lean4-htt/tests/elab/grind_fastEraseDups.lean
Garmelon 08eb78a5b2
chore: switch to new test/bench suite (#12590)
This PR sets up the new integrated test/bench suite. It then migrates
all benchmarks and some related tests to the new suite. There's also
some documentation and some linting.

For now, a lot of the old tests are left alone so this PR doesn't become
even larger than it already is. Eventually, all tests should be migrated
to the new suite though so there isn't a confusing mix of two systems.
2026-02-25 13:51:53 +00:00

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module
import Std.Data.HashSet
open Std
namespace List
-- Fast duplicate-removing function, using a hash set to check if an element was seen before
def fastEraseDups [BEq α] [Hashable α] (l : List α) : List α :=
go l [] ∅
where
go : List α → List α → Std.HashSet α → List α
| [], seenl, _ => seenl.reverse
| (x::l), seenl, seen => if x ∈ seen then go l seenl seen else go l (x::seenl) (seen.insert x)
-- Easy to verify using available hash set lemmas
theorem eraseDups_eq_fastEraseDups [BEq α] [Hashable α] [EquivBEq α] [LawfulHashable α]
(l : List α) : l.eraseDups = l.fastEraseDups :=
loop_eq_go _ _ _ (by simp)
where
loop_eq_go (l seenl : List α) (seen : Std.HashSet α) (hs : ∀ x, seenl.contains x ↔ x ∈ seen) :
eraseDupsBy.loop (· == ·) l seenl = fastEraseDups.go l seenl seen := by
induction l generalizing seenl seen with
| nil => grind [eraseDupsBy.loop, fastEraseDups.go]
| cons x =>
-- In the following example `BEq` is not lawful. To complete the proof we need to add `BEq.comm`
-- TODO: add support for arbitrary partial equivalence and equivalence relations.
-- Remark: `BEq.comm` is noise when `BEq` is lawful.
cases h : seenl.contains x <;> grind [eraseDupsBy.loop, fastEraseDups.go, BEq.comm]
end List