rs
+++ b/src/types/error.rs
@@ -174,7 +174,7 @@ impl fmt::Display for EvalAltResult {
             Self::ErrorStackOverflow(..) => f.write_str("Stack overflow")?,
             Self::ErrorTerminated(..) => f.write_str("Script terminated")?,
 
-            Self::ErrorRuntime(d, ..) if d.is::<()>() => f.write_str("Runtime error")?,
+            Self::ErrorRuntime(d, ..) if d.is_unit() => f.write_str("Runtime error")?,
             Self::ErrorRuntime(d, ..)
                 if d.read_lock::<ImmutableString>()
                     .map_or(false, |v| v.is_empty()) =>
diff --git a/src/types/float.rs b/src/types/float.rs
new file mode 100644
index 00000000..a3b934a6
--- /dev/null
+++ b/src/types/float.rs
@@ -0,0 +1,115 @@
+#![cfg(not(feature = "no_float"))]
+
+#[cfg(feature = "no_std")]
+use std::prelude::v1::*;
+use std::{
+    fmt,
+    hash::{Hash, Hasher},
+    ops::{Deref, DerefMut},
+    str::FromStr,
+};
+
+use num_traits::float::FloatCore as Float;
+
+/// A type that wraps a floating-point number and implements [`Hash`].
+///
+/// Not available under `no_float`.
+#[derive(Clone, Copy, PartialEq, PartialOrd)]
+pub struct FloatWrapper<F>(F);
+
+impl Hash for FloatWrapper<crate::FLOAT> {
+    #[inline]
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.to_ne_bytes().hash(state);
+    }
+}
+
+impl<F: Float> AsRef<F> for FloatWrapper<F> {
+    #[inline(always)]
+    #[must_use]
+    fn as_ref(&self) -> &F {
+        &self.0
+    }
+}
+
+impl<F: Float> AsMut<F> for FloatWrapper<F> {
+    #[inline(always)]
+    #[must_use]
+    fn as_mut(&mut self) -> &mut F {
+        &mut self.0
+    }
+}
+
+impl<F: Float> Deref for FloatWrapper<F> {
+    type Target = F;
+
+    #[inline(always)]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<F: Float> DerefMut for FloatWrapper<F> {
+    #[inline(always)]
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<F: Float + fmt::Debug> fmt::Debug for FloatWrapper<F> {
+    #[cold]
+    #[inline(never)]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&self.0, f)
+    }
+}
+
+impl<F: Float + fmt::Display + fmt::LowerExp + From<f32>> fmt::Display for FloatWrapper<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let abs = self.0.abs();
+        if abs.is_zero() {
+            f.write_str("0.0")
+        } else if abs > Self::MAX_NATURAL_FLOAT_FOR_DISPLAY.into()
+            || abs < Self::MIN_NATURAL_FLOAT_FOR_DISPLAY.into()
+        {
+            write!(f, "{:e}", self.0)
+        } else {
+            fmt::Display::fmt(&self.0, f)?;
+            if abs.fract().is_zero() {
+                f.write_str(".0")?;
+            }
+            Ok(())
+        }
+    }
+}
+
+impl<F: Float> From<F> for FloatWrapper<F> {
+    #[inline(always)]
+    fn from(value: F) -> Self {
+        Self::new(value)
+    }
+}
+
+impl<F: Float + FromStr> FromStr for FloatWrapper<F> {
+    type Err = <F as FromStr>::Err;
+
+    #[inline]
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        F::from_str(s).map(Into::into)
+    }
+}
+
+impl<F: Float> FloatWrapper<F> {
+    /// Maximum floating-point number for natural display before switching to scientific notation.
+    pub const MAX_NATURAL_FLOAT_FOR_DISPLAY: f32 = 10_000_000_000_000.0;
+
+    /// Minimum floating-point number for natural display before switching to scientific notation.
+    pub const MIN_NATURAL_FLOAT_FOR_DISPLAY: f32 = 0.000_000_000_000_1;
+
+    /// Create a new [`FloatWrapper`].
+    #[inline(always)]
+    #[must_use]
+    pub const fn new(value: F) -> Self {
+        Self(value)
+    }
+}
diff --git a/src/types/fn_ptr.rs b/src/types/fn_ptr.rs
index 5d087ef2..900b738b 100644
--- a/src/types/fn_ptr.rs
+++ b/src/types/fn_ptr.rs
@@ -5,7 +5,7 @@ use crate::tokenizer::is_valid_function_name;
 use crate::types::dynamic::Variant;
 use crate::{
     Dynamic, Engine, FuncArgs, ImmutableString, NativeCallContext, Position, RhaiError, RhaiResult,
-    RhaiResultOf, SharedModule, StaticVec, AST, ERR,
+    RhaiResultOf, StaticVec, AST, ERR,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -151,19 +151,12 @@ impl FnPtr {
         let mut arg_values = crate::StaticVec::new_const();
         args.parse(&mut arg_values);
 
-        let lib: &[SharedModule] = &[
-            #[cfg(not(feature = "no_function"))]
-            AsRef::<SharedModule>::as_ref(ast).clone(),
-        ];
-        let lib = if lib.first().map_or(true, |m| m.is_empty()) {
-            &[][..]
-        } else {
-            &lib
-        };
+        let global = &mut GlobalRuntimeState::new(engine);
 
-        let global = &GlobalRuntimeState::new(engine);
+        #[cfg(not(feature = "no_function"))]
+        global.lib.push(_ast.shared_lib().clone());
 
-        let ctx = (engine, self.fn_name(), None, global, lib, Position::NONE).into();
+        let ctx = (engine, self.fn_name(), None, &*global, Position::NONE).into();
 
         let result = self.call_raw(&ctx, None, arg_values)?;
 
diff --git a/src/types/mod.rs b/src/types/mod.rs
index 1fbf33d3..aad22a3c 100644
--- a/src/types/mod.rs
+++ b/src/types/mod.rs
@@ -4,6 +4,7 @@ pub mod bloom_filter;
 pub mod custom_types;
 pub mod dynamic;
 pub mod error;
+pub mod float;
 pub mod fn_ptr;
 pub mod immutable_string;
 pub mod interner;
@@ -18,6 +19,8 @@ pub use dynamic::Dynamic;
 #[cfg(not(feature = "no_time"))]
 pub use dynamic::Instant;
 pub use error::EvalAltResult;
+#[cfg(not(feature = "no_float"))]
+pub use float::FloatWrapper;
 pub use fn_ptr::FnPtr;
 pub use immutable_string::ImmutableString;
 pub use interner::StringsInterner;
diff --git a/tests/serde.rs b/tests/serde.rs
index 4a08bb81..28f3e1bb 100644
--- a/tests/serde.rs
+++ b/tests/serde.rs
@@ -19,11 +19,11 @@ use rust_decimal::Decimal;
 
 #[test]
 fn test_serde_ser_primary_types() -> Result<(), Box<EvalAltResult>> {
-    assert!(to_dynamic(42_u64)?.is::<INT>());
+    assert!(to_dynamic(42_u64)?.is_int());
     assert!(to_dynamic(u64::MAX)?.is::<u64>());
-    assert!(to_dynamic(42 as INT)?.is::<INT>());
-    assert!(to_dynamic(true)?.is::<bool>());
-    assert!(to_dynamic(())?.is::<()>());
+    assert!(to_dynamic(42 as INT)?.is_int());
+    assert!(to_dynamic(true)?.is_bool());
+    assert!(to_dynamic(())?.is_unit());
 
     #[cfg(not(feature = "no_float"))]
     {
@@ -45,14 +45,14 @@ fn test_serde_ser_primary_types() -> Result<(), Box<EvalAltResult>> {
 
 #[test]
 fn test_serde_ser_integer_types() -> Result<(), Box<EvalAltResult>> {
-    assert!(to_dynamic(42_i8)?.is::<INT>());
-    assert!(to_dynamic(42_i16)?.is::<INT>());
-    assert!(to_dynamic(42_i32)?.is::<INT>());
-    assert!(to_dynamic(42_i64)?.is::<INT>());
-    assert!(to_dynamic(42_u8)?.is::<INT>());
-    assert!(to_dynamic(42_u16)?.is::<INT>());
-    assert!(to_dynamic(42_u32)?.is::<INT>());
-    assert!(to_dynamic(42_u64)?.is::<INT>());
+    assert!(to_dynamic(42_i8)?.is_int());
+    assert!(to_dynamic(42_i16)?.is_int());
+    assert!(to_dynamic(42_i32)?.is_int());
+    assert!(to_dynamic(42_i64)?.is_int());
+    assert!(to_dynamic(42_u8)?.is_int());
+    assert!(to_dynamic(42_u16)?.is_int());
+    assert!(to_dynamic(42_u32)?.is_int());
+    assert!(to_dynamic(42_u64)?.is_int());
 
     Ok(())
 }
@@ -63,7 +63,7 @@ fn test_serde_ser_array() -> Result<(), Box<EvalAltResult>> {
     let arr: Vec<INT> = vec![123, 456, 42, 999];
 
     let d = to_dynamic(arr)?;
-    assert!(d.is::<Array>());
+    assert!(d.is_array());
     assert_eq!(4, d.cast::<Array>().len());
 
     Ok(())
@@ -94,7 +94,7 @@ fn test_serde_ser_struct() -> Result<(), Box<EvalAltResult>> {
 
     let d = to_dynamic(x)?;
 
-    assert!(d.is::<Map>());
+    assert!(d.is_map());
 
     let mut map = d.cast::<Map>();
     let obj = map.remove("obj").unwrap().cast::<Map>();
@@ -734,7 +734,7 @@ fn test_serde_json() -> serde_json::Result<()> {
 
     let d2: Dynamic = serde_json::from_str(&json)?;
 
-    assert!(d2.is::<Map>());
+    assert!(d2.is_map());
 
     let mut m = d2.cast::<Map>();
 
diff --git a/tests/throw.rs b/tests/throw.rs
index caf2fed9..b83dbce2 100644
--- a/tests/throw.rs
+++ b/tests/throw.rs
@@ -11,7 +11,7 @@ fn test_throw() {
 
     assert!(matches!(
         *engine.run(r#"throw"#).expect_err("expects error"),
-        EvalAltResult::ErrorRuntime(s, ..) if s.is::<()>()
+        EvalAltResult::ErrorRuntime(s, ..) if s.is_unit()
     ));
 }