mapErr

function Result.mapErr(
    result: Result<T, E>,
    transform: (error: E) => F
): Result<T, F>

Transforms the Err value using the transform function. If the result is an Err, applies the transform function to the error value and returns a new Err. If the result is Ok, returns it unchanged.

Example

data-first

Result.mapErr(err("fail"), (e) => `Error: ${e}`);
// Err<string>("Error: fail")

Result.mapErr(ok(5), (e) => `Error: ${e}`);
// Ok<number>(5)

data-last

pipe(
    err("fail"),
    Result.mapErr((e) => `Error: ${e}`),
);
// Err<string>("Error: fail")