On Fri, Jul 06, 2012 at 03:17:54PM -0300, Felipe Almeida Lessa wrote: > On Fri, Jul 6, 2012 at 2:11 PM, Sebastián Krynski <skryn...@gmail.com> wrote: > > As I was using predicates (a -> bool) , it appeared the need for combining > > them with a boolean operator (bool -> bool -> bool) in order to get a new > > predicate > > combining the previous two. So I wrote my function combinerPred (see code > > below). While I think this is JUST ok, i'm feeling a monad in the air. > > So.. where is the monad? > > > > combinerPred :: (a -> Bool) -> (a -> Bool) -> (Bool -> Bool -> Bool) -> > > (a -> Bool) > > combinerPred pred1 pred2 op = \x -> op (pred1 x) (pred2 x) > > That's the `(->) a` monad: > > import Control.Applicative > > combinerPred :: (a -> Bool) -> (a -> Bool) -> (Bool -> Bool -> > Bool) -> (a -> Bool) > combinerPred pred1 pred2 op = op <$> pred1 <*> pred2
By the way, I find it more natural to make 'op' the first argument, because it is more useful to partially apply combinerPred to an operation that it is to some predicates. Also, in that case combinerPred is simply liftA2: import Control.Applicative combinerPred :: (Bool -> Bool -> Bool) -> (a -> Bool) -> (a -> Bool) -> (a -> Bool) combinerPred = liftA2 -Brent _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
