Proposal for containers: Add 'pop' function to Data.Map

[Simon Jakobi]

Regarding the type signature:

pop :: Ord k => k -> Map k a -> (Maybe a, Map k a)

I think it might be better to be consistent with similar functions like

minView :: Map k a -> Maybe (a, Map k a)

and

uncons :: [a] -> Maybe (a, [a])

Therefore the type should be

pop :: Ord k => k -> Map k a -> Maybe (a, Map k a)

---

I like the "pop" name though – I think the analogy to stacks is pretty obvious.

---

Like Andreas Abel I believe, that if there is a good, simple
implementation, it might be a good first step to simply document the
implementation as an example.

If there's much demand for exporting the function or if a fast
implementation is more complex, we can still enhance the API later on.


Am So., 6. Dez. 2020 um 17:20 Uhr schrieb Martijn Bastiaan via
Libraries <libraries at haskell.org>:
>
> Hi all,
>
> Proposal:
>
>    * Add `pop` and `popWithDefault` to `Data.Map` and `Data.IntMap`.
>    * See https://github.com/haskell/containers/pull/757 for exact definition
>
> Why:
>
>    * They're useful functions I expected to be in `Data.Map` and
>      `Data.IntMap`. (This might be influenced by the fact that
>      they're defined on Python's `dict`.)
>
>    * Their implementations (~ `updateLookupWithKey (\_ _ -> Nothing)`)
>      are harder to parse than a simple `pop`, which should help Haskell
>      codebases become a bit cleaner :).
>
>    * Their implementations are a bit non-obvious. My first instinct was
>      to write `(Map.lookup ..., Map.delete ...)`, which would have done
>      two traversals. Having "properly" implemented functions in the lib
>      would prevent people from writing their own suboptimal ones.
>
> Details and implementation:
>
>    * https://github.com/haskell/containers/pull/757
>
> Kind regards,
> Martijn Bastiaan
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