There is definitely no pure way to get from ‘a’ to its constraints. * It is far from clear what “its constraints” are. Is (C a b) such a constraint? C [a] b? What about superclasses? * Constraints vary depending on where you are. GADT matches can bring into scope extra constraints on existing type variables.
So as Ben says, to give a sensible response you’ll need to explain more about your goal Simon From: ghc-devs <ghc-devs-boun...@haskell.org> On Behalf Of Alejandro Serrano Mena Sent: 16 January 2020 16:19 To: GHC developers <ghc-devs@haskell.org> Subject: Find constraints over type Dear GHC devs, I am trying to figure out a way to obtain the constraints that hold over a type. Let me give you an example: suppose that I write the following function: f :: Eq a => [a] -> Bool f xs = xs == [] If I ask for the type of the Var ' xs', I get back '[a]'. This is correct, but I am missing the crucial information that '[a]' must be Eq. Is there an easy way to get it? It seems that 'varType' doesn't give me enough information. Regards, Alejandro
_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
