Simon, Thank you *VERY* much for your effort to look into this problem. We have been searching for this loop for quite some time, and it caused us a lot of brain damage ;-) When we red your message last friday evening, we have given it a go and it sure was the problem. Looking back, I should have known better, but it shows I am human too, so blundering once in a while... These type of bugs can be hard to catch. We were close, but simply overlooked it. It certainly isn't a bug in ghc, as I suspected earlier this week. Ghc just did its job. However, it would be very helpful if it could give some kind of a clue. Using the -O option, ghc does detect the loop. I believe that in general that isn't trivial at all, but since it does the detection, It would probably be not too hard to give some sort of clue into the right direction. Such a clue could save days in hunting a bug. Anyways, thanks for helping out! A deep bow! Han Joosten -- View this message in context: http://www.nabble.com/Differences-in-pattern-matching-syntax--tp21416338p215... Sent from the Haskell - Glasgow-haskell-users mailing list archive at Nabble.com.