Data.Map.mapKeysMonotonic is a misleading name

[Elliot Cameron]

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> 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>> 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>> 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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