Grow List sorting from a numeric-only insertion sort into a small,
game-friendly toolkit that sorts records and query results by a key or a
full comparator, stably and in O(n log n).
- List.sort_by(s, keyfn) ascending by a key (draw order, price)
- List.sort_desc_by(s, keyfn) descending (leaderboards)
- List.sort_with(s, cmpfn) full cmp(a,b)->int comparator (multi-field)
Comparators/keys are passed as named top-level functions rather than
lambdas, so the toolkit ships without waiting on closures (#1).
Engine: a stable bottom-up merge sort. emit_takeright is the single
place stability is decided ("take the right run's head only on a strict
win" -> equal keys keep prior order). List.sort becomes a hybrid:
insertion sort for n<32, merge sort above; both stable, so output is
unchanged. Key functions must return an integer-ish type; record slices
hold pointer elements, so the key/comparator receives the record pointer.
Tests: selfhost/tests/sort.ludic (scalar large-n, sort_by, sort_desc_by,
stability, sort_with). Docs: list-sort_by/desc_by/with + updated
list-sort. All suites green (28 self-host / 46 test / 29 test-tools);
reseeded, C-free bootstrap fixpoint holds.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
