[FP] partial application

partial.js

// Reference: https://github.com/getify/Functional-Light-JS/blob/master/ch3.md#some-now-some-later

function partial(fn, ...presetArgs) {
  return function(...laterArgs) {
    return fn(...presetArgs, ...laterArgs); 
  };
}


// // Or:
// const partial = 
//       (fn, ...presetArgs) => 
//                 (...laterArgs) => 
//                       fn(...presetArgs, ...laterArgs)


// Usage:
function add (a, b) {
  return a + b;
}

const addThree = partial(add, 3);
const ret = [1, 2, 3].map(addThree);   // [3, 4, 5]