From 9a090c6e42fedc38466dc38418cf8e92251ae6a2 Mon Sep 17 00:00:00 2001
From: giles <giles.bradshaw@rose-ash.com>
Date: Thu, 7 May 2026 23:26:48 +0000
Subject: [PATCH] =?UTF-8?q?ocaml:=20phase=201=20expression=20parser=20(+37?=
 =?UTF-8?q?=20tests,=2095=20total)=20=E2=80=94=20consumes=20lib/guest/prat?=
 =?UTF-8?q?t.sx?=
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Atoms (literals/var/con/unit/list), application (left-assoc), prefix - / not,
29-op precedence table via pratt-op-lookup (incl. keyword-spelled mod/land/
lor/lxor/lsl/lsr/asr), tuples, parens, if/then/else, fun, let, let rec
with function shorthand. AST follows Haskell-on-SX (:int / :op / :fun / etc).
---
 lib/ocaml/parser.sx         | 418 ++++++++++++++++++++++++++++++++++++
 lib/ocaml/test.sh           | 138 +++++++++++-
 lib/ocaml/tests/tokenize.sx |  13 +-
 plans/ocaml-on-sx.md        |  21 +-
 4 files changed, 579 insertions(+), 11 deletions(-)
 create mode 100644 lib/ocaml/parser.sx

diff --git a/lib/ocaml/parser.sx b/lib/ocaml/parser.sx
new file mode 100644
index 00000000..5201d17c
--- /dev/null
+++ b/lib/ocaml/parser.sx
@@ -0,0 +1,418 @@
+;; lib/ocaml/parser.sx — OCaml expression parser.
+;;
+;; Input: token list from (ocaml-tokenize src).
+;; Output: an OCaml AST. Nodes are plain lists tagged by a keyword head;
+;; keywords serialize to their string name so `(list :var "x")` is the
+;; same value as `(list "var" "x")` at runtime.
+;;
+;; Scope (this iteration — expressions only):
+;;   atoms     int/float/string/char, true/false, unit (), var, con, list literal
+;;   application   left-associative, f x y z
+;;   prefix    -E unary minus, not E
+;;   infix     standard ops via lib/guest/pratt.sx table
+;;   tuple     a, b, c   (lower than infix, higher than let/if)
+;;   parens    (e)
+;;   if        if c then t else e   (else optional → unit)
+;;   fun       fun x y -> body
+;;   let       let x = e in body          (no rec)
+;;             let f x y = e in body      (function shorthand)
+;;             let rec f x = e in body
+;;
+;; AST shapes:
+;;   (:int N) (:float N) (:string S) (:char C) (:bool B) (:unit)
+;;   (:var NAME) (:con NAME)
+;;   (:app FN ARG)            — binary, chain for multi-arg
+;;   (:op OP LHS RHS)         — binary infix; OP is the source string
+;;   (:neg E) (:not E)
+;;   (:tuple ITEMS)
+;;   (:list ITEMS)
+;;   (:if C T E)
+;;   (:fun PARAMS BODY)        — PARAMS list of strings (idents)
+;;   (:let NAME PARAMS EXPR BODY)
+;;   (:let-rec NAME PARAMS EXPR BODY)
+
+(define ocaml-tok-type (fn (t) (if (= t nil) "eof" (get t :type))))
+
+(define ocaml-tok-value (fn (t) (if (= t nil) nil (get t :value))))
+
+;; Standard OCaml binary operator table.
+;; Higher precedence = tighter binding.
+;; ASSOC is :left or :right.
+(define
+  ocaml-op-table
+  (list
+    (list "||" 2 :right)
+    (list "or" 2 :right)
+    (list "&&" 3 :right)
+    (list "&" 3 :right)
+    (list "=" 4 :left)
+    (list "<" 4 :left)
+    (list ">" 4 :left)
+    (list "<=" 4 :left)
+    (list ">=" 4 :left)
+    (list "<>" 4 :left)
+    (list "==" 4 :left)
+    (list "!=" 4 :left)
+    (list "|>" 4 :left)
+    (list "@" 5 :right)
+    (list "^" 5 :right)
+    (list "::" 6 :right)
+    (list "+" 7 :left)
+    (list "-" 7 :left)
+    (list "*" 8 :left)
+    (list "/" 8 :left)
+    (list "%" 8 :left)
+    (list "mod" 8 :left)
+    (list "land" 8 :left)
+    (list "lor" 8 :left)
+    (list "lxor" 8 :left)
+    (list "**" 9 :right)
+    (list "lsl" 9 :right)
+    (list "lsr" 9 :right)
+    (list "asr" 9 :right)))
+
+(define
+  ocaml-binop-prec
+  (fn
+    (op)
+    (let
+      ((entry (pratt-op-lookup ocaml-op-table op)))
+      (if (= entry nil) 0 (pratt-op-prec entry)))))
+
+(define
+  ocaml-binop-right?
+  (fn
+    (op)
+    (let
+      ((entry (pratt-op-lookup ocaml-op-table op)))
+      (and (not (= entry nil)) (= (pratt-op-assoc entry) :right)))))
+
+;; Some OCaml binops are spelled with keyword tokens (mod / land / lor /
+;; lxor / lsl / lsr / asr / or). Recognise both shapes.
+(define
+  ocaml-tok-is-binop?
+  (fn
+    (tok)
+    (let
+      ((tt (ocaml-tok-type tok)) (tv (ocaml-tok-value tok)))
+      (cond
+        ((= tt "op") (not (= (ocaml-binop-prec tv) 0)))
+        ((= tt "keyword") (not (= (ocaml-binop-prec tv) 0)))
+        (else false)))))
+
+(define
+  ocaml-parse
+  (fn
+    (src)
+    (let
+      ((tokens (ocaml-tokenize src)) (idx 0) (tok-len 0))
+      (begin
+        (set! tok-len (len tokens))
+        (define peek-tok (fn () (nth tokens idx)))
+        (define advance-tok! (fn () (set! idx (+ idx 1))))
+        (define
+          check-tok?
+          (fn
+            (type value)
+            (let
+              ((t (peek-tok)))
+              (and
+                (= (ocaml-tok-type t) type)
+                (or (= value nil) (= (ocaml-tok-value t) value))))))
+        (define
+          consume!
+          (fn
+            (type value)
+            (if
+              (check-tok? type value)
+              (let ((t (peek-tok))) (begin (advance-tok!) t))
+              (error
+                (str
+                  "ocaml-parse: expected "
+                  type
+                  " "
+                  value
+                  " got "
+                  (ocaml-tok-type (peek-tok))
+                  " "
+                  (ocaml-tok-value (peek-tok)))))))
+        (define at-kw? (fn (kw) (check-tok? "keyword" kw)))
+        (define at-op? (fn (op) (check-tok? "op" op)))
+        (define parse-expr (fn () nil))
+        (define parse-tuple (fn () nil))
+        (define parse-binop-rhs (fn (lhs min-prec) lhs))
+        (define parse-prefix (fn () nil))
+        (define parse-app (fn () nil))
+        (define parse-atom (fn () nil))
+        (set!
+          parse-atom
+          (fn
+            ()
+            (let
+              ((t (peek-tok))
+                (tt (ocaml-tok-type (peek-tok)))
+                (tv (ocaml-tok-value (peek-tok))))
+              (cond
+                ((= tt "number")
+                  (begin
+                    (advance-tok!)
+                    (if (= (round tv) tv) (list :int tv) (list :float tv))))
+                ((= tt "string") (begin (advance-tok!) (list :string tv)))
+                ((= tt "char") (begin (advance-tok!) (list :char tv)))
+                ((and (= tt "keyword") (= tv "true"))
+                  (begin (advance-tok!) (list :bool true)))
+                ((and (= tt "keyword") (= tv "false"))
+                  (begin (advance-tok!) (list :bool false)))
+                ((= tt "ident") (begin (advance-tok!) (list :var tv)))
+                ((= tt "ctor") (begin (advance-tok!) (list :con tv)))
+                ((and (= tt "op") (= tv "("))
+                  (begin
+                    (advance-tok!)
+                    (cond
+                      ((at-op? ")") (begin (advance-tok!) (list :unit)))
+                      (else
+                        (let
+                          ((e (parse-expr)))
+                          (begin (consume! "op" ")") e))))))
+                ((and (= tt "op") (= tv "["))
+                  (begin
+                    (advance-tok!)
+                    (cond
+                      ((at-op? "]") (begin (advance-tok!) (list :list)))
+                      (else
+                        (let
+                          ((items (list)))
+                          (begin
+                            (append! items (parse-expr))
+                            (define
+                              loop
+                              (fn
+                                ()
+                                (when
+                                  (at-op? ";")
+                                  (begin
+                                    (advance-tok!)
+                                    (when
+                                      (not (at-op? "]"))
+                                      (begin
+                                        (append! items (parse-expr))
+                                        (loop)))))))
+                            (loop)
+                            (consume! "op" "]")
+                            (cons :list items)))))))
+                ((at-kw? "begin")
+                  (begin
+                    (advance-tok!)
+                    (let
+                      ((e (parse-expr)))
+                      (begin (consume! "keyword" "end") e))))
+                (else
+                  (error
+                    (str
+                      "ocaml-parse: unexpected token "
+                      tt
+                      " "
+                      tv
+                      " at idx "
+                      idx)))))))
+        (define
+          at-app-start?
+          (fn
+            ()
+            (let
+              ((tt (ocaml-tok-type (peek-tok)))
+                (tv (ocaml-tok-value (peek-tok))))
+              (cond
+                ((= tt "number") true)
+                ((= tt "string") true)
+                ((= tt "char") true)
+                ((= tt "ident") true)
+                ((= tt "ctor") true)
+                ((and (= tt "keyword") (or (= tv "true") (= tv "false") (= tv "begin")))
+                  true)
+                ((and (= tt "op") (or (= tv "(") (= tv "["))) true)
+                (else false)))))
+        (set!
+          parse-app
+          (fn
+            ()
+            (let
+              ((head (parse-atom)))
+              (begin
+                (define
+                  loop
+                  (fn
+                    ()
+                    (when
+                      (at-app-start?)
+                      (let
+                        ((arg (parse-atom)))
+                        (begin (set! head (list :app head arg)) (loop))))))
+                (loop)
+                head))))
+        (set!
+          parse-prefix
+          (fn
+            ()
+            (cond
+              ((at-op? "-")
+                (begin (advance-tok!) (list :neg (parse-prefix))))
+              ((at-kw? "not")
+                (begin (advance-tok!) (list :not (parse-prefix))))
+              (else (parse-app)))))
+        (set!
+          parse-binop-rhs
+          (fn
+            (lhs min-prec)
+            (let
+              ((tok (peek-tok)))
+              (cond
+                ((not (ocaml-tok-is-binop? tok)) lhs)
+                (else
+                  (let
+                    ((op (ocaml-tok-value tok))
+                      (prec (ocaml-binop-prec (ocaml-tok-value tok))))
+                    (cond
+                      ((< prec min-prec) lhs)
+                      (else
+                        (begin
+                          (advance-tok!)
+                          (let
+                            ((rhs (parse-prefix))
+                              (next-min
+                                (if
+                                  (ocaml-binop-right? op)
+                                  prec
+                                  (+ prec 1))))
+                            (begin
+                              (set! rhs (parse-binop-rhs rhs next-min))
+                              (parse-binop-rhs (list :op op lhs rhs) min-prec))))))))))))
+        (define
+          parse-binary
+          (fn
+            ()
+            (let ((lhs (parse-prefix))) (parse-binop-rhs lhs 1))))
+        (set!
+          parse-tuple
+          (fn
+            ()
+            (let
+              ((first (parse-binary)))
+              (cond
+                ((at-op? ",")
+                  (let
+                    ((items (list first)))
+                    (begin
+                      (define
+                        loop
+                        (fn
+                          ()
+                          (when
+                            (at-op? ",")
+                            (begin
+                              (advance-tok!)
+                              (append! items (parse-binary))
+                              (loop)))))
+                      (loop)
+                      (cons :tuple items))))
+                (else first)))))
+        (define
+          parse-fun
+          (fn
+            ()
+            (let
+              ((params (list)))
+              (begin
+                (define
+                  collect-params
+                  (fn
+                    ()
+                    (when
+                      (check-tok? "ident" nil)
+                      (begin
+                        (append! params (ocaml-tok-value (peek-tok)))
+                        (advance-tok!)
+                        (collect-params)))))
+                (collect-params)
+                (when
+                  (= (len params) 0)
+                  (error "ocaml-parse: fun expects at least one parameter"))
+                (consume! "op" "->")
+                (let ((body (parse-expr))) (list :fun params body))))))
+        (define
+          parse-let
+          (fn
+            ()
+            (let
+              ((reccy false))
+              (begin
+                (when
+                  (at-kw? "rec")
+                  (begin (advance-tok!) (set! reccy true)))
+                (let
+                  ((name (ocaml-tok-value (consume! "ident" nil)))
+                    (params (list)))
+                  (begin
+                    (define
+                      collect-params
+                      (fn
+                        ()
+                        (when
+                          (check-tok? "ident" nil)
+                          (begin
+                            (append! params (ocaml-tok-value (peek-tok)))
+                            (advance-tok!)
+                            (collect-params)))))
+                    (collect-params)
+                    (consume! "op" "=")
+                    (let
+                      ((rhs (parse-expr)))
+                      (begin
+                        (consume! "keyword" "in")
+                        (let
+                          ((body (parse-expr)))
+                          (if
+                            reccy
+                            (list :let-rec name params rhs body)
+                            (list :let name params rhs body)))))))))))
+        (define
+          parse-if
+          (fn
+            ()
+            (let
+              ((cond-expr (parse-expr)))
+              (begin
+                (consume! "keyword" "then")
+                (let
+                  ((then-expr (parse-expr)))
+                  (cond
+                    ((at-kw? "else")
+                      (begin
+                        (advance-tok!)
+                        (let
+                          ((else-expr (parse-expr)))
+                          (list :if cond-expr then-expr else-expr))))
+                    (else (list :if cond-expr then-expr (list :unit)))))))))
+        (set!
+          parse-expr
+          (fn
+            ()
+            (cond
+              ((at-kw? "fun") (begin (advance-tok!) (parse-fun)))
+              ((at-kw? "let") (begin (advance-tok!) (parse-let)))
+              ((at-kw? "if") (begin (advance-tok!) (parse-if)))
+              (else (parse-tuple)))))
+        (let
+          ((result (parse-expr)))
+          (begin
+            (when
+              (not (= (ocaml-tok-type (peek-tok)) "eof"))
+              (error
+                (str
+                  "ocaml-parse: trailing tokens at idx "
+                  idx
+                  " — got "
+                  (ocaml-tok-type (peek-tok))
+                  " "
+                  (ocaml-tok-value (peek-tok)))))
+            result))))))
diff --git a/lib/ocaml/test.sh b/lib/ocaml/test.sh
index 2750fa16..3b2fae6b 100755
--- a/lib/ocaml/test.sh
+++ b/lib/ocaml/test.sh
@@ -29,7 +29,9 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 1)
 (load "lib/guest/lex.sx")
 (load "lib/guest/prefix.sx")
+(load "lib/guest/pratt.sx")
 (load "lib/ocaml/tokenizer.sx")
+(load "lib/ocaml/parser.sx")
 (load "lib/ocaml/tests/tokenize.sx")
 
 ;; ── empty / eof ────────────────────────────────────────────────
@@ -169,6 +171,95 @@ cat > "$TMPFILE" << 'EPOCHS'
 (epoch 195)
 (eval "(ocaml-test-tok-value \"x := !y\" 1)")
 
+;; ── Phase 1.parse: parser ──────────────────────────────────────
+;; Atoms
+(epoch 200)
+(eval "(ocaml-parse \"42\")")
+(epoch 201)
+(eval "(ocaml-parse \"3.14\")")
+(epoch 202)
+(eval "(ocaml-parse \"\\\"hi\\\"\")")
+(epoch 203)
+(eval "(ocaml-parse \"'a'\")")
+(epoch 204)
+(eval "(ocaml-parse \"true\")")
+(epoch 205)
+(eval "(ocaml-parse \"false\")")
+(epoch 206)
+(eval "(ocaml-parse \"x\")")
+(epoch 207)
+(eval "(ocaml-parse \"Some\")")
+(epoch 208)
+(eval "(ocaml-parse \"()\")")
+
+;; Application (left-assoc)
+(epoch 210)
+(eval "(ocaml-parse \"f x\")")
+(epoch 211)
+(eval "(ocaml-parse \"f x y\")")
+(epoch 212)
+(eval "(ocaml-parse \"f (g x)\")")
+(epoch 213)
+(eval "(ocaml-parse \"Some 42\")")
+
+;; Binops with precedence
+(epoch 220)
+(eval "(ocaml-parse \"1 + 2\")")
+(epoch 221)
+(eval "(ocaml-parse \"a + b * c\")")
+(epoch 222)
+(eval "(ocaml-parse \"a * b + c\")")
+(epoch 223)
+(eval "(ocaml-parse \"a && b || c\")")
+(epoch 224)
+(eval "(ocaml-parse \"a = b\")")
+(epoch 225)
+(eval "(ocaml-parse \"a ^ b ^ c\")")
+(epoch 226)
+(eval "(ocaml-parse \"a :: b :: []\")")
+(epoch 227)
+(eval "(ocaml-parse \"(a + b) * c\")")
+(epoch 228)
+(eval "(ocaml-parse \"a |> f |> g\")")
+(epoch 229)
+(eval "(ocaml-parse \"x mod 2\")")
+
+;; Prefix
+(epoch 230)
+(eval "(ocaml-parse \"-x\")")
+(epoch 231)
+(eval "(ocaml-parse \"-1 + 2\")")
+
+;; Tuples & lists
+(epoch 240)
+(eval "(ocaml-parse \"(1, 2, 3)\")")
+(epoch 241)
+(eval "(ocaml-parse \"[1; 2; 3]\")")
+(epoch 242)
+(eval "(ocaml-parse \"[]\")")
+
+;; if / fun / let / let rec
+(epoch 250)
+(eval "(ocaml-parse \"if x then 1 else 2\")")
+(epoch 251)
+(eval "(ocaml-parse \"if c then x\")")
+(epoch 252)
+(eval "(ocaml-parse \"fun x -> x + 1\")")
+(epoch 253)
+(eval "(ocaml-parse \"fun x y -> x + y\")")
+(epoch 254)
+(eval "(ocaml-parse \"let x = 1 in x\")")
+(epoch 255)
+(eval "(ocaml-parse \"let f x = x + 1 in f 2\")")
+(epoch 256)
+(eval "(ocaml-parse \"let rec f x = f x in f 1\")")
+(epoch 257)
+(eval "(ocaml-parse \"let f x y = x + y in f 1 2\")")
+
+;; begin/end
+(epoch 260)
+(eval "(ocaml-parse \"begin 1 + 2 end\")")
+
 EPOCHS
 
 OUTPUT=$(timeout 60 "$SX_SERVER" < "$TMPFILE" 2>/dev/null)
@@ -278,9 +369,54 @@ check 193 "Some is ctor"                 '"ctor"'
 check 194 "first |> value"               '"|>"'
 check 195 "ref assign :="                '":="'
 
+# ── Parser tests ────────────────────────────────────────────────
+check 200 "parse int"                    '("int" 42)'
+check 201 "parse float"                  '("float" 3.14)'
+check 202 "parse string"                 '("string" "hi")'
+check 203 "parse char"                   '("char" "a")'
+check 204 "parse true"                   '("bool" true)'
+check 205 "parse false"                  '("bool" false)'
+check 206 "parse var"                    '("var" "x")'
+check 207 "parse ctor"                   '("con" "Some")'
+check 208 "parse unit"                   '("unit")'
+
+check 210 "parse f x"                    '("app" ("var" "f") ("var" "x"))'
+check 211 "parse f x y left-assoc"       '("app" ("app" ("var" "f") ("var" "x")) ("var" "y"))'
+check 212 "parse f (g x)"                '("app" ("var" "f") ("app" ("var" "g") ("var" "x")))'
+check 213 "parse Some 42"                '("app" ("con" "Some") ("int" 42))'
+
+check 220 "parse 1+2"                    '("op" "+" ("int" 1) ("int" 2))'
+check 221 "parse a + b * c prec"         '("op" "+" ("var" "a") ("op" "*"'
+check 222 "parse a*b + c prec"           '("op" "+" ("op" "*"'
+check 223 "parse && / || prec"           '("op" "||" ("op" "&&"'
+check 224 "parse a = b"                  '("op" "=" ("var" "a") ("var" "b"))'
+check 225 "parse ^ right-assoc"          '("op" "^" ("var" "a") ("op" "^"'
+check 226 "parse :: right-assoc"         '("op" "::" ("var" "a") ("op" "::"'
+check 227 "parse parens override"        '("op" "*" ("op" "+"'
+check 228 "parse |> chain"               '("op" "|>" ("op" "|>"'
+check 229 "parse mod kw-binop"           '("op" "mod" ("var" "x") ("int" 2))'
+
+check 230 "parse -x"                     '("neg" ("var" "x"))'
+check 231 "parse -1+2"                   '("op" "+" ("neg" ("int" 1)) ("int" 2))'
+
+check 240 "parse tuple"                  '("tuple" ("int" 1) ("int" 2) ("int" 3))'
+check 241 "parse list literal"           '("list" ("int" 1) ("int" 2) ("int" 3))'
+check 242 "parse []"                     '("list")'
+
+check 250 "parse if/then/else"           '("if" ("var" "x") ("int" 1) ("int" 2))'
+check 251 "parse if w/o else"            '("if" ("var" "c") ("var" "x") ("unit"))'
+check 252 "parse fun x -> ..."           '("fun" ("x") ("op" "+" ("var" "x") ("int" 1)))'
+check 253 "parse fun x y ->"             '("fun" ("x" "y")'
+check 254 "parse let x = 1 in x"         '("let" "x" () ("int" 1) ("var" "x"))'
+check 255 "parse let f x ="              '("let" "f" ("x") ("op" "+"'
+check 256 "parse let rec f x ="          '("let-rec" "f" ("x")'
+check 257 "parse let f x y ="            '("let" "f" ("x" "y")'
+
+check 260 "parse begin/end"              '("op" "+" ("int" 1) ("int" 2))'
+
 TOTAL=$((PASS + FAIL))
 if [ $FAIL -eq 0 ]; then
-  echo "ok $PASS/$TOTAL OCaml-on-SX tokenizer tests passed"
+  echo "ok $PASS/$TOTAL OCaml-on-SX tests passed"
 else
   echo "FAIL $PASS/$TOTAL passed, $FAIL failed:"
   echo ""
diff --git a/lib/ocaml/tests/tokenize.sx b/lib/ocaml/tests/tokenize.sx
index cdf8955a..68235703 100644
--- a/lib/ocaml/tests/tokenize.sx
+++ b/lib/ocaml/tests/tokenize.sx
@@ -1,9 +1,8 @@
-;; lib/ocaml/tests/tokenize.sx — smoke tests for the OCaml tokenizer.
+;; lib/ocaml/tests/tokenize.sx — smoke-test helpers.
 ;;
 ;; Tests are exercised via lib/ocaml/test.sh, which drives sx_server.exe
-;; over the epoch protocol. This file provides a small evaluator that
-;; returns short diagnostic values for each fixture so the runner can
-;; grep them out of one batched run.
+;; over the epoch protocol. This file provides small accessors so the
+;; bash runner can grep short diagnostic values out of one batched run.
 
 (define
   ocaml-test-tok-type
@@ -14,3 +13,9 @@
   (fn (src i) (get (nth (ocaml-tokenize src) i) :value)))
 
 (define ocaml-test-tok-count (fn (src) (len (ocaml-tokenize src))))
+
+(define ocaml-test-parse-str (fn (src) (ocaml-parse src)))
+
+(define
+  ocaml-test-parse-head
+  (fn (src) (nth (ocaml-parse src) 0)))
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index e16759aa..54bd98f2 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -125,12 +125,13 @@ SX CEK evaluator (both JS and OCaml hosts)
       int/float literals (incl. hex, exponent, underscores), nested block
       comments `(* ... *)`. _(labels `~label:` / `?label:` and heredoc `{|...|}`
       deferred — surface tokens already work via `~`/`?` punct + `{`/`|` punct.)_
-- [ ] **Parser:** top-level `let`/`let rec`/`type`/`module`/`exception`/`open`/`include`
-      declarations; expressions: literals, identifiers, constructor application,
-      lambda, application (left-assoc), binary ops with precedence table,
-      `if`/`then`/`else`, `match`/`with`, `try`/`with`, `let`/`in`, `begin`/`end`,
-      `fun`/`function`, tuples, list literals, record literals/updates, field access,
-      sequences `;`, unit `()`.
+- [~] **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 `()`. _(Pending:
+      top-level `let`/`type`/`module`/`exception`/`open`/`include` decls,
+      `match`/`with`, `try`/`with`, `function`, record literals/updates,
+      field access, sequences `;`.)_
 - [ ] **Patterns:** constructor, literal, variable, wildcard `_`, tuple, list cons `::`,
       list literal, record, `as`, or-pattern `P1 | P2`, `when` guard.
 - [ ] OCaml is **not** indentation-sensitive — no layout algorithm needed.
@@ -309,6 +310,14 @@ the "mother tongue" closure: OCaml → SX → OCaml. This means:
 
 _Newest first._
 
+- 2026-05-07 Phase 1 — `lib/ocaml/parser.sx` expression parser consuming
+  `lib/guest/pratt.sx` for binop precedence (29 operators across 8 levels,
+  incl. keyword-spelled binops `mod`/`land`/`lor`/`lxor`/`lsl`/`lsr`/`asr`).
+  Atoms (literals + var/con/unit/list), application (left-assoc), prefix
+  `-`/`not`, tuples, parens, `if`/`then`/`else`, `fun x y -> body`,
+  `let`/`let rec` with function shorthand. AST shapes match Haskell-on-SX
+  conventions (`(:int N)` `(:op OP L R)` `(:fun PARAMS BODY)` etc.). Total
+  95/95 tests now passing via `lib/ocaml/test.sh`.
 - 2026-05-07 Phase 1 — `lib/ocaml/tokenizer.sx` consuming `lib/guest/lex.sx`
   via `prefix-rename`. Covers idents, ctors, 51 keywords, numbers (int / float
   / hex / exponent / underscored), strings (with escapes), chars (with escapes),