ocaml: phase 6 List.sort + compare (+7 tests, 339 total)

compare is a host builtin returning -1/0/1 (Stdlib.compare semantics)
deferred to host SX </>. List.sort is insertion-sort in OCaml: O(n²)
but works correctly. List.stable_sort = sort.

Tested: ascending int sort, descending via custom comparator (b - a),
empty list, string sort.

lib/ocaml/eval.sx

@@ -67,6 +67,14 @@
       (list "print_string"  (fn (s) (begin (print s) nil)))
       (list "print_endline" (fn (s) (begin (println s) nil)))
       (list "print_int"     (fn (i) (begin (print (str i)) nil)))
+      ;; Polymorphic compare — returns negative / 0 / positive like
+      ;; OCaml's Stdlib.compare. Defers to host SX `<` and `>`.
+      (list "compare"
+        (fn (a) (fn (b)
+          (cond
+            ((< a b) -1)
+            ((> a b) 1)
+            (else 0)))))
       ;; Hashtbl primitives (one-element list cell holding a dict).
       ;; Keys are coerced to strings via `str` so any value type works
       ;; as a key (matches Hashtbl's polymorphic-key semantics).