Definitely a bug, thank you! I've created a Trac ticket for it. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Jan Jakubuv | Sent: 05 May 2009 11:06 | To: glasgow-haskell-users@haskell.org | Subject: GHC 6.10.2 the 'impossible' panic with type families | | Dear haskellers, | | with the following code: | | {-# OPTIONS -fglasgow-exts #-} | | class SUBST s where | type STerm s | | class OBJECT o where | type OTerm o | apply :: (SUBST s, OTerm o ~ STerm s) => s -> o | | fce' f = fce . apply $ f | | fce f = fce' f | | I have the following message in both GHCi and GHC (tested on GHC 6.10.1 | linux and win, and 6.10.2 linux): | | ghc: panic! (the 'impossible' happened) | (GHC version 6.10.2 for i386-unknown-linux): | idInfo co{v agz} [tv] | | Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug | | The above is the smallest example I have found that behaves in this way. It | is a striped version of an original and more complicated code. What seems | interesting to me is that when one defines `fce` as follows (instead of the | above): | | fce = fce' | | then everything is ok (= no panic message). In my original code `fce'` was a | monad computation, something like: | | fce' f = fce f >>= \s → fce (apply s) | | and this produces the same result (= the panic message). | | Is this a bug or a known issue? | | Sincerely, | Jan. | | | | -- | Heriot-Watt University is a Scottish charity | registered under charity number SC000278. | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users