Updating

The function List.update_with enables the replacement of elements of a given list according to a boolean function: if the call of that function on a element is true, then the element is replaced, otherwise it remains.

const nats = list([0, 1, 2, 3, 4]);

// evens_zeroed == list([0, 1, 0, 3, 0])

const evens_zeroed = List.update_with(x => x % 2 == 0n, 0, nats);

The function List.update enables the selective replacement of elements of a given list according to a function that returns an optional value, instead of a boolean as List.update_with above.

That function takes an element and returns an optional value: if that value is None(), then the element is left unchanged, otherwise, if the value is Some(v), then the element is replaced in the resulting list by v.

const f = x => x % 2 == 0n ? None() : Some(x*x);

// odds == list([0, 1, 2, 9, 4])

const odds_squared = List.update(f, nats);

See predefined namespace List.