It seems like if we could get fail out of Monad and into something like MonadFail/Zero, then it might make sense to make a lookup that returned an instance of that instead?
Dan On Wed, Jun 3, 2009 at 8:13 PM, Bertram Felgenhauer <bertram.felgenha...@googlemail.com> wrote: > Michael Snoyman wrote: >> On Wed, Jun 3, 2009 at 8:42 AM, Daniel Fischer >> <daniel.is.fisc...@web.de>wrote: >> > Am Mittwoch 03 Juni 2009 06:12:46 schrieb Michael Snoyman: >> > > 2. lookup does not return any generalized Monad, just Maybe (I think that >> > > should be changed). >> > >> > Data.Map.lookup used to return a value in any monad you wanted, I believe >> > until 6.8 >> > inclusive. >> > I don't think it's going to change again soon. >> >> Is there a reason why it only returns in the Maybe monad? I often times have >> to write a liftMaybe function to deal with that. > > Here's the proposal that changed it: > http://hackage.haskell.org/trac/ghc/ticket/2309 > > The discussion about the proposal can be found here: > http://www.haskell.org/pipermail/libraries/2008-May/009698.html > > (There's even the suggestion of adding a function like liftMaybe to > Data.Maybe, but apparently nobody turned that into a formal proposal.) > > Regards, > > Bertram > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe