Several fixes + integration test

src/ExpressionLanguage/ExpressionLanguage.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace uuf6429\ExpressionLanguage;
+
+use Symfony\Component\ExpressionLanguage\ExpressionLanguage as SymfonyExpressionLanguage;
+
+class ExpressionLanguage extends SymfonyExpressionLanguage
+{
+    /** @var Parser */
+    protected $parser;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __construct($cache = null, array $providers = array())
+    {
+        $this->parser = new Parser(array());
+
+        parent::__construct($cache, $providers);
+
+        $reflection = new \ReflectionClass(SymfonyExpressionLanguage::class);
+
+        $prop = $reflection->getProperty('lexer');
+        $prop->setAccessible(true);
+        $prop->setValue($this, new Lexer());
+        $prop->setAccessible(false);
+
+        $prop = $reflection->getProperty('parser');
+        $prop->setAccessible(true);
+        $prop->setValue($this, $this->parser);
+        $prop->setAccessible(false);
+    }
+
+    /**
+     * Hack to keep functions in parser up to date.
+     *
+     * {@inheritdoc}
+     */
+    public function register($name, callable $compiler, callable $evaluator)
+    {
+        parent::register($name, $compiler, $evaluator);
+        $this->parser->setFunctions($this->functions);
+    }
+}

src/ExpressionLanguage/Lexer.php

@@ -5,7 +5,7 @@
 use Symfony\Component\ExpressionLanguage\Token;
 use Symfony\Component\ExpressionLanguage\SyntaxError;
 
-class Lexer extends Symfony\Component\ExpressionLanguage\Lexer
+class Lexer extends \Symfony\Component\ExpressionLanguage\Lexer
 {
     /**
      * {@inheritdoc}