New syntax for lazy getters

[aaditmshah]

Lazy getters are really useful in functional programming. They are used to prevent stackoverflows (via tail recursion modulo cons), and they can be used to create infinite data structures. However, they are very verbose. Consider the following lazy take function:

const take = (n, xs) => n === 0 ? null : xs && {
    head: xs.head,
    get tail() {
        delete this.tail;
        return this.tail = take(n - 1, xs.tail);
    }
};

It would be nice to have syntactic sugar to create the lazy getter:

const tail = (n, xs) => n === 0 ? xs && {
    head: xs.head,
    lazy tail: take(n - 1, xs.tail)
};

This syntax could also be used to succinctly tie the knot to create cyclic data structures:

const xs = { head: 0, lazy tail: ys },
      ys = { head: 1, lazy tail: xs };

const zeros = { head: 0, lazy tail: zeros };

This enables a limited form of letrec without actually changing the semantics of let, const or var.

[ljharb]

Please see https://github.com/tc39/ecma262/blob/master/CONTRIBUTING.md for how to best suggest new ideas.

[ljharb]

Please see https://github.com/tc39/ecma262/blob/master/CONTRIBUTING.md for how to best suggest new ideas.