go: parse.sx — interface type expressions + 8 tests; type expressions DONE [nothing]

Adds Go interface type expressions:
  interface {}                              →  empty
  interface { Close() }                     →  no-param method
  interface { String() string }             →  with single return
  interface { Read([]byte) (int, error) }   →  multi-return method
  interface { Stringer }                    →  embedded named iface
  interface { io.Reader }                   →  qualified embedded
  interface { io.Reader; Close() error }    →  mixed

gp-parse-interface-elems walks elements tolerating ASI semis. Each
element is either:
  (list :method NAME PARAMS RESULTS)
  (list :embed TYPE)

Method params/results reuse gp-parse-func-type-params/results — the
shape is identical to a free-standing func type. Go 1.18+ type sets
(interface { ~int | ~float64 }) are deferred until the generics
sub-deliverable.

With this, the full Phase 2 **type expressions** sub-deliverable is
complete (pending only field tags, struct/iface embeds details,
variadic, named func params, generics — all flagged later).

parse 106/106, total 235/235.

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

lib/go/parse.sx

@@ -95,6 +95,58 @@
                       :else nil)))
                 (gp-args-rest)
                 args)))))
+      (define
+        gp-parse-interface-elems
+        ;; Caller positioned BEFORE '{'. Parses elements until '}'.
+        ;; Two element shapes:
+        ;;   M(params) [results]   →  (list :method "M" PARAMS RESULTS)
+        ;;   T  or  pkg.T          →  (list :embed TYPE)
+        ;; Type sets (Go 1.18+: ~int | ~float64) deferred.
+        (fn
+          ()
+          (when (and (= (gp-tok-type) "op") (= (gp-tok-value) "{"))
+            (gp-advance!))
+          (let ((elems (list)))
+            (define
+              gp-iface-loop
+              (fn
+                ()
+                (cond
+                  (= (gp-tok-type) "semi")
+                  (do (gp-advance!) (gp-iface-loop))
+                  (and (= (gp-tok-type) "op") (= (gp-tok-value) "}"))
+                  (gp-advance!)
+                  (= (gp-tok-type) "ident")
+                  (do
+                    (let ((name (gp-tok-value)))
+                      (gp-advance!)
+                      (cond
+                        (and (= (gp-tok-type) "op")
+                             (= (gp-tok-value) "("))
+                        (let ((params (gp-parse-func-type-params)))
+                          (let ((results (gp-parse-func-type-results)))
+                            (append! elems
+                              (list :method name params results))))
+                        (and (= (gp-tok-type) "op")
+                             (= (gp-tok-value) "."))
+                        (do
+                          (gp-advance!)
+                          (cond
+                            (= (gp-tok-type) "ident")
+                            (let ((sel-name (gp-tok-value)))
+                              (gp-advance!)
+                              (append! elems
+                                (list :embed
+                                  (list :ty-sel name sel-name))))
+                            :else
+                            (append! elems
+                              (list :embed (list :ty-name name)))))
+                        :else
+                        (append! elems (list :embed (list :ty-name name)))))
+                    (gp-iface-loop))
+                  :else nil)))
+            (gp-iface-loop)
+            elems)))
       (define
         gp-parse-struct-fields
         ;; Caller positioned BEFORE '{'. Parses fields until '}'.
@@ -251,6 +303,10 @@
             (do
               (gp-advance!)
               (list :ty-struct (gp-parse-struct-fields)))
+            (and (= (gp-tok-type) "keyword") (= (gp-tok-value) "interface"))
+            (do
+              (gp-advance!)
+              (list :ty-interface (gp-parse-interface-elems)))
             (= (gp-tok-type) "ident")
             (let ((name (gp-tok-value)))
               (gp-advance!)

lib/go/scoreboard.json

@@ -1,10 +1,10 @@
 {
   "language": "go",
-  "total_pass": 227,
-  "total": 227,
+  "total_pass": 235,
+  "total": 235,
   "suites": [
     {"name":"lex","pass":129,"total":129,"status":"ok"},
-    {"name":"parse","pass":98,"total":98,"status":"ok"},
+    {"name":"parse","pass":106,"total":106,"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: 227 / 227 tests passing**
+**Total: 235 / 235 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | lex | 129 | 129 |
-| ✅ | parse | 98 | 98 |
+| ✅ | parse | 106 | 106 |
 | ⬜ | types | 0 | 0 |
 | ⬜ | eval | 0 | 0 |
 | ⬜ | runtime | 0 | 0 |

lib/go/tests/parse.sx

@@ -577,6 +577,79 @@
           (list
             :ty-struct (list (list :field (list "x") (list :ty-name "int")))))))))
 
+(go-parse-test
+  "ty: interface {} (empty)"
+  (go-parse "v.(interface {})")
+  (list :assert (ast-var "v") (list :ty-interface (list))))
+
+(go-parse-test
+  "ty: interface { Close() } (single method, no params, no return)"
+  (go-parse "v.(interface { Close() })")
+  (list
+    :assert (ast-var "v")
+    (list :ty-interface (list (list :method "Close" (list) (list))))))
+
+(go-parse-test
+  "ty: interface { String() string } (single return)"
+  (go-parse "v.(interface { String() string })")
+  (list
+    :assert (ast-var "v")
+    (list
+      :ty-interface (list (list :method "String" (list) (list (list :ty-name "string")))))))
+
+(go-parse-test
+  "ty: interface { Read([]byte) (int, error) } (multi return)"
+  (go-parse "v.(interface { Read([]byte) (int, error) })")
+  (list
+    :assert (ast-var "v")
+    (list
+      :ty-interface (list
+        (list
+          :method "Read"
+          (list (list :ty-slice (list :ty-name "byte")))
+          (list (list :ty-name "int") (list :ty-name "error")))))))
+
+(go-parse-test
+  "ty: interface { Stringer } (embedded interface)"
+  (go-parse "v.(interface { Stringer })")
+  (list
+    :assert (ast-var "v")
+    (list :ty-interface (list (list :embed (list :ty-name "Stringer"))))))
+
+(go-parse-test
+  "ty: interface { io.Reader } (qualified embedded)"
+  (go-parse "v.(interface { io.Reader })")
+  (list
+    :assert (ast-var "v")
+    (list :ty-interface (list (list :embed (list :ty-sel "io" "Reader"))))))
+
+(go-parse-test
+  "ty: interface with embed + methods (io.ReadWriter style)"
+  (go-parse "v.(interface { io.Reader; Close() error })")
+  (list
+    :assert (ast-var "v")
+    (list
+      :ty-interface (list
+        (list :embed (list :ty-sel "io" "Reader"))
+        (list :method "Close" (list) (list (list :ty-name "error")))))))
+
+(go-parse-test
+  "ty: interface with multiple methods"
+  (go-parse "v.(interface { Read([]byte) int; Write([]byte) int; Close() })")
+  (list
+    :assert (ast-var "v")
+    (list
+      :ty-interface (list
+        (list
+          :method "Read"
+          (list (list :ty-slice (list :ty-name "byte")))
+          (list (list :ty-name "int")))
+        (list
+          :method "Write"
+          (list (list :ty-slice (list :ty-name "byte")))
+          (list (list :ty-name "int")))
+        (list :method "Close" (list) (list))))))
+
 (go-parse-test "non-primary: '+'" (go-parse "+") nil)
 
 (go-parse-test "non-primary: empty" (go-parse "") nil)

plans/go-on-sx.md

@@ -174,12 +174,13 @@ Progress-log line → push `origin/loops/go`.
 - [x] Type assertion `v.(T)`. `(list :assert OBJ TYPE)`. Includes a
       minimal `gp-parse-type` (named / qualified `pkg.T` / pointer
       `*T` / `**T`); full type grammar still pending below.
-- [/] Type expressions: **slice `[]T`, array `[N]T`, map `map[K]V`, chan
+- [x] Type expressions: **slice `[]T`, array `[N]T`, map `map[K]V`, chan
       `chan T` / `chan<- T` / `<-chan T`, pointer `*T`, named `T`,
       qualified `pkg.T`, func `func(...) ...`, struct `struct{...}` with
-      shared-type field rows (`x, y int`)** all done — kit has no type
-      primitives. Interface, embedded fields, field tags, variadic,
-      named func-params, generics deferred.
+      shared-type field rows (`x, y int`), interface `interface{...}`
+      with methods + embedded interfaces (named and qualified)** all
+      done — kit has no type primitives. Field tags, struct embeds,
+      variadic, named func-params, Go 1.18 type sets, generics deferred.
 - [ ] Composite literals: `T{...}`, `[]T{...}`, `map[K]V{...}`,
       `struct{...}{...}`.
 - [ ] Declarations: `package`, `import`, `var`, `const`, `type`, `func`
@@ -190,8 +191,8 @@ Progress-log line → push `origin/loops/go`.
 - [ ] End-to-end: hello-world, fibonacci, FizzBuzz, goroutine ping-pong,
       struct + method.
 - **Acceptance:** parse/ suite at 80+ tests. **Acceptance bar crossed:
-  98/98.** Remaining sub-items (interface types, composite literals,
-  decls, stmts, e2e) still keep Phase 2 open ⬜.
+  106/106.** Remaining sub-items (composite literals, decls, stmts,
+  e2e) still keep Phase 2 open ⬜.
 
 ### Phase 3 — Bidirectional type checker, MVP (`lib/go/types.sx`) ⬜
 - **Independent implementation.** Do NOT use lib/guest/static-types-
@@ -508,6 +509,18 @@ 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.: interface-type expressions. `interface {}`,
+  `interface { Close() }`, `interface { String() string }`,
+  `interface { Read([]byte) (int, error) }`, plus embedded interfaces
+  (`Stringer`, `io.Reader`). AST shape:
+  `(list :ty-interface ELEMS)` where each element is either
+  `(list :method NAME PARAMS RESULTS)` or `(list :embed TYPE)`. Method
+  params reuse `gp-parse-func-type-params` — same anonymous-only shape
+  as func types. Go 1.18+ type sets (`~int | ~float64`) deferred to
+  generics work. With this, all Phase-2 **type expressions** are
+  complete. +8 tests, parse 106/106, total 235/235. `[nothing]` — pure
+  Go parser; the field-binding-group kit-gap proposal from the previous
+  commit covers the cross-language angle.
 - 2026-05-27 — Phase 2 cont.: struct-type expressions. `struct {}`,
   `struct { x int }`, `struct { x int; y string }`, `struct { x, y int }`
   (shared type), nested struct fields. `gp-parse-struct-fields` walks