On 8 May 2016 at 06:45, David Feuer
I managed to find an implementation of Control.Lens.At.at for Data.Map that's fast enough to be useful. The function will be named alterF to match the name of Data.Map.alter. The remaining question is what order the arguments should go in. I had thought to follow those of alter for consistency, giving
alterF :: (Functor f, Ord k) => (Maybe a -> f (Maybe a)) -> k -> Map k a -> f (Map k a)
Edward Kmett thinks the ergonomics of that order are terrible, and prefers to follow lens at, giving
alterF :: (Functor f, Ord k) => k -> (Maybe a -> f (Maybe a)) -> Map k a -> f (Map k a)
How do other people feel about this?
I have a slight preference for the first one as I'm more likely to be applying the same function over multiple keys than having the same key being altered with different functions.
David Feuer
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