crocks/core/Unit.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 VERSION = 2

var _implements = require('./implements')
var type = require('./types').type('Unit')
var _type = require('./types').typeFn(type(), VERSION)
var fl = require('./flNames')

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

var _of =
  Unit

var _empty =
  Unit

function Unit() {
  var obj;

  var equals =
    function (m) { return isSameType(Unit, m); }

  var inspect =
    function () { return '()'; }

  var valueOf =
    function () { return undefined; }

  var of =
    _of

  var empty =
    _empty

  function concat(method) {
    return function(m) {
      if(!isSameType(Unit, m)) {
        throw new TypeError(("Unit." + method + ": Unit required"))
      }

      return Unit()
    }
  }

  function map(method) {
    return function(fn) {
      if(!isFunction(fn)) {
        throw new TypeError(("Unit." + method + ": Function required"))
      }

      return Unit()
    }
  }

  function ap(m) {
    if(!isSameType(Unit, m)) {
      throw new TypeError('Unit.ap: Unit required')
    }

    return Unit()
  }

  function chain(method) {
    return function(fn) {
      if(!isFunction(fn)) {
        throw new TypeError(("Unit." + method + ": Function required"))
      }

      return Unit()
    }
  }

  return ( obj = {
    inspect: inspect, toString: inspect, valueOf: valueOf,
    type: type, equals: equals, empty: empty, ap: ap, of: of,
    concat: concat('concat'),
    map: map('map'),
    chain: chain('chain')
  }, obj[fl.of] = of, obj[fl.empty] = empty, obj[fl.equals] = equals, obj[fl.concat] = concat(fl.concat), obj[fl.map] = map(fl.map), obj[fl.chain] = chain(fl.chain), obj['@@type'] = _type, obj.constructor = Unit, obj )
}

Unit.of = _of
Unit.empty = _empty
Unit.type = type

Unit[fl.of] = _of
Unit[fl.empty] = _empty
Unit['@@type'] = _type

Unit['@@implements'] = _implements(
  [ 'ap', 'chain', 'concat', 'empty', 'equals', 'map', 'of' ]
)

module.exports = Unit