diff --git a/src/ast.rs b/src/ast.rs
index fafc4394..06196a67 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -8,14 +8,13 @@ use crate::stdlib::{
     boxed::Box,
     collections::HashMap,
     fmt,
-    hash::Hash,
+    hash::{Hash, Hasher},
     num::{NonZeroU64, NonZeroUsize},
-    ops::{Add, AddAssign},
+    ops::{Add, AddAssign, Deref, DerefMut},
     string::String,
     vec,
     vec::Vec,
 };
-use crate::syntax::FnCustomSyntaxEval;
 use crate::token::Token;
 use crate::utils::StraightHasherBuilder;
 use crate::{
@@ -492,11 +491,7 @@ impl AST {
             (true, true) => vec![],
         };
 
-        let source = if other.source.is_some() {
-            other.source.clone()
-        } else {
-            self.source.clone()
-        };
+        let source = other.source.clone().or_else(|| self.source.clone());
 
         let mut functions = functions.as_ref().clone();
         functions.merge_filtered(&other.functions, &mut filter);
@@ -696,24 +691,68 @@ pub enum ReturnType {
     Exception,
 }
 
+/// A type that wraps a [`HashMap`]`<u64, Stmt>` for the `switch` statement and implements [`Hash`].
+#[derive(Clone)]
+pub struct SwitchHashWrapper(HashMap<u64, Stmt, StraightHasherBuilder>);
+
+impl From<HashMap<u64, Stmt, StraightHasherBuilder>> for SwitchHashWrapper {
+    fn from(value: HashMap<u64, Stmt, StraightHasherBuilder>) -> Self {
+        Self(value)
+    }
+}
+impl AsRef<HashMap<u64, Stmt, StraightHasherBuilder>> for SwitchHashWrapper {
+    fn as_ref(&self) -> &HashMap<u64, Stmt, StraightHasherBuilder> {
+        &self.0
+    }
+}
+impl AsMut<HashMap<u64, Stmt, StraightHasherBuilder>> for SwitchHashWrapper {
+    fn as_mut(&mut self) -> &mut HashMap<u64, Stmt, StraightHasherBuilder> {
+        &mut self.0
+    }
+}
+impl Deref for SwitchHashWrapper {
+    type Target = HashMap<u64, Stmt, StraightHasherBuilder>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+impl DerefMut for SwitchHashWrapper {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+impl fmt::Debug for SwitchHashWrapper {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+impl Hash for SwitchHashWrapper {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        let mut keys: Vec<_> = self.0.keys().collect();
+        keys.sort();
+
+        keys.into_iter().for_each(|key| {
+            key.hash(state);
+            self.0.get(&key).unwrap().hash(state);
+        });
+    }
+}
+
 /// _(INTERNALS)_ A statement.
 /// Exported under the `internals` feature only.
 ///
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub enum Stmt {
     /// No-op.
     Noop(Position),
     /// `if` expr `{` stmt `}` `else` `{` stmt `}`
     If(Expr, Box<(Stmt, Option<Stmt>)>, Position),
     /// `switch` expr `{` literal or _ `=>` stmt `,` ... `}`
-    Switch(
-        Expr,
-        Box<(HashMap<u64, Stmt, StraightHasherBuilder>, Option<Stmt>)>,
-        Position,
-    ),
+    Switch(Expr, Box<(SwitchHashWrapper, Option<Stmt>)>, Position),
     /// `while` expr `{` stmt `}`
     While(Expr, Box<Stmt>, Position),
     /// `do` `{` stmt `}` `while`|`until` expr
@@ -899,10 +938,8 @@ impl Stmt {
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Clone)]
+#[derive(Clone, Hash)]
 pub struct CustomExpr {
-    /// Implementation function.
-    pub func: Shared<FnCustomSyntaxEval>,
     /// List of keywords.
     pub keywords: StaticVec<Expr>,
     /// List of tokens actually parsed.
@@ -926,7 +963,7 @@ impl fmt::Debug for CustomExpr {
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub struct BinaryExpr {
     /// LHS expression.
     pub lhs: Expr,
@@ -940,7 +977,7 @@ pub struct BinaryExpr {
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Debug, Clone, Default)]
+#[derive(Debug, Clone, Default, Hash)]
 pub struct FnCallExpr {
     /// Pre-calculated hash for a script-defined function of the same name and number of parameters.
     /// None if native Rust only.
@@ -959,13 +996,83 @@ pub struct FnCallExpr {
     pub args: StaticVec<Expr>,
 }
 
+/// A type that wraps a [`FLOAT`] and implements [`Hash`].
+#[cfg(not(feature = "no_float"))]
+#[derive(Clone, Copy)]
+pub struct FloatWrapper(FLOAT);
+
+#[cfg(not(feature = "no_float"))]
+impl Hash for FloatWrapper {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.0.to_le_bytes().hash(state);
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl AsRef<FLOAT> for FloatWrapper {
+    fn as_ref(&self) -> &FLOAT {
+        &self.0
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl AsMut<FLOAT> for FloatWrapper {
+    fn as_mut(&mut self) -> &mut FLOAT {
+        &mut self.0
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl Deref for FloatWrapper {
+    type Target = FLOAT;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl DerefMut for FloatWrapper {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl fmt::Debug for FloatWrapper {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl fmt::Display for FloatWrapper {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl From<FLOAT> for FloatWrapper {
+    fn from(value: FLOAT) -> Self {
+        Self::new(value)
+    }
+}
+
+#[cfg(not(feature = "no_float"))]
+impl FloatWrapper {
+    pub const fn new(value: FLOAT) -> Self {
+        Self(value)
+    }
+}
+
 /// _(INTERNALS)_ An expression sub-tree.
 /// Exported under the `internals` feature only.
 ///
 /// # WARNING
 ///
 /// This type is volatile and may change.
-#[derive(Debug, Clone)]
+#[derive(Debug, Clone, Hash)]
 pub enum Expr {
     /// Dynamic constant.
     /// Used to hold either an [`Array`] or [`Map`] literal for quick cloning.
@@ -977,7 +1084,7 @@ pub enum Expr {
     IntegerConstant(INT, Position),
     /// Floating-point constant.
     #[cfg(not(feature = "no_float"))]
-    FloatConstant(FLOAT, Position),
+    FloatConstant(FloatWrapper, Position),
     /// Character constant.
     CharConstant(char, Position),
     /// [String][ImmutableString] constant.
@@ -1250,19 +1357,20 @@ mod tests {
     /// This test is to make sure no code changes increase the sizes of critical data structures.
     #[test]
     fn check_struct_sizes() {
-        use std::mem::size_of;
+        use crate::stdlib::mem::size_of;
+        use crate::*;
 
-        assert_eq!(size_of::<crate::Dynamic>(), 16);
-        assert_eq!(size_of::<Option<crate::Dynamic>>(), 16);
-        assert_eq!(size_of::<crate::Position>(), 4);
-        assert_eq!(size_of::<crate::ast::Expr>(), 16);
-        assert_eq!(size_of::<Option<crate::ast::Expr>>(), 16);
-        assert_eq!(size_of::<crate::ast::Stmt>(), 32);
-        assert_eq!(size_of::<Option<crate::ast::Stmt>>(), 32);
-        assert_eq!(size_of::<crate::FnPtr>(), 32);
-        assert_eq!(size_of::<crate::Scope>(), 48);
-        assert_eq!(size_of::<crate::LexError>(), 56);
-        assert_eq!(size_of::<crate::ParseError>(), 16);
-        assert_eq!(size_of::<crate::EvalAltResult>(), 72);
+        assert_eq!(size_of::<Dynamic>(), 16);
+        assert_eq!(size_of::<Option<Dynamic>>(), 16);
+        assert_eq!(size_of::<Position>(), 4);
+        assert_eq!(size_of::<ast::Expr>(), 16);
+        assert_eq!(size_of::<Option<ast::Expr>>(), 16);
+        assert_eq!(size_of::<ast::Stmt>(), 32);
+        assert_eq!(size_of::<Option<ast::Stmt>>(), 32);
+        assert_eq!(size_of::<FnPtr>(), 32);
+        assert_eq!(size_of::<Scope>(), 48);
+        assert_eq!(size_of::<LexError>(), 56);
+        assert_eq!(size_of::<ParseError>(), 16);
+        assert_eq!(size_of::<EvalAltResult>(), 72);
     }
 }
diff --git a/src/dynamic.rs b/src/dynamic.rs
index 47507ff6..fc5ab807 100644
--- a/src/dynamic.rs
+++ b/src/dynamic.rs
@@ -7,14 +7,13 @@ use crate::stdlib::{
     boxed::Box,
     fmt,
     hash::{Hash, Hasher},
-    mem,
     ops::{Deref, DerefMut},
     string::String,
 };
 use crate::{FnPtr, ImmutableString, INT};
 
 #[cfg(not(feature = "no_float"))]
-use crate::FLOAT;
+use crate::{ast::FloatWrapper, FLOAT};
 
 #[cfg(not(feature = "no_index"))]
 use crate::Array;
@@ -155,7 +154,7 @@ pub enum Union {
     Char(char, AccessMode),
     Int(INT, AccessMode),
     #[cfg(not(feature = "no_float"))]
-    Float(FLOAT, AccessMode),
+    Float(FloatWrapper, AccessMode),
     #[cfg(not(feature = "no_index"))]
     Array(Box<Array>, AccessMode),
     #[cfg(not(feature = "no_object"))]
@@ -362,8 +361,6 @@ impl Dynamic {
 
 impl Hash for Dynamic {
     fn hash<H: Hasher>(&self, state: &mut H) {
-        mem::discriminant(self).hash(state);
-
         match &self.0 {
             Union::Unit(_, _) => ().hash(state),
             Union::Bool(value, _) => value.hash(state),
@@ -371,7 +368,7 @@ impl Hash for Dynamic {
             Union::Char(ch, _) => ch.hash(state),
             Union::Int(i, _) => i.hash(state),
             #[cfg(not(feature = "no_float"))]
-            Union::Float(f, _) => f.to_le_bytes().hash(state),
+            Union::Float(f, _) => f.hash(state),
             #[cfg(not(feature = "no_index"))]
             Union::Array(a, _) => (**a).hash(state),
             #[cfg(not(feature = "no_object"))]
@@ -559,13 +556,16 @@ impl Dynamic {
     pub const NEGATIVE_ONE: Dynamic = Self(Union::Int(-1, AccessMode::ReadWrite));
     /// A [`Dynamic`] containing the floating-point zero.
     #[cfg(not(feature = "no_float"))]
-    pub const FLOAT_ZERO: Dynamic = Self(Union::Float(0.0, AccessMode::ReadWrite));
+    pub const FLOAT_ZERO: Dynamic =
+        Self(Union::Float(FloatWrapper::new(0.0), AccessMode::ReadWrite));
     /// A [`Dynamic`] containing the floating-point one.
     #[cfg(not(feature = "no_float"))]
-    pub const FLOAT_ONE: Dynamic = Self(Union::Float(1.0, AccessMode::ReadWrite));
+    pub const FLOAT_ONE: Dynamic =
+        Self(Union::Float(FloatWrapper::new(1.0), AccessMode::ReadWrite));
     /// A [`Dynamic`] containing the floating-point negative one.
     #[cfg(not(feature = "no_float"))]
-    pub const FLOAT_NEGATIVE_ONE: Dynamic = Self(Union::Float(-1.0, AccessMode::ReadWrite));
+    pub const FLOAT_NEGATIVE_ONE: Dynamic =
+        Self(Union::Float(FloatWrapper::new(-1.0), AccessMode::ReadWrite));
 
     /// Get the [`AccessMode`] for this [`Dynamic`].
     pub(crate) fn access_mode(&self) -> AccessMode {
@@ -836,7 +836,7 @@ impl Dynamic {
         #[cfg(not(feature = "no_float"))]
         if TypeId::of::<T>() == TypeId::of::<FLOAT>() {
             return match self.0 {
-                Union::Float(value, _) => unsafe_try_cast(value),
+                Union::Float(value, _) => unsafe_try_cast(*value),
                 _ => None,
             };
         }
@@ -1105,7 +1105,7 @@ impl Dynamic {
         #[cfg(not(feature = "no_float"))]
         if TypeId::of::<T>() == TypeId::of::<FLOAT>() {
             return match &self.0 {
-                Union::Float(value, _) => <dyn Any>::downcast_ref::<T>(value),
+                Union::Float(value, _) => <dyn Any>::downcast_ref::<T>(value.as_ref()),
                 _ => None,
             };
         }
@@ -1194,7 +1194,7 @@ impl Dynamic {
         #[cfg(not(feature = "no_float"))]
         if TypeId::of::<T>() == TypeId::of::<FLOAT>() {
             return match &mut self.0 {
-                Union::Float(value, _) => <dyn Any>::downcast_mut::<T>(value),
+                Union::Float(value, _) => <dyn Any>::downcast_mut::<T>(value.as_mut()),
                 _ => None,
             };
         }
@@ -1277,7 +1277,7 @@ impl Dynamic {
     #[inline(always)]
     pub fn as_float(&self) -> Result<FLOAT, &'static str> {
         match self.0 {
-            Union::Float(n, _) => Ok(n),
+            Union::Float(n, _) => Ok(*n),
             #[cfg(not(feature = "no_closure"))]
             Union::Shared(_, _) => self.read_lock().map(|v| *v).ok_or_else(|| self.type_name()),
             _ => Err(self.type_name()),
@@ -1380,6 +1380,13 @@ impl From<INT> for Dynamic {
 impl From<FLOAT> for Dynamic {
     #[inline(always)]
     fn from(value: FLOAT) -> Self {
+        Self(Union::Float(value.into(), AccessMode::ReadWrite))
+    }
+}
+#[cfg(not(feature = "no_float"))]
+impl From<FloatWrapper> for Dynamic {
+    #[inline(always)]
+    fn from(value: FloatWrapper) -> Self {
         Self(Union::Float(value, AccessMode::ReadWrite))
     }
 }
diff --git a/src/engine.rs b/src/engine.rs
index 05d67062..f11e1762 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -1923,6 +1923,10 @@ impl Engine {
                     .iter()
                     .map(Into::into)
                     .collect::<StaticVec<_>>();
+                let custom_def = self
+                    .custom_syntax
+                    .get(custom.tokens.first().unwrap())
+                    .unwrap();
                 let mut context = EvalContext {
                     engine: self,
                     scope,
@@ -1932,7 +1936,7 @@ impl Engine {
                     this_ptr,
                     level,
                 };
-                (custom.func)(&mut context, &expressions)
+                (custom_def.func)(&mut context, &expressions)
             }
 
             _ => unreachable!("expression cannot be evaluated: {:?}", expr),
@@ -2072,11 +2076,7 @@ impl Engine {
                             let args = &mut [lhs_ptr_inner, &mut rhs_val];
 
                             // Overriding exact implementation
-                            let source = if source.is_none() {
-                                state.source.as_ref()
-                            } else {
-                                source
-                            };
+                            let source = source.or_else(|| state.source.as_ref());
                             if func.is_plugin_fn() {
                                 func.get_plugin_fn()
                                     .call((self, source, &*mods, lib).into(), args)?;
@@ -2130,14 +2130,13 @@ impl Engine {
                         &mut rhs_val,
                     ];
 
-                    let result = self
-                        .exec_fn_call(
+                    Some(
+                        self.exec_fn_call(
                             mods, state, lib, op, None, args, false, false, false, *op_pos, None,
                             None, level,
                         )
-                        .map(|(v, _)| v)?;
-
-                    Some((result, rhs_expr.position()))
+                        .map(|(v, _)| (v, rhs_expr.position()))?,
+                    )
                 };
 
                 // Must be either `var[index] op= val` or `var.prop op= val`
diff --git a/src/engine_api.rs b/src/engine_api.rs
index 5f5b4b21..fed074bf 100644
--- a/src/engine_api.rs
+++ b/src/engine_api.rs
@@ -8,11 +8,9 @@ use crate::stdlib::{
     any::{type_name, TypeId},
     boxed::Box,
     format,
-    hash::{Hash, Hasher},
     string::String,
     vec::Vec,
 };
-use crate::utils::get_hasher;
 use crate::{
     scope::Scope, Dynamic, Engine, EvalAltResult, FnAccess, FnNamespace, Module, NativeCallContext,
     ParseError, Position, Shared, AST,
@@ -24,13 +22,6 @@ use crate::Array;
 #[cfg(not(feature = "no_object"))]
 use crate::Map;
 
-/// Calculate a unique hash for a script.
-fn calc_hash_for_scripts<'a>(scripts: impl IntoIterator<Item = &'a &'a str>) -> u64 {
-    let s = &mut get_hasher();
-    scripts.into_iter().for_each(|&script| script.hash(s));
-    s.finish()
-}
-
 /// Engine public API
 impl Engine {
     /// Register a function of the [`Engine`].
@@ -960,9 +951,8 @@ impl Engine {
         scripts: &[&str],
         optimization_level: OptimizationLevel,
     ) -> Result<AST, ParseError> {
-        let hash = calc_hash_for_scripts(scripts);
         let stream = self.lex(scripts);
-        self.parse(hash, &mut stream.peekable(), scope, optimization_level)
+        self.parse(&mut stream.peekable(), scope, optimization_level)
     }
     /// Read the contents of a file into a string.
     #[cfg(not(feature = "no_std"))]
@@ -1123,8 +1113,6 @@ impl Engine {
             .into());
         };
 
-        let hash = calc_hash_for_scripts(&scripts);
-
         let stream = self.lex_with_map(
             &scripts,
             if has_null {
@@ -1138,12 +1126,8 @@ impl Engine {
             },
         );
 
-        let ast = self.parse_global_expr(
-            hash,
-            &mut stream.peekable(),
-            &scope,
-            OptimizationLevel::None,
-        )?;
+        let ast =
+            self.parse_global_expr(&mut stream.peekable(), &scope, OptimizationLevel::None)?;
 
         // Handle null - map to ()
         if has_null {
@@ -1222,11 +1206,10 @@ impl Engine {
         script: &str,
     ) -> Result<AST, ParseError> {
         let scripts = [script];
-        let hash = calc_hash_for_scripts(&scripts);
         let stream = self.lex(&scripts);
 
         let mut peekable = stream.peekable();
-        self.parse_global_expr(hash, &mut peekable, scope, self.optimization_level)
+        self.parse_global_expr(&mut peekable, scope, self.optimization_level)
     }
     /// Evaluate a script file.
     ///
@@ -1384,12 +1367,10 @@ impl Engine {
         script: &str,
     ) -> Result<T, Box<EvalAltResult>> {
         let scripts = [script];
-        let hash = calc_hash_for_scripts(&scripts);
         let stream = self.lex(&scripts);
 
         // No need to optimize a lone expression
-        let ast =
-            self.parse_global_expr(hash, &mut stream.peekable(), scope, OptimizationLevel::None)?;
+        let ast = self.parse_global_expr(&mut stream.peekable(), scope, OptimizationLevel::None)?;
 
         self.eval_ast_with_scope(scope, &ast)
     }
@@ -1522,9 +1503,8 @@ impl Engine {
         script: &str,
     ) -> Result<(), Box<EvalAltResult>> {
         let scripts = [script];
-        let hash = calc_hash_for_scripts(&scripts);
         let stream = self.lex(&scripts);
-        let ast = self.parse(hash, &mut stream.peekable(), scope, self.optimization_level)?;
+        let ast = self.parse(&mut stream.peekable(), scope, self.optimization_level)?;
         self.consume_ast_with_scope(scope, &ast)
     }
     /// Evaluate an AST, but throw away the result and only return error (if any).
diff --git a/src/lib.rs b/src/lib.rs
index a618879d..642f6139 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -183,7 +183,10 @@ pub use token::{get_next_token, parse_string_literal, InputStream, Token, Tokeni
 
 #[cfg(feature = "internals")]
 #[deprecated = "this type is volatile and may change"]
-pub use ast::{BinaryExpr, CustomExpr, Expr, FnCallExpr, Ident, ReturnType, ScriptFnDef, Stmt};
+pub use ast::{
+    BinaryExpr, CustomExpr, Expr, FloatWrapper, FnCallExpr, Ident, ReturnType, ScriptFnDef, Stmt,
+    SwitchHashWrapper,
+};
 
 #[cfg(feature = "internals")]
 #[deprecated = "this type is volatile and may change"]
diff --git a/src/parser.rs b/src/parser.rs
index 10c7945b..a86095ac 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -41,8 +41,6 @@ type FunctionsLib = HashMap<NonZeroU64, ScriptFnDef, StraightHasherBuilder>;
 struct ParseState<'e> {
     /// Reference to the scripting [`Engine`].
     engine: &'e Engine,
-    /// Hash that uniquely identifies a script.
-    script_hash: u64,
     /// Interned strings.
     strings: HashMap<String, ImmutableString>,
     /// Encapsulates a local stack with variable names to simulate an actual runtime scope.
@@ -75,7 +73,6 @@ impl<'e> ParseState<'e> {
     #[inline(always)]
     pub fn new(
         engine: &'e Engine,
-        script_hash: u64,
         #[cfg(not(feature = "unchecked"))] max_expr_depth: usize,
         #[cfg(not(feature = "unchecked"))]
         #[cfg(not(feature = "no_function"))]
@@ -83,7 +80,6 @@ impl<'e> ParseState<'e> {
     ) -> Self {
         Self {
             engine,
-            script_hash,
             #[cfg(not(feature = "unchecked"))]
             max_expr_depth,
             #[cfg(not(feature = "unchecked"))]
@@ -919,7 +915,7 @@ fn parse_switch(
 
     Ok(Stmt::Switch(
         item,
-        Box::new((final_table, def_stmt)),
+        Box::new((final_table.into(), def_stmt)),
         settings.pos,
     ))
 }
@@ -956,7 +952,7 @@ fn parse_primary(
         },
         #[cfg(not(feature = "no_float"))]
         Token::FloatConstant(x) => {
-            let x = *x;
+            let x = (*x).into();
             input.next().unwrap();
             Expr::FloatConstant(x, settings.pos)
         }
@@ -986,7 +982,6 @@ fn parse_primary(
         Token::Pipe | Token::Or if settings.allow_anonymous_fn => {
             let mut new_state = ParseState::new(
                 state.engine,
-                state.script_hash,
                 #[cfg(not(feature = "unchecked"))]
                 state.max_function_expr_depth,
                 #[cfg(not(feature = "unchecked"))]
@@ -1284,7 +1279,7 @@ fn parse_unary(
                     .map(|i| Expr::IntegerConstant(i, pos))
                     .or_else(|| {
                         #[cfg(not(feature = "no_float"))]
-                        return Some(Expr::FloatConstant(-(num as FLOAT), pos));
+                        return Some(Expr::FloatConstant((-(num as FLOAT)).into(), pos));
                         #[cfg(feature = "no_float")]
                         return None;
                     })
@@ -1292,7 +1287,7 @@ fn parse_unary(
 
                 // Negative float
                 #[cfg(not(feature = "no_float"))]
-                Expr::FloatConstant(x, pos) => Ok(Expr::FloatConstant(-x, pos)),
+                Expr::FloatConstant(x, pos) => Ok(Expr::FloatConstant((-(*x)).into(), pos)),
 
                 // Call negative function
                 expr => {
@@ -1998,14 +1993,7 @@ fn parse_custom_syntax(
         }
     }
 
-    Ok(Expr::Custom(
-        Box::new(CustomExpr {
-            keywords,
-            func: syntax.func.clone(),
-            tokens,
-        }),
-        pos,
-    ))
+    Ok(Expr::Custom(Box::new(CustomExpr { keywords, tokens }), pos))
 }
 
 /// Parse an expression.
@@ -2600,7 +2588,6 @@ fn parse_stmt(
                 (Token::Fn, pos) => {
                     let mut new_state = ParseState::new(
                         state.engine,
-                        state.script_hash,
                         #[cfg(not(feature = "unchecked"))]
                         state.max_function_expr_depth,
                         #[cfg(not(feature = "unchecked"))]
@@ -3009,10 +2996,10 @@ fn parse_anon_fn(
         params.into_iter().map(|(v, _)| v).collect()
     };
 
-    // Create unique function name by hashing the script hash plus the position
+    // Create unique function name by hashing the script body plus the parameters.
     let hasher = &mut get_hasher();
-    state.script_hash.hash(hasher);
-    settings.pos.hash(hasher);
+    params.iter().for_each(|p| p.as_str().hash(hasher));
+    body.hash(hasher);
     let hash = hasher.finish();
 
     let fn_name: ImmutableString = format!("{}{:016x}", crate::engine::FN_ANONYMOUS, hash).into();
@@ -3045,7 +3032,6 @@ fn parse_anon_fn(
 impl Engine {
     pub(crate) fn parse_global_expr(
         &self,
-        script_hash: u64,
         input: &mut TokenStream,
         scope: &Scope,
         optimization_level: OptimizationLevel,
@@ -3053,7 +3039,6 @@ impl Engine {
         let mut functions = Default::default();
         let mut state = ParseState::new(
             self,
-            script_hash,
             #[cfg(not(feature = "unchecked"))]
             self.max_expr_depth(),
             #[cfg(not(feature = "unchecked"))]
@@ -3095,14 +3080,12 @@ impl Engine {
     /// Parse the global level statements.
     fn parse_global_level(
         &self,
-        script_hash: u64,
         input: &mut TokenStream,
     ) -> Result<(Vec<Stmt>, Vec<ScriptFnDef>), ParseError> {
         let mut statements = Vec::with_capacity(16);
         let mut functions = HashMap::with_capacity_and_hasher(16, StraightHasherBuilder);
         let mut state = ParseState::new(
             self,
-            script_hash,
             #[cfg(not(feature = "unchecked"))]
             self.max_expr_depth(),
             #[cfg(not(feature = "unchecked"))]
@@ -3165,12 +3148,11 @@ impl Engine {
     #[inline(always)]
     pub(crate) fn parse(
         &self,
-        script_hash: u64,
         input: &mut TokenStream,
         scope: &Scope,
         optimization_level: OptimizationLevel,
     ) -> Result<AST, ParseError> {
-        let (statements, lib) = self.parse_global_level(script_hash, input)?;
+        let (statements, lib) = self.parse_global_level(input)?;
 
         Ok(
             // Optimize AST