From 34513908df777daf4500c2fbaac48a2d62da15ad Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Thu, 7 May 2026 11:39:11 +0000
Subject: [PATCH] =?UTF-8?q?haskell:=20Phase=2012=20=E2=80=94=20Data.Set=20?=
 =?UTF-8?q?full=20API=20(union/intersection/difference/isSubsetOf/filter/m?=
 =?UTF-8?q?ap/foldr/foldl)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 lib/haskell/set.sx            | 32 ++++++++++++++++++++++++++++++++
 plans/haskell-completeness.md | 10 +++++++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/lib/haskell/set.sx b/lib/haskell/set.sx
index 5ae1026e..51884046 100644
--- a/lib/haskell/set.sx
+++ b/lib/haskell/set.sx
@@ -28,3 +28,35 @@
 (define hk-set-null hk-map-null)
 (define hk-set-to-asc-list hk-map-keys)
 (define hk-set-to-list hk-map-keys)
+
+(define
+  hk-set-from-list
+  (fn (xs) (reduce (fn (acc k) (hk-set-insert k acc)) hk-set-empty xs)))
+
+(define
+  hk-set-union
+  (fn (a b) (hk-map-union-with (fn (x y) hk-set-unit) a b)))
+
+(define
+  hk-set-intersection
+  (fn (a b) (hk-map-intersection-with (fn (x y) hk-set-unit) a b)))
+
+(define hk-set-difference hk-map-difference)
+
+(define
+  hk-set-is-subset-of
+  (fn (a b) (= (hk-map-size (hk-map-difference a b)) 0)))
+
+(define
+  hk-set-filter
+  (fn (p s) (hk-map-filter-with-key (fn (k v) (p k)) s)))
+
+(define hk-set-map (fn (f s) (hk-set-from-list (map f (hk-map-keys s)))))
+
+(define
+  hk-set-foldr
+  (fn (f z s) (hk-map-foldr-with-key (fn (k v acc) (f k acc)) z s)))
+
+(define
+  hk-set-foldl
+  (fn (f z s) (hk-map-foldl-with-key (fn (acc k v) (f acc k)) z s)))
diff --git a/plans/haskell-completeness.md b/plans/haskell-completeness.md
index 5e1c2d2d..8f16f145 100644
--- a/plans/haskell-completeness.md
+++ b/plans/haskell-completeness.md
@@ -206,7 +206,7 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 - [x] Implement `Data.Set` in `lib/haskell/set.sx`. Use a standalone
   weight-balanced BST (same structure as Map but no value field) or wrap
   `Data.Map` with unit values. _Chose the wrapper approach: Set k = Map k ()._
-- [ ] API: `empty`, `singleton`, `insert`, `delete`, `member`, `fromList`,
+- [x] API: `empty`, `singleton`, `insert`, `delete`, `member`, `fromList`,
   `toList`, `toAscList`, `size`, `null`, `union`, `intersection`, `difference`,
   `isSubsetOf`, `filter`, `map`, `foldr`, `foldl'`.
 - [ ] Module wiring: `import Data.Set` / `import qualified Data.Set as Set`.
@@ -307,6 +307,14 @@ No OCaml changes are needed. The view type is fully representable as an SX dict.
 
 _Newest first._
 
+**2026-05-07** — Phase 12 Data.Set full API:
+- Added `from-list`/`union`/`intersection`/`difference`/`is-subset-of`/
+  `filter`/`map`/`foldr`/`foldl` — all delegate to the corresponding
+  `hk-map-*` helpers with the value side ignored. `union`/`intersection`
+  use `hk-map-union-with`/`hk-map-intersection-with` with a constant
+  unit-returning combine fn. Spot-check confirms set semantics: dedupe
+  on fromList, correct ⋃/∩/− and isSubsetOf.
+
 **2026-05-07** — Phase 12 Data.Set skeleton (wraps Data.Map with unit values):
 - New `lib/haskell/set.sx`. `hk-set-empty/singleton/insert/delete/member/
   size/null/to-list` all delegate to the corresponding `hk-map-*`. Storage