crocks/First/index.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 VERSION = 2

var _implements = require('../core/implements')
var _inspect = require('../core/inspect')
var _equals = require('../core/equals')
var type = require('../core/types').type('First')
var _type = require('../core/types').typeFn(type(), VERSION)
var fl = require('../core/flNames')

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

var Maybe = require('../core/Maybe')

var _empty =
  function () { return First(Maybe.Nothing()); }

function First(x) {
  var obj;

  if(!arguments.length) {
    throw new TypeError('First: Requires one argument')
  }

  var maybe =
    !isSameType(Maybe, x) ? Maybe.of(x) : x.map(function (x) { return x; })

  var empty =
    _empty

  var inspect =
    function () { return ("First(" + (_inspect(maybe)) + " )"); }

  var equals =
  function (m) { return isSameType(First, m)
    && _equals(maybe, m.valueOf()); }

  var valueOf =
    function () { return maybe; }

  var option =
    maybe.option

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

      var n =
        m.valueOf().map(function (x) { return x; })

      return First(
        maybe.either(function () { return n; }, Maybe.Just)
      )
    }
  }

  return ( obj = {
    inspect: inspect, toString: inspect,
    equals: equals, empty: empty, option: option, type: type, valueOf: valueOf,
    concat: concat('concat')
  }, obj[fl.equals] = equals, obj[fl.empty] = _empty, obj[fl.concat] = concat(fl.concat), obj['@@type'] = _type, obj.constructor = First, obj )
}

First['@@implements'] = _implements(
  [ 'equals', 'concat', 'empty' ]
)

First.empty = _empty
First.type = type

First[fl.empty] = _empty
First['@@type'] = _type

module.exports = First