Data.Map.mapKeysMonotonic is a misleading name

[Andreas Abel]

 > I doubt this function is used very often.

You could be mistaken.  Me, too.  Without statistical data, I have 0 
confidence in such estimates of brain 1. 
https://en.wikipedia.org/wiki/Thinking,_Fast_and_Slow

On 2019-04-04 14:46, Elliot Cameron wrote:
> Well I'm proposing deprecation not removal. The deprecation could even 
> live forever for all I care. It would point to the new name as well. Not 
> to mention I doubt this function is used very often.
> 
> On Thu, Apr 4, 2019, 2:58 AM Andreas Abel <andreas.abel at ifi.lmu.de 
> <mailto:andreas.abel at ifi.lmu.de>> wrote:
> 
>     I am not sure this subtlety is worth the breakage and annoyance to
>     users
>     coming with the name change.
>     If you think about it, renaming the keys while preserving the tree
>     structure cannot work if two old keys map to the same new key.
> 
>     On 2019-04-03 17:13, Elliot Cameron wrote:
>      > Yeah the clearest names seem to be really long ones:
>      > mapKeysMonotonicDistinct, mapKeysInjectiveIncreasing,
>      > mapKeysReferToDocs, etc.
>      >
>      > On Wed, Apr 3, 2019 at 11:11 AM David Feuer
>     <david.feuer at gmail.com <mailto:david.feuer at gmail.com>
>      > <mailto:david.feuer at gmail.com <mailto:david.feuer at gmail.com>>> wrote:
>      >
>      >     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
>     <eacameron at gmail.com <mailto:eacameron at gmail.com>
>      >     <mailto:eacameron at gmail.com <mailto:eacameron at gmail.com>>> wrote:
>      >
>      >         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 |mapKeysIncreasing|or |mapKeysAsc| (to
>     follow the
>      >         pattern of other *Asc functions). We should also clarify
>     the docs.
>      >
>      >
>      >          From https://github.com/haskell/containers/issues/617
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