Sittampalam, Ganesh wrote:
Sittampalam, Ganesh wrote:
Ross Paterson wrote:
On Sun, Mar 22, 2009 at 06:31:08AM -0000, Sittampalam, Ganesh wrote:
Essentially we have the choice of producing full compatibility by keeping the separate type in mtl, in which case State from mtl is not State from transformers, or partial compatibility by re-exporting the transformers one.
Yes, we must choose between full compatibility with mtl and full compatibility with transformers. A quick implementation of the former is
http://code.haskell.org/~ross/mtl-compat/
The separate versions of State etc are present, but deprecated.
Cool. I've been been playing around with regression testing hackage following Duncan's blog post on the subject - I've got a baseline test running now and will try your mtl-compat out next,
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.
Here's the list of failures - though it doesn't cover packages that weren't installable on my machine for some other reason like needing gtk2hs or a C library. blogination-0.5 Functor instances depending on Functor, instance collision Applicative/Alternative ErrorT category-extras-0.53.5 Functor instances depending on Functor cgi-3001.1.7.1 Functor instances depending on Functor encoding-0.5.1 instance collision: Monad Either logict-0.2.3 instance collision: Applicative Identity monad-param-0.0.2 Functor instances depending on Functor mueval-0.7.1 Functor instances depending on Functor xcb-types-0.5.1 instance collision: Applicative/Alternative ReaderT xmonad-contrib-0.8.1 instance collision: Error [a] and also packages that depend on the above directly or indirectly: bff, cflp,cgi-undecidable, fastcgi, gitit, kibro, xmonad-eval and if we go one step further and remove State etc (so they become type synonyms, repo here: http://urchin.earth.li/darcs/ganesh/mtl-compat ), the following extra failures: FileManip-0.3.2 Missing data constructor: State HAppS-Server-0.9.3 Missing data constructor: Reader HaLeX-1.1.1 Missing data constructor: State LambdaHack-0.1.20080413 Missing data constructor: State applicative-extras-0.1.4 instance Applicative (State a) which now (a) needs TypeSynonymInstances and (b) overlaps derive-0.1.4 instance Applicative (Writer a) which now (a) needs TypeSynonymInstances and (b) overlaps lambdabot-4.2.2.1 Missing data constructor: State open-witness-0.1.1 Missing data constructor: State random-fu-0.0.0.2 instance MonadRandom (State StdGen) - needs TypeSynonymInstances or rewrite with StateT yhccore-0.9.1 instance UniqueIdM (State a) - needs TypeSynonymInstances or rewrite with StateT and dependencies: FermatsLastMargin, HappSHelpers, HSHHelpers, HStringTemplateHelpers, bff, firstify, formlets, happstack-helpers, hugs2yc, ycextra So, thoughts on how to proceed? Personally I would be inclined to go the whole hog as there isn't that much breakage - the downside being that it'll be hard for any of these packages to be compatible with both old mtl and new mtl simultaneously, with the exception of "Functor instances depending on Functor" which can be solved by having both Functor and Monad in the constraints. I've started contacting the authors of the directly affected packages and asking them to add mtl<1.2 to their dependencies so that if we do go ahead with any change the disruption will be minimised. Cheers, Ganesh =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ===============================================================================