Generalize filterM to Applicative

[Andreas Abel]

+1 generalize filterM to Applicative.

I am not fond of ...A functions if the ...M functions can be generalized 
to Applicative, so -1 on filterA.

On 29.12.2014 00:15, Edward Kmett wrote:
> The way we've been doing things so far is to just generalize the
> existing signature and keep the existing name.
>
> This avoids needless name proliferation and keeping needlessly
> over-constrained versions of code lying around.
>
> FWIW- I have no objection to a more general filterM.
>
> -Edward
>
> On Sun, Dec 28, 2014 at 1:14 PM, Yitzchak Gale <gale at sefer.org
> <mailto:gale at sefer.org>> wrote:
>
>     David Feuer wrote:
>     > filterM          :: (Monad m) => (a -> m Bool) -> [a] -> m [a]
>     > We could change this to
>     > filterM :: (Applicative f) => (a -> f Bool) -> [a] -> f [a]
>
>     Following the usual conventions, that should be filterA.
>
>     And I'm not sure where it should go. We could also
>     generalize the list parameter to a Foldable and put
>     it in Data.Foldable, but I don't think that would be
>     very useful, since in the end it anyway returns a list.
>
>     We could add a new "Filterable" class, but that's also
>     probably not too useful for anything not list-like. For
>     example, Data.Tree has two useful filters, filterGraft
>     and filterPrune.
>
>     So maybe it should go in Control.Applicative? Not very
>     satisfying. Any ideas?
>
>     As for the fate of the name filterM:
>
>     Personally, I would want filterM to remain a convenient
>     type-specialized version for monads. But recent madness
>     would turn it into yet another unsightly overly polymorphic
>     namespace wasting synonym for filterA.
>
>     Thanks,
>     Yitz
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-- 
Andreas Abel  <><      Du bist der geliebte Mensch.

Department of Computer Science and Engineering
Chalmers and Gothenburg University, Sweden

andreas.abel at gu.se
http://www2.tcs.ifi.lmu.de/~abel/