ads to_s to ast for better readability

lib/ast/while_expression.rb

@@ -7,6 +7,9 @@ module Ast
     def inspect
       self.class.name + ".new(" + condition.inspect + ", "  + body.inspect + " )"  
     end
+    def to_s
+      "while(#{condition}) do\n" + body.join("\n") + "\nend\n"
+    end
     def attributes
       [:condition, :body]
     end