Add futures

teep.js

@@ -143,7 +143,6 @@ var edc;
                    }
       };
     };
-
     if (tail === undefined || tail === null) {
       return list(head, _nil);
     } else if (head === undefined || head === null) {
@@ -166,13 +165,54 @@ var edc;
     }
   };
 
+  var future = function (f) {
+    return {
+      apply: function (k) {
+        return f(k);
+      },
+      map: function (g) {
+        return future (function (k) {
+          return f(function (x) {
+            return k(g(x));
+          });
+        });
+      },
+      flatMap: function (g) {
+        return future (function (k) {
+          return f(function (x) {
+            return g(x).apply(k);
+          });
+        });
+      },
+      sequence: function (f2) {
+        var xs = [];
+        return future(function (k) {
+          var kk = function() {
+            if (xs.length === 2) {
+              k(xs);
+            }
+          };
+          f(function (x) {
+            xs.unshift(x);
+            kk();
+          });
+          f2.apply(function (x) {
+            xs.push(x);
+            kk();
+          });
+        });
+      }
+    };
+  };
+
   edc.teep = {
     array: array,
     fn: fn,
     option: option,
     validation: validation,
     list: list,
     promise: promise,
+    future: future,
   };
 
   for (var i in edc.teep) {

test/future_test.js

@@ -0,0 +1,70 @@
+'use strict';
+
+var teep = require('../teep.js');
+var future = teep.future;
+var jsc = require('jsverify');
+
+var async = function(x) {
+  return function (k) {
+    k(x);
+  };
+};
+
+var asyncF = function (f) {
+  return function (x) {
+    return future(function (k) {
+      k(f(x));
+    });
+  };
+};
+
+exports.future = {
+  'future.apply': function (test) {
+    jsc.check(jsc.forall('number',
+      function (x) {
+        var verify = function (z) {
+          if (x === z) {
+            test.done();
+          }
+        };
+        future(async(x)).apply(verify);
+      }
+    ));
+  },
+  'future.map': function (test) {
+    jsc.check(jsc.forall('number', 'number -> number',
+      function (x, f) {
+        var verify = function (z) {
+          if (f(x) === z) {
+            test.done();
+          }
+        };
+        future(async(x)).map(f).apply(verify);
+      }
+    ));
+  },
+  'future.flatMap': function (test) {
+    jsc.check(jsc.forall('number', 'number -> number',
+      function (x, f) {
+        var verify = function (z) {
+          if (f(x) === z) {
+            test.done();
+          }
+        };
+        future(async(x)).flatMap(asyncF(f)).apply(verify);
+      }
+    ));
+  },
+  'future.sequence': function (test) {
+    jsc.check(jsc.forall('number',
+      function (x) {
+        var verify = function (z) {
+          if (z.length === 2 && z[0] === x && z[1] === x) {
+            test.done();
+          }
+        };
+        future(async(x)).sequence(future(async(x))).apply(verify);
+      }
+    ));
+  },
+};