[Haskell-cafe] guards in applicative style

felipe zapata tifonzafel at gmail.com
Wed Sep 12 16:40:11 CEST 2012

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

result = (,) <$> list1 <*> list2 (somePredicate ???)

The question is then,
there is a way for defining a guard in applicative Style?

Thanks in advance,

Felipe Zapata.
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