wip:

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/interpreter.rs

@@ -1,7 +1,7 @@
 use crate::{
     backend::environment::EnvironmentStack,
     common::{
-        ast::{AstNode, Expr, NodeId, Stmt},
+        ast::{AstNode, Expr, NodeId},
         base_value::{BaseValue, NativeFunction, Number, Truthy},
         lox_result::{runtime_error, LoxError, LoxResult},
     },
@@ -21,18 +21,9 @@ pub trait EvaluateInterpreter<T> {
     fn evaluate(&mut self, stmt: T) -> LoxResult<BaseValue>;
 }
 
-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.is_synthetic() => 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)
     }
 }
 
@@ -63,9 +54,9 @@ impl Interpreter {
 
     /// 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<Expr>) -> LoxResult<BaseValue> {
+    fn eval_expr(&mut self, node: &AstNode) -> LoxResult<BaseValue> {
         let result = match &node.node {
-            Expr::Literal { value } => match value {
+            Expr::Literal { value } => match &**value {
                 BaseValue::Function(func) => {
                     let mut func = func.clone();
                     func.closure = Some(self.enviorment.clone());
@@ -93,6 +84,67 @@ impl Interpreter {
                 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 {
@@ -125,11 +177,7 @@ impl Interpreter {
         }
     }
 
-    fn evaluate_call(
-        &mut self,
-        callee: &AstNode<Expr>,
-        arguments: &[AstNode<Expr>],
-    ) -> LoxResult<BaseValue> {
+    fn evaluate_call(&mut self, callee: &AstNode, arguments: &[AstNode]) -> LoxResult<BaseValue> {
         let source_slice = callee.source_slice.clone();
 
         // A bare identifier callee resolves through `locals`; anything else is
@@ -167,7 +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),
@@ -228,94 +276,22 @@ impl Interpreter {
         }
     }
 
-    fn interpret_stmt_inner(&mut self, stmt: Stmt) -> LoxResult<BaseValue> {
-        match stmt {
-            Stmt::Expression { expression, .. } => self.eval_expr(&expression),
-            Stmt::Print { expression, .. } => {
-                let value = self.eval_expr(&expression)?;
-                println!("{}", value);
-                Ok(BaseValue::Nil)
-            }
-            Stmt::Block { statements, .. } => self.evaluate_block(*statements),
-            Stmt::Return { expression, .. } => self.eval_expr(&expression),
-            Stmt::VarDeclaration {
-                name, initializer, ..
-            } => {
-                let value = match initializer {
-                    Some(expr_node) => self.eval_expr(&expr_node)?,
-                    None => BaseValue::Nil,
-                };
-                self.enviorment.declare(name.clone(), value)
-            }
-
-            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.eval_expr(&condition)?.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.eval_expr(&condition)?.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.eval_expr(&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.eval_expr(&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,
                         _ => {
@@ -328,7 +304,7 @@ impl Interpreter {
                     };
                 }
                 if let Some(else_block) = else_branch {
-                    self.evaluate(*else_block)
+                    self.eval_expr(else_block)
                 } else {
                     Ok(BaseValue::Nil)
                 }
@@ -341,25 +317,23 @@ impl Interpreter {
         }
     }
 
-    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.eval_expr(&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();
@@ -482,7 +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

@@ -1,5 +1,5 @@
 use crate::{
-    common::base_value::BaseValue,
+    common::{base_value::BaseValue, types::Type},
     frontend::{source_registry::SourceSlice, tokens::TokenType},
 };
 use std::fmt::{Debug, Display};
@@ -22,65 +22,66 @@ impl NodeId {
         NodeId(NEXT_NODE_ID.fetch_add(1, Ordering::Relaxed))
     }
 }
-/*
- * grammar:
- * program -> statement* EOF
- * statement -> expression_statement
- *             | print_statement
- *             | var_statement
- *             | block_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)? )* )
- * 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
- */
+
 #[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<Expr>>,
+        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>,
     },
 }
 
@@ -95,8 +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 ({}({}))",
@@ -108,6 +111,59 @@ impl std::fmt::Display for Expr {
                     .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
+            ),
         }
     }
 }
@@ -115,15 +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 ({}({}))",
@@ -132,306 +194,90 @@ impl Debug for Expr {
                     .iter()
                     .map(|arg| arg.node.to_string())
                     .collect::<Vec<String>>()
-                    .join(", ")
+                    .join(", "),
             ),
-            Expr::Assign { name, value } => write!(f, "(assign {:?} {:?})", name, value.node),
+            Expr::Assign { name, value } => {
+                write!(f, "(assign {:?} {:?})", name, value.node,)
             }
-    }
-}
-
-#[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>,
-    },
-    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::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::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::Return {
-                expression,
-                return_value,
-                label,
-            } => write!(
+            Expr::Return { expression, label } => {
+                write!(f, "Return({:?}, {}) ;", expression.node, label,)
+            }
+            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",
-            Expr::Assign { .. } => "assignment expression",
-        }
-    }
-}
-
-impl AstNodeKind for Stmt {
-    fn kind(&self) -> &'static str {
-        match self {
-            Stmt::Expression { .. } => "expression",
-            Stmt::VarDeclaration { .. } => "variable declaration",
-            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)]
-pub struct AstNode<T: AstNodeKind + Debug + Display> {
+pub struct AstNode {
     /// Stable identity, assigned at construction and preserved across clones.
     pub id: NodeId,
-    pub node: T,
+    pub node: Expr,
+    pub is_statement: bool,
     pub source_slice: SourceSlice,
+    pub return_type: Type,
 }
 
 // Identity (`id`) deliberately does not participate in equality: two nodes are
 // equal when their content and location match, regardless of node id.
-impl<T: AstNodeKind + Debug + Display + PartialEq> PartialEq for AstNode<T> {
+impl PartialEq for AstNode {
     fn eq(&self, other: &Self) -> bool {
         self.node == other.node && self.source_slice == other.source_slice
     }
 }
 
-impl<T: AstNodeKind + Debug + Display> Display for AstNode<T> {
+impl Display for AstNode {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         write!(
             f,
@@ -441,7 +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,
@@ -451,12 +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 {
+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 {

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

@@ -16,7 +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),
@@ -514,4 +514,32 @@ mod tests {
         assert_eq!(tokens[1].source_slice.start_position.line, 1);
         assert_eq!(tokens[1].source_slice.start_position.column, 0);
     }
+
+    #[test]
+    fn handle_struct() {
+        let tokens = lex("Cosa :: struct {field1: Number, field2: String}");
+        let tokens_tyepe: Vec<TokenType> = tokens.iter().map(|x| x.token_type.clone()).collect();
+        let tokent_for_check = vec![
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Colon,
+            TokenType::Struct,
+            TokenType::LeftBrace,
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Identifier,
+            TokenType::Comma,
+            TokenType::Identifier,
+            TokenType::Colon,
+            TokenType::Identifier,
+            TokenType::RightBrace,
+            TokenType::Eof,
+        ];
+        assert_eq!(tokens_tyepe, tokent_for_check);
+        assert_eq!(tokens[0].lexeme, "Cosa");
+        assert_eq!(tokens[5].lexeme, "field1");
+        assert_eq!(tokens[7].lexeme, "Number");
+        assert_eq!(tokens[9].lexeme, "field2");
+        assert_eq!(tokens[11].lexeme, "String");
+    }
 }

src/frontend/source_registry.rs

@@ -121,6 +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/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)]
@@ -264,33 +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());
@@ -303,7 +277,7 @@ impl PrettyPrint for Stmt {
                     write!(f, "{}}}", indent)
                 }
             }
-            Stmt::VarDeclaration {
+            Expr::VarDeclaration {
                 name, initializer, ..
             } => {
                 if ctx.config.compact {
@@ -331,8 +305,7 @@ impl PrettyPrint for Stmt {
                     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());
@@ -345,9 +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 {
@@ -366,12 +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 =
@@ -386,10 +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())?;
@@ -421,21 +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)?;
@@ -451,7 +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();
 
@@ -463,9 +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
                 )?;
             }
 
@@ -519,25 +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::{
@@ -175,7 +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| {
@@ -185,7 +184,7 @@ 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)?;
@@ -212,7 +211,7 @@ impl LoxInterpreter {
     // Static variable resolution; prints and returns the first error, if any.
     fn resolve(
         &self,
-        ast: &[AstNode<Stmt>],
+        ast: &[AstNode],
     ) -> LoxResult<std::collections::HashMap<crate::common::ast::NodeId, usize>> {
         Resolver::resolve_program(ast).map_err(|errors| {
             for err in &errors {
@@ -295,7 +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/variable_resolution.rs

@@ -17,13 +17,13 @@ use std::collections::HashMap;
 
 use crate::{
     common::{
-        ast::{AstNode, Expr, NodeId, Stmt},
+        ast::{AstNode, Expr, NodeId},
         base_value::{BaseValue, LoxFunction},
         lox_result::{ErrorSink, LoxError, LoxResult},
     },
     middleend::{
         scope_stack::ScopeStack,
-        visit_ast::{walk_expr, walk_function, walk_stmt, Visitor},
+        visit_ast::{walk_expr, walk_function, Visitor},
     },
 };
 
@@ -55,13 +55,13 @@ impl Resolver {
     /// Resolve a whole program, returning the per-reference scope distances or
     /// the accumulated resolution errors.
     pub fn resolve_program(
-        statements: &[AstNode<Stmt>],
+        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_stmt(statement);
+            let _ = resolver.visit_expr(statement);
         }
         if resolver.errors.has_errors() {
             Err(resolver.errors.into_errors())
@@ -105,52 +105,7 @@ impl Default for Resolver {
 }
 
 impl Visitor for Resolver {
-    fn visit_stmt(&mut self, stmt: &AstNode<Stmt>) -> LoxResult<()> {
-        match &stmt.node {
-            Stmt::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: BaseValue::Function(_)
-                    })
-                );
-                self.declare(name, &stmt.source_slice);
-                if is_function {
-                    self.define(name);
-                    walk_stmt(self, stmt)?;
-                } else {
-                    walk_stmt(self, stmt)?; // resolves the initializer, if any
-                    self.define(name);
-                }
-                Ok(())
-            }
-            Stmt::Block { .. } => {
-                self.scopes.begin_scope();
-                walk_stmt(self, stmt)?;
-                self.scopes.end_scope();
-                Ok(())
-            }
-            Stmt::Return { .. } => {
-                if self.current_function == FunctionType::None {
-                    self.errors.report(LoxError::ParseError {
-                        source_slice: stmt.source_slice.clone(),
-                        message: "Can't return from top-level code.".to_string(),
-                    });
-                }
-                walk_stmt(self, stmt) // resolve the returned expression
-            }
-            // Expression, Print, 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.get_local(name) == Some(&false) {
@@ -167,6 +122,42 @@ impl Visitor for Resolver {
                 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),
         }
     }
@@ -193,7 +184,7 @@ 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");
@@ -251,7 +242,7 @@ mod tests {
 
     #[test]
     fn return_inside_a_function_is_allowed() {
-        let locals = resolve("f :: fn (n) do return n; end").expect("should resolve");
+        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);

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)
     }
 
@@ -62,70 +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::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(())
@@ -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

@@ -4,14 +4,14 @@
 //! assert on the resulting AST, complementing the per-module unit tests inside
 //! `src/frontend/{lexer,parser}.rs`.
 
-use rlox::common::ast::{AstNode, Expr, Stmt};
+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<Stmt>>, String> {
+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}"))?;
@@ -21,23 +21,26 @@ fn parse(src: &str) -> Result<Vec<AstNode<Stmt>>, String> {
 }
 
 /// Parse `src`, panicking if the frontend reports any error.
-fn parse_ok(src: &str) -> Vec<AstNode<Stmt>> {
+fn parse_ok(src: &str) -> Vec<AstNode> {
     parse(src).expect("expected source to lex and parse")
 }
 
-/// Parse `src` and return the single statement it should produce.
-fn single_stmt(src: &str) -> Stmt {
+/// 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 the expression of its single expression-statement.
+/// 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 {
-    match single_stmt(src) {
-        Stmt::Expression { expression, .. } => expression.node,
-        other => panic!("expected expression statement, got {other:?}"),
-    }
+    single_stmt(src)
 }
 
 // ---------------------------------------------------------------------------
@@ -47,7 +50,7 @@ fn single_expr(src: &str) -> Expr {
 #[test]
 fn lexes_and_parses_number_literal() {
     match single_expr("42;") {
-        Expr::Literal { value } => assert_eq!(value, BaseValue::Number(Number::I32(42))),
+        Expr::Literal { value } => assert_eq!(*value, BaseValue::Number(Number::I32(42))),
         other => panic!("expected literal, got {other:?}"),
     }
 }
@@ -194,7 +197,7 @@ fn assignment_to_non_identifier_is_an_error() {
 #[test]
 fn parses_var_declaration() {
     match single_stmt("x := 5;") {
-        Stmt::VarDeclaration {
+        Expr::VarDeclaration {
             name, initializer, ..
         } => {
             assert_eq!(name, "x");
@@ -206,13 +209,13 @@ fn parses_var_declaration() {
 
 #[test]
 fn parses_print_statement() {
-    assert!(matches!(single_stmt("print 1;"), Stmt::Print { .. }));
+    assert!(matches!(single_stmt("print 1;"), Expr::Print { .. }));
 }
 
 #[test]
 fn parses_block_with_multiple_statements() {
     match single_stmt("do print 1; print 2; end") {
-        Stmt::Block { statements, .. } => assert_eq!(statements.len(), 2),
+        Expr::Block { statements, .. } => assert_eq!(statements.len(), 2),
         other => panic!("expected block, got {other:?}"),
     }
 }
@@ -220,7 +223,7 @@ fn parses_block_with_multiple_statements() {
 #[test]
 fn parses_if_else() {
     match single_stmt("if true then print 1; else print 2;") {
-        Stmt::If {
+        Expr::If {
             else_branch: Some(_),
             ..
         } => {}
@@ -232,37 +235,32 @@ fn parses_if_else() {
 fn parses_while_loop() {
     assert!(matches!(
         single_stmt("while true do print 1; end"),
-        Stmt::While { .. }
+        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") {
-        Stmt::For { increment, .. } => match increment.node {
-            // The increment desugars to an expression statement holding an assignment.
-            Stmt::Expression { expression, .. } => {
-                assert!(matches!(expression.node, Expr::Assign { .. }))
+        Expr::For { increment, .. } => {
+            // The increment is an assignment expression.
+            assert!(matches!(increment.node, Expr::Assign { .. }))
         }
-            other => panic!("expected expression-statement increment, got {other:?}"),
-        },
         other => panic!("expected for loop, got {other:?}"),
     }
 }
 
 #[test]
 fn parses_function_declaration() {
-    match single_stmt("add :: fn (a, b) do return a + b; end") {
-        Stmt::VarDeclaration {
+    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: BaseValue::Function(_)
-                    }
+                    &init.node,
+                    Expr::Literal { value } if matches!(&**value, BaseValue::Function(_))
                 )),
                 None => panic!("expected a function initializer"),
             }

tests/resolution.rs

@@ -37,13 +37,13 @@ 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 () do
+make :: fn (): Any do
     count := 10;
-    get :: fn () do
+    get :: fn (): Number do
         return count;
-    end
+    end;
     return get;
-end
+end;
 g := make();
 g();
 ";