Here's a very cut down version of the bug-exhibiting program mentioned earlier. Sorry, if I cut it down any more, it compiles! Slan, Alex. _____ swift.ucc.ie:~/filt4: ghc M.lhs MachRegs.lhs:563: Non-exhaustive patterns in function baseRegOffset swift.ucc.ie:~/filt4: cat M.lhs > module M where > data T = C Int > f a b c d e f g h = s a b > s x (C _ ) = ()