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

var type = require('../core/types').type('Equiv')
var _type = require('../core/types').typeFn(type(), VERSION)
var fl = require('../core/flNames')

var _empty =
  function () { return Equiv(function () { return true; }); }

function Equiv(compare) {
  var obj;

  if(!isFunction(compare)) {
    throw new TypeError('Equiv: Comparison function required')
  }

  var compareWith = curry(
    function (x, y) { return !!compare(x, y); }
  )

  var inspect =
    function () { return ("Equiv" + (_inspect(compare))); }

  var empty =
    _empty

  var valueOf =
    function () { return compareWith; }

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

      return Equiv(
        function (x, y) { return compareWith(fn(x), fn(y)); }
      )
    }
  }

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

      return Equiv(function (x, y) { return compareWith(x, y) && m.compareWith(x, y); }
      )
    }
  }

  return ( obj = {
    inspect: inspect, toString: inspect, type: type,
    compareWith: compareWith, valueOf: valueOf, empty: empty,
    concat: concat('concat'),
    contramap: contramap('contramap')
  }, obj[fl.empty] = empty, obj[fl.concat] = concat(fl.concat), obj[fl.contramap] = contramap(fl.contramap), obj['@@type'] = _type, obj.constructor = Equiv, obj )
}

Equiv.empty = _empty
Equiv.type = type

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

Equiv['@@implements'] = _implements(
  [ 'concat', 'contramap', 'empty' ]
)

module.exports = Equiv