feat(tazjin/rlox): Implement variable depth resolver

Implements the first part of the resolver from
https://craftinginterpreters.com/resolving-and-binding.html

This is wired up to the execution paths in main, but not yet in the
tests. The resolved depth is also not actually used for variable
lookups (yet).

Change-Id: I3a8615252b7b9b12d5a290c5ddf85988f61b9184
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2403
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
This commit is contained in:
Vincent Ambo 2021-01-16 15:11:36 +03:00 committed by tazjin
parent f472c82427
commit 29335a8b63
5 changed files with 217 additions and 16 deletions

View file

@ -14,6 +14,7 @@ pub enum ErrorKind {
InternalError(String),
InvalidAssignmentTarget(String),
RuntimeError(String),
StaticError(String),
// This variant is not an error, rather it is used for
// short-circuiting out of a function body that hits a `return`

View file

@ -107,13 +107,13 @@ impl Environment {
}
fn get(&self, name: &parser::Variable) -> Result<Value, Error> {
let ident = identifier_str(&name.0)?;
let ident = identifier_str(&name.name)?;
self.values
.get(ident)
.map(Clone::clone)
.ok_or_else(|| Error {
line: name.0.line,
line: name.name.line,
kind: ErrorKind::UndefinedVariable(ident.into()),
})
.or_else(|err| {

View file

@ -7,6 +7,7 @@ use std::process;
mod errors;
mod interpreter;
mod parser;
mod resolver;
mod scanner;
fn main() {
@ -48,17 +49,13 @@ fn run_prompt() {
fn run(lox: &mut interpreter::Interpreter, code: &str) {
let chars: Vec<char> = code.chars().collect();
match scanner::scan(&chars) {
Ok(tokens) => match parser::parse(tokens) {
Ok(program) => {
println!("Program:\n{:?}", program);
if let Err(err) = lox.interpret(&program) {
println!("Error in program: {:?}", err);
}
}
Err(errors) => report_errors(errors),
},
Err(errors) => report_errors(errors),
let result = scanner::scan(&chars)
.and_then(|tokens| parser::parse(tokens))
.and_then(|program| resolver::resolve(program).map_err(|e| vec![e]))
.and_then(|program| lox.interpret(&program).map_err(|e| vec![e]));
if let Err(errors) = result {
report_errors(errors);
}
}

View file

@ -15,6 +15,7 @@ use std::rc::Rc;
pub struct Assign {
pub name: Token,
pub value: Box<Expr>,
pub depth: Option<usize>,
}
#[derive(Debug)]
@ -57,7 +58,10 @@ pub struct Call {
// Not to be confused with `Var`, which is for assignment.
#[derive(Debug)]
pub struct Variable(pub Token);
pub struct Variable {
pub name: Token,
pub depth: Option<usize>,
}
#[derive(Debug)]
pub enum Expr {
@ -413,10 +417,11 @@ impl Parser {
let equals = self.previous().clone();
let value = self.assignment()?;
if let Expr::Variable(Variable(name)) = expr {
if let Expr::Variable(Variable { name, .. }) = expr {
return Ok(Expr::Assign(Assign {
name,
value: Box::new(value),
depth: None,
}));
}
@ -549,7 +554,12 @@ impl Parser {
return Ok(Expr::Grouping(Grouping(Box::new(expr))));
}
TokenKind::Identifier(_) => return Ok(Expr::Variable(Variable(next))),
TokenKind::Identifier(_) => {
return Ok(Expr::Variable(Variable {
name: next,
depth: None,
}))
}
unexpected => {
eprintln!("encountered {:?}", unexpected);

View file

@ -0,0 +1,193 @@
// Resolves variable access to their specific instances in the
// environment chain.
//
// https://craftinginterpreters.com/resolving-and-binding.html
use std::collections::HashMap;
use std::rc::Rc;
use crate::errors::{Error, ErrorKind};
use crate::parser::{self, Expr, Statement};
use crate::scanner::Token;
#[derive(Default)]
struct Resolver<'a> {
scopes: Vec<HashMap<&'a str, bool>>,
}
impl<'a> Resolver<'a> {
// AST traversal
fn resolve(&mut self, program: &'a mut parser::Block) -> Result<(), Error> {
self.begin_scope();
for stmt in program {
self.resolve_stmt(stmt)?;
}
self.end_scope();
Ok(())
}
fn resolve_stmt(&mut self, stmt: &'a mut Statement) -> Result<(), Error> {
match stmt {
Statement::Expr(expr) => self.resolve_expr(expr),
Statement::Print(expr) => self.resolve_expr(expr),
Statement::Var(var) => self.resolve_var(var),
Statement::Return(ret) => self.resolve_expr(&mut ret.value),
Statement::Block(block) => self.resolve(block),
Statement::If(if_stmt) => {
self.resolve_expr(&mut if_stmt.condition)?;
self.resolve_stmt(&mut if_stmt.then_branch)?;
if let Some(branch) = if_stmt.else_branch.as_mut() {
self.resolve_stmt(branch)?;
}
Ok(())
}
Statement::While(while_stmt) => {
self.resolve_expr(&mut while_stmt.condition)?;
self.resolve_stmt(&mut while_stmt.body)
}
Statement::Function(func) => match Rc::get_mut(func) {
Some(func) => self.resolve_function(func),
// The resolver does not clone references, so unless
// the interpreter is called before the resolver this
// case should never happen.
None => {
return Err(Error {
line: 0,
kind: ErrorKind::InternalError(
"multiple function references before interpretation".into(),
),
})
}
},
}
}
fn resolve_var(&mut self, var: &'a mut parser::Var) -> Result<(), Error> {
self.declare(&var.name);
if let Some(init) = &mut var.initialiser {
self.resolve_expr(init)?;
}
self.define(&var.name);
Ok(())
}
fn resolve_function(&mut self, func: &'a mut parser::Function) -> Result<(), Error> {
self.declare(&func.name);
self.define(&func.name);
self.begin_scope();
for param in &func.params {
self.declare(param);
self.define(param);
}
for stmt in &mut func.body {
self.resolve_stmt(stmt)?;
}
self.end_scope();
Ok(())
}
fn resolve_expr(&mut self, expr: &'a mut Expr) -> Result<(), Error> {
match expr {
Expr::Variable(var) => self.resolve_variable(var),
Expr::Assign(assign) => self.resolve_assign(assign),
Expr::Grouping(grouping) => self.resolve_expr(&mut grouping.0),
Expr::Call(call) => self.resolve_call(call),
Expr::Literal(_) => Ok(()),
Expr::Unary(unary) => self.resolve_expr(&mut unary.right),
Expr::Logical(log) => {
self.resolve_expr(&mut log.left)?;
self.resolve_expr(&mut log.right)
}
Expr::Binary(binary) => {
self.resolve_expr(&mut binary.left)?;
self.resolve_expr(&mut binary.right)
}
}
}
fn resolve_variable(&mut self, var: &'a mut parser::Variable) -> Result<(), Error> {
if let Some(scope) = self.scopes.last_mut() {
if let Some(false) = scope.get(var.name.lexeme.as_str()) {
return Err(Error {
line: var.name.line,
kind: ErrorKind::StaticError(
"can't read local variable in its own initialiser".into(),
),
});
}
}
var.depth = self.resolve_local(&var.name);
Ok(())
}
fn resolve_assign(&mut self, assign: &'a mut parser::Assign) -> Result<(), Error> {
self.resolve_expr(&mut assign.value)?;
assign.depth = self.resolve_local(&assign.name);
Ok(())
}
fn resolve_local(&mut self, name: &'a Token) -> Option<usize> {
for (c, scope) in self.scopes.iter().rev().enumerate() {
if scope.contains_key(name.lexeme.as_str()) {
return Some(c);
}
}
None
}
fn resolve_call(&mut self, call: &'a mut parser::Call) -> Result<(), Error> {
self.resolve_expr(&mut call.callee)?;
for arg in call.args.iter_mut() {
self.resolve_expr(arg)?;
}
Ok(())
}
// Internal helpers
fn declare(&mut self, name: &'a Token) {
if let Some(scope) = self.scopes.last_mut() {
scope.insert(&name.lexeme, false);
}
}
fn define(&mut self, name: &'a Token) {
if let Some(scope) = self.scopes.last_mut() {
scope.insert(&name.lexeme, true);
}
}
fn begin_scope(&mut self) {
self.scopes.push(Default::default());
}
fn end_scope(&mut self) {
self.scopes.pop();
}
}
pub fn resolve(mut block: parser::Block) -> Result<parser::Block, Error> {
let mut resolver: Resolver = Default::default();
resolver.resolve(&mut block)?;
Ok(block)
}