ocaml: phase 3 pattern matching + constructors (+18 tests, 183 total)

Constructor app: (:app (:con NAME) arg) -> (NAME …args). Tuple args
flatten so Pair(a,b) -> ("Pair" a b), matching the parser's pattern
flatten. Standalone (:con NAME) -> (NAME) nullary.

Pattern matcher: :pwild, :pvar, :plit, :pcon (head + arity), :pcons
(decompose), :plist (length match), :ptuple (after tuple tag). Match
walks clauses until first success; runtime error on exhaustion.
Recursive list functions (len, sum, fact) work end-to-end.

lib/ocaml/test.sh

@@ -430,6 +430,57 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 495)
 (eval "(ocaml-run \"let f x = x * 2 in 5 |> f\")")
 
+;; ── Phase 3: ADTs + match (eval) ───────────────────────────────
+;; Constructors
+(epoch 500)
+(eval "(ocaml-run \"None\")")
+(epoch 501)
+(eval "(ocaml-run \"Some 42\")")
+(epoch 502)
+(eval "(ocaml-run \"Some (1, 2)\")")
+
+;; Match — option
+(epoch 510)
+(eval "(ocaml-run \"match Some 5 with | None -> 0 | Some y -> y\")")
+(epoch 511)
+(eval "(ocaml-run \"match None with | None -> 0 | Some y -> y\")")
+
+;; Match — literals
+(epoch 520)
+(eval "(ocaml-run \"match 3 with | 1 -> 100 | 2 -> 200 | _ -> 999\")")
+(epoch 521)
+(eval "(ocaml-run \"match true with | true -> 1 | false -> 0\")")
+(epoch 522)
+(eval "(ocaml-run \"match \\\"hi\\\" with | \\\"hi\\\" -> 1 | _ -> 0\")")
+
+;; Match — tuples
+(epoch 530)
+(eval "(ocaml-run \"match (1, 2) with | (a, b) -> a + b\")")
+(epoch 531)
+(eval "(ocaml-run \"match (1, 2, 3) with | (a, b, c) -> a * b * c\")")
+
+;; Match — list cons / nil
+(epoch 540)
+(eval "(ocaml-run \"match [1; 2; 3] with | [] -> 0 | h :: _ -> h\")")
+(epoch 541)
+(eval "(ocaml-run \"match [] with | [] -> 0 | h :: _ -> h\")")
+(epoch 542)
+(eval "(ocaml-run \"match [1; 2; 3] with | [a; b; c] -> a + b + c | _ -> 0\")")
+(epoch 543)
+(eval "(ocaml-run \"let rec len lst = match lst with | [] -> 0 | _ :: t -> 1 + len t in len [1; 2; 3; 4; 5]\")")
+(epoch 544)
+(eval "(ocaml-run \"let rec sum lst = match lst with | [] -> 0 | h :: t -> h + sum t in sum [1; 2; 3; 4; 5]\")")
+
+;; Match — wildcard + var
+(epoch 550)
+(eval "(ocaml-run \"match 99 with | _ -> 1\")")
+(epoch 551)
+(eval "(ocaml-run \"match 99 with | x -> x + 1\")")
+
+;; Constructors with tuple args
+(epoch 560)
+(eval "(ocaml-run \"match Pair (1, 2) with | Pair (a, b) -> a * b\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -683,6 +734,39 @@ check 492 "run-prog inc + double"        '10'
 # pipe
 check 495 "eval x |> f"                  '10'
 
+# ── Phase 3: ADTs + match (eval) ────────────────────────────────
+# constructors
+check 500 "eval None"                    '("None")'
+check 501 "eval Some 42"                 '("Some" 42)'
+check 502 "eval Pair tuple-arg"          '("Some" 1 2)'
+
+# option match
+check 510 "match Some 5 -> 5"            '5'
+check 511 "match None -> 0"              '0'
+
+# literal match
+check 520 "match 3 -> _ -> 999"          '999'
+check 521 "match bool true"              '1'
+check 522 "match string lit"             '1'
+
+# tuple match
+check 530 "match (1,2)"                  '3'
+check 531 "match (1,2,3)"                '6'
+
+# list match
+check 540 "match list cons head"         '1'
+check 541 "match empty list"             '0'
+check 542 "match list literal pat"       '6'
+check 543 "match recursive len"          '5'
+check 544 "match recursive sum"          '15'
+
+# wildcard + var
+check 550 "match _ -> 1"                 '1'
+check 551 "match x -> x+1"               '100'
+
+# ctor with tuple arg
+check 560 "Pair(a,b) → a*b"              '2'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"