add operator to builder

just minus for now, easily extended

lib/risc/builtin/word.rb

@@ -69,11 +69,11 @@ module Risc
             space << Parfait.object_space
             space << space[:nil_object]
 
-            add Risc.op(source + "if method is nil", :- , space , typed_method )
+            space - typed_method
             if_zero exit_label
 
             name << typed_method[:name]
-            add Risc.op(source + " compare name with me", :- , name , word )
+            name - word
             if_not_zero false_label
 
             typed_method << typed_method[:binary]

lib/risc/risc_value.rb

@@ -77,6 +77,13 @@ module Risc
       return ins
     end
 
+    def -( right )
+      raise "operators only on registers, not #{right.class}" unless right.is_a? RiscValue
+      op = Risc.op("#{self.type} - #{right.type}", :- , self , right )
+      builder.add(op) if builder
+      op
+    end
+    
     # just capture the values in an intermediary object (RValue)
     # The RValue then gets used in a RegToSlot ot SlotToReg, where
     # the values are unpacked to call Risc.reg_to_slot or Risc.slot_to_reg