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implement List.max! and List.min! #1174

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implement List.max! and List.min! #1174

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14 changes: 14 additions & 0 deletions Batteries/Data/List/Basic.lean
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,20 @@ namespace List

/-! ## New definitions -/

/-- Get the maximum element of a list.
If the given list is empty, returns `(default : α)` and produces a panic error message. -/
def max! {α} [Inhabited α] [Max α] (xs : List α) : α :=
match xs.max? with
| none => panic! "List.max! called on empty list"
| some x => x

/-- Get the minimum element of a list.
If the given list is empty, returns `(default : α)` and produces a panic error message. -/
def min! {α} [Inhabited α] [Min α] (xs : List α) : α :=
match xs.min? with
| none => panic! "List.min! called on empty list"
| some x => x

/--
Computes the "bag intersection" of `l₁` and `l₂`, that is,
the collection of elements of `l₁` which are also in `l₂`. As each element
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