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javascriptfunctional-programmingramda.jssanctuaryfantasyland

Operating on two Eithers

Suppose that you have the following code:

import R from "ramda";
import S from "sanctuary";
import { Left, Right } from "sanctuary-either";

const add = R.curry((p1, p2) => p1 + p2);
const addOne = add(1);

const func1 = () => Right(2);
const func2 = () => Right(7);

Combining addOne with func1 or func2 is relatively easy:

const res = R.compose(
  S.map(addOne),
  func1
)();

but how can one call add using func1 and func2 as arguments?

p.s. I know that ramda offers an add function. Consider the example as an abstraction of a real world problem.

Solution

  • You are probably looking for the lift2 function:

    const addEithers = S.lift2(add)

console.log(addEithers(func1())(func2()))

    Alternatively, you can use ap:

    S.ap(S.map(add)(func1()))(func2())