add pattern Interpreter

Behavioral/Interpreter/VariableExp.php

@@ -0,0 +1,23 @@
+<?php declare(strict_types=1);
+
+namespace DesignPatterns\Behavioral\Interpreter;
+
+class VariableExp extends AbstractExp
+{
+    private string $name;
+
+    public function __construct(string $name)
+    {
+        $this->name = $name;
+    }
+
+    public function interpret(Context $context): bool
+    {
+        return $context->lookUp($this->name);
+    }
+
+    public function getName(): string
+    {
+        return $this->name;
+    }
+}