feat: Add basic fantasy land support to ArrayElement

Author: kylef

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Minim Changelog
 
+## Master
+
+### Enhancements
+
+- `ArrayElement` now conforms to parts of the [Fantasy
+  Land](https://github.com/fantasyland/fantasy-land) 3.5 specification.
+  `Functor`, `Semigroup`, `Monoid`, `Filterable`, `Chain`, and `Foldable` are
+  now supported.
+
 ## 0.21.1
 
 ### Bug Fixes

lib/primitives/array-element.js

@@ -312,7 +312,43 @@ var ArrayElement = Element.extend({
     return this.content.some(function (element) {
       return element.equals(value);
     });
-  }
+  },
+
+  // Fantasy Land
+
+  empty: function() {
+    return new this.constructor([]);
+  },
+
+  'fantasy-land/empty': function() {
+    return this.empty();
+  },
+
+  concat: function(other) {
+    return new this.constructor(this.content.concat(other.content));
+  },
+
+  'fantasy-land/concat': function(other) {
+    return this.concat(other);
+  },
+
+  'fantasy-land/map': function(transform) {
+    return new this.constructor(this.map(transform));
+  },
+
+  'fantasy-land/chain': function(transform) {
+    return this
+      .map(function (element) { return transform(element); }, this)
+      .reduce(function (a, b) { return a.concat(b); }, this.empty());
+  },
+
+  'fantasy-land/filter': function(callback) {
+    return new this.constructor(this.content.filter(callback));
+  },
+
+  'fantasy-land/reduce': function(transform, initialValue) {
+    return this.content.reduce(transform, initialValue);
+  },
 }, {}, {
   /**
    * Returns the length of the collection
@@ -375,6 +411,12 @@ var ArrayElement = Element.extend({
   },
 });
 
+ArrayElement.empty = function () {
+  return new this();
+};
+
+ArrayElement['fantasy-land/empty'] = ArrayElement.empty;
+
 if (typeof Symbol !== 'undefined') {
   ArrayElement.prototype[Symbol.iterator] = function () {
     return this.content[Symbol.iterator]();

package.json

@@ -35,6 +35,7 @@
     "chai": "^4.0.0",
     "coveralls": "^3.0.1",
     "eslint": "^4.19.1",
+    "fantasy-land": "^3.5.0",
     "istanbul": "^0.4.5",
     "karma": "^2.0.2",
     "karma-browserify": "^5.2.0",

test/primitives/array-element-fantasy-land-test.js

@@ -0,0 +1,83 @@
+'use strict';
+
+var fl = require('fantasy-land');
+var expect = require('../spec-helper').expect;
+var namespace = require('../../lib/minim').namespace();
+
+var ArrayElement = namespace.getElementClass('array');
+
+describe('ArrayElement', function() {
+  var array = new ArrayElement([1, 2, 3, 4]);
+
+  describe('Functor', function() {
+    it('can transform elements into new ArrayElement', function() {
+      var result = array[fl.map](function(n) {
+        return new namespace.elements.Number(n.toValue() * 2);
+      });
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([2, 4, 6, 8]);
+    });
+  });
+
+  describe('Semigroup', function() {
+    it('can concatinate two array elements', function() {
+      var result = array[fl.concat](new ArrayElement([5, 6]));
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([1, 2, 3, 4, 5, 6]);
+    });
+  });
+
+  describe('Monoid', function() {
+    it('can create an empty ArrayElement', function() {
+      var result = ArrayElement[fl.empty]();
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([]);
+    });
+
+    it('can create an empty ArrayElement from another ArrayElement', function() {
+      var result = array[fl.empty]();
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([]);
+    });
+  });
+
+  describe('Filterable', function() {
+    it('can filter all elements into equivilent ArrayElement', function() {
+      var result = array[fl.filter](function() { return true; });
+
+      expect(result).to.deep.equal(array);
+    });
+
+    it('can filter into empty ArrayElement', function() {
+      var result = array[fl.filter](function() { return false; });
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.isEmpty).to.be.true;
+    });
+  });
+
+  describe('Chain', function() {
+    it('can transform and chain results into new ArrayElement', function() {
+      var duplicate = function(n) { return new ArrayElement([n, n]); };
+      var result = array[fl.chain](duplicate);
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([1, 1, 2, 2, 3, 3, 4, 4]);
+    });
+  });
+
+  describe('Foldable', function() {
+    it('can reduce results into new ArrayElement', function() {
+      var result = array[fl.reduce](function (accumulator, element) {
+        return accumulator.concat(new ArrayElement([element.toValue(), element.toValue()]));
+      }, new ArrayElement());
+
+      expect(result).to.be.instanceof(ArrayElement);
+      expect(result.toValue()).to.deep.equal([1, 1, 2, 2, 3, 3, 4, 4]);
+    });
+  });
+});