feat(tazjin/rlox): Implement support for closures

Change-Id: I0ffc810807a1a6ec90455a4f2d2bd977833005bd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2396
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
This commit is contained in:
Vincent Ambo 2021-01-14 23:16:40 +03:00 committed by tazjin
parent 39439d59e8
commit 740a9a3565
2 changed files with 57 additions and 24 deletions

View file

@ -18,14 +18,17 @@ mod tests;
#[derive(Clone, Debug)]
pub enum Callable {
Builtin(&'static dyn builtins::Builtin),
Function(Rc<parser::Function>),
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(),
Callable::Function { func, .. } => func.params.len(),
}
}
@ -33,14 +36,15 @@ impl Callable {
match self {
Callable::Builtin(builtin) => builtin.call(args),
Callable::Function(func) => {
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(Rc::new(RwLock::new(fn_env)), &func.body);
let result = lox.interpret_block(Some(Rc::new(RwLock::new(fn_env))), &func.body);
match result {
// extract returned values if applicable
@ -90,7 +94,7 @@ impl Value {
}
#[derive(Debug, Default)]
struct Environment {
pub struct Environment {
enclosing: Option<Rc<RwLock<Environment>>>,
values: HashMap<String, Value>,
}
@ -200,13 +204,6 @@ impl Interpreter {
.get(var)
}
fn set_enclosing(&mut self, parent: Rc<RwLock<Environment>>) {
self.env
.write()
.expect("environment lock is poisoned")
.enclosing = Some(parent);
}
// Interpreter itself
pub fn interpret(&mut self, program: &Block) -> Result<Value, Error> {
let mut value = Value::Literal(Literal::Nil);
@ -228,7 +225,7 @@ impl Interpreter {
Value::Literal(Literal::String(output))
}
Statement::Var(var) => return self.interpret_var(var),
Statement::Block(block) => return self.interpret_block(Default::default(), block),
Statement::Block(block) => return self.interpret_block(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()),
@ -253,19 +250,24 @@ impl Interpreter {
Ok(value)
}
/// 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(
&mut self,
env: Rc<RwLock<Environment>>,
env: Option<Rc<RwLock<Environment>>>,
block: &parser::Block,
) -> Result<Value, Error> {
// Initialise a new environment and point it at the parent
// (this is a bit tedious because we need to wrap it in and
// out of the Rc).
//
// TODO(tazjin): Refactor this to use Rc on the interpreter itself.
let previous = std::mem::replace(&mut self.env, env);
self.set_enclosing(previous.clone());
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);
// Swap it back, discarding the child env.
@ -295,9 +297,12 @@ impl Interpreter {
Ok(value)
}
fn interpret_function(&mut self, stmt: Rc<parser::Function>) -> Result<Value, Error> {
let name = stmt.name.clone();
let value = Value::Callable(Callable::Function(stmt));
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)
}
@ -442,3 +447,9 @@ fn eval_truthy(lit: &Value) -> bool {
false
}
}
fn set_enclosing_env(this: &RwLock<Environment>, parent: Rc<RwLock<Environment>>) {
this.write()
.expect("environment lock is poisoned")
.enclosing = Some(parent);
}

View file

@ -76,3 +76,25 @@ add(1, 2, 3);
assert_eq!(Value::Literal(Literal::Number(6.0)), result);
}
#[test]
fn test_closure() {
let result = parse_eval(
r#"
fun makeCounter() {
var i = 0;
fun count() {
i = i + 1;
}
return count;
}
var counter = makeCounter();
counter(); // "1".
counter(); // "2".
"#,
);
assert_eq!(Value::Literal(Literal::Number(2.0)), result);
}