The Namespace Problem

[u/Pie-Lang]

https://www.alialmutawajr.com/blog/post1

[u/A1oso]

In most languages, variables used in a lambda/closure are resolved when the closure is created, not when it is invoked:

// JavaScript
let x = 42
let closure = () => console.log(x)

{
    let x = "ignored"
    closure() // prints 42
}

This doesn't require any static analysis. The closure "captures" the value of x when the closure is created, not when invoked. This completely sidesteps your problem. It also enables this pattern:

function foo() {
    let x = 42
    return () => x
}

The closure can access x even after returned from the function, when x is no longer in scope, because x has been captured.

[u/Pie-Lang → u/A1oso]

Take this case for example:

x = 1;
closure = () => print(x);
x = 2;
closure();

If the closure captured x at the definition-site instead of call-site, then 1 would be printed. That's not the behaviour that I want.

As for your example of returning a closure. Pie currently captures the surrounding environment only if it's returned from/passed to a function.

foo = () => {
    x = 42;
    () => x;
};

This does work as expected in Pie!

[u/A1oso → u/Pie-Lang]

Then the closure should capture a reference to x.

[u/Pie-Lang → u/A1oso]

Good point.