Merge pull request 'Ai/refactor' (#1) from ai/refactor into dev

Reviewed-on: https://gitea.lambstudios.eu/ProjectValkay/rlox/pulls/1

.gitignore

@@ -26,3 +26,5 @@ rust-project.json
 
 # End of https://www.toptal.com/developers/gitignore/api/rust,rust-analyzer
 .zed/
+
+.idea/

README.org

@@ -0,0 +1,36 @@
+#+title: README
+
+* Syntax example:
+#+begin_src
+funzione :: fn(parametro1: Number, parametro2: String): String do
+
+end
+#+end_src
+
+* Planning:
+allora quello che devo fare è:
+** TODO Controllare se ho finito la questione del retourn:labe
+** TODO implement struct:
+#+begin_src rlox
+Cosa :: struct{
+        field1: Number
+}
+#+end_src
+*** TODO update lexert
+*** TODO update ast
+*** TODO update parser
+** TODO implement partial function ...
+#+begin_src rlox
+cosa := make(Cosa, feld1: 42)
+function :: fn(self:Cosa, b: Number) -> Number
+res := function(cosa,44)
+#+end_src
+*** TODO ... to undericlty create method
+#+begin_src rlox
+res := cosa.function(44)
+#+end_src
+*** TODO ... to make pipeline
+#+begin_src rlox
+res := cosa |> function(44)
+#+end_src
+** TODO Understand what is a type system

examples/fail_error.lox

@@ -1,8 +1,9 @@
 // Test script to verify error positioning
-var a = 5;
-var b = "hello";
+"no"();
+var a := 5;
+var b := "hello";
 print 0;
-var result = a + b;  // This should cause a type error
+var result := a + b;  // This should cause a type error
 print 1;
 43 + "hello"; // This should cause a type error
 print result;

examples/function_call.lox

@@ -1,20 +0,0 @@
-
-function :: fn() do
-    print "Function";
-end
-
-
-function_factory :: fn() do
-    print "Function Factory";
-    function
-end
-
-function_fatcoty_factory :: fn() do
-    print "Function Factory Factory";
-    function_factory
-end
-
-//function();
-//function_factory()();
-function_fatcoty_factory()()();
-clock()

examples/test_closure.lox

@@ -0,0 +1,27 @@
+
+closure :: fn(): Any do
+    value := "Closure";
+    internal :: fn(): String do
+        print value;
+        return value;
+    end;
+    return internal;
+end;
+
+internal := closure();
+internal();
+
+a := "Global";
+b := a;
+c := b;
+c = b = a;
+d := c = b = a;
+do
+    showA :: fn(): Nil do
+        print a;
+    end;
+
+    showA();
+    a := "Local";
+    showA();
+end

examples/test_example.lox

@@ -4,25 +4,28 @@
 //     address: String,
 // }
 //func_name :: fn(param: Number, param2: String) {param is Int}  do
-func_name :: fn(param: Int, param2: String) do
+func_name :: fn(param: Int, param2: String): Any do
     print param;
-    cavallo := 5;
-    print cavallo;
-    while cavallo < 10 do
-        cavallo = cavallo + 1;
-        print cavallo;
+    print param2;
+    while param < param2 do
+         param = param + 1;
+         print param;
+         print param2;
+        //break;
     end
-    if True then do
+    if False then do
         print "this shoul be stop";
-        return False;
+        return "Hahahaha";
     end
     print "this shoud be un other stop";
-    return 42;
+    //return 42;
     for i := 11; i <= 21; i = i + 1; do
         print i;
+        print "hello";
+        break;
     end
 
     return False or True;
-end
+end;
 
-func_name(1,2)
+func_name(1,20);

examples/test_function_call.lox

@@ -0,0 +1,30 @@
+
+function :: fn(): Nil do
+    print "Function";
+end;
+
+
+function_factory :: fn(): Any do
+    print "Function Factory";
+    function;
+end;
+
+function_fatcoty_factory :: fn(): Any do
+    print "Function Factory Factory";
+    return function_factory;
+end;
+
+//function();
+//function_factory()();
+//function_fatcoty_factory()()();
+clock();
+
+closure :: fn(): Any do
+    value := "Closure";
+    internal :: fn(): Nil do
+        print value;
+    end;
+    return internal;
+end;
+
+closure();

examples/test_source_tracking.lox

@@ -1,10 +1,10 @@
 // Test file for source slice tracking
-var x = 42;
+var x := 42;
 print x;
 
 if x > 0 then do
     print "positive";
-    var y = x + 1;
+    var y := x + 1;
 end
 elif x == 0 then do
     print "zero";
@@ -19,7 +19,7 @@ while x > 0 do
 end
 
 do
-    var z = 10;
+    var z := 10;
     print z * 2;
 end
 

grammar.org

@@ -0,0 +1,57 @@
+
+statement -> print_statement
+           | return_statement
+           | break_statement
+           | block_statement
+           | var_statement
+           | if_statement
+           | while_statement
+           | for_statement
+           | expression_statement
+
+print_statement      -> "print" expression ";"
+return_statement     -> "return" expression? ";"
+break_statement      -> "break" ";"
+block_statement      -> "do" statement* "end"
+expression_statement -> expression ";"?
+
+; leading "var" optional; the ":" is required
+var_statement        -> "var"? IDENTIFIER ":" IDENTIFIER?
+                        ( variable_declaration
+                        | function_declaration
+                        | struct_declaration )     ; struct = WIP
+variable_declaration -> ( "=" expression )? ";"
+function_declaration -> ":" "fn" "(" parameters? ")" ( "{" expression "}" )? statement
+parameters           -> IDENTIFIER ( ":" IDENTIFIER )?
+                        ( "," IDENTIFIER ( ":" IDENTIFIER )? )*
+
+if_statement    -> "if" expression "then" statement
+                   ( "elif" expression "then" statement )*
+                   ( "else" statement )?
+while_statement -> "while" expression statement
+for_statement   -> "for" var_statement expression ";" expression_statement statement
+
+; ---------- expressions (lowest -> highest precedence) ----------
+expression -> assignment
+assignment -> IDENTIFIER "=" assignment            ; right-associative
+            | pipe
+pipe       -> logic ( "|>" logic )*                ; left-assoc; x |> f(a) == f(x, a)
+logic      -> is ( ( "or" | "and" ) is )*
+is         -> equality ( "is" equality )*
+equality   -> comparison ( ( "==" | "!=" ) comparison )*
+comparison -> term ( ( ">" | ">=" | "<" | "<=" ) term )*
+term       -> factor ( ( "+" | "-" ) factor )*
+factor     -> unary ( ( "*" | "/" ) unary )*
+unary      -> ( "!" | "-" ) unary | call
+call       -> primary ( "(" arguments? ")" )*
+arguments  -> expression ( "," expression )*
+primary    -> NUMBER | STRING | "true" | "false" | "nil"
+            | "(" expression ")" | IDENTIFIER
+            | dictionary | list | ATOM                   ; WIP
+
+; ---------- work in progress (lexed; parser support being added) ----------
+struct_declaration -> "struct" "{" field* "}"
+field              -> IDENTIFIER ( ":" IDENTIFIER )? ";"
+dictionary         -> "dict" "(" IDENTIFIER ":" expression
+                      ( "," IDENTIFIER ":" expression )* ")"
+list               -> "list" "(" expression ( "," expression )* ")"

src/backend/environment.rs

@@ -1,34 +1,45 @@
-use std::collections::HashMap;
-
 use crate::{
-    common::{
-        base_value::BaseValue,
-        lox_result::{runtime_error, LoxResult},
-    },
+    common::lox_result::{runtime_error, LoxResult},
     frontend::source_registry::SourceSlice,
 };
+use std::collections::HashMap;
+use std::fmt::Debug;
 
-#[derive(Debug, Clone, PartialEq)]
-pub struct EnvironmentStack {
-    stack: Vec<HashMap<String, BaseValue>>,
+pub type Environment<T> = HashMap<String, T>;
+
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct EnvironmentStack<T: Clone + Debug + PartialEq> {
+    stack: Vec<HashMap<String, T>>,
 }
 
-impl EnvironmentStack {
+impl<T: Clone + Debug + PartialEq> EnvironmentStack<T> {
     pub fn new() -> Self {
         EnvironmentStack {
             stack: vec![HashMap::new()],
         }
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.stack.is_empty()
+    }
+
     pub fn push_new_scope(&mut self) {
         self.stack.push(HashMap::new());
     }
 
+    pub fn push_existing_scope(&mut self, scope: HashMap<String, T>) {
+        self.stack.push(scope);
+    }
+
     pub fn pop_scope(&mut self) {
         self.stack.pop();
     }
 
-    pub fn get(&self, name: &str) -> LoxResult<BaseValue> {
+    pub fn clone_last_scope(&mut self) -> HashMap<String, T> {
+        self.stack.last().unwrap().clone()
+    }
+
+    pub fn get(&self, name: &str) -> LoxResult<T> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {
@@ -37,17 +48,49 @@ impl EnvironmentStack {
             }
         }
         runtime_error(
-            SourceSlice::default(), // todo change this to the actual source slice
+            SourceSlice::synthetic(), // todo change this to the actual source slice
             format!("Undefined variable '{}'", name),
         )
     }
 
-    pub fn declare(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
+    pub fn declare(&mut self, name: String, value: T) -> LoxResult<T> {
         self.stack.last_mut().unwrap().insert(name, value.clone());
         Ok(value)
     }
 
-    pub fn set(&mut self, name: String, value: BaseValue) -> LoxResult<BaseValue> {
+    /// Read a variable at a known scope `distance` from the innermost scope
+    /// (0 = innermost). Used with resolver-computed distances.
+    pub fn get_at(&self, distance: usize, name: &str) -> LoxResult<T> {
+        let index = self.stack.len().checked_sub(distance + 1);
+        match index
+            .and_then(|i| self.stack.get(i))
+            .and_then(|s| s.get(name))
+        {
+            Some(value) => Ok(value.clone()),
+            None => runtime_error(
+                SourceSlice::synthetic(),
+                format!("Undefined variable '{}'", name),
+            ),
+        }
+    }
+
+    /// Assign to a variable at a known scope `distance` from the innermost
+    /// scope (0 = innermost).
+    pub fn assign_at(&mut self, distance: usize, name: String, value: T) -> LoxResult<T> {
+        let index = self.stack.len().checked_sub(distance + 1);
+        match index {
+            Some(i) if i < self.stack.len() => {
+                self.stack[i].insert(name, value.clone());
+                Ok(value)
+            }
+            _ => runtime_error(
+                SourceSlice::synthetic(),
+                format!("Undefined variable '{}'", name),
+            ),
+        }
+    }
+
+    pub fn set(&mut self, name: String, value: T) -> LoxResult<T> {
         let size = self.stack.len();
 
         for i in (0..size).rev() {
@@ -64,8 +107,102 @@ impl EnvironmentStack {
             }
         }
         runtime_error(
-            SourceSlice::default(), // todo change this to the actual source slice
+            SourceSlice::synthetic(), // todo change this to the actual source slice
             format!("Undefined variable '{}'", name),
         )
     }
+
+    pub fn depth(&self) -> usize {
+        self.stack.len()
+    }
+    pub fn scope_contains(&self, index: usize, name: &str) -> bool {
+        self.stack[index].contains_key(name)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn declare_and_get() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn get_undefined_is_error() {
+        let env: EnvironmentStack<i32> = EnvironmentStack::new();
+        assert!(env.get("nope").is_err());
+    }
+
+    #[test]
+    fn declare_overwrites_in_same_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.declare("a".to_string(), 2).unwrap();
+        assert_eq!(env.get("a").unwrap(), 2);
+    }
+
+    #[test]
+    fn inner_scope_shadows_outer_and_unshadows_on_pop() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        env.declare("a".to_string(), 2).unwrap();
+        assert_eq!(env.get("a").unwrap(), 2);
+        env.pop_scope();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn get_falls_through_to_outer_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        assert_eq!(env.get("a").unwrap(), 1);
+    }
+
+    #[test]
+    fn set_updates_existing_value_in_outer_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        env.push_new_scope();
+        env.set("a".to_string(), 9).unwrap();
+        env.pop_scope();
+        assert_eq!(env.get("a").unwrap(), 9);
+    }
+
+    #[test]
+    fn set_undefined_is_error() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        assert!(env.set("a".to_string(), 1).is_err());
+    }
+
+    #[test]
+    fn pop_scope_discards_inner_declarations() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.push_new_scope();
+        env.declare("temp".to_string(), 5).unwrap();
+        env.pop_scope();
+        assert!(env.get("temp").is_err());
+    }
+
+    #[test]
+    fn push_existing_scope_makes_values_visible() {
+        let mut scope = HashMap::new();
+        scope.insert("k".to_string(), 7);
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.push_existing_scope(scope);
+        assert_eq!(env.get("k").unwrap(), 7);
+    }
+
+    #[test]
+    fn clone_last_scope_returns_top_scope() {
+        let mut env: EnvironmentStack<i32> = EnvironmentStack::new();
+        env.declare("a".to_string(), 1).unwrap();
+        let scope = env.clone_last_scope();
+        assert_eq!(scope.get("a"), Some(&1));
+    }
 }

src/backend/interpreter.rs

@@ -1,73 +1,29 @@
 use crate::{
     backend::environment::EnvironmentStack,
     common::{
-        ast::{AstNode, AstNodeKind, Expr, Stmt},
+        ast::{AstNode, Expr, NodeId},
         base_value::{BaseValue, NativeFunction, Number, Truthy},
         lox_result::{runtime_error, LoxError, LoxResult},
     },
     frontend::{source_registry::SourceSlice, tokens::TokenType},
 };
-use std::fmt::{Debug, Display};
+use std::collections::HashMap;
 
 pub struct Interpreter {
-    enviorment: EnvironmentStack,
+    enviorment: EnvironmentStack<BaseValue>,
+    /// Per-reference scope distances from the resolver. Empty means "no
+    /// resolution pass was run", in which case lookups fall back to a dynamic
+    /// search of the scope chain.
+    locals: HashMap<NodeId, usize>,
 }
 
 pub trait EvaluateInterpreter<T> {
     fn evaluate(&mut self, stmt: T) -> LoxResult<BaseValue>;
 }
 
-impl<'a, R: AstNodeKind + Clone + Debug + Display> EvaluateInterpreter<AstNode<R>> for Interpreter
-where
-    Interpreter: EvaluateInterpreter<R>,
-{
-    fn evaluate(&mut self, stmt: AstNode<R>) -> LoxResult<BaseValue> {
-        match self.evaluate(stmt.node.clone()) {
-            Ok(value) => Ok(value),
-            Err(err) => runtime_error(stmt.source_slice, err.get_message()),
-        }
-    }
-}
-
-// Direct Expr evaluation to avoid infinite recursion
-impl EvaluateInterpreter<Expr> for Interpreter {
-    fn evaluate(&mut self, expr: Expr) -> LoxResult<BaseValue> {
-        match expr {
-            Expr::Literal { value } => Ok(value),
-            Expr::Identifier { name } => self.enviorment.get(&name),
-            Expr::Binary {
-                left,
-                operator,
-                right,
-            } => {
-                let left_val = self.evaluate(*left)?;
-                let right_val = self.evaluate(*right)?;
-                self.evaluate_binary(left_val, operator, right_val)
-            }
-            Expr::Unary { operator, operand } => {
-                let operand_val = self.evaluate(*operand)?;
-                self.evaluate_unary(operator, operand_val)
-            }
-            Expr::Grouping { expression } => self.evaluate(*expression),
-            Expr::Call { callee, arguments } => self.evaluate_call(callee, arguments),
-        }
-    }
-}
-
-impl EvaluateInterpreter<AstNode<Stmt>> for Interpreter {
-    fn evaluate(&mut self, node: AstNode<Stmt>) -> LoxResult<BaseValue> {
-        let stmt = node.node;
-        let result = self.interpret_stmt_inner(stmt);
-        match result {
-            Ok(value) => Ok(value),
-            Err(LoxError::RuntimeError {
-                message,
-                source_slice,
-            }) if source_slice == SourceSlice::default() => {
-                runtime_error(node.source_slice.clone(), message)
-            }
-            Err(err) => Err(err),
-        }
+impl EvaluateInterpreter<AstNode> for Interpreter {
+    fn evaluate(&mut self, node: AstNode) -> LoxResult<BaseValue> {
+        self.eval_expr(&node)
     }
 }
 
@@ -85,27 +41,150 @@ impl Interpreter {
                 ))
             })),
         );
-        Self { enviorment: env }
+        Self {
+            enviorment: env,
+            locals: HashMap::new(),
         }
-    fn evaluate_call(
+    }
+
+    /// Install the resolver's per-reference scope distances.
+    pub fn set_locals(&mut self, locals: HashMap<NodeId, usize>) {
+        self.locals = locals;
+    }
+
+    /// Evaluate an expression node, threading its `NodeId` so resolved
+    /// variables and assignments can use their precomputed scope distance.
+    fn eval_expr(&mut self, node: &AstNode) -> LoxResult<BaseValue> {
+        let result = match &node.node {
+            Expr::Literal { value } => match &**value {
+                BaseValue::Function(func) => {
+                    let mut func = func.clone();
+                    func.closure = Some(self.enviorment.clone());
+                    Ok(BaseValue::Function(func))
+                }
+                other => Ok(other.clone()),
+            },
+            Expr::Identifier { name } => self.look_up_variable(name, node.id),
+            Expr::Binary {
+                left,
+                operator,
+                right,
+            } => {
+                let left_val = self.eval_expr(left)?;
+                let right_val = self.eval_expr(right)?;
+                self.evaluate_binary(left_val, operator.clone(), right_val)
+            }
+            Expr::Unary { operator, operand } => {
+                let operand_val = self.eval_expr(operand)?;
+                self.evaluate_unary(operator.clone(), operand_val)
+            }
+            Expr::Grouping { expression } => self.eval_expr(expression),
+            Expr::Call { callee, arguments } => self.evaluate_call(callee, arguments),
+            Expr::Assign { name, value } => {
+                let value = self.eval_expr(value)?;
+                self.assign_variable(name, node.id, value)
+            }
+            Expr::Print { expression } => {
+                let value = self.eval_expr(expression)?;
+                println!("{}", value);
+                Ok(BaseValue::Nil)
+            }
+            Expr::VarDeclaration {
+                name, initializer, ..
+            } => {
+                let value = match initializer {
+                    Some(expr_node) => self.eval_expr(expr_node)?,
+                    None => BaseValue::Nil,
+                };
+                self.enviorment.declare(name.clone(), value)
+            }
+            Expr::Return { expression, .. } => self.eval_expr(expression),
+            Expr::Block { statements, .. } => self.evaluate_block(statements),
+            Expr::If {
+                condition,
+                then_branch,
+                elif_branches,
+                else_branch,
+            } => self.evaluate_if(condition, then_branch, elif_branches, else_branch),
+            Expr::While { condition, body } => {
+                let mut ret = BaseValue::Nil;
+                while self.eval_expr(condition)?.is_truthy() {
+                    match self.eval_expr(body) {
+                        Ok(val) => ret = val,
+                        Err(LoxError::Return { value, .. }) => {
+                            ret = value;
+                            break;
+                        }
+                        Err(err) => return Err(err),
+                    };
+                }
+                Ok(ret)
+            }
+            Expr::For {
+                variable,
+                condition,
+                increment,
+                body,
+            } => {
+                let source_slice = variable.source_slice.clone();
+                let val = self.eval_expr(variable)?;
+                if !matches!(val, BaseValue::Number(..)) {
+                    return runtime_error(source_slice, "Expected number literal");
+                }
+                let mut ret = BaseValue::Nil;
+                while self.eval_expr(condition)?.is_truthy() {
+                    match self.eval_expr(body) {
+                        Ok(val) => ret = val,
+                        Err(LoxError::Return { value, .. }) => {
+                            ret = value;
+                            break;
+                        }
+                        Err(err) => return Err(err),
+                    };
+                    self.eval_expr(increment)?;
+                }
+                Ok(ret)
+            }
+        };
+        // Give location-less runtime errors this node's span.
+        match result {
+            Err(LoxError::RuntimeError {
+                message,
+                source_slice,
+            }) if source_slice.is_synthetic() => runtime_error(node.source_slice.clone(), message),
+            other => other,
+        }
+    }
+
+    /// Look up a variable: by resolved distance if known, else dynamically.
+    fn look_up_variable(&self, name: &str, id: NodeId) -> LoxResult<BaseValue> {
+        match self.locals.get(&id) {
+            Some(&distance) => self.enviorment.get_at(distance, name),
+            None => self.enviorment.get(name),
+        }
+    }
+
+    /// Assign a variable: at its resolved distance if known, else dynamically.
+    fn assign_variable(
         &mut self,
-        callee: Box<AstNode<Expr>>,
-        arguments: Vec<AstNode<Expr>>,
+        name: &str,
+        id: NodeId,
+        value: BaseValue,
     ) -> LoxResult<BaseValue> {
+        match self.locals.get(&id) {
+            Some(&distance) => self.enviorment.assign_at(distance, name.to_string(), value),
+            None => self.enviorment.set(name.to_string(), value),
+        }
+    }
+
+    fn evaluate_call(&mut self, callee: &AstNode, arguments: &[AstNode]) -> LoxResult<BaseValue> {
         let source_slice = callee.source_slice.clone();
 
-        // Estrai il nome della variabile se il callee è un identificatore
-        let function_name = match &callee.node {
-            Expr::Identifier { name } => Some(name.clone()),
-            _ => None,
-        };
-
-        let function = if let Some(name) = function_name {
-            // Se abbiamo un nome di variabile, ottieni la funzione dall'ambiente
-            self.enviorment.get(&name)?
-        } else {
-            // Altrimenti valuta l'espressione callee (per casi più complessi)
-            self.evaluate(*callee)?
+        // A bare identifier callee resolves through `locals`; anything else is
+        // evaluated as a general expression.
+        let function = match &callee.node {
+            Expr::Identifier { name } => self.look_up_variable(name, callee.id)?,
+            _ => self.eval_expr(callee)?,
         };
 
         if !function.is_callable() {
@@ -114,21 +193,38 @@ impl Interpreter {
 
         let evaluated_arguments = arguments
             .iter()
-            .map(|arg| self.evaluate(arg.clone()))
+            .map(|arg| self.eval_expr(arg))
             .collect::<Result<Vec<BaseValue>, LoxError>>()?;
 
         match function {
             BaseValue::NativeFunction(func) => Ok((func.function)(&evaluated_arguments)),
             BaseValue::Function(func) => {
-                func.parameters
-                    .iter()
-                    .enumerate()
-                    .map(|(index, par)| {
+                let saved_env = self.enviorment.clone();
+                // If the function captured a closure, use it as the base environment
+                if let Some(closure_env) = func.closure {
+                    self.enviorment = closure_env;
+                }
+
+                // Push a new scope for the function's parameters
+                self.enviorment.push_new_scope();
+
+                // Declare parameters in the new scope
+                for (index, par) in func.parameters.iter().enumerate() {
                     let value = evaluated_arguments.get(index).unwrap();
-                        self.enviorment.declare(par.0.clone(), value.clone())
-                    })
-                    .collect::<LoxResult<Vec<BaseValue>>>()?;
-                self.evaluate(func.body)
+                    self.enviorment.declare(par.0.clone(), value.clone())?;
+                }
+
+                // Execute the function body
+                let result = match self.eval_expr(&func.body) {
+                    Ok(value) => Ok(value),
+                    Err(LoxError::Return { value, .. }) => Ok(value),
+                    Err(err) => Err(err),
+                };
+
+                // Restore the original environment (cleanup is automatic)
+                self.enviorment = saved_env;
+
+                result
             }
             _ => runtime_error(
                 source_slice.clone(),
@@ -157,7 +253,7 @@ impl Interpreter {
             TokenType::And => Ok(BaseValue::Boolean(left.is_truthy() && right.is_truthy())),
             TokenType::Or => Ok(BaseValue::Boolean(left.is_truthy() || right.is_truthy())),
             _ => Err(LoxError::RuntimeError {
-                source_slice: SourceSlice::default(),
+                source_slice: SourceSlice::synthetic(),
                 message: format!("Unsupported binary operator: {:?}", operator),
             }),
         }
@@ -168,105 +264,39 @@ impl Interpreter {
             TokenType::Minus => match operand {
                 BaseValue::Number(n) => Ok(BaseValue::Number(n.neg())),
                 _ => Err(LoxError::RuntimeError {
-                    source_slice: SourceSlice::default(),
+                    source_slice: SourceSlice::synthetic(),
                     message: "Cannot negate non-numeric value".to_string(),
                 }),
             },
             TokenType::Bang => Ok(!operand),
             _ => Err(LoxError::RuntimeError {
-                source_slice: SourceSlice::default(),
+                source_slice: SourceSlice::synthetic(),
                 message: format!("Unsupported unary operator: {:?}", operator),
             }),
         }
     }
 
-    fn interpret_stmt_inner(&mut self, stmt: Stmt) -> LoxResult<BaseValue> {
-        match stmt {
-            Stmt::Expression { expression } => self.evaluate(*expression),
-            Stmt::Print { expression } => {
-                let value = self.evaluate(*expression)?;
-                println!("{}", value);
-                Ok(BaseValue::Nil)
-            }
-            Stmt::Block { statements } => self.evaluate_block(*statements),
-            Stmt::Stmt { expression } => self.evaluate(*expression.clone()),
-            Stmt::Return { expression } => self.evaluate(*expression),
-            Stmt::VarDeclaration { name, initializer } => {
-                let value = match initializer {
-                    Some(expr_node) => match &expr_node.node {
-                        Expr::Literal { value } => {
-                            if value.is_callable() {
-                                value.clone()
-                            } else {
-                                value.clone()
-                            }
-                        }
-                        _ => self.evaluate(*expr_node)?,
-                    },
-                    None => BaseValue::Nil,
-                };
-                self.enviorment.declare(name.clone(), value)
-            }
-
-            Stmt::VarAssigment { name, value } => {
-                let result = self.evaluate(*value)?;
-                self.enviorment.set(name.clone(), result)
-            }
-            Stmt::If {
-                condition,
-                then_branch,
-                elif_branch,
-                else_branch,
-            } => self.evaluate_if(condition, then_branch, elif_branch, else_branch),
-            Stmt::While { condition, body } => {
-                while self.evaluate(*condition.clone())?.is_truthy() {
-                    self.evaluate(*body.clone())?;
-                }
-                Ok(BaseValue::Nil)
-            }
-            Stmt::For {
-                variable,
-                condition,
-                increment,
-                body,
-            } => {
-                self.enviorment.push_new_scope();
-                let source_slice = variable.source_slice.clone();
-                let val = self.evaluate(*variable)?;
-                if !matches!(val, BaseValue::Number(..)) {
-                    return runtime_error(source_slice, "Expected number literal");
-                }
-                let mut ret = BaseValue::Nil;
-                while self.evaluate(*condition.clone())?.is_truthy() {
-                    ret = self.evaluate(*body.clone())?;
-                    self.evaluate(*increment.clone())?;
-                }
-
-                Ok(ret)
-            }
-        }
-    }
     fn evaluate_if(
         &mut self,
-        condition: Box<AstNode<Expr>>,
-        then_branch: Box<AstNode<Stmt>>,
-        elif_branch: Vec<(Box<AstNode<Expr>>, Box<AstNode<Stmt>>)>,
-        else_branch: Option<Box<AstNode<Stmt>>>,
+        condition: &AstNode,
+        then_branch: &AstNode,
+        elif_branch: &[(Box<AstNode>, Box<AstNode>)],
+        else_branch: &Option<Box<AstNode>>,
     ) -> LoxResult<BaseValue> {
-        let condition = self.evaluate(*condition)?;
+        let condition = self.eval_expr(condition)?;
         match condition {
-            BaseValue::Boolean(true) => self.evaluate(*then_branch),
+            BaseValue::Boolean(true) => self.eval_expr(then_branch),
             BaseValue::Boolean(false) => {
                 for (elif_condition, elif_then_branch) in elif_branch {
-                    let condition = self.evaluate(*elif_condition)?;
+                    let condition = self.eval_expr(elif_condition)?;
                     match condition {
                         BaseValue::Boolean(true) => {
-                            return self.evaluate(*elif_then_branch);
+                            return self.eval_expr(elif_then_branch);
                         }
                         BaseValue::Boolean(false) => continue,
                         _ => {
                             return Err(LoxError::TypeMismatch {
-                                source_slice: SourceSlice::default(), // todo change this to the actual source slice
+                                source_slice: SourceSlice::synthetic(), // todo change this to the actual source slice
                                 expected: "boolean".to_string(),
                                 found: condition.to_string(),
                             });
@@ -274,49 +304,179 @@ impl Interpreter {
                     };
                 }
                 if let Some(else_block) = else_branch {
-                    self.evaluate(*else_block)
+                    self.eval_expr(else_block)
                 } else {
                     Ok(BaseValue::Nil)
                 }
             }
             _ => Err(LoxError::TypeMismatch {
-                source_slice: SourceSlice::default(), // todo change this to the actual source slice
+                source_slice: SourceSlice::synthetic(), // todo change this to the actual source slice
                 expected: "boolean".to_string(),
                 found: condition.to_string(),
             }),
         }
     }
 
-    fn evaluate_block(&mut self, statements: Vec<AstNode<Stmt>>) -> LoxResult<BaseValue> {
+    fn evaluate_block(&mut self, statements: &[AstNode]) -> LoxResult<BaseValue> {
         self.enviorment.push_new_scope();
-        let (elements, final_expr) = match statements.split_last() {
-            Some((stmt, body)) => match &stmt.node {
-                Stmt::Expression { expression } => (body, Some(expression)),
-                Stmt::Return { expression } => (body, Some(expression)),
-                _ => (statements.as_slice(), None),
-            },
 
-            None => {
-                (&[][..], None) // Blocco vuoto
+        let mut result = Ok(BaseValue::Nil);
+        for statement in statements.iter() {
+            match &statement.node {
+                Expr::Return { expression, .. } => {
+                    let value = self.eval_expr(expression)?;
+
+                    result = Err(LoxError::Return {
+                        source_slice: statement.source_slice.clone(),
+                        value,
+                        return_label: "Hi".to_string(),
+                    });
+                    break;
                 }
+                _ => result = self.eval_expr(statement),
             };
-
-        // Ora elements è sempre disponibile
-        for statement in elements.iter() {
-            self.evaluate((*statement).clone())?;
         }
-
-        // Gestisci l'espressione finale se presente
-        match final_expr {
-            Some(expr) => {
-                let res = self.evaluate(*expr.clone());
         self.enviorment.pop_scope();
-                res
+        result
     }
-            None => {
-                self.enviorment.pop_scope();
-                Ok(BaseValue::Nil)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::frontend::lexer::Lexer;
+    use crate::frontend::parser::Parser;
+
+    /// Lex, parse and interpret `src`, returning the value of the last statement.
+    fn eval(src: &str) -> LoxResult<BaseValue> {
+        let tokens = Lexer::new(src.to_string(), 0)
+            .scans_tokens()
+            .expect("source should lex without errors");
+        let statements = Parser::new(tokens)
+            .parse()
+            .expect("source should parse without errors");
+        let mut interpreter = Interpreter::new();
+        let mut last = BaseValue::Nil;
+        for stmt in statements {
+            last = interpreter.evaluate(stmt)?;
         }
+        Ok(last)
     }
+
+    #[test]
+    fn evaluates_arithmetic_with_precedence() {
+        assert_eq!(eval("1 + 2 * 3;").unwrap().to_string(), "7");
+    }
+
+    #[test]
+    fn grouping_changes_precedence() {
+        assert_eq!(eval("(1 + 2) * 3;").unwrap().to_string(), "9");
+    }
+
+    #[test]
+    fn division_and_subtraction() {
+        assert_eq!(eval("10 - 4 / 2;").unwrap().to_string(), "8");
+    }
+
+    #[test]
+    fn comparison_yields_boolean() {
+        assert_eq!(eval("1 < 2;").unwrap(), BaseValue::Boolean(true));
+        assert_eq!(eval("2 < 1;").unwrap(), BaseValue::Boolean(false));
+    }
+
+    #[test]
+    fn equality_operators() {
+        assert_eq!(eval("1 == 1;").unwrap(), BaseValue::Boolean(true));
+        assert_eq!(eval("1 != 2;").unwrap(), BaseValue::Boolean(true));
+    }
+
+    #[test]
+    fn unary_negation() {
+        assert_eq!(eval("-5;").unwrap().to_string(), "-5");
+    }
+
+    #[test]
+    fn logical_not() {
+        assert_eq!(eval("!true;").unwrap(), BaseValue::Boolean(false));
+    }
+
+    #[test]
+    fn concatenates_strings() {
+        match eval("\"a\" + \"b\";").unwrap() {
+            BaseValue::String(s) => assert!(s.contains('a') && s.contains('b')),
+            other => panic!("expected string, got {:?}", other),
+        }
+    }
+
+    #[test]
+    fn declares_and_reads_variable() {
+        assert_eq!(eval("var x: Int = 10; x + 5;").unwrap().to_string(), "15");
+    }
+
+    #[test]
+    fn assignment_updates_variable() {
+        assert_eq!(
+            eval("var x: Int = 1; x = 42; x;").unwrap().to_string(),
+            "42"
+        );
+    }
+
+    #[test]
+    fn if_takes_then_branch_when_true() {
+        assert_eq!(
+            eval("var x: Int = 0; if true then x = 1; x;")
+                .unwrap()
+                .to_string(),
+            "1"
+        );
+    }
+
+    #[test]
+    fn if_takes_else_branch_when_false() {
+        assert_eq!(
+            eval("var x: Int = 0; if false then x = 1; else x = 2; x;")
+                .unwrap()
+                .to_string(),
+            "2"
+        );
+    }
+
+    #[test]
+    fn while_loop_runs_until_condition_false() {
+        let src = "var i: Int = 0; while i < 3 do i = i + 1; end i;";
+        assert_eq!(eval(src).unwrap().to_string(), "3");
+    }
+
+    #[test]
+    fn block_scope_does_not_leak_outer_assignment() {
+        // `set` walks outer scopes, so the outer `x` is updated from inside the block.
+        let src = "var x: Int = 1; do x = 5; end x;";
+        assert_eq!(eval(src).unwrap().to_string(), "5");
+    }
+
+    #[test]
+    fn defines_and_calls_a_function() {
+        let src = "add :: fn (a, b): Number do return a + b; end; add(2, 3);";
+        assert_eq!(eval(src).unwrap().to_string(), "5");
+    }
+
+    #[test]
+    fn clock_native_function_returns_a_number() {
+        assert!(matches!(eval("clock();").unwrap(), BaseValue::Number(..)));
+    }
+
+    #[test]
+    fn undefined_variable_is_runtime_error() {
+        assert!(eval("missing;").is_err());
+    }
+
+    #[test]
+    fn calling_a_non_function_is_runtime_error() {
+        assert!(eval("var x: Int = 5; x();").is_err());
+    }
+
+    #[test]
+    fn adding_incompatible_types_is_runtime_error() {
+        assert!(eval("1 + true;").is_err());
     }
 }

src/common/ast.rs

@@ -1,65 +1,87 @@
 use crate::{
-    common::base_value::BaseValue,
+    common::{base_value::BaseValue, types::Type},
     frontend::{source_registry::SourceSlice, tokens::TokenType},
 };
 use std::fmt::{Debug, Display};
-/*
- * grammar:
- * program -> statement* EOF
- * statement -> expression_statement
- *             | print_statement
- *             | var_statement
- *             | block_statement
- *             | assignment_statement
- *             | if_statement
- *
- * expression_statement -> expression ";"
- * print_statement -> "print" expression ";"
- * var_statement -> ("var"|"dyn"|"mut")? IDENTIFIER (":" IDENTIFIER)? (("=" expression)? ";")| function_declaration
- * function_declaration -> "::" "(" parameters? ")" ("->" IDENTIFIER)? block_statement
- * parameters -> ( IDENTIFIER (":" IDENTIFIER)? ("," IDENTIFIER (":" IDENTIFIER)? )* )
- * assignment_statement -> IDENTIFIER "=" expression ";"
- * block_statement -> "do" statement* "end"
- * if_statement -> "if" expression "then" statement ("elif" expression "then" statement)* ("else" statement)? "end"
- * while_statement -> "while" expression "do" statement "end"
- *
- * expression -> assignment
- * assignment -> IDENTIFIER "=" assignment | logical_or
- * logical_or -> logical_and (("or" logical_and)*
- * logical_and -> logical_is (("and" logical_is)*
- * logical_is -> equality (("is" equality)*
- * equality -> comparison (("==" | "!=") comparison)*
- * comparison -> term ((">" | ">=" | "<" | "<=") term)*
- * term -> factor (("+" | "-") factor)*
- * factor -> unary (("*" | "/") unary)*
- * unary -> ("!" | "-") unary | call
- * call -> primary ("(" arguments ")")*
- * arguments -> expression ("," expression)*
- * primary -> NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" | IDENTIFIER
- */
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+/// A unique identity for an AST node, assigned once at construction.
+///
+/// Unlike a [`SourceSlice`] (which describes *where* a node is, for
+/// diagnostics), a `NodeId` describes *which* node it is. It is stable across
+/// clones, so analyses such as the resolver can key per-reference data on it
+/// without relying on source positions being unique.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct NodeId(pub usize);
+
+static NEXT_NODE_ID: AtomicUsize = AtomicUsize::new(0);
+
+impl NodeId {
+    /// Allocate the next globally-unique node id.
+    pub fn next() -> Self {
+        NodeId(NEXT_NODE_ID.fetch_add(1, Ordering::Relaxed))
+    }
+}
+
 #[derive(Clone, PartialEq)]
 pub enum Expr {
     Literal {
-        value: BaseValue,
+        value: Box<BaseValue>,
     },
     Binary {
-        left: Box<AstNode<Expr>>,
+        left: Box<AstNode>,
         operator: TokenType,
-        right: Box<AstNode<Expr>>,
+        right: Box<AstNode>,
     },
     Unary {
         operator: TokenType,
-        operand: Box<AstNode<Expr>>,
+        operand: Box<AstNode>,
     },
     Grouping {
-        expression: Box<AstNode<Expr>>,
+        expression: Box<AstNode>,
     },
     Identifier {
         name: String,
     },
     Call {
-        callee: Box<AstNode<Expr>>,
-        arguments: Vec<AstNode<Expr>>,
+        callee: Box<AstNode>,
+        arguments: Vec<AstNode>,
+    },
+    Assign {
+        name: String,
+        value: Box<AstNode>,
+    },
+    Print {
+        expression: Box<AstNode>,
+    },
+    VarDeclaration {
+        name: String,
+        var_type: Type,
+        initializer: Option<Box<AstNode>>,
+    },
+    Return {
+        expression: Box<AstNode>,
+        label: String,
+    },
+    Block {
+        statements: Box<Vec<AstNode>>,
+        label: String,
+    },
+    If {
+        condition: Box<AstNode>,
+        then_branch: Box<AstNode>,
+        elif_branches: Vec<(Box<AstNode>, Box<AstNode>)>,
+        else_branch: Option<Box<AstNode>>,
+    },
+    While {
+        condition: Box<AstNode>,
+        body: Box<AstNode>,
+    },
+    For {
+        variable: Box<AstNode>,
+        condition: Box<AstNode>,
+        increment: Box<AstNode>,
+        body: Box<AstNode>,
     },
 }
 
@@ -74,8 +96,10 @@ impl std::fmt::Display for Expr {
                 right,
             } => write!(f, "Binary ({} {} {})", left.node, operator, right.node),
             Expr::Unary { operator, operand } => write!(f, "Unary ({} {})", operator, operand.node),
-            Expr::Grouping { expression } => write!(f, "Grouping (group {})", expression.node),
-            Expr::Identifier { name } => write!(f, "Identifier (variable {})", name),
+            Expr::Grouping { expression } => write!(f, "Grouping (group {})", expression.node,),
+            Expr::Identifier { name } => {
+                write!(f, "Identifier (variable {})", name)
+            }
             Expr::Call { callee, arguments } => write!(
                 f,
                 "Call ({}({}))",
@@ -86,94 +110,18 @@ impl std::fmt::Display for Expr {
                     .collect::<Vec<String>>()
                     .join(", ")
             ),
-        }
-    }
-}
-
-impl Debug for Expr {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Expr::Literal { value } => write!(f, "{:?}", value),
-            Expr::Binary {
-                left,
-                operator,
-                right,
-            } => write!(f, "({:?} {:?} {:?})", operator, left.node, right.node),
-            Expr::Unary { operator, operand } => write!(f, "({:?} {:?})", operator, operand.node),
-            Expr::Grouping { expression } => write!(f, "(group {:?})", expression.node),
-            Expr::Identifier { name } => write!(f, "(variable {:?})", name),
-            Expr::Call { callee, arguments } => write!(
-                f,
-                "Call ({}({}))",
-                callee.node,
-                arguments
-                    .iter()
-                    .map(|arg| arg.node.to_string())
-                    .collect::<Vec<String>>()
-                    .join(", ")
-            ),
-        }
-    }
-}
-
-#[derive(Clone, PartialEq)]
-pub enum Stmt {
-    Expression {
-        expression: Box<AstNode<Expr>>,
-    },
-    Print {
-        expression: Box<AstNode<Expr>>,
-    },
-    Stmt {
-        expression: Box<AstNode<Expr>>,
-    },
-    VarDeclaration {
-        name: String,
-        initializer: Option<Box<AstNode<Expr>>>,
-    },
-    VarAssigment {
-        name: String,
-        value: Box<AstNode<Expr>>,
-    },
-    Return {
-        expression: Box<AstNode<Expr>>,
-    },
-    Block {
-        statements: Box<Vec<AstNode<Stmt>>>,
-    },
-    If {
-        condition: Box<AstNode<Expr>>,
-        then_branch: Box<AstNode<Stmt>>,
-        elif_branch: Vec<(Box<AstNode<Expr>>, Box<AstNode<Stmt>>)>,
-        else_branch: Option<Box<AstNode<Stmt>>>,
-    },
-    While {
-        condition: Box<AstNode<Expr>>,
-        body: Box<AstNode<Stmt>>,
-    },
-    For {
-        variable: Box<AstNode<Stmt>>,
-        condition: Box<AstNode<Expr>>,
-        increment: Box<AstNode<Stmt>>,
-        body: Box<AstNode<Stmt>>,
-    },
-}
-
-impl Display for Stmt {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Stmt::Expression { expression } => write!(f, "Expression ({})", expression.node),
-            Stmt::If {
+            Expr::Assign { name, value } => write!(f, "Assign ({} = {})", name, value.node),
+            Expr::If {
                 condition,
                 then_branch,
-                elif_branch,
+                elif_branches,
                 else_branch,
             } => {
                 let mut result = format!("IF ({}) {{\n{}\n}}", condition.node, then_branch.node);
-                for (condition, branch) in elif_branch {
+                for (condition, branch) in elif_branches {
                     result.push_str(&format!(
                         " ELIF ({}) {{\n{}\n}}",
-                        condition.node, branch.node
+                        condition.node, branch.node,
                     ));
                 }
                 if let Some(else_branch) = else_branch {
@@ -181,27 +129,32 @@ impl Display for Stmt {
                 }
                 write!(f, "IfStmt {}", result)
             }
-            Stmt::Print { expression } => write!(f, "Print({});", expression.node),
-            Stmt::Stmt { expression } => write!(f, "Stmt({});", expression.node),
-            Stmt::VarDeclaration { name, initializer } => match initializer {
-                Some(init) => write!(f, "Var({} = {});", name, init.node),
-                None => write!(f, "Var({});", name),
+            Expr::Print { expression } => write!(f, "Print({})", expression.node),
+            Expr::VarDeclaration {
+                name,
+                initializer,
+                var_type,
+            } => match initializer {
+                Some(init) => write!(f, "Var({} : {:?} = {})", name, var_type, init.node),
+                None => write!(f, "Var({} : {:?})", name, var_type),
             },
-            Stmt::VarAssigment { name, value } => write!(f, "Assign({} = {});", name, value.node),
-            Stmt::Return { expression } => write!(f, "Return({});", expression.node),
-            Stmt::Block { statements } => write!(
+            Expr::Return { expression, label } => {
+                write!(f, "Return({}, {})", expression.node, label)
+            }
+            Expr::Block { statements, label } => write!(
                 f,
-                "Block([\n{}\n])",
+                "Block [{}] ([\n{}\n])",
+                label,
                 statements
                     .iter()
                     .map(|stmt| format!("\t \t{}", stmt.node))
                     .collect::<Vec<_>>()
-                    .join("\n")
+                    .join("\n"),
             ),
-            Stmt::While { condition, body } => {
+            Expr::While { condition, body } => {
                 write!(f, "While({}) {{\n{}\n}}", condition.node, body.node)
             }
-            Stmt::For {
+            Expr::For {
                 variable,
                 condition,
                 increment,
@@ -215,110 +168,116 @@ impl Display for Stmt {
     }
 }
 
-impl Debug for Stmt {
+impl Debug for Expr {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Stmt::Expression { expression } => write!(f, " Expression ({:?})", expression.node),
-            Stmt::If {
+            Expr::Literal { value } => write!(f, "{:?} ", value,),
+            Expr::Binary {
+                left,
+                operator,
+                right,
+            } => write!(f, "({:?} {:?} {:?}) ", operator, left.node, right.node,),
+            Expr::Unary { operator, operand } => {
+                write!(f, "(Unary {:?} {:?}) ", operator, operand.node,)
+            }
+            Expr::Grouping { expression } => {
+                write!(f, "(Grouping {:?})", expression.node,)
+            }
+            Expr::Identifier { name } => {
+                write!(f, "(variable {:?})", name,)
+            }
+            Expr::Call { callee, arguments } => write!(
+                f,
+                "Call ({}({}))",
+                callee.node,
+                arguments
+                    .iter()
+                    .map(|arg| arg.node.to_string())
+                    .collect::<Vec<String>>()
+                    .join(", "),
+            ),
+            Expr::Assign { name, value } => {
+                write!(f, "(assign {:?} {:?})", name, value.node,)
+            }
+            Expr::If {
                 condition,
                 then_branch,
-                elif_branch,
+                elif_branches,
                 else_branch,
             } => {
                 let mut result =
-                    format!("IF ({:?}) {{\n{:?}\n}}", condition.node, then_branch.node);
-                for (condition, branch) in elif_branch {
+                    format!("IF ({:?}) {{\n{:?}\n}}", condition.node, then_branch.node,);
+                for (condition, branch) in elif_branches {
                     result.push_str(&format!(
                         " ELIF ({:?}) {{\n{:?}\n}}",
-                        condition.node, branch.node
+                        condition.node, branch.node,
                     ));
                 }
                 if let Some(else_branch) = else_branch {
-                    result.push_str(&format!(" ELSE {{\n{:?}\n}}", else_branch.node));
+                    result.push_str(&format!(" ELSE {{\n{:?}\n}}", else_branch.node,));
                 }
                 write!(f, "IfStmt {:?}", result)
             }
-            Stmt::Print { expression } => write!(f, "Print({:?});", expression.node),
-            Stmt::Stmt { expression } => write!(f, "Stmt({:?});", expression.node),
-            Stmt::VarDeclaration { name, initializer } => match initializer {
-                Some(init) => write!(f, "Var({:?} = {:?});", name, init.node),
-                None => write!(f, "Var({:?});", name),
-            },
-            Stmt::VarAssigment { name, value } => {
-                write!(f, "Assign({:?} = {:?});", name, value.node)
+            Expr::Print { expression } => {
+                write!(f, "Print({:?});", expression.node,)
             }
-            Stmt::Return { expression } => write!(f, "Return({:?});", expression.node),
-            Stmt::Block { statements } => write!(
+            Expr::VarDeclaration {
+                name,
+                initializer,
+                var_type,
+            } => match initializer {
+                Some(init) => write!(f, "Var({:?}: {:?} = {:?});", name, var_type, init.node,),
+                None => write!(f, "Var({:?}: {:?});", name, var_type,),
+            },
+            Expr::Return { expression, label } => {
+                write!(f, "Return({:?}, {}) ;", expression.node, label,)
+            }
+            Expr::Block { label, statements } => write!(
                 f,
-                "Block([\n{:?}\n])",
+                "Block [{}] ([\n{:?}\n])",
+                label,
                 statements
                     .iter()
                     .map(|stmt| format!("{:?}", stmt.node))
                     .collect::<Vec<_>>()
-                    .join("\t\t\n")
+                    .join("\t\t\n"),
             ),
-            Stmt::While { condition, body } => {
-                write!(f, "While({:?}) {{\n{:?}\n}}", condition.node, body.node)
+            Expr::While { condition, body } => {
+                write!(f, "While({:?}) {{\n{:?}\n}}", condition.node, body.node,)
             }
-            Stmt::For {
+            Expr::For {
                 variable,
                 condition,
                 increment,
                 body,
             } => write!(
                 f,
-                "For({:?} = {:?} in {:?}) {{\n{:?}\n}}",
-                variable.node, condition.node, increment.node, body.node
+                "For({:?} = {:?} in {:?}) {{\n{:?}\n}} ",
+                variable.node, condition.node, increment.node, body.node,
             ),
         }
     }
 }
 
-pub trait AstNodeKind {
-    fn kind(&self) -> &'static str;
-}
-
-impl AstNodeKind for Expr {
-    fn kind(&self) -> &'static str {
-        match self {
-            Expr::Literal { value: _ } => "literal",
-            Expr::Binary {
-                left: _,
-                operator: _,
-                right: _,
-            } => "binary expression",
-            Expr::Unary { .. } => "unary expression",
-            Expr::Grouping { .. } => "grouping expression",
-            Expr::Identifier { .. } => "variable expression",
-            Expr::Call { .. } => "call expression",
-        }
-    }
-}
-
-impl AstNodeKind for Stmt {
-    fn kind(&self) -> &'static str {
-        match self {
-            Stmt::Expression { .. } => "expression",
-            Stmt::VarDeclaration { .. } => "variable declaration",
-            Stmt::VarAssigment { .. } => "assignment",
-            Stmt::Return { .. } => "return statement",
-            Stmt::Block { .. } => "block statement",
-            Stmt::If { .. } => "if statement",
-            Stmt::Print { .. } => "print statement",
-            Stmt::Stmt { .. } => "statement",
-            Stmt::While { .. } => "while statement",
-            Stmt::For { .. } => "for statement",
-        }
-    }
-}
-
-#[derive(Clone, PartialEq, Default)]
-pub struct AstNode<T: AstNodeKind + Debug + Display> {
-    pub node: T,
+#[derive(Clone)]
+pub struct AstNode {
+    /// Stable identity, assigned at construction and preserved across clones.
+    pub id: NodeId,
+    pub node: Expr,
+    pub is_statement: bool,
     pub source_slice: SourceSlice,
+    pub return_type: Type,
 }
 
-impl<T: AstNodeKind + Debug + Display> Display for AstNode<T> {
+// Identity (`id`) deliberately does not participate in equality: two nodes are
+// equal when their content and location match, regardless of node id.
+impl PartialEq for AstNode {
+    fn eq(&self, other: &Self) -> bool {
+        self.node == other.node && self.source_slice == other.source_slice
+    }
+}
+
+impl Display for AstNode {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(
             f,
@@ -328,7 +287,7 @@ impl<T: AstNodeKind + Debug + Display> Display for AstNode<T> {
     }
 }
 
-impl<T: AstNodeKind + Debug + Display> Debug for AstNode<T> {
+impl Debug for AstNode {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(
             f,
@@ -338,8 +297,22 @@ impl<T: AstNodeKind + Debug + Display> Debug for AstNode<T> {
     }
 }
 
-impl<T: AstNodeKind + Debug + Display> AstNode<T> {
-    pub fn new(node: T, source_slice: SourceSlice) -> Self {
-        AstNode { node, source_slice }
+impl AstNode {
+    fn new(node: Expr, source_slice: SourceSlice, type_name: String, is_statement: bool) -> Self {
+        AstNode {
+            id: NodeId::next(),
+            node,
+            is_statement,
+            source_slice,
+            return_type: Type::Unresolved(type_name),
+        }
+    }
+
+    pub fn new_statement(node: Expr, source_slice: SourceSlice) -> Self {
+        Self::new(node, source_slice, "Nil".to_string(), true)
+    }
+
+    pub fn new_expression(node: Expr, source_slice: SourceSlice, type_name: String) -> Self {
+        Self::new(node, source_slice, type_name, false)
     }
 }

src/common/base_value.rs

@@ -1,11 +1,12 @@
 use core::fmt;
+use std::collections::HashMap;
 use std::fmt::Display;
 use std::ops::{Add, Div, Mul, Not, Rem, Sub};
 
 use crate::common::lox_result::{runtime_error, LoxResult};
+use crate::common::types::Type;
 use crate::{
-    backend::environment::EnvironmentStack,
-    common::ast::{AstNode, Expr, Stmt},
+    backend::environment::EnvironmentStack, common::ast::AstNode,
     frontend::source_registry::SourceSlice,
 };
 #[derive(Debug, Clone, PartialEq)]
@@ -271,6 +272,22 @@ pub enum BaseValue {
     Nil,
     Function(LoxFunction),
     NativeFunction(NativeFunction),
+    Struct(Struct),
+}
+
+struct Dict {
+    map: HashMap<String, BaseValue>,
+}
+
+struct ReturnValue {
+    label: Vec<String>,
+    value: Type,
+}
+
+impl ReturnValue {
+    pub fn new(label: Vec<String>, value: Type) -> Self {
+        Self { label, value }
+    }
 }
 
 impl BaseValue {
@@ -292,36 +309,40 @@ impl Display for BaseValue {
             BaseValue::Nil => write!(f, "nil"),
             BaseValue::Function(..) => write!(f, "<fn lox function>"),
             BaseValue::NativeFunction(..) => write!(f, "<native native function>"),
+            BaseValue::Struct(_) => write!(f, "<struct>"),
         }
     }
 }
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct LoxFunction {
-    pub parameters: Vec<(String, String)>,
-    pub body: AstNode<Stmt>,
-    pub closure: Option<EnvironmentStack>,
-    pub guard: Option<Box<Expr>>,
+    pub parameters: Vec<(String, Type)>,
+    pub return_type: Type,
+    pub body: AstNode,
+    pub closure: Option<EnvironmentStack<BaseValue>>,
+    pub guard: Option<Box<AstNode>>,
 }
 
 impl LoxFunction {
     pub fn new(
-        parameters: Vec<(String, String)>,
-        body: AstNode<Stmt>,
-        closure: Option<EnvironmentStack>,
-        guard: Option<Box<Expr>>,
+        parameters: Vec<(String, Type)>,
+        body: AstNode,
+        closure: Option<EnvironmentStack<BaseValue>>,
+        guard: Option<Box<AstNode>>,
     ) -> Self {
         LoxFunction {
             parameters,
+            return_type: Type::Any,
             body,
             closure,
             guard,
         }
     }
 
-    pub fn anonymous_function(parameters: Vec<(String, String)>, body: AstNode<Stmt>) -> Self {
+    pub fn anonymous_function(parameters: Vec<(String, Type)>, body: AstNode) -> Self {
         LoxFunction {
             parameters,
+            return_type: Type::Any,
             body,
             closure: None,
             guard: None,
@@ -331,12 +352,12 @@ impl LoxFunction {
 
 #[derive(Debug, Clone, PartialEq)]
 pub struct NativeFunction {
-    pub parameters: Vec<(String, String)>,
+    pub parameters: Vec<(String, Type)>,
     pub function: fn(&[BaseValue]) -> BaseValue,
 }
 
 impl NativeFunction {
-    pub fn new(parameters: Vec<(String, String)>, function: fn(&[BaseValue]) -> BaseValue) -> Self {
+    pub fn new(parameters: Vec<(String, Type)>, function: fn(&[BaseValue]) -> BaseValue) -> Self {
         NativeFunction {
             parameters,
             function,
@@ -344,6 +365,11 @@ impl NativeFunction {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub struct Struct {
+    pub fields: Vec<(String, BaseValue)>,
+}
+
 // Trait implementations for BaseValue
 
 pub trait Truthy {
@@ -383,7 +409,7 @@ impl Add for BaseValue {
                 Ok(BaseValue::String(format!("{}{}", a, b)))
             }
             _ => runtime_error(
-                SourceSlice::default(),
+                SourceSlice::synthetic(),
                 "Cannot add non-numeric values".to_string(),
             ),
         }
@@ -413,7 +439,7 @@ impl Sub for BaseValue {
         match (self, other) {
             (BaseValue::Number(a), BaseValue::Number(b)) => Ok(BaseValue::Number(a.sub(b))),
             _ => runtime_error(
-                SourceSlice::default(),
+                SourceSlice::synthetic(),
                 "Cannot subtract non-numeric values".to_string(),
             ),
         }
@@ -427,10 +453,10 @@ impl Div for BaseValue {
         match (self, other) {
             (BaseValue::Number(a), BaseValue::Number(b)) => match a.div(b) {
                 Some(result) => Ok(BaseValue::Number(result)),
-                None => runtime_error(SourceSlice::default(), "Division by zero".to_string()),
+                None => runtime_error(SourceSlice::synthetic(), "Division by zero".to_string()),
             },
             _ => runtime_error(
-                SourceSlice::default(),
+                SourceSlice::synthetic(),
                 "Cannot divide non-numeric values".to_string(),
             ),
         }
@@ -444,7 +470,7 @@ impl Mul for BaseValue {
         match (self, other) {
             (BaseValue::Number(a), BaseValue::Number(b)) => Ok(BaseValue::Number(a.mul(b))),
             _ => runtime_error(
-                SourceSlice::default(),
+                SourceSlice::synthetic(),
                 "Cannot multiply non-numeric values".to_string(),
             ),
         }
@@ -458,10 +484,10 @@ impl Rem for BaseValue {
         match (self, other) {
             (BaseValue::Number(a), BaseValue::Number(b)) => match a.rem(b) {
                 Some(result) => Ok(BaseValue::Number(result)),
-                None => runtime_error(SourceSlice::default(), "Division by zero".to_string()),
+                None => runtime_error(SourceSlice::synthetic(), "Division by zero".to_string()),
             },
             _ => runtime_error(
-                SourceSlice::default(),
+                SourceSlice::synthetic(),
                 "Cannot divide non-numeric values".to_string(),
             ),
         }

src/common/lox_result.rs

@@ -1,5 +1,8 @@
-use crate::frontend::source_registry::{SourceRegistry, SourceSlice};
-use std::fmt;
+use crate::{
+    common::base_value::BaseValue,
+    frontend::source_registry::{SourceRegistry, SourceSlice},
+};
+use std::{error::Error, fmt};
 
 #[derive(Debug, Clone)]
 pub enum LoxError {
@@ -23,6 +26,11 @@ pub enum LoxError {
         expected: String,
         found: String,
     },
+    Return {
+        source_slice: SourceSlice,
+        value: BaseValue,
+        return_label: String,
+    },
 }
 
 /// Configuration for error display formatting
@@ -81,6 +89,13 @@ impl LoxError {
             } => {
                 format!("expected {}, found {}", expected, found)
             }
+            LoxError::Return {
+                value,
+                return_label,
+                ..
+            } => {
+                format!("return value: {} and label: {}", value, return_label)
+            }
         }
     }
 
@@ -91,6 +106,7 @@ impl LoxError {
             LoxError::ParseError { source_slice, .. } => Some(source_slice.clone()),
             LoxError::IoError { .. } => None,
             LoxError::TypeMismatch { source_slice, .. } => Some(source_slice.clone()),
+            LoxError::Return { .. } => None,
         }
     }
 
@@ -101,6 +117,7 @@ impl LoxError {
             LoxError::ParseError { .. } => "parse error",
             LoxError::IoError { .. } => "io error",
             LoxError::TypeMismatch { .. } => "type error",
+            LoxError::Return { .. } => "return error",
         }
     }
 
@@ -393,11 +410,25 @@ impl fmt::Display for LoxError {
                     found
                 )
             }
+            LoxError::Return {
+                value,
+                return_label,
+                source_slice,
+            } => {
+                write!(
+                    f,
+                    "Return error at {}:{}: value `{}`, label `{}`",
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1,
+                    value,
+                    return_label
+                )
+            }
         }
     }
 }
 
-impl std::error::Error for LoxError {}
+impl Error for LoxError {}
 
 pub type LoxResult<T> = Result<T, LoxError>;
 
@@ -448,3 +479,90 @@ pub fn io_error<T>(message: impl Into<String>) -> LoxResult<T> {
         message: message.into(),
     })
 }
+
+/// Accumulates diagnostics during a pass instead of bailing on the first one.
+///
+/// Static analyses (e.g. the resolver) `report` problems and keep traversing so
+/// the user sees every error at once, then surface them at the end.
+#[derive(Debug, Default)]
+pub struct ErrorSink {
+    errors: Vec<LoxError>,
+}
+
+impl ErrorSink {
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Record a diagnostic and keep going.
+    pub fn report(&mut self, error: LoxError) {
+        self.errors.push(error);
+    }
+
+    pub fn has_errors(&self) -> bool {
+        !self.errors.is_empty()
+    }
+
+    pub fn errors(&self) -> &[LoxError] {
+        &self.errors
+    }
+
+    /// Merge another sink's errors into this one (e.g. from a separate pass).
+    pub fn extend(&mut self, other: ErrorSink) {
+        self.errors.extend(other.errors);
+    }
+
+    pub fn into_errors(self) -> Vec<LoxError> {
+        self.errors
+    }
+
+    /// Bridge to the single-error [`LoxResult`] API: `Ok` if empty, otherwise
+    /// the first reported error.
+    pub fn into_result(self) -> LoxResult<()> {
+        match self.errors.into_iter().next() {
+            Some(error) => Err(error),
+            None => Ok(()),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::frontend::source_registry::SourceSlice;
+
+    fn parse_err(message: &str) -> LoxError {
+        LoxError::ParseError {
+            source_slice: SourceSlice::synthetic(),
+            message: message.to_string(),
+        }
+    }
+
+    #[test]
+    fn empty_sink_is_ok() {
+        let sink = ErrorSink::new();
+        assert!(!sink.has_errors());
+        assert!(sink.into_result().is_ok());
+    }
+
+    #[test]
+    fn accumulates_multiple_errors() {
+        let mut sink = ErrorSink::new();
+        sink.report(parse_err("first"));
+        sink.report(parse_err("second"));
+        assert!(sink.has_errors());
+        assert_eq!(sink.errors().len(), 2);
+        assert!(sink.into_result().is_err());
+    }
+
+    #[test]
+    fn extend_merges_sinks() {
+        let mut a = ErrorSink::new();
+        a.report(parse_err("a"));
+        let mut b = ErrorSink::new();
+        b.report(parse_err("b1"));
+        b.report(parse_err("b2"));
+        a.extend(b);
+        assert_eq!(a.into_errors().len(), 3);
+    }
+}

src/common/mod.rs

@@ -1,3 +1,4 @@
 pub mod ast;
 pub mod base_value;
 pub mod lox_result;
+pub mod types;

src/common/types.rs

@@ -0,0 +1,70 @@
+use std::{fmt::Display, rc::Rc};
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Type {
+    Any,
+    Number,
+    String,
+    Boolean,
+    Nil,
+    Function(FunctionType),
+    Struct(Rc<StructType>),
+    Unresolved(String),
+}
+
+impl Display for Type {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Type::Any => write!(f, "any"),
+            Type::Number => write!(f, "number"),
+            Type::String => write!(f, "string"),
+            Type::Boolean => write!(f, "boolean"),
+            Type::Nil => write!(f, "nil"),
+            Type::Function(fun) => write!(f, "{}", fun),
+            Type::Struct(struct_) => write!(f, "{}", struct_),
+            Type::Unresolved(name) => write!(f, "{}", name),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct FunctionType {
+    pub params: Vec<(String, Box<Type>)>,
+    pub return_type: Box<Type>,
+}
+
+impl Display for FunctionType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let rendered_params = self
+            .params
+            .iter()
+            .map(|(name, ty)| format!("{}: {}", name, ty))
+            .collect::<Vec<_>>()
+            .join(", ");
+        write!(f, "fn({}) -> {}", rendered_params, self.return_type)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct StructType {
+    pub fields: Vec<(String, Box<Type>)>,
+    pub methods: Vec<(String, FunctionType)>,
+}
+
+impl Display for StructType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let rendered_field = self
+            .fields
+            .iter()
+            .map(|(name, ty)| format!("{}: {}", name, ty))
+            .collect::<Vec<_>>()
+            .join(", ");
+        let rendered_method = self
+            .methods
+            .iter()
+            .map(|(name, ty)| format!("{}: {}", name, ty))
+            .collect::<Vec<_>>()
+            .join(", ");
+        write!(f, "struct {{ {}, {} }}", rendered_field, rendered_method)
+    }
+}

src/frontend/lexer.rs

@@ -5,8 +5,9 @@ use crate::frontend::tokens::{Token, TokenType};
 
 pub struct Lexer {
     input: String,
-    start_char: usize,
-    current_char: usize,
+    // Byte offsets into `input` (not char counts) so slicing is UTF-8 correct.
+    start: usize,
+    current: usize,
     start_pos: SourcePosition,
     end_pos: SourcePosition,
     source_id: SourceId,
@@ -15,7 +16,7 @@ pub struct Lexer {
 fn get_keyword_token(word: &str) -> Option<TokenType> {
     match word {
         "and" => Some(TokenType::And),
-        "class" => Some(TokenType::Class),
+        "struct" => Some(TokenType::Struct),
         "do" => Some(TokenType::StartBlock),
         "end" => Some(TokenType::EndBlock),
         "false" => Some(TokenType::False),
@@ -29,6 +30,7 @@ fn get_keyword_token(word: &str) -> Option<TokenType> {
         "in" => Some(TokenType::In),
         "print" => Some(TokenType::Print),
         "return" => Some(TokenType::Return),
+        "break" => Some(TokenType::Break),
         "super" => Some(TokenType::Super),
         "this" => Some(TokenType::This),
         "true" => Some(TokenType::True),
@@ -47,28 +49,18 @@ impl Lexer {
     pub fn new(input: String, source_id: SourceId) -> Lexer {
         Lexer {
             input,
-            start_char: 0,
-            current_char: 0,
+            start: 0,
+            current: 0,
             start_pos: SourcePosition::default(),
             end_pos: SourcePosition::default(),
             source_id,
         }
     }
 
-    fn advance_column(&mut self) {
-        self.current_char += 1;
-        self.end_pos.column += 1;
-    }
-
-    fn advance_line(&mut self) {
-        self.end_pos.line += 1;
-        self.end_pos.column = 0;
-    }
-
     pub fn scans_tokens(&mut self) -> LoxResult<Vec<Token>> {
         let mut tokens = Vec::new();
         while !self.is_at_end() {
-            self.start_char = self.current_char;
+            self.start = self.current;
             self.start_pos = self.end_pos.clone();
             match self.scan_token() {
                 Ok(Some(token)) => tokens.push(token),
@@ -81,32 +73,31 @@ impl Lexer {
     }
 
     fn is_at_end(&self) -> bool {
-        self.current_char >= self.input.len()
+        self.current >= self.input.len()
     }
 
     fn advance(&mut self) -> char {
-        self.advance_column();
-        self.input.chars().nth(self.current_char - 1).unwrap()
+        let c = self.input[self.current..].chars().next().unwrap();
+        self.current += c.len_utf8();
+        if c == '\n' {
+            self.end_pos.line += 1;
+            self.end_pos.column = 0;
+        } else {
+            self.end_pos.column += 1;
+        }
+        c
     }
 
     fn peek(&self) -> char {
-        if self.is_at_end() {
-            '\0'
-        } else {
-            self.input.chars().nth(self.current_char).unwrap()
-        }
+        self.input[self.current..].chars().next().unwrap_or('\0')
     }
 
     fn peek_next(&self) -> char {
-        if self.current_char + 1 >= self.input.len() {
-            '\0'
-        } else {
-            self.input.chars().nth(self.current_char + 1).unwrap()
-        }
+        self.input[self.current..].chars().nth(1).unwrap_or('\0')
     }
 
     fn make_token(&self, token_type: TokenType) -> Token {
-        let text = self.input[self.start_char..self.current_char].to_string();
+        let text = self.input[self.start..self.current].to_string();
         Token::new(
             token_type,
             text,
@@ -118,7 +109,7 @@ impl Lexer {
         )
     }
     fn make_token_with_literal(&self, token_type: TokenType, literal: BaseValue) -> Token {
-        let text = self.input[self.start_char..self.current_char].to_string();
+        let text = self.input[self.start..self.current].to_string();
         Token::new_complete(
             token_type,
             text,
@@ -178,9 +169,6 @@ impl Lexer {
             ('/', '*') => {
                 // Commento multi-line
                 while (self.peek() != '*' || self.peek_next() != '/') && !self.is_at_end() {
-                    if self.peek() == '\n' {
-                        self.advance_line();
-                    }
                     self.advance();
                 }
                 if self.is_at_end() {
@@ -200,10 +188,7 @@ impl Lexer {
             }
             ('/', _) => Ok(Some(self.make_token(TokenType::Slash))),
             (' ', _) | ('\r', _) | ('\t', _) => Ok(None),
-            ('\n', _) => {
-                self.advance_line();
-                Ok(None)
-            }
+            ('\n', _) => Ok(None),
             ('"', _) => self.string(),
             (c, _) if c.is_digit(10) => self.number(),
             (c, _) if c.is_alphanumeric() || c == '_' => self.identifier(),
@@ -235,7 +220,7 @@ impl Lexer {
         self.advance();
         Ok(Some(self.make_token_with_literal(
             TokenType::String,
-            BaseValue::String(self.input[self.start_char..self.current_char].to_string()),
+            BaseValue::String(self.input[self.start..self.current].to_string()),
         )))
     }
 
@@ -265,7 +250,7 @@ impl Lexer {
             None
         };
 
-        let num_str = &self.input[self.start_char..self.current_char];
+        let num_str = &self.input[self.start..self.current];
         let num_str_without_suffix = if suffix.is_some() {
             &num_str[..num_str.len() - 1]
         } else {
@@ -302,7 +287,7 @@ impl Lexer {
         while self.peek().is_alphanumeric() || self.peek() == '_' {
             self.advance();
         }
-        let text = self.input[self.start_char..self.current_char].to_string();
+        let text = self.input[self.start..self.current].to_string();
         match get_keyword_token(&text) {
             Some(TokenType::True) => Ok(Some(
                 self.make_token_with_literal(TokenType::True, BaseValue::Boolean(true)),
@@ -321,3 +306,240 @@ impl Lexer {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use std::f64;
+
+    use super::*;
+
+    /// Lex `input` and return the resulting tokens, panicking on lexical errors.
+    fn lex(input: &str) -> Vec<Token> {
+        Lexer::new(input.to_string(), 0)
+            .scans_tokens()
+            .expect("expected input to lex without errors")
+    }
+
+    /// Lex `input` and collect just the token types (including the trailing EOF).
+    fn token_types(input: &str) -> Vec<TokenType> {
+        lex(input).into_iter().map(|t| t.token_type).collect()
+    }
+
+    #[test]
+    fn scans_single_character_tokens() {
+        assert_eq!(
+            token_types("(){}[],.-+;:*%"),
+            vec![
+                TokenType::LeftParen,
+                TokenType::RightParen,
+                TokenType::LeftBrace,
+                TokenType::RightBrace,
+                TokenType::LeftBracket,
+                TokenType::RightBracket,
+                TokenType::Comma,
+                TokenType::Dot,
+                TokenType::Minus,
+                TokenType::Plus,
+                TokenType::Semicolon,
+                TokenType::Colon,
+                TokenType::Star,
+                TokenType::Percent,
+                TokenType::Eof,
+            ]
+        );
+    }
+
+    #[test]
+    fn scans_one_and_two_char_operators() {
+        assert_eq!(
+            token_types("! != = == < <= > >= /"),
+            vec![
+                TokenType::Bang,
+                TokenType::BangEqual,
+                TokenType::Equal,
+                TokenType::EqualEqual,
+                TokenType::Less,
+                TokenType::LessEqual,
+                TokenType::Greater,
+                TokenType::GreaterEqual,
+                TokenType::Slash,
+                TokenType::Eof,
+            ]
+        );
+    }
+
+    #[test]
+    fn keyword_lookup_matches_known_words() {
+        assert_eq!(get_keyword_token("and"), Some(TokenType::And));
+        assert_eq!(get_keyword_token("if"), Some(TokenType::If));
+        assert_eq!(get_keyword_token("then"), Some(TokenType::Then));
+        assert_eq!(get_keyword_token("while"), Some(TokenType::While));
+        assert_eq!(get_keyword_token("do"), Some(TokenType::StartBlock));
+        assert_eq!(get_keyword_token("end"), Some(TokenType::EndBlock));
+        assert_eq!(get_keyword_token("not_a_keyword"), None);
+    }
+
+    #[test]
+    fn scans_keywords_in_a_stream() {
+        assert_eq!(
+            token_types("if then else while print return"),
+            vec![
+                TokenType::If,
+                TokenType::Then,
+                TokenType::Else,
+                TokenType::While,
+                TokenType::Print,
+                TokenType::Return,
+                TokenType::Eof,
+            ]
+        );
+    }
+
+    #[test]
+    fn scans_integer_number() {
+        let tokens = lex("42");
+        assert_eq!(tokens[0].token_type, TokenType::Number);
+        assert_eq!(tokens[0].literal, Some(BaseValue::Number(Number::I32(42))));
+    }
+
+    #[test]
+    fn scans_float_number() {
+        let tokens = lex("3.141592653589793");
+        assert_eq!(
+            tokens[0].literal,
+            Some(BaseValue::Number(Number::F64(f64::consts::PI)))
+        );
+    }
+
+    #[test]
+    fn scans_number_with_float_suffix() {
+        let tokens = lex("5f");
+        assert_eq!(tokens[0].literal, Some(BaseValue::Number(Number::F64(5.0))));
+    }
+
+    #[test]
+    fn scans_number_with_unsigned_suffix() {
+        let tokens = lex("7u");
+        assert_eq!(tokens[0].literal, Some(BaseValue::Number(Number::U128(7))));
+    }
+
+    #[test]
+    fn scans_string_literal_including_quotes() {
+        // The lexer slices from the opening quote through the closing quote,
+        // so the literal currently retains the surrounding quotes.
+        let tokens = lex("\"hello\"");
+        assert_eq!(tokens[0].token_type, TokenType::String);
+        assert_eq!(
+            tokens[0].literal,
+            Some(BaseValue::String("\"hello\"".to_string()))
+        );
+    }
+
+    #[test]
+    fn scans_identifier() {
+        let tokens = lex("foo_bar");
+        assert_eq!(tokens[0].token_type, TokenType::Identifier);
+        assert_eq!(
+            tokens[0].literal,
+            Some(BaseValue::String("foo_bar".to_string()))
+        );
+    }
+
+    #[test]
+    fn scans_boolean_and_nil_literals() {
+        let tokens = lex("true false Nil");
+        assert_eq!(tokens[0].literal, Some(BaseValue::Boolean(true)));
+        assert_eq!(tokens[1].literal, Some(BaseValue::Boolean(false)));
+        assert_eq!(tokens[2].literal, Some(BaseValue::Nil));
+    }
+
+    #[test]
+    fn ignores_line_comments() {
+        assert_eq!(
+            token_types("1 // a comment\n2"),
+            vec![TokenType::Number, TokenType::Number, TokenType::Eof]
+        );
+    }
+
+    #[test]
+    fn ignores_block_comments() {
+        assert_eq!(
+            token_types("1 /* multi\nline */ 2"),
+            vec![TokenType::Number, TokenType::Number, TokenType::Eof]
+        );
+    }
+
+    #[test]
+    fn always_appends_eof_even_for_empty_input() {
+        let tokens = lex("");
+        assert_eq!(tokens.len(), 1);
+        assert_eq!(tokens[0].token_type, TokenType::Eof);
+    }
+
+    #[test]
+    fn unterminated_string_is_a_lexical_error() {
+        let result = Lexer::new("\"oops".to_string(), 0).scans_tokens();
+        assert!(matches!(result, Err(LoxError::LexicalError { .. })));
+    }
+
+    #[test]
+    fn unterminated_block_comment_is_a_lexical_error() {
+        let result = Lexer::new("/* never ends".to_string(), 0).scans_tokens();
+        assert!(matches!(result, Err(LoxError::LexicalError { .. })));
+    }
+
+    #[test]
+    fn unexpected_character_is_a_lexical_error() {
+        let result = Lexer::new("@".to_string(), 0).scans_tokens();
+        assert!(result.is_err());
+    }
+
+    #[test]
+    fn handles_multibyte_identifier() {
+        // `é` is two UTF-8 bytes; the old char-counted slicing would panic or
+        // slice mid-codepoint here. Byte offsets make this correct.
+        let tokens = lex("café");
+        assert_eq!(tokens[0].token_type, TokenType::Identifier);
+        assert_eq!(
+            tokens[0].literal,
+            Some(BaseValue::String("café".to_string()))
+        );
+    }
+
+    #[test]
+    fn tracks_line_and_column_across_newlines() {
+        // "1\n22": the second token sits at the start of line 1.
+        let tokens = lex("1\n22");
+        assert_eq!(tokens[1].lexeme, "22");
+        assert_eq!(tokens[1].source_slice.start_position.line, 1);
+        assert_eq!(tokens[1].source_slice.start_position.column, 0);
+    }
+
+    #[test]
+    fn handle_struct() {
+        let tokens = lex("Cosa :: struct {field1: Number, field2: String}");
+        let tokens_tyepe: Vec<TokenType> = tokens.iter().map(|x| x.token_type.clone()).collect();
+        let tokent_for_check = vec![
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Colon,
+            TokenType::Struct,
+            TokenType::LeftBrace,
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Identifier,
+            TokenType::Comma,
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Identifier,
+            TokenType::RightBrace,
+            TokenType::Eof,
+        ];
+        assert_eq!(tokens_tyepe, tokent_for_check);
+        assert_eq!(tokens[0].lexeme, "Cosa");
+        assert_eq!(tokens[5].lexeme, "field1");
+        assert_eq!(tokens[7].lexeme, "Number");
+        assert_eq!(tokens[9].lexeme, "field2");
+        assert_eq!(tokens[11].lexeme, "String");
+    }
+}

src/frontend/source_registry.rs

@@ -4,7 +4,7 @@ use std::{
     io::ErrorKind,
 };
 
-use crate::common::lox_result::{io_error, LoxError, LoxResult};
+use crate::common::lox_result::{io_error, LoxResult};
 
 pub struct SourceRegistry {
     pub sources: Vec<SourceFile>,
@@ -51,7 +51,7 @@ impl SourceFile {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Default)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash, Default)]
 pub struct SourcePosition {
     pub line: usize,
     pub column: usize,
@@ -63,7 +63,7 @@ impl Display for SourcePosition {
     }
 }
 
-#[derive(Clone, PartialEq, Default)]
+#[derive(Clone, PartialEq, Eq, Hash)]
 pub struct SourceSlice {
     pub source_id: SourceId,
     pub start_position: SourcePosition,
@@ -91,6 +91,25 @@ impl Display for SourceSlice {
 }
 
 impl SourceSlice {
+    /// An explicit, non-located placeholder span.
+    ///
+    /// Use this only when a real span is genuinely unavailable. Unlike the old
+    /// `Default` impl, it is greppable and obviously intentional, so it can't be
+    /// produced by accident.
+    pub fn synthetic() -> Self {
+        Self {
+            source_id: 0,
+            start_position: SourcePosition::default(),
+            end_position: SourcePosition::default(),
+        }
+    }
+
+    /// Whether this span is the non-located placeholder produced by
+    /// [`SourceSlice::synthetic`].
+    pub fn is_synthetic(&self) -> bool {
+        *self == Self::synthetic()
+    }
+
     pub fn from_positions(
         source_id: SourceId,
         start_position: SourcePosition,
@@ -102,6 +121,14 @@ impl SourceSlice {
             end_position,
         }
     }
+
+    pub fn from_source_slices(start_point: SourceSlice, end_point: SourceSlice) -> Self {
+        Self {
+            source_id: start_point.source_id,
+            start_position: start_point.start_position,
+            end_position: end_point.end_position,
+        }
+    }
     pub fn tree_point(
         source_id: SourceId,
         column_start: usize,

src/frontend/tokens.rs

@@ -35,11 +35,12 @@ pub enum TokenType {
     Identifier,
     String,
     Number,
+    Atom,
 
     // Keywords
     Fn,
     And,
-    Class,
+    Struct,
     StartBlock,
     EndBlock,
     False,
@@ -57,6 +58,7 @@ pub enum TokenType {
     Is,
     Print,
     Return,
+    Break,
     Super,
     This,
     Var,
@@ -79,8 +81,9 @@ impl fmt::Display for TokenType {
             TokenType::Identifier => write!(f, "IDENTIFIER"),
             TokenType::String => write!(f, "STRING"),
             TokenType::Number => write!(f, "NUMBER"),
+            TokenType::Atom => write!(f, "ATOM"),
             TokenType::And => write!(f, "and"),
-            TokenType::Class => write!(f, "class"),
+            TokenType::Struct => write!(f, "struct"),
             TokenType::Else => write!(f, "else"),
             TokenType::False => write!(f, "false"),
             TokenType::True => write!(f, "true"),
@@ -92,6 +95,7 @@ impl fmt::Display for TokenType {
             TokenType::Or => write!(f, "or"),
             TokenType::Print => write!(f, "print"),
             TokenType::Return => write!(f, "return"),
+            TokenType::Break => write!(f, "break"),
             TokenType::Super => write!(f, "super"),
             TokenType::This => write!(f, "this"),
             TokenType::Var => write!(f, "var"),

src/lib.rs

@@ -1,3 +1,5 @@
 pub mod backend;
 pub mod common;
 pub mod frontend;
+pub mod logging;
+pub mod middleend;

src/logging/display_ast.rs

@@ -5,7 +5,7 @@
 
 use std::fmt::{self, Write};
 
-use crate::common::ast::{AstNode, AstNodeKind, Expr, Stmt};
+use crate::common::ast::{AstNode, Expr};
 
 /// Configuration for pretty printing output
 #[derive(Clone, Debug)]
@@ -234,6 +234,20 @@ impl PrettyPrint for Expr {
                     write!(f, "{}Identifier {{ name: {:?} }}", indent, name)
                 }
             }
+            Expr::Assign { name, value } => {
+                if ctx.config.compact {
+                    let value_str =
+                        pretty_print_with_config(value.as_ref(), &PrettyConfig::compact());
+                    write!(f, "{} = {}", name, value_str)
+                } else {
+                    writeln!(f, "{}Assign {{", indent)?;
+                    writeln!(f, "{}name: {:?},", ctx.child_context(false).indent(), name)?;
+                    write!(f, "{}value: ", ctx.child_context(true).indent())?;
+                    value.pretty_print(&ctx.child_context(true), f)?;
+                    writeln!(f)?;
+                    write!(f, "{}}}", indent)
+                }
+            }
             Expr::Call { callee, arguments } => {
                 if ctx.config.compact {
                     write!(f, "{}", callee)
@@ -250,33 +264,7 @@ impl PrettyPrint for Expr {
                     write!(f, "] }}")
                 }
             }
-        }
-    }
-}
-
-impl PrettyPrint for Stmt {
-    fn pretty_print(&self, ctx: &PrettyContext, f: &mut fmt::Formatter) -> fmt::Result {
-        if ctx.should_truncate() {
-            return write!(f, "{}...", ctx.indent());
-        }
-
-        let indent = ctx.indent();
-
-        match self {
-            Stmt::Expression { expression } => {
-                if ctx.config.compact {
-                    let expr_str =
-                        pretty_print_with_config(expression.as_ref(), &PrettyConfig::compact());
-                    write!(f, "{};", expr_str)
-                } else {
-                    writeln!(f, "{}Expression {{", indent)?;
-                    write!(f, "{}expression: ", ctx.child_context(true).indent())?;
-                    expression.pretty_print(&ctx.child_context(true), f)?;
-                    writeln!(f)?;
-                    write!(f, "{}}}", indent)
-                }
-            }
-            Stmt::Print { expression } => {
+            Expr::Print { expression } => {
                 if ctx.config.compact {
                     let expr_str =
                         pretty_print_with_config(expression.as_ref(), &PrettyConfig::compact());
@@ -289,7 +277,9 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::VarDeclaration { name, initializer } => {
+            Expr::VarDeclaration {
+                name, initializer, ..
+            } => {
                 if ctx.config.compact {
                     match initializer {
                         Some(init) => {
@@ -315,21 +305,7 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::VarAssigment { name, value } => {
-                if ctx.config.compact {
-                    let value_str =
-                        pretty_print_with_config(value.as_ref(), &PrettyConfig::compact());
-                    write!(f, "{} = {};", name, value_str)
-                } else {
-                    writeln!(f, "{}Assign {{", indent)?;
-                    writeln!(f, "{}name: {:?},", ctx.child_context(false).indent(), name)?;
-                    write!(f, "{}value: ", ctx.child_context(true).indent())?;
-                    value.pretty_print(&ctx.child_context(true), f)?;
-                    writeln!(f)?;
-                    write!(f, "{}}}", indent)
-                }
-            }
-            Stmt::Return { expression } => {
+            Expr::Return { expression, .. } => {
                 if ctx.config.compact {
                     let expr_str =
                         pretty_print_with_config(expression.as_ref(), &PrettyConfig::compact());
@@ -342,11 +318,11 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::Block { statements } => {
+            Expr::Block { statements, label } => {
                 if ctx.config.compact {
-                    write!(f, "{{ ... ({} statements) }}", statements.len())
+                    write!(f, "{{ ... [{}] ({} statements) }}", label, statements.len())
                 } else {
-                    writeln!(f, "{}Block {{", indent)?;
+                    writeln!(f, "{}Block [{}] {{", label, indent)?;
                     writeln!(f, "{}statements: [", ctx.child_context(false).indent())?;
                     for (i, stmt) in statements.iter().enumerate() {
                         let is_last = i == statements.len() - 1;
@@ -361,10 +337,10 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::If {
+            Expr::If {
                 condition,
                 then_branch,
-                elif_branch,
+                elif_branches,
                 else_branch,
             } => {
                 if ctx.config.compact {
@@ -380,10 +356,10 @@ impl PrettyPrint for Stmt {
                     then_branch.pretty_print(&ctx.child_context(false), f)?;
                     writeln!(f, ",")?;
 
-                    if !elif_branch.is_empty() {
+                    if !elif_branches.is_empty() {
                         writeln!(f, "{}elif_branches: [", ctx.child_context(false).indent())?;
-                        for (i, (cond, branch)) in elif_branch.iter().enumerate() {
-                            let is_last = i == elif_branch.len() - 1;
+                        for (i, (cond, branch)) in elif_branches.iter().enumerate() {
+                            let is_last = i == elif_branches.len() - 1;
                             let child_ctx = ctx.child_context(false).child_context(is_last);
                             writeln!(f, "{}(", child_ctx.indent())?;
                             write!(f, "{}condition: ", child_ctx.child_context(false).indent())?;
@@ -415,15 +391,14 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::Stmt { expression } => expression.pretty_print(ctx, f),
-            Stmt::While { condition, body } => {
+            Expr::While { condition, body } => {
                 write!(f, "{}while (", ctx.child_context(true).indent())?;
                 condition.pretty_print(&ctx.child_context(true), f)?;
                 writeln!(f, ") {{")?;
                 body.pretty_print(&ctx.child_context(true), f)?;
                 writeln!(f, "{}}}", ctx.child_context(true).indent())
             }
-            Stmt::For {
+            Expr::For {
                 variable,
                 condition,
                 increment,
@@ -443,7 +418,7 @@ impl PrettyPrint for Stmt {
     }
 }
 
-impl<T: AstNodeKind + fmt::Debug + fmt::Display + PrettyPrint> PrettyPrint for AstNode<T> {
+impl PrettyPrint for AstNode {
     fn pretty_print(&self, ctx: &PrettyContext, f: &mut fmt::Formatter) -> fmt::Result {
         let indent = ctx.indent();
 
@@ -455,9 +430,9 @@ impl<T: AstNodeKind + fmt::Debug + fmt::Display + PrettyPrint> PrettyPrint for A
             if ctx.config.show_types {
                 writeln!(
                     f,
-                    "{}kind: {:?},",
+                    "{}type: {},",
                     ctx.child_context(false).indent(),
-                    self.node.kind()
+                    self.return_type
                 )?;
             }
 
@@ -511,25 +486,7 @@ impl PrettyPrintExt for Expr {
     }
 }
 
-impl PrettyPrintExt for Stmt {
-    fn pretty(&self) -> String {
-        pretty_print(self)
-    }
-
-    fn pretty_compact(&self) -> String {
-        pretty_print_with_config(self, &PrettyConfig::compact())
-    }
-
-    fn pretty_tree(&self) -> String {
-        pretty_print_with_config(self, &PrettyConfig::tree())
-    }
-
-    fn pretty_with_config(&self, config: &PrettyConfig) -> String {
-        pretty_print_with_config(self, config)
-    }
-}
-
-impl<T: AstNodeKind + fmt::Debug + fmt::Display + PrettyPrint> PrettyPrintExt for AstNode<T> {
+impl PrettyPrintExt for AstNode {
     fn pretty(&self) -> String {
         pretty_print(self)
     }

src/logging/display_token.rs

@@ -174,7 +174,8 @@ impl Token {
             TokenType::String => "STR",
             TokenType::Number => "NUM",
             TokenType::And => "AND",
-            TokenType::Class => "CLASS",
+            TokenType::Struct => "STRUCT",
+            TokenType::Atom => "ATOM",
             TokenType::StartBlock => "DO",
             TokenType::EndBlock => "END",
             TokenType::False => "FALSE",
@@ -190,6 +191,7 @@ impl Token {
             TokenType::Or => "OR",
             TokenType::Print => "PRINT",
             TokenType::Return => "RETURN",
+            TokenType::Break => "BREAK",
             TokenType::Super => "SUPER",
             TokenType::This => "THIS",
             TokenType::Var => "VAR",
@@ -218,7 +220,7 @@ impl Token {
             | TokenType::Less
             | TokenType::LessEqual => ("\x1b[31m", self.token_type_symbol()),
             TokenType::And
-            | TokenType::Class
+            | TokenType::Struct
             | TokenType::False
             | TokenType::True
             | TokenType::Fun
@@ -232,11 +234,13 @@ impl Token {
             | TokenType::Or
             | TokenType::Print
             | TokenType::Return
+            | TokenType::Break
             | TokenType::Super
             | TokenType::This
             | TokenType::Var
             | TokenType::Fn
             | TokenType::Is
+            | TokenType::Atom
             | TokenType::Val => ("\x1b[34m", self.token_type_symbol()),
             TokenType::Identifier | TokenType::String | TokenType::Number => {
                 ("\x1b[32m", self.token_type_symbol())

src/main.rs

@@ -1,12 +1,12 @@
-mod backend;
-mod common;
-mod frontend;
-mod logging;
-
+pub mod backend;
+pub mod common;
+pub mod frontend;
+pub mod logging;
+pub mod middleend;
 use crate::{
     backend::interpreter::{EvaluateInterpreter, Interpreter},
     common::{
-        ast::{AstNode, Stmt},
+        ast::AstNode,
         lox_result::{LoxError, LoxResult},
     },
     frontend::{
@@ -14,6 +14,7 @@ use crate::{
         parser::Parser,
         source_registry::{SourceId, SourceRegistry},
     },
+    middleend::variable_resolution::Resolver,
 };
 use std::env;
 use std::fs;
@@ -29,109 +30,35 @@ fn main() -> LoxResult<()> {
     let args: Vec<String> = env::args().collect();
 
     let (stage, file_path, debug) = parse_args(&args);
+    println!("running {file_path:?}");
     let mut lox = LoxInterpreter::new(debug);
 
-    let _ = match file_path {
+    let res = match file_path {
         Some(path) => lox.run_file(&path, stage),
         None => lox.run_prompt(stage),
     };
 
-    Ok(())
+    res
 }
 
 fn parse_args(args: &[String]) -> (ExecutionStage, Option<String>, bool) {
-    if args.len() == 1 {
-        // Solo il nome del programma: modalità interattiva completa
-        (ExecutionStage::Full, None, false)
-    } else if args.len() == 2 {
-        // Un argomento: potrebbe essere file o flag
-        let arg = &args[1];
-        if arg == "--tokens" || arg == "--ast" || arg == "--full" || arg == "--debug" {
-            // Flag senza file: modalità interattiva
-            let stage = match arg.as_str() {
-                "--tokens" => ExecutionStage::Tokens,
-                "--ast" => ExecutionStage::Ast,
-                "--full" => ExecutionStage::Full,
-                "--debug" => ExecutionStage::Full,
-                _ => ExecutionStage::Full,
-            };
-            let debug = arg == "--debug";
-            (stage, None, debug)
-        } else {
-            // File senza flag: esecuzione completa del file
-            (ExecutionStage::Full, Some(arg.clone()), false)
-        }
-    } else if args.len() == 3 {
-        // Due argomenti: potrebbero essere flag + file o due flag
-        let mut debug = false;
+    println!("{args:?}");
+
     let mut stage = ExecutionStage::Full;
     let mut file_path = None;
+    let mut debug = false;
 
-        for arg in &args[1..3] {
-            if arg == "--debug" {
-                debug = true;
-            } else if arg == "--tokens" || arg == "--ast" || arg == "--full" {
-                stage = match arg.as_str() {
-                    "--tokens" => ExecutionStage::Tokens,
-                    "--ast" => ExecutionStage::Ast,
-                    "--full" => ExecutionStage::Full,
-                    _ => ExecutionStage::Full,
-                };
-            } else if !arg.starts_with("--") {
-                file_path = Some(arg.clone());
-            } else {
-                eprintln!(
-                    "Unknown flag: {}. Use --tokens, --ast, --full, or --debug",
-                    arg
-                );
-                eprintln!(
-                    "Usage: {} [--tokens|--ast|--full] [--debug] [script]",
-                    args[0]
-                );
-                std::process::exit(64);
+    for arg in args.iter().skip(1) {
+        match arg.as_str() {
+            "-t" | "--tokens" => stage = ExecutionStage::Tokens,
+            "-a" | "--ast" => stage = ExecutionStage::Ast,
+            "-f" | "--full" => stage = ExecutionStage::Full,
+            "-d" | "--debug" => debug = true,
+            _ => file_path = Some(arg.clone()),
         }
     }
 
     (stage, file_path, debug)
-    } else if args.len() == 4 {
-        // Tre argomenti: flag + flag + file
-        let mut debug = false;
-        let mut stage = ExecutionStage::Full;
-        let mut file_path = None;
-
-        for arg in &args[1..4] {
-            if arg == "--debug" {
-                debug = true;
-            } else if arg == "--tokens" || arg == "--ast" || arg == "--full" {
-                stage = match arg.as_str() {
-                    "--tokens" => ExecutionStage::Tokens,
-                    "--ast" => ExecutionStage::Ast,
-                    "--full" => ExecutionStage::Full,
-                    _ => ExecutionStage::Full,
-                };
-            } else if !arg.starts_with("--") {
-                file_path = Some(arg.clone());
-            } else {
-                eprintln!(
-                    "Unknown flag: {}. Use --tokens, --ast, --full, or --debug",
-                    arg
-                );
-                eprintln!(
-                    "Usage: {} [--tokens|--ast|--full] [--debug] [script]",
-                    args[0]
-                );
-                std::process::exit(64);
-            }
-        }
-
-        (stage, file_path, debug)
-    } else {
-        eprintln!(
-            "Usage: {} [--tokens|--ast|--full] [--debug] [script]",
-            args[0]
-        );
-        std::process::exit(64);
-    }
 }
 
 struct LoxInterpreter {
@@ -247,7 +174,7 @@ impl LoxInterpreter {
     }
 
     // Funzione per parsare fino all'AST
-    fn parse_to_ast(&self, source_id: SourceId) -> LoxResult<Vec<AstNode<Stmt>>> {
+    fn parse_to_ast(&self, source_id: SourceId) -> LoxResult<Vec<AstNode>> {
         let tokens = self.tokenize(source_id)?;
 
         Parser::new(tokens).parse().or_else(|err| {
@@ -257,8 +184,12 @@ impl LoxInterpreter {
     }
 
     // Funzione per eseguire l'AST
-    fn execute_ast(&self, ast: Vec<AstNode<Stmt>>, debug: bool) -> LoxResult<String> {
+    fn execute_ast(&self, ast: Vec<AstNode>, debug: bool) -> LoxResult<String> {
+        // Static resolution pass: compute variable scope distances and report
+        // any resolution errors before executing.
+        let locals = self.resolve(&ast)?;
         let mut interpreter = Interpreter::new();
+        interpreter.set_locals(locals);
         let mut result = None;
 
         for (index, stmt) in ast.iter().enumerate() {
@@ -277,6 +208,19 @@ impl LoxInterpreter {
         }
     }
 
+    // Static variable resolution; prints and returns the first error, if any.
+    fn resolve(
+        &self,
+        ast: &[AstNode],
+    ) -> LoxResult<std::collections::HashMap<crate::common::ast::NodeId, usize>> {
+        Resolver::resolve_program(ast).map_err(|errors| {
+            for err in &errors {
+                err.print_with_context(&self.source_registry);
+            }
+            errors.into_iter().next().unwrap()
+        })
+    }
+
     fn process_source(
         &self,
         source_id: SourceId,
@@ -318,8 +262,10 @@ impl LoxInterpreter {
             return Ok(format_ast(&ast));
         }
 
-        // Stage 3: Interpretation
+        // Stage 3: Resolution + Interpretation
+        let locals = self.resolve(&ast)?;
         let mut interpreter = Interpreter::new();
+        interpreter.set_locals(locals);
         let mut result = None;
 
         for (index, stmt) in ast.iter().enumerate() {
@@ -348,7 +294,7 @@ fn format_tokens(tokens: &[crate::frontend::tokens::Token]) -> String {
         .join("\n")
 }
 
-fn format_ast(ast: &[AstNode<Stmt>]) -> String {
+fn format_ast(ast: &[AstNode]) -> String {
     use crate::logging::display_ast::{pretty_print_with_config, PrettyConfig};
 
     let config = PrettyConfig {

src/middleend/mod.rs

@@ -0,0 +1,3 @@
+pub mod scope_stack;
+pub mod variable_resolution;
+pub mod visit_ast;

src/middleend/scope_stack.rs

@@ -0,0 +1,146 @@
+//! A reusable lexical-scope stack for static analyses.
+//!
+//! Unlike [`EnvironmentStack`](crate::backend::environment::EnvironmentStack),
+//! which stores runtime *values*, this stores per-binding *analysis state*
+//! (for the resolver, a `bool` meaning "defined yet?"). It is generic over that
+//! state so other passes (a type checker, an unused-variable lint, ...) can
+//! reuse the same machinery.
+//!
+//! It starts **empty**: the global scope is intentionally untracked, so
+//! [`ScopeStack::resolve`] returning `None` means "not local — assume global".
+
+use std::collections::HashMap;
+
+#[derive(Debug)]
+pub struct ScopeStack<T> {
+    scopes: Vec<HashMap<String, T>>,
+}
+
+impl<T> Default for ScopeStack<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T> ScopeStack<T> {
+    pub fn new() -> Self {
+        ScopeStack { scopes: Vec::new() }
+    }
+
+    pub fn begin_scope(&mut self) {
+        self.scopes.push(HashMap::new());
+    }
+
+    pub fn end_scope(&mut self) {
+        self.scopes.pop();
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.scopes.is_empty()
+    }
+
+    pub fn depth(&self) -> usize {
+        self.scopes.len()
+    }
+
+    /// Insert `name` with `state` into the innermost scope (no-op at global).
+    pub fn declare(&mut self, name: impl Into<String>, state: T) {
+        if let Some(scope) = self.scopes.last_mut() {
+            scope.insert(name.into(), state);
+        }
+    }
+
+    /// Update an existing binding in the innermost scope (no-op if absent).
+    pub fn set_local(&mut self, name: &str, state: T) {
+        if let Some(scope) = self.scopes.last_mut() {
+            if let Some(slot) = scope.get_mut(name) {
+                *slot = state;
+            }
+        }
+    }
+
+    /// Look up `name` in the innermost scope only.
+    pub fn get_local(&self, name: &str) -> Option<&T> {
+        self.scopes.last().and_then(|scope| scope.get(name))
+    }
+
+    /// Whether the innermost scope already declares `name`.
+    pub fn declared_in_current(&self, name: &str) -> bool {
+        self.scopes
+            .last()
+            .map_or(false, |scope| scope.contains_key(name))
+    }
+
+    /// Distance (in scopes) from the innermost scope to the one declaring
+    /// `name`, or `None` if it isn't in any scope (i.e. global).
+    pub fn resolve(&self, name: &str) -> Option<usize> {
+        self.scopes
+            .iter()
+            .rev()
+            .enumerate()
+            .find_map(|(distance, scope)| scope.contains_key(name).then_some(distance))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn declare_and_get_local() {
+        let mut scopes: ScopeStack<bool> = ScopeStack::new();
+        scopes.begin_scope();
+        scopes.declare("a", false);
+        assert_eq!(scopes.get_local("a"), Some(&false));
+        scopes.set_local("a", true);
+        assert_eq!(scopes.get_local("a"), Some(&true));
+        assert_eq!(scopes.get_local("missing"), None);
+    }
+
+    #[test]
+    fn resolve_returns_distance_from_innermost() {
+        let mut scopes: ScopeStack<bool> = ScopeStack::new();
+        scopes.begin_scope();
+        scopes.declare("a", true);
+        scopes.begin_scope();
+        scopes.declare("b", true);
+        assert_eq!(scopes.resolve("b"), Some(0));
+        assert_eq!(scopes.resolve("a"), Some(1));
+        assert_eq!(scopes.resolve("missing"), None);
+    }
+
+    #[test]
+    fn shadowing_and_end_scope() {
+        let mut scopes: ScopeStack<bool> = ScopeStack::new();
+        scopes.begin_scope();
+        scopes.declare("a", true);
+        scopes.begin_scope();
+        scopes.declare("a", false);
+        assert_eq!(scopes.get_local("a"), Some(&false));
+        assert_eq!(scopes.resolve("a"), Some(0));
+        scopes.end_scope();
+        assert_eq!(scopes.get_local("a"), Some(&true));
+        assert_eq!(scopes.resolve("a"), Some(0));
+    }
+
+    #[test]
+    fn declared_in_current_checks_only_innermost() {
+        let mut scopes: ScopeStack<bool> = ScopeStack::new();
+        scopes.begin_scope();
+        scopes.declare("a", true);
+        scopes.begin_scope();
+        assert!(!scopes.declared_in_current("a"));
+        scopes.declare("a", true);
+        assert!(scopes.declared_in_current("a"));
+    }
+
+    #[test]
+    fn global_scope_is_untracked() {
+        let mut scopes: ScopeStack<bool> = ScopeStack::new();
+        // No scope pushed: declarations are no-ops and nothing resolves locally.
+        scopes.declare("a", true);
+        assert!(scopes.is_empty());
+        assert_eq!(scopes.resolve("a"), None);
+        assert_eq!(scopes.get_local("a"), None);
+    }
+}

src/middleend/variable_resolution.rs

@@ -0,0 +1,258 @@
+//! Static variable resolution (Crafting Interpreters, chapter 11).
+//!
+//! Walks the AST with the shared [`Visitor`] traversal, tracking lexical scopes
+//! in a [`ScopeStack`], and records for every variable *reference* how many
+//! scopes up its declaration lives (`locals: NodeId -> distance`). It also
+//! reports the resolution errors from chapter 11:
+//!
+//! * reading a local variable in its own initializer (`var a = a;`),
+//! * declaring two variables with the same name in one local scope,
+//! * `return` outside of any function.
+//!
+//! Diagnostics accumulate in an [`ErrorSink`] so a single pass surfaces them
+//! all. The produced `locals` map is keyed by [`NodeId`] (stable identity),
+//! ready for the interpreter to consume via distance-based lookup.
+
+use std::collections::HashMap;
+
+use crate::{
+    common::{
+        ast::{AstNode, Expr, NodeId},
+        base_value::{BaseValue, LoxFunction},
+        lox_result::{ErrorSink, LoxError, LoxResult},
+    },
+    middleend::{
+        scope_stack::ScopeStack,
+        visit_ast::{walk_expr, walk_function, Visitor},
+    },
+};
+
+/// Tracks whether resolution is currently inside a function body, so a
+/// top-level `return` can be reported.
+#[derive(Clone, Copy, PartialEq)]
+enum FunctionType {
+    None,
+    Function,
+}
+
+pub struct Resolver {
+    scopes: ScopeStack<bool>,
+    locals: HashMap<NodeId, usize>,
+    errors: ErrorSink,
+    current_function: FunctionType,
+}
+
+impl Resolver {
+    pub fn new() -> Self {
+        Resolver {
+            scopes: ScopeStack::new(),
+            locals: HashMap::new(),
+            errors: ErrorSink::new(),
+            current_function: FunctionType::None,
+        }
+    }
+
+    /// Resolve a whole program, returning the per-reference scope distances or
+    /// the accumulated resolution errors.
+    pub fn resolve_program(
+        statements: &[AstNode],
+    ) -> Result<HashMap<NodeId, usize>, Vec<LoxError>> {
+        let mut resolver = Resolver::new();
+        for statement in statements {
+            // Visiting only fails for fatal/internal errors, which this pass
+            // never produces; user-facing diagnostics go to `errors`.
+            let _ = resolver.visit_expr(statement);
+        }
+        if resolver.errors.has_errors() {
+            Err(resolver.errors.into_errors())
+        } else {
+            Ok(resolver.locals)
+        }
+    }
+
+    fn declare(&mut self, name: &str, slice: &crate::frontend::source_registry::SourceSlice) {
+        if self.scopes.is_empty() {
+            return; // global scope is untracked
+        }
+        if self.scopes.declared_in_current(name) {
+            self.errors.report(LoxError::ParseError {
+                source_slice: slice.clone(),
+                message: format!("Already a variable named '{}' in this scope.", name),
+            });
+        }
+        self.scopes.declare(name.to_string(), false);
+    }
+
+    fn define(&mut self, name: &str) {
+        if self.scopes.is_empty() {
+            return;
+        }
+        self.scopes.set_local(name, true);
+    }
+
+    fn resolve_local(&mut self, id: NodeId, name: &str) {
+        if let Some(distance) = self.scopes.resolve(name) {
+            self.locals.insert(id, distance);
+        }
+        // Not found locally: assume global, record nothing.
+    }
+}
+
+impl Default for Resolver {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Visitor for Resolver {
+    fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
+        match &expr.node {
+            Expr::Identifier { name } => {
+                if self.scopes.get_local(name) == Some(&false) {
+                    self.errors.report(LoxError::ParseError {
+                        source_slice: expr.source_slice.clone(),
+                        message: "Can't read local variable in its own initializer.".to_string(),
+                    });
+                }
+                self.resolve_local(expr.id, name);
+                Ok(())
+            }
+            Expr::Assign { name, .. } => {
+                walk_expr(self, expr)?; // resolve the assigned value first
+                self.resolve_local(expr.id, name);
+                Ok(())
+            }
+            Expr::VarDeclaration {
+                name, initializer, ..
+            } => {
+                // A function declaration is a var bound to a function literal.
+                // Define its name *before* resolving the body so it can recurse;
+                // a plain variable is defined *after* its initializer so that
+                // `var a = a;` is caught.
+                let is_function = matches!(
+                    initializer.as_deref().map(|node| &node.node),
+                    Some(Expr::Literal { value }) if matches!(**value, BaseValue::Function(_))
+                );
+                self.declare(name, &expr.source_slice);
+                if is_function {
+                    self.define(name);
+                    walk_expr(self, expr)?;
+                } else {
+                    walk_expr(self, expr)?; // resolves the initializer, if any
+                    self.define(name);
+                }
+                Ok(())
+            }
+            Expr::Block { .. } => {
+                self.scopes.begin_scope();
+                walk_expr(self, expr)?;
+                self.scopes.end_scope();
+                Ok(())
+            }
+            Expr::Return { .. } => {
+                if self.current_function == FunctionType::None {
+                    self.errors.report(LoxError::ParseError {
+                        source_slice: expr.source_slice.clone(),
+                        message: "Can't return from top-level code.".to_string(),
+                    });
+                }
+                walk_expr(self, expr) // resolve the returned expression
+            }
+            _ => walk_expr(self, expr),
+        }
+    }
+
+    fn visit_function(&mut self, function: &LoxFunction) -> LoxResult<()> {
+        let enclosing = std::mem::replace(&mut self.current_function, FunctionType::Function);
+        self.scopes.begin_scope();
+        // Parameters carry no source slice of their own; use the body's.
+        let param_slice = function.body.source_slice.clone();
+        for (param, _ty) in &function.parameters {
+            self.declare(param, &param_slice);
+            self.define(param);
+        }
+        walk_function(self, function)?; // resolves guard + body
+        self.scopes.end_scope();
+        self.current_function = enclosing;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::frontend::lexer::Lexer;
+    use crate::frontend::parser::Parser;
+
+    fn parse(src: &str) -> Vec<AstNode> {
+        let tokens = Lexer::new(src.to_string(), 0)
+            .scans_tokens()
+            .expect("source should lex");
+        Parser::new(tokens).parse().expect("source should parse")
+    }
+
+    fn resolve(src: &str) -> Result<HashMap<NodeId, usize>, Vec<LoxError>> {
+        Resolver::resolve_program(&parse(src))
+    }
+
+    #[test]
+    fn global_variables_are_not_resolved() {
+        // Top-level (global) scope is untracked, so nothing is recorded.
+        let locals = resolve("x := 1; print x;").expect("should resolve");
+        assert!(locals.is_empty());
+    }
+
+    #[test]
+    fn local_read_resolves_to_distance_zero() {
+        let locals = resolve("do x := 1; print x; end").expect("should resolve");
+        assert_eq!(locals.len(), 1);
+        assert_eq!(*locals.values().next().unwrap(), 0);
+    }
+
+    #[test]
+    fn nested_scope_resolves_to_outer_distance() {
+        let src = "do x := 1; do print x; end end";
+        let locals = resolve(src).expect("should resolve");
+        assert_eq!(locals.len(), 1);
+        // `x` is read one scope above where it is read from.
+        assert_eq!(*locals.values().next().unwrap(), 1);
+    }
+
+    #[test]
+    fn reading_a_variable_in_its_own_initializer_is_an_error() {
+        let errors = resolve("do x := x; end").expect_err("should fail");
+        assert!(errors
+            .iter()
+            .any(|e| e.get_message().contains("its own initializer")));
+    }
+
+    #[test]
+    fn duplicate_declaration_in_same_scope_is_an_error() {
+        let errors = resolve("do x := 1; x := 2; end").expect_err("should fail");
+        assert!(errors
+            .iter()
+            .any(|e| e.get_message().contains("Already a variable")));
+    }
+
+    #[test]
+    fn return_at_top_level_is_an_error() {
+        let errors = resolve("return 1;").expect_err("should fail");
+        assert!(errors.iter().any(|e| e.get_message().contains("top-level")));
+    }
+
+    #[test]
+    fn return_inside_a_function_is_allowed() {
+        let locals = resolve("f :: fn (n): Number do return n; end;").expect("should resolve");
+        // `n` resolves from the body block up to the parameter scope.
+        assert_eq!(locals.len(), 1);
+        assert_eq!(*locals.values().next().unwrap(), 1);
+    }
+
+    #[test]
+    fn assignment_target_is_resolved() {
+        let locals = resolve("do x := 1; x = 2; end").expect("should resolve");
+        // Both the assignment target and... only the target is a reference here.
+        assert!(locals.values().all(|&d| d == 0));
+        assert!(!locals.is_empty());
+    }
+}

src/middleend/visit_ast.rs

@@ -0,0 +1,228 @@
+//! A reusable, read-only AST visitor with default traversal.
+//!
+//! The traversal is split into two layers so that many different static
+//! analyses can share a single definition of "how to walk the tree":
+//!
+//! * The `walk_*` free functions contain the canonical recursion. For each
+//!   node they call back into the visitor on every child. This is the only
+//!   place that needs to know the shape of the AST.
+//! * The [`Visitor`] trait's `visit_*` methods are the overridable hooks. Each
+//!   one defaults to calling the matching `walk_*` function, so a visitor that
+//!   overrides nothing still performs a complete traversal.
+//!
+//! To implement an analysis, implement [`Visitor`] and override only the hooks
+//! you care about. Inside an override, call the corresponding `walk_*` function
+//! whenever you want the default "descend into children" behaviour to happen.
+//! Accumulate results in your own struct fields (errors, scope tables, type
+//! information, ...) rather than through the return value, which is only used
+//! to short-circuit on error.
+//!
+//! # Example
+//!
+//! ```ignore
+//! struct IdentifierCounter { count: usize }
+//!
+//! impl Visitor for IdentifierCounter {
+//!     fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
+//!         if let Expr::Identifier { .. } = &expr.node {
+//!             self.count += 1;
+//!         }
+//!         walk_expr(self, expr) // keep descending into children
+//!     }
+//! }
+//! ```
+
+use crate::common::{
+    ast::{AstNode, Expr},
+    base_value::{BaseValue, LoxFunction},
+    lox_result::LoxResult,
+};
+
+/// A read-only visitor over the AST.
+///
+/// Every hook has a default implementation that performs the standard
+/// recursive traversal, so implementors only override the cases they need.
+pub trait Visitor: Sized {
+    /// Visit an expression node. Defaults to [`walk_expr`].
+    fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
+        walk_expr(self, expr)
+    }
+
+    /// Visit a function literal (parameters, optional guard and body).
+    ///
+    /// Defaults to [`walk_function`], which walks the guard (if any) and the
+    /// body. Override this to manage a parameter scope before descending.
+    fn visit_function(&mut self, function: &LoxFunction) -> LoxResult<()> {
+        walk_function(self, function)
+    }
+}
+
+/// Recurse into the children of `expr`, calling back into `visitor`.
+pub fn walk_expr<V: Visitor>(visitor: &mut V, expr: &AstNode) -> LoxResult<()> {
+    match &expr.node {
+        // A function literal carries an entire sub-tree (its body), so it is
+        // not a leaf: hand it to the dedicated function hook.
+        Expr::Literal { value } => {
+            if let BaseValue::Function(function) = &**value {
+                visitor.visit_function(function)?;
+            }
+            Ok(())
+        }
+        Expr::Identifier { .. } => Ok(()),
+        Expr::Binary { left, right, .. } => {
+            visitor.visit_expr(left)?;
+            visitor.visit_expr(right)
+        }
+        Expr::Unary { operand, .. } => visitor.visit_expr(operand),
+        Expr::Assign { value, .. } => visitor.visit_expr(value),
+        Expr::Grouping { expression } => visitor.visit_expr(expression),
+        Expr::Call {
+            callee, arguments, ..
+        } => {
+            visitor.visit_expr(callee)?;
+            for argument in arguments.iter() {
+                visitor.visit_expr(argument)?;
+            }
+            Ok(())
+        }
+
+        Expr::Print { expression, .. } => visitor.visit_expr(expression),
+        Expr::VarDeclaration { initializer, .. } => {
+            if let Some(initializer) = initializer {
+                visitor.visit_expr(initializer)?;
+            }
+            Ok(())
+        }
+        Expr::Return { expression, .. } => visitor.visit_expr(expression),
+        Expr::Block { statements, .. } => {
+            for statement in statements.iter() {
+                visitor.visit_expr(statement)?;
+            }
+            Ok(())
+        }
+        Expr::If {
+            condition,
+            then_branch,
+            elif_branches,
+            else_branch,
+            ..
+        } => {
+            visitor.visit_expr(condition)?;
+            visitor.visit_expr(then_branch)?;
+            for (elif_condition, elif_body) in elif_branches.iter() {
+                visitor.visit_expr(elif_condition)?;
+                visitor.visit_expr(elif_body)?;
+            }
+            if let Some(else_body) = else_branch {
+                visitor.visit_expr(else_body)?;
+            }
+            Ok(())
+        }
+        Expr::While {
+            condition, body, ..
+        } => {
+            visitor.visit_expr(condition)?;
+            visitor.visit_expr(body)
+        }
+        Expr::For {
+            variable,
+            condition,
+            increment,
+            body,
+            ..
+        } => {
+            visitor.visit_expr(variable)?;
+            visitor.visit_expr(condition)?;
+            visitor.visit_expr(increment)?;
+            visitor.visit_expr(body)
+        }
+    }
+}
+
+/// Walk the guard (if present) and body of a function literal.
+pub fn walk_function<V: Visitor>(visitor: &mut V, function: &LoxFunction) -> LoxResult<()> {
+    if let Some(guard) = &function.guard {
+        visitor.visit_expr(guard)?;
+    }
+    visitor.visit_expr(&function.body)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::common::lox_result::runtime_error;
+    use crate::frontend::lexer::Lexer;
+    use crate::frontend::parser::Parser;
+
+    fn parse(src: &str) -> Vec<AstNode> {
+        let tokens = Lexer::new(src.to_string(), 0)
+            .scans_tokens()
+            .expect("source should lex");
+        Parser::new(tokens).parse().expect("source should parse")
+    }
+
+    /// A visitor that relies entirely on the default traversal and just counts
+    /// how many nodes it sees.
+    #[derive(Default)]
+    struct Counter {
+        nodes: usize,
+    }
+
+    impl Visitor for Counter {
+        fn visit_expr(&mut self, node: &AstNode) -> LoxResult<()> {
+            self.nodes += 1;
+            walk_expr(self, node)
+        }
+    }
+
+    fn count(src: &str) -> Counter {
+        let mut counter = Counter::default();
+        for stmt in parse(src).iter() {
+            counter.visit_expr(stmt).unwrap();
+        }
+        counter
+    }
+
+    #[test]
+    fn counts_every_node_via_default_traversal() {
+        // 1 + 2 * 3  =>  Binary(+){ Literal, Binary(*){ Literal, Literal } }
+        let counter = count("1 + 2 * 3;");
+        assert_eq!(counter.nodes, 5);
+    }
+
+    #[test]
+    fn descends_into_function_bodies() {
+        // The function body must be traversed through `visit_function`, so the
+        // `return a;` inside it should contribute to the counts.
+        let counter = count("f :: fn (a): Number do return a; end;");
+        // VarDeclaration + Function literal + Block + Return + identifier `a`
+        assert_eq!(counter.nodes, 5);
+    }
+
+    /// A visitor that aborts as soon as it sees an identifier, used to check
+    /// that errors short-circuit the traversal.
+    struct FailOnIdentifier;
+
+    impl Visitor for FailOnIdentifier {
+        fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
+            if let Expr::Identifier { .. } = &expr.node {
+                return runtime_error(expr.source_slice.clone(), "found an identifier");
+            }
+            walk_expr(self, expr)
+        }
+    }
+
+    #[test]
+    fn errors_propagate_through_traversal() {
+        let stmts = parse("var x: Int = 1; x;");
+        let mut visitor = FailOnIdentifier;
+        let mut result = Ok(());
+        for stmt in stmts.iter() {
+            result = visitor.visit_expr(stmt);
+            if result.is_err() {
+                break;
+            }
+        }
+        assert!(result.is_err());
+    }
+}

tests/frontend.rs

@@ -0,0 +1,296 @@
+//! End-to-end frontend tests: source text -> lexer -> parser -> AST.
+//!
+//! These exercise the lexer and parser together through the public API and
+//! assert on the resulting AST, complementing the per-module unit tests inside
+//! `src/frontend/{lexer,parser}.rs`.
+
+use rlox::common::ast::{AstNode, Expr};
+use rlox::common::base_value::{BaseValue, Number};
+use rlox::frontend::lexer::Lexer;
+use rlox::frontend::parser::Parser;
+use rlox::frontend::tokens::TokenType;
+
+/// Run the full frontend pipeline on `src`.
+fn parse(src: &str) -> Result<Vec<AstNode>, String> {
+    let tokens = Lexer::new(src.to_string(), 0)
+        .scans_tokens()
+        .map_err(|e| format!("lex error: {e}"))?;
+    Parser::new(tokens)
+        .parse()
+        .map_err(|e| format!("parse error: {e}"))
+}
+
+/// Parse `src`, panicking if the frontend reports any error.
+fn parse_ok(src: &str) -> Vec<AstNode> {
+    parse(src).expect("expected source to lex and parse")
+}
+
+/// Parse `src` and return the single node it should produce.
+///
+/// Statements and expressions share the unified `Expr`/`AstNode` type, so this
+/// simply returns the node of the sole top-level statement.
+fn single_stmt(src: &str) -> Expr {
+    let mut stmts = parse_ok(src);
+    assert_eq!(stmts.len(), 1, "expected exactly one statement for {src:?}");
+    stmts.remove(0).node
+}
+
+/// Parse `src` and return its single expression-statement's expression.
+///
+/// Expression statements aren't wrapped in a dedicated variant anymore; the
+/// node itself is the expression.
+fn single_expr(src: &str) -> Expr {
+    single_stmt(src)
+}
+
+// ---------------------------------------------------------------------------
+// Expressions
+// ---------------------------------------------------------------------------
+
+#[test]
+fn lexes_and_parses_number_literal() {
+    match single_expr("42;") {
+        Expr::Literal { value } => assert_eq!(*value, BaseValue::Number(Number::I32(42))),
+        other => panic!("expected literal, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_string_and_boolean_literals() {
+    assert!(matches!(single_expr("true;"), Expr::Literal { .. }));
+    assert!(matches!(single_expr("\"hi\";"), Expr::Literal { .. }));
+}
+
+#[test]
+fn multiplication_binds_tighter_than_addition() {
+    // 1 + 2 * 3 => (+ 1 (* 2 3))
+    match single_expr("1 + 2 * 3;") {
+        Expr::Binary {
+            operator, right, ..
+        } => {
+            assert_eq!(operator, TokenType::Plus);
+            assert!(matches!(
+                right.node,
+                Expr::Binary {
+                    operator: TokenType::Star,
+                    ..
+                }
+            ));
+        }
+        other => panic!("expected binary, got {other:?}"),
+    }
+}
+
+#[test]
+fn grouping_overrides_precedence() {
+    // (1 + 2) * 3 => (* (group (+ 1 2)) 3)
+    match single_expr("(1 + 2) * 3;") {
+        Expr::Binary { operator, left, .. } => {
+            assert_eq!(operator, TokenType::Star);
+            assert!(matches!(left.node, Expr::Grouping { .. }));
+        }
+        other => panic!("expected binary, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_unary_operators() {
+    assert!(matches!(
+        single_expr("-5;"),
+        Expr::Unary {
+            operator: TokenType::Minus,
+            ..
+        }
+    ));
+    assert!(matches!(
+        single_expr("!true;"),
+        Expr::Unary {
+            operator: TokenType::Bang,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn parses_comparison_and_equality() {
+    assert!(matches!(
+        single_expr("1 < 2;"),
+        Expr::Binary {
+            operator: TokenType::Less,
+            ..
+        }
+    ));
+    assert!(matches!(
+        single_expr("1 == 2;"),
+        Expr::Binary {
+            operator: TokenType::EqualEqual,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn parses_logical_operators() {
+    assert!(matches!(
+        single_expr("true or false;"),
+        Expr::Binary {
+            operator: TokenType::Or,
+            ..
+        }
+    ));
+    assert!(matches!(
+        single_expr("true and false;"),
+        Expr::Binary {
+            operator: TokenType::And,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn parses_call_with_arguments() {
+    match single_expr("add(1, 2);") {
+        Expr::Call { callee, arguments } => {
+            assert!(matches!(callee.node, Expr::Identifier { .. }));
+            assert_eq!(arguments.len(), 2);
+        }
+        other => panic!("expected call, got {other:?}"),
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Assignment (now an expression)
+// ---------------------------------------------------------------------------
+
+#[test]
+fn assignment_is_an_expression_statement() {
+    match single_expr("x = 5;") {
+        Expr::Assign { name, .. } => assert_eq!(name, "x"),
+        other => panic!("expected assign, got {other:?}"),
+    }
+}
+
+#[test]
+fn assignment_is_right_associative() {
+    // a = b = c => (assign a (assign b c))
+    match single_expr("a = b = c;") {
+        Expr::Assign { name, value } => {
+            assert_eq!(name, "a");
+            match value.node {
+                Expr::Assign { name, .. } => assert_eq!(name, "b"),
+                other => panic!("expected nested assign, got {other:?}"),
+            }
+        }
+        other => panic!("expected assign, got {other:?}"),
+    }
+}
+
+#[test]
+fn assignment_to_non_identifier_is_an_error() {
+    assert!(parse("1 = 2;").is_err());
+}
+
+// ---------------------------------------------------------------------------
+// Statements
+// ---------------------------------------------------------------------------
+
+#[test]
+fn parses_var_declaration() {
+    match single_stmt("x := 5;") {
+        Expr::VarDeclaration {
+            name, initializer, ..
+        } => {
+            assert_eq!(name, "x");
+            assert!(initializer.is_some());
+        }
+        other => panic!("expected var declaration, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_print_statement() {
+    assert!(matches!(single_stmt("print 1;"), Expr::Print { .. }));
+}
+
+#[test]
+fn parses_block_with_multiple_statements() {
+    match single_stmt("do print 1; print 2; end") {
+        Expr::Block { statements, .. } => assert_eq!(statements.len(), 2),
+        other => panic!("expected block, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_if_else() {
+    match single_stmt("if true then print 1; else print 2;") {
+        Expr::If {
+            else_branch: Some(_),
+            ..
+        } => {}
+        other => panic!("expected if/else, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_while_loop() {
+    assert!(matches!(
+        single_stmt("while true do print 1; end"),
+        Expr::While { .. }
+    ));
+}
+
+#[test]
+fn parses_for_loop_with_assignment_increment() {
+    match single_stmt("for i := 0; i <= 2; i = i + 1; do print i; end") {
+        Expr::For { increment, .. } => {
+            // The increment is an assignment expression.
+            assert!(matches!(increment.node, Expr::Assign { .. }))
+        }
+        other => panic!("expected for loop, got {other:?}"),
+    }
+}
+
+#[test]
+fn parses_function_declaration() {
+    match single_stmt("add :: fn (a, b): Number do return a + b; end;") {
+        Expr::VarDeclaration {
+            name, initializer, ..
+        } => {
+            assert_eq!(name, "add");
+            match initializer {
+                Some(init) => assert!(matches!(
+                    &init.node,
+                    Expr::Literal { value } if matches!(&**value, BaseValue::Function(_))
+                )),
+                None => panic!("expected a function initializer"),
+            }
+        }
+        other => panic!("expected function declaration, got {other:?}"),
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Whole-program / error handling
+// ---------------------------------------------------------------------------
+
+#[test]
+fn parses_a_multi_statement_program() {
+    let stmts = parse_ok("x := 1; y := 2; print x + y;");
+    assert_eq!(stmts.len(), 3);
+}
+
+#[test]
+fn lexer_errors_surface_through_the_frontend() {
+    // Unterminated string is a lexical error reported by the lexer stage.
+    assert!(parse("\"unterminated;").is_err());
+}
+
+#[test]
+fn missing_semicolon_is_a_parse_error() {
+    assert!(parse("print 1").is_err());
+}
+
+#[test]
+fn unclosed_grouping_is_a_parse_error() {
+    assert!(parse("(1 + 2;").is_err());
+}

tests/resolution.rs

@@ -0,0 +1,69 @@
+//! End-to-end pipeline tests: lexer -> parser -> resolver -> interpreter.
+//!
+//! These verify chapter-11 resolution wired into execution: a variable's
+//! resolved scope distance is used for lookup (`get_at`), and resolution errors
+//! abort before running.
+
+use rlox::backend::interpreter::{EvaluateInterpreter, Interpreter};
+use rlox::common::base_value::BaseValue;
+use rlox::frontend::lexer::Lexer;
+use rlox::frontend::parser::Parser;
+use rlox::middleend::variable_resolution::Resolver;
+
+/// Run the whole pipeline, returning the value of the last statement.
+fn run(src: &str) -> Result<BaseValue, String> {
+    let tokens = Lexer::new(src.to_string(), 0)
+        .scans_tokens()
+        .map_err(|e| e.to_string())?;
+    let ast = Parser::new(tokens).parse().map_err(|e| e.to_string())?;
+    let locals = Resolver::resolve_program(&ast)
+        .map_err(|errors| errors.into_iter().next().unwrap().to_string())?;
+    let mut interpreter = Interpreter::new();
+    interpreter.set_locals(locals);
+    let mut last = BaseValue::Nil;
+    for stmt in ast {
+        last = interpreter.evaluate(stmt).map_err(|e| e.to_string())?;
+    }
+    Ok(last)
+}
+
+#[test]
+fn block_local_variables_evaluate() {
+    assert_eq!(run("do x := 10; x + 5; end").unwrap().to_string(), "15");
+}
+
+#[test]
+fn resolved_nested_closure_reads_captured_local() {
+    // `count` is read from inside a nested function, two scopes up; the
+    // resolver records distance 2 and the interpreter uses `get_at(2, ..)`.
+    let src = "\
+make :: fn (): Any do
+    count := 10;
+    get :: fn (): Number do
+        return count;
+    end;
+    return get;
+end;
+g := make();
+g();
+";
+    assert_eq!(run(src).unwrap().to_string(), "10");
+}
+
+#[test]
+fn use_before_initializer_is_rejected() {
+    let err = run("do x := x; end").expect_err("should be a resolution error");
+    assert!(err.contains("its own initializer"));
+}
+
+#[test]
+fn top_level_return_is_rejected() {
+    let err = run("return 1;").expect_err("should be a resolution error");
+    assert!(err.contains("top-level"));
+}
+
+#[test]
+fn duplicate_declaration_in_block_is_rejected() {
+    let err = run("do x := 1; x := 2; end").expect_err("should be a resolution error");
+    assert!(err.contains("Already a variable"));
+}

tests/test_example.rs

@@ -0,0 +1,207 @@
+use rlox::backend::interpreter::{EvaluateInterpreter, Interpreter};
+use rlox::frontend::lexer::Lexer;
+use rlox::frontend::parser::Parser;
+use rlox::frontend::source_registry::SourceRegistry;
+use std::fs;
+use std::path::Path;
+
+#[test]
+fn test_all_examples() {
+    let examples_dir = Path::new("examples");
+
+    // Trova tutti i file .lox nella directory examples
+    let entries = fs::read_dir(examples_dir).expect("Failed to read examples directory");
+
+    let mut test_files_passed = Vec::new();
+    let mut test_files_failed = Vec::new();
+    let mut fail_files_passed = Vec::new();
+    let mut fail_files_failed = Vec::new();
+
+    for entry in entries {
+        let entry = entry.expect("Failed to read directory entry");
+        let path = entry.path();
+
+        // Controlla se è un file .lox
+        if path.extension().and_then(|s| s.to_str()) == Some("lox") {
+            let file_name = path.file_name().unwrap().to_str().unwrap().to_string();
+
+            // Ignora i file che non iniziano con test_ o fail_
+            if !file_name.starts_with("test_") && !file_name.starts_with("fail_") {
+                continue;
+            }
+
+            // Leggi il contenuto del file
+            let source = match fs::read_to_string(&path) {
+                Ok(content) => content,
+                Err(e) => {
+                    if file_name.starts_with("test_") {
+                        test_files_failed.push((file_name, format!("Failed to read file: {}", e)));
+                    } else {
+                        fail_files_failed.push((file_name, format!("Failed to read file: {}", e)));
+                    }
+                    continue;
+                }
+            };
+
+            // Esegui il file e categorizza il risultato
+            match run_lox_file(source, &file_name) {
+                Ok(_) => {
+                    if file_name.starts_with("test_") {
+                        test_files_passed.push(file_name);
+                    } else {
+                        fail_files_passed.push(file_name);
+                    }
+                }
+                Err(error) => {
+                    if file_name.starts_with("test_") {
+                        test_files_failed.push((file_name, error));
+                    } else {
+                        fail_files_failed.push((file_name, error));
+                    }
+                }
+            }
+        }
+    }
+
+    // Stampa i risultati
+    println!("\n========== TEST RESULTS ==========");
+
+    // File test_ (dovrebbero passare)
+    if !test_files_passed.is_empty() || !test_files_failed.is_empty() {
+        println!("\n📝 TEST FILES (should pass):");
+        if !test_files_passed.is_empty() {
+            println!("  ✅ Passed ({}):", test_files_passed.len());
+            for file in &test_files_passed {
+                println!("     - {}", file);
+            }
+        }
+        if !test_files_failed.is_empty() {
+            println!("  ❌ Failed ({}):", test_files_failed.len());
+            for (file, error) in &test_files_failed {
+                println!("\n     - {}", file);
+                println!("{}", error);
+            }
+        }
+    }
+
+    // File fail_ (dovrebbero fallire)
+    if !fail_files_failed.is_empty() || !fail_files_passed.is_empty() {
+        println!("\n🚫 FAIL FILES (should fail):");
+        if !fail_files_failed.is_empty() {
+            println!("  ✅ Failed as expected ({}):", fail_files_failed.len());
+            for (file, error) in &fail_files_failed {
+                println!("\n     - {}", file);
+                println!("{}", error);
+            }
+        }
+        if !fail_files_passed.is_empty() {
+            println!("  ❌ Passed unexpectedly ({}):", fail_files_passed.len());
+            for file in &fail_files_passed {
+                println!("     - {} (should have failed but passed!)", file);
+            }
+        }
+    }
+
+    println!("\n==================================");
+
+    // Riepilogo
+    let total_test_files = test_files_passed.len() + test_files_failed.len();
+    let total_fail_files = fail_files_passed.len() + fail_files_failed.len();
+    let total_files = total_test_files + total_fail_files;
+
+    println!("Summary:");
+    if total_test_files > 0 {
+        println!(
+            "  test_ files: {}/{} passed",
+            test_files_passed.len(),
+            total_test_files
+        );
+    }
+    if total_fail_files > 0 {
+        println!(
+            "  fail_ files: {}/{} failed (as expected)",
+            fail_files_failed.len(),
+            total_fail_files
+        );
+    }
+    println!("  Total files tested: {}", total_files);
+
+    // Assicurati che almeno un file sia stato testato
+    assert!(
+        total_files > 0,
+        "No test_ or fail_ .lox files found in examples directory"
+    );
+
+    // Asserzioni per far fallire il test se le aspettative non sono rispettate
+    if !test_files_failed.is_empty() {
+        println!("\n❌ TEST FAILURE: The following test_ files failed but should have passed:");
+        for (file, _) in &test_files_failed {
+            println!("   - {}", file);
+        }
+        panic!(
+            "{} test_ files failed unexpectedly",
+            test_files_failed.len()
+        );
+    }
+
+    if !fail_files_passed.is_empty() {
+        println!("\n❌ TEST FAILURE: The following fail_ files passed but should have failed:");
+        for file in &fail_files_passed {
+            println!("   - {}", file);
+        }
+        panic!(
+            "{} fail_ files passed unexpectedly",
+            fail_files_passed.len()
+        );
+    }
+
+    println!(
+        "\n✅ All {} test/fail files behaved as expected!",
+        total_files
+    );
+}
+
+fn run_lox_file(source: String, _filename: &str) -> Result<(), String> {
+    // Crea un source registry e mantienilo per il pretty printing degli errori
+    let mut source_registry = SourceRegistry::new();
+
+    // Aggiungi il source con il nome del file corretto
+    let source_id = match source_registry.add_source_string(source.clone()) {
+        Ok(id) => id,
+        Err(e) => return Err(format!("Failed to add source: {}", e)),
+    };
+
+    // Tokenizza
+    let source_content = source_registry.get_by_id(source_id).content.clone();
+    let mut lexer = Lexer::new(source_content, source_id);
+    let tokens = match lexer.scans_tokens() {
+        Ok(tokens) => tokens,
+        Err(err) => {
+            // Usa il pretty printing con source context
+            return Err(err.display_with_source(&source_registry));
+        }
+    };
+
+    // Parsa
+    let ast = match Parser::new(tokens).parse() {
+        Ok(ast) => ast,
+        Err(err) => {
+            // Usa il pretty printing con source context
+            return Err(err.display_with_source(&source_registry));
+        }
+    };
+
+    // Esegui
+    let mut interpreter = Interpreter::new();
+    for stmt in ast.iter() {
+        match interpreter.evaluate(stmt.clone()) {
+            Ok(_) => {}
+            Err(err) => {
+                // Usa il pretty printing con source context
+                return Err(err.display_with_source(&source_registry));
+            }
+        }
+    }
+
+    Ok(())
+}