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Diffstat (limited to 'users/tazjin/rlox/src/treewalk/interpreter.rs')
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/interpreter.rs | 482 |
1 files changed, 482 insertions, 0 deletions
diff --git a/users/tazjin/rlox/src/treewalk/interpreter.rs b/users/tazjin/rlox/src/treewalk/interpreter.rs new file mode 100644 index 000000000000..32822d72face --- /dev/null +++ b/users/tazjin/rlox/src/treewalk/interpreter.rs @@ -0,0 +1,482 @@ +use crate::errors::{Error, ErrorKind}; +use crate::parser::{self, Block, Expr, Literal, Statement}; +use crate::treewalk::resolver; +use crate::scanner::{self, TokenKind}; +use std::collections::HashMap; +use std::rc::Rc; +use std::sync::RwLock; + +// Implementation of built-in functions. +mod builtins; + +#[cfg(test)] +mod tests; + +// Tree-walk interpreter + +// Representation of all callables, including builtins & user-defined +// functions. +#[derive(Clone, Debug)] +pub enum Callable { + Builtin(&'static dyn builtins::Builtin), + Function { + func: Rc<parser::Function>, + closure: Rc<RwLock<Environment>>, + }, +} + +impl Callable { + fn arity(&self) -> usize { + match self { + Callable::Builtin(builtin) => builtin.arity(), + Callable::Function { func, .. } => func.params.len(), + } + } + + fn call(&self, lox: &mut Interpreter, args: Vec<Value>) -> Result<Value, Error> { + match self { + Callable::Builtin(builtin) => builtin.call(args), + + Callable::Function { func, closure } => { + let mut fn_env: Environment = Default::default(); + fn_env.enclosing = Some(closure.clone()); + + for (param, value) in func.params.iter().zip(args.into_iter()) { + fn_env.define(param, value)?; + } + + let result = + lox.interpret_block_with_env(Some(Rc::new(RwLock::new(fn_env))), &func.body); + + match result { + // extract returned values if applicable + Err(Error { + kind: ErrorKind::FunctionReturn(value), + .. + }) => Ok(value), + + // otherwise just return the result itself + _ => result, + } + } + } + } +} + +// Representation of an in-language value. +#[derive(Clone, Debug)] +pub enum Value { + Literal(Literal), + Callable(Callable), +} + +impl PartialEq for Value { + fn eq(&self, other: &Self) -> bool { + match (self, other) { + (Value::Literal(lhs), Value::Literal(rhs)) => lhs == rhs, + // functions do not have equality + _ => false, + } + } +} + +impl From<Literal> for Value { + fn from(lit: Literal) -> Value { + Value::Literal(lit) + } +} + +impl Value { + fn expect_literal(self) -> Result<Literal, Error> { + match self { + Value::Literal(lit) => Ok(lit), + _ => unimplemented!(), // which error? which line? + } + } +} + +#[derive(Debug, Default)] +pub struct Environment { + enclosing: Option<Rc<RwLock<Environment>>>, + values: HashMap<String, Value>, +} + +impl Environment { + fn define(&mut self, name: &scanner::Token, value: Value) -> Result<(), Error> { + let ident = identifier_str(name)?; + self.values.insert(ident.into(), value); + Ok(()) + } + + fn get(&self, ident: &str, line: usize, depth: usize) -> Result<Value, Error> { + if depth > 0 { + match &self.enclosing { + None => { + return Err(Error { + line, + kind: ErrorKind::InternalError(format!( + "invalid depth {} for {}", + depth, ident + )), + }) + } + Some(parent) => { + let env = parent.read().expect("fatal: environment lock poisoned"); + return env.get(ident, line, depth - 1); + } + } + } + + self.values + .get(ident) + .map(Clone::clone) + .ok_or_else(|| Error { + line, + kind: ErrorKind::UndefinedVariable(ident.into()), + }) + } + + fn assign(&mut self, name: &scanner::Token, value: Value) -> Result<(), Error> { + let ident = identifier_str(name)?; + + match self.values.get_mut(ident) { + Some(target) => { + *target = value; + Ok(()) + } + None => { + if let Some(parent) = &self.enclosing { + return parent.write().unwrap().assign(name, value); + } + + Err(Error { + line: name.line, + kind: ErrorKind::UndefinedVariable(ident.into()), + }) + } + } + } +} + +fn identifier_str(name: &scanner::Token) -> Result<&str, Error> { + if let TokenKind::Identifier(ident) = &name.kind { + Ok(ident) + } else { + Err(Error { + line: name.line, + kind: ErrorKind::InternalError("unexpected identifier kind".into()), + }) + } +} + +#[derive(Debug)] +pub struct Interpreter { + env: Rc<RwLock<Environment>>, +} + +impl Interpreter { + /// Create a new interpreter and configure the initial global + /// variable set. + pub fn create() -> Self { + let mut globals = HashMap::new(); + + globals.insert( + "clock".into(), + Value::Callable(Callable::Builtin(&builtins::Clock {})), + ); + + Interpreter { + env: Rc::new(RwLock::new(Environment { + enclosing: None, + values: globals, + })), + } + } + + // Environment modification helpers + fn define_var(&mut self, name: &scanner::Token, value: Value) -> Result<(), Error> { + self.env + .write() + .expect("environment lock is poisoned") + .define(name, value) + } + + fn assign_var(&mut self, name: &scanner::Token, value: Value) -> Result<(), Error> { + self.env + .write() + .expect("environment lock is poisoned") + .assign(name, value) + } + + fn get_var(&mut self, var: &parser::Variable) -> Result<Value, Error> { + let ident = identifier_str(&var.name)?; + let depth = var.depth.ok_or_else(|| Error { + line: var.name.line, + kind: ErrorKind::UndefinedVariable(ident.into()), + })?; + + self.env + .read() + .expect("environment lock is poisoned") + .get(ident, var.name.line, depth) + } + + // Interpreter itself + pub fn interpret(&mut self, mut program: Block) -> Result<Value, Error> { + let globals = self.env.read() + .expect("static globals lock poisoned") + .values.keys().map(Clone::clone) + .collect::<Vec<String>>(); + + resolver::resolve(&globals, &mut program)?; + self.interpret_block_with_env(None, &program) + } + + /// Interpret the block in the supplied environment. If no + /// environment is supplied, a new one is created using the + /// current one as its parent. + fn interpret_block_with_env( + &mut self, + env: Option<Rc<RwLock<Environment>>>, + block: &parser::Block, + ) -> Result<Value, Error> { + let env = match env { + Some(env) => env, + None => { + let env: Rc<RwLock<Environment>> = Default::default(); + set_enclosing_env(&env, self.env.clone()); + env + } + }; + + let previous = std::mem::replace(&mut self.env, env); + let result = self.interpret_block(block); + + // Swap it back, discarding the child env. + self.env = previous; + + return result; + } + + fn interpret_block(&mut self, program: &Block) -> Result<Value, Error> { + let mut value = Value::Literal(Literal::Nil); + + for stmt in program { + value = self.interpret_stmt(stmt)?; + } + + Ok(value) + } + + fn interpret_stmt(&mut self, stmt: &Statement) -> Result<Value, Error> { + let value = match stmt { + Statement::Expr(expr) => self.eval(expr)?, + Statement::Print(expr) => { + let result = self.eval(expr)?; + let output = format!("{:?}", result); + println!("{}", output); + Value::Literal(Literal::String(output)) + } + Statement::Var(var) => return self.interpret_var(var), + Statement::Block(block) => return self.interpret_block_with_env(None, block), + Statement::If(if_stmt) => return self.interpret_if(if_stmt), + Statement::While(while_stmt) => return self.interpret_while(while_stmt), + Statement::Function(func) => return self.interpret_function(func.clone()), + Statement::Return(ret) => { + return Err(Error { + line: 0, + kind: ErrorKind::FunctionReturn(self.eval(&ret.value)?), + }) + } + }; + + Ok(value) + } + + fn interpret_var(&mut self, var: &parser::Var) -> Result<Value, Error> { + let init = var.initialiser.as_ref().ok_or_else(|| Error { + line: var.name.line, + kind: ErrorKind::InternalError("missing variable initialiser".into()), + })?; + let value = self.eval(init)?; + self.define_var(&var.name, value.clone())?; + Ok(value) + } + + fn interpret_if(&mut self, if_stmt: &parser::If) -> Result<Value, Error> { + let condition = self.eval(&if_stmt.condition)?; + + if eval_truthy(&condition) { + self.interpret_stmt(&if_stmt.then_branch) + } else if let Some(else_branch) = &if_stmt.else_branch { + self.interpret_stmt(else_branch) + } else { + Ok(Value::Literal(Literal::Nil)) + } + } + + fn interpret_while(&mut self, stmt: &parser::While) -> Result<Value, Error> { + let mut value = Value::Literal(Literal::Nil); + while eval_truthy(&self.eval(&stmt.condition)?) { + value = self.interpret_stmt(&stmt.body)?; + } + + Ok(value) + } + + fn interpret_function(&mut self, func: Rc<parser::Function>) -> Result<Value, Error> { + let name = func.name.clone(); + let value = Value::Callable(Callable::Function { + func, + closure: self.env.clone(), + }); + self.define_var(&name, value.clone())?; + Ok(value) + } + + fn eval(&mut self, expr: &Expr) -> Result<Value, Error> { + match expr { + Expr::Assign(assign) => self.eval_assign(assign), + Expr::Literal(lit) => Ok(lit.clone().into()), + Expr::Grouping(grouping) => self.eval(&*grouping.0), + Expr::Unary(unary) => self.eval_unary(unary), + Expr::Binary(binary) => self.eval_binary(binary), + Expr::Variable(var) => self.get_var(var), + Expr::Logical(log) => self.eval_logical(log), + Expr::Call(call) => self.eval_call(call), + } + } + + fn eval_unary(&mut self, expr: &parser::Unary) -> Result<Value, Error> { + let right = self.eval(&*expr.right)?; + + match (&expr.operator.kind, right) { + (TokenKind::Minus, Value::Literal(Literal::Number(num))) => { + Ok(Literal::Number(-num).into()) + } + (TokenKind::Bang, right) => Ok(Literal::Boolean(!eval_truthy(&right)).into()), + + (op, right) => Err(Error { + line: expr.operator.line, + kind: ErrorKind::TypeError(format!( + "Operator '{:?}' can not be called with argument '{:?}'", + op, right + )), + }), + } + } + + fn eval_binary(&mut self, expr: &parser::Binary) -> Result<Value, Error> { + let left = self.eval(&*expr.left)?.expect_literal()?; + let right = self.eval(&*expr.right)?.expect_literal()?; + + let result = match (&expr.operator.kind, left, right) { + // Numeric + (TokenKind::Minus, Literal::Number(l), Literal::Number(r)) => Literal::Number(l - r), + (TokenKind::Slash, Literal::Number(l), Literal::Number(r)) => Literal::Number(l / r), + (TokenKind::Star, Literal::Number(l), Literal::Number(r)) => Literal::Number(l * r), + (TokenKind::Plus, Literal::Number(l), Literal::Number(r)) => Literal::Number(l + r), + + // Strings + (TokenKind::Plus, Literal::String(l), Literal::String(r)) => { + Literal::String(format!("{}{}", l, r)) + } + + // Comparators (on numbers only?) + (TokenKind::Greater, Literal::Number(l), Literal::Number(r)) => Literal::Boolean(l > r), + (TokenKind::GreaterEqual, Literal::Number(l), Literal::Number(r)) => { + Literal::Boolean(l >= r) + } + (TokenKind::Less, Literal::Number(l), Literal::Number(r)) => Literal::Boolean(l < r), + (TokenKind::LessEqual, Literal::Number(l), Literal::Number(r)) => { + Literal::Boolean(l <= r) + } + + // Equality + (TokenKind::Equal, l, r) => Literal::Boolean(l == r), + (TokenKind::BangEqual, l, r) => Literal::Boolean(l != r), + + (op, left, right) => { + return Err(Error { + line: expr.operator.line, + kind: ErrorKind::TypeError(format!( + "Operator '{:?}' can not be called with arguments '({:?}, {:?})'", + op, left, right + )), + }) + } + }; + + Ok(result.into()) + } + + fn eval_assign(&mut self, assign: &parser::Assign) -> Result<Value, Error> { + let value = self.eval(&assign.value)?; + self.assign_var(&assign.name, value.clone())?; + Ok(value) + } + + fn eval_logical(&mut self, logical: &parser::Logical) -> Result<Value, Error> { + let left = eval_truthy(&self.eval(&logical.left)?); + let right = eval_truthy(&self.eval(&logical.right)?); + + match &logical.operator.kind { + TokenKind::And => Ok(Literal::Boolean(left && right).into()), + TokenKind::Or => Ok(Literal::Boolean(left || right).into()), + kind => Err(Error { + line: logical.operator.line, + kind: ErrorKind::InternalError(format!("Invalid logical operator: {:?}", kind)), + }), + } + } + + fn eval_call(&mut self, call: &parser::Call) -> Result<Value, Error> { + let callable = match self.eval(&call.callee)? { + Value::Callable(c) => c, + Value::Literal(v) => { + return Err(Error { + line: call.paren.line, + kind: ErrorKind::RuntimeError(format!("not callable: {:?}", v)), + }) + } + }; + + let mut args = vec![]; + for arg in &call.args { + args.push(self.eval(arg)?); + } + + if callable.arity() != args.len() { + return Err(Error { + line: call.paren.line, + kind: ErrorKind::RuntimeError(format!( + "Expected {} arguments, but got {}", + callable.arity(), + args.len(), + )), + }); + } + + callable.call(self, args) + } +} + +// Interpreter functions not dependent on interpreter-state. + +fn eval_truthy(lit: &Value) -> bool { + if let Value::Literal(lit) = lit { + match lit { + Literal::Nil => false, + Literal::Boolean(b) => *b, + _ => true, + } + } else { + false + } +} + +fn set_enclosing_env(this: &RwLock<Environment>, parent: Rc<RwLock<Environment>>) { + this.write() + .expect("environment lock is poisoned") + .enclosing = Some(parent); +} |