We can't use "increasing" because mathematically that usually means
non-strictly increasing. Using "ascending" gets us in trouble with the
other functions in the module that use the word in a non-strict sense.
On Wed, Apr 3, 2019, 10:46 AM Elliot Cameron
Hello!
In some recent analysis I ran into a subtlety that caught me by surprise: Data.Map.mapKeysMonotonic has a misleading name.
A monotonic function is not a strictly *increasing* function, but merely non-decreasing. However, mapKeysMonotonic requires that it's mapping function be injective, which means it really only supports *increasing* functions.
valid (mapKeysMonotonic (\x -> if x `elem` [1,2] then 2 else x) (fromList [(1, "a"), (2, "b"), (3, "c")])) == False
The docs hint at this with "This means that @f https://github.com/f@ maps distinct original keys to distinct resulting keys."
However, I'd propose that we deprecate this name and rename to something like mapKeysIncreasingor mapKeysAsc (to follow the pattern of other *Asc functions). We should also clarify the docs.
From https://github.com/haskell/containers/issues/617 _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries