Add source location tracking to AST nodes

The commit expands the source location tracking through the AST by:

1. Switching from raw Expr/Stmt nodes to AstNode wrappers containing
source slices 2. Updating interpreter and parser to preserve location
info through node traversal 3. Enhancing error reporting with richer
source context information

src/backend/interpreter.rs

@@ -19,6 +19,13 @@ fn error(message: String) -> LoxError {
     }
 }
 
+fn error_at(source_slice: SourceSlice, message: String) -> LoxError {
+    LoxError::RuntimeError {
+        source_slice,
+        message,
+    }
+}
+
 impl Not for LiteralValue {
     type Output = LiteralValue;
 
@@ -68,6 +75,25 @@ impl Add for LiteralValue {
     }
 }
 
+impl LiteralValue {
+    pub fn add_with_source(
+        self,
+        other: LiteralValue,
+        source_slice: SourceSlice,
+    ) -> LoxResult<LiteralValue> {
+        match (self, other) {
+            (LiteralValue::Number(a), LiteralValue::Number(b)) => Ok(LiteralValue::Number(a + b)),
+            (LiteralValue::String(a), LiteralValue::String(b)) => {
+                Ok(LiteralValue::String(format!("{}{}", a, b)))
+            }
+            _ => Err(error_at(
+                source_slice,
+                "Cannot add non-numeric values".to_string(),
+            )),
+        }
+    }
+}
+
 impl Sub for LiteralValue {
     type Output = LoxResult<LiteralValue>;
 
@@ -154,15 +180,16 @@ impl<'a> Interpreter<'a> {
 
     fn interpret_binary(
         &mut self,
-        left: Expr,
+        left: AstNode<Expr>,
         operator: TokenType,
-        right: Expr,
+        right: AstNode<Expr>,
+        source_slice: SourceSlice,
     ) -> LoxResult<LiteralValue> {
         let left_value = self.interpret(left)?;
         let right_value = self.interpret(right)?;
         match operator {
             TokenType::Minus => left_value - right_value,
-            TokenType::Plus => left_value + right_value,
+            TokenType::Plus => left_value.add_with_source(right_value, source_slice.clone()),
             TokenType::Slash => left_value / right_value,
             TokenType::Star => left_value * right_value,
             TokenType::EqualEqual => Ok(LiteralValue::Boolean(left_value == right_value)),
@@ -207,31 +234,76 @@ where
     }
 }
 
+// Direct Expr evaluation to avoid infinite recursion
 impl<'a> EvaluateInterpreter<Expr> for Interpreter<'a> {
-    fn interpret(&mut self, stmt: Expr) -> LoxResult<LiteralValue> {
-        match stmt {
-            Expr::Literal { value } => Ok(value.clone()),
+    fn interpret(&mut self, expr: Expr) -> LoxResult<LiteralValue> {
+        match expr {
+            Expr::Literal { value } => Ok(value),
+            Expr::Variable { name } => self.enviorment.get(&name),
             Expr::Binary {
                 left,
                 operator,
                 right,
-            } => self.interpret_binary(*left, operator, *right),
+            } => {
+                let left_val = self.interpret(*left)?;
+                let right_val = self.interpret(*right)?;
+                self.evaluate_binary(left_val, operator, right_val)
+            }
             Expr::Unary { operator, operand } => {
-                let right = self.interpret(*operand)?;
-                match operator {
-                    TokenType::Minus => Ok((-right)?),
-                    TokenType::Bang => Ok(!right),
-                    _ => Err(error("Unsupported unary operator".to_string())),
-                }
+                let operand_val = self.interpret(*operand)?;
+                self.evaluate_unary(operator, operand_val)
             }
             Expr::Grouping { expression } => self.interpret(*expression),
-            Expr::Variable { name } => self.enviorment.get(&name),
         }
     }
 }
 
-impl<'a> EvaluateInterpreter<Stmt> for Interpreter<'a> {
-    fn interpret(&mut self, stmt: Stmt) -> LoxResult<LiteralValue> {
+impl<'a> EvaluateInterpreter<AstNode<Stmt>> for Interpreter<'a> {
+    fn interpret(&mut self, node: AstNode<Stmt>) -> LoxResult<LiteralValue> {
+        let stmt = node.node;
+        let _source_slice = node.source_slice;
+        self.interpret_stmt_inner(stmt)
+    }
+}
+
+impl<'a> Interpreter<'a> {
+    fn evaluate_binary(
+        &mut self,
+        left: LiteralValue,
+        operator: TokenType,
+        right: LiteralValue,
+    ) -> LoxResult<LiteralValue> {
+        match operator {
+            TokenType::Plus => left + right,
+            TokenType::Minus => left - right,
+            TokenType::Star => left * right,
+            TokenType::Slash => left / right,
+            TokenType::Greater => Ok(LiteralValue::Boolean(left > right)),
+            TokenType::GreaterEqual => Ok(LiteralValue::Boolean(left >= right)),
+            TokenType::Less => Ok(LiteralValue::Boolean(left < right)),
+            TokenType::LessEqual => Ok(LiteralValue::Boolean(left <= right)),
+            TokenType::EqualEqual => Ok(LiteralValue::Boolean(left == right)),
+            TokenType::BangEqual => Ok(LiteralValue::Boolean(left != right)),
+            _ => Err(error(format!(
+                "Unsupported binary operator: {:?}",
+                operator
+            ))),
+        }
+    }
+
+    fn evaluate_unary(
+        &mut self,
+        operator: TokenType,
+        operand: LiteralValue,
+    ) -> LoxResult<LiteralValue> {
+        match operator {
+            TokenType::Minus => -operand,
+            TokenType::Bang => Ok(!operand),
+            _ => Err(error(format!("Unsupported unary operator: {:?}", operator))),
+        }
+    }
+
+    fn interpret_stmt_inner(&mut self, stmt: Stmt) -> LoxResult<LiteralValue> {
         match stmt {
             Stmt::Expression { expression } => self.interpret(*expression),
             Stmt::Print { expression } => {
@@ -241,11 +313,12 @@ impl<'a> EvaluateInterpreter<Stmt> for Interpreter<'a> {
             }
             Stmt::Block { statements } => {
                 let (elements, final_expr) = match statements.split_last() {
-                    Some((Stmt::Expression { expression }, body)) => (body, Some(expression)),
-                    Some((Stmt::Return { expression }, body)) => (body, Some(expression)),
-                    Some((_last_stmt, _body)) => {
-                        (statements.as_slice(), None) // Non è un'Expression finale
-                    }
+                    Some((stmt, body)) => match &stmt.node {
+                        Stmt::Expression { expression } => (body, Some(expression)),
+                        Stmt::Return { expression } => (body, Some(expression)),
+                        _ => (statements.as_slice(), None),
+                    },
+
                     None => {
                         (&[][..], None) // Blocco vuoto
                     }
@@ -258,14 +331,11 @@ impl<'a> EvaluateInterpreter<Stmt> for Interpreter<'a> {
 
                 // Gestisci l'espressione finale se presente
                 match final_expr {
-                    Some(expr) => self.interpret((**expr).clone()),
+                    Some(expr) => self.interpret(*expr.clone()),
                     None => Ok(LiteralValue::Nil),
                 }
             }
-            Stmt::Stmt { expression } => {
-                let _ = self.interpret(*expression);
-                Ok(LiteralValue::Nil)
-            }
+            Stmt::Stmt { expression } => self.interpret(*expression.clone()),
             Stmt::Return { expression } => self.interpret(*expression),
             Stmt::Var { name, initializer } => {
                 let value = if let Some(expr) = initializer {
@@ -277,8 +347,8 @@ impl<'a> EvaluateInterpreter<Stmt> for Interpreter<'a> {
                 return Ok(LiteralValue::Nil);
             }
             Stmt::Assign { name, value } => {
-                let value = self.interpret(*value)?;
-                self.enviorment.set(name.clone(), value);
+                let result = self.interpret(*value)?;
+                self.enviorment.set(name.clone(), result);
                 Ok(LiteralValue::Nil)
             }
             Stmt::If {

src/frontend/ast.rs

@@ -38,16 +38,16 @@ pub enum Expr {
         value: LiteralValue,
     },
     Binary {
-        left: Box<Expr>,
+        left: Box<AstNode<Expr>>,
         operator: TokenType,
-        right: Box<Expr>,
+        right: Box<AstNode<Expr>>,
     },
     Unary {
         operator: TokenType,
-        operand: Box<Expr>,
+        operand: Box<AstNode<Expr>>,
     },
     Grouping {
-        expression: Box<Expr>,
+        expression: Box<AstNode<Expr>>,
     },
     Variable {
         name: String,
@@ -67,13 +67,13 @@ impl ExprPrint for Expr {
                 operator,
                 right,
             } => {
-                format!("Binary ({} {} {})", left, operator, right)
+                format!("Binary ({} {} {})", left.node, operator, right.node)
             }
             Expr::Unary { operator, operand } => {
-                format!("Unary ({} {})", operator, operand)
+                format!("Unary ({} {})", operator, operand.node)
             }
             Expr::Grouping { expression } => {
-                format!("Grouping (group {})", expression)
+                format!("Grouping (group {})", expression.node)
             }
             Expr::Variable { name } => {
                 format!("Variable (variable {})", name)
@@ -91,9 +91,9 @@ impl std::fmt::Display for Expr {
                 left,
                 operator,
                 right,
-            } => write!(f, "Binary ({} {} {})", left, operator, right),
-            Expr::Unary { operator, operand } => write!(f, "Unary ({} {})", operator, operand),
-            Expr::Grouping { expression } => write!(f, "Grouping (group {})", expression),
+            } => 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::Variable { name } => write!(f, "Variable (variable {})", name),
         }
     }
@@ -107,9 +107,9 @@ impl Debug for Expr {
                 left,
                 operator,
                 right,
-            } => write!(f, "({:?} {:?} {:?})", operator, left, right),
-            Expr::Unary { operator, operand } => write!(f, "({:?} {:?})", operator, operand),
-            Expr::Grouping { expression } => write!(f, "(group {:?})", expression),
+            } => 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::Variable { name } => write!(f, "(variable {:?})", name),
         }
     }
@@ -118,86 +118,96 @@ impl Debug for Expr {
 #[derive(Clone)]
 pub enum Stmt {
     Expression {
-        expression: Box<Expr>,
+        expression: Box<AstNode<Expr>>,
     },
     Print {
-        expression: Box<Expr>,
+        expression: Box<AstNode<Expr>>,
     },
     Stmt {
-        expression: Box<Expr>,
+        expression: Box<AstNode<Expr>>,
     },
     Var {
         name: String,
-        initializer: Option<Box<Expr>>,
+        initializer: Option<Box<AstNode<Expr>>>,
     },
     Assign {
         name: String,
-        value: Box<Expr>,
+        value: Box<AstNode<Expr>>,
     },
     Return {
-        expression: Box<Expr>,
+        expression: Box<AstNode<Expr>>,
     },
     Block {
-        statements: Box<Vec<Stmt>>,
+        statements: Box<Vec<AstNode<Stmt>>>,
     },
     If {
-        condition: Box<Expr>,
-        then_branch: Box<Stmt>,
-        elif_branch: Vec<(Box<Expr>, Box<Stmt>)>,
-        else_branch: Option<Box<Stmt>>,
+        condition: Box<AstNode<Expr>>,
+        then_branch: Box<AstNode<Stmt>>,
+        elif_branch: Vec<(Box<AstNode<Expr>>, Box<AstNode<Stmt>>)>,
+        else_branch: Option<Box<AstNode<Stmt>>>,
     },
     While {
-        condition: Box<Expr>,
-        body: Box<Stmt>,
+        condition: Box<AstNode<Expr>>,
+        body: Box<AstNode<Stmt>>,
     },
     For {
-        variable: Box<Expr>,
-        iterable: Box<Expr>,
-        body: Box<Stmt>,
+        variable: Box<AstNode<Expr>>,
+        iterable: Box<AstNode<Expr>>,
+        body: Box<AstNode<Stmt>>,
     },
 }
 
 impl Display for Stmt {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Stmt::Expression { expression } => write!(f, "Expression ({})", expression),
+            Stmt::Expression { expression } => write!(f, "Expression ({})", expression.node),
             Stmt::If {
                 condition,
                 then_branch,
                 elif_branch,
                 else_branch,
             } => {
-                let mut result = format!("IF ({}) {{\n{}\n}}", condition, then_branch);
+                let mut result = format!("IF ({}) {{\n{}\n}}", condition.node, then_branch.node);
                 for (condition, branch) in elif_branch {
-                    result.push_str(&format!(" ELIF ({}) {{\n{}\n}}", condition, branch));
+                    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));
+                    result.push_str(&format!(" ELSE {{\n{}\n}}", else_branch.node));
                 }
                 write!(f, "IfStmt {}", result)
             }
-            Stmt::Print { expression } => write!(f, "Print({});", expression),
-            Stmt::Stmt { expression } => write!(f, "Stmt({});", expression),
-            Stmt::Var { name, initializer } => {
-                write!(f, "Var({} = {:?});", name, initializer)
-            }
-            Stmt::Assign { name, value } => write!(f, "Assign({} = {});", name, value),
-            Stmt::Return { expression } => write!(f, "Return({});", expression),
+            Stmt::Print { expression } => write!(f, "Print({});", expression.node),
+            Stmt::Stmt { expression } => write!(f, "Stmt({});", expression.node),
+            Stmt::Var { name, initializer } => match initializer {
+                Some(init) => write!(f, "Var({} = {});", name, init.node),
+                None => write!(f, "Var({});", name),
+            },
+            Stmt::Assign { name, value } => write!(f, "Assign({} = {});", name, value.node),
+            Stmt::Return { expression } => write!(f, "Return({});", expression.node),
             Stmt::Block { statements } => write!(
                 f,
                 "Block([\n{}\n])",
                 statements
                     .iter()
-                    .map(|stmt| format!("\t \t{}", stmt))
+                    .map(|stmt| format!("\t \t{}", stmt.node))
                     .collect::<Vec<_>>()
                     .join("\n")
             ),
-            Stmt::While { condition, body } => todo!(),
+            Stmt::While { condition, body } => {
+                write!(f, "While({}) {{\n{}\n}}", condition.node, body.node)
+            }
             Stmt::For {
                 variable,
                 iterable,
                 body,
-            } => todo!(),
+            } => write!(
+                f,
+                "For({} in {}) {{\n{}\n}}",
+                variable.node, iterable.node, body.node
+            ),
         }
     }
 }
@@ -205,44 +215,55 @@ impl Display for Stmt {
 impl Debug for Stmt {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Stmt::Expression { expression } => write!(f, " Expression ({:?})", expression),
+            Stmt::Expression { expression } => write!(f, " Expression ({:?})", expression.node),
             Stmt::If {
                 condition,
                 then_branch,
                 elif_branch,
                 else_branch,
             } => {
-                let mut result = format!("IF ({:?}) {{\n{:?}\n}}", condition, then_branch);
+                let mut result =
+                    format!("IF ({:?}) {{\n{:?}\n}}", condition.node, then_branch.node);
                 for (condition, branch) in elif_branch {
-                    result.push_str(&format!(" ELIF ({:?}) {{\n{:?}\n}}", condition, branch));
+                    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));
+                    result.push_str(&format!(" ELSE {{\n{:?}\n}}", else_branch.node));
                 }
                 write!(f, "IfStmt {:?}", result)
             }
-            Stmt::Print { expression } => write!(f, "Print({:?});", expression),
-            Stmt::Stmt { expression } => write!(f, "Stmt({:?});", expression),
-            Stmt::Var { name, initializer } => {
-                write!(f, "Var({:?} = {:?});", name, initializer)
-            }
-            Stmt::Assign { name, value } => write!(f, "Assign({:?} = {:?});", name, value),
-            Stmt::Return { expression } => write!(f, "Return({:?});", expression),
+            Stmt::Print { expression } => write!(f, "Print({:?});", expression.node),
+            Stmt::Stmt { expression } => write!(f, "Stmt({:?});", expression.node),
+            Stmt::Var { name, initializer } => match initializer {
+                Some(init) => write!(f, "Var({:?} = {:?});", name, init.node),
+                None => write!(f, "Var({:?});", name),
+            },
+            Stmt::Assign { name, value } => write!(f, "Assign({:?} = {:?});", name, value.node),
+            Stmt::Return { expression } => write!(f, "Return({:?});", expression.node),
             Stmt::Block { statements } => write!(
                 f,
                 "Block([\n{:?}\n])",
                 statements
                     .iter()
-                    .map(|stmt| format!("{:?}", stmt))
+                    .map(|stmt| format!("{:?}", stmt.node))
                     .collect::<Vec<_>>()
                     .join("\t\t\n")
             ),
-            Stmt::While { condition, body } => todo!(),
+            Stmt::While { condition, body } => {
+                write!(f, "While({:?}) {{\n{:?}\n}}", condition.node, body.node)
+            }
             Stmt::For {
                 variable,
                 iterable,
                 body,
-            } => todo!(),
+            } => write!(
+                f,
+                "For({:?} in {:?}) {{\n{:?}\n}}",
+                variable.node, iterable.node, body.node
+            ),
         }
     }
 }
@@ -289,12 +310,12 @@ impl AstNodeKind for Stmt {
             } => "if statement",
             Stmt::Print { expression: _ } => "print statement",
             Stmt::Stmt { expression: _ } => "statement",
-            Stmt::While { condition, body } => todo!(),
+            Stmt::While { condition, body } => "while statement",
             Stmt::For {
                 variable,
                 iterable,
                 body,
-            } => todo!(),
+            } => "for statement",
         }
     }
 }

src/frontend/lexer.rs

@@ -22,6 +22,7 @@ fn get_keyword_token(word: &str) -> Option<TokenType> {
         "for" => Some(TokenType::For),
         "fun" => Some(TokenType::Fun),
         "if" => Some(TokenType::If),
+        "then" => Some(TokenType::Then),
         "elif" => Some(TokenType::Elif),
         "else" => Some(TokenType::Else),
         "or" => Some(TokenType::Or),

src/frontend/parser.rs

@@ -1,9 +1,10 @@
 use crate::{
     frontend::{
         ast::{AstNode, Expr, Stmt},
+        source_registry::SourceSlice,
         tokens::{LiteralValue, Token, TokenType},
     },
-    logging::display_ast::{pretty_print_with_config, PrettyConfig, PrettyPrint},
+    logging::display_ast::{pretty_print_with_config, PrettyConfig},
     result::{LoxError, LoxResult},
 };
 
@@ -57,193 +58,284 @@ impl Parser {
 
     fn statement(&mut self) -> LoxResult<AstNode<Stmt>> {
         match (&self.peek().token_type, &self.peek_next().token_type) {
-            (TokenType::Var, _) => Ok(AstNode::new(
-                self.var_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::Print, _) => Ok(AstNode::new(
-                self.print_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::Return, _) => Ok(AstNode::new(
-                self.return_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::StartBlock, _) => Ok(AstNode::new(
-                self.block_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::Identifier, TokenType::Equal) => Ok(AstNode::new(
-                self.assignment_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::If, _) => Ok(AstNode::new(
-                self.if_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            (TokenType::While, _) => Ok(AstNode::new(
-                self.while_statement()?,
-                self.peek().source_slice.clone(),
-            )),
-            _ => Ok(AstNode::new(
-                self.expression_statement()?,
-                self.peek().source_slice.clone(),
-            )),
+            (TokenType::Var, _) => self.var_statement(),
+            (TokenType::Print, _) => self.print_statement(),
+            (TokenType::Return, _) => self.return_statement(),
+            (TokenType::StartBlock, _) => self.block_statement(),
+            (TokenType::Identifier, TokenType::Equal) => self.assignment_statement(),
+            (TokenType::If, _) => self.if_statement(),
+            (TokenType::While, _) => self.while_statement(),
+            _ => self.expression_statement(),
         }
     }
 
-    fn while_statement(&mut self) -> LoxResult<Stmt> {
+    fn while_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         self.advance();
         let condition = self.expression()?;
-        let body = self.block_statement()?;
-        Ok(Stmt::While {
-            condition: Box::new(condition),
-            body: Box::new(body),
-        })
+        let body = self.statement()?;
+        let end_slice = body.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::While {
+                condition: Box::new(condition),
+                body: Box::new(body),
+            },
+            combined_slice,
+        ))
     }
 
-    fn if_statement(&mut self) -> LoxResult<Stmt> {
-        self.advance();
+    fn if_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
+        self.advance(); // consume 'if'
         let condition = self.expression()?;
+        self.consume(TokenType::Then, "Expect 'then' after if condition.")?;
         let then_branch = self.statement()?;
         let mut elif_branches = Vec::new();
+        let mut last_slice = then_branch.source_slice.clone();
+
         while self.peek().token_type == TokenType::Elif {
-            self.advance();
-            let condition = self.expression()?;
-            let then_branch = self.statement()?;
-            elif_branches.push((Box::new(condition), Box::new(then_branch.node)));
+            self.advance(); // consume 'elif'
+            let elif_condition = self.expression()?;
+            self.consume(TokenType::Then, "Expect 'then' after elif condition.")?;
+            let elif_branch = self.statement()?;
+            last_slice = elif_branch.source_slice.clone();
+            elif_branches.push((Box::new(elif_condition), Box::new(elif_branch)));
         }
+
         let else_branch = if self.peek().token_type == TokenType::Else {
-            self.advance();
-            Some(Box::new(self.statement()?.node))
+            self.advance(); // consume 'else'
+            let else_stmt = self.statement()?;
+            last_slice = else_stmt.source_slice.clone();
+            Some(Box::new(else_stmt))
         } else {
             None
         };
-        Ok(Stmt::If {
-            condition: Box::new(condition),
-            then_branch: Box::new(then_branch.node),
-            elif_branch: elif_branches,
-            else_branch: else_branch,
-        })
+
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            last_slice.end_position,
+        );
+
+        Ok(AstNode::new(
+            Stmt::If {
+                condition: Box::new(condition),
+                then_branch: Box::new(then_branch),
+                elif_branch: elif_branches,
+                else_branch: else_branch,
+            },
+            combined_slice,
+        ))
     }
 
-    fn var_statement(&mut self) -> LoxResult<Stmt> {
+    fn var_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         self.advance();
         let name = self.consume(TokenType::Identifier, "Expect variable name.")?;
         let name_lexeme = name.lexeme.clone();
         self.consume(TokenType::Equal, "Expect '=' after variable name.")?;
         let value = self.expression()?;
-        self.consume(
+        let semicolon = self.consume(
             TokenType::Semicolon,
             "Expect ';' after variable declaration.",
         )?;
-        Ok(Stmt::Var {
-            name: name_lexeme,
-            initializer: Some(Box::new(value)),
-        })
+        let end_slice = semicolon.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::Var {
+                name: name_lexeme,
+                initializer: Some(Box::new(value)),
+            },
+            combined_slice,
+        ))
     }
 
-    fn assignment_statement(&mut self) -> LoxResult<Stmt> {
+    fn assignment_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         let name = self.consume(TokenType::Identifier, "Expect variable name.")?;
         let name_lexeme = name.lexeme.clone();
         self.consume(TokenType::Equal, "Expect '=' after variable name.")?;
         let value = self.expression()?;
-        self.consume(
+        let semicolon = self.consume(
             TokenType::Semicolon,
             "Expect ';' after variable declaration.",
         )?;
-        Ok(Stmt::Assign {
-            name: name_lexeme,
-            value: Box::new(value),
-        })
+        let end_slice = semicolon.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::Assign {
+                name: name_lexeme,
+                value: Box::new(value),
+            },
+            combined_slice,
+        ))
     }
 
-    fn print_statement(&mut self) -> LoxResult<Stmt> {
+    fn print_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
         // consume the print keyword
+        let start_slice = self.peek().source_slice.clone();
         self.advance();
         let expr = self.expression()?;
-        self.consume(TokenType::Semicolon, "Expect ';' after value.")?;
-        Ok(Stmt::Print {
-            expression: Box::new(expr),
-        })
+        let semicolon = self.consume(TokenType::Semicolon, "Expect ';' after value.")?;
+        let end_slice = semicolon.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::Print {
+                expression: Box::new(expr),
+            },
+            combined_slice,
+        ))
     }
 
-    fn block_statement(&mut self) -> LoxResult<Stmt> {
+    fn block_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         self.advance();
         let mut statements = Vec::new();
         while self.peek().token_type != TokenType::EndBlock && !self.is_at_end() {
             let stmt = self.statement()?;
-            statements.push(stmt.node.clone());
-            if let Stmt::Expression { .. } = stmt.node {
+            let should_break = matches!(stmt.node, Stmt::Expression { .. });
+            statements.push(stmt);
+            if should_break {
                 break;
             }
         }
-        self.consume(TokenType::EndBlock, "Expect 'end' after block.")?;
-        Ok(Stmt::Block {
-            statements: Box::new(statements),
-        })
+        let end_token = self.consume(TokenType::EndBlock, "Expect 'end' after block.")?;
+        let end_slice = end_token.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::Block {
+                statements: Box::new(statements),
+            },
+            combined_slice,
+        ))
     }
 
-    fn expression_statement(&mut self) -> LoxResult<Stmt> {
+    fn expression_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         let expr = self.expression()?;
         if self.peek().token_type == TokenType::Semicolon {
-            self.advance();
-            return Ok(Stmt::Stmt {
-                expression: Box::new(expr),
-            });
+            let semicolon = self.advance();
+            let end_slice = semicolon.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            return Ok(AstNode::new(
+                Stmt::Stmt {
+                    expression: Box::new(expr),
+                },
+                combined_slice,
+            ));
         }
-        Ok(Stmt::Expression {
-            expression: Box::new(expr),
-        })
+        // Use the expression's source slice for expression statements without semicolon
+        let expr_slice = expr.source_slice.clone();
+        Ok(AstNode::new(
+            Stmt::Expression {
+                expression: Box::new(expr),
+            },
+            expr_slice,
+        ))
     }
 
-    fn return_statement(&mut self) -> LoxResult<Stmt> {
+    fn return_statement(&mut self) -> LoxResult<AstNode<Stmt>> {
+        let start_slice = self.peek().source_slice.clone();
         self.advance();
         let expr = self.expression()?;
-        self.consume(TokenType::Semicolon, "Expect ';' after return value.")?;
-        Ok(Stmt::Return {
-            expression: Box::new(expr),
-        })
+        let semicolon = self.consume(TokenType::Semicolon, "Expect ';' after return value.")?;
+        let end_slice = semicolon.source_slice.clone();
+        let combined_slice = SourceSlice::from_positions(
+            start_slice.source_id,
+            start_slice.start_position,
+            end_slice.end_position,
+        );
+        Ok(AstNode::new(
+            Stmt::Return {
+                expression: Box::new(expr),
+            },
+            combined_slice,
+        ))
     }
 
-    fn expression(&mut self) -> LoxResult<Expr> {
+    fn expression(&mut self) -> LoxResult<AstNode<Expr>> {
         self.or_and()
     }
 
-    fn or_and(&mut self) -> LoxResult<Expr> {
+    fn or_and(&mut self) -> LoxResult<AstNode<Expr>> {
         let mut expr = self.equality()?;
 
         while [TokenType::Or, TokenType::And].contains(&self.peek().token_type) {
+            let start_slice = expr.source_slice.clone();
             let operator = self.peek().token_type.clone();
             self.advance();
             let right = self.equality()?;
-            expr = Expr::Binary {
-                left: Box::new(expr),
-                operator,
-                right: Box::new(right),
-            };
+            let end_slice = right.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            expr = AstNode::new(
+                Expr::Binary {
+                    left: Box::new(expr),
+                    operator,
+                    right: Box::new(right),
+                },
+                combined_slice,
+            );
         }
 
         Ok(expr)
     }
-    fn equality(&mut self) -> LoxResult<Expr> {
+    fn equality(&mut self) -> LoxResult<AstNode<Expr>> {
         let mut expr = self.comparison()?;
 
         while [TokenType::BangEqual, TokenType::EqualEqual].contains(&self.peek().token_type) {
+            let start_slice = expr.source_slice.clone();
             let operator = self.peek().token_type.clone();
             self.advance();
             let right = self.comparison()?;
-            expr = Expr::Binary {
-                left: Box::new(expr),
-                operator,
-                right: Box::new(right),
-            };
+            let end_slice = right.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            expr = AstNode::new(
+                Expr::Binary {
+                    left: Box::new(expr),
+                    operator,
+                    right: Box::new(right),
+                },
+                combined_slice,
+            );
         }
 
         Ok(expr)
     }
 
-    fn comparison(&mut self) -> LoxResult<Expr> {
+    fn comparison(&mut self) -> LoxResult<AstNode<Expr>> {
         let mut expr = self.term()?;
 
         while [
@@ -254,121 +346,174 @@ impl Parser {
         ]
         .contains(&self.peek().token_type)
         {
+            let start_slice = expr.source_slice.clone();
             let operator = self.peek().token_type.clone();
             self.advance();
             let right = self.term()?;
-            expr = Expr::Binary {
-                left: Box::new(expr),
-                operator,
-                right: Box::new(right),
-            };
+            let end_slice = right.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            expr = AstNode::new(
+                Expr::Binary {
+                    left: Box::new(expr),
+                    operator,
+                    right: Box::new(right),
+                },
+                combined_slice,
+            );
         }
 
         Ok(expr)
     }
 
-    fn term(&mut self) -> LoxResult<Expr> {
+    fn term(&mut self) -> LoxResult<AstNode<Expr>> {
         let mut expr = self.factor()?;
 
         while [TokenType::Plus, TokenType::Minus].contains(&self.peek().token_type) {
+            let start_slice = expr.source_slice.clone();
             let operator = self.peek().token_type.clone();
             self.advance();
             let right = self.factor()?;
-            expr = Expr::Binary {
-                left: Box::new(expr),
-                operator,
-                right: Box::new(right),
-            };
+            let end_slice = right.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            expr = AstNode::new(
+                Expr::Binary {
+                    left: Box::new(expr),
+                    operator,
+                    right: Box::new(right),
+                },
+                combined_slice,
+            );
         }
 
         Ok(expr)
     }
 
-    fn factor(&mut self) -> LoxResult<Expr> {
+    fn factor(&mut self) -> LoxResult<AstNode<Expr>> {
         let mut expr = self.unary()?;
 
         while [TokenType::Slash, TokenType::Star].contains(&self.peek().token_type) {
+            let start_slice = expr.source_slice.clone();
             let operator = self.peek().token_type.clone();
             self.advance();
             let right = self.unary()?;
-            expr = Expr::Binary {
-                left: Box::new(expr),
-                operator,
-                right: Box::new(right),
-            };
+            let end_slice = right.source_slice.clone();
+            let combined_slice = SourceSlice::from_positions(
+                start_slice.source_id,
+                start_slice.start_position,
+                end_slice.end_position,
+            );
+            expr = AstNode::new(
+                Expr::Binary {
+                    left: Box::new(expr),
+                    operator,
+                    right: Box::new(right),
+                },
+                combined_slice,
+            );
         }
 
         Ok(expr)
     }
 
-    fn unary(&mut self) -> LoxResult<Expr> {
+    fn unary(&mut self) -> LoxResult<AstNode<Expr>> {
         if [TokenType::Bang, TokenType::Minus].contains(&self.peek().token_type) {
             let operator = self.peek().token_type.clone();
+            let source_slice = self.peek().source_slice.clone();
             self.advance();
             let right = self.unary()?;
-            return Ok(Expr::Unary {
-                operator,
-                operand: Box::new(right),
-            });
+            return Ok(AstNode::new(
+                Expr::Unary {
+                    operator,
+                    operand: Box::new(right),
+                },
+                source_slice,
+            ));
         }
 
         self.primary()
     }
 
-    fn primary(&mut self) -> LoxResult<Expr> {
+    fn primary(&mut self) -> LoxResult<AstNode<Expr>> {
         match self.peek().token_type {
             TokenType::False => {
+                let source_slice = self.peek().source_slice.clone();
                 self.advance();
-                Ok(Expr::Literal {
-                    value: LiteralValue::Boolean(false),
-                })
+                Ok(AstNode::new(
+                    Expr::Literal {
+                        value: LiteralValue::Boolean(false),
+                    },
+                    source_slice,
+                ))
             }
             TokenType::True => {
+                let source_slice = self.peek().source_slice.clone();
                 self.advance();
-                Ok(Expr::Literal {
-                    value: LiteralValue::Boolean(true),
-                })
+                Ok(AstNode::new(
+                    Expr::Literal {
+                        value: LiteralValue::Boolean(true),
+                    },
+                    source_slice,
+                ))
             }
             TokenType::Nil => {
+                let source_slice = self.peek().source_slice.clone();
                 self.advance();
-                Ok(Expr::Literal {
-                    value: LiteralValue::Nil,
-                })
+                Ok(AstNode::new(
+                    Expr::Literal {
+                        value: LiteralValue::Nil,
+                    },
+                    source_slice,
+                ))
             }
             TokenType::Number => {
+                let source_slice = self.peek().source_slice.clone();
+                let literal = self.peek().literal.clone();
                 self.advance();
-                let token = self.previous();
-                if let Some(literal) = &token.literal {
-                    Ok(Expr::Literal {
-                        value: literal.clone(),
-                    })
+                if let Some(literal) = literal {
+                    Ok(AstNode::new(Expr::Literal { value: literal }, source_slice))
                 } else {
-                    Err(self.error(token, "Expected number literal").into())
+                    Err(self
+                        .error(self.previous(), "Expected number literal")
+                        .into())
                 }
             }
             TokenType::String => {
+                let source_slice = self.peek().source_slice.clone();
+                let literal = self.peek().literal.clone();
                 self.advance();
-                let token = self.previous();
-                if let Some(literal) = &token.literal {
-                    Ok(Expr::Literal {
-                        value: literal.clone(),
-                    })
+                if let Some(literal) = literal {
+                    Ok(AstNode::new(Expr::Literal { value: literal }, source_slice))
                 } else {
-                    Err(self.error(token, "Expected string literal").into())
+                    Err(self
+                        .error(self.previous(), "Expected string literal")
+                        .into())
                 }
             }
             TokenType::LeftParen => {
+                let source_slice = self.peek().source_slice.clone();
                 self.advance();
                 let expr = self.expression()?;
                 self.consume(TokenType::RightParen, "Expect ')' after expression.")?;
-                Ok(Expr::Grouping {
-                    expression: Box::new(expr),
-                })
+                Ok(AstNode::new(
+                    Expr::Grouping {
+                        expression: Box::new(expr),
+                    },
+                    source_slice,
+                ))
             }
             TokenType::Identifier => {
                 let name = self.peek().lexeme.clone();
+                let source_slice = self.peek().source_slice.clone();
                 self.advance();
-                Ok(Expr::Variable { name: name })
+                Ok(AstNode::new(Expr::Variable { name }, source_slice))
             }
             _ => Err(self.error(self.peek(), "Expect expression.").into()),
         }
@@ -386,7 +531,7 @@ impl Parser {
         if !self.is_at_end() {
             self.current += 1;
         }
-        self.peek()
+        self.previous()
     }
 
     fn peek(&self) -> &Token {
@@ -406,7 +551,11 @@ impl Parser {
     }
 
     fn previous(&self) -> &Token {
-        &self.tokens[self.current - 1]
+        if self.current == 0 {
+            &self.tokens[0]
+        } else {
+            &self.tokens[self.current - 1]
+        }
     }
 
     fn consume(&mut self, token_type: TokenType, message: &str) -> LoxResult<&Token> {

src/frontend/tokens.rs

@@ -67,6 +67,7 @@ pub enum TokenType {
     For,
     While,
     If,
+    Then,
     Elif,
     Else,
     Nil,
@@ -103,6 +104,7 @@ impl fmt::Display for TokenType {
             TokenType::Fun => write!(f, "fun"),
             TokenType::For => write!(f, "for"),
             TokenType::If => write!(f, "if"),
+            TokenType::Then => write!(f, "then"),
             TokenType::Nil => write!(f, "nil"),
             TokenType::Or => write!(f, "or"),
             TokenType::Print => write!(f, "print"),

src/logging/display_ast.rs

@@ -552,43 +552,3 @@ pub fn pretty_stmt_compact(stmt: &Stmt) -> String {
 pub fn pretty_tree<T: PrettyPrint>(item: &T) -> String {
     pretty_print_with_config(item, &PrettyConfig::tree())
 }
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::frontend::{
-        source_registry::{SourceId, SourcePosition, SourceSlice},
-        tokens::{LiteralValue, TokenType},
-    };
-
-    #[test]
-    fn test_pretty_expr_literal() {
-        let expr = Expr::Literal {
-            value: LiteralValue::Number(42.0),
-        };
-
-        let compact = expr.pretty_compact();
-        assert!(compact.contains("42"));
-
-        let full = expr.pretty();
-        assert!(full.contains("Literal"));
-        assert!(full.contains("42"));
-    }
-
-    #[test]
-    fn test_pretty_expr_binary() {
-        let expr = Expr::Binary {
-            left: Box::new(Expr::Literal {
-                value: LiteralValue::Number(1.0),
-            }),
-            operator: TokenType::Plus,
-            right: Box::new(Expr::Literal {
-                value: LiteralValue::Number(2.0),
-            }),
-        };
-
-        let compact = expr.pretty_compact();
-        assert!(compact.contains("1"));
-        assert!(compact.contains("2"));
-    }
-}

src/logging/display_token.rs

@@ -187,6 +187,7 @@ impl Token {
             TokenType::For => "FOR",
             TokenType::While => "WHILE",
             TokenType::If => "IF",
+            TokenType::Then => "THEN",
             TokenType::Elif => "ELIF",
             TokenType::Else => "ELSE",
             TokenType::Nil => "NIL",
@@ -227,6 +228,7 @@ impl Token {
             | TokenType::For
             | TokenType::While
             | TokenType::If
+            | TokenType::Then
             | TokenType::Elif
             | TokenType::Else
             | TokenType::Nil

src/main.rs

@@ -24,16 +24,16 @@ fn main() -> LoxResult<()> {
     let args: Vec<String> = env::args().collect();
     let mut lox = LoxInterpreter::new();
 
-    if args.len() > 2 {
+    let _ = if args.len() > 2 {
         eprintln!("Usage: {} [script]", args[0]);
         std::process::exit(64);
     } else if args.len() == 2 {
         // Esegui file
-        lox.run_file(&args[1])?;
+        lox.run_file(&args[1])
     } else {
         // Modalità interattiva
-        lox.run_prompt()?;
-    }
+        lox.run_prompt()
+    };
 
     Ok(())
 }
@@ -86,8 +86,9 @@ impl LoxInterpreter {
                 let mut env = Environment::new();
                 let mut interpreter = Interpreter::new(&mut env);
                 let mut result = None;
-                for stmt in stmts {
-                    result = Some(interpreter.interpret(stmt)?);
+                for (index, stmt) in stmts.iter().enumerate() {
+                    println!("executing stmt {}: {:?}", index, stmt);
+                    result = Some(interpreter.interpret(stmt.clone())?);
                 }
                 match result {
                     Some(res) => Ok(res),

src/result.rs

@@ -1,4 +1,5 @@
-use crate::frontend::source_registry::{SourcePosition, SourceRegistry, SourceSlice};
+use crate::frontend::source_registry::{SourceRegistry, SourceSlice};
+use std::fmt;
 
 #[derive(Debug, Clone)]
 pub enum LoxError {
@@ -24,6 +25,50 @@ pub enum LoxError {
     },
 }
 
+/// Configuration for error display formatting
+#[derive(Clone, Debug)]
+pub struct ErrorDisplayConfig {
+    /// Show colored output (for terminals that support it)
+    pub colored: bool,
+    /// Number of context lines to show before and after the error
+    pub context_lines: usize,
+    /// Show line numbers
+    pub show_line_numbers: bool,
+    /// Use Unicode characters for arrows and decorations
+    pub use_unicode: bool,
+}
+
+impl Default for ErrorDisplayConfig {
+    fn default() -> Self {
+        Self {
+            colored: true,
+            context_lines: 2,
+            show_line_numbers: true,
+            use_unicode: true,
+        }
+    }
+}
+
+impl ErrorDisplayConfig {
+    pub fn simple() -> Self {
+        Self {
+            colored: false,
+            context_lines: 1,
+            show_line_numbers: false,
+            use_unicode: false,
+        }
+    }
+
+    pub fn verbose() -> Self {
+        Self {
+            colored: true,
+            context_lines: 3,
+            show_line_numbers: true,
+            use_unicode: true,
+        }
+    }
+}
+
 impl LoxError {
     pub fn get_message(&self) -> String {
         match self {
@@ -49,88 +94,289 @@ impl LoxError {
         }
     }
 
-    pub fn print_with_context(&self, source_registry: &SourceRegistry) {
-        match self.get_source_slice() {
-            Some(source_slice) => {
-                let source_code = source_registry.get_source_code(&source_slice);
-                println!(
-                    "\n =============================================== \n DATA:{} \n CODE \n {} | {}",
-                    self, source_slice.start_position.line ,source_code
-                );
+    pub fn error_kind(&self) -> &'static str {
+        match self {
+            LoxError::LexicalError { .. } => "lexical error",
+            LoxError::RuntimeError { .. } => "runtime error",
+            LoxError::ParseError { .. } => "parse error",
+            LoxError::IoError { .. } => "io error",
+            LoxError::TypeMismatch { .. } => "type error",
+        }
+    }
+
+    /// Display error with source code context using default configuration
+    pub fn display_with_source(&self, source_registry: &SourceRegistry) -> String {
+        self.display_with_source_and_config(source_registry, &ErrorDisplayConfig::default())
+    }
+
+    /// Display error with source code context using custom configuration
+    pub fn display_with_source_and_config(
+        &self,
+        source_registry: &SourceRegistry,
+        config: &ErrorDisplayConfig,
+    ) -> String {
+        let mut output = String::new();
+
+        // Error header
+        let header = if config.colored {
+            format!(
+                "\x1b[1;31merror\x1b[0m: [{}] {}",
+                self.error_kind(),
+                self.get_message()
+            )
+        } else {
+            format!("error: [{}] {}", self.error_kind(), self.get_message())
+        };
+        output.push_str(&header);
+        output.push('\n');
+
+        // If we have source location, show it
+        if let Some(source_slice) = self.get_source_slice() {
+            let source_info = source_registry.get_by_id(source_slice.source_id);
+
+            // File location line
+            let location = if config.colored {
+                format!(
+                    "  \x1b[34m-->\x1b[0m {}:{}:{}",
+                    source_info.file_name,
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1
+                )
+            } else {
+                format!(
+                    "  --> {}:{}:{}",
+                    source_info.file_name,
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1
+                )
+            };
+            output.push_str(&location);
+            output.push('\n');
+
+            // Source code context
+            if let Some(source_context) =
+                self.get_source_context(source_registry, &source_slice, config)
+            {
+                output.push_str(&source_context);
             }
-            None => println!("{}", self),
         }
+
+        output
+    }
+
+    fn get_source_context(
+        &self,
+        source_registry: &SourceRegistry,
+        source_slice: &SourceSlice,
+        config: &ErrorDisplayConfig,
+    ) -> Option<String> {
+        let source_info = source_registry.get_by_id(source_slice.source_id);
+        let lines: Vec<&str> = source_info.content.lines().collect();
+
+        if lines.is_empty() || source_slice.start_position.line >= lines.len() {
+            return None;
+        }
+
+        let mut output = String::new();
+        let error_line = source_slice.start_position.line;
+        let start_line = error_line.saturating_sub(config.context_lines);
+        let end_line = (error_line + config.context_lines + 1).min(lines.len());
+
+        // Calculate the width needed for line numbers
+        let line_number_width = if config.show_line_numbers {
+            (end_line + 1).to_string().len()
+        } else {
+            0
+        };
+
+        // Show context lines
+        for line_idx in start_line..end_line {
+            let line_content = lines[line_idx];
+            let line_number = line_idx + 1;
+
+            if config.show_line_numbers {
+                let line_num_str = if config.colored {
+                    if line_idx == error_line {
+                        format!(
+                            "\x1b[1;34m{:width$}\x1b[0m",
+                            line_number,
+                            width = line_number_width
+                        )
+                    } else {
+                        format!(
+                            "\x1b[34m{:width$}\x1b[0m",
+                            line_number,
+                            width = line_number_width
+                        )
+                    }
+                } else {
+                    format!("{:width$}", line_number, width = line_number_width)
+                };
+
+                let separator = if config.colored {
+                    if line_idx == error_line {
+                        "\x1b[1;34m |\x1b[0m "
+                    } else {
+                        "\x1b[34m |\x1b[0m "
+                    }
+                } else {
+                    " | "
+                };
+
+                output.push_str(&format!(
+                    "   {}{}{}\n",
+                    line_num_str, separator, line_content
+                ));
+            } else {
+                output.push_str(&format!("   {}\n", line_content));
+            }
+
+            // Add error indicator on the error line
+            if line_idx == error_line {
+                let spaces_before =
+                    " ".repeat(3 + line_number_width + 3 + source_slice.start_position.column);
+
+                let error_length = if source_slice.start_position.line
+                    == source_slice.end_position.line
+                {
+                    (source_slice.end_position.column - source_slice.start_position.column).max(1)
+                } else {
+                    line_content.len() - source_slice.start_position.column
+                };
+
+                let indicator = if config.use_unicode {
+                    "^".repeat(error_length)
+                } else {
+                    "^".repeat(error_length)
+                };
+
+                let colored_indicator = if config.colored {
+                    format!("\x1b[1;31m{}\x1b[0m", indicator)
+                } else {
+                    indicator
+                };
+
+                // Add the indicator line
+                if config.show_line_numbers {
+                    let empty_line_number = " ".repeat(line_number_width);
+                    let separator = if config.colored {
+                        "\x1b[34m |\x1b[0m "
+                    } else {
+                        " | "
+                    };
+                    output.push_str(&format!(
+                        "   {}{}{}{}\n",
+                        empty_line_number,
+                        separator,
+                        spaces_before[3 + line_number_width + 3..].to_string(),
+                        colored_indicator
+                    ));
+                } else {
+                    output.push_str(&format!(
+                        "   {}{}\n",
+                        spaces_before[3..].to_string(),
+                        colored_indicator
+                    ));
+                }
+
+                // Add error type and additional context
+                let error_note = match self {
+                    LoxError::TypeMismatch {
+                        expected, found, ..
+                    } => Some(format!("expected `{}`, found `{}`", expected, found)),
+                    _ => None,
+                };
+
+                if let Some(note) = error_note {
+                    let note_prefix = if config.show_line_numbers {
+                        format!(
+                            "   {} {} ",
+                            " ".repeat(line_number_width),
+                            if config.colored {
+                                "\x1b[34m|\x1b[0m"
+                            } else {
+                                "|"
+                            }
+                        )
+                    } else {
+                        "   ".to_string()
+                    };
+
+                    let colored_note = if config.colored {
+                        format!("\x1b[1;36mnote\x1b[0m: {}", note)
+                    } else {
+                        format!("note: {}", note)
+                    };
+
+                    output.push_str(&format!("{}{}\n", note_prefix, colored_note));
+                }
+            }
+        }
+
+        Some(output)
+    }
+
+    /// Print error with source context to stdout
+    pub fn print_with_source(&self, source_registry: &SourceRegistry) {
+        println!("{}", self.display_with_source(source_registry));
+    }
+
+    /// Print error with source context and custom config to stdout
+    pub fn print_with_source_and_config(
+        &self,
+        source_registry: &SourceRegistry,
+        config: &ErrorDisplayConfig,
+    ) {
+        println!(
+            "{}",
+            self.display_with_source_and_config(source_registry, config)
+        );
+    }
+
+    /// Legacy method for backwards compatibility
+    pub fn print_with_context(&self, source_registry: &SourceRegistry) {
+        self.print_with_source(source_registry);
     }
 }
 
-fn fetch_source_code(path: &str, start: SourcePosition, end: SourcePosition) -> LoxResult<String> {
-    let source_code = std::fs::read_to_string(path).map_err(|e| LoxError::IoError {
-        message: format!("Failed to read file: {}", e),
-    })?;
-
-    let lines: Vec<&str> = source_code.split('\n').collect();
-
-    // Verifica bounds
-    if start.line >= lines.len() || end.line >= lines.len() {
-        return Err(LoxError::IoError {
-            message: "Line number out of bounds".to_string(),
-        });
-    }
-
-    let mut result = String::new();
-
-    if start.line == end.line {
-        // Caso speciale: stessa riga
-        let line = lines[start.line];
-        if end.column <= line.len() && start.column <= end.column {
-            result.push_str(&line[start.column..end.column]);
-        }
-    } else {
-        // Caso generale: righe multiple
-
-        // Prima riga: da start.column alla fine della riga
-        let first_line = lines[start.line];
-        if start.column < first_line.len() {
-            result.push_str(&first_line[start.column..]);
-        }
-        result.push('\n');
-
-        // Righe intermedie: complete
-        for i in (start.line + 1)..end.line {
-            result.push_str(lines[i]);
-            result.push('\n');
-        }
-
-        // Ultima riga: dall'inizio fino a end.column
-        let last_line = lines[end.line];
-        if end.column <= last_line.len() {
-            result.push_str(&last_line[..end.column]);
-        }
-    }
-
-    Ok(result)
-}
-
-impl std::fmt::Display for LoxError {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+impl fmt::Display for LoxError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
             LoxError::LexicalError {
                 source_slice,
                 message,
             } => {
-                write!(f, "Lexical error on {:?}: \n {}", source_slice, message)
+                write!(
+                    f,
+                    "Lexical error at {}:{}: {}",
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1,
+                    message
+                )
             }
             LoxError::RuntimeError {
                 source_slice,
                 message,
             } => {
-                write!(f, "Runtime error on {:?}: \n{}", source_slice, message)
+                write!(
+                    f,
+                    "Runtime error at {}:{}: {}",
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1,
+                    message
+                )
             }
             LoxError::ParseError {
                 source_slice,
                 message,
             } => {
-                write!(f, "Parse error on {:?}: \n{}", source_slice, message)
+                write!(
+                    f,
+                    "Parse error at {}:{}: {}",
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1,
+                    message
+                )
             }
             LoxError::IoError { message } => write!(f, "IO error: {}", message),
             LoxError::TypeMismatch {
@@ -140,8 +386,11 @@ impl std::fmt::Display for LoxError {
             } => {
                 write!(
                     f,
-                    "Type mismatch on {:?}: \n expected {}, found {}",
-                    source_slice, expected, found
+                    "Type mismatch at {}:{}: expected `{}`, found `{}`",
+                    source_slice.start_position.line + 1,
+                    source_slice.start_position.column + 1,
+                    expected,
+                    found
                 )
             }
         }
@@ -151,3 +400,47 @@ impl std::fmt::Display for LoxError {
 impl std::error::Error for LoxError {}
 
 pub type LoxResult<T> = Result<T, LoxError>;
+
+/// Helper function to create a lexical error
+pub fn lexical_error(source_slice: SourceSlice, message: impl Into<String>) -> LoxError {
+    LoxError::LexicalError {
+        source_slice,
+        message: message.into(),
+    }
+}
+
+/// Helper function to create a parse error
+pub fn parse_error(source_slice: SourceSlice, message: impl Into<String>) -> LoxError {
+    LoxError::ParseError {
+        source_slice,
+        message: message.into(),
+    }
+}
+
+/// Helper function to create a runtime error
+pub fn runtime_error(source_slice: SourceSlice, message: impl Into<String>) -> LoxError {
+    LoxError::RuntimeError {
+        source_slice,
+        message: message.into(),
+    }
+}
+
+/// Helper function to create a type mismatch error
+pub fn type_mismatch_error(
+    source_slice: SourceSlice,
+    expected: impl Into<String>,
+    found: impl Into<String>,
+) -> LoxError {
+    LoxError::TypeMismatch {
+        source_slice,
+        expected: expected.into(),
+        found: found.into(),
+    }
+}
+
+/// Helper function to create an IO error
+pub fn io_error(message: impl Into<String>) -> LoxError {
+    LoxError::IoError {
+        message: message.into(),
+    }
+}

test_error.lox

@@ -0,0 +1,9 @@
+// Test script to verify error positioning
+var a = 5;
+var b = "hello";
+print 0;
+var result = a + b;  // This should cause a type error
+print 1;
+43 + "hello"; // This should cause a type error
+print result;
+print 46 + "world"; // This should cause a type error

test_source_tracking.lox

@@ -0,0 +1,26 @@
+// Test file for source slice tracking
+var x = 42;
+print x;
+
+if x > 0 then do
+    print "positive";
+    var y = x + 1;
+end
+elif x == 0 then do
+    print "zero";
+end
+else do
+    print "negative";
+end
+
+while x > 0 do
+    x = x - 1;
+    print x;
+end
+
+do
+    var z = 10;
+    print z * 2;
+end
+
+return x + 5;