Quite right; that's just as specified. The coverage condition is documented in the manual. (GHC 6.4 and Hugs are too liberal, and thereby risk divergence during type checking.) If you want this program to work, use -fallow-undecidable-instances Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Bulat Ziganshin | Sent: 20 September 2006 14:14 | To: glasgow-haskell-users@haskell.org | Subject: 6.6 strikes me again :) | | Hello glasgow-haskell-users, | | attached module compiles fine with ghc 6.4.2, hugs 2003+, but not with | my ghc 6.5 snapshot. it says: | | 66.hs:9:0: | Illegal instance declaration for `Stream m (StringReader r)' | (the Coverage Condition fails for one of the functional dependencies) | In the instance declaration for `Stream m (StringReader r)' | | -- | Best regards, | Bulat mailto:Bulat.Ziganshin@gmail.com