go: parse.sx — switch + select + 8 tests; stmts done [shapes-scheduler]

Adds Go's switch and select statements:

  switch TAG { case V1, V2: a; case V3: b; default: c }
  switch { case cond: ... }                            — tagless
  select { case x := <-ch: a; case ch <- v: b; default: c }

AST shapes:
  (list :switch TAG CASES)             — TAG nil for tagless
  (list :case VALUES BODY)             — VALUES is expr-list
  (list :select CASES)
  (list :select-case COMM-STMT BODY)   — COMM-STMT is send/recv-assign/bare-recv
  (list :default BODY)

gp-parse-case-body reads stmts until the next case/default/}/eof
without consuming the terminator — used by both switch and select.

select-case parsing reuses gp-parse-stmt for the comm-stmt, so all
four shapes (send, x := <-ch, x = <-ch, bare <-ch) fall out from the
existing stmt parser. Composite-lit suppression is engaged for the
switch tag expression.

Type-switch (`switch v := x.(type) { case int: ... }`) is the one
deferred shape; needs the `.(type)` pseudo-syntax recognised in the
expression layer. Phase 2 statement coverage is otherwise complete.

This is also a chiselling iteration for scheduler sister kit. Diary
updated with select-case design insights:

  * All four select-case shapes share (list :select-case STMT BODY)
    — kit primitive sched-select accepts a uniform list of cases.
  * Default vs no-default determines blocking semantics. Erlang's
    `receive ... after Timeout -> ...` is the analogue — both fit
    "non-blocking fallback case" in the kit API.

parse 169/169, total 298/298.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/go/parse.sx

@@ -728,6 +728,126 @@
                         :else
                         (list :method-decl recv name params results body))))))
               :else nil))))
+      (define
+        gp-parse-case-body
+        ;; Stmts inside a switch/select case clause. Reads until the next
+        ;; 'case'/'default'/'}'/eof without consuming those terminators.
+        (fn
+          ()
+          (let ((stmts (list)))
+            (define
+              gp-cb-loop
+              (fn
+                ()
+                (cond
+                  (= (gp-tok-type) "eof") nil
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) "}")) nil
+                  (and (= (gp-tok-type) "keyword")
+                       (or (= (gp-tok-value) "case")
+                           (= (gp-tok-value) "default")))
+                  nil
+                  (= (gp-tok-type) "semi") (do (gp-advance!) (gp-cb-loop))
+                  :else
+                  (do
+                    (let ((saved-idx gp-idx))
+                      (let ((s (gp-parse-stmt)))
+                        (when (not (= s nil)) (append! stmts s)))
+                      (when (= gp-idx saved-idx) (gp-advance!)))
+                    (gp-cb-loop)))))
+            (gp-cb-loop)
+            stmts)))
+      (define
+        gp-parse-switch
+        ;; Caller has consumed 'switch'. Two shapes:
+        ;;   switch { ...cases... }       — tagless (each case is a bool)
+        ;;   switch TAG { ...cases... }   — tagged (match against TAG)
+        ;; AST: (list :switch TAG CASES) — TAG may be nil.
+        ;; Each case: (list :case VALUES BODY) or (list :default BODY).
+        ;; Type-switch (`switch v := x.(type)`) deferred to a follow-up.
+        (fn
+          ()
+          (set! gp-no-comp-lit (+ gp-no-comp-lit 1))
+          (let ((tag nil) (cases (list)))
+            (when (not (and (= (gp-tok-type) "op") (= (gp-tok-value) "{")))
+              (set! tag (gp-parse-expr 1)))
+            (set! gp-no-comp-lit (- gp-no-comp-lit 1))
+            (when (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
+              (gp-advance!))
+            (define
+              gp-sw-loop
+              (fn
+                ()
+                (cond
+                  (= (gp-tok-type) "semi")
+                  (do (gp-advance!) (gp-sw-loop))
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) "}"))
+                  (gp-advance!)
+                  (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "case"))
+                  (do
+                    (gp-advance!)
+                    (let ((vals (gp-parse-expr-list)))
+                      (when (and (= (gp-tok-type) "op")
+                                 (= (gp-tok-value) ":"))
+                        (gp-advance!))
+                      (append! cases
+                        (list :case vals (gp-parse-case-body))))
+                    (gp-sw-loop))
+                  (and (= (gp-tok-type) "keyword")
+                       (= (gp-tok-value) "default"))
+                  (do
+                    (gp-advance!)
+                    (when (and (= (gp-tok-type) "op")
+                               (= (gp-tok-value) ":"))
+                      (gp-advance!))
+                    (append! cases
+                      (list :default (gp-parse-case-body)))
+                    (gp-sw-loop))
+                  :else (do (gp-advance!) (gp-sw-loop)))))
+            (gp-sw-loop)
+            (list :switch tag cases))))
+      (define
+        gp-parse-select
+        ;; Caller has consumed 'select'. Each case is a communication stmt
+        ;; (send / recv) or a recv-assignment.
+        ;; AST: (list :select CASES).
+        ;; Each case: (list :select-case COMM-STMT BODY) or (list :default BODY).
+        (fn
+          ()
+          (let ((cases (list)))
+            (when (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
+              (gp-advance!))
+            (define
+              gp-sel-loop
+              (fn
+                ()
+                (cond
+                  (= (gp-tok-type) "semi")
+                  (do (gp-advance!) (gp-sel-loop))
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) "}"))
+                  (gp-advance!)
+                  (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "case"))
+                  (do
+                    (gp-advance!)
+                    (let ((comm (gp-parse-stmt)))
+                      (when (and (= (gp-tok-type) "op")
+                                 (= (gp-tok-value) ":"))
+                        (gp-advance!))
+                      (append! cases
+                        (list :select-case comm (gp-parse-case-body))))
+                    (gp-sel-loop))
+                  (and (= (gp-tok-type) "keyword")
+                       (= (gp-tok-value) "default"))
+                  (do
+                    (gp-advance!)
+                    (when (and (= (gp-tok-type) "op")
+                               (= (gp-tok-value) ":"))
+                      (gp-advance!))
+                    (append! cases
+                      (list :default (gp-parse-case-body)))
+                    (gp-sel-loop))
+                  :else (do (gp-advance!) (gp-sel-loop)))))
+            (gp-sel-loop)
+            (list :select cases))))
       (define
         gp-parse-control-cond
         ;; Parses an expression as a control-flow condition with the
@@ -915,6 +1035,10 @@
             (do (gp-advance!) (gp-parse-if))
             (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "for"))
             (do (gp-advance!) (gp-parse-for))
+            (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "switch"))
+            (do (gp-advance!) (gp-parse-switch))
+            (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "select"))
+            (do (gp-advance!) (gp-parse-select))
             (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
             (do (gp-advance!) (gp-parse-block-body))
             :else

lib/go/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "language": "go",
-  "total_pass": 290,
-  "total": 290,
+  "total_pass": 298,
+  "total": 298,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
-    {"name":"parse","pass":161,"total":161,"status":"ok"},
+    {"name":"parse","pass":169,"total":169,"status":"ok"},
     {"name":"types","pass":0,"total":0,"status":"pending"},
     {"name":"eval","pass":0,"total":0,"status":"pending"},
     {"name":"runtime","pass":0,"total":0,"status":"pending"},

lib/go/scoreboard.md

@@ -1,11 +1,11 @@
 # Go-on-SX Scoreboard
 
-**Total: 290 / 290 tests passing**
+**Total: 298 / 298 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 161 | 161 |
+| ✅ | parse | 169 | 169 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |

lib/go/tests/parse.sx

@@ -1047,6 +1047,86 @@
         (list :defer (ast-app (ast-var "cleanup") (list)))
         (list :go (ast-app (ast-var "worker") (list)))))))
 
+(go-parse-test
+  "switch: tagged with two cases"
+  (go-parse "switch x { case 1: a; case 2: b }")
+  (list
+    :switch (ast-var "x")
+    (list
+      (list :case (list (ast-literal "1")) (list (ast-var "a")))
+      (list :case (list (ast-literal "2")) (list (ast-var "b"))))))
+
+(go-parse-test
+  "switch: multi-value case"
+  (go-parse "switch x { case 1, 2: a; case 3: b }")
+  (list
+    :switch (ast-var "x")
+    (list
+      (list
+        :case (list (ast-literal "1") (ast-literal "2"))
+        (list (ast-var "a")))
+      (list :case (list (ast-literal "3")) (list (ast-var "b"))))))
+
+(go-parse-test
+  "switch: tagless (if-else chain)"
+  (go-parse "switch { case x > 0: a; case x < 0: b; default: c }")
+  (list
+    :switch nil
+    (list
+      (list
+        :case (list
+          (ast-app (ast-var ">") (list (ast-var "x") (ast-literal "0"))))
+        (list (ast-var "a")))
+      (list
+        :case (list
+          (ast-app (ast-var "<") (list (ast-var "x") (ast-literal "0"))))
+        (list (ast-var "b")))
+      (list :default (list (ast-var "c"))))))
+
+(go-parse-test
+  "switch: with default only"
+  (go-parse "switch x { default: y }")
+  (list :switch (ast-var "x") (list (list :default (list (ast-var "y"))))))
+
+(go-parse-test
+  "select: recv-into-var case"
+  (go-parse "select { case x := <-ch: a }")
+  (list
+    :select (list
+      (list
+        :select-case (list
+          :short-decl (list (ast-var "x"))
+          (list (ast-app (ast-var "<-") (list (ast-var "ch")))))
+        (list (ast-var "a"))))))
+
+(go-parse-test
+  "select: send case"
+  (go-parse "select { case ch <- v: done() }")
+  (list
+    :select (list
+      (list
+        :select-case (list :send (ast-var "ch") (ast-var "v"))
+        (list (ast-app (ast-var "done") (list)))))))
+
+(go-parse-test
+  "select: recv (discard) case"
+  (go-parse "select { case <-ch: a }")
+  (list
+    :select (list
+      (list
+        :select-case (ast-app (ast-var "<-") (list (ast-var "ch")))
+        (list (ast-var "a"))))))
+
+(go-parse-test
+  "select: with default (non-blocking)"
+  (go-parse "select { case <-ch: a; default: b }")
+  (list
+    :select (list
+      (list
+        :select-case (ast-app (ast-var "<-") (list (ast-var "ch")))
+        (list (ast-var "a")))
+      (list :default (list (ast-var "b"))))))
+
 (go-parse-test "non-primary: '+'" (go-parse "+") nil)
 
 (go-parse-test "non-primary: empty" (go-parse "") nil)

plans/go-on-sx.md

@@ -196,17 +196,18 @@ Progress-log line → push `origin/loops/go`.
       canonical AST kit. Grouped/parenthesized decls (`var (...)`, etc.)
       and variadic params deferred. Anonymous param-list disambiguation
       (`func(int, string)`) is a known parser-greedy limitation, flagged.
-- [/] Statements: return, short-decl, assign, compound assign, expr stmt,
+- [x] Statements: return, short-decl, assign, compound assign, expr stmt,
       block, if/else (chained), for (4 shapes incl. range), break,
-      continue, inc-dec, **`go EXPR`, `defer EXPR`, send `ch <- v`,
-      `for k, v := range coll`** all done. Composite-literal `{`
-      suppression active in control-flow conditions. `switch` and
-      `select` deferred.
+      continue, inc-dec, go, defer, send, **switch (tagged / tagless,
+      multi-value cases, default), select (recv-into-var / send /
+      bare-recv / default)** all done. Composite-literal `{` suppression
+      active in control-flow conditions. Type-switch (`switch v :=
+      x.(type)`) deferred to a follow-up.
 - [ ] End-to-end: hello-world, fibonacci, FizzBuzz, goroutine ping-pong,
       struct + method.
 - **Acceptance:** parse/ suite at 80+ tests. **Acceptance bar crossed:
-  161/161.** Remaining sub-items (switch/select, end-to-end programs)
-  keep Phase 2 open ⬜.
+  169/169.** Remaining sub-item (end-to-end programs) keeps Phase 2
+  open ⬜.
 
 ### Phase 3 — Bidirectional type checker, MVP (`lib/go/types.sx`) ⬜
 - **Independent implementation.** Do NOT use lib/guest/static-types-
@@ -523,6 +524,24 @@ Minimal repro: see `lib/go/lex.sx#gl-oct-digit?` and `#gl-match-op`.
 
 _Newest first. Append one dated entry per commit._
 
+- 2026-05-27 — Phase 2 cont.: `switch` and `select` statements.
+  Tagged + tagless switch, multi-value cases, `default`, and select
+  with recv-into-var / send / bare-recv / default cases. New
+  `gp-parse-case-body` reads stmts until the next `case`/`default`/`}`
+  without consuming the terminator. AST shapes:
+  `(list :switch TAG CASES)`,
+  `(list :case VALUES BODY)`,
+  `(list :select CASES)`,
+  `(list :select-case COMM-STMT BODY)`,
+  `(list :default BODY)`. With this, **Phase 2 statement coverage
+  is complete** — type-switch is the one remaining shape (deferred).
+  +8 tests, parse 169/169, total 298/298. `[shapes-scheduler]` —
+  sister-plan diary updated with the `:select-case` uniform shape
+  insight (single kit primitive covers all four Go case kinds; default
+  vs no-default determines blocking semantics; cross-references to
+  Erlang's `receive ... after`).
+
+  Sister-plan diary update follows.
 - 2026-05-27 — Phase 2 cont.: concurrency + iteration statements.
   `go EXPR`, `defer EXPR`, channel send `ch <- v`, and the four
   `for ... range` shapes (no-kv / k-only / k,v / assign-form). New

plans/lib-guest-scheduler.md

@@ -231,6 +231,24 @@ real result.
 
 _Newest first. Append one dated entry per milestone landed._
 
+- 2026-05-27 — Follow-up from same Phase 2 work: **`select` AST shape**
+  landed. Each case is `(list :select-case COMM-STMT BODY)` where
+  COMM-STMT is one of `:send`, `:short-decl` (recv into new var),
+  `:assign` (recv into existing var), or a bare receive expression
+  `(:app (:var "<-") [chan])`. The shape is uniform across all four
+  comm-stmt kinds — the kit's `sched-select` primitive should accept a
+  list of cases each described by `(direction chan value-target?)` and
+  let the kit's runtime pick a ready case. That uniformity is what
+  makes a single kit primitive cover all four Go case shapes.
+
+  Also: Go's `select` with `default` makes the multiplexer non-blocking;
+  without default it blocks until a case is ready. The kit primitive
+  should mirror this — present-or-absent default determines blocking
+  semantics. Erlang's `receive ... after Timeout -> ...` is a similar
+  pattern with a timeout case rather than default; the kit primitive
+  should handle both as instances of "non-blocking-fallback case."
+  Source: Go-on-SX commit `parse.sx — switch + select`.
+
 - 2026-05-27 — From Go-on-SX Phase 2 (parser side, ahead of scheduler
   implementation): the **parsed AST shapes** for Go's concurrency
   primitives have landed and are worth recording before Phase 5 builds