I'm no expert at all, but I would say "no". "guard" type is: guard :: MonadPlus m => Bool -> m ()
and "MonadPlus" is a monad "plus" (ehm...) mzero and mplus (http://en.wikibooks.org/wiki/Haskell/MonadPlus). On the other hand Applicative is "less" than a monad (http://www.haskell.org/haskellwiki/Applicative_functor), therefore "guard" as is cannot be defined. But, in your specific example, with lists, you can always use "filter": filter (uncurry somePredicate) ((,) <$> list1 <*> list2 (somePredicate ???)) hth, L. On Wed, Sep 12, 2012 at 3:40 PM, felipe zapata <tifonza...@gmail.com> wrote: > > Hi Haskellers, > > Suppose I have two list and I want to calculate > the cartesian product between the two of them, > constrained to a predicate. > In List comprehension notation is just > > result = [ (x, y) | x <- list1, y <-list2, somePredicate x y ] > > or in monadic notation > > result = do > x <- list1 > y <- list2 > guard (somePredicate x y) > return $ (x,y) > > Then I was wondering if we can do something similar using an applicative style > > result = (,) <$> list1 <*> list2 (somePredicate ???) > > The question is then, > there is a way for defining a guard in applicative Style? > > Thanks in advance, > > Felipe Zapata. > > > > _______________________________________________ > 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