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.
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