Merge pull request #12 from earldouglas/readert

Add ReaderT

package.json

@@ -1,7 +1,7 @@
 {
   "name": "teep",
   "description": "A JavaScript library for functional programming.",
-  "version": "1.0.0",
+  "version": "1.1.0",
   "homepage": "https://github.com/earldouglas/teep",
   "author": {
     "name": "James Earl Douglas",

src/teep.ts

@@ -26,7 +26,7 @@ module edc {
     put: (A, B) => void;
   }
 
-  class DumbCache<A,B> implements Cache<A,B> {
+  class DumbCache<A,B> {
     cache = {};
     get = (k) => { return this.cache[k]; };
     put = (k,v) => { this.cache[k] = v; };
@@ -78,7 +78,12 @@ module edc {
     },
   };
 
-  export interface Option<A> {
+  export interface Monad<A> {
+    map: <B>(f: (A) => B) => Monad<B>;
+    flatMap: <B>(f: (A) => Monad<B>) => Monad<B>;
+  }
+
+  export interface Option<A> extends Monad<A> {
     empty    : boolean;
     map      : <B>(f: (A) => B) => Option<B>;
     flatMap  : <B>(f: (A) => Option<B>) => Option<B>;
@@ -115,7 +120,7 @@ module edc {
     }
   }
 
-  export interface Validation<A> {
+  export interface Validation<A> extends Monad<A> {
     valid    : boolean;
     map      : <B>(f: (A) => B) => Validation<B>;
     flatMap  : <B>(f: (A) => Validation<B>) => Validation<B>;
@@ -151,7 +156,7 @@ module edc {
     invalid: (errors: Array<String>) => { return new Invalid(errors); },
   };
 
-  export interface List<A> {
+  export interface List<A> extends Monad<A> {
     length   : number;
     map      : <B>(f: (A) => B) => List<B>;
     flatMap  : <B>(f: (A) => List<B>) => List<B>;
@@ -273,15 +278,38 @@ module edc {
 
   var future = <A>(f: (A) => any) => { return new Future(f); }
 
+  class ReaderT<A,B> {
+    f: (A) => Monad<B>;
+    constructor(f: (A) => Monad<B>) {
+      this.f = f;
+    }
+    apply(a: A): Monad<B> {
+      return this.f(a);
+    };
+    map<C>(g: (B) => C): ReaderT<A,C> {
+      return new ReaderT((a) => {
+        return this.f(a).map(g);
+      });
+    };
+    flatMap<C>(g: (B) => ReaderT<A,C>): ReaderT<A,C> {
+      return new ReaderT((a) => {
+        return this.f(a).map(g).flatMap((r) => { return r.apply(a); });
+      });
+    };
+  }
+
+  var readerT = <A,B>(f: (A) => Monad<B>) => { return new ReaderT(f); }
+
   export var teep = {
-    array: array,
-    fn: fn,
-    option: option,
+    array:      array,
+    fn:         fn,
+    option:     option,
     validation: validation,
-    list: list,
-    promise: promise,
-    reader: reader,
-    future: future,
+    list:       list,
+    promise:    promise,
+    reader:     reader,
+    future:     future,
+    readerT:    readerT,
   };
 
   var setExports = function () {
@@ -296,4 +324,3 @@ module edc {
   !exports || setExports();
 
 }
-

teep.js

@@ -253,6 +253,31 @@ var edc;
         return Future;
     })();
     var future = function (f) { return new Future(f); };
+    var ReaderT = (function () {
+        function ReaderT(f) {
+            this.f = f;
+        }
+        ReaderT.prototype.apply = function (a) {
+            return this.f(a);
+        };
+        ;
+        ReaderT.prototype.map = function (g) {
+            var _this = this;
+            return new ReaderT(function (a) {
+                return _this.f(a).map(g);
+            });
+        };
+        ;
+        ReaderT.prototype.flatMap = function (g) {
+            var _this = this;
+            return new ReaderT(function (a) {
+                return _this.f(a).map(g).flatMap(function (r) { return r.apply(a); });
+            });
+        };
+        ;
+        return ReaderT;
+    })();
+    var readerT = function (f) { return new ReaderT(f); };
     edc.teep = {
         array: array,
         fn: fn,
@@ -261,7 +286,8 @@ var edc;
         list: list,
         promise: promise,
         reader: reader,
-        future: future
+        future: future,
+        readerT: readerT
     };
     var setExports = function () {
         for (var i in edc.teep) {

test/examples.js

@@ -288,7 +288,6 @@ describe('examples', function () {
 
   });
 
-
   describe('future', function () {
     var async = function(x) {
       return function (k) {
@@ -337,4 +336,50 @@ describe('examples', function () {
 
   });
 
+  describe('readerT', function () {
+
+    var db = {
+      answer: 42,
+    };
+
+    var getAnswer = function (db) {
+      return teep.future(function (k) {
+        return k(db.answer);
+      });
+    };
+
+    function addToAnswer(x) {
+      return teep.readerT(function (db) {
+        return teep.future(function (k) {
+          return k(db.answer + x);
+        });
+      });
+    };
+
+    function verify(x, done) {
+      return function (y) {
+        if (x === y) {
+          done();
+        }
+      };
+    };
+
+    it('apply', function (done) {
+      teep.readerT(getAnswer).apply(db).apply(verify(42, done));
+    });
+
+    it('map', function (done) {
+      teep.readerT(getAnswer).map(function (x) {
+        return x + 1;
+      }).apply(db).apply(verify(43, done));
+    });
+
+    it('flatMap', function (done) {
+      teep.readerT(getAnswer).flatMap(function (x) {
+        return addToAnswer(x + 1);
+      }).apply(db).apply(verify(85, done));
+    });
+
+  });
+
 });