[Haskell-cafe] MonadLib usage

[Ben Millwood]

On Sun, Jul 18, 2010 at 5:59 PM, Emil Melnikov <emilmeln at gmail.com> wrote:
> On 2010, July 18, 23:27
> Ivan Lazar Miljenovic <ivan.miljenovic at gmail.com> wrote:
>
>> When discussing a similar issue with Manuel Chakravarty, he convinced me
>> that cunning newtype deriving is actually rather bad in practice and
>> shouldn't be used as there's a lack of proofs or some such (I can't
>> remember the arguments, but I remember being convinced by them :p).
>
> Hmm...  I can't imagine how it is possible, since new and
> original types are isomorphic.
>
> Can you give me some pointers to this discussion (links or
> keywords)?
>

They are isomorphic, but distinct. This trac ticket is relevant:

http://hackage.haskell.org/trac/ghc/ticket/1496