crocks/List/maybeToList.js

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

/** @license ISC License (c) copyright 2019 original and current authors */
/** @author Ian Hofmann-Hicks (evil) */

var List = require('.')
var Maybe = require('../core/types').proxy('Maybe')

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

var applyTransform = function (maybe) { return maybe.either(
    List.empty,
    List.of
  ); }

var err =
  'maybeToList: Argument must be a Maybe instanstace or a Maybe returning function'

// maybeToList : Maybe a -> List a
// maybeToList : (a -> Maybe b) -> a -> List b
function maybeToList(maybe) {
  if(isFunction(maybe)) {
    return function(x) {
      var m = maybe(x)

      if(!isSameType(Maybe, m)) {
        throw new TypeError(err)
      }

      return applyTransform(m)
    }
  }

  if(isSameType(Maybe, maybe)) {
    return applyTransform(maybe)
  }

  throw new TypeError(err)
}

module.exports = curry(maybeToList)