splitting assignment into three, for args, locals and ivars

The decision on which is moving up to the ruby  compiler, so it can at
the same time emit the correct assignment form.
Just another example of moving away from a language and to an
intermediate form (that has no language equivalent)

lib/vm/tree/assignment.rb

@@ -1,13 +1,30 @@
 module Vm
   module Tree
+
     class Assignment < Statement
       attr_accessor :name , :value
-      def initialize(n = nil , v = nil )
-        @name , @value = n , v
+
+      def initialize(name  , value = nil )
+        @name , @value = name , value
       end
+
       def to_s
         "#{name} = #{value}\n"
       end
+
     end
+
+    class IvarAssignment < Assignment
+      def to_s
+        "@#{name} = #{value}\n"
+      end
+    end
+
+    class ArgAssignment < Assignment
+    end
+
+    class LocalAssignment < Assignment
+    end
+
   end
 end

lib/vm/tree/to_code.rb

@@ -120,12 +120,23 @@ module Vm
       Tree::ClassExpression.new(expression.children.first)
     end
 
-    def on_assignment statement
+    def on_i_assignment statement
+      assignment_for( statement, Vm::Tree::IvarAssignment)
+    end
+
+    def on_a_assignment statement
+      assignment_for( statement, Vm::Tree::ArgAssignment)
+    end
+
+    def on_l_assignment( statement )
+      assignment_for( statement, Vm::Tree::LocalAssignment)
+    end
+
+    def assignment_for( statement , clazz)
       name , value = *statement
-      w = Vm::Tree::Assignment.new()
-      w.name = process name
-      w.value = process(value)
-      w
+      p_name = process name
+      p_value = process(value)
+      clazz.new(p_name , p_value)
     end
 
   end