introduce return_sequence instruction to mom

lib/mom/instruction.rb

@@ -7,3 +7,4 @@ module Mom
 end
 
 require_relative "slot_load"
+require_relative "return_sequence"

lib/mom/return_sequence.rb

@@ -0,0 +1,24 @@
+module Mom
+
+  # The ReturnSequence models the return from a method.
+  #
+  # This involves the jump to the return address stored in the message, and
+  # the reinstantiation of the previous message.
+  #
+  # The machine (mom) only ever "knows" one message, the current message.
+  # Messages are a double linked list, calling involves going forward,
+  # returning means going back.
+  #
+  # The return value of the current message is transferred into the return value of the
+  # callers return value during the swap of messages, and just before the jump.
+  #
+  # The callers perspective of a call is the magical apperance of a return_value
+  # in it's message at the instruction after the call.
+  #
+  # The instruction is not parameterized as it translates to a constant
+  # set of lower level instructions.
+  #
+  class ReturnSequence < Instruction
+  end
+
+end