crocks/helpers/composeS.js

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

/** @license ISC License (c) copyright 2017 original and current authors */
/** @author Ian Hofmann-Hicks (evil) */

var isSameType = require('../core/isSameType')
var isSemigroupoid = require('../core/isSemigroupoid')

var err = 'composeS: Semigroupoids of the same type required'

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

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

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

  var head =
    ms[0]

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

  if(ms.length === 1) {
    return head
  }

  return ms.slice().reduce(function (comp, m) {
    if(!isSameType(comp, m)) {
      throw new TypeError(err)
    }

    return comp.compose(m)
  })
}

module.exports = composeS