[Haskell-cafe] Type alias in constraints
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk
Fri Oct 14 17:31:36 UTC 2016
On Fri, Oct 14, 2016 at 07:25:40PM +0200, Sylvain Henry wrote:
> I have been using constraints of the form:
> xxx :: forall x xs ys zs m.
> ( Monad m
> , zs ~ Union (Filter x xs) ys
> , Catchable x xs
> , Liftable (Filter x xs) zs
> , Liftable ys zs
> ) => Variant xs -> (x -> Flow m ys) -> Flow m zs
> Where "zs" is used as a type alias. Now with GHC8 and
> -Wredundant-constraints, GHC complaints that "zs" is redundant
> (indeed it is).
Why is it redundant? Surely a redundant constraint is one you can freely
remove. I don't see any constraint you can remove in that type.
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