repurpose RValue as RegisterSlot

with the idea of the better name came also the one about not needing the builder anymore

lib/risc/register_slot.rb

@@ -0,0 +1,42 @@
+module Risc
+
+  # A RegisterSlot is a description of a slot into an object in a register.
+  #
+  # In many ways, it is like a variable in programming it can be a value, or it
+  # can be assigned a value. An l-value or r-value, and since we don't know at
+  # the time they are created (because of the dsl nature) we delay.
+  #
+  # RegisterSlots are created trough the array operator on a register.
+  # ie message[:caller], and this can either be further indexed, assigned
+  # something or assigned to something. So we overload those operators here.
+  #
+  # Ultimately SlotToReg or RegToSlot instructions are created for the l-value
+  # or r-vlalue respectively.
+
+  class RegisterSlot
+    attr_reader :register , :index , :builder
+
+    def initialize(register, index , builder)
+      @register , @index , @builder = register , index , builder
+    end
+
+    # fullfil the objects purpose by creating a RegToSlot instruction from
+    # itself (the slot) and the register given
+    def <<( reg )
+      raise "not reg #{reg}" unless reg.is_a?(RegisterValue)
+      reg_to_slot = Risc.reg_to_slot("#{reg.class_name} -> #{register.class_name}[#{index}]" , reg , register, index)
+      builder.add_code(reg_to_slot) if builder
+      reg_to_slot
+    end
+
+    # similar to above (<< which produces reg_to_slot), this produces reg_to_byte
+    # from itself (the slot) and the register given
+    def <=( reg )
+      raise "not reg #{reg}" unless reg.is_a?(RegisterValue)
+      reg_to_byte = Risc.reg_to_byte("#{reg.class_name} -> #{register.class_name}[#{index}]" , reg , register, index)
+      builder.add_code(reg_to_byte) if builder
+      reg_to_byte
+    end
+
+  end
+end