On Tue, Feb 15, 2011 at 7:58 PM, Ivan Lazar Miljenovic <ivan.miljeno...@gmail.com> wrote: > On 16 February 2011 14:46, Evan Laforge <qdun...@gmail.com> wrote: >> I just got started on this because packages are starting to use mtl2. >> I had hoped it would be simple, and hopefully it is, but... >> >> Do I really have to add (Functor m) to the 300 or so functions with >> (Monad m) on them? Or just not use fmap or applicative? > > Use liftM instead of fmap if all of your functions are polymorphic in > the type of Monad and you don't want to bother putting in the Functor > constraint.
There are hundreds of 'fmap's in there too. And even more <$>s and a scattering of <*>s. And... these functions are convenient! I like using them. If "upgrading" to mtl2 means porting away from Functor and Applicative... then that's even less of a "minor incompatibility"! At least the class context mangling can be mostly done with search and replace. >> Says that the only benefit of 'transformers' is that it's "haskell 98 >> and thus more portable," but doesn't that come with the caveat that >> "only if you don't use classes and do all the lifting manually"? > > Yes, but some people don't want the extensions. Ok, so does that mean the migration to transformers so mtl could be deleted is cancelled? Or was rendered obsolete by mtl-2? Or maybe I was imagining it? I think minimal extensions is a worthy goal, but you can hardly position Y as "the next step" for X when all it is is X minus features that people still like... _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
