mapLeft

mapLeft<E, T>(x, f): E extends Left<unknown> ? Left<T> : E

If the given Either is a Right, return it, otherwise return a new Left with the result of applying the given function to the Left value.

Example

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

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

Type Parameters

• E extends Either<unknown, unknown>

• T

The mapped type.

Parameters

x

E

The either value to map.

f

(l) => T

The map function.

Returns

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

The mapped either object.