add source to instruction

for debug

lib/virtual/instructions/virtual_main.rb

@@ -15,5 +15,9 @@ module Virtual
     def word_length
       4
     end
+
+    def to_s
+      "#{self.class.name}( method: #{method.name})"
+    end
   end
 end

lib/virtual/machine.rb

@@ -35,6 +35,8 @@ module Virtual
   class Machine
 
     FIRST_PASS = "Virtual::SendImplementation"
+    LAST_PASS = "Virtual::SetOptimisation"
+    
     def initialize
       @parser  = Parser::Salama.new
       @passes = [  FIRST_PASS ]