diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5d7c0965..3126de3d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,7 @@ Bug fixes
 * `map` and `filter` for arrays are marked `pure`. Warnings are added to the documentation of pure array methods that take `this` closures.
 * Syntax such as `foo.bar::baz` no longer panics, but returns a proper parse error.
 * `x += y` where `x` and `y` are `char` now works correctly.
+* Expressions such as `!inside` now parses correctly instead of as `!in` followed by `side`.
 
 Enhancements
 ------------
diff --git a/src/api/deprecated.rs b/src/api/deprecated.rs
index dca53e94..47dd8d93 100644
--- a/src/api/deprecated.rs
+++ b/src/api/deprecated.rs
@@ -1133,7 +1133,7 @@ pub mod deprecated_array_functions {
         array: &mut Array,
         comparer: &str,
     ) -> RhaiResultOf<()> {
-        sort(ctx, array, FnPtr::new(comparer)?)
+        Ok(sort(ctx, array, FnPtr::new(comparer)?))
     }
     /// Remove all elements in the array that returns `true` when applied a function named by `filter`
     /// and return them as a new array.
diff --git a/src/ast/expr.rs b/src/ast/expr.rs
index c8cdedb1..957a195e 100644
--- a/src/ast/expr.rs
+++ b/src/ast/expr.rs
@@ -2,12 +2,11 @@
 
 use super::{ASTFlags, ASTNode, Ident, Namespace, Stmt, StmtBlock};
 use crate::engine::{KEYWORD_FN_PTR, OP_EXCLUSIVE_RANGE, OP_INCLUSIVE_RANGE};
-use crate::func::hashing::ALT_ZERO_HASH;
 use crate::tokenizer::Token;
 use crate::types::dynamic::Union;
 use crate::{
-    calc_fn_hash, Dynamic, FnPtr, Identifier, ImmutableString, Position, SmartString, StaticVec,
-    INT,
+    calc_fn_hash, Dynamic, FnArgsVec, FnPtr, Identifier, ImmutableString, Position, SmartString,
+    StaticVec, INT,
 };
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
@@ -17,7 +16,7 @@ use std::{
     fmt::Write,
     hash::Hash,
     iter::once,
-    num::{NonZeroU64, NonZeroU8, NonZeroUsize},
+    num::{NonZeroU8, NonZeroUsize},
 };
 
 /// _(internals)_ A binary expression.
@@ -103,9 +102,9 @@ impl CustomExpr {
 pub struct FnCallHashes {
     /// Pre-calculated hash for a script-defined function ([`None`] if native functions only).
     #[cfg(not(feature = "no_function"))]
-    script: Option<NonZeroU64>,
+    script: Option<u64>,
     /// Pre-calculated hash for a native Rust function with no parameter types.
-    native: NonZeroU64,
+    native: u64,
 }
 
 impl fmt::Debug for FnCallHashes {
@@ -125,38 +124,37 @@ impl fmt::Debug for FnCallHashes {
     }
 }
 
-impl From<u64> for FnCallHashes {
+impl FnCallHashes {
+    /// Create a [`FnCallHashes`] from a single hash.
     #[inline]
-    fn from(hash: u64) -> Self {
-        let hash = NonZeroU64::new(if hash == 0 { ALT_ZERO_HASH } else { hash }).unwrap();
-
+    #[must_use]
+    pub const fn from_hash(hash: u64) -> Self {
         Self {
             #[cfg(not(feature = "no_function"))]
             script: Some(hash),
             native: hash,
         }
     }
-}
-
-impl FnCallHashes {
     /// Create a [`FnCallHashes`] with only the native Rust hash.
     #[inline]
     #[must_use]
-    pub fn from_native(hash: u64) -> Self {
+    pub const fn from_native_only(hash: u64) -> Self {
         Self {
             #[cfg(not(feature = "no_function"))]
             script: None,
-            native: NonZeroU64::new(if hash == 0 { ALT_ZERO_HASH } else { hash }).unwrap(),
+            native: hash,
         }
     }
-    /// Create a [`FnCallHashes`] with both native Rust and script function hashes.
+    /// Create a [`FnCallHashes`] with both script function and native Rust hashes.
+    ///
+    /// Not available under `no_function`.
+    #[cfg(not(feature = "no_function"))]
     #[inline]
     #[must_use]
-    pub fn from_all(#[cfg(not(feature = "no_function"))] script: u64, native: u64) -> Self {
+    pub const fn from_script_and_native(script: u64, native: u64) -> Self {
         Self {
-            #[cfg(not(feature = "no_function"))]
-            script: NonZeroU64::new(if script == 0 { ALT_ZERO_HASH } else { script }),
-            native: NonZeroU64::new(if native == 0 { ALT_ZERO_HASH } else { native }).unwrap(),
+            script: Some(script),
+            native,
         }
     }
     /// Is this [`FnCallHashes`] native-only?
@@ -174,7 +172,7 @@ impl FnCallHashes {
     #[inline(always)]
     #[must_use]
     pub const fn native(&self) -> u64 {
-        self.native.get()
+        self.native
     }
     /// Get the script hash.
     ///
@@ -188,7 +186,7 @@ impl FnCallHashes {
     #[must_use]
     pub fn script(&self) -> u64 {
         assert!(self.script.is_some());
-        self.script.as_ref().unwrap().get()
+        self.script.unwrap()
     }
 }
 
@@ -203,7 +201,7 @@ pub struct FnCallExpr {
     /// Pre-calculated hashes.
     pub hashes: FnCallHashes,
     /// List of function call argument expressions.
-    pub args: StaticVec<Expr>,
+    pub args: FnArgsVec<Expr>,
     /// Does this function call capture the parent scope?
     pub capture_parent_scope: bool,
     /// Is this function call a native operator?
@@ -580,7 +578,7 @@ impl Expr {
                 FnCallExpr {
                     namespace: Namespace::NONE,
                     name: KEYWORD_FN_PTR.into(),
-                    hashes: calc_fn_hash(None, f.fn_name(), 1).into(),
+                    hashes: FnCallHashes::from_hash(calc_fn_hash(None, f.fn_name(), 1)),
                     args: once(Self::StringConstant(f.fn_name().into(), pos)).collect(),
                     capture_parent_scope: false,
                     op_token: None,
diff --git a/src/ast/stmt.rs b/src/ast/stmt.rs
index af4ff064..139475cf 100644
--- a/src/ast/stmt.rs
+++ b/src/ast/stmt.rs
@@ -24,15 +24,15 @@ use std::{
 #[derive(Clone, PartialEq, Hash)]
 pub struct OpAssignment {
     /// Hash of the op-assignment call.
-    pub hash_op_assign: u64,
+    hash_op_assign: u64,
     /// Hash of the underlying operator call (for fallback).
-    pub hash_op: u64,
+    hash_op: u64,
     /// Op-assignment operator.
-    pub op_assign: Token,
+    op_assign: Token,
     /// Underlying operator.
-    pub op: Token,
+    op: Token,
     /// [Position] of the op-assignment operator.
-    pub pos: Position,
+    pos: Position,
 }
 
 impl OpAssignment {
@@ -51,8 +51,31 @@ impl OpAssignment {
     /// Is this an op-assignment?
     #[must_use]
     #[inline(always)]
-    pub const fn is_op_assignment(&self) -> bool {
-        self.hash_op_assign != 0 || self.hash_op != 0
+    pub fn is_op_assignment(&self) -> bool {
+        !matches!(self.op, Token::Equals)
+    }
+    /// Get information if this [`OpAssignment`] is an op-assignment.
+    ///
+    /// Returns `( hash_op_assign, hash_op, op_assign, op )`:
+    ///
+    /// * `hash_op_assign`: Hash of the op-assignment call.
+    /// * `hash_op`: Hash of the underlying operator call (for fallback).
+    /// * `op_assign`: Op-assignment operator.
+    /// * `op`: Underlying operator.
+    #[must_use]
+    #[inline]
+    pub fn get_op_assignment_info(&self) -> Option<(u64, u64, &Token, &Token)> {
+        if self.is_op_assignment() {
+            Some((self.hash_op_assign, self.hash_op, &self.op_assign, &self.op))
+        } else {
+            None
+        }
+    }
+    /// Get the [position][Position] of this [`OpAssignment`].
+    #[must_use]
+    #[inline(always)]
+    pub const fn position(&self) -> Position {
+        self.pos
     }
     /// Create a new [`OpAssignment`].
     ///
@@ -93,7 +116,7 @@ impl OpAssignment {
     #[inline(always)]
     pub fn new_op_assignment_from_base(name: &str, pos: Position) -> Self {
         let op = Token::lookup_symbol_from_syntax(name).expect("operator");
-        Self::new_op_assignment_from_base_token(op, pos)
+        Self::new_op_assignment_from_base_token(&op, pos)
     }
     /// Convert a [`Token`] into a new [`OpAssignment`].
     ///
@@ -102,7 +125,7 @@ impl OpAssignment {
     /// Panics if the token is cannot be converted into an op-assignment operator.
     #[inline(always)]
     #[must_use]
-    pub fn new_op_assignment_from_base_token(op: Token, pos: Position) -> Self {
+    pub fn new_op_assignment_from_base_token(op: &Token, pos: Position) -> Self {
         Self::new_op_assignment_from_token(op.convert_to_op_assignment().expect("operator"), pos)
     }
 }
diff --git a/src/bin/rhai-dbg.rs b/src/bin/rhai-dbg.rs
index db929a4b..6fedabb5 100644
--- a/src/bin/rhai-dbg.rs
+++ b/src/bin/rhai-dbg.rs
@@ -166,10 +166,7 @@ fn load_script(engine: &Engine) -> (rhai::AST, String) {
 
         let filename = match Path::new(&filename).canonicalize() {
             Err(err) => {
-                eprintln!(
-                    "\x1b[31mError script file path: {}\n{}\x1b[39m",
-                    filename, err
-                );
+                eprintln!("\x1b[31mError script file path: {filename}\n{err}\x1b[39m");
                 exit(1);
             }
             Ok(f) => {
@@ -315,7 +312,7 @@ fn debug_callback(
                 }
                 ["node"] => {
                     if pos.is_none() {
-                        println!("{:?}", node);
+                        println!("{node:?}");
                     } else {
                         match source {
                             Some(source) => println!("{node:?} {source} @ {pos:?}"),
@@ -400,7 +397,7 @@ fn debug_callback(
                         #[cfg(not(feature = "no_position"))]
                         rhai::debugger::BreakPoint::AtPosition { pos, .. } => {
                             let line_num = format!("[{}] line ", i + 1);
-                            print!("{}", line_num);
+                            print!("{line_num}");
                             print_source(lines, *pos, line_num.len(), (0, 0));
                         }
                         _ => println!("[{}] {bp}", i + 1),
diff --git a/src/eval/chaining.rs b/src/eval/chaining.rs
index 6833e923..09066c8c 100644
--- a/src/eval/chaining.rs
+++ b/src/eval/chaining.rs
@@ -621,7 +621,7 @@ impl Engine {
                                 self.eval_op_assignment(
                                     global, caches, op_info, root, obj_ptr, new_val,
                                 )?;
-                                self.check_data_size(obj_ptr.as_ref(), op_info.pos)?;
+                                self.check_data_size(obj_ptr.as_ref(), op_info.position())?;
                                 None
                             }
                             // Indexed value cannot be referenced - use indexer
@@ -647,7 +647,7 @@ impl Engine {
                                     )?;
                                     // Replace new value
                                     new_val = val.take_or_clone();
-                                    self.check_data_size(&new_val, op_info.pos)?;
+                                    self.check_data_size(&new_val, op_info.position())?;
                                 }
                             }
 
@@ -729,7 +729,7 @@ impl Engine {
                                 global, caches, op_info, root, val_target, new_val,
                             )?;
                         }
-                        self.check_data_size(target.source(), op_info.pos)?;
+                        self.check_data_size(target.source(), op_info.position())?;
                         Ok((Dynamic::UNIT, true))
                     }
                     // {xxx:map}.id
diff --git a/src/eval/debugger.rs b/src/eval/debugger.rs
index 652134a3..0302bdc2 100644
--- a/src/eval/debugger.rs
+++ b/src/eval/debugger.rs
@@ -495,13 +495,13 @@ impl Engine {
     ///
     /// It is up to the [`Engine`] to reactivate the debugger.
     #[inline]
-    pub(crate) fn run_debugger_raw<'a>(
+    pub(crate) fn run_debugger_raw(
         &self,
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
         scope: &mut Scope,
         this_ptr: Option<&mut Dynamic>,
-        node: ASTNode<'a>,
+        node: ASTNode,
         event: DebuggerEvent,
     ) -> Result<Option<DebuggerStatus>, Box<crate::EvalAltResult>> {
         if let Some(ref x) = self.debugger_interface {
diff --git a/src/eval/stmt.rs b/src/eval/stmt.rs
index f9111ce6..417049b8 100644
--- a/src/eval/stmt.rs
+++ b/src/eval/stmt.rs
@@ -125,23 +125,15 @@ impl Engine {
             return Err(ERR::ErrorAssignmentToConstant(name.to_string(), pos).into());
         }
 
-        if op_info.is_op_assignment() {
-            let OpAssignment {
-                hash_op_assign,
-                hash_op,
-                op_assign,
-                op,
-                pos,
-            } = op_info;
+        let pos = op_info.position();
 
+        if let Some((hash1, hash2, op_assign, op)) = op_info.get_op_assignment_info() {
             let mut lock_guard = target.write_lock::<Dynamic>().unwrap();
-
-            let hash = *hash_op_assign;
             let args = &mut [&mut *lock_guard, &mut new_val];
 
             if self.fast_operators() {
                 if let Some((func, need_context)) =
-                    get_builtin_op_assignment_fn(op_assign.clone(), args[0], args[1])
+                    get_builtin_op_assignment_fn(op_assign, args[0], args[1])
                 {
                     // Built-in found
                     auto_restore! { let orig_level = global.level; global.level += 1 }
@@ -149,7 +141,7 @@ impl Engine {
                     let context = if need_context {
                         let op = op_assign.literal_syntax();
                         let source = global.source();
-                        Some((self, op, source, &*global, *pos).into())
+                        Some((self, op, source, &*global, pos).into())
                     } else {
                         None
                     };
@@ -157,20 +149,20 @@ impl Engine {
                 }
             }
 
-            let token = Some(op_assign.clone());
+            let token = Some(op_assign);
             let op_assign = op_assign.literal_syntax();
 
-            match self.exec_native_fn_call(global, caches, op_assign, token, hash, args, true, *pos)
+            match self.exec_native_fn_call(global, caches, op_assign, token, hash1, args, true, pos)
             {
                 Ok(_) => (),
                 Err(err) if matches!(*err, ERR::ErrorFunctionNotFound(ref f, ..) if f.starts_with(op_assign)) =>
                 {
                     // Expand to `var = var op rhs`
-                    let token = Some(op.clone());
+                    let token = Some(op);
                     let op = op.literal_syntax();
 
                     *args[0] = self
-                        .exec_native_fn_call(global, caches, op, token, *hash_op, args, true, *pos)?
+                        .exec_native_fn_call(global, caches, op, token, hash2, args, true, pos)?
                         .0;
                 }
                 Err(err) => return Err(err),
@@ -189,7 +181,7 @@ impl Engine {
             }
         }
 
-        target.propagate_changed_value(op_info.pos)
+        target.propagate_changed_value(pos)
     }
 
     /// Evaluate a statement.
diff --git a/src/func/builtin.rs b/src/func/builtin.rs
index 592297af..1b69ba43 100644
--- a/src/func/builtin.rs
+++ b/src/func/builtin.rs
@@ -86,7 +86,7 @@ fn const_false_fn(_: Option<NativeCallContext>, _: &mut [&mut Dynamic]) -> RhaiR
 ///
 /// The return function will be registered as a _method_, so the first parameter cannot be consumed.
 #[must_use]
-pub fn get_builtin_binary_op_fn(op: Token, x: &Dynamic, y: &Dynamic) -> Option<FnBuiltin> {
+pub fn get_builtin_binary_op_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Option<FnBuiltin> {
     let type1 = x.type_id();
     let type2 = y.type_id();
 
@@ -621,7 +621,7 @@ pub fn get_builtin_binary_op_fn(op: Token, x: &Dynamic, y: &Dynamic) -> Option<F
 ///
 /// The return function is registered as a _method_, so the first parameter cannot be consumed.
 #[must_use]
-pub fn get_builtin_op_assignment_fn(op: Token, x: &Dynamic, y: &Dynamic) -> Option<FnBuiltin> {
+pub fn get_builtin_op_assignment_fn(op: &Token, x: &Dynamic, y: &Dynamic) -> Option<FnBuiltin> {
     let type1 = x.type_id();
     let type2 = y.type_id();
 
diff --git a/src/func/call.rs b/src/func/call.rs
index 837d6fb7..bdcdf899 100644
--- a/src/func/call.rs
+++ b/src/func/call.rs
@@ -164,15 +164,11 @@ impl Engine {
         _global: &GlobalRuntimeState,
         caches: &'s mut Caches,
         local_entry: &'s mut Option<FnResolutionCacheEntry>,
-        op_token: Option<Token>,
+        op_token: Option<&Token>,
         hash_base: u64,
         args: Option<&mut FnCallArgs>,
         allow_dynamic: bool,
     ) -> Option<&'s FnResolutionCacheEntry> {
-        if hash_base == 0 {
-            return None;
-        }
-
         let mut hash = args.as_deref().map_or(hash_base, |args| {
             calc_fn_hash_full(hash_base, args.iter().map(|a| a.type_id()))
         });
@@ -345,7 +341,7 @@ impl Engine {
         global: &mut GlobalRuntimeState,
         caches: &mut Caches,
         name: &str,
-        op_token: Option<Token>,
+        op_token: Option<&Token>,
         hash: u64,
         args: &mut FnCallArgs,
         is_ref_mut: bool,
@@ -567,7 +563,7 @@ impl Engine {
         caches: &mut Caches,
         _scope: Option<&mut Scope>,
         fn_name: &str,
-        op_token: Option<Token>,
+        op_token: Option<&Token>,
         hashes: FnCallHashes,
         mut _args: &mut FnCallArgs,
         is_ref_mut: bool,
@@ -789,9 +785,9 @@ impl Engine {
                 let fn_name = fn_ptr.fn_name();
                 // Recalculate hashes
                 let new_hash = if !is_anon && !is_valid_function_name(fn_name) {
-                    FnCallHashes::from_native(calc_fn_hash(None, fn_name, args.len()))
+                    FnCallHashes::from_native_only(calc_fn_hash(None, fn_name, args.len()))
                 } else {
-                    calc_fn_hash(None, fn_name, args.len()).into()
+                    FnCallHashes::from_hash(calc_fn_hash(None, fn_name, args.len()))
                 };
 
                 // Map it to name(args) in function-call style
@@ -871,14 +867,17 @@ impl Engine {
                 args.insert(0, target.as_mut());
 
                 // Recalculate hash
-                let new_hash = if !is_anon && !is_valid_function_name(&fn_name) {
-                    FnCallHashes::from_native(calc_fn_hash(None, &fn_name, args.len()))
-                } else {
-                    FnCallHashes::from_all(
-                        #[cfg(not(feature = "no_function"))]
+                let new_hash = match is_anon {
+                    false if !is_valid_function_name(&fn_name) => {
+                        FnCallHashes::from_native_only(calc_fn_hash(None, &fn_name, args.len()))
+                    }
+                    #[cfg(not(feature = "no_function"))]
+                    _ => FnCallHashes::from_script_and_native(
                         calc_fn_hash(None, &fn_name, args.len() - 1),
                         calc_fn_hash(None, &fn_name, args.len()),
-                    )
+                    ),
+                    #[cfg(feature = "no_function")]
+                    _ => FnCallHashes::from_native_only(calc_fn_hash(None, &fn_name, args.len())),
                 };
 
                 // Map it to name(args) in function-call style
@@ -947,18 +946,22 @@ impl Engine {
                                 call_args = &mut _arg_values;
                             }
                             // Recalculate the hash based on the new function name and new arguments
-                            hash = if !is_anon && !is_valid_function_name(fn_name) {
-                                FnCallHashes::from_native(calc_fn_hash(
-                                    None,
-                                    fn_name,
-                                    call_args.len() + 1,
-                                ))
-                            } else {
-                                FnCallHashes::from_all(
-                                    #[cfg(not(feature = "no_function"))]
-                                    calc_fn_hash(None, fn_name, call_args.len()),
-                                    calc_fn_hash(None, fn_name, call_args.len() + 1),
-                                )
+                            let args_len = call_args.len() + 1;
+                            hash = match is_anon {
+                                false if !is_valid_function_name(fn_name) => {
+                                    FnCallHashes::from_native_only(calc_fn_hash(
+                                        None, fn_name, args_len,
+                                    ))
+                                }
+                                #[cfg(not(feature = "no_function"))]
+                                _ => FnCallHashes::from_script_and_native(
+                                    calc_fn_hash(None, fn_name, args_len - 1),
+                                    calc_fn_hash(None, fn_name, args_len),
+                                ),
+                                #[cfg(feature = "no_function")]
+                                _ => FnCallHashes::from_native_only(calc_fn_hash(
+                                    None, fn_name, args_len,
+                                )),
                             };
                         }
                     }
@@ -1000,7 +1003,7 @@ impl Engine {
         scope: &mut Scope,
         mut this_ptr: Option<&mut Dynamic>,
         fn_name: &str,
-        op_token: Option<Token>,
+        op_token: Option<&Token>,
         first_arg: Option<&Expr>,
         args_expr: &[Expr],
         hashes: FnCallHashes,
@@ -1084,9 +1087,9 @@ impl Engine {
                 let args_len = total_args + curry.len();
 
                 hashes = if !is_anon && !is_valid_function_name(name) {
-                    FnCallHashes::from_native(calc_fn_hash(None, name, args_len))
+                    FnCallHashes::from_native_only(calc_fn_hash(None, name, args_len))
                 } else {
-                    calc_fn_hash(None, name, args_len).into()
+                    FnCallHashes::from_hash(calc_fn_hash(None, name, args_len))
                 };
             }
             // Handle Fn()
@@ -1564,10 +1567,10 @@ impl Engine {
             ..
         } = expr;
 
-        let op_token = op_token.clone();
+        let op_token = op_token.as_ref();
 
         // Short-circuit native unary operator call if under Fast Operators mode
-        if op_token == Some(Token::Bang) && self.fast_operators() && args.len() == 1 {
+        if op_token == Some(&Token::Bang) && self.fast_operators() && args.len() == 1 {
             let mut value = self
                 .get_arg_value(global, caches, scope, this_ptr.as_deref_mut(), &args[0])?
                 .0
@@ -1597,7 +1600,7 @@ impl Engine {
             let operands = &mut [&mut lhs, &mut rhs];
 
             if let Some((func, need_context)) =
-                get_builtin_binary_op_fn(op_token.clone().unwrap(), operands[0], operands[1])
+                get_builtin_binary_op_fn(op_token.as_ref().unwrap(), operands[0], operands[1])
             {
                 // Built-in found
                 auto_restore! { let orig_level = global.level; global.level += 1 }
diff --git a/src/func/hashing.rs b/src/func/hashing.rs
index cffe5d9b..b3e04613 100644
--- a/src/func/hashing.rs
+++ b/src/func/hashing.rs
@@ -13,25 +13,7 @@ pub type StraightHashMap<V> = hashbrown::HashMap<u64, V, StraightHasherBuilder>;
 
 #[cfg(not(feature = "no_std"))]
 pub type StraightHashMap<V> = std::collections::HashMap<u64, V, StraightHasherBuilder>;
-
-/// Dummy hash value to map zeros to. This value can be anything.
-///
-/// # Notes
-///
-/// Hashes are `u64`, and they can be zero (although extremely unlikely).
-/// It is possible to hijack the zero value to indicate non-existence,
-/// like [`None`] in [`Option<u64>`].
-///
-/// When a hash is calculated to be zero, it gets mapped to this alternate hash value.
-/// This has the effect of releasing the zero value at the expense of causing the probability of
-/// this value to double, which has minor impacts.
-pub const ALT_ZERO_HASH: u64 = 42;
-
-/// A hasher that only takes one single [`u64`] and returns it as a non-zero hash key.
-///
-/// # Zeros
-///
-/// If the value is zero, it is mapped to `ALT_ZERO_HASH`.
+/// A hasher that only takes one single [`u64`] and returns it as a hash key.
 ///
 /// # Panics
 ///
@@ -81,15 +63,11 @@ pub fn get_hasher() -> ahash::AHasher {
     }
 }
 
-/// Calculate a non-zero [`u64`] hash key from a namespace-qualified variable name.
+/// Calculate a [`u64`] hash key from a namespace-qualified variable name.
 ///
 /// Module names are passed in via `&str` references from an iterator.
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
 ///
-/// # Zeros
-///
-/// If the hash happens to be zero, it is mapped to `ALT_ZERO_HASH`.
-///
 /// # Note
 ///
 /// The first module name is skipped.  Hashing starts from the _second_ module in the chain.
@@ -110,13 +88,10 @@ pub fn calc_var_hash<'a>(namespace: impl IntoIterator<Item = &'a str>, var_name:
     count.hash(s);
     var_name.hash(s);
 
-    match s.finish() {
-        0 => ALT_ZERO_HASH,
-        r => r,
-    }
+    s.finish()
 }
 
-/// Calculate a non-zero [`u64`] hash key from a namespace-qualified function name
+/// Calculate a [`u64`] hash key from a namespace-qualified function name
 /// and the number of parameters, but no parameter types.
 ///
 /// Module names making up the namespace are passed in via `&str` references from an iterator.
@@ -124,10 +99,6 @@ pub fn calc_var_hash<'a>(namespace: impl IntoIterator<Item = &'a str>, var_name:
 ///
 /// If the function is not namespace-qualified, pass [`None`] as the namespace.
 ///
-/// # Zeros
-///
-/// If the hash happens to be zero, it is mapped to `ALT_ZERO_HASH`.
-///
 /// # Note
 ///
 /// The first module name is skipped.  Hashing starts from the _second_ module in the chain.
@@ -152,19 +123,12 @@ pub fn calc_fn_hash<'a>(
     fn_name.hash(s);
     num.hash(s);
 
-    match s.finish() {
-        0 => ALT_ZERO_HASH,
-        r => r,
-    }
+    s.finish()
 }
 
-/// Calculate a non-zero [`u64`] hash key from a base [`u64`] hash key and a list of parameter types.
+/// Calculate a [`u64`] hash key from a base [`u64`] hash key and a list of parameter types.
 ///
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
-///
-/// # Zeros
-///
-/// If the hash happens to be zero, it is mapped to `ALT_ZERO_HASH`.
 #[inline]
 #[must_use]
 pub fn calc_fn_hash_full(base: u64, params: impl IntoIterator<Item = TypeId>) -> u64 {
@@ -177,8 +141,5 @@ pub fn calc_fn_hash_full(base: u64, params: impl IntoIterator<Item = TypeId>) ->
     });
     count.hash(s);
 
-    match s.finish() {
-        0 => ALT_ZERO_HASH,
-        r => r,
-    }
+    s.finish()
 }
diff --git a/src/func/native.rs b/src/func/native.rs
index eaedd0ed..409e3948 100644
--- a/src/func/native.rs
+++ b/src/func/native.rs
@@ -446,7 +446,7 @@ impl<'a> NativeCallContext<'a> {
                     global,
                     caches,
                     fn_name,
-                    op_token,
+                    op_token.as_ref(),
                     calc_fn_hash(None, fn_name, args_len),
                     args,
                     is_ref_mut,
@@ -457,14 +457,15 @@ impl<'a> NativeCallContext<'a> {
 
         // Native or script
 
-        let hash = if is_method_call {
-            FnCallHashes::from_all(
-                #[cfg(not(feature = "no_function"))]
+        let hash = match is_method_call {
+            #[cfg(not(feature = "no_function"))]
+            true => FnCallHashes::from_script_and_native(
                 calc_fn_hash(None, fn_name, args_len - 1),
                 calc_fn_hash(None, fn_name, args_len),
-            )
-        } else {
-            calc_fn_hash(None, fn_name, args_len).into()
+            ),
+            #[cfg(feature = "no_function")]
+            true => FnCallHashes::from_native_only(calc_fn_hash(None, fn_name, args_len)),
+            _ => FnCallHashes::from_hash(calc_fn_hash(None, fn_name, args_len)),
         };
 
         self.engine()
@@ -473,7 +474,7 @@ impl<'a> NativeCallContext<'a> {
                 caches,
                 None,
                 fn_name,
-                op_token,
+                op_token.as_ref(),
                 hash,
                 args,
                 is_ref_mut,
diff --git a/src/lib.rs b/src/lib.rs
index 9ac564bb..d27a2a4d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -80,11 +80,14 @@
 #![allow(clippy::upper_case_acronyms)]
 #![allow(clippy::match_same_arms)]
 // The lints below can be turned off to reduce signal/noise ratio
-// #![allow(clippy::too_many_lines)]
-// #![allow(clippy::let_underscore_drop)]
+#![allow(clippy::too_many_lines)]
+#![allow(clippy::let_underscore_drop)]
 #![allow(clippy::absurd_extreme_comparisons)]
 #![allow(clippy::unnecessary_cast)]
-// #![allow(clippy::wildcard_imports)]
+#![allow(clippy::wildcard_imports)]
+#![allow(clippy::no_effect_underscore_binding)]
+#![allow(clippy::semicolon_if_nothing_returned)]
+#![allow(clippy::type_complexity)]
 
 #[cfg(feature = "no_std")]
 extern crate alloc;
@@ -166,7 +169,8 @@ const MAX_USIZE_INT: INT = INT::MAX;
 const MAX_USIZE_INT: INT = usize::MAX as INT;
 
 /// The maximum integer that can fit into a [`usize`].
-#[cfg(all(feature = "only_i32", target_pointer_width = "32"))]
+#[cfg(feature = "only_i32")]
+#[cfg(target_pointer_width = "32")]
 const MAX_USIZE_INT: INT = INT::MAX;
 
 /// Number of bits in [`INT`].
@@ -315,7 +319,8 @@ pub type OptimizationLevel = ();
 #[cfg(feature = "internals")]
 pub use types::dynamic::{AccessMode, DynamicReadLock, DynamicWriteLock, Variant};
 
-#[cfg(all(feature = "internals", not(feature = "no_float")))]
+#[cfg(feature = "internals")]
+#[cfg(not(feature = "no_float"))]
 pub use types::FloatWrapper;
 
 #[cfg(feature = "internals")]
diff --git a/src/module/mod.rs b/src/module/mod.rs
index e299b2a5..962938ec 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -145,7 +145,7 @@ impl FuncInfo {
     }
 }
 
-/// _(internals)_ Calculate a non-zero [`u64`] hash key from a namespace-qualified function name and parameter types.
+/// _(internals)_ Calculate a [`u64`] hash key from a namespace-qualified function name and parameter types.
 /// Exported under the `internals` feature only.
 ///
 /// Module names are passed in via `&str` references from an iterator.
@@ -233,7 +233,7 @@ impl fmt::Debug for Module {
                     .modules
                     .as_deref()
                     .into_iter()
-                    .flat_map(|m| m.keys())
+                    .flat_map(BTreeMap::keys)
                     .map(SmartString::as_str)
                     .collect::<Vec<_>>(),
             )
@@ -991,7 +991,7 @@ impl Module {
         type_id
     }
 
-    /// Set a Rust function into the [`Module`], returning a non-zero hash key.
+    /// Set a Rust function into the [`Module`], returning a [`u64`] hash key.
     ///
     /// If there is an existing Rust function of the same hash, it is replaced.
     ///
@@ -1089,7 +1089,7 @@ impl Module {
         hash_fn
     }
 
-    /// _(metadata)_ Set a Rust function into the [`Module`], returning a non-zero hash key.
+    /// _(metadata)_ Set a Rust function into the [`Module`], returning a [`u64`] hash key.
     /// Exported under the `metadata` feature only.
     ///
     /// If there is an existing Rust function of the same hash, it is replaced.
@@ -1144,7 +1144,7 @@ impl Module {
 
     /// Set a Rust function taking a reference to the scripting [`Engine`][crate::Engine],
     /// the current set of functions, plus a list of mutable [`Dynamic`] references
-    /// into the [`Module`], returning a non-zero hash key.
+    /// into the [`Module`], returning a [`u64`] hash key.
     ///
     /// Use this to register a built-in function which must reference settings on the scripting
     /// [`Engine`][crate::Engine] (e.g. to prevent growing an array beyond the allowed maximum size),
@@ -1234,7 +1234,7 @@ impl Module {
         )
     }
 
-    /// Set a Rust function into the [`Module`], returning a non-zero hash key.
+    /// Set a Rust function into the [`Module`], returning a [`u64`] hash key.
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
@@ -1287,7 +1287,7 @@ impl Module {
         )
     }
 
-    /// Set a Rust getter function taking one mutable parameter, returning a non-zero hash key.
+    /// Set a Rust getter function taking one mutable parameter, returning a [`u64`] hash key.
     /// This function is automatically exposed to the global namespace.
     ///
     /// If there is a similar existing Rust getter function, it is replaced.
@@ -1327,7 +1327,7 @@ impl Module {
     }
 
     /// Set a Rust setter function taking two parameters (the first one mutable) into the [`Module`],
-    /// returning a non-zero hash key.
+    /// returning a [`u64`] hash key.
     /// This function is automatically exposed to the global namespace.
     ///
     /// If there is a similar existing setter Rust function, it is replaced.
@@ -1370,7 +1370,7 @@ impl Module {
         )
     }
 
-    /// Set a pair of Rust getter and setter functions into the [`Module`], returning both non-zero hash keys.
+    /// Set a pair of Rust getter and setter functions into the [`Module`], returning both [`u64`] hash keys.
     /// This is a short-hand for [`set_getter_fn`][Module::set_getter_fn] and [`set_setter_fn`][Module::set_setter_fn].
     ///
     /// These function are automatically exposed to the global namespace.
@@ -1418,7 +1418,7 @@ impl Module {
     }
 
     /// Set a Rust index getter taking two parameters (the first one mutable) into the [`Module`],
-    /// returning a non-zero hash key.
+    /// returning a [`u64`] hash key.
     /// This function is automatically exposed to the global namespace.
     ///
     /// If there is a similar existing setter Rust function, it is replaced.
@@ -1479,7 +1479,7 @@ impl Module {
     }
 
     /// Set a Rust index setter taking three parameters (the first one mutable) into the [`Module`],
-    /// returning a non-zero hash key.
+    /// returning a [`u64`] hash key.
     /// This function is automatically exposed to the global namespace.
     ///
     /// If there is a similar existing Rust function, it is replaced.
@@ -1539,7 +1539,7 @@ impl Module {
         )
     }
 
-    /// Set a pair of Rust index getter and setter functions into the [`Module`], returning both non-zero hash keys.
+    /// Set a pair of Rust index getter and setter functions into the [`Module`], returning both [`u64`] hash keys.
     /// This is a short-hand for [`set_indexer_get_fn`][Module::set_indexer_get_fn] and
     /// [`set_indexer_set_fn`][Module::set_indexer_set_fn].
     ///
@@ -2202,7 +2202,7 @@ impl Module {
                     environ: ref mut e, ..
                 } = f.func
                 {
-                    *e = Some(environ.clone())
+                    *e = Some(environ.clone());
                 }
             });
 
diff --git a/src/optimizer.rs b/src/optimizer.rs
index 67211427..6de5862f 100644
--- a/src/optimizer.rs
+++ b/src/optimizer.rs
@@ -147,7 +147,7 @@ impl<'a> OptimizerState<'a> {
     pub fn call_fn_with_constant_arguments(
         &mut self,
         fn_name: &str,
-        op_token: Option<Token>,
+        op_token: Option<&Token>,
         arg_values: &mut [Dynamic],
     ) -> Option<Dynamic> {
         self.engine
@@ -1138,7 +1138,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
                 }
                 // Overloaded operators can override built-in.
                 _ if x.args.len() == 2 && x.op_token.is_some() && (state.engine.fast_operators() || !state.engine.has_native_fn_override(x.hashes.native(), &arg_types)) => {
-                    if let Some(result) = get_builtin_binary_op_fn(x.op_token.clone().unwrap(), &arg_values[0], &arg_values[1])
+                    if let Some(result) = get_builtin_binary_op_fn(x.op_token.as_ref().unwrap(), &arg_values[0], &arg_values[1])
                         .and_then(|(f, ctx)| {
                             let context = if ctx {
                                 Some((state.engine, x.name.as_str(), None, &state.global, *pos).into())
@@ -1193,7 +1193,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
                     KEYWORD_TYPE_OF if arg_values.len() == 1 => Some(state.engine.map_type_name(arg_values[0].type_name()).into()),
                     #[cfg(not(feature = "no_closure"))]
                     crate::engine::KEYWORD_IS_SHARED if arg_values.len() == 1 => Some(Dynamic::FALSE),
-                    _ => state.call_fn_with_constant_arguments(&x.name, x.op_token.clone(), arg_values)
+                    _ => state.call_fn_with_constant_arguments(&x.name, x.op_token.as_ref(), arg_values)
                 };
 
                 if let Some(r) = result {
diff --git a/src/packages/array_basic.rs b/src/packages/array_basic.rs
index 7dabd569..0e968c4c 100644
--- a/src/packages/array_basic.rs
+++ b/src/packages/array_basic.rs
@@ -1468,10 +1468,9 @@ pub mod array_functions {
     ///
     /// print(x);       // prints "[10, 9, 8, 7, 6, 5, 4, 3, 2, 1]"
     /// ```
-    #[rhai_fn(return_raw)]
-    pub fn sort(ctx: NativeCallContext, array: &mut Array, comparer: FnPtr) -> RhaiResultOf<()> {
+    pub fn sort(ctx: NativeCallContext, array: &mut Array, comparer: FnPtr) {
         if array.len() <= 1 {
-            return Ok(());
+            return;
         }
 
         array.sort_by(|x, y| {
@@ -1489,8 +1488,6 @@ pub mod array_functions {
                     },
                 )
         });
-
-        Ok(())
     }
     /// Sort the array.
     ///
diff --git a/src/packages/blob_basic.rs b/src/packages/blob_basic.rs
index 430b89c0..a5af5296 100644
--- a/src/packages/blob_basic.rs
+++ b/src/packages/blob_basic.rs
@@ -513,11 +513,17 @@ pub mod blob_functions {
     ///
     /// print(b);           // prints "[030405]"
     /// ```
-    #[allow(clippy::cast_sign_loss, clippy::needless_pass_by_value)]
+    #[allow(
+        clippy::cast_sign_loss,
+        clippy::needless_pass_by_value,
+        clippy::cast_possible_truncation
+    )]
     pub fn chop(blob: &mut Blob, len: INT) {
         if !blob.is_empty() {
             if len <= 0 {
                 blob.clear();
+            } else if len > MAX_USIZE_INT {
+                // len > BLOB length
             } else if (len as usize) < blob.len() {
                 blob.drain(0..blob.len() - len as usize);
             }
diff --git a/src/packages/lang_core.rs b/src/packages/lang_core.rs
index 6b55f2e1..ce75f7ef 100644
--- a/src/packages/lang_core.rs
+++ b/src/packages/lang_core.rs
@@ -109,10 +109,10 @@ mod core_functions {
     /// ```
     #[cfg(not(feature = "no_std"))]
     pub fn sleep(seconds: INT) {
-        if seconds <= 0 {
-            return;
+        if seconds > 0 {
+            #[allow(clippy::cast_sign_loss)]
+            std::thread::sleep(std::time::Duration::from_secs(seconds as u64));
         }
-        std::thread::sleep(std::time::Duration::from_secs(seconds as u64));
     }
 
     /// Parse a JSON string into a value.
@@ -142,23 +142,23 @@ mod reflection_functions {
 
     /// Return an array of object maps containing metadata of all script-defined functions.
     pub fn get_fn_metadata_list(ctx: NativeCallContext) -> Array {
-        collect_fn_metadata(ctx, |_, _, _, _, _| true)
+        collect_fn_metadata(&ctx, |_, _, _, _, _| true)
     }
     /// Return an array of object maps containing metadata of all script-defined functions
     /// matching the specified name.
     #[rhai_fn(name = "get_fn_metadata_list")]
     pub fn get_fn_metadata(ctx: NativeCallContext, name: &str) -> Array {
-        collect_fn_metadata(ctx, |_, _, n, _, _| n == name)
+        collect_fn_metadata(&ctx, |_, _, n, _, _| n == name)
     }
     /// Return an array of object maps containing metadata of all script-defined functions
     /// matching the specified name and arity (number of parameters).
     #[rhai_fn(name = "get_fn_metadata_list")]
     #[allow(clippy::cast_sign_loss, clippy::cast_possible_truncation)]
     pub fn get_fn_metadata2(ctx: NativeCallContext, name: &str, params: INT) -> Array {
-        if !(0..=crate::MAX_USIZE_INT).contains(&params) {
-            Array::new()
+        if (0..=crate::MAX_USIZE_INT).contains(&params) {
+            collect_fn_metadata(&ctx, |_, _, n, p, _| p == (params as usize) && n == name)
         } else {
-            collect_fn_metadata(ctx, |_, _, n, p, _| p == (params as usize) && n == name)
+            Array::new()
         }
     }
 }
@@ -167,7 +167,7 @@ mod reflection_functions {
 #[cfg(not(feature = "no_index"))]
 #[cfg(not(feature = "no_object"))]
 fn collect_fn_metadata(
-    ctx: NativeCallContext,
+    ctx: &NativeCallContext,
     filter: impl Fn(FnNamespace, FnAccess, &str, usize, &crate::Shared<crate::ast::ScriptFnDef>) -> bool
         + Copy,
 ) -> crate::Array {
diff --git a/src/parser.rs b/src/parser.rs
index 9051b65d..9f8c6e1f 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -17,9 +17,9 @@ use crate::tokenizer::{
 use crate::types::dynamic::AccessMode;
 use crate::types::StringsInterner;
 use crate::{
-    calc_fn_hash, Dynamic, Engine, EvalAltResult, EvalContext, ExclusiveRange, Identifier,
-    ImmutableString, InclusiveRange, LexError, OptimizationLevel, ParseError, Position, Scope,
-    Shared, SmartString, StaticVec, AST, INT, PERR,
+    calc_fn_hash, Dynamic, Engine, EvalAltResult, EvalContext, ExclusiveRange, FnArgsVec,
+    Identifier, ImmutableString, InclusiveRange, LexError, OptimizationLevel, ParseError, Position,
+    Scope, Shared, SmartString, StaticVec, AST, INT, PERR,
 };
 use bitflags::bitflags;
 #[cfg(feature = "no_std")]
@@ -567,7 +567,7 @@ impl Engine {
         };
 
         let mut _namespace = namespace;
-        let mut args = StaticVec::new_const();
+        let mut args = FnArgsVec::new_const();
 
         match token {
             // id( <EOF>
@@ -625,9 +625,9 @@ impl Engine {
                 let hash = calc_fn_hash(None, &id, 0);
 
                 let hashes = if is_valid_function_name(&id) {
-                    hash.into()
+                    FnCallHashes::from_hash(hash)
                 } else {
-                    FnCallHashes::from_native(hash)
+                    FnCallHashes::from_native_only(hash)
                 };
 
                 args.shrink_to_fit();
@@ -700,9 +700,9 @@ impl Engine {
                     let hash = calc_fn_hash(None, &id, args.len());
 
                     let hashes = if is_valid_function_name(&id) {
-                        hash.into()
+                        FnCallHashes::from_hash(hash)
                     } else {
-                        FnCallHashes::from_native(hash)
+                        FnCallHashes::from_native_only(hash)
                     };
 
                     args.shrink_to_fit();
@@ -1945,14 +1945,14 @@ impl Engine {
 
                     // Call negative function
                     expr => {
-                        let mut args = StaticVec::new_const();
+                        let mut args = FnArgsVec::new_const();
                         args.push(expr);
                         args.shrink_to_fit();
 
                         Ok(FnCallExpr {
                             namespace: Namespace::NONE,
                             name: state.get_interned_string("-"),
-                            hashes: FnCallHashes::from_native(calc_fn_hash(None, "-", 1)),
+                            hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "-", 1)),
                             args,
                             op_token: Some(token),
                             capture_parent_scope: false,
@@ -1973,14 +1973,14 @@ impl Engine {
 
                     // Call plus function
                     expr => {
-                        let mut args = StaticVec::new_const();
+                        let mut args = FnArgsVec::new_const();
                         args.push(expr);
                         args.shrink_to_fit();
 
                         Ok(FnCallExpr {
                             namespace: Namespace::NONE,
                             name: state.get_interned_string("+"),
-                            hashes: FnCallHashes::from_native(calc_fn_hash(None, "+", 1)),
+                            hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "+", 1)),
                             args,
                             op_token: Some(token),
                             capture_parent_scope: false,
@@ -1994,14 +1994,14 @@ impl Engine {
                 let token = token.clone();
                 let pos = eat_token(input, Token::Bang);
 
-                let mut args = StaticVec::new_const();
+                let mut args = FnArgsVec::new_const();
                 args.push(self.parse_unary(input, state, lib, settings.level_up()?)?);
                 args.shrink_to_fit();
 
                 Ok(FnCallExpr {
                     namespace: Namespace::NONE,
                     name: state.get_interned_string("!"),
-                    hashes: FnCallHashes::from_native(calc_fn_hash(None, "!", 1)),
+                    hashes: FnCallHashes::from_native_only(calc_fn_hash(None, "!", 1)),
                     args,
                     op_token: Some(token),
                     capture_parent_scope: false,
@@ -2180,14 +2180,21 @@ impl Engine {
             // lhs.func(...)
             (lhs, Expr::FnCall(mut f, func_pos)) => {
                 // Recalculate hash
+                let args_len = f.args.len() + 1;
                 f.hashes = if is_valid_function_name(&f.name) {
-                    FnCallHashes::from_all(
-                        #[cfg(not(feature = "no_function"))]
-                        calc_fn_hash(None, &f.name, f.args.len()),
-                        calc_fn_hash(None, &f.name, f.args.len() + 1),
-                    )
+                    #[cfg(not(feature = "no_function"))]
+                    {
+                        FnCallHashes::from_script_and_native(
+                            calc_fn_hash(None, &f.name, args_len - 1),
+                            calc_fn_hash(None, &f.name, args_len),
+                        )
+                    }
+                    #[cfg(feature = "no_function")]
+                    {
+                        FnCallHashes::from_native_only(calc_fn_hash(None, &f.name, args_len))
+                    }
                 } else {
-                    FnCallHashes::from_native(calc_fn_hash(None, &f.name, f.args.len() + 1))
+                    FnCallHashes::from_native_only(calc_fn_hash(None, &f.name, args_len))
                 };
 
                 let rhs = Expr::MethodCall(f, func_pos);
@@ -2228,14 +2235,23 @@ impl Engine {
                     // lhs.func().dot_rhs or lhs.func()[idx_rhs]
                     Expr::FnCall(mut f, func_pos) => {
                         // Recalculate hash
+                        let args_len = f.args.len() + 1;
                         f.hashes = if is_valid_function_name(&f.name) {
-                            FnCallHashes::from_all(
-                                #[cfg(not(feature = "no_function"))]
-                                calc_fn_hash(None, &f.name, f.args.len()),
-                                calc_fn_hash(None, &f.name, f.args.len() + 1),
-                            )
+                            #[cfg(not(feature = "no_function"))]
+                            {
+                                FnCallHashes::from_script_and_native(
+                                    calc_fn_hash(None, &f.name, args_len - 1),
+                                    calc_fn_hash(None, &f.name, args_len),
+                                )
+                            }
+                            #[cfg(feature = "no_function")]
+                            {
+                                FnCallHashes::from_native_only(calc_fn_hash(
+                                    None, &f.name, args_len,
+                                ))
+                            }
                         } else {
-                            FnCallHashes::from_native(calc_fn_hash(None, &f.name, f.args.len() + 1))
+                            FnCallHashes::from_native_only(calc_fn_hash(None, &f.name, args_len))
                         };
 
                         let new_lhs = BinaryExpr {
@@ -2343,7 +2359,7 @@ impl Engine {
                 Some(op_token.clone())
             };
 
-            let mut args = StaticVec::new_const();
+            let mut args = FnArgsVec::new_const();
             args.push(root);
             args.push(rhs);
             args.shrink_to_fit();
@@ -2351,7 +2367,7 @@ impl Engine {
             let mut op_base = FnCallExpr {
                 namespace: Namespace::NONE,
                 name: state.get_interned_string(&op),
-                hashes: FnCallHashes::from_native(hash),
+                hashes: FnCallHashes::from_native_only(hash),
                 args,
                 op_token: operator_token,
                 capture_parent_scope: false,
@@ -2394,7 +2410,7 @@ impl Engine {
                     op_base.args.shrink_to_fit();
 
                     // Convert into a call to `contains`
-                    op_base.hashes = calc_fn_hash(None, OP_CONTAINS, 2).into();
+                    op_base.hashes = FnCallHashes::from_hash(calc_fn_hash(None, OP_CONTAINS, 2));
                     op_base.name = state.get_interned_string(OP_CONTAINS);
                     let fn_call = op_base.into_fn_call_expr(pos);
 
@@ -2403,13 +2419,13 @@ impl Engine {
                     } else {
                         // Put a `!` call in front
                         let op = Token::Bang.literal_syntax();
-                        let mut args = StaticVec::new_const();
+                        let mut args = FnArgsVec::new_const();
                         args.push(fn_call);
 
                         let not_base = FnCallExpr {
                             namespace: Namespace::NONE,
                             name: state.get_interned_string(op),
-                            hashes: FnCallHashes::from_native(calc_fn_hash(None, op, 1)),
+                            hashes: FnCallHashes::from_native_only(calc_fn_hash(None, op, 1)),
                             args,
                             op_token: Some(Token::Bang),
                             capture_parent_scope: false,
@@ -2427,9 +2443,9 @@ impl Engine {
                         .map_or(false, Option::is_some) =>
                 {
                     op_base.hashes = if is_valid_script_function {
-                        calc_fn_hash(None, &s, 2).into()
+                        FnCallHashes::from_hash(calc_fn_hash(None, &s, 2))
                     } else {
-                        FnCallHashes::from_native(calc_fn_hash(None, &s, 2))
+                        FnCallHashes::from_native_only(calc_fn_hash(None, &s, 2))
                     };
                     op_base.into_fn_call_expr(pos)
                 }
@@ -3560,7 +3576,9 @@ impl Engine {
         // try { try_block } catch ( var ) { catch_block }
         let branch = self.parse_block(input, state, lib, settings)?.into();
 
-        let expr = if !catch_var.is_empty() {
+        let expr = if catch_var.is_empty() {
+            Expr::Unit(catch_var.pos)
+        } else {
             // Remove the error variable from the stack
             state.stack.as_deref_mut().unwrap().pop();
 
@@ -3569,12 +3587,10 @@ impl Engine {
                 None,
                 catch_var.pos,
             )
-        } else {
-            Expr::Unit(catch_var.pos)
         };
 
         Ok(Stmt::TryCatch(
-            FlowControl { body, expr, branch }.into(),
+            FlowControl { expr, body, branch }.into(),
             settings.pos,
         ))
     }
@@ -3692,7 +3708,7 @@ impl Engine {
         }
 
         let num_externals = externals.len();
-        let mut args = StaticVec::with_capacity(externals.len() + 1);
+        let mut args = FnArgsVec::with_capacity(externals.len() + 1);
 
         args.push(fn_expr);
 
@@ -3709,7 +3725,7 @@ impl Engine {
         let expr = FnCallExpr {
             namespace: Namespace::NONE,
             name: state.get_interned_string(crate::engine::KEYWORD_FN_PTR_CURRY),
-            hashes: FnCallHashes::from_native(calc_fn_hash(
+            hashes: FnCallHashes::from_native_only(calc_fn_hash(
                 None,
                 crate::engine::KEYWORD_FN_PTR_CURRY,
                 num_externals + 1,
diff --git a/src/tokenizer.rs b/src/tokenizer.rs
index f6a0a72e..717b7282 100644
--- a/src/tokenizer.rs
+++ b/src/tokenizer.rs
@@ -6,6 +6,7 @@ use crate::engine::{
 };
 use crate::func::native::OnParseTokenCallback;
 use crate::{Engine, Identifier, LexError, Position, SmartString, StaticVec, INT, UNSIGNED_INT};
+use smallvec::SmallVec;
 #[cfg(feature = "no_std")]
 use std::prelude::v1::*;
 use std::{
@@ -980,7 +981,7 @@ pub fn parse_string_literal(
         if termination_char == next_char && escape.is_empty() {
             // Double wrapper
             if stream.peek_next().map_or(false, |c| c == termination_char) {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 if let Some(ref mut last) = state.last_token {
                     last.push(termination_char);
                 }
@@ -1122,7 +1123,7 @@ pub fn parse_string_literal(
 
 /// Consume the next character.
 #[inline(always)]
-fn eat_next(stream: &mut impl InputStream, pos: &mut Position) -> Option<char> {
+fn eat_next_and_advance(stream: &mut impl InputStream, pos: &mut Position) -> Option<char> {
     pos.advance();
     stream.get_next()
 }
@@ -1147,7 +1148,7 @@ fn scan_block_comment(
         match c {
             '/' => {
                 if let Some(c2) = stream.peek_next().filter(|&c2| c2 == '*') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     if let Some(comment) = comment.as_mut() {
                         comment.push(c2);
                     }
@@ -1156,7 +1157,7 @@ fn scan_block_comment(
             }
             '*' => {
                 if let Some(c2) = stream.peek_next().filter(|&c2| c2 == '/') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     if let Some(comment) = comment.as_mut() {
                         comment.push(c2);
                     }
@@ -1287,11 +1288,11 @@ fn get_next_token_inner(
                 while let Some(next_char) = stream.peek_next() {
                     match next_char {
                         NUMBER_SEPARATOR => {
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                         }
                         ch if valid(ch) => {
                             result.push(next_char);
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                         }
                         #[cfg(any(not(feature = "no_float"), feature = "decimal"))]
                         '.' => {
@@ -1357,7 +1358,7 @@ fn get_next_token_inner(
                             if c == '0' && result.len() <= 1 =>
                         {
                             result.push(next_char);
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
 
                             valid = match ch {
                                 'x' | 'X' => is_hex_digit,
@@ -1461,16 +1462,16 @@ fn get_next_token_inner(
                 match stream.peek_next() {
                     // `\r - start from next line
                     Some('\r') => {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         // `\r\n
                         if stream.peek_next() == Some('\n') {
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                         }
                         pos.new_line();
                     }
                     // `\n - start from next line
                     Some('\n') => {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         pos.new_line();
                     }
                     _ => (),
@@ -1522,13 +1523,13 @@ fn get_next_token_inner(
 
             // Unit
             ('(', ')') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Unit, start_pos));
             }
 
             // Parentheses
             ('(', '*') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("(*".into())), start_pos));
             }
             ('(', ..) => return Some((Token::LeftParen, start_pos)),
@@ -1541,16 +1542,16 @@ fn get_next_token_inner(
             // Map literal
             #[cfg(not(feature = "no_object"))]
             ('#', '{') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::MapStart, start_pos));
             }
             // Shebang
             ('#', '!') => return Some((Token::Reserved(Box::new("#!".into())), start_pos)),
 
             ('#', ' ') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 let token = if stream.peek_next() == Some('{') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     "# {"
                 } else {
                     "#"
@@ -1562,11 +1563,11 @@ fn get_next_token_inner(
 
             // Operators
             ('+', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::PlusAssign, start_pos));
             }
             ('+', '+') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("++".into())), start_pos));
             }
             ('+', ..) if !state.next_token_cannot_be_unary => {
@@ -1577,15 +1578,15 @@ fn get_next_token_inner(
             ('-', '0'..='9') if !state.next_token_cannot_be_unary => negated = Some(start_pos),
             ('-', '0'..='9') => return Some((Token::Minus, start_pos)),
             ('-', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::MinusAssign, start_pos));
             }
             ('-', '>') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("->".into())), start_pos));
             }
             ('-', '-') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("--".into())), start_pos));
             }
             ('-', ..) if !state.next_token_cannot_be_unary => {
@@ -1594,19 +1595,19 @@ fn get_next_token_inner(
             ('-', ..) => return Some((Token::Minus, start_pos)),
 
             ('*', ')') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("*)".into())), start_pos));
             }
             ('*', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::MultiplyAssign, start_pos));
             }
             ('*', '*') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 return Some((
                     if stream.peek_next() == Some('=') {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         Token::PowerOfAssign
                     } else {
                         Token::PowerOf
@@ -1618,13 +1619,13 @@ fn get_next_token_inner(
 
             // Comments
             ('/', '/') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 let mut comment: Option<String> = match stream.peek_next() {
                     #[cfg(not(feature = "no_function"))]
                     #[cfg(feature = "metadata")]
                     Some('/') => {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
 
                         // Long streams of `///...` are not doc-comments
                         match stream.peek_next() {
@@ -1634,7 +1635,7 @@ fn get_next_token_inner(
                     }
                     #[cfg(feature = "metadata")]
                     Some('!') => {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         Some("//!".into())
                     }
                     _ if state.include_comments => Some("//".into()),
@@ -1645,7 +1646,7 @@ fn get_next_token_inner(
                     if c == '\r' {
                         // \r\n
                         if stream.peek_next() == Some('\n') {
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                         }
                         pos.new_line();
                         break;
@@ -1676,13 +1677,13 @@ fn get_next_token_inner(
             }
             ('/', '*') => {
                 state.comment_level = 1;
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 let mut comment: Option<String> = match stream.peek_next() {
                     #[cfg(not(feature = "no_function"))]
                     #[cfg(feature = "metadata")]
                     Some('*') => {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
 
                         // Long streams of `/****...` are not doc-comments
                         match stream.peek_next() {
@@ -1703,7 +1704,7 @@ fn get_next_token_inner(
             }
 
             ('/', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::DivideAssign, start_pos));
             }
             ('/', ..) => return Some((Token::Divide, start_pos)),
@@ -1712,15 +1713,15 @@ fn get_next_token_inner(
             (',', ..) => return Some((Token::Comma, start_pos)),
 
             ('.', '.') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((
                     match stream.peek_next() {
                         Some('.') => {
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                             Token::Reserved(Box::new("...".into()))
                         }
                         Some('=') => {
-                            eat_next(stream, pos);
+                            eat_next_and_advance(stream, pos);
                             Token::InclusiveRange
                         }
                         _ => Token::ExclusiveRange,
@@ -1731,56 +1732,56 @@ fn get_next_token_inner(
             ('.', ..) => return Some((Token::Period, start_pos)),
 
             ('=', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 if stream.peek_next() == Some('=') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     return Some((Token::Reserved(Box::new("===".into())), start_pos));
                 }
 
                 return Some((Token::EqualsTo, start_pos));
             }
             ('=', '>') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::DoubleArrow, start_pos));
             }
             ('=', ..) => return Some((Token::Equals, start_pos)),
 
             #[cfg(not(feature = "no_module"))]
             (':', ':') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 if stream.peek_next() == Some('<') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     return Some((Token::Reserved(Box::new("::<".into())), start_pos));
                 }
 
                 return Some((Token::DoubleColon, start_pos));
             }
             (':', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new(":=".into())), start_pos));
             }
             (':', ';') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new(":;".into())), start_pos));
             }
             (':', ..) => return Some((Token::Colon, start_pos)),
 
             ('<', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::LessThanEqualsTo, start_pos));
             }
             ('<', '-') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("<-".into())), start_pos));
             }
             ('<', '<') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 return Some((
                     if stream.peek_next() == Some('=') {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         Token::LeftShiftAssign
                     } else {
                         Token::LeftShift
@@ -1789,21 +1790,21 @@ fn get_next_token_inner(
                 ));
             }
             ('<', '|') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("<|".into())), start_pos));
             }
             ('<', ..) => return Some((Token::LessThan, start_pos)),
 
             ('>', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::GreaterThanEqualsTo, start_pos));
             }
             ('>', '>') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 return Some((
                     if stream.peek_next() == Some('=') {
-                        eat_next(stream, pos);
+                        eat_next_and_advance(stream, pos);
                         Token::RightShiftAssign
                     } else {
                         Token::RightShift
@@ -1814,56 +1815,68 @@ fn get_next_token_inner(
             ('>', ..) => return Some((Token::GreaterThan, start_pos)),
 
             ('!', 'i') => {
-                eat_next(stream, pos);
+                stream.get_next().unwrap();
                 if stream.peek_next() == Some('n') {
-                    eat_next(stream, pos);
-                    return Some((Token::NotIn, start_pos));
+                    stream.get_next().unwrap();
+                    match stream.peek_next() {
+                        Some(c) if is_id_continue(c) => {
+                            stream.unget('n');
+                            stream.unget('i');
+                            return Some((Token::Bang, start_pos));
+                        }
+                        _ => {
+                            pos.advance();
+                            pos.advance();
+                            return Some((Token::NotIn, start_pos));
+                        }
+                    }
                 }
+
                 stream.unget('i');
                 return Some((Token::Bang, start_pos));
             }
             ('!', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
 
                 if stream.peek_next() == Some('=') {
-                    eat_next(stream, pos);
+                    eat_next_and_advance(stream, pos);
                     return Some((Token::Reserved(Box::new("!==".into())), start_pos));
                 }
 
                 return Some((Token::NotEqualsTo, start_pos));
             }
             ('!', '.') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("!.".into())), start_pos));
             }
             ('!', ..) => return Some((Token::Bang, start_pos)),
 
             ('|', '|') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Or, start_pos));
             }
             ('|', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::OrAssign, start_pos));
             }
             ('|', '>') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::Reserved(Box::new("|>".into())), start_pos));
             }
             ('|', ..) => return Some((Token::Pipe, start_pos)),
 
             ('&', '&') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::And, start_pos));
             }
             ('&', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::AndAssign, start_pos));
             }
             ('&', ..) => return Some((Token::Ampersand, start_pos)),
 
             ('^', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::XOrAssign, start_pos));
             }
             ('^', ..) => return Some((Token::XOr, start_pos)),
@@ -1871,7 +1884,7 @@ fn get_next_token_inner(
             ('~', ..) => return Some((Token::Reserved(Box::new("~".into())), start_pos)),
 
             ('%', '=') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::ModuloAssign, start_pos));
             }
             ('%', ..) => return Some((Token::Modulo, start_pos)),
@@ -1881,7 +1894,7 @@ fn get_next_token_inner(
             ('$', ..) => return Some((Token::Reserved(Box::new("$".into())), start_pos)),
 
             ('?', '.') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((
                     #[cfg(not(feature = "no_object"))]
                     Token::Elvis,
@@ -1891,11 +1904,11 @@ fn get_next_token_inner(
                 ));
             }
             ('?', '?') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((Token::DoubleQuestion, start_pos));
             }
             ('?', '[') => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 return Some((
                     #[cfg(not(feature = "no_index"))]
                     Token::QuestionBracket,
@@ -1940,7 +1953,7 @@ fn parse_identifier_token(
     while let Some(next_char) = stream.peek_next() {
         match next_char {
             x if is_id_continue(x) => {
-                eat_next(stream, pos);
+                eat_next_and_advance(stream, pos);
                 identifier.push(x);
                 if let Some(ref mut last) = state.last_token {
                     last.push(x);
@@ -2091,8 +2104,8 @@ pub fn is_reserved_keyword_or_symbol(syntax: &str) -> bool {
 ///
 /// Multiple character streams are jointed together to form one single stream.
 pub struct MultiInputsStream<'a> {
-    /// Buffered character, if any.
-    pub buf: Option<char>,
+    /// Buffered characters, if any.
+    pub buf: SmallVec<[char; 2]>,
     /// The current stream index.
     pub index: usize,
     /// The input character streams.
@@ -2102,15 +2115,11 @@ pub struct MultiInputsStream<'a> {
 impl InputStream for MultiInputsStream<'_> {
     #[inline]
     fn unget(&mut self, ch: char) {
-        if self.buf.is_some() {
-            panic!("cannot unget two characters in a row");
-        }
-
-        self.buf = Some(ch);
+        self.buf.push(ch);
     }
     fn get_next(&mut self) -> Option<char> {
-        if let Some(ch) = self.buf.take() {
-            return Some(ch);
+        if let ch @ Some(..) = self.buf.pop() {
+            return ch;
         }
 
         loop {
@@ -2127,8 +2136,8 @@ impl InputStream for MultiInputsStream<'_> {
         }
     }
     fn peek_next(&mut self) -> Option<char> {
-        if let Some(ch) = self.buf {
-            return Some(ch);
+        if let ch @ Some(..) = self.buf.last() {
+            return ch.copied();
         }
 
         loop {
@@ -2368,7 +2377,7 @@ impl Engine {
                 },
                 pos: Position::new(1, 0),
                 stream: MultiInputsStream {
-                    buf: None,
+                    buf: SmallVec::new_const(),
                     streams: input
                         .into_iter()
                         .map(|s| s.as_ref().chars().peekable())