Compose.js

'use strict';

var FL = require ('fantasy-land');

var ap = require ('./ap');
var equals = require ('./equals');
var map = require ('./map');
var of = require ('./of');
var toString = require ('./toString');


//  Compose :: (Apply f, Apply g) => TypeRep f -> TypeRep g -> f (g a) -> Compose f g a
module.exports = function Compose(F) {
  return function ComposeF(G) {
    function ComposeFG(value) {
      if (!(this instanceof ComposeFG)) return new ComposeFG (value);
      this.value = value;
    }

    ComposeFG['@@type'] = 'sanctuary/Compose';

    ComposeFG[FL.of] = function(x) {
      return ComposeFG (of (F) (of (G) (x)));
    };

    ComposeFG.prototype[FL.equals] = function(other) {
      return equals (this.value) (other.value);
    };

    ComposeFG.prototype[FL.map] = function(f) {
      return ComposeFG (map (map (f)) (this.value));
    };

    ComposeFG.prototype[FL.ap] = function(other) {
      return ComposeFG (ap (map (ap) (other.value)) (this.value));
    };

    //  name :: TypeRep a -> String
    function name(typeRep) {
      return typeof typeRep['@@type'] === 'string' ?
               typeRep['@@type'].replace (/^[^/]*[/]/, '') :
               typeRep.name;
    }

    ComposeFG.prototype.inspect =
    ComposeFG.prototype.toString = function() {
      return 'Compose(' + name (F) + ')' +
                    '(' + name (G) + ')' +
                    '(' + toString (this.value) + ')';
    };

    return ComposeFG;
  };
};