Work on #226, #213, added references of Gang Of Four to all GoF patterns, added tag for Gang Of Four, added difficulty tags to some of them

interpreter/index.md

@@ -4,7 +4,9 @@ title: Interpreter
 folder: interpreter
 permalink: /patterns/interpreter/
 categories: Behavioral
-tags: Java
+tags: 
+ - Java
+ - Gang Of Four
 ---
 
 **Intent:** Given a language, define a representation for its grammar along
@@ -19,3 +21,7 @@ trees. The Interpreter pattern works best when
 
 * the grammar is simple. For complex grammars, the class hierarchy for the grammar becomes large and unmanageable. Tools such as parser generators are a better alternative in such cases. They can interpret expressions without building abstract syntax trees, which can save space and possibly time
 * efficiency is not a critical concern. The most efficient interpreters are usually not implemented by interpreting parse trees directly but by first translating them into another form. For example, regular expressions are often transformed into state machines. But even then, the translator can be implemented by the Interpreter pattern, so the pattern is still applicable
+
+**Credits**
+
+* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)