Update parser.rs

Add type system and refator for having only epression

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/test_closure.lox

@@ -1,12 +1,12 @@
 
-closure :: fn() do
+closure :: fn(): Any do
     value := "Closure";
-    internal :: fn() do
+    internal :: fn(): String do
         print value;
         return value;
-    end
+    end;
     return internal;
-end
+end;
 
 internal := closure();
 internal();
@@ -17,9 +17,9 @@ c := b;
 c = b = a;
 d := c = b = a;
 do
-    showA :: fn() do
+    showA :: fn(): Nil do
         print a;
-    end
+    end;
 
     showA();
     a := "Local";

examples/test_example.lox

@@ -4,7 +4,7 @@
 //     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;
     print param2;
     while param < param2 do
@@ -26,6 +26,6 @@ func_name :: fn(param: Int, param2: String) do
     end
 
     return False or True;
-end
+end;
 
-func_name(1,20)
+func_name(1,20);

examples/test_function_call.lox

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

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

@@ -48,7 +48,7 @@ impl<T: Clone + Debug + PartialEq> EnvironmentStack<T> {
             }
         }
         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),
         )
     }
@@ -58,6 +58,38 @@ impl<T: Clone + Debug + PartialEq> EnvironmentStack<T> {
         Ok(value)
     }
 
+    /// 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();
 
@@ -75,7 +107,7 @@ impl<T: Clone + Debug + PartialEq> EnvironmentStack<T> {
             }
         }
         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),
         )
     }

src/backend/interpreter.rs

@@ -1,79 +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<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<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 } => match value {
-                BaseValue::Function(mut func) => {
-                    func.closure = Some(self.enviorment.clone());
-                    Ok(BaseValue::Function(func))
-                }
-                _ => 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)
     }
 }
 
@@ -91,27 +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() {
@@ -120,7 +193,7 @@ 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 {
@@ -142,7 +215,7 @@ impl Interpreter {
                 }
 
                 // Execute the function body
-                let result = match self.evaluate(func.body) {
+                let result = match self.eval_expr(&func.body) {
                     Ok(value) => Ok(value),
                     Err(LoxError::Return { value, .. }) => Ok(value),
                     Err(err) => Err(err),
@@ -180,7 +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),
             }),
         }
@@ -191,114 +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::Return { expression, .. } => self.evaluate(*expression),
-            Stmt::VarDeclaration {
-                name, initializer, ..
-            } => {
-                let value = match initializer {
-                    Some(expr_node) => 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, ..
-            } => {
-                let mut ret = BaseValue::Nil;
-                while self.evaluate(*condition.clone())?.is_truthy() {
-                    match self.evaluate(*body.clone()) {
-                        Ok(val) => ret = val,
-                        Err(LoxError::Return { value, .. }) => {
-                            ret = value;
-                            break;
-                        }
-                        Err(err) => return Err(err),
-                    };
-                }
-                Ok(ret)
-            }
-            Stmt::For {
-                variable,
-                condition,
-                increment,
-                body,
-                ..
-            } => {
-                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() {
-                    match self.evaluate(*body.clone()) {
-                        Ok(val) => ret = val,
-                        Err(LoxError::Return { value, .. }) => {
-                            ret = value;
-                            break;
-                        }
-                        Err(err) => return Err(err),
-                    };
-                    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(),
                             });
@@ -306,38 +304,36 @@ 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();
 
-        // Ora elements è sempre disponibile
         let mut result = Ok(BaseValue::Nil);
         for statement in statements.iter() {
-            let node = statement.node.clone();
-            match node {
-                Stmt::Return { expression, .. } => {
-                    let value = self.evaluate(*expression)?;
+            match &statement.node {
+                Expr::Return { expression, .. } => {
+                    let value = self.eval_expr(expression)?;
 
                     result = Err(LoxError::Return {
                         source_slice: statement.source_slice.clone(),
-                        value: value,
+                        value,
                         return_label: "Hi".to_string(),
                     });
                     break;
                 }
-                _ => result = self.evaluate((*statement).clone()),
+                _ => result = self.eval_expr(statement),
             };
         }
         self.enviorment.pop_scope();
@@ -460,7 +456,7 @@ mod tests {
 
     #[test]
     fn defines_and_calls_a_function() {
-        let src = "add :: fn (a, b) do return a + b; end add(2, 3);";
+        let src = "add :: fn (a, b): Number do return a + b; end; add(2, 3);";
         assert_eq!(eval(src).unwrap().to_string(), "5");
     }
 

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 ({}({}))",
@@ -86,6 +110,60 @@ impl std::fmt::Display for Expr {
                     .collect::<Vec<String>>()
                     .join(", ")
             ),
+            Expr::Assign { name, value } => write!(f, "Assign ({} = {})", name, value.node),
+            Expr::If {
+                condition,
+                then_branch,
+                elif_branches,
+                else_branch,
+            } => {
+                let mut result = 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,
+                    ));
+                }
+                if let Some(else_branch) = else_branch {
+                    result.push_str(&format!(" ELSE {{\n{}\n}}", else_branch.node));
+                }
+                write!(f, "IfStmt {}", result)
+            }
+            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),
+            },
+            Expr::Return { expression, label } => {
+                write!(f, "Return({}, {})", expression.node, label)
+            }
+            Expr::Block { statements, label } => write!(
+                f,
+                "Block [{}] ([\n{}\n])",
+                label,
+                statements
+                    .iter()
+                    .map(|stmt| format!("\t \t{}", stmt.node))
+                    .collect::<Vec<_>>()
+                    .join("\n"),
+            ),
+            Expr::While { condition, body } => {
+                write!(f, "While({}) {{\n{}\n}}", condition.node, body.node)
+            }
+            Expr::For {
+                variable,
+                condition,
+                increment,
+                body,
+            } => write!(
+                f,
+                "For({} = {} in {}) {{\n{}\n}}",
+                variable.node, condition.node, increment.node, body.node
+            ),
         }
     }
 }
@@ -93,15 +171,21 @@ impl std::fmt::Display for Expr {
 impl Debug for Expr {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Expr::Literal { value } => write!(f, "{:?}", value),
+            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),
+            } => 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 ({}({}))",
@@ -110,320 +194,90 @@ impl Debug for Expr {
                     .iter()
                     .map(|arg| arg.node.to_string())
                     .collect::<Vec<String>>()
-                    .join(", ")
+                    .join(", "),
             ),
-        }
-    }
-}
-
-#[derive(Clone, PartialEq)]
-pub enum Stmt {
-    Expression {
-        expression: Box<AstNode<Expr>>,
-        return_value: Box<BaseValue>,
-    },
-    Print {
-        expression: Box<AstNode<Expr>>,
-        return_value: Box<BaseValue>,
-    },
-    VarDeclaration {
-        name: String,
-        initializer: Option<Box<AstNode<Expr>>>,
-        return_value: Box<BaseValue>,
-    },
-    VarAssigment {
-        name: String,
-        value: Box<AstNode<Expr>>,
-        return_value: Box<BaseValue>,
-    },
-    Return {
-        expression: Box<AstNode<Expr>>,
-        label: String,
-        return_value: Box<BaseValue>,
-    },
-    Block {
-        statements: Box<Vec<AstNode<Stmt>>>,
-        label: String,
-        return_value: Box<BaseValue>,
-    },
-    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>>>,
-        return_value: Box<BaseValue>,
-    },
-    While {
-        condition: Box<AstNode<Expr>>,
-        body: Box<AstNode<Stmt>>,
-        return_value: Box<BaseValue>,
-    },
-    For {
-        variable: Box<AstNode<Stmt>>,
-        condition: Box<AstNode<Expr>>,
-        increment: Box<AstNode<Stmt>>,
-        body: Box<AstNode<Stmt>>,
-        return_value: Box<BaseValue>,
-    },
-}
-
-impl Display for Stmt {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Stmt::Expression {
-                expression,
-                return_value,
-            } => write!(f, "Expression ({}) -> {:?}", expression.node, return_value),
-            Stmt::If {
+            Expr::Assign { name, value } => {
+                write!(f, "(assign {:?} {:?})", name, value.node,)
+            }
+            Expr::If {
                 condition,
                 then_branch,
-                elif_branch,
+                elif_branches,
                 else_branch,
-                return_value,
             } => {
-                let mut result = format!("IF ({}) {{\n{}\n}}", condition.node, then_branch.node);
-                for (condition, branch) in elif_branch {
+                let mut result =
+                    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, return_value
+                        " ELIF ({:?}) {{\n{:?}\n}}",
+                        condition.node, branch.node,
                     ));
                 }
                 if let Some(else_branch) = else_branch {
-                    result.push_str(&format!(
-                        " ELSE {{\n{}\n}} -> {:?}",
-                        else_branch.node, return_value
-                    ));
-                }
-                write!(f, "IfStmt {}", result)
-            }
-            Stmt::Print {
-                expression,
-                return_value,
-            } => write!(f, "Print({}) -> {:?};", expression.node, return_value),
-            Stmt::VarDeclaration {
-                name,
-                initializer,
-                return_value,
-            } => match initializer {
-                Some(init) => write!(f, "Var({} = {}) -> {:?};", name, init.node, return_value),
-                None => write!(f, "Var({}) -> {:?};", name, return_value),
-            },
-            Stmt::VarAssigment {
-                name,
-                value,
-                return_value,
-            } => write!(
-                f,
-                "Assign({} = {}) -> {:?};",
-                name, value.node, return_value
-            ),
-            Stmt::Return {
-                expression,
-                return_value,
-                label,
-            } => write!(
-                f,
-                "Return({}, {}) -> {:?};",
-                expression.node, label, return_value
-            ),
-            Stmt::Block {
-                statements,
-                label,
-                return_value,
-            } => write!(
-                f,
-                "Block [{}] ([\n{}\n]) -> {:?}",
-                label,
-                statements
-                    .iter()
-                    .map(|stmt| format!("\t \t{}", stmt.node))
-                    .collect::<Vec<_>>()
-                    .join("\n"),
-                return_value
-            ),
-            Stmt::While {
-                condition,
-                body,
-                return_value,
-            } => {
-                write!(
-                    f,
-                    "While({}) {{\n{}\n}} -> {:?}",
-                    condition.node, body.node, return_value
-                )
-            }
-            Stmt::For {
-                variable,
-                condition,
-                increment,
-                body,
-                return_value,
-            } => write!(
-                f,
-                "For({} = {} in {}) {{\n{}\n}} -> {:?}",
-                variable.node, condition.node, increment.node, body.node, return_value
-            ),
-        }
-    }
-}
-
-impl Debug for Stmt {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Stmt::Expression {
-                expression,
-                return_value,
-            } => write!(
-                f,
-                " Expression ({:?}) -> {:?}",
-                expression.node, return_value
-            ),
-            Stmt::If {
-                condition,
-                then_branch,
-                elif_branch,
-                else_branch,
-                return_value,
-            } => {
-                let mut result = format!(
-                    "IF ({:?}) {{\n{:?}\n}} -> {:?} ",
-                    condition.node, then_branch.node, return_value
-                );
-                for (condition, branch) in elif_branch {
-                    result.push_str(&format!(
-                        " ELIF ({:?}) {{\n{:?}\n}} -> {:?} ",
-                        condition.node, branch.node, return_value
-                    ));
-                }
-                if let Some(else_branch) = else_branch {
-                    result.push_str(&format!(
-                        " ELSE {{\n{:?}\n}} -> {:?}",
-                        else_branch.node, return_value
-                    ));
+                    result.push_str(&format!(" ELSE {{\n{:?}\n}}", else_branch.node,));
                 }
                 write!(f, "IfStmt {:?}", result)
             }
-            Stmt::Print {
-                expression,
-                return_value,
-            } => write!(f, "Print({:?}) -> {:?};", expression.node, return_value),
-            Stmt::VarDeclaration {
+            Expr::Print { expression } => {
+                write!(f, "Print({:?});", expression.node,)
+            }
+            Expr::VarDeclaration {
                 name,
                 initializer,
-                return_value,
+                var_type,
             } => match initializer {
-                Some(init) => write!(
-                    f,
-                    "Var({:?} = {:?}) -> {:?};",
-                    name, init.node, return_value
-                ),
-                None => write!(f, "Var({:?}) -> {:?};", name, return_value),
+                Some(init) => write!(f, "Var({:?}: {:?} = {:?});", name, var_type, init.node,),
+                None => write!(f, "Var({:?}: {:?});", name, var_type,),
             },
-            Stmt::VarAssigment {
-                name,
-                value,
-                return_value,
-            } => {
-                write!(
-                    f,
-                    "Assign({:?} = {:?}) -> {:?};",
-                    name, value.node, return_value
-                )
+            Expr::Return { expression, label } => {
+                write!(f, "Return({:?}, {}) ;", expression.node, label,)
             }
-            Stmt::Return {
-                expression,
-                return_value,
-                label,
-            } => write!(
+            Expr::Block { label, statements } => write!(
                 f,
-                "Return({:?}, {}) -> {:?};",
-                expression.node, label, return_value
-            ),
-            Stmt::Block {
-                label,
-                statements,
-                return_value,
-            } => write!(
-                f,
-                "Block [{}] ([\n{:?}\n]) -> {:?}",
+                "Block [{}] ([\n{:?}\n])",
                 label,
                 statements
                     .iter()
                     .map(|stmt| format!("{:?}", stmt.node))
                     .collect::<Vec<_>>()
                     .join("\t\t\n"),
-                return_value
             ),
-            Stmt::While {
-                condition,
-                body,
-                return_value,
-            } => {
-                write!(
-                    f,
-                    "While({:?}) {{\n{:?}\n}} -> {:?}",
-                    condition.node, body.node, return_value
-                )
+            Expr::While { condition, body } => {
+                write!(f, "While({:?}) {{\n{:?}\n}}", condition.node, body.node,)
             }
-            Stmt::For {
+            Expr::For {
                 variable,
                 condition,
                 increment,
                 body,
-                return_value,
             } => write!(
                 f,
-                "For({:?} = {:?} in {:?}) {{\n{:?}\n}} -> {:?}",
-                variable.node, condition.node, increment.node, body.node, return_value
+                "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::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,
@@ -433,7 +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,
@@ -443,8 +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

@@ -1,12 +1,12 @@
 use core::fmt;
+use std::collections::HashMap;
 use std::fmt::Display;
 use std::ops::{Add, Div, Mul, Not, Rem, Sub};
 
-use crate::backend::environment::Environment;
 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)]
@@ -272,15 +272,20 @@ pub enum BaseValue {
     Nil,
     Function(LoxFunction),
     NativeFunction(NativeFunction),
+    Struct(Struct),
+}
+
+struct Dict {
+    map: HashMap<String, BaseValue>,
 }
 
 struct ReturnValue {
     label: Vec<String>,
-    value: BaseValue,
+    value: Type,
 }
 
 impl ReturnValue {
-    pub fn new(label: Vec<String>, value: BaseValue) -> Self {
+    pub fn new(label: Vec<String>, value: Type) -> Self {
         Self { label, value }
     }
 }
@@ -304,39 +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 return_type: Option<String>,
-    pub body: AstNode<Stmt>,
+    pub parameters: Vec<(String, Type)>,
+    pub return_type: Type,
+    pub body: AstNode,
     pub closure: Option<EnvironmentStack<BaseValue>>,
-    pub guard: Option<Box<AstNode<Expr>>>,
+    pub guard: Option<Box<AstNode>>,
 }
 
 impl LoxFunction {
     pub fn new(
-        parameters: Vec<(String, String)>,
-        body: AstNode<Stmt>,
+        parameters: Vec<(String, Type)>,
+        body: AstNode,
         closure: Option<EnvironmentStack<BaseValue>>,
-        guard: Option<Box<AstNode<Expr>>>,
+        guard: Option<Box<AstNode>>,
     ) -> Self {
         LoxFunction {
             parameters,
-            return_type: None,
+            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: None,
+            return_type: Type::Any,
             body,
             closure: None,
             guard: None,
@@ -346,12 +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,
@@ -359,6 +365,11 @@ impl NativeFunction {
     }
 }
 
+#[derive(Debug, Clone, PartialEq)]
+pub struct Struct {
+    pub fields: Vec<(String, BaseValue)>,
+}
+
 // Trait implementations for BaseValue
 
 pub trait Truthy {
@@ -398,7 +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(),
             ),
         }
@@ -428,7 +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(),
             ),
         }
@@ -442,10 +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(),
             ),
         }
@@ -459,7 +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(),
             ),
         }
@@ -473,10 +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

@@ -479,3 +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),
@@ -48,28 +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),
@@ -82,32 +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,
@@ -119,7 +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,
@@ -179,9 +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() {
@@ -201,10 +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(),
@@ -236,7 +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()),
         )))
     }
 
@@ -266,7 +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 {
@@ -303,7 +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)),
@@ -509,4 +493,53 @@ mod tests {
         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/mod.rs

@@ -2,4 +2,3 @@ pub mod lexer;
 pub mod parser;
 pub mod source_registry;
 pub mod tokens;
-pub mod variable_resolution;

src/frontend/source_registry.rs

@@ -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,
@@ -80,8 +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"),

src/frontend/variable_resolution.rs

@@ -1,204 +0,0 @@
-use crate::{
-    backend::environment::EnvironmentStack,
-    common::{
-        ast::{AstNode, AstNodeKind, Expr, Stmt},
-        lox_result::{runtime_error, LoxError, LoxResult},
-    },
-    frontend::source_registry::SourceSlice,
-};
-
-use std::fmt::{Debug, Display};
-struct Resolver {
-    scopes: EnvironmentStack<bool>,
-}
-
-impl Resolver {
-    pub fn new() -> Self {
-        Resolver {
-            scopes: EnvironmentStack::new(),
-        }
-    }
-
-    fn declare(&mut self, name: &String) {
-        if self.scopes.is_empty() {
-            return;
-        }
-        let _ = self.scopes.set(name.clone(), false);
-    }
-
-    fn define(&mut self, name: &String) {
-        if self.scopes.is_empty() {
-            return;
-        }
-        let _ = self.scopes.set(name.clone(), true);
-    }
-}
-
-pub trait StaticAnalyzer<T> {
-    fn resolve(&mut self, node: &T) -> LoxResult<bool>;
-}
-
-impl<R: AstNodeKind + Clone + Debug + Display> StaticAnalyzer<AstNode<R>> for Resolver
-where
-    Resolver: StaticAnalyzer<R>,
-{
-    fn resolve(&mut self, node: &AstNode<R>) -> LoxResult<bool> {
-        self.resolve(&node.node)
-    }
-}
-
-impl StaticAnalyzer<Stmt> for Resolver {
-    fn resolve(&mut self, node: &Stmt) -> LoxResult<bool> {
-        match node {
-            Stmt::Expression { expression, .. } => {
-                // Visit the expression
-                self.resolve(expression.as_ref())
-            }
-            Stmt::Print { expression, .. } => {
-                // Visit the expression
-                self.resolve(expression.as_ref())
-            }
-            Stmt::VarDeclaration {
-                initializer, name, ..
-            } => {
-                self.declare(name);
-                // Visit the initializer if present
-                if let Some(init) = initializer {
-                    self.resolve(init.as_ref())?;
-                }
-                self.define(name);
-                Ok(true)
-            }
-            Stmt::VarAssigment { value, name, .. } => {
-                match self.scopes.get(name) {
-                    Ok(true) => (),
-                    Ok(false) => {
-                        return Err(LoxError::RuntimeError {
-                            source_slice: SourceSlice::default(),
-                            message: "Cant read loac variable in it own lintilizer".to_string(),
-                        })
-                    }
-                    Err(err) => return Err(err),
-                }
-                self.resolve(value.as_ref())
-            }
-            Stmt::Return { expression, .. } => {
-                // Visit the return expression
-                self.resolve(expression.as_ref())
-            }
-            Stmt::Block { statements, .. } => {
-                self.scopes.push_new_scope();
-                // Visit all statements in the block
-                for stmt in statements.iter() {
-                    self.resolve(stmt)?;
-                }
-                self.scopes.pop_scope();
-                Ok(true)
-            }
-            Stmt::If {
-                condition,
-                then_branch,
-                elif_branch,
-                else_branch,
-                ..
-            } => {
-                // Visit the condition
-                self.resolve(condition.as_ref())?;
-
-                // Visit the then branch
-                self.resolve(then_branch.as_ref())?;
-
-                // Visit all elif branches
-                for (elif_condition, elif_stmt) in elif_branch.iter() {
-                    self.resolve(elif_condition.as_ref())?;
-                    self.resolve(elif_stmt.as_ref())?;
-                }
-
-                // Visit the else branch if present
-                if let Some(else_stmt) = else_branch {
-                    self.resolve(else_stmt.as_ref())?;
-                }
-
-                Ok(true)
-            }
-            Stmt::While {
-                condition, body, ..
-            } => {
-                // Visit the condition
-                self.resolve(condition.as_ref())?;
-
-                // Visit the body
-                self.resolve(body.as_ref())?;
-                Ok(true)
-            }
-            Stmt::For {
-                variable,
-                condition,
-                increment,
-                body,
-                ..
-            } => {
-                // Visit the variable initialization
-                self.resolve(variable.as_ref())?;
-
-                // Visit the condition
-                self.resolve(condition.as_ref())?;
-
-                // Visit the increment
-                self.resolve(increment.as_ref())?;
-
-                // Visit the body
-                self.resolve(body.as_ref())?;
-                Ok(true)
-            }
-        }
-    }
-}
-
-impl StaticAnalyzer<Expr> for Resolver {
-    fn resolve(&mut self, node: &Expr) -> LoxResult<bool> {
-        match node {
-            Expr::Literal { .. } => {
-                // Leaf node - no children to visit
-                Ok(true)
-            }
-            Expr::Binary { left, right, .. } => {
-                // Visit left operand
-                self.resolve(left.as_ref())?;
-
-                // Visit right operand
-                self.resolve(right.as_ref())
-            }
-            Expr::Unary { operand, .. } => {
-                // Visit the operand
-                self.resolve(operand.as_ref())
-            }
-            Expr::Grouping { expression } => {
-                // Visit the grouped expression
-                self.resolve(expression.as_ref())
-            }
-            Expr::Identifier { name, .. } => {
-                if !self.scopes.is_empty() && self.scopes.get(name).is_ok() {
-                    return Err(LoxError::ParseError {
-                        source_slice: SourceSlice::default(),
-                        message: "Cant read local varialbe in it own initializer".to_string(),
-                    });
-                }
-                Ok(true)
-            }
-            Expr::Call {
-                callee, arguments, ..
-            } => {
-                // Visit the callee
-                self.resolve(callee.as_ref())?;
-
-                // Visit all arguments
-                for arg in arguments.iter() {
-                    self.resolve(arg)?;
-                }
-
-                Ok(true)
-            }
-        }
-    }
-}

src/lib.rs

@@ -1,4 +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 +277,7 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::VarDeclaration {
+            Expr::VarDeclaration {
                 name, initializer, ..
             } => {
                 if ctx.config.compact {
@@ -317,21 +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());
@@ -344,9 +318,7 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::Block {
-                statements, label, ..
-            } => {
+            Expr::Block { statements, label } => {
                 if ctx.config.compact {
                     write!(f, "{{ ... [{}] ({} statements) }}", label, statements.len())
                 } else {
@@ -365,12 +337,11 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::If {
+            Expr::If {
                 condition,
                 then_branch,
-                elif_branch,
+                elif_branches,
                 else_branch,
-                ..
             } => {
                 if ctx.config.compact {
                     let cond_str =
@@ -385,10 +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())?;
@@ -420,21 +391,18 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            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,
                 body,
-                ..
             } => {
                 write!(f, "{}for (", ctx.child_context(true).indent())?;
                 variable.pretty_print(&ctx.child_context(true), f)?;
@@ -450,7 +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();
 
@@ -462,9 +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
                 )?;
             }
 
@@ -518,25 +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",
@@ -219,7 +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
@@ -239,6 +240,7 @@ impl Token {
             | 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

@@ -1,13 +1,12 @@
-mod backend;
-mod common;
-mod frontend;
-mod logging;
-mod middleend;
-
+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::{
@@ -15,6 +14,7 @@ use crate::{
         parser::Parser,
         source_registry::{SourceId, SourceRegistry},
     },
+    middleend::variable_resolution::Resolver,
 };
 use std::env;
 use std::fs;
@@ -174,7 +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| {
@@ -184,8 +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() {
@@ -204,6 +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,
@@ -245,8 +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() {
@@ -275,7 +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

@@ -1,2 +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

@@ -1,99 +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::{
-    backend::environment::EnvironmentStack,
     common::{
-        ast::{AstNode, Expr, Stmt},
-        lox_result::{LoxError, LoxResult},
+        ast::{AstNode, Expr, NodeId},
+        base_value::{BaseValue, LoxFunction},
+        lox_result::{ErrorSink, LoxError, LoxResult},
+    },
+    middleend::{
+        scope_stack::ScopeStack,
+        visit_ast::{walk_expr, walk_function, Visitor},
     },
-    frontend::source_registry::SourceSlice,
-    middleend::visit_ast::{walk_expr, walk_stmt, Visitor},
 };
 
-struct Resolver {
-    scopes: EnvironmentStack<bool>,
-    locals: HashMap<SourceSlice, usize>,
+/// 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: EnvironmentStack::new(),
+            scopes: ScopeStack::new(),
             locals: HashMap::new(),
+            errors: ErrorSink::new(),
+            current_function: FunctionType::None,
         }
     }
 
-    fn declare(&mut self, name: &String) {
+    /// 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;
         }
-        let _ = self.scopes.set(name.clone(), false);
+        self.scopes.set_local(name, true);
     }
 
-    fn define(&mut self, name: &String) {
-        if self.scopes.is_empty() {
-            return;
+    fn resolve_local(&mut self, id: NodeId, name: &str) {
+        if let Some(distance) = self.scopes.resolve(name) {
+            self.locals.insert(id, distance);
         }
-        let _ = self.scopes.set(name.clone(), true);
+        // Not found locally: assume global, record nothing.
     }
+}
 
-    fn resolve_local(&mut self, name: &String) {
-        let depth = self.scopes.depth();
-        for i in (0..depth).rev() {
-            if self.scopes.scope_contains(i, name) {
-                self.locals.insert(, i);
-            }
-        }
+impl Default for Resolver {
+    fn default() -> Self {
+        Self::new()
     }
 }
 
 impl Visitor for Resolver {
-    fn visit_stmt(&mut self, stmt: &AstNode<Stmt>) -> LoxResult<()> {
-        match &stmt.node {
-            Stmt::VarDeclaration { name, .. } => {
-                self.declare(name);
-                // `walk_stmt` resolves the initializer (if present).
-                walk_stmt(self, stmt)?;
-                self.define(name);
-                Ok(())
-            }
-            Stmt::VarAssigment { name, .. } => {
-                match self.scopes.get(name) {
-                    Ok(true) => (),
-                    Ok(false) => {
-                        return Err(LoxError::RuntimeError {
-                            source_slice: SourceSlice::default(),
-                            message: "Cant read local variable in it own lintilizer".to_string(),
-                        })
-                    }
-                    Err(err) => return Err(err),
-                }
-                // `walk_stmt` resolves the assigned value.
-                walk_stmt(self, stmt)
-            }
-            Stmt::Block { .. } => {
-                self.scopes.push_new_scope();
-                walk_stmt(self, stmt)?;
-                self.scopes.pop_scope();
-                Ok(())
-            }
-            // Expression, Print, Return, If, While, For: default traversal.
-            _ => walk_stmt(self, stmt),
-        }
-    }
-
-    fn visit_expr(&mut self, expr: &AstNode<Expr>) -> LoxResult<()> {
+    fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
         match &expr.node {
-            Expr::Identifier { name, .. } => {
-                if !self.scopes.is_empty() && self.scopes.get(name).is_ok() {
-                    return Err(LoxError::ParseError {
-                        source_slice: SourceSlice::default(),
-                        message: "Cant read local varialbe in it own initializer".to_string(),
+            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

@@ -23,7 +23,7 @@
 //! struct IdentifierCounter { count: usize }
 //!
 //! impl Visitor for IdentifierCounter {
-//!     fn visit_expr(&mut self, expr: &AstNode<Expr>) -> LoxResult<()> {
+//!     fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
 //!         if let Expr::Identifier { .. } = &expr.node {
 //!             self.count += 1;
 //!         }
@@ -33,7 +33,7 @@
 //! ```
 
 use crate::common::{
-    ast::{AstNode, Expr, Stmt},
+    ast::{AstNode, Expr},
     base_value::{BaseValue, LoxFunction},
     lox_result::LoxResult,
 };
@@ -43,13 +43,8 @@ use crate::common::{
 /// 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 a statement node. Defaults to [`walk_stmt`].
-    fn visit_stmt(&mut self, stmt: &AstNode<Stmt>) -> LoxResult<()> {
-        walk_stmt(self, stmt)
-    }
-
     /// Visit an expression node. Defaults to [`walk_expr`].
-    fn visit_expr(&mut self, expr: &AstNode<Expr>) -> LoxResult<()> {
+    fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
         walk_expr(self, expr)
     }
 
@@ -62,71 +57,13 @@ pub trait Visitor: Sized {
     }
 }
 
-/// Recurse into the children of `stmt`, calling back into `visitor`.
-pub fn walk_stmt<V: Visitor>(visitor: &mut V, stmt: &AstNode<Stmt>) -> LoxResult<()> {
-    match &stmt.node {
-        Stmt::Expression { expression, .. } => visitor.visit_expr(expression),
-        Stmt::Print { expression, .. } => visitor.visit_expr(expression),
-        Stmt::VarDeclaration { initializer, .. } => {
-            if let Some(initializer) = initializer {
-                visitor.visit_expr(initializer)?;
-            }
-            Ok(())
-        }
-        Stmt::VarAssigment { value, .. } => visitor.visit_expr(value),
-        Stmt::Return { expression, .. } => visitor.visit_expr(expression),
-        Stmt::Block { statements, .. } => {
-            for statement in statements.iter() {
-                visitor.visit_stmt(statement)?;
-            }
-            Ok(())
-        }
-        Stmt::If {
-            condition,
-            then_branch,
-            elif_branch,
-            else_branch,
-            ..
-        } => {
-            visitor.visit_expr(condition)?;
-            visitor.visit_stmt(then_branch)?;
-            for (elif_condition, elif_body) in elif_branch.iter() {
-                visitor.visit_expr(elif_condition)?;
-                visitor.visit_stmt(elif_body)?;
-            }
-            if let Some(else_body) = else_branch {
-                visitor.visit_stmt(else_body)?;
-            }
-            Ok(())
-        }
-        Stmt::While {
-            condition, body, ..
-        } => {
-            visitor.visit_expr(condition)?;
-            visitor.visit_stmt(body)
-        }
-        Stmt::For {
-            variable,
-            condition,
-            increment,
-            body,
-            ..
-        } => {
-            visitor.visit_stmt(variable)?;
-            visitor.visit_expr(condition)?;
-            visitor.visit_stmt(increment)?;
-            visitor.visit_stmt(body)
-        }
-    }
-}
-
 /// Recurse into the children of `expr`, calling back into `visitor`.
-pub fn walk_expr<V: Visitor>(visitor: &mut V, expr: &AstNode<Expr>) -> LoxResult<()> {
+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 {
+            if let BaseValue::Function(function) = &**value {
                 visitor.visit_function(function)?;
             }
             Ok(())
@@ -137,6 +74,7 @@ pub fn walk_expr<V: Visitor>(visitor: &mut V, expr: &AstNode<Expr>) -> LoxResult
             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, ..
@@ -147,6 +85,57 @@ pub fn walk_expr<V: Visitor>(visitor: &mut V, expr: &AstNode<Expr>) -> LoxResult
             }
             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)
+        }
     }
 }
 
@@ -155,7 +144,7 @@ pub fn walk_function<V: Visitor>(visitor: &mut V, function: &LoxFunction) -> Lox
     if let Some(guard) = &function.guard {
         visitor.visit_expr(guard)?;
     }
-    visitor.visit_stmt(&function.body)
+    visitor.visit_expr(&function.body)
 }
 
 #[cfg(test)]
@@ -165,7 +154,7 @@ mod tests {
     use crate::frontend::lexer::Lexer;
     use crate::frontend::parser::Parser;
 
-    fn parse(src: &str) -> Vec<AstNode<Stmt>> {
+    fn parse(src: &str) -> Vec<AstNode> {
         let tokens = Lexer::new(src.to_string(), 0)
             .scans_tokens()
             .expect("source should lex");
@@ -173,29 +162,23 @@ mod tests {
     }
 
     /// A visitor that relies entirely on the default traversal and just counts
-    /// how many statement and expression nodes it sees.
+    /// how many nodes it sees.
     #[derive(Default)]
     struct Counter {
-        stmts: usize,
-        exprs: usize,
+        nodes: usize,
     }
 
     impl Visitor for Counter {
-        fn visit_stmt(&mut self, stmt: &AstNode<Stmt>) -> LoxResult<()> {
-            self.stmts += 1;
-            walk_stmt(self, stmt)
-        }
-
-        fn visit_expr(&mut self, expr: &AstNode<Expr>) -> LoxResult<()> {
-            self.exprs += 1;
-            walk_expr(self, expr)
+        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_stmt(stmt).unwrap();
+            counter.visit_expr(stmt).unwrap();
         }
         counter
     }
@@ -204,19 +187,16 @@ mod tests {
     fn counts_every_node_via_default_traversal() {
         // 1 + 2 * 3  =>  Binary(+){ Literal, Binary(*){ Literal, Literal } }
         let counter = count("1 + 2 * 3;");
-        assert_eq!(counter.stmts, 1);
-        assert_eq!(counter.exprs, 5);
+        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) do return a; end");
-        // VarDeclaration + Block + Return
-        assert_eq!(counter.stmts, 3);
-        // Function literal + identifier `a`
-        assert_eq!(counter.exprs, 2);
+        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
@@ -224,7 +204,7 @@ mod tests {
     struct FailOnIdentifier;
 
     impl Visitor for FailOnIdentifier {
-        fn visit_expr(&mut self, expr: &AstNode<Expr>) -> LoxResult<()> {
+        fn visit_expr(&mut self, expr: &AstNode) -> LoxResult<()> {
             if let Expr::Identifier { .. } = &expr.node {
                 return runtime_error(expr.source_slice.clone(), "found an identifier");
             }
@@ -238,7 +218,7 @@ mod tests {
         let mut visitor = FailOnIdentifier;
         let mut result = Ok(());
         for stmt in stmts.iter() {
-            result = visitor.visit_stmt(stmt);
+            result = visitor.visit_expr(stmt);
             if result.is_err() {
                 break;
             }

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"));
+}