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 > >
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