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, 20
Brent Yorgey wrote:
> However, guardA is not as useful as guard, and it is not possible to
> do the equivalent of the example shown using a list comprehension with
> a guard. The reason is that whereas monadic computations can make use
> of intermediate computed values to decide what to do next,
Lorenzo is correct, but actually for the wrong reason. =) The *type*
of guard is a historical accident, and the fact that it requires
MonadPlus doesn't really tell us anything. Let's take a look at its
implementation:
guard :: (MonadPlus m) => Bool -> m ()
guard True = return
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/Ap
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 <- li
