[Haskell-cafe] Typeable typeclass and type-level naturals

[Roman Cheplyaka]

* TP <paratribulations at free.fr> [2013-06-05 00:37:36+0200]
> Roman Cheplyaka wrote:
> 
> > Try adding
> > 
> >   deriving instance Typeable 'Zero
> >   deriving instance Typeable a => Typeable ('Succ a)
> > 
> > to your module.
> > 
> > (I haven't tested it — you might need to tweak it a bit.)
> 
> Thanks Roman.
> Unfortunately, I already tried that (without the constraint "Typeable a =>", 
> what a fool), but it did not work. The error is the same with the 
> constraint:
> 
>     Derived typeable instance must be of form (Typeable 'Succ)
>     In the stand-alone deriving instance for
>       ‛Typeable a => Typeable (Succ a)’
> 
> What is the problem?

Oh, it should probably be simply

  deriving instance Typeable 'Zero
  deriving instance Typeable 'Succ

Roman