filter

function Result.filter(
    result: Result<T, E>,
    predicate: (value: T) => boolean
): Result<T, E | void>

Filters the Ok value using the predicate function. If the result is Ok and the predicate returns true, returns the original result. If the predicate returns false, returns an Err with void. If the result is already an Err, returns it unchanged.

Can be used for type narrowing.

Example

data-first

Result.filter(ok(5), (x) => x > 3);
// Ok<number>(5)

Result.filter(ok(1), (x) => x > 3);
// Err<void>

Result.filter(err("fail"), (x) => x > 3);
// Err<string>("fail")

data-last

pipe(
    ok(5),
    Result.filter((x) => x > 3),
);
// Ok<number>(5)