Add map2, map3, map4 to Apply?

[gcanti]

What I do now

import { Option } from 'fp-ts/lib/Option'

const mapOption2 = <A, B, R>(fa: Option<A>, fb: Option<B>, f: (a: A, b: B) => R): Option<R> => {
  return fb.ap(fa.map(a => (b: B) => f(a, b)))
}

const r = mapOption2(some(1), some(2), (a, b) => a + b)

versus

import { option } from 'fp-ts/lib/Option'
import { map2 } from 'fp-ts/lib/Apply'

const r = map2(option)(some(1), some(2), (a, b) => a + b)

[raveclassic]

I'm using specialized version of sequence (specialized to array as traversable):

export function combine<A>(a: Option<A>): Option<[A]>;
export function combine<A, B>(a: Option<A>, b: Option<B>): Option<[A, B]>;
export function combine<A, B, C>(a: Option<A>, b: Option<B>, c: Option<C>): Option<[A, B, C]>;
export function combine<A, B, C, D>(a: Option<A>, b: Option<B>, c: Option<C>, d: Option<D>): Option<[A, B, C, D]>;
export function combine<T>(...list: Option<T>[]): Option<T[]> {
	return sequence(option, array)(list);
}

const foo = combine(some(1), some(2)).map(([a, b]) => a + b);

Applicative (option) can be generalized though.

[volrk]

Hey, I'm new in the open-source world and I'm trying to find a projet where I can help. Is this feature still needed ?

[giogonzo]

Hi @volrk , and sorry for the late reply. As of now we have sequenceT (and the S variant) which pretty much cover the same use case, more generically. I'm closing this