fix class function test

lib/ast/function_expression.rb

@@ -8,7 +8,8 @@ module Ast
       frame = frame.new_frame
       return_type = nil
       body.each do |ex|
-        return_type = ex.compile(frame , method )
+        val = ex.compile(frame , method )
+        return_type = val.type
       end
       method.return_type = return_type
       method

lib/virtual/instruction.rb

@@ -18,6 +18,9 @@ module Virtual
     def initialize nex = nil
       @next = nex
     end
+    def type
+      Reference
+    end
   end
 
   # the first instruction we need is to stop. Off course in a real machine this would be a syscall, but that is just