Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

Predis/Command/ScriptedCommand.php

@@ -0,0 +1,76 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) Daniele Alessandri <suppakilla@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Command;
+
+/**
+ * Base class used to implement an higher level abstraction for "virtual"
+ * commands based on EVAL.
+ *
+ * @link http://redis.io/commands/eval
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+abstract class ScriptedCommand extends ServerEvalSHA
+{
+    /**
+     * Gets the body of a Lua script.
+     *
+     * @return string
+     */
+    abstract public function getScript();
+
+    /**
+     * Specifies the number of arguments that should be considered as keys.
+     *
+     * The default behaviour for the base class is to return 0 to indicate that
+     * all the elements of the arguments array should be considered as keys, but
+     * subclasses can enforce a static number of keys.
+     *
+     * @return int
+     */
+    protected function getKeysCount()
+    {
+        return 0;
+    }
+
+    /**
+     * Returns the elements from the arguments that are identified as keys.
+     *
+     * @return array
+     */
+    public function getKeys()
+    {
+        return array_slice($this->getArguments(), 2, $this->getKeysCount());
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function filterArguments(Array $arguments)
+    {
+        if (($numkeys = $this->getKeysCount()) && $numkeys < 0) {
+            $numkeys = count($arguments) + $numkeys;
+        }
+
+        return array_merge(array(sha1($this->getScript()), (int) $numkeys), $arguments);
+    }
+
+    /**
+     * @return array
+     */
+    public function getEvalArguments()
+    {
+        $arguments = $this->getArguments();
+        $arguments[0] = $this->getScript();
+
+        return $arguments;
+    }
+}