transformers versus mtl

Antoine Latter aslatter at
Tue Mar 24 21:30:57 EDT 2009

On Tue, Mar 24, 2009 at 4:42 PM, Sittampalam, Ganesh
<ganesh.sittampalam at> wrote:
> Sittampalam, Ganesh wrote:
> I've tried this now. Various new failures, which I don't have time
> to investigate all of tonight, but the first one I looked at is in
> the 'cgi' package, and is because the Functor instances for
> ReaderT r m and WriterT w m now (correctly) depend on Functor m,
> whereas in mtl they depend on Monad m.

As long as we're on the topic of class constraints, is there any
reason that the Monad instance for ContT m has a class constraint on
the type of 'm'?  I'm pretty sure we can lose it, as well as the
similar class constraint on the instance of MonadCont.

That's one of the most important things about the (ContT m) monad to
me - it's a monad transformer that doesn't hit the class dictionary of
what it's wrapping around.


More information about the Libraries mailing list