crocks/helpers/fromPairs.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 Pair = require('../core/types').proxy('Pair')

var isFoldable = require('../core/isFoldable')
var isSameType = require('../core/isSameType')
var isString = require('../core/isString')

function foldPairs(acc, pair) {
  var obj;

  if(!isSameType(Pair, pair)) {
    throw new TypeError('fromPairs: Foldable of Pairs required for argument')
  }

  var key = pair.fst()
  var value = pair.snd()

  if(!isString(key)) {
    throw new TypeError('fromPairs: String required for fst of every Pair')
  }

  return value !== undefined
    ? Object.assign(acc, ( obj = {}, obj[key] = value, obj ))
    : acc
}

// fromPairs : Foldable f => f (Pair String a) -> Object
function fromPairs(xs) {
  if(!isFoldable(xs)) {
    throw new TypeError('fromPairs: Foldable of Pairs required for argument')
  }

  return xs.reduce(foldPairs, {})
}

module.exports = fromPairs