Move internal modules to “internal” folder.

.internal/createFlow.js

@@ -0,0 +1,38 @@
+/**
+ * Creates a `flow` or `flowRight` function.
+ *
+ * @private
+ * @param {boolean} [fromRight] Specify iterating from right to left.
+ * @returns {Function} Returns the new flow function.
+ */
+function createFlow(fromRight) {
+  return (...funcs) => {
+    const length = funcs.length;
+
+    let func;
+    let wrapper;
+    let index = length;
+
+    if (fromRight) {
+      funcs.reverse();
+    }
+    while (index--) {
+      func = funcs[index];
+      if (typeof func != 'function') {
+        throw new TypeError('Expected a function');
+      }
+    }
+    return function(...args) {
+      const value = args[0];
+      let index = 0;
+      let result = length ? funcs[index].apply(this, args) : value;
+
+      while (++index < length) {
+        result = funcs[index].call(this, result);
+      }
+      return result;
+    };
+  };
+}
+
+export default createFlow;