diff --git a/lib/parfait/indexed.rb b/lib/parfait/indexed.rb
index cf6ecb4f..310e4131 100644
--- a/lib/parfait/indexed.rb
+++ b/lib/parfait/indexed.rb
@@ -8,159 +8,167 @@
 #
 # Using ruby include does not work for similar reasons, so Indexed.at is the main
 # function that generates the methods
+ # ( do have to use a marker module so we can test with is_a?)
 
-module Indexed
-
-  def self.at( offset , clazz )
-
-    clazz.send :define_method , :get_length do
-      internal_object_length - 1
+module Parfait
+  module Indexed # marker module
+    def self.included(base)
+      base.extend(Methods)
     end
 
-    # index of item, remeber first item has index 1
-    # return  nil if no such item
-    clazz.send :define_method , :index_of do |item|
-      max = self.get_length
-      counter = 1
-      while( counter <= max )
-        if( get(counter) == item)
-          return counter
+    module Methods
+      def offset( offset  )
+
+        define_method  :get_length do
+          internal_object_length - 1
         end
-        counter = counter + 1
-      end
-      return nil
-    end
 
-    # include? means non nil index
-    clazz.send :define_method , :include? do |item|
-      return index_of(item) != nil
-    end
+        # index of item, remeber first item has index 1
+        # return  nil if no such item
+        define_method  :index_of do |item|
+          max = self.get_length
+          counter = 1
+          while( counter <= max )
+            if( get(counter) == item)
+              return counter
+            end
+            counter = counter + 1
+          end
+          return nil
+        end
 
-    # push means add to the end
-    # this automatically grows the List
-    clazz.send :define_method , :push do |value|
-      set( self.get_length + 1 , value)
-    end
+        # include? means non nil index
+        define_method  :include? do |item|
+          return index_of(item) != nil
+        end
 
-    clazz.send :define_method , :delete do |value|
-      index = index_of value
-      return false unless index
-      delete_at index
-    end
+        # push means add to the end
+        # this automatically grows the List
+        define_method  :push do |value|
+          set( self.get_length + 1 , value)
+        end
 
-    clazz.send :define_method , :delete_at do |index|
-      # TODO bounds check
-      while(index < self.get_length)
-        set( index , get(index + 1))
-        index = index + 1
-      end
-      set_length( self.get_length - 1)
-      true
-    end
+        define_method  :delete do |value|
+          index = index_of value
+          return false unless index
+          delete_at index
+        end
+
+        define_method  :delete_at do |index|
+          # TODO bounds check
+          while(index < self.get_length)
+            set( index , get(index + 1))
+            index = index + 1
+          end
+          set_length( self.get_length - 1)
+          true
+        end
 
 
-    clazz.send :define_method , :first do
-      return nil if empty?
-      get(1)
-    end
+        define_method  :first do
+          return nil if empty?
+          get(1)
+        end
 
-    clazz.send :define_method , :last do
-      return nil if empty?
-      get(get_length())
-    end
+        define_method  :last do
+          return nil if empty?
+          get(get_length())
+        end
 
-    # set the value at index.
-    # Lists start from index 1
-    clazz.send :define_method , :set do | index , value|
-      raise "Only positive indexes #{index}" if index <= 0
-      if index > self.get_length
-        grow_to(index)
-      end
-      # internally 1 is reserved for the layout
-      internal_object_set( index + 1, value)
-    end
+        # set the value at index.
+        # Lists start from index 1
+        define_method  :set do | index , value|
+          raise "Only positive indexes #{index}" if index <= 0
+          if index > self.get_length
+            grow_to(index)
+          end
+          # internally 1 is reserved for the layout
+          internal_object_set( index + 1, value)
+        end
+
+        # set the value at index.
+        # Lists start from index 1
+        define_method  :get do | index|
+          raise "Only positive indexes, #{index}" if index <= 0
+          if index > self.get_length
+            return nil
+          else
+            return internal_object_get(index + 1)
+          end
+        end
+
+        define_method  :empty? do
+          self.get_length == 0
+        end
+
+        define_method  :set_length do | len|
+          was = self.get_length
+          return if was == len
+          if(was < len)
+            grow_to len
+          else
+            shrink_to len
+          end
+        end
+
+        define_method  :grow_to do | len|
+          raise "Only positive lenths, #{len}" if len < 0
+          old_length = self.get_length
+          return if old_length >= len
+          internal_object_grow(len + 1)
+        end
+
+        define_method  :shrink_to do | len|
+          raise "Only positive lenths, #{len}" if len < 0
+          old_length = self.get_length
+          return if old_length <= len
+          internal_object_shrink(len + 1)
+        end
+
+        define_method  :equal? do | other|
+          # this should call parfait get_class, alas that is not implemented yet
+          return false if other.class != self.class
+          return false if other.get_length != self.get_length
+          index = self.get_length
+          while(index > 0)
+            return false if other.get(index) != self.get(index)
+            index = index - 1
+          end
+          return true
+        end
+
+        # above, correct, implementation causes problems in the machine object space
+        # because when a second empty (newly created) list is added, it is not actually
+        # added as it exists already. TODO, but hack with below identity function
+        define_method  :== do | other|
+          self.object_id == other.object_id
+        end
+
+        # word length (padded) is the amount of space taken by the object
+        # For your basic object this means the number of instance variables as determined by layout
+        # This is off course 0 for a list, unless someone squeezed an instance variable in
+        # but additionally, the amount of data comes on top.
+        # unfortuntely we can't just use super because of the Padding
+        define_method  :word_length do
+          padded_words( get_layout().get_length() +  get_length() )
+        end
+
+        define_method  :inspect do
+          inspect_from 1
+        end
+
+        define_method  :inspect_from do |index|
+          ret = ""
+          while index <= self.get_length
+            item = get(index)
+            ret += item.inspect
+            ret += "," unless index == self.get_length
+            index = index + 1
+          end
+          ret
+        end
 
-    # set the value at index.
-    # Lists start from index 1
-    clazz.send :define_method , :get do | index|
-      raise "Only positive indexes, #{index}" if index <= 0
-      if index > self.get_length
-        return nil
-      else
-        return internal_object_get(index + 1)
       end
     end
-
-    clazz.send :define_method , :empty? do
-      self.get_length == 0
-    end
-
-    clazz.send :define_method , :set_length do | len|
-      was = self.get_length
-      return if was == len
-      if(was < len)
-        grow_to len
-      else
-        shrink_to len
-      end
-    end
-
-    clazz.send :define_method , :grow_to do | len|
-      raise "Only positive lenths, #{len}" if len < 0
-      old_length = self.get_length
-      return if old_length >= len
-      internal_object_grow(len + 1)
-    end
-
-    clazz.send :define_method , :shrink_to do | len|
-      raise "Only positive lenths, #{len}" if len < 0
-      old_length = self.get_length
-      return if old_length <= len
-      internal_object_shrink(len + 1)
-    end
-
-    clazz.send :define_method , :equal? do | other|
-      # this should call parfait get_class, alas that is not implemented yet
-      return false if other.class != self.class
-      return false if other.get_length != self.get_length
-      index = self.get_length
-      while(index > 0)
-        return false if other.get(index) != self.get(index)
-        index = index - 1
-      end
-      return true
-    end
-
-    # above, correct, implementation causes problems in the machine object space
-    # because when a second empty (newly created) list is added, it is not actually
-    # added as it exists already. TODO, but hack with below identity function
-    clazz.send :define_method , :== do | other|
-      self.object_id == other.object_id
-    end
-
-    # word length (padded) is the amount of space taken by the object
-    # For your basic object this means the number of instance variables as determined by layout
-    # This is off course 0 for a list, unless someone squeezed an instance variable in
-    # but additionally, the amount of data comes on top.
-    # unfortuntely we can't just use super because of the Padding
-    clazz.send :define_method , :word_length do
-      padded_words( get_layout().get_length() +  get_length() )
-    end
-
-    clazz.send :define_method , :inspect do
-      inspect_from 1
-    end
-
-    clazz.send :define_method , :inspect_from do |index|
-      ret = ""
-      while index <= self.get_length
-        item = get(index)
-        ret += item.inspect
-        ret += "," unless index == self.get_length
-        index = index + 1
-      end
-      ret
-    end
-
   end
 end
diff --git a/lib/parfait/layout.rb b/lib/parfait/layout.rb
index 91977eec..188658fc 100644
--- a/lib/parfait/layout.rb
+++ b/lib/parfait/layout.rb
@@ -21,7 +21,22 @@
 # Together they turn the object into a hash like structure
 
 module Parfait
-  class Layout < List
+  class Layout < Object
+    include Indexed
+    self.offset(0)
+
+    def each
+      # not sure how to do this with define_method, because of the double block issue.
+      # probably some clever way around that, but not important
+      index = 1
+      while index <= self.get_length
+        item = get(index)
+        yield item
+        index = index + 1
+      end
+      self
+    end
+
     attribute :object_class
 
     def initialize( object_class )
diff --git a/lib/parfait/list.rb b/lib/parfait/list.rb
index c7854d60..c93c78ec 100644
--- a/lib/parfait/list.rb
+++ b/lib/parfait/list.rb
@@ -14,7 +14,8 @@ require_relative "indexed"
 
 module Parfait
   class List < Object
-    Indexed.at(0 , self)
+    include Indexed
+    self.offset(0)
 
     def initialize(  )
       super()
diff --git a/lib/register/assembler.rb b/lib/register/assembler.rb
index 73a3a159..5552d094 100644
--- a/lib/register/assembler.rb
+++ b/lib/register/assembler.rb
@@ -168,7 +168,7 @@ module Register
       end
       #puts "layout length=#{layout.get_length.to_s(16)} mem_len=#{layout.word_length.to_s(16)}"
       l = layout.get_length
-      if( object.is_a? Parfait::List)
+      if( object.is_a? Parfait::Indexed)
         object.each do |inst|
           write_ref_for(inst)
         end
diff --git a/lib/register/collector.rb b/lib/register/collector.rb
index 1d13e689..7ce49329 100644
--- a/lib/register/collector.rb
+++ b/lib/register/collector.rb
@@ -27,7 +27,7 @@ module Register
         inst = object.get_instance_variable name
         keep(inst , depth + 1)
       end
-      if object.is_a? Parfait::List
+      if object.is_a? Parfait::Indexed
         object.each do |item|
           #puts "Keep item "
           keep(item , depth + 1)
diff --git a/test/parfait/test_list.rb b/test/parfait/test_list.rb
index e020f36f..adc3d51d 100644
--- a/test/parfait/test_list.rb
+++ b/test/parfait/test_list.rb
@@ -6,6 +6,10 @@ class TestList < MiniTest::Test
     Register.machine.boot unless Register.machine.booted
     @list = ::Parfait::List.new
   end
+  def test_isa
+    assert @list.is_a? Parfait::List
+    assert @list.is_a? Parfait::Indexed
+  end
   def test_old_layout
     assert_equal Parfait::Layout , Register.machine.space.classes.keys.get_layout.class
   end