ocaml: phase 2 try/with + raise (+6 tests, 204 total)

Parser: try EXPR with | pat -> handler | ... -> (:try EXPR CLAUSES).
Eval delegates to SX guard with else matching the raised value against
clause patterns; re-raises on no-match. raise/failwith/invalid_arg
shipped as builtins. failwith "msg" raises ("Failure" msg) so
| Failure msg -> ... patterns match.

lib/ocaml/eval.sx

@@ -41,7 +41,13 @@
       (list "ignore" (fn (x) nil))
       ;; References. A ref cell is a one-element list; ! reads it and
       ;; := mutates it via set-nth!.
-      (list "ref" (fn (x) (list x))))))
+      (list "ref" (fn (x) (list x)))
+      ;; Exceptions: `raise e` invokes the host-SX raise; values are
+      ;; tagged like other ctors so `try ... with | Exn x -> handler`
+      ;; can pattern-match them.
+      (list "raise" (fn (e) (raise e)))
+      (list "failwith" (fn (msg) (raise (list "Failure" msg))))
+      (list "invalid_arg" (fn (msg) (raise (list "Invalid_argument" msg)))))))
 
 (define ocaml-env-lookup
   (fn (env name)
@@ -342,6 +348,28 @@
                               (loop)))))
                       (loop)))))
               nil)))
+        ((= tag "try")
+          ;; (:try EXPR CLAUSES) — evaluate EXPR; if it raises, match the
+          ;; raised value against CLAUSES. Re-raise on no-match.
+          (let ((expr (nth ast 1)) (clauses (nth ast 2)) (env-cap env))
+            (guard (e
+                    (else
+                      (begin
+                        (define try-clauses
+                          (fn (cs)
+                            (cond
+                              ((empty? cs) (raise e))
+                              (else
+                                (let ((clause (first cs)))
+                                  (let ((pat (nth clause 1))
+                                        (body (nth clause 2)))
+                                    (let ((env2 (ocaml-match-pat pat e env-cap)))
+                                      (cond
+                                        ((= env2 ocaml-match-fail)
+                                          (try-clauses (rest cs)))
+                                        (else (ocaml-eval body env2))))))))))
+                        (try-clauses clauses))))
+              (ocaml-eval expr env-cap))))
         ((= tag "while")
           (let ((cond-ast (nth ast 1)) (body (nth ast 2)))
             (begin

lib/ocaml/parser.sx

@@ -573,6 +573,28 @@
                           (begin (advance-tok!) (one) (loop)))))
                     (loop)
                     (cons :match (cons scrut (list cases)))))))))
+        (define parse-try
+          (fn ()
+            (let ((expr (parse-expr-no-seq)))
+              (begin
+                (consume! "keyword" "with")
+                (when (at-op? "|") (advance-tok!))
+                (let ((cases (list)))
+                  (begin
+                    (define one
+                      (fn ()
+                        (let ((p (parse-pattern)))
+                          (begin
+                            (consume! "op" "->")
+                            (let ((body (parse-expr)))
+                              (append! cases (list :case p body)))))))
+                    (one)
+                    (define loop
+                      (fn ()
+                        (when (at-op? "|")
+                          (begin (advance-tok!) (one) (loop)))))
+                    (loop)
+                    (list :try expr cases)))))))
         (define parse-function
           (fn ()
             ;; `function | pat -> body | …` ≡ fun x -> match x with | pat -> body
@@ -634,6 +656,7 @@
               ((at-kw? "function") (begin (advance-tok!) (parse-function)))
               ((at-kw? "for") (begin (advance-tok!) (parse-for)))
               ((at-kw? "while") (begin (advance-tok!) (parse-while)))
+              ((at-kw? "try") (begin (advance-tok!) (parse-try)))
               (else (parse-tuple)))))
         (set!
           parse-expr

lib/ocaml/test.sh

@@ -517,6 +517,20 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 643)
 (eval "(ocaml-run-program \"let rec map f = function | [] -> [] | h :: t -> f h :: map f t;; map (fun x -> x * x) [1; 2; 3; 4]\")")
 
+;; ── try / with / raise ─────────────────────────────────────────
+(epoch 660)
+(eval "(ocaml-run \"try 1 + 2 with | _ -> 0\")")
+(epoch 661)
+(eval "(ocaml-run \"try raise (Foo 5) with | Foo x -> x | Bar -> 99\")")
+(epoch 662)
+(eval "(ocaml-run \"try raise Bar with | Foo x -> x | Bar -> 99\")")
+(epoch 663)
+(eval "(ocaml-run \"try failwith \\\"oops\\\" with | Failure msg -> msg\")")
+(epoch 664)
+(eval "(ocaml-run \"try (raise (Foo 1); 999) with | Foo x -> x + 100\")")
+(epoch 665)
+(eval "(ocaml-run \"let f x = if x < 0 then raise (NegArg x) else x * 2 in try f (-5) with | NegArg n -> n\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -824,6 +838,14 @@ check 641 "function None=0"              '0'
 check 642 "rec function len"             '3'
 check 643 "rec function map x*x"         '(1 4 9 16)'
 
+# ── try / with / raise ──────────────────────────────────────────
+check 660 "try success"                  '3'
+check 661 "try Foo caught"               '5'
+check 662 "try Bar caught"               '99'
+check 663 "try failwith"                 '"oops"'
+check 664 "try sequence raises"          '101'
+check 665 "raise from function"          '-5'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"

plans/ocaml-on-sx.md

@@ -156,7 +156,8 @@ SX CEK evaluator (both JS and OCaml hosts)
 - [ ] Mutable record fields.
 - [x] `for i = lo to hi do ... done` loop; `while cond do ... done` (incl.
       `downto` direction).
-- [ ] `try`/`with` — maps to SX `guard`; `raise` via perform.
+- [x] `try`/`with` — maps to SX `guard`; `raise` is a builtin that calls
+      host SX `raise`. `failwith` and `invalid_arg` ship as builtins.
 - [ ] Tests in `lib/ocaml/tests/eval.sx` — 50+ tests, pure + imperative.
 
 ### Phase 3 — ADTs + pattern matching
@@ -320,6 +321,12 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-08 Phase 2 — `try`/`with` + `raise` builtin. Parser produces
+  `(:try EXPR CLAUSES)`; eval delegates to SX `guard` with `else`
+  matching the raised value against clause patterns and re-raising on
+  no-match. `raise`/`failwith`/`invalid_arg` exposed as builtins;
+  failwith builds `("Failure" msg)` so `Failure msg -> ...` patterns
+  match. 204/204 (+6).
 - 2026-05-08 Phase 2 — `function | pat -> body | …` parser + eval.
   Sugar for `fun x -> match x with | …`. AST: `(:function CLAUSES)`
   evaluated to a unary closure that runs `ocaml-match-clauses` on the