With these three declarations
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE UndecidableInstances #-}
class C a where c :: a
class C a => D a where d :: a
instance C a => D a where d = c
ghci exhibits this behavior:
*> :t d
d :: (C a) => a
Where I would prefer "d :: (D a) => a". In my actual examples, the
context is much larger and I can't involve overlapping instances. Is
there a known workaround? I didn't find a related bug on the GHC trac,
and I don't know if other compilers behave in the same way.
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