#+title: partial application

Partial application is a form of [[file:20210314121301-functional_application.org][functional application]] wherein the first =n=
arguments are bound.

This is not to be confused with [[file:20210607204228-currying.org][currying]],

In [[file:20200720132835-javascript.org][JavaScript]] in particular, a built-in method on functions called =.bind=
can accomplish this:

#+begin_src js :results output
const add = (x, y) => x + y;
const add10 = add.bind(null, 10);
console.log(add10(20));
#+end_src

#+RESULTS:
: 30

We could implement a free function as such in [[file:20210607203539-typescript.org][TypeScript]]:

#+begin_src typescript
type Variadic<R> = (...args: any[]) => R;

function partial<T>(fn: Variadic<T>, ...args: any[]): Variadic<T> {
    return function(...rest: any[]) {
        return fn(...args, ...rest);
    }
}

const add = (x: number, y: number): number => x + y;
const add10 = partial(add, 10);
console.log(add10(100));
#+end_src

#+RESULTS:
: 110