Functor.md

MODULE Functor

Functor

type class

interface Functor<F> {
  readonly URI: F
  map: <A, B>(fa: HKT<F, A>, f: (a: A) => B) => HKT<F, B>
}

A Functor is a type constructor which supports a mapping operation map.

map can be used to turn functions a -> b into functions f a -> f b whose argument and return types use the type constructor f to represent some computational context.

Instances must satisfy the following laws:

1. Identity: F.map(fa, a => a) = fa
2. Composition: F.map(fa, a => bc(ab(a))) = F.map(F.map(fa, ab), bc)

   flap

   function

flap<F>(functor: Functor<F>): <A, B>(a: A, ff: HKT<F, (a: A) => B>) => HKT<F, B>

Apply a value in a computational context to a value in no context. Generalizes flip

getFunctorComposition

function

getFunctorComposition<F, G>(F: Functor<F>, G: Functor<G>): FunctorComposition<F, G>

lift

function

lift<F>(F: Functor<F>): <A, B>(f: (a: A) => B) => (fa: HKT<F, A>) => HKT<F, B>

Lift a function of one argument to a function which accepts and returns values wrapped with the type constructor F

voidLeft

function

voidLeft<F>(F: Functor<F>): <A, B>(fa: HKT<F, A>, b: B) => HKT<F, B>

A version of voidRight with its arguments flipped ($>)

voidRight

function

voidRight<F>(F: Functor<F>): <A, B>(a: A, fb: HKT<F, B>) => HKT<F, A>

Ignore the return value of a computation, using the specified return value instead (<$)