implement chapter 12 in rust

rust/rox/src/class.rs

@@ -0,0 +1,58 @@
+use std::{collections::HashMap, fmt::Display};
+
+use crate::{
+    callable::{Callable, CallingError},
+    function::Function,
+    instance::Instance,
+    value::Value,
+};
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Class {
+    pub name: String,
+    pub methods: HashMap<String, Function>,
+}
+
+impl Display for Class {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.name)
+    }
+}
+
+impl Class {
+    pub fn new(name: String, methods: HashMap<String, Function>) -> Self {
+        Self { name, methods }
+    }
+
+    pub fn find_method(&self, name: &str) -> Option<&Function> {
+        self.methods.get(name)
+    }
+}
+
+impl Callable for Class {
+    fn name(&self) -> String {
+        self.name.clone()
+    }
+
+    fn arity(&self) -> usize {
+        if let Some(initializer) = self.find_method("init") {
+            initializer.arity()
+        } else {
+            0
+        }
+    }
+
+    fn call(
+        &self,
+        interpreter: &mut crate::interpreter::Interpreter,
+        args: Vec<crate::value::Value>,
+    ) -> Result<Value, CallingError> {
+        let class = self.clone();
+        let instance = Instance::new(class);
+        if let Some(initializer) = self.find_method("init") {
+            initializer.bind(instance.clone()).call(interpreter, args)?;
+        };
+
+        Ok(Value::Instance(instance))
+    }
+}

rust/rox/src/expression.rs

@@ -17,6 +17,18 @@ pub enum Expression {
         paren: Token,
         args: Vec<Expression>,
     },
+    Get {
+        object: Box<Expression>,
+        name: Token,
+    },
+    Set {
+        object: Box<Expression>,
+        name: Token,
+        value: Box<Expression>,
+    },
+    This {
+        keyword: Token,
+    },
     Grouping {
         expression: Box<Expression>,
     },

rust/rox/src/function.rs

@@ -1,6 +1,7 @@
 use crate::{
     callable::{Callable, CallingError},
     environment::Environment,
+    instance::Instance,
     interpreter::Interpreter,
     statement::Statement,
     token::Token,
@@ -13,6 +14,7 @@ use std::{cell::RefCell, fmt::Display, rc::Rc};
 #[derive(Debug, Clone)]
 pub struct Function {
     pub name: Token,
+    pub is_initializer: bool,
     pub params: Vec<Token>,
     pub body: Vec<Statement>,
     pub closure: Rc<RefCell<Environment>>,
@@ -52,10 +54,24 @@ impl Callable for Function {
             env.define(param.lexeme.clone(), arg);
         }
 
-        let result = interpreter
+        Ok(interpreter
             .block(&self.body, env)
             .map_err(|e| CallingError::CallInterpretationFailed(e.to_string()))?
-            .unwrap_or(Value::Nil);
-        Ok(result)
+            .unwrap_or(Value::Nil))
+    }
+}
+
+impl Function {
+    pub fn bind(&self, instance: Rc<RefCell<Instance>>) -> Self {
+        let mut env = Environment::with_enclosing(self.closure.clone());
+        env.define("this".to_string(), Value::Instance(instance));
+
+        Self {
+            name: self.name.clone(),
+            is_initializer: self.is_initializer,
+            params: self.params.clone(),
+            body: self.body.clone(),
+            closure: Rc::new(RefCell::new(env)),
+        }
     }
 }

rust/rox/src/instance.rs

@@ -0,0 +1,49 @@
+use std::{cell::RefCell, collections::HashMap, fmt::Display, rc::Rc};
+
+use thiserror::Error;
+
+use crate::{class::Class, token::Token, value::Value};
+
+#[derive(Error, Debug)]
+pub enum InstanceError {
+    #[error("line {0}: no property named {1}.")]
+    NoSuchProperty(usize, String),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Instance {
+    class: Class,
+    fields: HashMap<String, Value>,
+}
+
+impl Display for Instance {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{} instance", self.class.name)
+    }
+}
+
+impl Instance {
+    pub fn new(class: Class) -> Rc<RefCell<Self>> {
+        Rc::new(RefCell::new(Self {
+            class,
+            fields: HashMap::default(),
+        }))
+    }
+
+    pub fn get(&self, name: &Token, instance: Rc<RefCell<Self>>) -> Result<Value, InstanceError> {
+        if let Some(field) = self.fields.get(name.lexeme.as_str()) {
+            Ok(field.clone())
+        } else if let Some(method) = self.class.find_method(name.lexeme.as_str()) {
+            Ok(Value::Callable(Rc::new(method.bind(instance))))
+        } else {
+            Err(InstanceError::NoSuchProperty(
+                name.line,
+                name.lexeme.clone(),
+            ))
+        }
+    }
+
+    pub fn set(&mut self, name: &Token, value: Value) {
+        self.fields.insert(name.lexeme.clone(), value);
+    }
+}

rust/rox/src/interpreter.rs

@@ -6,9 +6,10 @@ use tracing::error;
 
 use crate::{
     callable::CallingError,
+    class::Class,
     environment::{Environment, EnvironmentError},
     expression::Expression,
-    function::Function,
+    function::{self, Function},
     native_functions,
     statement::Statement,
     token::{Literal, Token, TokenType},
@@ -33,6 +34,10 @@ pub enum InterpreterError {
     NotACallable(usize, Value),
     #[error("line {0}: {1}.")]
     FailedToCall(usize, CallingError),
+    #[error("line {0}: only instances have fields.")]
+    OnlyInstancesHaveFields(usize),
+    #[error("{0}")]
+    InstanceError(#[from] crate::instance::InstanceError),
 }
 
 /// Interpreter for the Lox language.
@@ -106,6 +111,7 @@ impl Interpreter {
                 self.function_statement(name, params, body)
             }
             Statement::Return { keyword: _, value } => self.return_statement(value),
+            Statement::Class { name, methods } => self.class(name, methods),
         }
     }
 
@@ -138,6 +144,39 @@ impl Interpreter {
         Ok(None)
     }
 
+    fn class(
+        &mut self,
+        name: &Token,
+        methods: &[Statement],
+    ) -> Result<Option<Value>, InterpreterError> {
+        self.environment
+            .borrow_mut()
+            .define(name.lexeme.clone(), Value::Nil);
+
+        let mut class_methods: HashMap<String, Function> = HashMap::new();
+
+        for method in methods {
+            if let Statement::Function { name, params, body } = method {
+                let function = function::Function {
+                    name: name.clone(),
+                    is_initializer: name.lexeme == "init",
+                    params: params.clone(),
+                    body: body.clone(),
+                    closure: self.environment.clone(),
+                };
+                class_methods.insert(name.lexeme.clone(), function);
+            }
+        }
+
+        let class = Class::new(name.lexeme.clone(), class_methods);
+        self.environment
+            .borrow_mut()
+            .assign(name, Value::Callable(Rc::new(class)))
+            .map_err(InterpreterError::UndefinedVariable)?;
+
+        Ok(None)
+    }
+
     /// Evaluate an expression and return its value.
     fn evaluate(&mut self, expression: &Expression) -> Result<Value, InterpreterError> {
         match expression {
@@ -164,6 +203,13 @@ impl Interpreter {
                 paren,
                 args,
             } => self.call(callee, paren, args),
+            Expression::Get { object, name } => self.get(object, name),
+            Expression::Set {
+                object,
+                name,
+                value,
+            } => self.set(object, name, value),
+            Expression::This { keyword } => self.lookup_var(keyword, expression),
         }
     }
 
@@ -190,6 +236,29 @@ impl Interpreter {
         }
     }
 
+    fn get(&mut self, object: &Expression, name: &Token) -> Result<Value, InterpreterError> {
+        match self.evaluate(object)? {
+            Value::Instance(instance) => Ok(instance.borrow().get(name, instance.clone())?),
+            _ => Err(InterpreterError::OnlyInstancesHaveFields(name.line)),
+        }
+    }
+    fn set(
+        &mut self,
+        object: &Expression,
+        name: &Token,
+        value: &Expression,
+    ) -> Result<Value, InterpreterError> {
+        match self.evaluate(object)? {
+            Value::Instance(instance) => {
+                let value = self.evaluate(value)?;
+                instance.borrow_mut().set(name, value.clone());
+
+                Ok(value)
+            }
+            _ => Err(InterpreterError::OnlyInstancesHaveFields(name.line)),
+        }
+    }
+
     /// Define a new function.
     fn function_statement(
         &mut self,
@@ -200,6 +269,7 @@ impl Interpreter {
         let fn_name = name.lexeme.clone();
         let fun = Function {
             name: name.clone(),
+            is_initializer: false,
             params: params.to_vec(),
             body: body.to_vec(),
             closure: self.environment.clone(),

rust/rox/src/lib.rs

@@ -14,10 +14,12 @@ use thiserror::Error;
 use tracing::error;
 
 pub mod callable;
+pub mod class;
 pub mod cli;
 pub mod environment;
 pub mod expression;
 pub mod function;
+pub mod instance;
 pub mod interpreter;
 pub mod keywords;
 pub mod native_functions;

rust/rox/src/parser.rs

@@ -25,6 +25,8 @@ pub enum ParserError {
     SemicolonAfterValueExpected(usize),
     #[error("line {0}: expected ';' after expression.")]
     SemicolonAfterExpressionExpected(usize),
+    #[error("line {0}: expected class name.")]
+    ClassNameExpected(usize),
     #[error("line {0}: expected variable name.")]
     VariableNameExpected(usize),
     #[error("line {0}: invalid assignment target.")]
@@ -57,6 +59,12 @@ pub enum ParserError {
     LeftBraceBeforeFunctionBodyExpected(usize),
     #[error("line {0}: expected ';' after return value.")]
     SemicolonAfterReturnExpected(usize),
+    #[error("line {0}: expected '{{' before class body.")]
+    LeftBraceBeforeClassExpected(usize),
+    #[error("line {0}: expected '}}' after class body.")]
+    RightBraceAfterClassExpected(usize),
+    #[error("line {0}: expected property name after '.'.")]
+    PropertyNameAfterDotExpected(usize),
 }
 
 /// Parse the Lox language.
@@ -174,7 +182,9 @@ impl Parser {
     }
 
     fn declaration(&mut self) -> Result<Statement, ParserError> {
-        if self.matches(&[Fun]) {
+        if self.matches(&[Class]) {
+            self.class_declaration()
+        } else if self.matches(&[Fun]) {
             self.function()
         } else if self.matches(&[Var]) {
             self.var_declaration()
@@ -297,6 +307,28 @@ impl Parser {
         Ok(Statement::Return { keyword, value })
     }
 
+    fn class_declaration(&mut self) -> Result<Statement, ParserError> {
+        let line = self.current_token.line;
+        let name = self
+            .consume(&Identifier)
+            .ok_or(ParserError::ClassNameExpected(line))?
+            .clone();
+
+        self.consume(&LeftBrace)
+            .ok_or(ParserError::LeftBraceBeforeClassExpected(line))?;
+
+        let mut methods = Vec::new();
+        while !self.check(&RightBrace) && !self.is_at_end() {
+            let method = self.function()?;
+            methods.push(method);
+        }
+
+        self.consume(&RightBrace)
+            .ok_or(ParserError::RightBraceAfterClassExpected(line))?;
+
+        Ok(Statement::Class { name, methods })
+    }
+
     fn var_declaration(&mut self) -> Result<Statement, ParserError> {
         let line = self.current_token.line;
         let name = self
@@ -409,6 +441,12 @@ impl Parser {
                     name,
                     value: Box::new(value),
                 })
+            } else if let Expression::Get { object, name } = expr {
+                Ok(Expression::Set {
+                    object,
+                    name,
+                    value: Box::new(value),
+                })
             } else {
                 Err(ParserError::InvalidAssignmentTarget(equals.line))
             }
@@ -490,6 +528,17 @@ impl Parser {
         loop {
             if self.matches(&[LeftParen]) {
                 expr = self.finish_call(expr)?;
+            } else if self.matches(&[Dot]) {
+                let line = self.current_token.line;
+
+                let name = self
+                    .consume(&Identifier)
+                    .ok_or(ParserError::PropertyNameAfterDotExpected(line))?
+                    .clone();
+                expr = Expression::Get {
+                    object: Box::new(expr),
+                    name,
+                }
             } else {
                 break;
             }
@@ -536,6 +585,10 @@ impl Parser {
             Ok(Expression::Literal {
                 value: token::Literal::Nil,
             })
+        } else if self.matches(&[This]) {
+            Ok(Expression::This {
+                keyword: self.previous()?.clone(),
+            })
         } else if self.matches(&[Identifier]) {
             let prev = self.previous()?.clone();
             Ok(Expression::Variable { name: prev })

rust/rox/src/resolver.rs

@@ -10,12 +10,24 @@ pub enum ResolverError {
     NameRedefinition(usize),
     #[error("line {0}: can not return from top-level code.")]
     TopLevelReturn(usize),
+    #[error("line {0}: can not use 'this' outside of a class.")]
+    ThisOutsideClass(usize),
+    #[error("line {0}: can not return a value from an initializer.")]
+    ReturnFromInitializer(usize),
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 enum FunctionType {
     None,
     Function,
+    Initializer,
+    Method,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum ClassType {
+    None,
+    Class,
 }
 
 #[derive(Debug)]
@@ -23,6 +35,7 @@ pub struct Resolver<'a> {
     scopes: Vec<HashMap<String, bool>>,
     interpreter: &'a mut Interpreter,
     current_fun: FunctionType,
+    current_class: ClassType,
 }
 
 impl<'a> Resolver<'a> {
@@ -31,6 +44,7 @@ impl<'a> Resolver<'a> {
             scopes: Vec::default(),
             interpreter,
             current_fun: FunctionType::None,
+            current_class: ClassType::None,
         }
     }
 
@@ -60,16 +74,8 @@ impl<'a> Resolver<'a> {
             Statement::Function { name, params, body } => {
                 self.resolve_function_stmt(name, params, body)
             }
-            Statement::Return { keyword, value } => {
-                if self.current_fun == FunctionType::None {
-                    return Err(ResolverError::TopLevelReturn(keyword.line));
-                }
-                if let Some(value) = value {
-                    self.resolve_expression(value)
-                } else {
-                    Ok(())
-                }
-            }
+            Statement::Return { keyword, value } => self.resolve_return_stmt(keyword, value),
+            Statement::Class { name, methods } => self.resolve_class_stmt(name, methods),
         }
     }
 
@@ -95,6 +101,19 @@ impl<'a> Resolver<'a> {
             } => self.resolve_binary_expr(left, right),
             Expression::Unary { operator: _, right } => self.resolve_expression(right),
             Expression::Variable { name } => self.resolve_var_expr(expr, name),
+            Expression::Get { object, name: _ } => self.resolve_expression(object),
+            Expression::Set {
+                object,
+                name: _,
+                value,
+            } => self.resolve_set_expression(object, value),
+            Expression::This { keyword } => {
+                if self.current_class == ClassType::None {
+                    return Err(ResolverError::ThisOutsideClass(keyword.line));
+                }
+
+                self.resolve_local(expr, keyword)
+            }
         }
     }
 
@@ -132,6 +151,59 @@ impl<'a> Resolver<'a> {
         Ok(())
     }
 
+    fn resolve_class_stmt(
+        &mut self,
+        name: &Token,
+        methods: &[Statement],
+    ) -> Result<(), ResolverError> {
+        let enclosing_class = self.current_class;
+        self.current_class = ClassType::Class;
+
+        self.declare(name)?;
+        self.define(name);
+
+        self.begin_scope();
+
+        if let Some(scope) = self.scopes.last_mut() {
+            scope.insert("this".to_string(), true);
+        }
+
+        for method in methods {
+            if let Statement::Function { name, params, body } = method {
+                let declaration = if name.lexeme == "init" {
+                    FunctionType::Initializer
+                } else {
+                    FunctionType::Method
+                };
+                self.resolve_function(params, body, declaration)?;
+            }
+        }
+
+        self.end_scope();
+
+        self.current_class = enclosing_class;
+
+        Ok(())
+    }
+
+    fn resolve_return_stmt(
+        &mut self,
+        keyword: &Token,
+        value: &Option<Expression>,
+    ) -> Result<(), ResolverError> {
+        if self.current_fun == FunctionType::None {
+            return Err(ResolverError::TopLevelReturn(keyword.line));
+        }
+        if let Some(value) = value {
+            if self.current_fun == FunctionType::Initializer {
+                return Err(ResolverError::ReturnFromInitializer(keyword.line));
+            }
+            self.resolve_expression(value)
+        } else {
+            Ok(())
+        }
+    }
+
     fn resolve_var(
         &mut self,
         name: &Token,
@@ -205,6 +277,17 @@ impl<'a> Resolver<'a> {
         Ok(())
     }
 
+    fn resolve_set_expression(
+        &mut self,
+        object: &Expression,
+        value: &Expression,
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(value)?;
+        self.resolve_expression(object)?;
+
+        Ok(())
+    }
+
     fn resolve_if_stmt(
         &mut self,
         condition: &Expression,

rust/rox/src/statement.rs

@@ -28,4 +28,8 @@ pub enum Statement {
         keyword: Token,
         value: Option<Expression>,
     },
+    Class {
+        name: Token,
+        methods: Vec<Statement>,
+    },
 }

rust/rox/src/value.rs

@@ -1,8 +1,8 @@
-use std::{fmt::Display, rc::Rc};
+use std::{cell::RefCell, fmt::Display, rc::Rc};
 
 use ordered_float::OrderedFloat;
 
-use crate::{callable::Callable, token::Literal};
+use crate::{callable::Callable, instance, token::Literal};
 
 /// Concrete value in the interpreter.
 #[derive(Clone, Debug, PartialEq)]
@@ -12,6 +12,7 @@ pub enum Value {
     String(String),
     Number(OrderedFloat<f64>),
     Boolean(bool),
+    Instance(Rc<RefCell<instance::Instance>>),
     Nil,
 }
 
@@ -23,6 +24,7 @@ impl Display for Value {
             Value::String(x) => write!(f, "{x}"),
             Value::Number(x) => write!(f, "{x}"),
             Value::Boolean(x) => write!(f, "{x}"),
+            Value::Instance(x) => write!(f, "{}", x.borrow()),
             Value::Nil => write!(f, "nil"),
         }
     }