Hi all,

I have played quite a bit with the ConstraintKinds extension, pretty cool.

But I found a problem which I thought would be made better, plz correct me if I am wrong

take a contrived example,

class C B => B a where

here B :: * -> Constraint, I think this definition is reasonable, since B does not appears in the

first position of the context.

Previously, we require acyclic class declarations since we don't have ConstraintKinds extension

but now since type class could be abstracted, I think the definition above should be ok.

the ghc-manual cited the program below is valid

class C a where {op :: D b => a -> b -> b}

class C a => D a where { ... }

I think there are no reasons to reject

class C B => B where (and this style is pretty useful in some cases)

...

B :: * -> Constraint

C :: (*->Constraint) -> Constraint

Any comments are welcome

--
Best, bob