MTL vs Transformers. Any status update?

Duncan Coutts duncan.coutts at
Sun Nov 29 08:03:06 EST 2009

On Sat, 2009-11-28 at 16:56 +0000, Ross Paterson wrote:
> On Sat, Nov 28, 2009 at 04:40:49PM +0000, Duncan Coutts wrote:
> > Could someone remind me why it's better for use to ask everyone to
> > switch to monads-fd / transformers rather than to mtl-2? Does that make
> > the transition easier?
> The problem is that transformers and mtl use the same module names,
> such as Control.Monad.Identity.  Unless one of these packages is hidden,
> people using ghci or ghc --make will have problems.

Right, so having transformers + mtl is bad, but why do we want to end up
with a situation where we have both? If you've all agreed what should go
into the new monad package, can't we call that mtl-2 ? Why would we want
to define things in one package and re-export them in another?


More information about the Libraries mailing list