ocaml: phase 1 sequence operator ; (+10 tests, 123 total)

Two-phase grammar: parse-expr-no-seq (prior entry) + parse-expr wraps
it with ;-chaining. List bodies keep parse-expr-no-seq so ; remains a
separator inside [...]. Match clause bodies use the seq variant and stop
at | — real OCaml semantics. Trailing ; before end/)/|/in/then/else/eof
permitted.

lib/ocaml/parser.sx

@@ -17,6 +17,7 @@
 ;;   let       let x = e in body          (no rec, function shorthand)
 ;;             let rec f x = e in body
 ;;   match     match e with [|] p -> body | p -> body | ...
+;;   sequence  e1 ; e2  → (:seq e1 e2 …)   (lowest-precedence binary)
 ;;
 ;; Pattern scope:
 ;;   _ (wildcard), int/string/char/bool literals, ident (var binding),
@@ -30,6 +31,7 @@
 ;;   (:op OP LHS RHS)
 ;;   (:neg E) (:not E)
 ;;   (:tuple ITEMS) (:list ITEMS)
+;;   (:seq EXPRS)
 ;;   (:if C T E)
 ;;   (:fun PARAMS BODY)
 ;;   (:let NAME PARAMS EXPR BODY) (:let-rec NAME PARAMS EXPR BODY)
@@ -280,6 +282,7 @@
                 (else lhs)))))
         (set! parse-pattern (fn () (parse-pattern-cons)))
         (define parse-expr (fn () nil))
+        (define parse-expr-no-seq (fn () nil))
         (define parse-tuple (fn () nil))
         (define parse-binop-rhs (fn (lhs min-prec) lhs))
         (define parse-prefix (fn () nil))
@@ -324,7 +327,7 @@
                         (let
                           ((items (list)))
                           (begin
-                            (append! items (parse-expr))
+                            (append! items (parse-expr-no-seq))
                             (define
                               loop
                               (fn
@@ -336,7 +339,7 @@
                                     (when
                                       (not (at-op? "]"))
                                       (begin
-                                        (append! items (parse-expr))
+                                        (append! items (parse-expr-no-seq))
                                         (loop)))))))
                             (loop)
                             (consume! "op" "]")
@@ -521,17 +524,17 @@
           (fn
             ()
             (let
-              ((cond-expr (parse-expr)))
+              ((cond-expr (parse-expr-no-seq)))
               (begin
                 (consume! "keyword" "then")
                 (let
-                  ((then-expr (parse-expr)))
+                  ((then-expr (parse-expr-no-seq)))
                   (cond
                     ((at-kw? "else")
                       (begin
                         (advance-tok!)
                         (let
-                          ((else-expr (parse-expr)))
+                          ((else-expr (parse-expr-no-seq)))
                           (list :if cond-expr then-expr else-expr))))
                     (else (list :if cond-expr then-expr (list :unit)))))))))
         (define
@@ -539,7 +542,7 @@
           (fn
             ()
             (let
-              ((scrut (parse-expr)))
+              ((scrut (parse-expr-no-seq)))
               (begin
                 (consume! "keyword" "with")
                 (when (at-op? "|") (advance-tok!))
@@ -555,7 +558,7 @@
                           (begin
                             (consume! "op" "->")
                             (let
-                              ((body (parse-match-body)))
+                              ((body (parse-expr)))
                               (append! cases (list :case p body)))))))
                     (one)
                     (define
@@ -567,9 +570,8 @@
                           (begin (advance-tok!) (one) (loop)))))
                     (loop)
                     (cons :match (cons scrut (list cases)))))))))
-        (define parse-match-body (fn () (parse-expr)))
         (set!
-          parse-expr
+          parse-expr-no-seq
           (fn
             ()
             (cond
@@ -578,6 +580,40 @@
               ((at-kw? "if") (begin (advance-tok!) (parse-if)))
               ((at-kw? "match") (begin (advance-tok!) (parse-match)))
               (else (parse-tuple)))))
+        (set!
+          parse-expr
+          (fn
+            ()
+            (let
+              ((lhs (parse-expr-no-seq)))
+              (cond
+                ((at-op? ";")
+                  (let
+                    ((items (list lhs)))
+                    (begin
+                      (define
+                        loop
+                        (fn
+                          ()
+                          (when
+                            (at-op? ";")
+                            (begin
+                              (advance-tok!)
+                              (cond
+                                ((at-kw? "end") nil)
+                                ((at-op? ")") nil)
+                                ((at-op? "|") nil)
+                                ((at-kw? "in") nil)
+                                ((at-kw? "then") nil)
+                                ((at-kw? "else") nil)
+                                ((= (ocaml-tok-type (peek-tok)) "eof") nil)
+                                (else
+                                  (begin
+                                    (append! items (parse-expr-no-seq))
+                                    (loop))))))))
+                      (loop)
+                      (cons :seq items))))
+                (else lhs)))))
         (let
           ((result (parse-expr)))
           (begin

lib/ocaml/test.sh

@@ -300,6 +300,28 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 308)
 (eval "(ocaml-parse \"match x with | () -> 0\")")
 
+;; ── Sequences (;) ──────────────────────────────────────────────
+(epoch 320)
+(eval "(ocaml-parse \"1; 2\")")
+(epoch 321)
+(eval "(ocaml-parse \"1; 2; 3\")")
+(epoch 322)
+(eval "(ocaml-parse \"(1; 2)\")")
+(epoch 323)
+(eval "(ocaml-parse \"begin a; b; c end\")")
+(epoch 324)
+(eval "(ocaml-parse \"let x = 1 in x; x\")")
+(epoch 325)
+(eval "(ocaml-parse \"if c then (a; b) else c\")")
+(epoch 326)
+(eval "(ocaml-parse \"[1; 2; 3]\")")
+(epoch 327)
+(eval "(ocaml-parse \"1; 2;\")")
+(epoch 328)
+(eval "(ocaml-parse \"begin a; end\")")
+(epoch 329)
+(eval "(ocaml-parse \"match x with | _ -> a; b\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -476,6 +498,18 @@ check 306 "match ctor with tuple arg"    '("pcon" "Pair" ("pvar" "a") ("pvar" "b
 check 307 "match string literal"         '("plit" ("string" "hi"))'
 check 308 "match unit pattern"           '("plit" ("unit"))'
 
+# ── Sequences ───────────────────────────────────────────────────
+check 320 "seq 1;2"                      '("seq" ("int" 1) ("int" 2))'
+check 321 "seq 1;2;3"                    '("seq" ("int" 1) ("int" 2) ("int" 3))'
+check 322 "seq in parens"                '("seq" ("int" 1) ("int" 2))'
+check 323 "seq in begin/end"             '("seq" ("var" "a") ("var" "b") ("var" "c"))'
+check 324 "let body absorbs seq"         '("let" "x" () ("int" 1) ("seq" ("var" "x") ("var" "x")))'
+check 325 "if-branch parens for seq"     '("if" ("var" "c") ("seq" ("var" "a") ("var" "b"))'
+check 326 "list ; is separator"          '("list" ("int" 1) ("int" 2) ("int" 3))'
+check 327 "trailing ; OK"                '("seq" ("int" 1) ("int" 2))'
+check 328 "begin a; end singleton seq"   '("seq" ("var" "a"))'
+check 329 "match clause body absorbs ;"  '("case" ("pwild") ("seq" ("var" "a") ("var" "b")))'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
   echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"

plans/ocaml-on-sx.md

@@ -128,11 +128,12 @@ SX CEK evaluator (both JS and OCaml hosts)
 - [~] **Parser:** expressions: literals, identifiers, constructor application,
       lambda, application (left-assoc), binary ops with precedence (29 ops via
       `lib/guest/pratt.sx`), `if`/`then`/`else`, `let`/`in`, `let rec`,
-      `fun`/`->`, tuples, list literals, `begin`/`end`, unit `()`. Top-level
-      decls: `let [rec] name params* = expr` and bare expressions, `;;`-separated
-      via `ocaml-parse-program`. _(Pending: `type`/`module`/`exception`/`open`/
-      `include` decls, `match`/`with`, `try`/`with`, `function`, record literals/
-      updates, field access, sequences `;`, `and` mutually-recursive bindings.)_
+      `fun`/`->`, `match`/`with`, tuples, list literals, sequences `;`,
+      `begin`/`end`, unit `()`. Top-level decls: `let [rec] name params* = expr`
+      and bare expressions, `;;`-separated via `ocaml-parse-program`. _(Pending:
+      `type`/`module`/`exception`/`open`/`include` decls, `try`/`with`,
+      `function`, record literals/updates, field access, `and` mutually-recursive
+      bindings.)_
 - [~] **Patterns:** constructor (nullary + with args, incl. flattened tuple
       args `Pair (a, b)` → `(:pcon "Pair" PA PB)`), literal (int/string/char/
       bool/unit), variable, wildcard `_`, tuple, list cons `::`, list literal.
@@ -314,6 +315,14 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-07 Phase 1 — sequence operator `;`. Lowest-precedence binary;
+  `e1; e2; e3` → `(:seq e1 e2 e3)`. Two-phase grammar: `parse-expr-no-seq`
+  is the prior expression entry point; new `parse-expr` wraps it with
+  `;` chaining. List-literal items still use `parse-expr-no-seq` so `;`
+  retains its separator role inside `[…]`. Match-clause bodies use the
+  seq variant and stop at `|`, matching real OCaml semantics. Trailing `;`
+  before `end`/`)`/`|`/`in`/`then`/`else`/eof is permitted. 123/123 tests
+  passing (+10).
 - 2026-05-07 Phase 1 — `match`/`with` + pattern parser. Patterns: wildcard,
   literal, var, ctor (nullary + with arg, with tuple-arg flattening so
   `Pair (a, b)` → `(:pcon "Pair" PA PB)`), tuple, list literal, cons `::`