Re: [Haskell-cafe] Proposal: new function for lifting
On 27 September 2013 21:51, Thiago Negri wrote: > Stop lifting, start using shinny operators like this one: > > (^$) :: Monad m => m a -> (a -> b -> c) -> m b -> m c > (^$) = flip liftM2 Note that something like this is already provided by the InfixApplicative library: http://hackage.haskell.org/package/InfixApplicative ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: new function for lifting
this is a funny trick, and it looks saner than the more general <$> <*> combinators. i see many situations where i could use that to lift my own combinators, or to replace the backticks (``) to lift the infix function. thx - marc Gesendet: Freitag, 27. September 2013 um 21:51 Uhr Von: "Thiago Negri" An: Haskell-Cafe Betreff: [Haskell-cafe] Proposal: new function for lifting Everybody is claiming that using lift is a bad thing. So, I come to remedy this problem. Stop lifting, start using shinny operators like this one: (^$) :: Monad m => m a -> (a -> b -> c) -> m b -> m c (^$) = flip liftM2 Then you can do wonderful stuff and you will never read the four-letter word in your code again: \> Just 42 ^$(+)$ Nothing Nothing \> Just 10 ^$(+)$ Just 20 Just 30 \> let add = (+) \> Just 30 ^$ add $ Just 12 Just 42 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: new function for lifting
Sorry for sending this twice; I didn't reply to the list initially. I thought people [1] were generally talking about lift from Control.Monad.Trans: class MonadTrans t where lift :: Monad m => m a -> t m a The idea being that lifting through a monad stack feels tedious. The proposed solution is to use instances to do the lifting for you, like in mtl. So we've got instances like: MonadState s m => MonadState s (ReaderT r m) Which let you automatically lift get/put/modify up a stack, without doing any work. This is different from liftM*, which are about applying a pure function to monadic arguments. This can be done quite nicely with (<$>) and (<*>) from Data.Functor and Control.Applicative, respectively. Your first example can be written: (+) <$> (Just 42) <*> Nothing Nick [1] http://blog.ezyang.com/2013/09/if-youre-using-lift-youre-doing-it-wrong-probably/ signature.asc Description: OpenPGP digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Proposal: new function for lifting
Which "lift"? This one? class MonadTrans t where lift :: Monad m => m a -> t m a -- View this message in context: http://haskell.1045720.n5.nabble.com/Proposal-new-function-for-lifting-tp5737189p5737196.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
