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chore: rename List.groupBy to splitBy #5879

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Oct 30, 2024
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chore: rename List.groupBy to splitBy #5879

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18 changes: 10 additions & 8 deletions src/Init/Data/List/Basic.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,7 @@ The operations are organized as follow:
* Zippers: `zipWith`, `zip`, `zipWithAll`, and `unzip`.
* Ranges and enumeration: `range`, `iota`, `enumFrom`, and `enum`.
* Minima and maxima: `min?` and `max?`.
* Other functions: `intersperse`, `intercalate`, `eraseDups`, `eraseReps`, `span`, `groupBy`,
* Other functions: `intersperse`, `intercalate`, `eraseDups`, `eraseReps`, `span`, `splitBy`,
`removeAll`
(currently these functions are mostly only used in meta code,
and do not have API suitable for verification).
Expand Down Expand Up @@ -1639,23 +1639,23 @@ where
| true => loop as (a::rs)
| false => (rs.reverse, a::as)

/-! ### groupBy -/
/-! ### splitBy -/

/--
`O(|l|)`. `groupBy R l` splits `l` into chains of elements
`O(|l|)`. `splitBy R l` splits `l` into chains of elements
such that adjacent elements are related by `R`.

* `groupBy (·==·) [1, 1, 2, 2, 2, 3, 2] = [[1, 1], [2, 2, 2], [3], [2]]`
* `groupBy (·<·) [1, 2, 5, 4, 5, 1, 4] = [[1, 2, 5], [4, 5], [1, 4]]`
* `splitBy (·==·) [1, 1, 2, 2, 2, 3, 2] = [[1, 1], [2, 2, 2], [3], [2]]`
* `splitBy (·<·) [1, 2, 5, 4, 5, 1, 4] = [[1, 2, 5], [4, 5], [1, 4]]`
-/
@[specialize] def groupBy (R : α → α → Bool) : List α → List (List α)
@[specialize] def splitBy (R : α → α → Bool) : List α → List (List α)
| [] => []
| a::as => loop as a [] []
where
/--
The arguments of `groupBy.loop l ag g gs` represent the following:
The arguments of `splitBy.loop l ag g gs` represent the following:

- `l : List α` are the elements which we still need to group.
- `l : List α` are the elements which we still need to split.
- `ag : α` is the previous element for which a comparison was performed.
- `g : List α` is the group currently being assembled, in **reverse order**.
- `gs : List (List α)` is all of the groups that have been completed, in **reverse order**.
Expand All @@ -1666,6 +1666,8 @@ where
| false => loop as a [] ((ag::g).reverse::gs)
| [], ag, g, gs => ((ag::g).reverse::gs).reverse

@[deprecated splitBy (since := "2024-10-30"), inherit_doc splitBy] abbrev groupBy := @splitBy

/-! ### removeAll -/

/-- `O(|xs|)`. Computes the "set difference" of lists,
Expand Down
2 changes: 1 addition & 1 deletion src/Init/Data/List/Impl.lean
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Expand Up @@ -23,7 +23,7 @@ namespace List
The following operations are already tail-recursive, and do not need `@[csimp]` replacements:
`get`, `foldl`, `beq`, `isEqv`, `reverse`, `elem` (and hence `contains`), `drop`, `dropWhile`,
`partition`, `isPrefixOf`, `isPrefixOf?`, `find?`, `findSome?`, `lookup`, `any` (and hence `or`),
`all` (and hence `and`) , `range`, `eraseDups`, `eraseReps`, `span`, `groupBy`.
`all` (and hence `and`) , `range`, `eraseDups`, `eraseReps`, `span`, `splitBy`.

The following operations are still missing `@[csimp]` replacements:
`concat`, `zipWithAll`.
Expand Down
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