On Tue, 2009-12-29 at 23:00 +0000, Conor McBride wrote:
Hi Maciej
On 29 Dec 2009, at 20:52, Maciej Piechotka wrote:
On Tue, 2009-12-29 at 18:20 +0000, Conor McBride wrote:
ala AppLift foldMap
What is benefit of it over: concatMapA f = foldr (liftA2 mappend . f) (pure mempty)
Given that applicative functors take monoids to monoids, it's nice to exploit that property by name, rather than reconstructing it by engineered coincidence.
I wouldn't state it as 'coincidence'. I don't need to create explicit map where implicit (liftA2 mappend and pure mempty) is sufficient. In this case I have one line when you have many (however it might be other case with more complicated examples - but I don't quite see how)[1]. Also I'm not quite sure if ala is something general and therefore should be exposed instead of just putting it. But I may be wrong Regards [1] http://www.willamette.edu/~fruehr/haskell/evolution.html ;)