What is 'Currying'?

Question

I\'ve seen references to curried functions in several articles and blogs but I can\'t find a good explanation (or at least one that makes sense!)

Answer 1

Currying is translating a function from callable as f(a, b, c) into callable as f(a)(b)(c).

Otherwise currying is when you break down a function that takes multiple arguments into a series of functions that take part of the arguments.

Literally, currying is a transformation of functions: from one way of calling into another. In JavaScript, we usually make a wrapper to keep the original function.

Currying doesn’t call a function. It just transforms it.

Let’s make curry function that performs currying for two-argument functions. In other words, curry(f) for two-argument f(a, b) translates it into f(a)(b)

function curry(f) { // curry(f) does the currying transform
  return function(a) {
    return function(b) {
      return f(a, b);
    };
  };
}

// usage
function sum(a, b) {
  return a + b;
}

let carriedSum = curry(sum);

alert( carriedSum(1)(2) ); // 3

As you can see, the implementation is a series of wrappers.

• The result of curry(func) is a wrapper function(a).
• When it is called like sum(1), the argument is saved in the Lexical Environment, and a new wrapper is returned function(b).
• Then sum(1)(2) finally calls function(b) providing 2, and it passes the call to the original multi-argument sum.