Stefan Holdermans wrote:
Peter,
I've run into a bug that looks to be the same as the one described here:
http://hackage.haskell.org/trac/ghc/ticket/1897
It does not seem like a bug, although the type-error message may be a
bit confusing as is the fact that GHC happily infers a type for the
signature-less function: these are I guess the real issues here. But,
apart from that, the contents of a previous discussion seems to apply here:
http://www.haskell.org/pipermail/haskell-cafe/2008-April/041385.html
Short version: the type of isValid involves |Depend s| and not |s|.
Since |Depend s| does not uniquely determine |s|, it is not possible to
resolve which dictionary for Bug to supply for a particular call to
isValid.
Or---am I overlooking something?
No, that makes perfect sense to me now. Thanks.
I put up a note on #1897 pointing to that thread, but left it open
because the error message needs to be fixed :)
Pete
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