crocks/helpers/compose.js

A collection of well known Algebraic Datatypes for your utter enjoyment.

/** @license ISC License (c) copyright 2016 original and current authors */
/** @author Ian Hofmann-Hicks (evil) */

var isFunction = require('../core/isFunction')

var err = 'compose: Functions required'

function applyPipe(f, g) {
  if(!isFunction(g)) {
    throw new TypeError(err)
  }

  return function () {
      var args = [], len = arguments.length;
      while ( len-- ) args[ len ] = arguments[ len ];

      return g.call(null, f.apply(null, args));
  }
}

// compose : ((y -> z), (x -> y), ..., (a -> b)) -> a -> z
function compose() {
  var args = [], len = arguments.length;
  while ( len-- ) args[ len ] = arguments[ len ];

  if(!arguments.length) {
    throw new TypeError(err)
  }

  var fns =
    args.slice().reverse()

  var head =
    fns[0]

  if(!isFunction(head)) {
    throw new TypeError(err)
  }

  var tail =
    fns.slice(1).concat(function (x) { return x; })

  return tail.reduce(applyPipe, head)
}

module.exports = compose