erlang: send + selective receive via shift/reset (+13 tests)

lib/erlang/tests/eval.sx

@@ -327,6 +327,48 @@
     (er-io-buffer-content))
   "true;true")
 
+;; ── ! (send) + receive ──────────────────────────────────────────
+(er-eval-test "self-send + receive"
+  (nm (ev "Me = self(), Me ! hello, receive Msg -> Msg end")) "hello")
+(er-eval-test "send returns msg"
+  (nm (ev "Me = self(), Msg = Me ! ok, Me ! x, receive _ -> Msg end")) "ok")
+(er-eval-test "receive int"
+  (ev "Me = self(), Me ! 42, receive N -> N + 1 end") 43)
+(er-eval-test "receive with pattern"
+  (ev "Me = self(), Me ! {ok, 7}, receive {ok, V} -> V * 2 end") 14)
+(er-eval-test "receive with guard"
+  (ev "Me = self(), Me ! 5, receive N when N > 0 -> positive end")
+  (er-mk-atom "positive"))
+(er-eval-test "receive skips non-match"
+  (nm (ev "Me = self(), Me ! wrong, Me ! right, receive right -> ok end"))
+  "ok")
+(er-eval-test "receive selective leaves others"
+  (nm (ev "Me = self(), Me ! a, Me ! b, receive b -> got_b end"))
+  "got_b")
+(er-eval-test "two receives consume both"
+  (ev "Me = self(), Me ! 1, Me ! 2, X = receive A -> A end, Y = receive B -> B end, X + Y") 3)
+
+;; ── spawn + send + receive (real process communication) ─────────
+(er-eval-test "spawn sends back"
+  (nm
+    (ev "Me = self(), spawn(fun () -> Me ! pong end), receive pong -> got_pong end"))
+  "got_pong")
+(er-eval-test "ping-pong"
+  (do
+    (er-io-flush!)
+    (ev "Me = self(), Child = spawn(fun () -> receive {ping, From} -> From ! pong end end), Child ! {ping, Me}, receive pong -> io:format(\"pong~n\") end")
+    (er-io-buffer-content))
+  "pong\n")
+(er-eval-test "echo server"
+  (ev "Me = self(), Echo = spawn(fun () -> receive {From, Msg} -> From ! Msg end end), Echo ! {Me, 99}, receive R -> R end") 99)
+
+;; ── receive with multiple clauses ────────────────────────────────
+(er-eval-test "receive multi-clause"
+  (nm (ev "Me = self(), Me ! foo, receive ok -> a; foo -> b; bar -> c end"))
+  "b")
+(er-eval-test "receive nested tuple"
+  (ev "Me = self(), Me ! {result, {ok, 42}}, receive {result, {ok, V}} -> V end") 42)
+
 (define
   er-eval-test-summary
   (str "eval " er-eval-test-pass "/" er-eval-test-count))