diff --git a/RELEASES.md b/RELEASES.md
index cb37b9d8..db52a753 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -11,6 +11,7 @@ Breaking changes
 * `EvalAltResult::ErrorReadingScriptFile` is removed in favor of the new `EvalAltResult::ErrorSystem`.
 * `EvalAltResult::ErrorLoopBreak` is renamed to `EvalAltResult::LoopBreak`.
 * `Engine::register_raw_fn` and `FnPtr::call_dynamic` function signatures have changed.
+* Callback signatures to `Engine::on_var` and `Engine::register_custom_syntax` have changed.
 
 New features
 ------------
diff --git a/doc/src/engine/custom-syntax.md b/doc/src/engine/custom-syntax.md
index a0d38b9a..6bbe1157 100644
--- a/doc/src/engine/custom-syntax.md
+++ b/doc/src/engine/custom-syntax.md
@@ -114,25 +114,19 @@ Any custom syntax must include an _implementation_ of it.
 
 The function signature of an implementation is:
 
-> `Fn(scope: &mut Scope, context: &mut EvalContext, inputs: &[Expression])`  
-> `-> Result<Dynamic, Box<EvalAltResult>>`
+> `Fn(context: &mut EvalContext, inputs: &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>`
 
 where:
 
-* `scope: &mut Scope` - mutable reference to the current [`Scope`]; variables can be added to it.
-
-* `context: &mut EvalContext` - mutable reference to the current evaluation _context_ (**do not touch**) which exposes the following fields:
+* `context: &mut EvalContext` - mutable reference to the current evaluation _context_, exposing the following:
+  * `context.scope: &mut Scope` - mutable reference to the current [`Scope`]; variables can be added to/removed from it.
   * `context.engine(): &Engine` - reference to the current [`Engine`].
   * `context.namespace(): &Module` - reference to the current _global namespace_ (as a [module]) containing all script-defined functions.
+  * `context.this_ptr(): Option<&Dynamic>` - reference to the current bound [`this`] pointer, if any.
   * `context.call_level(): usize` - the current nesting level of function calls.
 
 * `inputs: &[Expression]` - a list of input expression trees.
 
-#### WARNING - Lark's Vomit
-
-The `context` parameter contains the evaluation _context_ and should not be touched or Bad Things Happen™.
-It should simply be passed straight-through the the [`Engine`].
-
 ### Access Arguments
 
 The most important argument is `inputs` where the matched identifiers (`$ident$`), expressions/statements (`$expr$`)
@@ -152,8 +146,8 @@ Use the `EvalContext::eval_expression_tree` method to evaluate an arbitrary expr
 within the current evaluation context.
 
 ```rust
-let expr = inputs.get(0).unwrap();
-let result = context.eval_expression_tree(scope, expr)?;
+let expression = inputs.get(0).unwrap();
+let result = context.eval_expression_tree(expression)?;
 ```
 
 ### Declare Variables
@@ -163,15 +157,16 @@ New variables maybe declared (usually with a variable name that is passed in via
 It can simply be pushed into the [`Scope`].
 
 However, beware that all new variables must be declared _prior_ to evaluating any expression tree.
-In other words, any `Scope::push` calls must come _before_ any `EvalContext::eval_expression_tree` calls.
+In other words, any [`Scope`] calls that change the list of must come _before_ any
+`EvalContext::eval_expression_tree` calls.
 
 ```rust
-let var_name = inputs[0].get_variable_name().unwrap().to_string();
-let expr = inputs.get(1).unwrap();
+let var_name = inputs[0].get_variable_name().unwrap();
+let expression = inputs.get(1).unwrap();
 
-scope.push(var_name, 0 as INT);     // do this BEFORE 'context.eval_expression_tree'!
+context.scope.push(var_name, 0 as INT);     // do this BEFORE 'context.eval_expression_tree'!
 
-let result = context.eval_expression_tree(context, scope, expr)?;
+let result = context.eval_expression_tree(expression)?;
 ```
 
 
@@ -188,7 +183,6 @@ The syntax is passed simply as a slice of `&str`.
 ```rust
 // Custom syntax implementation
 fn implementation_func(
-    scope: &mut Scope,
     context: &mut EvalContext,
     inputs: &[Expression]
 ) -> Result<Dynamic, Box<EvalAltResult>> {
@@ -196,15 +190,15 @@ fn implementation_func(
     let stmt = inputs.get(1).unwrap();
     let condition = inputs.get(2).unwrap();
 
-    // Push one new variable into the 'scope' BEFORE 'context.eval_expression_tree'
-    scope.push(var_name, 0 as INT);
+    // Push one new variable into the scope BEFORE 'context.eval_expression_tree'
+    context.scope.push(var_name, 0 as INT);
 
     loop {
         // Evaluate the statement block
-        context.eval_expression_tree(scope, stmt)?;
+        context.eval_expression_tree(stmt)?;
 
         // Evaluate the condition expression
-        let stop = !context.eval_expression_tree(scope, condition)?
+        let stop = !context.eval_expression_tree(condition)?
                             .as_bool().map_err(|err| Box::new(
                                 EvalAltResult::ErrorMismatchDataType(
                                     "bool".to_string(),
diff --git a/doc/src/engine/var.md b/doc/src/engine/var.md
index f1119117..00b6a4fd 100644
--- a/doc/src/engine/var.md
+++ b/doc/src/engine/var.md
@@ -62,7 +62,7 @@ Function Signature
 
 The function signature passed to `Engine::on_var` takes the following form:
 
-> `Fn(name: &str, index: usize, scope: &Scope, context: &EvalContext)`  
+> `Fn(name: &str, index: usize, context: &EvalContext)`  
 > `-> Result<Option<Dynamic>, Box<EvalAltResult>> + 'static`
 
 where:
@@ -74,11 +74,11 @@ where:
 
   If `index` is zero, then there is no pre-calculated offset position and a search through the current [`Scope`] must be performed.
 
-* `scope: &Scope` - reference to the current [`Scope`] containing all variables up to the current evaluation position.
-
 * `context: &EvalContext` - reference to the current evaluation _context_, which exposes the following fields:
+  * `context.scope: &Scope` - reference to the current [`Scope`] containing all variables up to the current evaluation position.
   * `context.engine(): &Engine` - reference to the current [`Engine`].
   * `context.namespace(): &Module` - reference to the current _global namespace_ (as a [module]) containing all script-defined functions.
+  * `context.this_ptr(): Option<&Dynamic>` - reference to the current bound [`this`] pointer, if any.
   * `context.call_level(): usize` - the current nesting level of function calls.
 
 ### Return Value
diff --git a/src/api.rs b/src/api.rs
index 07f0cef1..2e962b4f 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -3,12 +3,12 @@
 use crate::any::{Dynamic, Variant};
 use crate::engine::{Engine, EvalContext, Imports, State};
 use crate::error::ParseError;
-use crate::fn_native::{NativeCallContext, SendSync};
+use crate::fn_native::{FnCallArgs, NativeCallContext, SendSync};
 use crate::optimize::OptimizationLevel;
 use crate::parser::AST;
 use crate::result::EvalAltResult;
 use crate::scope::Scope;
-use crate::token::{lex, Position};
+use crate::token::Position;
 
 #[cfg(not(feature = "no_index"))]
 use crate::{
@@ -68,7 +68,7 @@ impl Engine {
         &mut self,
         name: &str,
         arg_types: &[TypeId],
-        func: impl Fn(NativeCallContext, &mut [&mut Dynamic]) -> Result<T, Box<EvalAltResult>>
+        func: impl Fn(NativeCallContext, &mut FnCallArgs) -> Result<T, Box<EvalAltResult>>
             + SendSync
             + 'static,
     ) -> &mut Self {
@@ -913,7 +913,7 @@ impl Engine {
         scripts: &[&str],
         optimization_level: OptimizationLevel,
     ) -> Result<AST, ParseError> {
-        let stream = lex(scripts, None, self);
+        let stream = self.lex(scripts, None);
         self.parse(&mut stream.peekable(), scope, optimization_level)
     }
 
@@ -1067,7 +1067,7 @@ impl Engine {
             .into());
         };
 
-        let stream = lex(
+        let stream = self.lex(
             &scripts,
             if has_null {
                 Some(Box::new(|token| match token {
@@ -1078,7 +1078,6 @@ impl Engine {
             } else {
                 None
             },
-            self,
         );
         let ast =
             self.parse_global_expr(&mut stream.peekable(), &scope, OptimizationLevel::None)?;
@@ -1162,7 +1161,7 @@ impl Engine {
         script: &str,
     ) -> Result<AST, ParseError> {
         let scripts = [script];
-        let stream = lex(&scripts, None, self);
+        let stream = self.lex(&scripts, None);
         {
             let mut peekable = stream.peekable();
             self.parse_global_expr(&mut peekable, scope, self.optimization_level)
@@ -1323,7 +1322,7 @@ impl Engine {
         script: &str,
     ) -> Result<T, Box<EvalAltResult>> {
         let scripts = [script];
-        let stream = lex(&scripts, None, self);
+        let stream = self.lex(&scripts, None);
 
         // No need to optimize a lone expression
         let ast = self.parse_global_expr(&mut stream.peekable(), scope, OptimizationLevel::None)?;
@@ -1421,6 +1420,7 @@ impl Engine {
             })
             .or_else(|err| match *err {
                 EvalAltResult::Return(out, _) => Ok(out),
+                EvalAltResult::LoopBreak(_, _) => unreachable!(),
                 _ => Err(err),
             })
             .map(|v| (v, state.operations))
@@ -1464,7 +1464,7 @@ impl Engine {
         script: &str,
     ) -> Result<(), Box<EvalAltResult>> {
         let scripts = [script];
-        let stream = lex(&scripts, None, self);
+        let stream = self.lex(&scripts, None);
         let ast = self.parse(&mut stream.peekable(), scope, self.optimization_level)?;
         self.consume_ast_with_scope(scope, &ast)
     }
@@ -1495,7 +1495,8 @@ impl Engine {
             .map_or_else(
                 |err| match *err {
                     EvalAltResult::Return(_, _) => Ok(()),
-                    err => Err(Box::new(err)),
+                    EvalAltResult::LoopBreak(_, _) => unreachable!(),
+                    _ => Err(err),
                 },
                 |_| Ok(()),
             )
@@ -1643,7 +1644,7 @@ impl Engine {
         lib: &Module,
         name: &str,
         this_ptr: &mut Option<&mut Dynamic>,
-        args: &mut [&mut Dynamic],
+        args: &mut FnCallArgs,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
         let fn_def = lib
             .get_script_fn(name, args.len(), true)
@@ -1713,7 +1714,7 @@ impl Engine {
     /// let mut engine = Engine::new();
     ///
     /// // Register a variable resolver.
-    /// engine.on_var(|name, _, _, _| {
+    /// engine.on_var(|name, _, _| {
     ///     match name {
     ///         "MYSTIC_NUMBER" => Ok(Some(42_i64.into())),
     ///         _ => Ok(None)
@@ -1728,7 +1729,7 @@ impl Engine {
     #[inline(always)]
     pub fn on_var(
         &mut self,
-        callback: impl Fn(&str, usize, &Scope, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>>
+        callback: impl Fn(&str, usize, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>>
             + SendSync
             + 'static,
     ) -> &mut Self {
diff --git a/src/engine.rs b/src/engine.rs
index f5ce3981..5f1022c5 100644
--- a/src/engine.rs
+++ b/src/engine.rs
@@ -441,16 +441,17 @@ pub struct Limits {
 
 /// Context of a script evaluation process.
 #[derive(Debug)]
-pub struct EvalContext<'e, 'a, 's, 'm, 't, 'd: 't> {
+pub struct EvalContext<'e, 'x, 'px: 'x, 'a, 's, 'm, 't, 'pt: 't> {
     engine: &'e Engine,
+    pub scope: &'x mut Scope<'px>,
     pub(crate) mods: &'a mut Imports,
     pub(crate) state: &'s mut State,
     lib: &'m Module,
-    pub(crate) this_ptr: &'t mut Option<&'d mut Dynamic>,
+    pub(crate) this_ptr: &'t mut Option<&'pt mut Dynamic>,
     level: usize,
 }
 
-impl<'e, 'a, 's, 'm, 't, 'd> EvalContext<'e, 'a, 's, 'm, 't, 'd> {
+impl<'e, 'x, 'px, 'a, 's, 'm, 't, 'pt> EvalContext<'e, 'x, 'px, 'a, 's, 'm, 't, 'pt> {
     /// The current `Engine`.
     #[inline(always)]
     pub fn engine(&self) -> &'e Engine {
@@ -469,6 +470,11 @@ impl<'e, 'a, 's, 'm, 't, 'd> EvalContext<'e, 'a, 's, 'm, 't, 'd> {
     pub fn namespace(&self) -> &'m Module {
         self.lib
     }
+    /// The current bound `this` pointer, if any.
+    #[inline(always)]
+    pub fn this_ptr(&self) -> Option<&Dynamic> {
+        self.this_ptr.as_ref().map(|v| &**v)
+    }
     /// The current nesting level of function calls.
     #[inline(always)]
     pub fn call_level(&self) -> usize {
@@ -815,6 +821,7 @@ impl Engine {
         if let Some(ref resolve_var) = self.resolve_var {
             let context = EvalContext {
                 engine: self,
+                scope,
                 mods,
                 state,
                 lib,
@@ -822,7 +829,7 @@ impl Engine {
                 level: 0,
             };
             if let Some(result) =
-                resolve_var(name, index, scope, &context).map_err(|err| err.fill_position(*pos))?
+                resolve_var(name, index, &context).map_err(|err| err.fill_position(*pos))?
             {
                 return Ok((result.into(), name, ScopeEntryType::Constant, *pos));
             }
@@ -1742,17 +1749,22 @@ impl Engine {
             Expr::Unit(_) => Ok(().into()),
 
             Expr::Custom(x) => {
-                let func = (x.0).1.as_ref();
-                let ep = (x.0).0.iter().map(|e| e.into()).collect::<StaticVec<_>>();
+                let func = (x.0).func();
+                let expressions = (x.0)
+                    .keywords()
+                    .iter()
+                    .map(Into::into)
+                    .collect::<StaticVec<_>>();
                 let mut context = EvalContext {
                     engine: self,
+                    scope,
                     mods,
                     state,
                     lib,
                     this_ptr,
                     level,
                 };
-                func(scope, &mut context, ep.as_ref())
+                func(&mut context, &expressions)
             }
 
             _ => unreachable!(),
diff --git a/src/fn_call.rs b/src/fn_call.rs
index 8260c0e1..8e9c1940 100644
--- a/src/fn_call.rs
+++ b/src/fn_call.rs
@@ -435,9 +435,11 @@ impl Engine {
         &self,
         lib: &Module,
         name: &str,
-        arg_types: &[TypeId],
+        arg_types: impl AsRef<[TypeId]>,
         pub_only: bool,
     ) -> bool {
+        let arg_types = arg_types.as_ref();
+
         let arg_len = if arg_types.is_empty() {
             usize::MAX
         } else {
@@ -840,7 +842,7 @@ impl Engine {
         lib: &Module,
         this_ptr: &mut Option<&mut Dynamic>,
         name: &str,
-        args_expr: &[Expr],
+        args_expr: impl AsRef<[Expr]>,
         def_val: &Option<Dynamic>,
         mut hash_script: u64,
         native: bool,
@@ -848,6 +850,8 @@ impl Engine {
         capture: bool,
         level: usize,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
+        let args_expr = args_expr.as_ref();
+
         // Handle Fn()
         if name == KEYWORD_FN_PTR && args_expr.len() == 1 {
             let hash_fn = calc_fn_hash(empty(), name, 1, once(TypeId::of::<ImmutableString>()));
@@ -1085,11 +1089,13 @@ impl Engine {
         this_ptr: &mut Option<&mut Dynamic>,
         modules: &Option<Box<ModuleRef>>,
         name: &str,
-        args_expr: &[Expr],
+        args_expr: impl AsRef<[Expr]>,
         def_val: Option<bool>,
         hash_script: u64,
         level: usize,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
+        let args_expr = args_expr.as_ref();
+
         let modules = modules.as_ref().unwrap();
         let mut arg_values: StaticVec<_>;
         let mut first_arg_value = None;
diff --git a/src/fn_native.rs b/src/fn_native.rs
index 8a3c9a1d..c37c8b28 100644
--- a/src/fn_native.rs
+++ b/src/fn_native.rs
@@ -6,7 +6,6 @@ use crate::module::Module;
 use crate::parser::{FnAccess, ScriptFnDef};
 use crate::plugin::PluginFunction;
 use crate::result::EvalAltResult;
-use crate::scope::Scope;
 use crate::token::{is_valid_identifier, Position};
 use crate::utils::ImmutableString;
 use crate::{calc_fn_hash, StaticVec};
@@ -265,14 +264,12 @@ pub type Callback<T, R> = Box<dyn Fn(&T) -> R + Send + Sync + 'static>;
 
 /// A standard callback function.
 #[cfg(not(feature = "sync"))]
-pub type OnVarCallback = Box<
-    dyn Fn(&str, usize, &Scope, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>>
-        + 'static,
->;
+pub type OnVarCallback =
+    Box<dyn Fn(&str, usize, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>> + 'static>;
 /// A standard callback function.
 #[cfg(feature = "sync")]
 pub type OnVarCallback = Box<
-    dyn Fn(&str, usize, &Scope, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>>
+    dyn Fn(&str, usize, &EvalContext) -> Result<Option<Dynamic>, Box<EvalAltResult>>
         + Send
         + Sync
         + 'static,
diff --git a/src/module/mod.rs b/src/module/mod.rs
index 53fd915f..4c2b3780 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -536,11 +536,11 @@ impl Module {
         &mut self,
         name: impl Into<String>,
         arg_types: &[TypeId],
-        func: impl Fn(NativeCallContext, &mut [&mut Dynamic]) -> Result<T, Box<EvalAltResult>>
+        func: impl Fn(NativeCallContext, &mut FnCallArgs) -> Result<T, Box<EvalAltResult>>
             + SendSync
             + 'static,
     ) -> u64 {
-        let f = move |context: NativeCallContext, args: &mut [&mut Dynamic]| {
+        let f = move |context: NativeCallContext, args: &mut FnCallArgs| {
             func(context, args).map(Dynamic::from)
         };
         self.set_fn(
diff --git a/src/parser.rs b/src/parser.rs
index 8cedfae7..8f503caf 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -919,6 +919,19 @@ impl Hash for CustomExpr {
     }
 }
 
+impl CustomExpr {
+    /// Get the keywords for this `CustomExpr`.
+    #[inline(always)]
+    pub fn keywords(&self) -> &[Expr] {
+        &self.0
+    }
+    /// Get the implementation function for this `CustomExpr`.
+    #[inline(always)]
+    pub fn func(&self) -> &FnCustomSyntaxEval {
+        self.1.as_ref()
+    }
+}
+
 /// _[INTERNALS]_ A type wrapping a floating-point number.
 /// Exported under the `internals` feature only.
 ///
@@ -2670,7 +2683,10 @@ fn parse_expr(
                 // Adjust the variables stack
                 match syntax.scope_delta {
                     delta if delta > 0 => {
-                        state.stack.push(("".to_string(), ScopeEntryType::Normal))
+                        state.stack.resize(
+                            state.stack.len() + delta as usize,
+                            ("".to_string(), ScopeEntryType::Normal),
+                        );
                     }
                     delta if delta < 0 && state.stack.len() <= delta.abs() as usize => {
                         state.stack.clear()
diff --git a/src/plugin.rs b/src/plugin.rs
index 30edcc25..b2fde8e6 100644
--- a/src/plugin.rs
+++ b/src/plugin.rs
@@ -2,7 +2,7 @@
 
 pub use crate::any::Dynamic;
 pub use crate::engine::Engine;
-pub use crate::fn_native::{CallableFunction, NativeCallContext};
+pub use crate::fn_native::{CallableFunction, FnCallArgs, NativeCallContext};
 pub use crate::fn_register::{RegisterFn, RegisterResultFn};
 pub use crate::module::Module;
 pub use crate::parser::FnAccess;
@@ -25,7 +25,7 @@ pub trait PluginFunction {
     fn call(
         &self,
         context: NativeCallContext,
-        args: &mut [&mut Dynamic],
+        args: &mut FnCallArgs,
     ) -> Result<Dynamic, Box<EvalAltResult>>;
 
     /// Is this plugin function a method?
diff --git a/src/syntax.rs b/src/syntax.rs
index 08b102b7..4e305f41 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -6,7 +6,6 @@ use crate::error::{LexError, ParseError};
 use crate::fn_native::{SendSync, Shared};
 use crate::parser::Expr;
 use crate::result::EvalAltResult;
-use crate::scope::Scope;
 use crate::token::{is_valid_identifier, Position, Token};
 use crate::StaticVec;
 
@@ -19,12 +18,11 @@ use crate::stdlib::{
 /// A general expression evaluation trait object.
 #[cfg(not(feature = "sync"))]
 pub type FnCustomSyntaxEval =
-    dyn Fn(&mut Scope, &mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>;
+    dyn Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>;
 /// A general expression evaluation trait object.
 #[cfg(feature = "sync")]
-pub type FnCustomSyntaxEval = dyn Fn(&mut Scope, &mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>
-    + Send
-    + Sync;
+pub type FnCustomSyntaxEval =
+    dyn Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>> + Send + Sync;
 
 /// An expression sub-tree in an AST.
 #[derive(Debug, Clone, Hash)]
@@ -55,7 +53,7 @@ impl Expression<'_> {
     }
 }
 
-impl EvalContext<'_, '_, '_, '_, '_, '_> {
+impl EvalContext<'_, '_, '_, '_, '_, '_, '_, '_> {
     /// Evaluate an expression tree.
     ///
     /// ## WARNING - Low Level API
@@ -64,11 +62,10 @@ impl EvalContext<'_, '_, '_, '_, '_, '_> {
     #[inline(always)]
     pub fn eval_expression_tree(
         &mut self,
-        scope: &mut Scope,
         expr: &Expression,
     ) -> Result<Dynamic, Box<EvalAltResult>> {
         self.engine().eval_expr(
-            scope,
+            self.scope,
             self.mods,
             self.state,
             self.namespace(),
@@ -101,12 +98,14 @@ impl Engine {
     /// * `func` is the implementation function.
     pub fn register_custom_syntax<S: AsRef<str> + ToString>(
         &mut self,
-        keywords: &[S],
+        keywords: impl AsRef<[S]>,
         new_vars: isize,
-        func: impl Fn(&mut Scope, &mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>
+        func: impl Fn(&mut EvalContext, &[Expression]) -> Result<Dynamic, Box<EvalAltResult>>
             + SendSync
             + 'static,
     ) -> Result<&mut Self, ParseError> {
+        let keywords = keywords.as_ref();
+
         let mut segments: StaticVec<_> = Default::default();
 
         for s in keywords {
diff --git a/src/token.rs b/src/token.rs
index 418765d6..55dc2d38 100644
--- a/src/token.rs
+++ b/src/token.rs
@@ -1736,31 +1736,33 @@ impl<'a> Iterator for TokenIterator<'a, '_> {
     }
 }
 
-/// Tokenize an input text stream.
-#[inline]
-pub fn lex<'a, 'e>(
-    input: &'a [&'a str],
-    map: Option<Box<dyn Fn(Token) -> Token>>,
-    engine: &'e Engine,
-) -> TokenIterator<'a, 'e> {
-    TokenIterator {
-        engine,
-        state: TokenizeState {
-            #[cfg(not(feature = "unchecked"))]
-            max_string_size: engine.limits_set.max_string_size,
-            #[cfg(feature = "unchecked")]
-            max_string_size: 0,
-            non_unary: false,
-            comment_level: 0,
-            end_with_none: false,
-            include_comments: false,
-        },
-        pos: Position::new(1, 0),
-        stream: MultiInputsStream {
-            buf: None,
-            streams: input.iter().map(|s| s.chars().peekable()).collect(),
-            index: 0,
-        },
-        map,
+impl Engine {
+    /// Tokenize an input text stream.
+    #[inline]
+    pub fn lex<'a, 'e>(
+        &'e self,
+        input: impl IntoIterator<Item = &'a &'a str>,
+        map: Option<Box<dyn Fn(Token) -> Token>>,
+    ) -> TokenIterator<'a, 'e> {
+        TokenIterator {
+            engine: self,
+            state: TokenizeState {
+                #[cfg(not(feature = "unchecked"))]
+                max_string_size: self.limits_set.max_string_size,
+                #[cfg(feature = "unchecked")]
+                max_string_size: 0,
+                non_unary: false,
+                comment_level: 0,
+                end_with_none: false,
+                include_comments: false,
+            },
+            pos: Position::new(1, 0),
+            stream: MultiInputsStream {
+                buf: None,
+                streams: input.into_iter().map(|s| s.chars().peekable()).collect(),
+                index: 0,
+            },
+            map,
+        }
     }
 }
diff --git a/tests/call_fn.rs b/tests/call_fn.rs
index 4d4e3552..7e9170b0 100644
--- a/tests/call_fn.rs
+++ b/tests/call_fn.rs
@@ -1,7 +1,5 @@
 #![cfg(not(feature = "no_function"))]
-use rhai::{
-    Dynamic, Engine, EvalAltResult, FnPtr, Func, Module, ParseErrorType, RegisterFn, Scope, INT,
-};
+use rhai::{Engine, EvalAltResult, FnPtr, Func, ParseErrorType, RegisterFn, Scope, INT};
 use std::any::TypeId;
 
 #[test]
diff --git a/tests/syntax.rs b/tests/syntax.rs
index f9c5acda..c0433e9e 100644
--- a/tests/syntax.rs
+++ b/tests/syntax.rs
@@ -1,4 +1,4 @@
-use rhai::{Engine, EvalAltResult, EvalContext, Expression, ParseErrorType, Scope, INT};
+use rhai::{Engine, EvalAltResult, EvalContext, Expression, ParseErrorType, INT};
 
 #[test]
 fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
@@ -22,18 +22,18 @@ fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
             "do", "|", "$ident$", "|", "->", "$block$", "while", "$expr$",
         ],
         1,
-        |scope: &mut Scope, context: &mut EvalContext, inputs: &[Expression]| {
+        |context: &mut EvalContext, inputs: &[Expression]| {
             let var_name = inputs[0].get_variable_name().unwrap().to_string();
             let stmt = inputs.get(1).unwrap();
             let condition = inputs.get(2).unwrap();
 
-            scope.push(var_name, 0 as INT);
+            context.scope.push(var_name, 0 as INT);
 
             loop {
-                context.eval_expression_tree(scope, stmt)?;
+                context.eval_expression_tree(stmt)?;
 
                 let stop = !context
-                    .eval_expression_tree(scope, condition)?
+                    .eval_expression_tree(condition)?
                     .as_bool()
                     .map_err(|err| {
                         Box::new(EvalAltResult::ErrorMismatchDataType(
@@ -68,7 +68,7 @@ fn test_custom_syntax() -> Result<(), Box<EvalAltResult>> {
     // The first symbol must be an identifier
     assert_eq!(
         *engine
-            .register_custom_syntax(&["!"], 0, |_, _, _| Ok(().into()))
+            .register_custom_syntax(&["!"], 0, |_, _| Ok(().into()))
             .expect_err("should error")
             .0,
         ParseErrorType::BadInput("Improper symbol for custom syntax: '!'".to_string())
diff --git a/tests/var_scope.rs b/tests/var_scope.rs
index ede4ef1d..4faf37b5 100644
--- a/tests/var_scope.rs
+++ b/tests/var_scope.rs
@@ -62,7 +62,7 @@ fn test_var_resolver() -> Result<(), Box<EvalAltResult>> {
     scope.push("chameleon", 123 as INT);
     scope.push("DO_NOT_USE", 999 as INT);
 
-    engine.on_var(|name, _, scope, _| {
+    engine.on_var(|name, _, context| {
         match name {
             "MYSTIC_NUMBER" => Ok(Some((42 as INT).into())),
             // Override a variable - make it not found even if it exists!
@@ -70,9 +70,13 @@ fn test_var_resolver() -> Result<(), Box<EvalAltResult>> {
                 Err(EvalAltResult::ErrorVariableNotFound(name.to_string(), Position::none()).into())
             }
             // Silently maps 'chameleon' into 'innocent'.
-            "chameleon" => scope.get_value("innocent").map(Some).ok_or_else(|| {
-                EvalAltResult::ErrorVariableNotFound(name.to_string(), Position::none()).into()
-            }),
+            "chameleon" => context
+                .scope
+                .get_value("innocent")
+                .map(Some)
+                .ok_or_else(|| {
+                    EvalAltResult::ErrorVariableNotFound(name.to_string(), Position::none()).into()
+                }),
             // Return Ok(None) to continue with the normal variable resolution process.
             _ => Ok(None),
         }