filterOrElse

function Result.filterOrElse(
    result: Result<T, E>,
    predicate: (value: T) => boolean,
    orElse: (value: T) => F
): Result<T, E | F>

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, calls orElse with the Ok value and returns an Err with the result. If the result is already an Err, returns it unchanged.

Can be used for type narrowing.

Example

data-first

Result.filterOrElse(
    ok(5),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Ok<number>(5)

Result.filterOrElse(
    ok(1),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Err<string>("1 is too small")

Result.filterOrElse(
    err("fail"),
    (x) => x > 3,
    (x) => `${x} is too small`,
);
// Err<string>("fail")

data-last

pipe(
    ok(1),
    Result.filterOrElse(
        (x) => x > 3,
        (x) => `${x} is too small`,
    ),
);
// Err<string>("1 is too small")