go: parse.sx — go/defer/send/for-range + 9 tests [shapes-scheduler]

Adds Go's concurrency + iteration primitives to the statement parser:

  go EXPR                     →  (list :go EXPR)
  defer EXPR                  →  (list :defer EXPR)
  ch <- v                     →  (list :send CHAN VALUE)
  for range COLL { ... }      →  (list :range-for nil nil nil COLL BODY)
  for k := range C { ... }    →  (list :range-for :short-decl KEY nil COLL BODY)
  for k, v := range C { }     →  (list :range-for :short-decl KEY VAL COLL BODY)
  for k, v = range C { ... }  →  (list :range-for :assign KEY VAL COLL BODY)

gp-for-find-range pre-scans the for-header (to '{' or eof) looking
for the 'range' keyword; if present, dispatches to gp-parse-for-range
which handles the four range shapes. C-style and while-like and
infinite are now in gp-parse-for-c-style — gp-parse-for is just a
dispatcher.

Send statement detection lives in the LHS-list branch of gp-parse-stmt:
after parsing a single LHS expression, '<-' triggers (:send LHS RHS).
Channel-recv (`<-ch`) was already parsed as unary `<-` in the expression
layer, so both directions cover.

This is the **chiselling-relevant iteration** for the scheduler sister
kit: the AST shapes Go-on-SX will eventually feed into the kit's
scheduler primitives (sched-spawn, sched-defer, chan-op) have landed.
Sister-plan diary updated with three design insights:

  * :go / :defer both wrap a single expr — kit's sched-spawn should
    accept a thunk uniformly across Erlang's spawn(M,F,A) and Go's
    go fn().
  * :send carries CHAN+VALUE symmetrically with the unary <- recv —
    both reduce to (chan-op direction chan value) in the kit.
  * `for v := range ch` uses the same :range-for shape as range-over-
    slice; the scheduler kit's range dispatch is where chan-recv ⇄
    iteration polymorphism lives.

parse 161/161, total 290/290.

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

lib/go/parse.sx

@@ -765,21 +765,76 @@
                 (do (gp-advance!) (set! els (gp-parse-block-body)))))
             (list :if cnd then els))))
       (define
-        gp-parse-for
-        ;; Caller has consumed 'for'.
-        ;;   for { BODY }                       — infinite
-        ;;   for COND { BODY }                  — while-like
-        ;;   for INIT; COND; POST { BODY }      — C-style
-        ;;   for k, v := range coll { BODY }    — deferred (range)
-        ;; AST: (list :for INIT COND POST BODY); any of INIT/COND/POST may be nil.
+        gp-for-find-range
+        ;; Scan tokens from current idx looking for the `range` keyword;
+        ;; stops at '{' or eof. Restores idx before returning. Returns
+        ;; true iff the for-header contains a range clause.
+        (fn
+          ()
+          (let ((saved-idx gp-idx) (found false))
+            (define
+              gp-scan-rng
               (fn
                 ()
-          (set! gp-no-comp-lit (+ gp-no-comp-lit 1))
-          (let ((init nil) (cnd nil) (post nil) (body nil))
                 (cond
-              (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
+                  (or (= (gp-tok-type) "eof")
+                      (and (= (gp-tok-type) "op")
+                           (= (gp-tok-value) "{")))
+                  nil
+                  (and (= (gp-tok-type) "keyword")
+                       (= (gp-tok-value) "range"))
+                  (set! found true)
+                  :else (do (gp-advance!) (gp-scan-rng)))))
+            (gp-scan-rng)
+            (set! gp-idx saved-idx)
+            found)))
+      (define
+        gp-parse-for-range
+        ;; Range form:
+        ;;   for range COLL { ... }
+        ;;   for k := range COLL { ... }
+        ;;   for k, v := range COLL { ... }
+        ;;   for k, v = range COLL { ... }     (reuse existing vars)
+        ;; AST: (list :range-for DECL-KIND KEY VALUE COLL BODY)
+        ;;   DECL-KIND  : :short-decl | :assign | nil (no kv)
+        ;;   KEY/VALUE  : ast-var nodes or nil
+        (fn
+          ()
+          (let ((decl-kind nil) (key nil) (value nil)
+                (coll nil) (body nil))
+            (cond
+              (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "range"))
               nil
               :else
+              (do
+                (when (= (gp-tok-type) "ident")
+                  (set! key (ast-var (gp-tok-value)))
+                  (gp-advance!))
+                (when (and (= (gp-tok-type) "op") (= (gp-tok-value) ","))
+                  (gp-advance!)
+                  (when (= (gp-tok-type) "ident")
+                    (set! value (ast-var (gp-tok-value)))
+                    (gp-advance!)))
+                (cond
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) ":="))
+                  (do (gp-advance!) (set! decl-kind :short-decl))
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) "="))
+                  (do (gp-advance!) (set! decl-kind :assign)))))
+            (when (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "range"))
+              (gp-advance!))
+            (set! coll (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!)
+              (set! body (gp-parse-block-body)))
+            (list :range-for decl-kind key value coll body))))
+      (define
+        gp-parse-for-c-style
+        ;; for COND { ... }   OR   for INIT; COND; POST { ... }
+        ;; AST: (list :for INIT COND POST BODY).
+        (fn
+          ()
+          (let ((init nil) (cnd nil) (post nil) (body nil))
             (let ((first (gp-parse-stmt)))
               (cond
                 (= (gp-tok-type) "semi")
@@ -795,12 +850,26 @@
                   (when (not (and (= (gp-tok-type) "op")
                                   (= (gp-tok-value) "{")))
                     (set! post (gp-parse-stmt))))
-                  :else (set! cnd first))))
+                :else (set! cnd first)))
             (set! gp-no-comp-lit (- gp-no-comp-lit 1))
             (when (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
               (gp-advance!)
               (set! body (gp-parse-block-body)))
             (list :for init cnd post body))))
+      (define
+        gp-parse-for
+        ;; Caller has consumed 'for'. Dispatches on header shape.
+        (fn
+          ()
+          (set! gp-no-comp-lit (+ gp-no-comp-lit 1))
+          (cond
+            (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
+            (do
+              (set! gp-no-comp-lit (- gp-no-comp-lit 1))
+              (gp-advance!)
+              (list :for nil nil nil (gp-parse-block-body)))
+            (gp-for-find-range) (gp-parse-for-range)
+            :else (gp-parse-for-c-style))))
       (define
         gp-stmt-assign-ops
         ;; Compound assignment operators per Go spec § Assignment operations.
@@ -838,6 +907,10 @@
             (do (gp-advance!) (list :break nil))
             (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "continue"))
             (do (gp-advance!) (list :continue nil))
+            (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "go"))
+            (do (gp-advance!) (list :go (gp-parse-expr 1)))
+            (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "defer"))
+            (do (gp-advance!) (list :defer (gp-parse-expr 1)))
             (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "if"))
             (do (gp-advance!) (gp-parse-if))
             (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "for"))
@@ -881,6 +954,13 @@
                     (let ((op (gp-tok-value)))
                       (gp-advance!)
                       (list :inc-dec op lhs))
+                    ;; Channel send statement: ch <- v (Go spec § Send
+                    ;; statements). Only valid when LHS is a single expr.
+                    (and (= (gp-tok-type) "op") (= (gp-tok-value) "<-")
+                         (= (len lhs-list) 1))
+                    (do
+                      (gp-advance!)
+                      (list :send lhs (gp-parse-expr 1)))
                     :else
                     ;; Plain expression statement — return the single expr.
                     ;; (If somehow there was a comma chain without =/:=, just

lib/go/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "language": "go",
-  "total_pass": 281,
-  "total": 281,
+  "total_pass": 290,
+  "total": 290,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
-    {"name":"parse","pass":152,"total":152,"status":"ok"},
+    {"name":"parse","pass":161,"total":161,"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: 281 / 281 tests passing**
+**Total: 290 / 290 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 152 | 152 |
+| ✅ | parse | 161 | 161 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |

lib/go/tests/parse.sx

@@ -977,6 +977,76 @@
   (go-parse "if Foo {}")
   (list :if (ast-var "Foo") (list :block (list)) nil))
 
+(go-parse-test
+  "stmt: go f()"
+  (go-parse "go f()")
+  (list :go (ast-app (ast-var "f") (list))))
+
+(go-parse-test
+  "stmt: go method(x, y)"
+  (go-parse "go obj.method(x, y)")
+  (list
+    :go (ast-app
+      (list :select (ast-var "obj") "method")
+      (list (ast-var "x") (ast-var "y")))))
+
+(go-parse-test
+  "stmt: defer cleanup()"
+  (go-parse "defer cleanup()")
+  (list :defer (ast-app (ast-var "cleanup") (list))))
+
+(go-parse-test
+  "stmt: send ch <- v"
+  (go-parse "ch <- 42")
+  (list :send (ast-var "ch") (ast-literal "42")))
+
+(go-parse-test
+  "for-range: no kv — for range coll { }"
+  (go-parse "for range coll { }")
+  (list :range-for nil nil nil (ast-var "coll") (list :block (list))))
+
+(go-parse-test
+  "for-range: key only — for k := range m { }"
+  (go-parse "for k := range m { }")
+  (list
+    :range-for :short-decl
+    (ast-var "k")
+    nil
+    (ast-var "m")
+    (list :block (list))))
+
+(go-parse-test
+  "for-range: k, v := range m"
+  (go-parse "for k, v := range m { }")
+  (list
+    :range-for :short-decl
+    (ast-var "k")
+    (ast-var "v")
+    (ast-var "m")
+    (list :block (list))))
+
+(go-parse-test
+  "for-range: assign form k = range coll"
+  (go-parse "for k = range coll { }")
+  (list
+    :range-for :assign
+    (ast-var "k")
+    nil
+    (ast-var "coll")
+    (list :block (list))))
+
+(go-parse-test
+  "concurrency: defer + go in func body"
+  (go-parse "func main() { defer cleanup(); go worker() }")
+  (list
+    :func-decl "main"
+    (list)
+    (list)
+    (list
+      :block (list
+        (list :defer (ast-app (ast-var "cleanup") (list)))
+        (list :go (ast-app (ast-var "worker") (list)))))))
+
 (go-parse-test "non-primary: '+'" (go-parse "+") nil)
 
 (go-parse-test "non-primary: empty" (go-parse "") nil)

plans/go-on-sx.md

@@ -196,19 +196,17 @@ 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
-      (`+=` etc.), expression stmt, block `{...}`, **if/else (with chained
-      else-if), for (infinite / while-like / C-style), break, continue,
-      inc-dec (`x++` / `x--`)** all done. **Composite-literal `{`
-      suppression** active in control-flow conditions via
-      `gp-no-comp-lit` counter — closes the parser-mode caveat flagged
-      when composite literals landed. `switch`/`select`/`defer`/`go`/
-      `for...range`/send `ch<-v` deferred.
+- [/] 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.
 - [ ] End-to-end: hello-world, fibonacci, FizzBuzz, goroutine ping-pong,
       struct + method.
 - **Acceptance:** parse/ suite at 80+ tests. **Acceptance bar crossed:
-  152/152.** Remaining sub-items (switch/select/defer/go/range,
-  end-to-end programs) keep Phase 2 open ⬜.
+  161/161.** Remaining sub-items (switch/select, end-to-end programs)
+  keep Phase 2 open ⬜.
 
 ### Phase 3 — Bidirectional type checker, MVP (`lib/go/types.sx`) ⬜
 - **Independent implementation.** Do NOT use lib/guest/static-types-
@@ -525,6 +523,19 @@ 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.: 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
+  `gp-for-find-range` pre-scans the for-header to dispatch between
+  range and C-style/while forms cleanly. Send-stmt detection added to
+  the LHS-list branch (after lhs, `<-` → send). +9 tests, parse
+  161/161, total 290/290. `[shapes-scheduler]` — Go's concurrency-
+  primitive AST shapes (`:go`, `:defer`, `:send`, `:range-for`) all
+  landed; sister-plan diary updated with the corresponding kit-API
+  insights (uniform spawn-thunk shape, channel-recv ⇄ iteration
+  polymorphism at the range-coll dispatch).
+
+  Sister-plan diary update follows.
 - 2026-05-27 — Phase 2 cont.: control-flow statements. `if cond { } [else
   { }]` with chained else-if, `for { }` (infinite), `for cond { }`
   (while-like), `for init; cond; post { }` (C-style), `break`,

plans/lib-guest-scheduler.md

@@ -231,5 +231,37 @@ real result.
 
 _Newest first. Append one dated entry per milestone landed._
 
+- 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
+  the scheduler.
+
+  ```
+  go EXPR              → (list :go EXPR)
+  defer EXPR           → (list :defer EXPR)
+  ch <- v              → (list :send CHAN VALUE)
+  <-ch                 → (list :app (:var "<-") [CHAN])   ; unary recv
+  for range COLL { }   → (list :range-for nil nil nil COLL BODY)
+  for k, v := range C  → (list :range-for :short-decl KEY VAL COLL BODY)
+  ```
+
+  **Design insight for the kit**: the `:go` and `:defer` shapes are
+  pleasingly minimal — both wrap a single expression. Erlang's
+  `spawn(Mod, Fun, Args)` will produce something more elaborate; the
+  scheduler kit primitive `(sched-spawn task)` should accept a thunk so
+  both languages reduce to a uniform spawn API.
+
+  The `:send` shape carries CHAN + VALUE — symmetric with channel-recv
+  as the unary `<-` form. Once the scheduler has channel primitives,
+  both shapes thunk-down to a single `(chan-op direction chan value)`
+  abstraction.
+
+  Range over channels (`for v := range ch`) is currently parsed as
+  range-for with `coll = ch`; the scheduler kit will dispatch on the
+  type of `coll` at execution time (channels yield via receive,
+  collections via iteration). This dispatch is the right place for the
+  scheduler kit to express the channel-receive ⇄ iteration polymorphism.
+  Source: Go-on-SX commit `parse.sx — go/defer/send/range`.
+
 - 2026-05-26 — Plan drafted. Phase 0 unstarted. Awaiting Go-on-SX to begin
   Phase 1.