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feat: merging functions on List + mergeSort #763

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@digama0 digama0 commented Apr 23, 2024

Complement to #762. Adds List version of all the definitions in Data.Array.Merge. Also adds List.mergeSort (upstreamed from mathlib), as a replacement for Array.qsort on lists (because qsort cannot easily be expressed as is).

@digama0 digama0 added the awaiting-review This PR is ready for review; the author thinks it is ready to be merged. label Apr 23, 2024
(i.e. for all `x`, `y`, `y'`, `z`, if `x < y < z` and `x < y' < z` then `x < merge y y' < z`)
then the resulting list is again sorted.
-/
def mergeDedupWith [Ord α] (merge : α → α → α) : (xs ys : List α) → List α
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The merge parameter is a bit confusing. How about dedup, join or meld?

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combine?

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@digama0 digama0 Apr 24, 2024

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or just f. I think most of the other list functions don't give their predicate and function arguments long names, and while there are some downsides to having lots of one letter variables in context, one upside is that it makes it visibly distinct from global definitions. I assume that's the reason you flagged merge as being a bad name...

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Yes, the issue is that merge clashes with a definition in this file. I'm happy with f, combine or whatever you decide.

Std/Data/List/Basic.lean Outdated Show resolved Hide resolved
Co-authored-by: François G. Dorais <fgdorais@gmail.com>
@semorrison semorrison added awaiting-author Waiting for PR author to address issues and removed awaiting-review This PR is ready for review; the author thinks it is ready to be merged. labels Apr 30, 2024
@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot added the merge-conflict This PR has merge conflicts with the `main` branch which must be resolved by the author. label Apr 30, 2024
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4 participants