On Sat, Dec 20, 2008 at 7:09 PM, Bas van Dijk
Hello,
In a project of mine I needed an Applicative instance for Identity and noticed it didn't exist. So I decided to add Applicative (and Alternative instances where possible) for all MTL types.
When I was about to submit a library proposal I saw there already existed one. So I added my patch to that ticket.
My patch I different in that my Applicative instances don't require a Monad constraint. This also means that most Functor instances now also depend on Applicative rather than on Monad.
See the ticket for the details:
http://hackage.haskell.org/trac/ghc/ticket/2316
Discussion period: 5 weeks (taking the holidays into account)
This is the old thread about this proposal:
http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9140/focus=9154
regards,
Bas
getCurrentTime >>= \c -> print (realToFrac (diffUTCTime c (readTime defaultTimeLocale "%c" "Sat Dec 20 19:09:00 2008")) / 60 / 60 / 24 / 7) ~ 3.5 weeks ago I sended this previous message ;-) Can we have some discussion about my patch? As listed in the ticket I have these questions: * Does it make sense adding Applicative counterparts to the Monad* classes? For example: o class Applicative f => ApplicativeError e g | f -> e where ... o class Applicative f => ApplicativeState s f | f -> s where ... o class Applicative f => ApplicativeReader r f | f -> r where ... o class (Applicative f, Monoid w) => ApplicativeWriter w f | f -> w where ... o class (Monoid w, ApplicativeReader r f, ApplicativeWriter w f, ApplicatveState s f) => ApplicativeRWS r w s f | f -> r, f -> w, f -> s where ... o class (Applicative m) => ApplicativeCont m where ... o class ApplicativeTrans t where lift :: Applicative f => f a -> t f a * Can we get rid of the Monad and MonadPlus constraints in the Applicative and Alternative instances for StateT and RWST? Thanks, Bas