CODEWITHSUNDEEP
javascriptecmascript-6bindcurryingpartial-application
Vangogh500
Vangogh500

Reputation: 959

Partial functions with bind

So recently I discovered that you can do partial functions/currying with js using bind. For example:

const foo = (a, b, c) => (a + (b / c))
foo.bind(null, 1, 2) //gives me (c) => (1 + (2 / c))

However this only works if the parts you want to curry are in order. What if I wanted to achieve the following using bind?

(b) => (1 + (b / 2))

Tried various solutions such as:

foo.bind(null, 1, null, 2)

Any ideas? Is it possible to accomplish this with vanilla es6?

Upvotes: 4

Views: 718

Answers (3)

Aonghus O Nia
Aonghus O Nia

Reputation: 1

you can wrap it in a function

const foo = (a, b, c) => (a + (b / c))

_ => foo(1, _, 2) //gives you (b) => (1 + (b / 2))

Upvotes: 0

Nina Scholz
Nina Scholz

Reputation: 386512

You could use a wrapper for a reordering of arguments.

const
    foo = (a, b, c) => a + b / c,
    acb = (a, c, b) => foo(a, b, c);

console.log(acb.bind(null, 1, 2)(5));

Upvotes: 4

J. Pichardo
J. Pichardo

Reputation: 3115

Currently I think about two ways to implement this (besides the wrapper from @NinaSholz, which is pretty nice):

1. Using a curry function that merges two argument arrays:

const foo = (a, b, c) => a + b / c;

function curry(fn, ...args) {
  return function(...newArgs) {
    const finalArgs = args.map(arg => arg || newArgs.pop());
    return fn(...finalArgs);
  };
}

const curriedFoo = curry(foo, 1, null, 2);

console.log(curriedFoo(4)) // Should print 1 + 4 / 2 = 3

Here we are just sending null or undefined in the place of the parameters we want to skip and in the second call we send those parameters in order

2. Using objects for named parameters

const foo = ({a, b, c}) => a + b / c;

function curry(fn, args) {
  return (newArgs) => fn({ ...args,
    ...newArgs
  });
}

const curriedFoo = curry(foo, {
  a: 1,
  c: 2
});

console.log(curriedFoo({
  b: 4
}));

Here we are taking advantage of the ...(spread) operator and object syntax in the funcion signature to merge two argument objects;

Upvotes: 0

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