= getUniqueNat `thenNat` \ u ->
returnNat (UnmappedReg u pk)
-instance Text Reg where
+instance Show Reg where
showsPrec _ (FixedReg i) = showString "%" . shows IBOX(i)
showsPrec _ (MappedReg i) = showString "%" . shows IBOX(i)
showsPrec _ (MemoryReg i _) = showString "%M" . shows i