There is a ticket with discussion and a patch here [0]. Erik
[0] http://ghc.haskell.org/trac/ghc/ticket/7633 On Thu, Aug 8, 2013 at 8:11 PM, David Thomas <davidleotho...@gmail.com> wrote: > I do wish there was a compiler-checked way of specifying a minimum complete > definition. > > > On Thu, Aug 8, 2013 at 11:02 AM, Joey Adams <joeyadams3.14...@gmail.com> > wrote: >> >> On Thu, Aug 8, 2013 at 12:22 PM, Lyle Kopnicky <li...@qseep.net> wrote: >>> >>> ... >>> >>> >>> So I went to the Data.Hashable page and looked up examples on how to >>> derive a Hashable instance for my datatype: >>> >>> http://hackage.haskell.org/packages/archive/hashable/latest/doc/html/Data-Hashable.html >>> >>> The problem occurs even when using the sample code on the page: >>> >>> >>> {-# LANGUAGE DeriveGeneric #-} >>> >>> import GHC.Generics (Generic) >>> import Data.Hashable >>> >>> data Colour = Red | Green | Blue >>> deriving Generic >>> >>> instance Hashable Colour >>> >>> If I then type `hash Red` I get a stack overflow. >>> >>> I am using the Haskell Platform, so I have hashable-1.1.2.5, but I notice >>> the docs are for hashable-1.2.0.10. If I install 1.2.0.10 though, other code >>> in my project breaks - seems like one part doesn't recognize the instances >>> from another part. So I'll stick with the platform version. >>> >>> ... >> >> >> Generic support was added in hashable-1.2. Before then, the default >> implementations for `hash` and `hashWithSalt` were written in terms of each >> other: >> >> hash = hashWithSalt defaultSalt >> hashWithSalt salt x = salt `combine` hash x >> >> Because you did not give an implementation for either of these, both >> default implementations were used, leading to a loop. >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe@haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
