crocks/helpers/mapReduce.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 curry = require('../core/curry')
var isFoldable = require('../core/isFoldable')
var isFunction = require('../core/isFunction')

function mapReduce(mapFn, reduceFn, empty, xs) {
  if(!isFunction(mapFn)) {
    throw new TypeError('mapReduce: Unary mapping function required for first argument')
  }

  if(!isFunction(reduceFn)) {
    throw new TypeError('mapReduce: Binary reduction function required for second argument')
  }

  if(!isFoldable(xs)) {
    throw new TypeError('mapReduce: Foldable required for fourth argument')
  }

  return xs.reduce(
    function (acc, x) { return reduceFn(acc, mapFn(x)); },
    empty
  )
}

module.exports = curry(mapReduce)