mapRight

mapRight<E, T>(x, f): E extends Right<unknown> ? Right<T> : E

Applies a transformation function to the Right value of an Either type, if present. If the input is a Left, it remains unchanged.

Example

mapRight({ right: 'bar' }, (x) => `${x}${x}`)
// => { right: "barbar" }

mapRight({ left: 'bar' }, (x) => `${x}${x}`)
// => { left: "bar" }

Type Parameters

• E extends Either<unknown, unknown>

The type of the Either.

• T

The type of the transformed Right value.

Parameters

x

E

The Either value to map.

f

(r) => T

The transformation function to apply to the Right value.

Returns

E extends Right<unknown> ? Right<T> : E

An Either object where the Right has been transformed if present, or the original Left.