Not exactly what you asked for, but...
filter (uncurry somePredicate) $ (,) <$> list1 <*> list2
does the job.
Using only applicative operations, it's impossible to affect the 'shape' of
the result--this is the difference in power between applicative and monad.
-- ryan
On Wed, Sep 12, 2012 at 7:40 AM, felipe zapata
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.
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