erlang: link/unlink/monitor/demonitor + refs (+17 tests)

lib/erlang/runtime.sx

@@ -117,6 +117,24 @@
   er-pid-equal?
   (fn (a b) (and (er-pid? a) (er-pid? b) (= (er-pid-id a) (er-pid-id b)))))
 
+;; ── refs ─────────────────────────────────────────────────────────
+(define er-mk-ref (fn (id) {:id id :tag "ref"}))
+(define er-ref? (fn (v) (er-is-tagged? v "ref")))
+(define
+  er-ref-equal?
+  (fn (a b) (and (er-ref? a) (er-ref? b) (= (get a :id) (get b :id)))))
+
+(define
+  er-ref-new!
+  (fn
+    ()
+    (let
+      ((s (er-sched)))
+      (let
+        ((n (get s :next-ref)))
+        (dict-set! s :next-ref (+ n 1))
+        (er-mk-ref n)))))
+
 ;; ── scheduler state ──────────────────────────────────────────────
 (define er-scheduler (list nil))
 
@@ -128,6 +146,7 @@
       er-scheduler
       0
       {:next-pid 0
+        :next-ref 0
         :current nil
         :processes {}
         :runnable (er-q-new)})))
@@ -190,6 +209,7 @@
             :mailbox (er-q-new)
             :state "runnable"
             :monitors (list)
+            :monitored-by (list)
             :continuation nil
             :receive-pats nil
             :trap-exit false
@@ -296,9 +316,165 @@
       (= (len vs) 1) (raise (er-mk-exit-marker (nth vs 0)))
       (= (len vs) 2)
       (error
-        "Erlang: exit/2 (signal another process) deferred to Phase 4 (links)")
+        "Erlang: exit/2 (signal another process) deferred to next Phase 4 step (signal propagation)")
       :else (error "Erlang: exit: wrong arity"))))
 
+;; ── links / monitors / refs ─────────────────────────────────────
+(define
+  er-bif-is-reference
+  (fn (vs) (er-bool (er-ref? (er-bif-arg1 vs "is_reference")))))
+
+(define
+  er-bif-make-ref
+  (fn
+    (vs)
+    (if
+      (not (= (len vs) 0))
+      (error "Erlang: make_ref/0: arity")
+      (er-ref-new!))))
+
+;; Add `target` to `pid`'s :links list if not already there.
+(define
+  er-link-add-one!
+  (fn
+    (pid target)
+    (let
+      ((links (er-proc-field pid :links)))
+      (when
+        (not (er-link-has? links target))
+        (append! links target)))))
+
+(define
+  er-link-has?
+  (fn
+    (links target)
+    (cond
+      (= (len links) 0) false
+      (er-pid-equal? (nth links 0) target) true
+      :else (er-link-has? (er-slice-list links 1) target))))
+
+(define
+  er-link-remove-one!
+  (fn
+    (pid target)
+    (let
+      ((old (er-proc-field pid :links)) (out (list)))
+      (for-each
+        (fn
+          (i)
+          (let
+            ((p (nth old i)))
+            (when (not (er-pid-equal? p target)) (append! out p))))
+        (range 0 (len old)))
+      (er-proc-set! pid :links out))))
+
+(define
+  er-bif-link
+  (fn
+    (vs)
+    (let
+      ((target (er-bif-arg1 vs "link")) (me (er-sched-current-pid)))
+      (cond
+        (not (er-pid? target)) (error "Erlang: link: not a pid")
+        (er-pid-equal? target me) (er-mk-atom "true")
+        (not (er-proc-exists? target))
+        (raise (er-mk-exit-marker (er-mk-atom "noproc")))
+        :else (do
+          (er-link-add-one! me target)
+          (er-link-add-one! target me)
+          (er-mk-atom "true"))))))
+
+(define
+  er-bif-unlink
+  (fn
+    (vs)
+    (let
+      ((target (er-bif-arg1 vs "unlink")) (me (er-sched-current-pid)))
+      (cond
+        (not (er-pid? target)) (error "Erlang: unlink: not a pid")
+        :else (do
+          (er-link-remove-one! me target)
+          (when
+            (er-proc-exists? target)
+            (er-link-remove-one! target me))
+          (er-mk-atom "true"))))))
+
+(define
+  er-bif-monitor
+  (fn
+    (vs)
+    (if
+      (not (= (len vs) 2))
+      (error "Erlang: monitor/2: arity")
+      (let
+        ((kind (nth vs 0))
+          (target (nth vs 1))
+          (me (er-sched-current-pid)))
+        (cond
+          (not (and (er-atom? kind) (= (get kind :name) "process")))
+          (error "Erlang: monitor: only 'process' supported")
+          (not (er-pid? target)) (error "Erlang: monitor: not a pid")
+          :else (let
+            ((ref (er-ref-new!)))
+            (append!
+              (er-proc-field me :monitors)
+              {:ref ref :pid target})
+            (when
+              (er-proc-exists? target)
+              (append!
+                (er-proc-field target :monitored-by)
+                {:from me :ref ref}))
+            ref))))))
+
+(define
+  er-bif-demonitor
+  (fn
+    (vs)
+    (let
+      ((ref (er-bif-arg1 vs "demonitor")) (me (er-sched-current-pid)))
+      (if
+        (not (er-ref? ref))
+        (error "Erlang: demonitor: not a reference")
+        (do
+          (er-demonitor-purge! me ref)
+          (er-mk-atom "true"))))))
+
+(define
+  er-demonitor-purge!
+  (fn
+    (me ref)
+    (let
+      ((old (er-proc-field me :monitors)) (out (list)) (target-ref (list nil)))
+      (for-each
+        (fn
+          (i)
+          (let
+            ((m (nth old i)))
+            (if
+              (er-ref-equal? (get m :ref) ref)
+              (set-nth! target-ref 0 (get m :pid))
+              (append! out m))))
+        (range 0 (len old)))
+      (er-proc-set! me :monitors out)
+      (when
+        (and
+          (not (= (nth target-ref 0) nil))
+          (er-proc-exists? (nth target-ref 0)))
+        (let
+          ((target (nth target-ref 0))
+            (oldby (er-proc-field (nth target-ref 0) :monitored-by))
+            (out2 (list)))
+          (for-each
+            (fn
+              (i)
+              (let
+                ((m (nth oldby i)))
+                (when
+                  (not (er-ref-equal? (get m :ref) ref))
+                  (append! out2 m))))
+            (range 0 (len oldby)))
+          (er-proc-set! target :monitored-by out2))))))
+
 ;; ── scheduler loop ──────────────────────────────────────────────
 ;; Each scheduler step wraps the process body in `guard`. `receive`
 ;; with no match captures a `call/cc` continuation onto the proc

lib/erlang/scoreboard.json

@@ -1,11 +1,11 @@
 {
   "language": "erlang",
-  "total_pass": 358,
-  "total": 358,
+  "total_pass": 375,
+  "total": 375,
   "suites": [
     {"name":"tokenize","pass":62,"total":62,"status":"ok"},
     {"name":"parse","pass":52,"total":52,"status":"ok"},
-    {"name":"eval","pass":174,"total":174,"status":"ok"},
+    {"name":"eval","pass":191,"total":191,"status":"ok"},
     {"name":"runtime","pass":39,"total":39,"status":"ok"},
     {"name":"ring","pass":4,"total":4,"status":"ok"},
     {"name":"ping-pong","pass":4,"total":4,"status":"ok"},

lib/erlang/scoreboard.md

@@ -1,12 +1,12 @@
 # Erlang-on-SX Scoreboard
 
-**Total: 358 / 358 tests passing**
+**Total: 375 / 375 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
 | ✅ | tokenize | 62 | 62 |
 | ✅ | parse | 52 | 52 |
-| ✅ | eval | 174 | 174 |
+| ✅ | eval | 191 | 191 |
 | ✅ | runtime | 39 | 39 |
 | ✅ | ring | 4 | 4 |
 | ✅ | ping-pong | 4 | 4 |

lib/erlang/tests/eval.sx

@@ -432,6 +432,76 @@
     (nm (er-last-main-exit-reason)))
   "from_fn")
 
+;; ── refs / link / monitor ──────────────────────────────────────
+(er-eval-test "make_ref tag"
+  (get (ev "make_ref()") :tag) "ref")
+(er-eval-test "is_reference fresh"
+  (nm (ev "R = make_ref(), is_reference(R)")) "true")
+(er-eval-test "is_reference pid"
+  (nm (ev "is_reference(self())")) "false")
+(er-eval-test "is_reference number"
+  (nm (ev "is_reference(42)")) "false")
+(er-eval-test "make_ref distinct"
+  (nm (ev "R1 = make_ref(), R2 = make_ref(), R1 =:= R2")) "false")
+(er-eval-test "make_ref same id eq"
+  (nm (ev "R = make_ref(), R =:= R")) "true")
+
+(er-eval-test "link returns true"
+  (nm (ev "P = spawn(fun () -> ok end), link(P)")) "true")
+(er-eval-test "self link returns true"
+  (nm (ev "link(self())")) "true")
+(er-eval-test "unlink returns true"
+  (nm (ev "P = spawn(fun () -> ok end), link(P), unlink(P)")) "true")
+(er-eval-test "unlink without link"
+  (nm (ev "P = spawn(fun () -> ok end), unlink(P)")) "true")
+
+(er-eval-test "monitor returns ref"
+  (get (ev "P = spawn(fun () -> ok end), monitor(process, P)") :tag)
+  "ref")
+(er-eval-test "monitor refs distinct"
+  (nm (ev "P = spawn(fun () -> ok end), R1 = monitor(process, P), R2 = monitor(process, P), R1 =:= R2"))
+  "false")
+(er-eval-test "demonitor returns true"
+  (nm (ev "P = spawn(fun () -> ok end), R = monitor(process, P), demonitor(R)"))
+  "true")
+
+;; Bidirectional link recorded on both sides.
+(er-eval-test "link bidirectional"
+  (do
+    (ev "P = spawn(fun () -> receive forever -> ok end end), link(P)")
+    ;; After eval, check links on main + child via accessors.
+    (and
+      (= (len (er-proc-field (er-mk-pid 0) :links)) 1)
+      (= (len (er-proc-field (er-mk-pid 1) :links)) 1)))
+  true)
+
+;; unlink clears both sides.
+(er-eval-test "unlink clears both"
+  (do
+    (ev "P = spawn(fun () -> receive forever -> ok end end), link(P), unlink(P)")
+    (and
+      (= (len (er-proc-field (er-mk-pid 0) :links)) 0)
+      (= (len (er-proc-field (er-mk-pid 1) :links)) 0)))
+  true)
+
+;; monitor adds entries to both lists.
+(er-eval-test "monitor records both sides"
+  (do
+    (ev "P = spawn(fun () -> receive forever -> ok end end), monitor(process, P)")
+    (and
+      (= (len (er-proc-field (er-mk-pid 0) :monitors)) 1)
+      (= (len (er-proc-field (er-mk-pid 1) :monitored-by)) 1)))
+  true)
+
+;; demonitor clears both lists.
+(er-eval-test "demonitor clears both"
+  (do
+    (ev "P = spawn(fun () -> receive forever -> ok end end), R = monitor(process, P), demonitor(R)")
+    (and
+      (= (len (er-proc-field (er-mk-pid 0) :monitors)) 0)
+      (= (len (er-proc-field (er-mk-pid 1) :monitored-by)) 0)))
+  true)
+
 (define
   er-eval-test-summary
   (str "eval " er-eval-test-pass "/" er-eval-test-count))

lib/erlang/transpile.sx

@@ -372,6 +372,7 @@
             (range 0 (len ea)))))
       (and (= (type-of a) "string") (= (type-of b) "string")) (= a b)
       (and (er-pid? a) (er-pid? b)) (= (get a :id) (get b :id))
+      (and (er-ref? a) (er-ref? b)) (= (get a :id) (get b :id))
       :else false)))
 
 ;; Exact equality: 1 =/= 1.0 in Erlang.
@@ -562,9 +563,15 @@
       (= name "atom_to_list") (er-bif-atom-to-list vs)
       (= name "list_to_atom") (er-bif-list-to-atom vs)
       (= name "is_pid") (er-bif-is-pid vs)
+      (= name "is_reference") (er-bif-is-reference vs)
       (= name "self") (er-bif-self vs)
       (= name "spawn") (er-bif-spawn vs)
       (= name "exit") (er-bif-exit vs)
+      (= name "make_ref") (er-bif-make-ref vs)
+      (= name "link") (er-bif-link vs)
+      (= name "unlink") (er-bif-unlink vs)
+      (= name "monitor") (er-bif-monitor vs)
+      (= name "demonitor") (er-bif-demonitor vs)
       :else (error
         (str "Erlang: undefined function '" name "/" (len vs) "'")))))
 
@@ -894,6 +901,7 @@
       (er-tuple? v) (str "{" (er-format-tuple-elems (get v :elements)) "}")
       (er-fun? v) "#Fun"
       (er-pid? v) (str "<pid:" (get v :id) ">")
+      (er-ref? v) (str "#Ref<" (get v :id) ">")
       :else (str v))))
 
 (define

plans/erlang-on-sx.md

@@ -79,7 +79,7 @@ Core mapping:
 - [x] Target: 5/5 classic programs + 1M-process ring benchmark runs — **5/5 classic programs green; ring benchmark runs correctly at every measured size up to N=1000 (33s, ~34 hops/s); 1M target NOT met in current synchronous-scheduler architecture (would take ~9h at observed throughput)**. See `lib/erlang/bench_ring.sh` and `lib/erlang/bench_ring_results.md`.
 
 ### Phase 4 — links, monitors, exit signals
-- [ ] `link/1`, `unlink/1`, `monitor/2`, `demonitor/1`
+- [x] `link/1`, `unlink/1`, `monitor/2`, `demonitor/1` — **17 new eval tests**; `make_ref/0`, `is_reference/1`, refs in `=:=`/format wired
 - [ ] Exit-signal propagation; trap_exit flag
 - [ ] `try/catch/of/end`
 
@@ -99,6 +99,7 @@ Core mapping:
 
 _Newest first._
 
+- **2026-04-25 link/unlink/monitor/demonitor + refs green** — Refs added to scheduler (`:next-ref`, `er-ref-new!`); `er-mk-ref`, `er-ref?`, `er-ref-equal?` in runtime. Process record gains `:monitored-by`. New BIFs in `lib/erlang/runtime.sx`: `make_ref/0`, `is_reference/1`, `link/1` (bidirectional, no-op for self, raises `noproc` for missing target), `unlink/1` (removes both sides; tolerates missing target), `monitor(process, Pid)` (returns fresh ref, adds entries to monitor's `:monitors` and target's `:monitored-by`), `demonitor(Ref)` (purges both sides). Refs participate in `er-equal?` (id compare) and render as `#Ref<N>`. 17 new eval tests covering `make_ref` distinctness, link return values, bidirectional link recording, unlink clearing both sides, monitor recording both sides, demonitor purging. Total suite 375/375. Signal propagation (the next checkbox) will hook into these data structures.
 - **2026-04-25 ring benchmark recorded — Phase 3 closed** — `lib/erlang/bench_ring.sh` runs the ring at N ∈ {10, 50, 100, 500, 1000} and times each end-to-end via wall clock. `lib/erlang/bench_ring_results.md` captures the table. Throughput plateaus at ~30-34 hops/s. 1M-process target IS NOT MET in this architecture — extrapolation = ~9h. The sub-task is ticked as complete with that fact recorded inline because the perf gap is architectural (env-copy per call, call/cc per receive, mailbox rebuild on delete-at) and out of scope for this loop's iterations. Phase 3 done; Phase 4 (links, monitors, exit signals, try/catch) is next.
 - **2026-04-25 conformance harness + scoreboard green** — `lib/erlang/conformance.sh` loads every test suite via the epoch protocol, parses pass/total per suite via the `(N M)` lists, sums to a grand total, and writes both `lib/erlang/scoreboard.json` (machine-readable) and `lib/erlang/scoreboard.md` (Markdown table with ✅/❌ markers). 9 suites × full pass = 358/358. Exits non-zero on any failure. `bash lib/erlang/conformance.sh -v` prints per-suite counts. Phase 3's only remaining checkbox is the 1M-process ring benchmark target.
 - **2026-04-25 fib_server.erl green — all 5 classic programs landed** — `lib/erlang/tests/programs/fib_server.sx` with 8 tests. Server runs `Fib` (recursive `fun (0) -> 0; (1) -> 1; (N) -> Fib(N-1) + Fib(N-2) end`) inside its receive loop. Tests cover base cases, fib(10)=55, fib(15)=610, sequential queries summed, recurrence check (`fib(12) - fib(11) - fib(10) = 0`), two clients sharing one server, io-buffer trace `"0 1 1 2 3 5 8 "`. Total suite 358/358. Phase 3 sub-list: 5/5 classic programs done; only conformance harness + benchmark target remain.