mapLefts

mapLefts<Xs, T>(xs, f): ArgLefts<Xs> extends never[] ? Right<ArgRights<Xs>[number]> : ArgRights<Xs>[number] extends never[] ? Left<T> : Left<T> | Right<ArgRights<Xs>[number]>

mapLefts takes a tuple of Eithers and a function that takes the left values of the Eithers and returns a new Either with the left value being the result of the function and the right value being the right value of the first Either in the tuple.

Example

mapLefts([{ left: 'foo' }, { left: 'bar' }], ([x0, x1]) => `${x0}${x1}`)
// => { left: "foobar" }

mapLefts([{ right: 'bar' }, { left: 'fooz' }], ([x0, x1]) => `${x0}${x1}`)
// => { right: "bar" }

Type Parameters

• Xs extends Either<unknown, unknown>[]

• T

The mapped type.

Parameters

xs

readonly [Xs]

The either values to map.

f

(ls) => T

The map function.

Returns

ArgLefts<Xs> extends never[] ? Right<ArgRights<Xs>[number]> : ArgRights<Xs>[number] extends never[] ? Left<T> : Left<T> | Right<ArgRights<Xs>[number]>

The mapped either object.