Hi, if you desugar the definition that's causing the type error, perhaps it becomes a little bit clearer what's going on, i.e., from problematic :: MyAnnotatedType Int problematic = defaultVal{theInt=42,theAnnotation=10} you expand this to problematic' = case defaultVal of { MAT a b c -> MAT 42 b 10 } Clearly, the type of 'c' is ambiguous here. Interestingly, if Haskell 98 had defined record update expr "e{fields}" as having the same type as "e", this wouldn't have been an issue: no_probs = case defaultVal of { m@(MAT a b c) -> (MAT 42 b 10) `asTypeOf` m} hth --sigbjorn ----- Original Message ----- From: "Magnus Björk" <mab@cs.chalmers.se> To: <glasgow-haskell-bugs@haskell.org>; <hugs-bugs@haskell.org> Sent: Monday, May 29, 2006 03:34 Subject: Strange behaviour with classes (both Hugs and GHC)

I just ran into a strange behaviour of both Hugs and GHC. I discussed it with John Hughes who managed to find a workaround, and suggested that I ask you whether this is really expected behaviour.

The attached file contains a small example that exhibits the problem.

-- /MpB

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