erlang: receive...after Ms timeout clause (+9 tests)

lib/erlang/runtime.sx

@@ -193,6 +193,8 @@
             :continuation nil
             :receive-pats nil
             :trap-exit false
+            :has-timeout false
+            :timed-out false
             :exit-reason nil}))
         (dict-set! (er-sched-processes) (er-pid-key pid) proc)
         (er-sched-enqueue! pid)
@@ -292,10 +294,40 @@
     ()
     (let
       ((pid (er-sched-next-runnable!)))
-      (when
+      (cond
         (not (= pid nil))
-        (er-sched-step! pid)
-        (er-sched-run-all!)))))
+        (do (er-sched-step! pid) (er-sched-run-all!))
+        ;; Queue empty — fire one pending receive-with-timeout and go again.
+        (er-sched-fire-one-timeout!) (er-sched-run-all!)
+        :else nil))))
+
+;; Wake one waiting process whose receive had an `after Ms` clause.
+;; Returns true if one fired. In our synchronous model "time passes"
+;; once the runnable queue drains — timeouts only fire then.
+(define
+  er-sched-fire-one-timeout!
+  (fn
+    ()
+    (let
+      ((ks (keys (er-sched-processes))) (fired (list false)))
+      (for-each
+        (fn
+          (k)
+          (when
+            (not (nth fired 0))
+            (let
+              ((p (get (er-sched-processes) k)))
+              (when
+                (and
+                  (= (get p :state) "waiting")
+                  (get p :has-timeout))
+                (dict-set! p :timed-out true)
+                (dict-set! p :has-timeout false)
+                (dict-set! p :state "runnable")
+                (er-sched-enqueue! (get p :pid))
+                (set-nth! fired 0 true)))))
+        ks)
+      (nth fired 0))))
 
 (define
   er-sched-step!

lib/erlang/tests/eval.sx

@@ -369,6 +369,37 @@
 (er-eval-test "receive nested tuple"
   (ev "Me = self(), Me ! {result, {ok, 42}}, receive {result, {ok, V}} -> V end") 42)
 
+;; ── receive ... after ... ───────────────────────────────────────
+(er-eval-test "after 0 empty mailbox"
+  (nm (ev "receive _ -> got after 0 -> timeout end"))
+  "timeout")
+(er-eval-test "after 0 match wins"
+  (nm (ev "Me = self(), Me ! ok, receive ok -> got after 0 -> timeout end"))
+  "got")
+(er-eval-test "after 0 non-match fires timeout"
+  (nm (ev "Me = self(), Me ! wrong, receive right -> got after 0 -> timeout end"))
+  "timeout")
+(er-eval-test "after 0 leaves non-match"
+  (ev "Me = self(), Me ! wrong, receive right -> got after 0 -> to end, receive X -> X end")
+  (er-mk-atom "wrong"))
+(er-eval-test "after Ms no sender — timeout fires"
+  (nm (ev "receive _ -> got after 100 -> timed_out end"))
+  "timed_out")
+(er-eval-test "after Ms with sender — match wins"
+  (nm (ev "Me = self(), spawn(fun () -> Me ! hi end), receive hi -> got after 100 -> to end"))
+  "got")
+(er-eval-test "after Ms computed"
+  (nm (ev "Ms = 50, receive _ -> got after Ms -> done end"))
+  "done")
+(er-eval-test "after 0 body side effect"
+  (do (er-io-flush!)
+    (ev "receive _ -> ok after 0 -> io:format(\"to~n\") end")
+    (er-io-buffer-content))
+  "to\n")
+(er-eval-test "after zero poll selective"
+  (ev "Me = self(), Me ! first, Me ! second, X = receive second -> got_second after 0 -> to end, Y = receive first -> got_first after 0 -> to end, {X, Y}")
+  (er-mk-tuple (list (er-mk-atom "got_second") (er-mk-atom "got_first"))))
+
 (define
   er-eval-test-summary
   (str "eval " er-eval-test-pass "/" er-eval-test-count))

lib/erlang/transpile.sx

@@ -954,8 +954,12 @@
   (fn
     (node env)
     (let
-      ((pid (er-sched-current-pid)))
-      (er-eval-receive-loop node pid env))))
+      ((pid (er-sched-current-pid))
+        (after-node (get node :after-ms)))
+      (if
+        (= after-node nil)
+        (er-eval-receive-loop node pid env)
+        (er-eval-receive-with-after node pid env after-node)))))
 
 (define
   er-eval-receive-loop
@@ -975,6 +979,57 @@
               er-suspend-marker))
           (er-eval-receive-loop node pid env))))))
 
+(define
+  er-eval-receive-with-after
+  (fn
+    (node pid env after-node)
+    (let
+      ((ms (er-eval-expr after-node env)))
+      (cond
+        (and (er-atom? ms) (= (get ms :name) "infinity"))
+        (er-eval-receive-loop node pid env)
+        (= ms 0) (er-eval-receive-poll node pid env)
+        :else (er-eval-receive-timed node pid env)))))
+
+;; after 0 — poll once; on no match, run the after-body immediately.
+(define
+  er-eval-receive-poll
+  (fn
+    (node pid env)
+    (let
+      ((r (er-try-receive (get node :clauses) pid env)))
+      (if
+        (get r :matched)
+        (get r :value)
+        (er-eval-body (get node :after-body) env)))))
+
+;; after Ms — suspend; on resume check :timed-out. When the scheduler
+;; runs out of other work it fires one pending timeout per round.
+(define
+  er-eval-receive-timed
+  (fn
+    (node pid env)
+    (let
+      ((r (er-try-receive (get node :clauses) pid env)))
+      (if
+        (get r :matched)
+        (get r :value)
+        (do
+          (er-proc-set! pid :has-timeout true)
+          (shift
+            k
+            (do
+              (er-proc-set! pid :continuation k)
+              (er-proc-set! pid :state "waiting")
+              er-suspend-marker))
+          (if
+            (er-proc-field pid :timed-out)
+            (do
+              (er-proc-set! pid :timed-out false)
+              (er-proc-set! pid :has-timeout false)
+              (er-eval-body (get node :after-body) env))
+            (er-eval-receive-timed node pid env)))))))
+
 ;; Scan mailbox in arrival order. For each msg, try every clause.
 ;; On first match: remove that msg from mailbox and return body value.
 (define

plans/erlang-on-sx.md

@@ -67,7 +67,7 @@ Core mapping:
 - [x] Scheduler in `runtime.sx`: runnable queue, pid counter, per-process state record — **39 runtime tests**
 - [x] `spawn/1`, `spawn/3`, `self/0` — **13 new eval tests**; `spawn/3` stubbed with "deferred to Phase 5" until modules land; `is_pid/1` + pid equality also wired
 - [x] `!` (send), `receive ... end` with selective pattern matching — **13 new eval tests**; delimited continuations (`shift`/`reset`) power receive suspension; sync scheduler loop
-- [ ] `receive ... after Ms -> ...` timeout clause (use SX timer primitive)
+- [x] `receive ... after Ms -> ...` timeout clause (use SX timer primitive) — **9 new eval tests**; synchronous-scheduler semantics: `after 0` polls once; `after Ms` fires when runnable queue drains; `after infinity` = no timeout
 - [ ] `exit/1`, basic process termination
 - [ ] Classic programs in `lib/erlang/tests/programs/`:
   - [ ] `ring.erl` — N processes in a ring, pass a token around M times
@@ -99,6 +99,7 @@ Core mapping:
 
 _Newest first._
 
+- **2026-04-24 receive...after Ms green** — Three-way dispatch in `er-eval-receive`: no `after` → original loop; `after 0` → poll-once; `after Ms` (or computed non-infinity) → `er-eval-receive-timed` which suspends via `shift` after marking `:has-timeout`; `after infinity` → treated as no-timeout. `er-sched-run-all!` now recurses into `er-sched-fire-one-timeout!` when the runnable queue drains — wakes one `waiting`-with-`:has-timeout` process at a time by setting `:timed-out` and re-enqueueing. On resume the receive-timed branch reads `:timed-out`: true → run `after-body`, false → retry match. "Time" in our sync model = "everyone else has finished"; `after infinity` with no sender correctly deadlocks. 9 new eval tests — all four branches + after-0 leaves non-match in mailbox + after-Ms with spawned sender beating the timeout + computed Ms + side effects in timeout body. Total eval 165/165; suite 318/318.
 - **2026-04-24 send + selective receive green — THE SHOWCASE** — `!` (send) in `lib/erlang/transpile.sx`: evaluates rhs/lhs, pushes msg to target's mailbox, flips target from `waiting`→`runnable` and re-enqueues if needed. `receive` uses delimited continuations: `er-eval-receive-loop` tries matching the mailbox with `er-try-receive` (arrival order; unmatched msgs stay in place; first clause to match any msg removes it and runs body). On no match, `(shift k ...)` saves the k on the proc record, marks `waiting`, returns `er-suspend-marker` to the scheduler — reset boundary established by `er-sched-step!`. Scheduler loop `er-sched-run-all!` pops runnable pids and calls either `(reset ...)` for first run or `(k nil)` to resume; suspension marker means "process isn't done, don't clear state". `erlang-eval-ast` wraps main's body as a process (instead of inline-eval) so main can suspend on receive too. Queue helpers added: `er-q-nth`, `er-q-delete-at!`. 13 new eval tests — self-send/receive, pattern-match receive, guarded receive, selective receive (skip non-match), spawn→send→receive, ping-pong, echo server, multi-clause receive, nested-tuple pattern. Total eval 156/156; suite 309/309. Deadlock detected if main never terminates.
 - **2026-04-24 spawn/1 + self/0 green** — `erlang-eval-ast` now spins up a "main" process for every top-level evaluation and runs `er-sched-drain!` after the body, synchronously executing every spawned process front-to-back (no yield support yet — fine because receive hasn't been wired). BIFs added in `lib/erlang/runtime.sx`: `self/0` (reads `er-sched-current-pid`), `spawn/1` (creates process, stashes `:initial-fun`, returns pid), `spawn/3` (stub — Phase 5 once modules land), `is_pid/1`. Pids added to `er-equal?` (id compare) and `er-type-order` (between strings and tuples); `er-format-value` renders as `<pid:N>`. 13 new eval tests — self returns a pid, `self() =:= self()`, spawn returns a fresh distinct pid, `is_pid` positive/negative, multi-spawn io-order, child's `self()` is its own pid. Total eval 143/143; runtime 39/39; suite 296/296. Next: `!` (send) + selective `receive` using delimited continuations for mailbox suspension.
 - **2026-04-24 scheduler foundation green** — `lib/erlang/runtime.sx` + `lib/erlang/tests/runtime.sx`. Amortised-O(1) FIFO queue (`er-q-new`, `er-q-push!`, `er-q-pop!`, `er-q-peek`, `er-q-compact!` at 128-entry head drift), tagged pids `{:tag "pid" :id N}` with `er-pid?`/`er-pid-equal?`, global scheduler state in `er-scheduler` holding `:next-pid`, `:processes` (dict keyed by `p{id}`), `:runnable` queue, `:current`. Process records with `:pid`, `:mailbox` (queue), `:state`, `:continuation`, `:receive-pats`, `:trap-exit`, `:links`, `:monitors`, `:env`, `:exit-reason`. 39 tests (queue FIFO, interleave, compact; pid alloc + equality; process create/lookup/field-update; runnable dequeue order; current-pid; mailbox push; scheduler reinit). Total erlang suite 283/283. Next: `spawn/1`, `!`, `receive` wired into the evaluator.