feat: finish chapter 10 (functions)

this was a big chapter, but the most fun i had!

I plan to add some native functions in the future and do the challenges
of course

src/ast.rs

@@ -12,6 +12,11 @@ pub enum Expr {
         op: Token,
         right: Box<Expr>,
     },
+    Call {
+        callee: Box<Expr>,
+        paren: Token,
+        args: Vec<Expr>,
+    },
     Grouping {
         expression: Box<Expr>,
     },
@@ -36,6 +41,7 @@ pub enum Expr {
     },
 }
 
+#[derive(Debug, Clone)]
 pub enum Stmt {
     Block {
         statements: Vec<Stmt>,
@@ -44,6 +50,11 @@ pub enum Stmt {
     Expression {
         expression: Expr,
     },
+    Function {
+        name: Token,
+        params: Vec<Token>,
+        body: Vec<Stmt>,
+    },
     If {
         condition: Expr,
         then_branch: Box<Stmt>,
@@ -52,6 +63,10 @@ pub enum Stmt {
     Print {
         expression: Expr,
     },
+    Return {
+        keyword: Token,
+        value: Option<Expr>,
+    },
     Var {
         name: Token,
         initializer: Option<Expr>,

src/callable.rs

@@ -0,0 +1,105 @@
+use std::{cell::RefCell, fmt::Display, rc::Rc};
+
+use crate::{
+    ast::Stmt,
+    environment::Environment,
+    interpreter::{execute_block, InterpreterEnvironment, InterpreterSignal, RuntimeError},
+    token::{LiteralType, Token},
+};
+
+pub trait CallableTrait {
+    fn arity(&self) -> u8;
+    fn call(
+        &self,
+        args: &[LiteralType],
+        env: &InterpreterEnvironment,
+    ) -> Result<LiteralType, InterpreterSignal>;
+}
+
+#[derive(Debug, Clone)]
+pub enum Callable {
+    Function {
+        name: Box<Token>,
+        params: Vec<Token>,
+        body: Vec<Stmt>,
+        closure: Rc<RefCell<Environment>>,
+    },
+    NativeFunction(NativeFunction),
+}
+
+impl CallableTrait for Callable {
+    fn arity(&self) -> u8 {
+        match self {
+            Callable::Function { params, .. } => params.len() as u8,
+            Callable::NativeFunction(native_function) => native_function.arity,
+        }
+    }
+
+    fn call(
+        &self,
+        args: &[LiteralType],
+        env: &InterpreterEnvironment,
+    ) -> Result<LiteralType, InterpreterSignal> {
+        match self {
+            Callable::Function {
+                name: _,
+                params,
+                body,
+                closure,
+            } => {
+                let environment = Rc::new(RefCell::new(Environment::with_enclosing(closure)));
+
+                for (param, arg) in params.iter().zip(args) {
+                    environment
+                        .borrow_mut()
+                        .define(&param.lexeme, Some(arg.clone()));
+                }
+
+                let environment = InterpreterEnvironment {
+                    globals: Rc::clone(&env.globals),
+                    environment,
+                };
+
+                match execute_block(body, &environment) {
+                    Err(InterpreterSignal::Return(v)) => Ok(v),
+                    v => v.map(|_| LiteralType::Nil),
+                }
+            }
+            Callable::NativeFunction(native_function) => (native_function.call_impl)(args),
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct NativeFunction {
+    name: String,
+    arity: u8,
+    call_impl: fn(&[LiteralType]) -> Result<LiteralType, InterpreterSignal>,
+}
+
+impl NativeFunction {
+    pub fn new(
+        name: String,
+        arity: u8,
+        call_impl: fn(&[LiteralType]) -> Result<LiteralType, InterpreterSignal>,
+    ) -> Self {
+        Self {
+            name,
+            arity,
+            call_impl,
+        }
+    }
+}
+
+impl Display for Callable {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Callable::Function { name, .. } => {
+                write!(f, "{}", name.lexeme)
+            }
+            Callable::NativeFunction(native_function) => {
+                write!(f, "{}", native_function.name)
+            }
+        }
+    }
+}

src/environment.rs

@@ -1,7 +1,11 @@
 use std::{cell::RefCell, collections::HashMap, rc::Rc};
 
-use crate::token::{LiteralType, Token};
+use crate::{
+    callable::Callable,
+    token::{LiteralType, Token},
+};
 
+#[derive(Debug, Clone)]
 pub struct Environment {
     values: HashMap<String, Option<LiteralType>>,
     enclosing: Option<Rc<RefCell<Environment>>>,

src/interpreter.rs

@@ -1,18 +1,30 @@
 use core::panic;
-use std::{cell::RefCell, rc::Rc};
+use std::{
+    cell::RefCell,
+    rc::Rc,
+    time::{SystemTime, UNIX_EPOCH},
+};
 
 use crate::{
     ast::{Expr, Stmt},
+    callable::{Callable, CallableTrait, NativeFunction},
     environment::Environment,
     token::{LiteralType, Token, TokenType},
 };
 
+type InterpreterResult = Result<LiteralType, InterpreterSignal>;
+
 #[derive(Debug)]
 pub struct RuntimeError {
     pub token: Token,
     pub message: String,
 }
 
+pub struct InterpreterEnvironment {
+    pub globals: Rc<RefCell<Environment>>,
+    pub environment: Rc<RefCell<Environment>>,
+}
+
 impl RuntimeError {
     pub fn new(token: &Token, message: &str) -> RuntimeError {
         RuntimeError {
@@ -22,22 +34,29 @@ impl RuntimeError {
     }
 }
 
-pub enum InterpreterError {
+pub enum InterpreterSignal {
     RuntimeError(RuntimeError),
-    BreakSignal,
+    Break,
+    Return(LiteralType),
 }
+/*
+    This two impl blocks are for the ? operator. I'm too lazy to write the wrapping code for the enums and it also looks ugly,
+    so i just abuse the ? operator lol
+    Instead of InterpreterError::RuntimeError(RuntimeError {...} ) i can just RuntimeError {...}? to turn it into a InterpreterError
+*/
 
-impl From<RuntimeError> for InterpreterError {
+impl From<RuntimeError> for InterpreterSignal {
     fn from(value: RuntimeError) -> Self {
         Self::RuntimeError(value)
     }
 }
 
-impl From<InterpreterError> for RuntimeError {
-    fn from(value: InterpreterError) -> Self {
+impl From<InterpreterSignal> for RuntimeError {
+    fn from(value: InterpreterSignal) -> Self {
         match value {
-            InterpreterError::RuntimeError(runtime_error) => runtime_error,
-            InterpreterError::BreakSignal => panic!("Not a runtime error"),
+            InterpreterSignal::RuntimeError(runtime_error) => runtime_error,
+            InterpreterSignal::Break => panic!("Not a runtime error"),
+            InterpreterSignal::Return(_) => panic!("Not a runtime error"),
         }
     }
 }
@@ -45,9 +64,30 @@ impl From<InterpreterError> for RuntimeError {
 pub fn interpret(
     statements: &Vec<Stmt>,
     environment: &Rc<RefCell<Environment>>,
-) -> Result<(), InterpreterError> {
+) -> Result<(), InterpreterSignal> {
+    let clock = |_arg: &[LiteralType]| {
+        Ok(LiteralType::Number(
+            SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .expect("Time went backwards")
+                .as_secs_f64()
+                / 1000.0,
+        ))
+    };
+
+    let clock_function = NativeFunction::new("clock".to_string(), 0, clock);
+    let environment = InterpreterEnvironment {
+        globals: Rc::clone(environment),
+        environment: Rc::clone(environment),
+    };
+    environment.globals.borrow_mut().define(
+        "clock",
+        Some(LiteralType::Callable(Callable::NativeFunction(
+            clock_function,
+        ))),
+    );
     for statement in statements {
-        execute(statement, environment)?;
+        execute(statement, &environment)?
     }
 
     Ok(())
@@ -55,23 +95,24 @@ pub fn interpret(
 
 fn execute(
     statement: &Stmt,
-    environment: &Rc<RefCell<Environment>>,
-) -> Result<(), InterpreterError> {
+    environment: &InterpreterEnvironment,
+) -> Result<(), InterpreterSignal> {
+    let curr_environment = &environment.environment;
     match statement {
         Stmt::Expression { expression } => {
-            evaluate(expression, &mut environment.borrow_mut())?;
+            evaluate(expression, environment)?;
         }
         Stmt::Print { expression } => {
-            let expr = evaluate(expression, &mut environment.borrow_mut())?;
+            let expr = evaluate(expression, environment)?;
             println!("{expr}");
         }
         Stmt::Var { name, initializer } => {
             let value = if let Some(initializer) = initializer {
-                Some(evaluate(initializer, &mut environment.borrow_mut())?)
+                Some(evaluate(initializer, environment)?)
             } else {
                 None
             };
-            environment.borrow_mut().define(&name.lexeme, value);
+            curr_environment.borrow_mut().define(&name.lexeme, value);
         }
         Stmt::Block { statements } => {
             execute_block(statements, environment)?;
@@ -81,39 +122,69 @@ fn execute(
             then_branch,
             else_branch,
         } => {
-            if is_truthy(&evaluate(condition, &mut environment.borrow_mut())?) {
+            if is_truthy(&evaluate(condition, environment)?) {
                 execute(then_branch, environment)?;
             } else if let Some(else_branch) = else_branch {
                 execute(else_branch, environment)?;
             }
         }
         Stmt::While { condition, body } => {
-            while is_truthy(&evaluate(condition, &mut environment.borrow_mut())?) {
+            while is_truthy(&evaluate(condition, environment)?) {
                 let result = execute(body, environment);
                 if result.is_err() {
                     break;
                 }
             }
         }
-        Stmt::Break => Err(InterpreterError::BreakSignal)?,
+        Stmt::Break => Err(InterpreterSignal::Break)?,
+        Stmt::Function { name, params, body } => {
+            let function = Callable::Function {
+                name: Box::new(name.clone()),
+                body: body.to_vec(),
+                params: params.to_vec(),
+                closure: Rc::clone(curr_environment),
+            };
+            environment
+                .globals
+                .borrow_mut()
+                .define(&name.lexeme, Some(LiteralType::Callable(function)));
+        }
+        Stmt::Return { value, .. } => {
+            let value = if let Some(v) = value {
+                evaluate(v, environment)?
+            } else {
+                LiteralType::Nil
+            };
+
+            return Err(InterpreterSignal::Return(value));
+        }
     }
 
     Ok(())
 }
 
-fn execute_block(
+pub fn execute_block(
     statements: &Vec<Stmt>,
-    environment: &Rc<RefCell<Environment>>,
-) -> Result<(), InterpreterError> {
-    let block_enviroment = Rc::new(RefCell::new(Environment::with_enclosing(environment)));
+    environment: &InterpreterEnvironment,
+) -> Result<(), InterpreterSignal> {
+    let block_enviroment = Rc::new(RefCell::new(Environment::with_enclosing(
+        &environment.environment,
+    )));
+    // we just move the block_enviroment to a new InterpreterEnvironment and clone the reference to
+    // globals, bcs outer environments might have the globals reference
+    let environment = InterpreterEnvironment {
+        globals: Rc::clone(&environment.globals),
+        environment: block_enviroment,
+    };
     for stmt in statements {
-        execute(stmt, &block_enviroment)?;
+        execute(stmt, &environment)?;
     }
 
     Ok(())
 }
 
-fn evaluate(expr: &Expr, environment: &mut Environment) -> Result<LiteralType, InterpreterError> {
+fn evaluate(expr: &Expr, environment: &InterpreterEnvironment) -> InterpreterResult {
+    let curr_environment = &environment.environment;
     match expr {
         Expr::Ternary {
             first,
@@ -129,7 +200,8 @@ fn evaluate(expr: &Expr, environment: &mut Environment) -> Result<LiteralType, I
         Expr::Grouping { expression } => evaluate(expression, environment),
         Expr::Literal { value } => Ok(value.clone()),
         Expr::Unary { op, right } => Ok(unary(&evaluate(right, environment)?, op)),
-        Expr::Variable { name } => environment
+        Expr::Variable { name } => curr_environment
+            .borrow()
             .get(name)
             .ok_or_else(|| RuntimeError {
                 token: name.clone(),
@@ -141,10 +213,11 @@ fn evaluate(expr: &Expr, environment: &mut Environment) -> Result<LiteralType, I
                     message: format!("Uninitialized variable {}.", name.lexeme),
                 })
             })
-            .map_err(InterpreterError::RuntimeError),
+            .map_err(InterpreterSignal::RuntimeError),
         Expr::Assign { name, value } => {
             let value = evaluate(value, environment)?;
-            environment
+            curr_environment
+                .borrow_mut()
                 .assign(name, value.clone())
                 .map_err(|_| RuntimeError {
                     token: name.clone(),
@@ -166,6 +239,38 @@ fn evaluate(expr: &Expr, environment: &mut Environment) -> Result<LiteralType, I
 
             evaluate(right, environment)
         }
+        Expr::Call {
+            callee,
+            paren,
+            args,
+        } => {
+            let callee_result = evaluate(callee, environment)?;
+
+            let mut arguments = Vec::new();
+            for arg in args {
+                arguments.push(evaluate(arg, environment)?);
+            }
+
+            match callee_result {
+                LiteralType::Callable(function) => {
+                    if arguments.len() as u8 != function.arity() {
+                        Err(RuntimeError {
+                            token: paren.clone(),
+                            message: format!(
+                                "Expected {} arguments but got {}.",
+                                function.arity(),
+                                args.len()
+                            ),
+                        })?
+                    }
+                    Ok(function.call(&arguments, environment)?)
+                }
+                _ => Err(RuntimeError {
+                    token: paren.clone(),
+                    message: "Can only call functions and classes".to_string(),
+                })?,
+            }
+        }
     }
 }
 
@@ -173,8 +278,8 @@ fn ternary(
     first: &Expr,
     second: &Expr,
     third: &Expr,
-    environment: &mut Environment,
-) -> Result<LiteralType, InterpreterError> {
+    environment: &InterpreterEnvironment,
+) -> InterpreterResult {
     let first = evaluate(first, environment)?;
     if is_truthy(&first) {
         return evaluate(second, environment);
@@ -182,11 +287,7 @@ fn ternary(
     evaluate(third, environment)
 }
 
-fn binary(
-    left: &LiteralType,
-    right: &LiteralType,
-    op: &Token,
-) -> Result<LiteralType, InterpreterError> {
+fn binary(left: &LiteralType, right: &LiteralType, op: &Token) -> InterpreterResult {
     use LiteralType::{Bool, Number, String};
     use TokenType::{
         BangEqual, Comma, EqualEqual, Greater, GreaterEqual, Less, LessEqual, Minus, Plus, Slash,
@@ -232,10 +333,14 @@ fn is_truthy(literal: &LiteralType) -> bool {
     }
 }
 
-fn is_equal(left: &LiteralType, right: &LiteralType) -> bool {
+pub fn is_equal(left: &LiteralType, right: &LiteralType) -> bool {
     match (left, right) {
         (LiteralType::Nil, LiteralType::Nil) => true,
         (LiteralType::Nil, _) => false,
-        _ => left == right,
+        // i could've implemeneted PartialEq but it doesn't make sense for every LiteralType
+        (LiteralType::String(s), LiteralType::String(s2)) => s == s2,
+        (LiteralType::Number(n1), LiteralType::Number(n2)) => n1 == n2,
+        (LiteralType::Bool(t1), LiteralType::Bool(t2)) => t1 == t2,
+        _ => false,
     }
 }

src/lib.rs

@@ -13,6 +13,7 @@ use scanner::Scanner;
 use token::TokenType;
 
 mod ast;
+mod callable;
 mod environment;
 mod interpreter;
 mod parser;

src/parser.rs

@@ -55,7 +55,9 @@ impl Parser<'_> {
     }
 
     fn declaration(&mut self) -> Result<Stmt, ParseError> {
-        let stmt = if self.match_token(&[TokenType::Var]) {
+        let stmt = if self.match_token(&[TokenType::Fun]) {
+            self.function("function")
+        } else if self.match_token(&[TokenType::Var]) {
             self.var_declaration()
         } else {
             self.statement()
@@ -64,6 +66,42 @@ impl Parser<'_> {
         stmt.inspect_err(|_| self.synchronize())
     }
 
+    fn function(&mut self, kind: &str) -> Result<Stmt, ParseError> {
+        let name = self.consume(TokenType::Identifier, &format!("Expect {} name.", kind))?;
+        self.consume(
+            TokenType::LeftParen,
+            &format!("Expect '(' after {kind} name."),
+        )?;
+        let mut params = Vec::new();
+        if !self.check(TokenType::RightParen) {
+            loop {
+                if params.len() >= 255 {
+                    return Err(ParseError {
+                        token: self.peek().clone(),
+                        msg: "Can't have more than 255 parameters".to_string(),
+                    });
+                }
+
+                params.push(self.consume(TokenType::Identifier, "Expect parameter name.")?);
+
+                if !self.match_token(&[TokenType::Comma]) {
+                    break;
+                }
+            }
+        }
+
+        self.consume(TokenType::RightParen, "Expect ')' after parameters")?;
+
+        self.consume(
+            TokenType::LeftBrace,
+            &format!("Expect '{{' before {} body.", kind),
+        )?;
+
+        let body = self.block()?;
+
+        Ok(Stmt::Function { name, params, body })
+    }
+
     fn var_declaration(&mut self) -> Result<Stmt, ParseError> {
         let name = self.consume(TokenType::Identifier, "Expect variable name")?;
         let initializer = if self.match_token(&[TokenType::Equal]) {
@@ -90,6 +128,9 @@ impl Parser<'_> {
         if self.match_token(&[TokenType::Print]) {
             return self.print_statement();
         }
+        if self.match_token(&[TokenType::Return]) {
+            return self.return_statement();
+        }
         if self.match_token(&[TokenType::While]) {
             return self.while_statement();
         }
@@ -227,6 +268,19 @@ impl Parser<'_> {
         Ok(Stmt::Print { expression })
     }
 
+    fn return_statement(&mut self) -> Result<Stmt, ParseError> {
+        let keyword = self.previous().clone();
+        let value = if !self.check(TokenType::Semicolon) {
+            Some(self.expression()?)
+        } else {
+            None
+        };
+
+        self.consume(TokenType::Semicolon, "Expect ';' after return value.");
+
+        Ok(Stmt::Return { keyword, value })
+    }
+
     fn expression_statement(&mut self) -> Result<Stmt, ParseError> {
         let expression = self.expression()?;
         self.consume(TokenType::Semicolon, "Expect ';' after expression.")?;
@@ -348,7 +402,46 @@ impl Parser<'_> {
             });
         }
 
-        self.primary()
+        self.call()
+    }
+
+    fn call(&mut self) -> Result<Expr, ParseError> {
+        let mut expr = self.primary()?;
+
+        loop {
+            if self.match_token(&[TokenType::LeftParen]) {
+                expr = self.finish_call(expr)?;
+            } else {
+                break;
+            }
+        }
+
+        Ok(expr)
+    }
+
+    fn finish_call(&mut self, callee: Expr) -> Result<Expr, ParseError> {
+        let mut args = Vec::new();
+        if !self.check(TokenType::RightParen) {
+            loop {
+                if args.len() >= 255 {
+                    return Err(ParseError {
+                        token: self.peek().clone(),
+                        msg: "Can't have more than 255 arguments".to_string(),
+                    });
+                }
+                args.push(self.equality()?);
+                if !self.match_token(&[TokenType::Comma]) {
+                    break;
+                }
+            }
+        }
+        let paren = self.consume(TokenType::RightParen, "Expect ')' after arguments")?;
+
+        Ok(Expr::Call {
+            callee: Box::new(callee),
+            paren,
+            args,
+        })
     }
 
     /* error boundaries:

src/printer.rs

@@ -9,6 +9,7 @@ pub fn pretty_print(expr: &Expr) -> String {
             LiteralType::Number(v) => v.to_string(),
             LiteralType::Bool(v) => v.to_string(),
             LiteralType::Nil => "Nil".to_string(),
+            LiteralType::Callable(_) => todo!(),
         },
         Expr::Unary { op, right } => parenthesize(&op.lexeme, &[right]),
         Expr::Ternary {
@@ -19,6 +20,11 @@ pub fn pretty_print(expr: &Expr) -> String {
         Expr::Variable { name } => name.lexeme.clone(),
         Expr::Assign { name, value } => parenthesize(&name.lexeme, &[value]),
         Expr::Logical { left, op, right } => parenthesize(&op.lexeme, &[left, right]),
+        Expr::Call {
+            callee: _,
+            paren: _,
+            args: _,
+        } => todo!(),
     }
 }
 

src/scanner.rs

@@ -273,6 +273,8 @@ fn get_identified_keyword(identifier: &str) -> Option<TokenType> {
 
 #[cfg(test)]
 mod tests {
+    use crate::interpreter::is_equal;
+
     use super::*;
     use TokenType::*;
 
@@ -325,7 +327,10 @@ mod tests {
 
         let expected = LiteralType::String("salam!".to_string());
 
-        assert_eq!(expected, actual.literal.as_ref().unwrap().clone());
+        assert!(is_equal(
+            &expected,
+            &actual.literal.as_ref().unwrap().clone(),
+        ))
     }
 
     #[test]
@@ -375,7 +380,10 @@ mod tests {
 
         let actual_value = &token.literal;
 
-        assert_eq!(expected_value, actual_value.as_ref().unwrap().clone())
+        assert!(is_equal(
+            &expected_value,
+            &actual_value.as_ref().unwrap().clone()
+        ))
     }
 
     #[test]
@@ -398,6 +406,9 @@ mod tests {
 
         let actual_value = &token.literal;
 
-        assert_eq!(expected_value, actual_value.as_ref().unwrap().clone())
+        assert!(is_equal(
+            &expected_value,
+            &actual_value.as_ref().unwrap().clone()
+        ))
     }
 }

src/token.rs

@@ -1,5 +1,7 @@
 use std::fmt::Display;
 
+use crate::callable::Callable;
+
 #[derive(Debug, PartialEq, Clone, Copy)]
 pub enum TokenType {
     LeftParen,
@@ -51,12 +53,13 @@ pub enum TokenType {
 }
 
 // i've seen this implementation in the wild
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone)]
 pub enum LiteralType {
     String(String),
     Number(f64),
     Bool(bool),
     Nil,
+    Callable(Callable),
 }
 
 impl LiteralType {
@@ -76,6 +79,7 @@ impl Display for LiteralType {
             LiteralType::Number(v) => write!(f, "{v:.2}"),
             LiteralType::Bool(v) => write!(f, "{v}"),
             LiteralType::Nil => write!(f, "nil"),
+            LiteralType::Callable(c) => write!(f, "<fn {c}>"),
         }
     }
 }