ocaml: phase 1+3 or-patterns (P1 | P2 | ...) parens-only (+5 tests, 394 total)

Parser: when | follows a pattern inside parens, build (:por ALT1 ALT2
...). Eval: try alternatives, succeed on first match. Top-level |
remains the clause separator — parens-only avoids ambiguity without
lookahead.

Examples now work:
  match n with | (1 | 2 | 3) -> 100 | _ -> 0
  match c with | (Red | Green) -> 1 | Blue -> 2

lib/ocaml/eval.sx

@@ -259,6 +259,22 @@
                     (= (len (rest val)) (len arg-pats)))
                 (ocaml-match-list arg-pats (rest val) env))
               (else ocaml-match-fail))))
+        ((= tag "por")
+          ;; (:por ALT1 ALT2 ...) — try each alternative; succeed on the
+          ;; first match. Note: for now, alternatives must bind the same
+          ;; set of variables (OCaml constraint) — we don't enforce this.
+          (let ((alts (rest pat)) (result ocaml-match-fail) (done false))
+            (begin
+              (define try-alts
+                (fn (xs)
+                  (when (and (not done) (not (= xs (list))))
+                    (let ((env2 (ocaml-match-pat (first xs) val env)))
+                      (cond
+                        ((not (= env2 ocaml-match-fail))
+                          (begin (set! result env2) (set! done true)))
+                        (else (try-alts (rest xs))))))))
+              (try-alts alts)
+              result)))
         ((= tag "pas")
           ;; (:pas INNER NAME) — match inner pattern, also bind NAME → val.
           (let ((inner (nth pat 1)) (alias (nth pat 2)))