How do currying and partial application differ from each other?

TL;DR

Currying transforms a function with multiple arguments into a sequence of functions, each taking a single argument. For example, a function f(a, b, c) becomes f(a)(b)(c). Partial application, on the other hand, fixes a few arguments of a function and produces another function with a smaller number of arguments. For example, if you partially apply f(a, b, c) with a, you get a new function f'(b, c).

Currying vs partial application

Currying

Currying is a technique where a function with multiple arguments is transformed into a sequence of functions, each taking a single argument. This allows for more flexible function composition and reuse.

Example

function add(a) {
  return function (b) {
    return function (c) {
      return a + b + c;
    };
  };
}

const result = add(1)(2)(3); // 6

In this example, add is a curried function that takes three arguments one at a time.

Partial application

Partial application is a technique where you fix a few arguments of a function, producing another function with a smaller number of arguments. This is useful for creating specialized functions from more general ones.

Example

function add(a, b, c) {
  return a + b + c;
}

const addOne = add.bind(null, 1);
const result = addOne(2, 3); // 6

In this example, addOne is a partially applied function that fixes the first argument of add to 1.

Key differences

• Currying: Transforms a function with multiple arguments into a sequence of functions, each taking a single argument.
• Partial application: Fixes a few arguments of a function and produces another function with a smaller number of arguments.

Further reading

• Currying on MDN
• Partial application on MDN
• JavaScript.info on currying and partial application