implement chapter 11 in rust

lox/fibonacci.lox

@@ -0,0 +1,9 @@
+var a = 0;
+var temp;
+
+var b = 1;
+for(var b = 1; a < 1000; b = temp + b) {
+    print a;
+    temp = a;
+    a = b;
+}

lox/name_redefinition.lox

@@ -0,0 +1,4 @@
+fun bad() {
+  var a = "first";
+  var a = "second";
+}

lox/scoping.lox

@@ -0,0 +1,10 @@
+var a = "global";
+{
+  fun showA() {
+    print a;
+  }
+
+  showA();
+  var a = "block";
+  showA();
+}

lox/top_level_return.lox

@@ -0,0 +1 @@
+return "at top level";

rust/rox/Cargo.lock

@@ -61,6 +61,12 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "autocfg"
+version = "1.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ace50bade8e6234aa140d9a2f552bbee1db4d353f69b8217bc503490fc1a9f26"
+
 [[package]]
 name = "cfg-if"
 version = "1.0.0"
@@ -162,12 +168,30 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "num-traits"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.20.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1261fe7e33c73b354eab43b1273a57c8f967d0391e80353e51f764ac02cf6775"
 
+[[package]]
+name = "ordered-float"
+version = "5.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e2c1f9f56e534ac6a9b8a4600bdf0f530fb393b5f393e7b4d03489c3cf0c3f01"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "overload"
 version = "0.1.1"
@@ -248,6 +272,7 @@ version = "0.1.0"
 dependencies = [
  "clap",
  "lazy_static",
+ "ordered-float",
  "thiserror",
  "tracing",
  "tracing-subscriber",

rust/rox/Cargo.toml

@@ -8,6 +8,7 @@ authors = ["Sebastian Hugentobler <shu@vanwa.ch>"]
 [dependencies]
 clap = { version = "4.5.28", features = ["derive"] }
 lazy_static = "1.5.0"
+ordered-float = "5.0.0"
 thiserror = "2.0.11"
 tracing = "0.1.41"
 tracing-subscriber = { version = "0.3.19", features = ["env-filter"] }

rust/rox/src/environment.rs

@@ -8,6 +8,8 @@ use crate::{token::Token, value::Value};
 pub enum EnvironmentError {
     #[error("line {0}: undefined variable: {1}")]
     UndefinedVariable(usize, String),
+    #[error("invalid environment distance")]
+    InvalidDistance,
 }
 
 /// Environment mapping variable names to their respective values. Can have an optional enclosing
@@ -50,6 +52,18 @@ impl Environment {
         }
     }
 
+    pub fn assign_at(
+        &mut self,
+        distance: usize,
+        token: &Token,
+        value: Value,
+    ) -> Result<(), EnvironmentError> {
+        self.ancestor(distance)?
+            .values
+            .insert(token.lexeme.clone(), value);
+        Ok(())
+    }
+
     /// Get the value of an existing (defined) variable. Error if there is no such variable in
     /// this environment or any of the enclosing ones.
     pub fn get(&self, token: &Token) -> Result<Value, EnvironmentError> {
@@ -64,4 +78,29 @@ impl Environment {
             ))
         }
     }
+
+    pub fn get_at(&self, distance: usize, token: &Token) -> Result<Value, EnvironmentError> {
+        if let Some(v) = self.ancestor(distance)?.values.get(token.lexeme.as_str()) {
+            Ok(v.clone())
+        } else {
+            Err(EnvironmentError::UndefinedVariable(
+                token.line,
+                token.lexeme.clone(),
+            ))
+        }
+    }
+
+    fn ancestor(&self, distance: usize) -> Result<Environment, EnvironmentError> {
+        let mut environment = self.clone();
+
+        for _ in 0..distance {
+            let enclosing = match &environment.enclosing {
+                Some(enc) => enc.borrow().clone(),
+                None => return Err(EnvironmentError::InvalidDistance),
+            };
+            environment = enclosing;
+        }
+
+        Ok(environment)
+    }
 }

rust/rox/src/expression.rs

@@ -1,7 +1,7 @@
 use crate::token::{self, Token};
 
 /// Enumeration of all types of expressions.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub enum Expression {
     Assign {
         name: Token,

rust/rox/src/interpreter.rs

@@ -1,5 +1,6 @@
-use std::{cell::RefCell, rc::Rc};
+use std::{cell::RefCell, collections::HashMap, rc::Rc};
 
+use ordered_float::OrderedFloat;
 use thiserror::Error;
 use tracing::error;
 
@@ -39,6 +40,7 @@ pub enum InterpreterError {
 pub struct Interpreter {
     pub globals: Rc<RefCell<Environment>>,
     environment: Rc<RefCell<Environment>>,
+    locals: HashMap<Expression, usize>,
 }
 
 /// Default configuration for the interpreter, with builtin native functions.
@@ -57,6 +59,7 @@ impl Default for Interpreter {
         Self {
             globals: env.clone(),
             environment: env.clone(),
+            locals: HashMap::new(),
         }
     }
 }
@@ -74,6 +77,10 @@ impl Interpreter {
         Ok(())
     }
 
+    pub fn resolve(&mut self, expression: Expression, depth: usize) {
+        self.locals.insert(expression, depth);
+    }
+
     ///Execute a statement.
     fn execute(&mut self, statement: &Statement) -> Result<Option<Value>, InterpreterError> {
         match statement {
@@ -145,7 +152,7 @@ impl Interpreter {
                 operator,
                 right,
             } => self.binary(left, operator, right),
-            Expression::Variable { name } => self.var_expression(name),
+            Expression::Variable { name } => self.var_expression(name, expression),
             Expression::Assign { name, value } => self.assign(name, value),
             Expression::Logical {
                 left,
@@ -276,13 +283,26 @@ impl Interpreter {
     }
 
     /// Assign the value of an expression to a variable.
-    fn assign(&mut self, name: &Token, value: &Expression) -> Result<Value, InterpreterError> {
-        let value = self.evaluate(value)?;
+    fn assign(&mut self, name: &Token, expression: &Expression) -> Result<Value, InterpreterError> {
+        let value = self.evaluate(expression)?;
 
         self.environment
             .borrow_mut()
             .assign(name, value.clone())
             .map_err(InterpreterError::UndefinedVariable)?;
+
+        if let Some(distance) = self.locals.get(expression) {
+            self.environment
+                .borrow_mut()
+                .assign_at(*distance, name, value.clone())
+                .map_err(InterpreterError::UndefinedVariable)?;
+        } else {
+            self.globals
+                .borrow_mut()
+                .assign(name, value.clone())
+                .map_err(InterpreterError::UndefinedVariable)?;
+        }
+
         Ok(value)
     }
 
@@ -340,12 +360,31 @@ impl Interpreter {
     }
 
     /// Get the value of a variable.
-    fn var_expression(&mut self, name: &Token) -> Result<Value, InterpreterError> {
+    fn var_expression(
+        &mut self,
+        name: &Token,
+        expression: &Expression,
+    ) -> Result<Value, InterpreterError> {
+        self.lookup_var(name, expression)
+    }
+
+    fn lookup_var(
+        &mut self,
+        name: &Token,
+        expression: &Expression,
+    ) -> Result<Value, InterpreterError> {
+        if let Some(distance) = self.locals.get(expression) {
             self.environment
+                .borrow()
+                .get_at(*distance, name)
+                .map_err(InterpreterError::UndefinedVariable)
+        } else {
+            self.globals
                 .borrow()
                 .get(name)
                 .map_err(InterpreterError::UndefinedVariable)
         }
+    }
 
     /// Calculate number operations.
     fn number_op(&self, left: f64, op: TokenType, right: f64) -> f64 {
@@ -383,7 +422,11 @@ impl Interpreter {
         match op.token_type {
             TokenType::Minus | TokenType::Slash | TokenType::Star | TokenType::Plus => {
                 if let (Value::Number(left), Value::Number(right)) = (left.clone(), right.clone()) {
-                    Ok(Value::Number(self.number_op(left, op.token_type, right)))
+                    Ok(Value::Number(OrderedFloat(self.number_op(
+                        *left,
+                        op.token_type,
+                        *right,
+                    ))))
                 } else if let (Value::String(left), Value::String(right)) = (left, right) {
                     Ok(Value::String(format!("{}{}", left.clone(), right.clone())))
                 } else {
@@ -397,7 +440,11 @@ impl Interpreter {
             | TokenType::Less
             | TokenType::LessEqual => {
                 if let (Value::Number(left), Value::Number(right)) = (left, right) {
-                    Ok(Value::Boolean(self.boolean_op(left, op.token_type, right)))
+                    Ok(Value::Boolean(self.boolean_op(
+                        *left,
+                        op.token_type,
+                        *right,
+                    )))
                 } else {
                     Err(InterpreterError::BinaryExpressionNeedsNumber(op.line))
                 }

rust/rox/src/lib.rs

@@ -7,7 +7,10 @@ use std::{
     path::Path,
 };
 
-use interpreter::Interpreter;
+use interpreter::{Interpreter, InterpreterError};
+use parser::ParserError;
+use resolver::{Resolver, ResolverError};
+use thiserror::Error;
 use tracing::error;
 
 pub mod callable;
@@ -19,6 +22,7 @@ pub mod interpreter;
 pub mod keywords;
 pub mod native_functions;
 pub mod parser;
+pub mod resolver;
 pub mod scanner;
 pub mod statement;
 pub mod token;
@@ -35,6 +39,16 @@ pub mod tokenizer {
 }
 pub mod value;
 
+#[derive(Error, Debug)]
+pub enum RoxError {
+    #[error("parser failed: {0}")]
+    ParseError(#[from] ParserError),
+    #[error("resolver failed: {0}")]
+    ResolverError(#[from] ResolverError),
+    #[error("interpreter failed: {0}")]
+    InterpreterError(#[from] InterpreterError),
+}
+
 /// Read the source code in a file and scan it to tokens.
 pub fn compile(source: &Path) -> Result<(), io::Error> {
     let input = fs::read_to_string(source)?;
@@ -64,12 +78,18 @@ pub fn repl() {
 
 /// Evaluate a Lox input string and print errors or output.
 fn run(input: &str, interpreter: &mut Interpreter) {
+    if let Err(e) = run_rox(input, interpreter) {
+        error!("{e}");
+    }
+}
+
+fn run_rox(input: &str, interpreter: &mut Interpreter) -> Result<(), RoxError> {
     let tokens = scanner::tokenize(input);
-    match parser::ast(tokens) {
-        Ok(ast) => match interpreter.run(ast) {
-            Ok(_) => {}
-            Err(e) => error!("{e}"),
-        },
-        Err(e) => error!("{e}"),
-    }
+    let mut resolver = Resolver::new(interpreter);
+
+    let ast = parser::ast(tokens)?;
+    resolver.resolve(&ast)?;
+    interpreter.run(ast)?;
+
+    Ok(())
 }

rust/rox/src/native_functions.rs

@@ -3,6 +3,8 @@ use std::{
     time::{SystemTime, UNIX_EPOCH},
 };
 
+use ordered_float::OrderedFloat;
+
 use crate::{
     callable::{Callable, CallingError},
     interpreter::Interpreter,
@@ -30,7 +32,7 @@ impl Callable for Clock {
             .duration_since(UNIX_EPOCH)
             .map_err(|e| CallingError::CallFailed(e.to_string()))?;
 
-        Ok(Value::Number(since_the_epoch.as_secs_f64()))
+        Ok(Value::Number(OrderedFloat(since_the_epoch.as_secs_f64())))
     }
 }
 

rust/rox/src/resolver.rs

@@ -0,0 +1,273 @@
+use crate::{expression::Expression, interpreter::Interpreter, statement::Statement, token::Token};
+use std::collections::HashMap;
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum ResolverError {
+    #[error("line {0}: can not read local variable in its own initializer.")]
+    ReadVarInOwnInitializer(usize),
+    #[error("line {0}: already a variable with this name in this scope.")]
+    NameRedefinition(usize),
+    #[error("line {0}: can not return from top-level code.")]
+    TopLevelReturn(usize),
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum FunctionType {
+    None,
+    Function,
+}
+
+#[derive(Debug)]
+pub struct Resolver<'a> {
+    scopes: Vec<HashMap<String, bool>>,
+    interpreter: &'a mut Interpreter,
+    current_fun: FunctionType,
+}
+
+impl<'a> Resolver<'a> {
+    pub fn new(interpreter: &'a mut Interpreter) -> Self {
+        Self {
+            scopes: Vec::default(),
+            interpreter,
+            current_fun: FunctionType::None,
+        }
+    }
+
+    pub fn resolve(&mut self, statements: &[Statement]) -> Result<(), ResolverError> {
+        for stm in statements {
+            self.resolve_statement(stm)?;
+        }
+        Ok(())
+    }
+
+    fn resolve_statement(&mut self, statement: &Statement) -> Result<(), ResolverError> {
+        match statement {
+            Statement::Block(statements) => self.resolve_block(statements),
+            Statement::Print(expression) => self.resolve_expression(expression),
+            Statement::Expression(expression) => self.resolve_expression(expression),
+            Statement::Var { name, initializer } => self.resolve_var(name, *initializer.clone()),
+            Statement::If {
+                condition,
+                then_branch,
+                else_branch,
+            } => self.resolve_if_stmt(
+                condition,
+                then_branch,
+                else_branch.as_ref().map(|boxed| *boxed.clone()),
+            ),
+            Statement::While { condition, body } => self.resolve_while_stmt(condition, body),
+            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(())
+                }
+            }
+        }
+    }
+
+    fn resolve_expression(&mut self, expr: &Expression) -> Result<(), ResolverError> {
+        match expr {
+            Expression::Assign { name, value } => self.resolve_assign_expr(expr, name, value),
+            Expression::Binary {
+                left,
+                operator: _,
+                right,
+            } => self.resolve_binary_expr(left, right),
+            Expression::Call {
+                callee,
+                paren: _,
+                args,
+            } => self.resolve_call_expr(callee, args),
+            Expression::Grouping { expression } => self.resolve_expression(expression),
+            Expression::Literal { value: _ } => Ok(()),
+            Expression::Logical {
+                left,
+                operator: _,
+                right,
+            } => self.resolve_binary_expr(left, right),
+            Expression::Unary { operator: _, right } => self.resolve_expression(right),
+            Expression::Variable { name } => self.resolve_var_expr(expr, name),
+        }
+    }
+
+    fn begin_scope(&mut self) {
+        self.scopes.push(HashMap::new());
+    }
+
+    fn end_scope(&mut self) {
+        self.scopes.pop();
+    }
+
+    fn declare(&mut self, name: &Token) -> Result<(), ResolverError> {
+        if let Some(scope) = self.scopes.last_mut() {
+            if scope.contains_key(&name.lexeme) {
+                return Err(ResolverError::NameRedefinition(name.line));
+            }
+
+            scope.insert(name.lexeme.clone(), false);
+        }
+
+        Ok(())
+    }
+
+    fn define(&mut self, name: &Token) {
+        if let Some(scope) = self.scopes.last_mut() {
+            scope.insert(name.lexeme.clone(), true);
+        }
+    }
+
+    fn resolve_block(&mut self, statements: &[Statement]) -> Result<(), ResolverError> {
+        self.begin_scope();
+        self.resolve(statements)?;
+        self.end_scope();
+
+        Ok(())
+    }
+
+    fn resolve_var(
+        &mut self,
+        name: &Token,
+        initializer: Option<Expression>,
+    ) -> Result<(), ResolverError> {
+        self.declare(name)?;
+
+        if let Some(initializer) = initializer {
+            self.resolve_expression(&initializer)?;
+        }
+
+        self.define(name);
+        Ok(())
+    }
+
+    fn resolve_var_expr(&mut self, expr: &Expression, name: &Token) -> Result<(), ResolverError> {
+        if let Some(scope) = self.scopes.last() {
+            if !scope.get(&name.lexeme).unwrap_or(&true) {
+                return Err(ResolverError::ReadVarInOwnInitializer(name.line));
+            }
+        }
+        self.resolve_local(expr, name)?;
+        Ok(())
+    }
+
+    fn resolve_assign_expr(
+        &mut self,
+        expr: &Expression,
+        name: &Token,
+        val: &Expression,
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(val)?;
+        self.resolve_local(expr, name)?;
+        Ok(())
+    }
+
+    fn resolve_binary_expr(
+        &mut self,
+        left: &Expression,
+        right: &Expression,
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(left)?;
+        self.resolve_expression(right)?;
+        Ok(())
+    }
+
+    fn resolve_function_stmt(
+        &mut self,
+        name: &Token,
+        params: &[Token],
+        body: &[Statement],
+    ) -> Result<(), ResolverError> {
+        self.declare(name)?;
+        self.define(name);
+        self.resolve_function(params, body, FunctionType::Function)?;
+
+        Ok(())
+    }
+
+    fn resolve_call_expr(
+        &mut self,
+        callee: &Expression,
+        args: &[Expression],
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(callee)?;
+
+        for arg in args {
+            self.resolve_expression(arg)?;
+        }
+
+        Ok(())
+    }
+
+    fn resolve_if_stmt(
+        &mut self,
+        condition: &Expression,
+        then_branch: &Statement,
+        else_branch: Option<Statement>,
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(condition)?;
+        self.resolve_statement(then_branch)?;
+
+        if let Some(stmt) = else_branch {
+            self.resolve_statement(&stmt)?;
+        }
+
+        Ok(())
+    }
+
+    fn resolve_while_stmt(
+        &mut self,
+        condition: &Expression,
+        body: &Statement,
+    ) -> Result<(), ResolverError> {
+        self.resolve_expression(condition)?;
+        self.resolve_statement(body)?;
+
+        Ok(())
+    }
+
+    fn resolve_function(
+        &mut self,
+        params: &[Token],
+        body: &[Statement],
+        fun_type: FunctionType,
+    ) -> Result<(), ResolverError> {
+        let enclosing_fun = self.current_fun;
+        self.current_fun = fun_type;
+
+        self.begin_scope();
+
+        for param in params {
+            self.declare(param)?;
+            self.define(param);
+        }
+        self.resolve(body)?;
+
+        self.end_scope();
+
+        self.current_fun = enclosing_fun;
+
+        Ok(())
+    }
+
+    fn resolve_local(
+        &mut self,
+        expression: &Expression,
+        name: &Token,
+    ) -> Result<(), ResolverError> {
+        for (idx, scope) in self.scopes.iter().rev().enumerate() {
+            if scope.contains_key(&name.lexeme) {
+                self.interpreter.resolve(expression.clone(), idx);
+                return Ok(());
+            }
+        }
+
+        Ok(())
+    }
+}

rust/rox/src/scanner.rs

@@ -64,6 +64,8 @@ pub fn tokenize(source: &str) -> Vec<Token> {
 
 #[cfg(test)]
 mod tests {
+    use ordered_float::OrderedFloat;
+
     use crate::token::Literal;
     use crate::token::Token;
     use crate::token::TokenType::*;
@@ -88,13 +90,13 @@ mod tests {
             vec![Token {
                 token_type: Number,
                 lexeme: "0".into(),
-                literal: Some(Literal::Number(0.0)),
+                literal: Some(Literal::Number(OrderedFloat(0.0))),
                 line: 1
             },],
             vec![Token {
                 token_type: Number,
                 lexeme: "0".into(),
-                literal: Some(Literal::Number(0.0)),
+                literal: Some(Literal::Number(OrderedFloat(0.0))),
                 line: 1
             },]
         );
@@ -153,7 +155,7 @@ mod tests {
                 Token {
                     token_type: Number,
                     lexeme: "0".into(),
-                    literal: Some(Literal::Number(0.0)),
+                    literal: Some(Literal::Number(OrderedFloat(0.0))),
                     line: 3
                 },
                 Token {
@@ -213,7 +215,7 @@ mod tests {
                 Token {
                     token_type: Number,
                     lexeme: "1".into(),
-                    literal: Some(Literal::Number(1.0)),
+                    literal: Some(Literal::Number(OrderedFloat(1.0))),
                     line: 6
                 },
                 Token {
@@ -237,7 +239,7 @@ mod tests {
                 Token {
                     token_type: Number,
                     lexeme: "10000".into(),
-                    literal: Some(Literal::Number(10000.0)),
+                    literal: Some(Literal::Number(OrderedFloat(10000.0))),
                     line: 6
                 },
                 Token {

rust/rox/src/token.rs

@@ -2,8 +2,10 @@
 
 use std::fmt::Display;
 
+use ordered_float::OrderedFloat;
+
 /// Exhaustive enumeration of all types of different tokens.
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
 pub enum TokenType {
     // Single-character tokens.
     LeftParen,
@@ -55,12 +57,12 @@ pub enum TokenType {
 }
 
 /// Literal value.
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Literal {
     /// String literal.
     String(String),
     // Number literal, represented as f64 (thus it can be decimal).
-    Number(f64),
+    Number(OrderedFloat<f64>),
     /// Boolean literal.
     Boolean(bool),
     /// Null literal.
@@ -68,7 +70,7 @@ pub enum Literal {
 }
 
 /// Consumed token.
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct Token {
     /// Type of the token.
     pub token_type: TokenType,

rust/rox/src/tokenizer/number.rs

@@ -1,4 +1,5 @@
 use crate::token::{Literal, Token, TokenType};
+use ordered_float::OrderedFloat;
 use std::{iter::Peekable, str::CharIndices};
 use tracing::error;
 
@@ -29,7 +30,7 @@ impl Tokenizer for Number {
                 Ok(literal) => Some(Token {
                     token_type: TokenType::Number,
                     lexeme,
-                    literal: Some(Literal::Number(literal)),
+                    literal: Some(Literal::Number(OrderedFloat(literal))),
                     line,
                 }),
                 Err(e) => {

rust/rox/src/value.rs

@@ -1,5 +1,7 @@
 use std::{fmt::Display, rc::Rc};
 
+use ordered_float::OrderedFloat;
+
 use crate::{callable::Callable, token::Literal};
 
 /// Concrete value in the interpreter.
@@ -8,7 +10,7 @@ pub enum Value {
     Return(Box<Value>),
     Callable(Rc<dyn Callable>),
     String(String),
-    Number(f64),
+    Number(OrderedFloat<f64>),
     Boolean(bool),
     Nil,
 }