Add createComposer to reduce the definition of _.flow and _.flowRight.

lodash.src.js

@@ -3217,6 +3217,41 @@
       return new SetCache(values);
     };
 
+    /**
+     * Creates a function to compose other functions into a single function.
+     *
+     * @private
+     * @param {boolean} [fromRight] Specify iterating from right to left.
+     * @returns {Function} Returns the new composer function.
+     */
+    function createComposer(fromRight) {
+      return function() {
+        var length = arguments.length,
+            index = length,
+            fromIndex = fromRight ? length - 1 : 0;
+
+        if (!length) {
+          return function() { return arguments[0]; };
+        }
+        var funcs = Array(length);
+        while (index--) {
+          funcs[index] = arguments[index];
+          if (typeof funcs[index] != 'function') {
+            throw new TypeError(FUNC_ERROR_TEXT);
+          }
+        }
+        return function() {
+          var index = fromIndex,
+              result = funcs[index].apply(this, arguments);
+
+          while ((fromRight ? index-- : ++index < length)) {
+            result = funcs[index].call(this, result);
+          }
+          return result;
+        };
+      };
+    }
+
     /**
      * Creates a function that produces compound words out of the words in a
      * given string.
@@ -7588,26 +7623,7 @@
      * addSquare(1, 2);
      * // => 9
      */
-    function flow() {
+    var flow = createComposer();
-      var funcs = arguments,
-          length = funcs.length;
-
-      if (!length) {
-        return function() { return arguments[0]; };
-      }
-      if (!arrayEvery(funcs, baseIsFunction)) {
-        throw new TypeError(FUNC_ERROR_TEXT);
-      }
-      return function() {
-        var index = 0,
-            result = funcs[index].apply(this, arguments);
-
-        while (++index < length) {
-          result = funcs[index].call(this, result);
-        }
-        return result;
-      };
-    }
 
     /**
      * This method is like `_.flow` except that it creates a function that
@@ -7629,26 +7645,7 @@
      * addSquare(1, 2);
      * // => 9
      */
-    function flowRight() {
+    var flowRight = createComposer(true);
-      var funcs = arguments,
-          fromIndex = funcs.length - 1;
-
-      if (fromIndex < 0) {
-        return function() { return arguments[0]; };
-      }
-      if (!arrayEvery(funcs, baseIsFunction)) {
-        throw new TypeError(FUNC_ERROR_TEXT);
-      }
-      return function() {
-        var index = fromIndex,
-            result = funcs[index].apply(this, arguments);
-
-        while (index--) {
-          result = funcs[index].call(this, result);
-        }
-        return result;
-      };
-    }
 
     /**
      * Creates a function that memoizes the result of `func`. If `resolver` is