On Sun, Apr 09, 2017 at 03:27:02PM -0500, amindfv@gmail.com wrote:
Genuinely curious: can people point to specific examples in their (or others') code where the ((,) a) instance for Foldable is really helpful and difficult to replace?
I asked in the other thread, these are some of the answers I got: Oliver Charles:
Personally, I think it would be a shame to lose foldMap on EIther. I frequently foldMap over Maybe values (where mempty is suitable in case of "failure"), and I can certainly see myself doing the same thing with Either.
Oleg Grenrus:
Anecdotally, today I wrote `foldMap toList`, to use as `Maybe (NonEmpty a) -> [a]`. Also I rely heavily in lens-based code on the `folded :: Fold (Maybe a) a`.
There haven't been replies on specific usage of functions length/sum/ maximum/etc. I can't recall where, but someone else was making a point that a {-# Poison something #-} pragma would fracture the ecosystem. I don't think this holds much weight though, as library authors would most likely toggle the flag in development (to avoid calling length Either, etc.) and toggle it back on release. -F