add Maybe type for testing Alternative laws and refactor tests

- move patches and test structures into `internal`
  - `Compose` and patching of `Array` form `laws/traversable`
  - `equality`, `Sum` and patching of `String` form `id_test`
  - `Id` from `id`
- rename `id_test` to `test` as it's not just testing `Id` but `Maybe` and `Sum`

bower.json

@@ -29,7 +29,7 @@
     "/node_modules/",
     "/.*",
     "/id.js",
-    "/id_test.js",
+    "/test.js",
     "/implementations.md",
     "/logo.png",
     "/package.json"

internal/compose.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const {tagged} = require('daggy');
+
+const fl = require('..');
+const {equality} = require('./func');
+
+const Compose = module.exports = tagged('c');
+Compose[fl.of] = Compose;
+Compose.prototype[fl.ap] = function(f) {
+  return Compose(this.c[fl.ap](f.c[fl.map](u => y => y[fl.ap](u))));
+};
+Compose.prototype[fl.map] = function(f) {
+  return Compose(this.c[fl.map](y => y[fl.map](f)));
+};
+Compose.prototype[fl.equals] = function(x) {
+  return equality(this.c, x.c);
+};

internal/func.js

@@ -0,0 +1,8 @@
+'use strict';
+
+const fl = require('../');
+const equality = (x, y) => typeof x[fl.equals] === 'function' ? x[fl.equals](y) : x === y;
+
+module.exports = {
+  equality,
+};

id.js → internal/id.js

@@ -1,14 +1,15 @@
 'use strict';
 
-const fl = require('./');
+const fl = require('../');
+const {equality} = require('./func');
 
-const Id = function Id(a) {
-  this.value = a;
-};
+const {tagged} = require('daggy');
+
+const Id = module.exports = tagged('value');
 
 // Setoid
 Id.prototype[fl.equals] = function(b) {
-  return typeof this.value[fl.equals] === 'function' ? this.value[fl.equals](b.value) : this.value === b.value;
+  return equality(this.value, b.value);
 };
 
 // Semigroup (value must also be a Semigroup)
@@ -73,5 +74,3 @@ Id[fl.of] = function(a) {
 Id.prototype[fl.extract] = function() {
   return this.value;
 };
-
-module.exports = Id;

internal/index.js

@@ -0,0 +1,17 @@
+'use strict';
+
+const patch = require('./patch');
+const Maybe = require('./maybe');
+const Id = require('./id');
+const Sum = require('./string_sum');
+const Compose = require('./compose');
+const {equality} = require('./func');
+
+module.exports = {
+  Maybe,
+  Id,
+  Sum,
+  Compose,
+  equality,
+  patch,
+};

internal/maybe.js

@@ -0,0 +1,50 @@
+'use strict';
+
+const {taggedSum} = require('daggy');
+
+const fl = require('..');
+const {equality} = require('./func');
+
+const Maybe = module.exports = taggedSum({
+  Just: ['x'],
+  Nothing: [],
+});
+
+Maybe.prototype[fl.equals] = function(b) {
+  return this.cata({
+    Just: x =>  this.cata({
+      Just: y => equality(x, y),
+      Nothing: () => false,
+    }),
+    Nothing: () => this.cata({
+      Just: _ => false,
+      Nothing: () => true,
+    }),
+  });
+};
+
+Maybe.prototype[fl.chain] = function(f) {
+  return this.cata({
+    Just: x => f(x),
+    Nothing: () => this,
+  });
+};
+
+Maybe.prototype[fl.ap] = function(m) {
+  return m[fl.chain](f => this[fl.map](f));
+};
+
+Maybe[fl.of] = Maybe.Just;
+
+Maybe.prototype[fl.map] = function(f) {
+  return this[fl.chain](a => Maybe[fl.of](f(a)));
+};
+
+Maybe[fl.zero] = () => Maybe.Nothing;
+
+Maybe.prototype[fl.alt] = function(b) {
+  return this.cata({
+    Just: _ => this,
+    Nothing: () => b,
+  });
+};

internal/patch.js

@@ -0,0 +1,19 @@
+'use strict';
+
+const fl = require('..');
+
+module.exports = () => {
+  String.prototype[fl.concat] = String.prototype.concat;
+  Array.prototype[fl.equals] = function(y) {
+    return this.length === y.length && this.join('') === y.join('');
+  };
+  Array.prototype[fl.map] = Array.prototype.map;
+  Array.prototype[fl.reduce] = Array.prototype.reduce;
+  Array.prototype[fl.concat] = Array.prototype.concat;
+  Array.prototype[fl.traverse] = function(f, p) {
+    return this.map(f)[fl.reduce](
+      (ys, x) => ys[fl.ap](x[fl.map](y => z => z[fl.concat](y))),
+      p([])
+    );
+  };
+};

internal/string_sum.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const {tagged} = require('daggy');
+
+const fl = require('..');
+const {equality} = require('./func');
+
+// Special type of sum for the type of string.
+const Sum = module.exports = tagged('v');
+Sum[fl.of] = Sum;
+Sum[fl.empty] = () => Sum('');
+Sum.prototype[fl.map] = function(f) {
+  return Sum(f(this.v));
+};
+Sum.prototype[fl.concat] = function(x) {
+  return Sum(this.v + x.v);
+};
+Sum.prototype[fl.equals] = function(x) {
+  return equality(this.v, x.v);
+};

laws/traversable.js

@@ -1,34 +1,8 @@
 'use strict';
 
-const Id = require('../id');
+const {Id, Compose} = require('../internal');
 const {identity} = require('fantasy-combinators');
-const {of, ap, reduce, traverse, map, equals, concat} = require('..');
-const {tagged} = require('daggy');
-
-const Compose = tagged('c');
-Compose[of] = Compose;
-Compose.prototype[ap] = function(f) {
-  return Compose(this.c[ap](f.c[map](u => y => y[ap](u))));
-};
-Compose.prototype[map] = function(f) {
-  return Compose(this.c[map](y => y[map](f)));
-};
-Compose.prototype[equals] = function(x) {
-  return this.c[equals] ? this.c[equals](x.c) : this.c === x.c;
-};
-
-Array.prototype[equals] = function(y) {
-  return this.length === y.length && this.join('') === y.join('');
-};
-Array.prototype[map] = Array.prototype.map;
-Array.prototype[reduce] = Array.prototype.reduce;
-Array.prototype[concat] = Array.prototype.concat;
-Array.prototype[traverse] = function(f, p) {
-  return this.map(f)[reduce](
-    (ys, x) => ys[ap](x[map](y => z => z[concat](y))),
-    p([])
-  );
-};
+const {of, traverse, map} = require('..');
 
 /**
 

package.json

@@ -33,14 +33,15 @@
     "url": "https://github.com/fantasyland/fantasy-land.git"
   },
   "files": [
-    "id.js",
     "index.js",
+    "internal/*.js",
     "laws/*.js"
   ],
   "main": "index.js",
   "scripts": {
-    "lint": "eslint --config node_modules/sanctuary-style/eslint-es6.json --env es6 --env node --rule 'max-len: [off]' -- *.js laws/*.js",
-    "test": "npm run-script lint && nodeunit id_test.js",
+    "lint": "eslint --config node_modules/sanctuary-style/eslint-es6.json --env es6 --env node --rule 'max-len: [off]' -- *.js laws/*.js internal/*.js",
+    "unit": "nodeunit test.js",
+    "test": "npm run-script lint && npm run-script unit",
     "release-major": "xyz --repo [email protected]:fantasyland/fantasy-land.git --increment major",
     "release-minor": "xyz --repo [email protected]:fantasyland/fantasy-land.git --increment minor",
     "release-patch": "xyz --repo [email protected]:fantasyland/fantasy-land.git --increment patch"