diff --git a/src/engine.rs b/src/engine.rs
index d72b2dac..95dbf331 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1235,13 +1235,14 @@ impl Engine {
         target: &mut Target,
         root: (&str, Position),
         rhs: &Expr,
-        _terminate_chaining: bool,
+        terminate_chaining: bool,
         idx_values: &mut StaticVec<ChainArgument>,
         chain_type: ChainType,
         level: usize,
         new_val: Option<((Dynamic, Position), (Option<OpAssignment>, Position))>,
     ) -> Result<(Dynamic, bool), Box<EvalAltResult>> {
         let is_ref_mut = target.is_ref();
+        let _terminate_chaining = terminate_chaining;
 
         // Pop the last index value
         let idx_val = idx_values
@@ -1725,7 +1726,7 @@ impl Engine {
         this_ptr: &mut Option<&mut Dynamic>,
         expr: &Expr,
         terminate_chaining: bool,
-        _parent_chain_type: ChainType,
+        parent_chain_type: ChainType,
         idx_values: &mut StaticVec<ChainArgument>,
         size: usize,
         level: usize,
@@ -1733,6 +1734,8 @@ impl Engine {
         #[cfg(not(feature = "unchecked"))]
         self.inc_operations(state, expr.position())?;
 
+        let _parent_chain_type = parent_chain_type;
+
         match expr {
             #[cfg(not(feature = "no_object"))]
             Expr::FnCall(x, _) if _parent_chain_type == ChainType::Dotting && !x.is_qualified() => {
@@ -1848,15 +1851,18 @@ impl Engine {
         state: &mut EvalState,
         lib: &[&Module],
         target: &'t mut Dynamic,
-        mut idx: Dynamic,
+        idx: Dynamic,
         idx_pos: Position,
-        _create: bool,
-        indexers: bool,
+        add_if_not_found: bool,
+        use_indexers: bool,
         level: usize,
     ) -> Result<Target<'t>, Box<EvalAltResult>> {
         #[cfg(not(feature = "unchecked"))]
         self.inc_operations(state, Position::NONE)?;
 
+        let mut idx = idx;
+        let _add_if_not_found = add_if_not_found;
+
         match target {
             #[cfg(not(feature = "no_index"))]
             Dynamic(Union::Array(arr, _, _)) => {
@@ -1907,7 +1913,7 @@ impl Engine {
                     self.make_type_mismatch_err::<ImmutableString>(idx.type_name(), idx_pos)
                 })?;
 
-                if _create && !map.contains_key(index.as_str()) {
+                if _add_if_not_found && !map.contains_key(index.as_str()) {
                     map.insert(index.clone().into(), Default::default());
                 }
 
@@ -1988,7 +1994,7 @@ impl Engine {
                 Ok(Target::StringChar(target, offset, ch.into()))
             }
 
-            _ if indexers => {
+            _ if use_indexers => {
                 let args = &mut [target, &mut idx];
                 let hash_get = FnCallHashes::from_native(crate::calc_fn_hash(FN_IDX_GET, 2));
                 let idx_pos = Position::NONE;
@@ -2298,13 +2304,15 @@ impl Engine {
         op_pos: Position,
         target: &mut Target,
         root: (&str, Position),
-        mut new_val: Dynamic,
+        new_val: Dynamic,
     ) -> Result<(), Box<EvalAltResult>> {
         if target.is_read_only() {
             // Assignment to constant variable
             return EvalAltResult::ErrorAssignmentToConstant(root.0.to_string(), root.1).into();
         }
 
+        let mut new_val = new_val;
+
         if let Some(OpAssignment {
             hash_op_assign,
             hash_op,
diff --git a/src/fn_call.rs b/src/fn_call.rs
index e79e906a..8ed8430c 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -611,7 +611,7 @@ impl Engine {
         hashes: FnCallHashes,
         args: &mut FnCallArgs,
         is_ref_mut: bool,
-        _is_method_call: bool,
+        is_method_call: bool,
         pos: Position,
         _capture_scope: Option<Scope>,
         _level: usize,
@@ -625,6 +625,8 @@ impl Engine {
         #[cfg(not(feature = "no_closure"))]
         ensure_no_data_race(fn_name, args, is_ref_mut)?;
 
+        let _is_method_call = is_method_call;
+
         // These may be redirected from method style calls.
         match fn_name {
             // Handle type_of()
diff --git a/src/optimize.rs b/src/optimize.rs
index 08f3fadd..299098c0 100644
--- a/src/optimize.rs
+++ b/src/optimize.rs
@@ -686,7 +686,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
 }
 
 /// Optimize an [expression][Expr].
-fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
+fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, chaining: bool) {
     // These keywords are handled specially
     const DONT_EVAL_KEYWORDS: &[&str] = &[
         KEYWORD_PRINT, // side effects
@@ -694,6 +694,8 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
         KEYWORD_EVAL,  // arbitrary scripts
     ];
 
+    let _chaining = chaining;
+
     match expr {
         // {}
         Expr::Stmt(x) if x.is_empty() => { state.set_dirty(); *expr = Expr::Unit(x.position()) }
@@ -1061,12 +1063,14 @@ fn optimize_expr(expr: &mut Expr, state: &mut OptimizerState, _chaining: bool) {
 
 /// Optimize a block of [statements][Stmt] at top level.
 fn optimize_top_level(
-    mut statements: Vec<Stmt>,
+    statements: Vec<Stmt>,
     engine: &Engine,
     scope: &Scope,
     lib: &[&Module],
     optimization_level: OptimizationLevel,
 ) -> Vec<Stmt> {
+    let mut statements = statements;
+
     // If optimization level is None then skip optimizing
     if optimization_level == OptimizationLevel::None {
         statements.shrink_to_fit();
@@ -1093,8 +1097,8 @@ fn optimize_top_level(
 pub fn optimize_into_ast(
     engine: &Engine,
     scope: &Scope,
-    mut statements: Vec<Stmt>,
-    _functions: Vec<crate::Shared<crate::ast::ScriptFnDef>>,
+    statements: Vec<Stmt>,
+    functions: Vec<crate::Shared<crate::ast::ScriptFnDef>>,
     optimization_level: OptimizationLevel,
 ) -> AST {
     let level = if cfg!(feature = "no_optimize") {
@@ -1103,6 +1107,9 @@ pub fn optimize_into_ast(
         optimization_level
     };
 
+    let mut statements = statements;
+    let _functions = functions;
+
     #[cfg(not(feature = "no_function"))]
     let lib = {
         let mut module = Module::new();
diff --git a/src/packages/array_basic.rs b/src/packages/array_basic.rs
index 3400f1d1..a8422e98 100644
--- a/src/packages/array_basic.rs
+++ b/src/packages/array_basic.rs
@@ -753,17 +753,19 @@ mod array_functions {
     #[rhai_fn(name = "==", return_raw, pure)]
     pub fn equals(
         ctx: NativeCallContext,
-        array: &mut Array,
-        mut array2: Array,
+        array1: &mut Array,
+        array2: Array,
     ) -> Result<bool, Box<EvalAltResult>> {
-        if array.len() != array2.len() {
+        if array1.len() != array2.len() {
             return Ok(false);
         }
-        if array.is_empty() {
+        if array1.is_empty() {
             return Ok(true);
         }
 
-        for (a1, a2) in array.iter_mut().zip(array2.iter_mut()) {
+        let mut array2 = array2;
+
+        for (a1, a2) in array1.iter_mut().zip(array2.iter_mut()) {
             if !ctx
                 .call_fn_dynamic_raw(OP_EQUALS, true, &mut [a1, a2])
                 .or_else(|err| match *err {
@@ -791,9 +793,9 @@ mod array_functions {
     #[rhai_fn(name = "!=", return_raw, pure)]
     pub fn not_equals(
         ctx: NativeCallContext,
-        array: &mut Array,
+        array1: &mut Array,
         array2: Array,
     ) -> Result<bool, Box<EvalAltResult>> {
-        equals(ctx, array, array2).map(|r| !r)
+        equals(ctx, array1, array2).map(|r| !r)
     }
 }
diff --git a/src/packages/fn_basic.rs b/src/packages/fn_basic.rs
index 063bd42c..dbe86112 100644
--- a/src/packages/fn_basic.rs
+++ b/src/packages/fn_basic.rs
@@ -10,15 +10,15 @@ def_package!(crate:BasicFnPackage:"Basic Fn functions.", lib, {
 #[export_module]
 mod fn_ptr_functions {
     #[rhai_fn(name = "name", get = "name", pure)]
-    pub fn name(f: &mut FnPtr) -> ImmutableString {
-        f.fn_name_raw().into()
+    pub fn name(fn_ptr: &mut FnPtr) -> ImmutableString {
+        fn_ptr.fn_name_raw().into()
     }
 
     #[cfg(not(feature = "no_function"))]
     pub mod functions {
         #[rhai_fn(name = "is_anonymous", get = "is_anonymous", pure)]
-        pub fn is_anonymous(f: &mut FnPtr) -> bool {
-            f.is_anonymous()
+        pub fn is_anonymous(fn_ptr: &mut FnPtr) -> bool {
+            fn_ptr.is_anonymous()
         }
     }
 
diff --git a/src/packages/map_basic.rs b/src/packages/map_basic.rs
index a7f068da..b7e52bc3 100644
--- a/src/packages/map_basic.rs
+++ b/src/packages/map_basic.rs
@@ -34,9 +34,10 @@ mod map_functions {
         map.extend(map2.into_iter());
     }
     #[rhai_fn(name = "+")]
-    pub fn merge(mut map: Map, map2: Map) -> Map {
-        map.extend(map2.into_iter());
-        map
+    pub fn merge(map1: Map, map2: Map) -> Map {
+        let mut map1 = map1;
+        map1.extend(map2.into_iter());
+        map1
     }
     pub fn fill_with(map: &mut Map, map2: Map) {
         map2.into_iter().for_each(|(key, value)| {
@@ -46,17 +47,19 @@ mod map_functions {
     #[rhai_fn(name = "==", return_raw, pure)]
     pub fn equals(
         ctx: NativeCallContext,
-        map: &mut Map,
-        mut map2: Map,
+        map1: &mut Map,
+        map2: Map,
     ) -> Result<bool, Box<EvalAltResult>> {
-        if map.len() != map2.len() {
+        if map1.len() != map2.len() {
             return Ok(false);
         }
-        if map.is_empty() {
+        if map1.is_empty() {
             return Ok(true);
         }
 
-        for (m1, v1) in map.iter_mut() {
+        let mut map2 = map2;
+
+        for (m1, v1) in map1.iter_mut() {
             if let Some(v2) = map2.get_mut(m1) {
                 let equals = ctx
                     .call_fn_dynamic_raw(OP_EQUALS, true, &mut [v1, v2])
@@ -75,10 +78,10 @@ mod map_functions {
     #[rhai_fn(name = "!=", return_raw, pure)]
     pub fn not_equals(
         ctx: NativeCallContext,
-        map: &mut Map,
+        map1: &mut Map,
         map2: Map,
     ) -> Result<bool, Box<EvalAltResult>> {
-        equals(ctx, map, map2).map(|r| !r)
+        equals(ctx, map1, map2).map(|r| !r)
     }
 
     #[cfg(not(feature = "no_index"))]
diff --git a/src/packages/math_basic.rs b/src/packages/math_basic.rs
index 674a6a2e..1f281390 100644
--- a/src/packages/math_basic.rs
+++ b/src/packages/math_basic.rs
@@ -112,7 +112,7 @@ def_package!(crate:BasicMathPackage:"Basic mathematic functions.", lib, {
 #[export_module]
 mod int_functions {
     #[rhai_fn(name = "parse_int", return_raw)]
-    pub fn parse_int_radix(s: &str, radix: INT) -> Result<INT, Box<EvalAltResult>> {
+    pub fn parse_int_radix(string: &str, radix: INT) -> Result<INT, Box<EvalAltResult>> {
         if !(2..=36).contains(&radix) {
             return EvalAltResult::ErrorArithmetic(
                 format!("Invalid radix: '{}'", radix),
@@ -121,17 +121,17 @@ mod int_functions {
             .into();
         }
 
-        INT::from_str_radix(s.trim(), radix as u32).map_err(|err| {
+        INT::from_str_radix(string.trim(), radix as u32).map_err(|err| {
             EvalAltResult::ErrorArithmetic(
-                format!("Error parsing integer number '{}': {}", s, err),
+                format!("Error parsing integer number '{}': {}", string, err),
                 Position::NONE,
             )
             .into()
         })
     }
     #[rhai_fn(name = "parse_int", return_raw)]
-    pub fn parse_int(s: &str) -> Result<INT, Box<EvalAltResult>> {
-        parse_int_radix(s, 10)
+    pub fn parse_int(string: &str) -> Result<INT, Box<EvalAltResult>> {
+        parse_int_radix(string, 10)
     }
 }
 
@@ -283,10 +283,10 @@ mod float_functions {
         }
     }
     #[rhai_fn(return_raw)]
-    pub fn parse_float(s: &str) -> Result<FLOAT, Box<EvalAltResult>> {
-        s.trim().parse::<FLOAT>().map_err(|err| {
+    pub fn parse_float(string: &str) -> Result<FLOAT, Box<EvalAltResult>> {
+        string.trim().parse::<FLOAT>().map_err(|err| {
             EvalAltResult::ErrorArithmetic(
-                format!("Error parsing floating-point number '{}': {}", s, err),
+                format!("Error parsing floating-point number '{}': {}", string, err),
                 Position::NONE,
             )
             .into()
@@ -427,12 +427,12 @@ mod decimal_functions {
         x.fract()
     }
     #[rhai_fn(return_raw)]
-    pub fn parse_decimal(s: &str) -> Result<Decimal, Box<EvalAltResult>> {
-        Decimal::from_str(s)
+    pub fn parse_decimal(string: &str) -> Result<Decimal, Box<EvalAltResult>> {
+        Decimal::from_str(string)
             .or_else(|_| Decimal::from_scientific(s))
             .map_err(|err| {
                 EvalAltResult::ErrorArithmetic(
-                    format!("Error parsing decimal number '{}': {}", s, err),
+                    format!("Error parsing decimal number '{}': {}", string, err),
                     Position::NONE,
                 )
                 .into()
diff --git a/src/packages/string_more.rs b/src/packages/string_more.rs
index 22c9074d..c72a695a 100644
--- a/src/packages/string_more.rs
+++ b/src/packages/string_more.rs
@@ -50,12 +50,13 @@ mod string_functions {
         string1 + string2
     }
     #[rhai_fn(name = "+", name = "append")]
-    pub fn add_append_char(string: ImmutableString, ch: char) -> ImmutableString {
-        string + ch
+    pub fn add_append_char(string: ImmutableString, character: char) -> ImmutableString {
+        string + character
     }
 
     #[rhai_fn(name = "+", name = "append")]
-    pub fn add_append_unit(string: ImmutableString, _item: ()) -> ImmutableString {
+    pub fn add_append_unit(string: ImmutableString, item: ()) -> ImmutableString {
+        let _item = item;
         string
     }
     #[rhai_fn(name = "+")]
@@ -369,11 +370,13 @@ mod string_functions {
 
     #[rhai_fn(return_raw)]
     pub fn pad(
-        _ctx: NativeCallContext,
+        ctx: NativeCallContext,
         string: &mut ImmutableString,
         len: INT,
         character: char,
     ) -> Result<(), Box<crate::EvalAltResult>> {
+        let _ctx = ctx;
+
         // Check if string will be over max size limit
         #[cfg(not(feature = "unchecked"))]
         if _ctx.engine().max_string_size() > 0 && len as usize > _ctx.engine().max_string_size() {
@@ -411,11 +414,13 @@ mod string_functions {
     }
     #[rhai_fn(name = "pad", return_raw)]
     pub fn pad_with_string(
-        _ctx: NativeCallContext,
+        ctx: NativeCallContext,
         string: &mut ImmutableString,
         len: INT,
         padding: &str,
     ) -> Result<(), Box<crate::EvalAltResult>> {
+        let _ctx = ctx;
+
         // Check if string will be over max size limit
         #[cfg(not(feature = "unchecked"))]
         if _ctx.engine().max_string_size() > 0 && len as usize > _ctx.engine().max_string_size() {
diff --git a/src/packages/time_basic.rs b/src/packages/time_basic.rs
index 0ef705c9..44961872 100644
--- a/src/packages/time_basic.rs
+++ b/src/packages/time_basic.rs
@@ -54,14 +54,14 @@ mod time_functions {
 
     #[rhai_fn(return_raw, name = "-")]
     pub fn time_diff(
-        timestamp: Instant,
+        timestamp1: Instant,
         timestamp2: Instant,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
         #[cfg(not(feature = "no_float"))]
-        return Ok(if timestamp2 > timestamp {
-            -(timestamp2 - timestamp).as_secs_f64() as FLOAT
+        return Ok(if timestamp2 > timestamp1 {
+            -(timestamp2 - timestamp1).as_secs_f64() as FLOAT
         } else {
-            (timestamp - timestamp2).as_secs_f64() as FLOAT
+            (timestamp1 - timestamp2).as_secs_f64() as FLOAT
         }
         .into());
 
@@ -225,27 +225,27 @@ mod time_functions {
     }
 
     #[rhai_fn(name = "==")]
-    pub fn eq(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp == timestamp2
+    pub fn eq(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 == timestamp2
     }
     #[rhai_fn(name = "!=")]
-    pub fn ne(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp != timestamp2
+    pub fn ne(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 != timestamp2
     }
     #[rhai_fn(name = "<")]
-    pub fn lt(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp < timestamp2
+    pub fn lt(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 < timestamp2
     }
     #[rhai_fn(name = "<=")]
-    pub fn lte(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp <= timestamp2
+    pub fn lte(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 <= timestamp2
     }
     #[rhai_fn(name = ">")]
-    pub fn gt(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp > timestamp2
+    pub fn gt(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 > timestamp2
     }
     #[rhai_fn(name = ">=")]
-    pub fn gte(timestamp: Instant, timestamp2: Instant) -> bool {
-        timestamp >= timestamp2
+    pub fn gte(timestamp1: Instant, timestamp2: Instant) -> bool {
+        timestamp1 >= timestamp2
     }
 }
diff --git a/src/parse.rs b/src/parse.rs
index 777020d8..4b132653 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -142,8 +142,9 @@ impl<'e> ParseState<'e> {
     ///
     /// Return `None` when the variable name is not found in the `stack`.
     #[inline]
-    pub fn access_var(&mut self, name: &str, _pos: Position) -> Option<NonZeroUsize> {
+    pub fn access_var(&mut self, name: &str, pos: Position) -> Option<NonZeroUsize> {
         let mut barrier = false;
+        let _pos = pos;
 
         let index = self
             .stack
@@ -393,8 +394,10 @@ fn parse_paren_expr(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -428,7 +431,7 @@ fn parse_fn_call(
     lib: &mut FunctionsLib,
     id: Identifier,
     capture: bool,
-    mut namespace: Option<NamespaceRef>,
+    namespace: Option<NamespaceRef>,
     settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
     #[cfg(not(feature = "unchecked"))]
@@ -436,6 +439,7 @@ fn parse_fn_call(
 
     let (token, token_pos) = input.peek().expect(NEVER_ENDS);
 
+    let mut namespace = namespace;
     let mut args = StaticVec::new();
 
     match token {
@@ -565,8 +569,10 @@ fn parse_index_chain(
     state: &mut ParseState,
     lib: &mut FunctionsLib,
     lhs: Expr,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -726,8 +732,10 @@ fn parse_array_literal(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -798,8 +806,10 @@ fn parse_map_literal(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -914,8 +924,10 @@ fn parse_switch(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -1059,8 +1071,10 @@ fn parse_primary(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -1439,8 +1453,10 @@ fn parse_unary(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     let (token, token_pos) = input.peek().expect(NEVER_ENDS);
     settings.pos = *token_pos;
 
@@ -1623,8 +1639,10 @@ fn parse_op_assignment_stmt(
     state: &mut ParseState,
     lib: &mut FunctionsLib,
     lhs: Expr,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -1774,8 +1792,10 @@ fn parse_binary_op(
     lib: &mut FunctionsLib,
     parent_precedence: Option<Precedence>,
     lhs: Expr,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -1955,11 +1975,12 @@ fn parse_custom_syntax(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
     key: &str,
     syntax: &CustomSyntax,
     pos: Position,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
     let mut keywords: StaticVec<Expr> = Default::default();
     let mut segments: StaticVec<_> = Default::default();
     let mut tokens: StaticVec<_> = Default::default();
@@ -2101,8 +2122,10 @@ fn parse_expr(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Expr, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2144,8 +2167,10 @@ fn parse_if(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2183,8 +2208,10 @@ fn parse_while_loop(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2212,8 +2239,10 @@ fn parse_do(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2254,8 +2283,10 @@ fn parse_for(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2353,9 +2384,11 @@ fn parse_let(
     state: &mut ParseState,
     lib: &mut FunctionsLib,
     var_type: AccessMode,
-    export: bool,
-    mut settings: ParseSettings,
+    is_export: bool,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2381,7 +2414,7 @@ fn parse_let(
 
     state.stack.push((name, var_type));
 
-    let export = if export {
+    let export = if is_export {
         AST_OPTION_EXPORTED
     } else {
         AST_OPTION_NONE
@@ -2406,8 +2439,10 @@ fn parse_import(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2446,8 +2481,10 @@ fn parse_export(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2518,8 +2555,10 @@ fn parse_block(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     // Must start with {
     settings.pos = match input.next().expect(NEVER_ENDS) {
         (Token::LeftBrace, pos) => pos,
@@ -2619,8 +2658,10 @@ fn parse_expr_stmt(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2636,10 +2677,12 @@ fn parse_stmt(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
     use AccessMode::{ReadOnly, ReadWrite};
 
+    let mut settings = settings;
+
     #[cfg(not(feature = "no_function"))]
     #[cfg(feature = "metadata")]
     let comments = {
@@ -2836,8 +2879,10 @@ fn parse_try_catch(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<Stmt, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -2892,11 +2937,13 @@ fn parse_fn(
     state: &mut ParseState,
     lib: &mut FunctionsLib,
     access: FnAccess,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
     #[cfg(not(feature = "no_function"))]
     #[cfg(feature = "metadata")]
     comments: StaticVec<String>,
 ) -> Result<ScriptFnDef, ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
@@ -3039,8 +3086,10 @@ fn parse_anon_fn(
     input: &mut TokenStream,
     state: &mut ParseState,
     lib: &mut FunctionsLib,
-    mut settings: ParseSettings,
+    settings: ParseSettings,
 ) -> Result<(Expr, ScriptFnDef), ParseError> {
+    let mut settings = settings;
+
     #[cfg(not(feature = "unchecked"))]
     settings.ensure_level_within_max_limit(state.max_expr_depth)?;
 
diff --git a/src/token.rs b/src/token.rs
index cc425efd..3fd2d8b3 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -1266,11 +1266,12 @@ fn eat_next(stream: &mut impl InputStream, pos: &mut Position) -> Option<char> {
 /// Scan for a block comment until the end.
 fn scan_block_comment(
     stream: &mut impl InputStream,
-    mut level: usize,
+    level: usize,
     pos: &mut Position,
-    mut comment: Option<&mut String>,
+    comment: Option<&mut String>,
 ) -> usize {
-    let comment = &mut comment;
+    let mut level = level;
+    let mut comment = comment;
 
     while let Some(c) = stream.get_next() {
         pos.advance();