Oops! I was very confused! Sorry, ignore that. I think ghc doesn't "know" which case you're in (after the pattern match) to allow the coercal. ======= Georgi -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20201202/d79cacd1/attachment.html>