plans: tick quicksort.hs, progress log 2026-04-25

plans/haskell-on-sx.md

@@ -84,7 +84,7 @@ Key mappings:
 - [ ] Classic programs in `lib/haskell/tests/programs/`:
   - [x] `fib.hs` — infinite Fibonacci stream
   - [x] `sieve.hs` — lazy sieve of Eratosthenes
-  - [ ] `quicksort.hs` — naive QS
+  - [x] `quicksort.hs` — naive QS
   - [ ] `nqueens.hs`
   - [ ] `calculator.hs` — parser combinator style expression evaluator
 - [ ] `lib/haskell/conformance.sh` + runner; `scoreboard.json` + `scoreboard.md`
@@ -114,6 +114,11 @@ Key mappings:
 
 _Newest first._
 
+- **2026-04-25** — Classic program `quicksort.hs`: naive functional quicksort.
+  `qsort (x:xs) = qsort smaller ++ [x] ++ qsort larger where smaller = filter (< x) xs; larger = filter (>= x) xs`.
+  No new runtime additions needed — right sections, `filter`, `++` all worked out of the box.
+  5 tests (general sort, empty, singleton, already-sorted, reverse-sorted). 395/395 green.
+
 - **2026-04-25** — Classic program `sieve.hs`: lazy sieve of Eratosthenes.
   Added `mod`, `div`, `rem`, `quot` to `hk-binop` (and as first-class
   values in `hk-init-env`), enabling backtick operator use. The filter-based