Chaddaï Fouché:
2008/4/8, Manuel M T Chakravarty <[EMAIL PROTECTED]>:
You need to write the instance as
instance (b ~ TheFoo a, Foo a) => Bar (Either a b) where
bar (Left a) = foo' a
bar (Right b) = foo' (foo b :: a)
If you do that, the program compile, but res still raise a panic in
GHC6.8.2 .
Before you sent your solution, I also tried to do
class (TheFoo a ~ b) => Foo a b where ...
instance (Foo a b) => Bar (Either a b) where ...
But it didn't compile, it seems to me both versions should have the
same behaviour ?
6.8.2 has many bugs concerning type families that have been removed in
the development version of GHC.
Manuel
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