Merge 7eebe3b into d76a7cd

index.js

@@ -29,18 +29,29 @@ function Wrap(fn, ctx, next) {
   this._fn = fn;
   this._ctx = ctx;
   this._next = next;
+  this._called = false;
+  this._value = undefined;
+  this._promise = undefined;
+  this._generator = undefined;
 }
 
 /**
  * Lazily call the function.
  * Note that if it's not an async or generator function,
- * throws may mess things up.
  *
  * @returns {Mixed}
  */
 
 Wrap.prototype._getValue = function () {
-  return this._fn.call(this._ctx, this._next);
+  if (!this._called) {
+    this._called = true;
+    try {
+      this._value = this._fn.call(this._ctx, this._next);
+    } catch (e) {
+      this._value = Promise.reject(e);
+    }
+  }
+  return this._value
 };
 
 /**
@@ -50,10 +61,13 @@ Wrap.prototype._getValue = function () {
  */
 
 Wrap.prototype._getPromise = function () {
-  var value = this._getValue();
-  return isGenerator(value)
-    ? co.call(this._ctx, value)
-    : Promise.resolve(value);
+  if (this._promise === undefined) {
+    var value = this._getValue();
+    this._promise = isGenerator(value)
+      ? co.call(this._ctx, value)
+      : Promise.resolve(value);
+  }
+  return this._promise
 }
 
 /**
@@ -63,10 +77,13 @@ Wrap.prototype._getPromise = function () {
  */
 
 Wrap.prototype._getGenerator = function () {
-  var value = this._getValue();
-  return isGenerator(value)
-    ? value
-    : promiseToGenerator.call(this._ctx, value);
+  if (this._generator === undefined) {
+    var value = this._getValue();
+    this._generator = isGenerator(value)
+      ? value
+      : promiseToGenerator.call(this._ctx, value);
+  }
+  return this._generator
 }
 
 /**

test/test.js

@@ -35,6 +35,25 @@ it('should support delegating-yielding a random value', function () {
   })
 })
 
+it('should support return another wrap', function (done) {
+  var i = 0
+  var stack = [
+    function (next) {
+      i++;
+      return next
+    },
+    function (next) {
+      i++;
+      return next
+    }
+  ]
+
+  return compose(stack)().then(function () {
+    assert.equal(i, 2)
+    done()
+  })
+})
+
 it('should support an empty array', function () {
   return compose([])().then(function () {