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While reading an article on implementation of a generalised curry in Javascript, I stumbled upon this piece of code. 

function curry(fn) {
  return (...xs) => {
    if (xs.length === 0) {
      throw Error('EMPTY INVOCATION');
    }
    if (xs.length >= fn.length) {
      return fn(...xs);
    }
    return curry(fn.bind(null, ...xs));
  };
}

I am unable to grok the part of the explanation which states

We create a copy of fn that has the first k arguments bound (partially applied) and pass it to curry as the next fn, with its reduced arity of N - k.

How does the arity of fn reduced to N-k in the subsequent calls? A bound function with k arguments should have an arity of k right?

Varun
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    A bound function returns a function with partially applied arguments, so `f(a, b, c)` becomes `f.bind(null, a).bind(null, b)(c)` – elclanrs May 31 '18 at 03:15
  • @elclanrs Now it makes sense to me. Thanks. – Varun May 31 '18 at 07:02
  • Cute: [Function.prototype.length](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/length) ; it's been around since "forever", and I've never used/seen it before >_ – user2864740 Oct 01 '19 at 19:34

1 Answers1

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A bound function returns a function with partially applied arguments, so f(a, b, c) becomes f.bind(null, a).bind(null, b)(c).

elclanrs
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