adds crystals parser code

lib/parser/control.rb

@@ -0,0 +1,20 @@
+module Parser
+  module Control
+    include Parslet
+    rule(:conditional) do
+      keyword_if >> 
+      (( (value_expression|operator_expression).as(:conditional) ) |
+        left_parenthesis >> (operator_expression|value_expression).as(:conditional) >>  right_parenthesis) >>
+      newline >> expressions_else.as(:if_true) >> newline >> expressions_end.as(:if_false)
+      end
+    
+    rule(:while_do) do
+      keyword_while  >> left_parenthesis >> (operator_expression|value_expression).as(:while_cond)  >>
+                                          right_parenthesis >> keyword_do >> newline >>
+                              expressions_end.as(:body)
+    end
+    rule(:simple_return) do
+      keyword_return >> (operator_expression|value_expression).as(:return_expression)
+    end
+  end
+end