diff --git a/lib/mom/slot_load.rb b/lib/mom/slot_load.rb
index c834d20d..089d66fe 100644
--- a/lib/mom/slot_load.rb
+++ b/lib/mom/slot_load.rb
@@ -28,15 +28,17 @@ module Mom
   class SlotLoad < Instruction
     attr_reader :left , :right
     def initialize(left , right)
+      left = SlotDefinition.new(left.shift , left) if left.is_a? Array
       @left , @right = left , right
+      raise "right not SlotDefinition, #{left}" unless left.is_a? SlotDefinition
     end
   end
 
-  # A SlotConstant moves a constant into a know Slot.
+  # A SlotConstant moves a constant into a known Slot.
   # Eg when you write a = 5 , the 5 becomes a constant, and so the right side
   # the a is an instance variable on the current frame, and the frame is an instance
   # of the current message, so the effect is something like message.frame.a = 5
-  # @left:  See SlotLoad, and array of symbols
+  # @left:  See SlotLoad, an array of symbols
   # @right: A Constant from parse, ie an instance of classes in basc_value, like TrueStatement
   class SlotConstant < SlotLoad
 
@@ -47,6 +49,7 @@ module Mom
 
   end
 
+  #SlotMove is a SlotLoad where the right side is a slot, just like the left.
   class SlotMove < SlotLoad
   end
 
diff --git a/test/vool/to_mom/send/simple_send_harness.rb b/test/vool/to_mom/send/simple_send_harness.rb
index a00a7d0d..a258a8e3 100644
--- a/test/vool/to_mom/send/simple_send_harness.rb
+++ b/test/vool/to_mom/send/simple_send_harness.rb
@@ -14,7 +14,7 @@ module Vool
       assert_equal Mom::ArgumentTransfer,  @stats[1].class
     end
     def test_receiver_move
-      assert_equal :receiver,  @stats[1].receiver.left[2]
+      assert_equal :receiver,  @stats[1].receiver.left.slots[1]
     end
     def test_receiver
       type , value = receiver
diff --git a/test/vool/to_mom/send/test_send_cached_simple.rb b/test/vool/to_mom/send/test_send_cached_simple.rb
index 1641930a..199a0f36 100644
--- a/test/vool/to_mom/send/test_send_cached_simple.rb
+++ b/test/vool/to_mom/send/test_send_cached_simple.rb
@@ -44,7 +44,8 @@ module Vool
     end
 
     def test_call_third
-      assert @fourth.method_var_name.start_with?("cached_") , @fourth.to_rxf
+      assert @fourth.cached_method.start_with?("cached_") , @fourth.to_rxf
+      assert @fourth.cached_type.start_with?("cached_") , @fourth.to_rxf
     end
 
     def est_receiver_move_class
diff --git a/test/vool/to_mom/send/test_send_simple_args.rb b/test/vool/to_mom/send/test_send_simple_args.rb
index 59b82cd7..8eb6e629 100644
--- a/test/vool/to_mom/send/test_send_simple_args.rb
+++ b/test/vool/to_mom/send/test_send_simple_args.rb
@@ -15,8 +15,8 @@ module Vool
       [IntegerStatement , 5]
     end
     def test_args_two_move
-      assert_equal :next_message, @stats[1].arguments[1].left[1]
-      assert_equal :arguments,    @stats[1].arguments[1].left[2]
+      assert_equal :next_message, @stats[1].arguments[1].left.slots[0]
+      assert_equal :arguments,    @stats[1].arguments[1].left.slots[1]
     end
     def test_args_two_str
       assert_equal IntegerStatement,    @stats[1].arguments[1].right.class
diff --git a/test/vool/to_mom/send/test_send_simple_string.rb b/test/vool/to_mom/send/test_send_simple_string.rb
index d252e88c..a08c977f 100644
--- a/test/vool/to_mom/send/test_send_simple_string.rb
+++ b/test/vool/to_mom/send/test_send_simple_string.rb
@@ -16,8 +16,8 @@ module Vool
     end
 
     def test_args_one_move
-      assert_equal :next_message, @stats[1].arguments[0].left[1]
-      assert_equal :arguments,    @stats[1].arguments[0].left[2]
+      assert_equal :next_message, @stats[1].arguments[0].left.slots[0]
+      assert_equal :arguments,    @stats[1].arguments[0].left.slots[1]
     end
     def test_args_one_str
       assert_equal IntegerStatement,    @stats[1].arguments[0].right.class
diff --git a/test/vool/to_mom/test_ivar.rb b/test/vool/to_mom/test_ivar.rb
index ae099b2a..61bd285e 100644
--- a/test/vool/to_mom/test_ivar.rb
+++ b/test/vool/to_mom/test_ivar.rb
@@ -19,13 +19,13 @@ module Vool
       assert @method.first.left
     end
     def test_slot_starts_at_message
-      assert_equal :message , @method.first.left[0]
+      assert_equal :message , @method.first.left.known_object
     end
     def test_slot_gets_self
-      assert_equal :self , @method.first.left[1]
+      assert_equal :self , @method.first.left.slots[0]
     end
     def test_slot_assigns_to_local
-      assert_equal :a , @method.first.left[-1]
+      assert_equal :a , @method.first.left.slots[-1]
     end
     def test_slot_assigns_something
       assert @method.first.right
diff --git a/test/vool/to_mom/test_return.rb b/test/vool/to_mom/test_return.rb
index 998b4f23..4f0883a9 100644
--- a/test/vool/to_mom/test_return.rb
+++ b/test/vool/to_mom/test_return.rb
@@ -25,10 +25,10 @@ module Vool
       assert_equal Mom::ReturnSequence,  @stats.last.class
     end
     def test_slot_starts_at_message
-      assert_equal :message , @stats.first.left[0]
+      assert_equal :message , @stats.first.left.known_object
     end
     def test_slot_gets_return
-      assert_equal :return_value , @stats.first.left[1]
+      assert_equal :return_value , @stats.first.left.slots[0]
     end
     def test_slot_assigns_something
       assert @stats.first.right