-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 2/16/11 00:51 , Evan Laforge wrote: > 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...
Yes; as I understand it, mtl2 is transformers + monad-fd, and the standard upgrade path is to go to mtl2. monads-tf is expected to eventually replace monads-fd, but it's not a near future change (for one thing, type families are still being figured out; see the recent thread about injective type functions as an example). It was decided that the mtl2 route would be easier than forcing people to replace mtl with transofrmers + monads-fd. - -- brandon s. allbery [linux,solaris,freebsd,perl] allber...@gmail.com system administrator [openafs,heimdal,too many hats] kf8nh -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk1dtWMACgkQIn7hlCsL25WPFwCaA8MbZYbZr/gQ9pa/ttj/E5a0 pTgAoIZ9LMNuq4o7arXmTUZa5qTUFjx4 =NLta -----END PGP SIGNATURE----- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
