How to curry a function across an unknown number of parameters

Question

Say I have a function called multiplyDivide

If I were to call multiplyDivide(2)(3)(4)(6) it would be equivalent to 2 * 3 / 4 * 6

Answer 1

Using a functional approach, you can create a function that "curries" arguments for another function. You will need a way to tell the function to return the value, so in this case, calling the function without passing any arguments will return the result:

function curry(fn, ...values) {
    return (...next) => (next.length) ? curry(fn, ...values, ...next) : fn(...values);
}

The cool thing about this function is that you can pass multiple arguments and/or keep invoking the function (1)(2, 3, 4)(5).

Here's a couple of examples:

function curry(fn, ...values) {
  return (...next) => (next.length) ? curry(fn, ...values, ...next) : fn(...values);
}

function multiplyDivide(...args) {
  return args.reduce((total, next, i) => (i % 2) ? (total / next) : (total * next), args.shift());
}

let x = curry(multiplyDivide)(2)(3, 4)(6)();
console.log(x);

let y = curry(multiplyDivide)(5, 4, 2)(3);
y = y(3, 5)(1)();
console.log(y);

Of course, this example does hint at just simply overloading the multiplyDivide function and passing your values to that when you're ready:

function multiplyDivide(...args) {
  return args.reduce((total, next, i) => (i % 2) ? (total / next) : (total * next), args.shift());
}

const values = [5, 4, 2, 3, 3];
values.push(5, 1);

console.log(multiplyDivide(...values));