[oftl@dukhat sl]$ ghc IxSet.hs

[1 of 1] Compiling Main             ( IxSet.hs, IxSet.o )

 

IxSet.hs:34:46:

    Couldn't match type ‘Integer’ with ‘PostId’

    arising from the coercion of the method ‘safecopy-0.8.5:Data.SafeCopy.SafeCopy.kind’

      from type ‘safecopy-0.8.5:Data.SafeCopy.SafeCopy.Kind Integer’

        to type ‘safecopy-0.8.5:Data.SafeCopy.SafeCopy.Kind PostId’

    Relevant role signatures:

      type role safecopy-0.8.5:Data.SafeCopy.SafeCopy.Kind nominal

    When deriving the instance for (SafeCopy PostId)