[Haskell-cafe] Confused about type seen in the wild

Andres Löh andres at well-typed.com
Thu Apr 10 18:51:26 UTC 2014

> I don't have a GHC 7.8 handy.  Can you check to see if:
> whee :: Show a => Eq a => (a -> Bool)
> works over there?

Yes, it does. I also see no problem with this one. Even this works
(but funnily enough, it requires RankNTypes, even though it translates
to the same type):

let whee :: a -> Show a => Eq a => Bool; whee = undefined

None of these are kind errors though. And while I don't know if it's
clearly specified what exactly is possible, it makes sense to me to
allow these.


Andres Löh, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com

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