erlang: supervisor one-for-one (+7 tests)

lib/erlang/runtime.sx

@@ -869,3 +869,58 @@
 (define
   er-load-gen-server!
   (fn () (erlang-load-module er-gen-server-source)))
+
+;; ── supervisor (OTP-lite, one-for-one) ──────────────────────────
+;; Each child spec is `{Id, StartFn}` — `StartFn/0` returns the
+;; child's pid. The supervisor `process_flag(trap_exit, true)`,
+;; links to every child, and on `{'EXIT', DeadPid, _}` calls the
+;; matching `StartFn` to bring up a fresh replacement. Strategy is
+;; one-for-one: only the dead child restarts; siblings keep running.
+(define
+  er-supervisor-source
+  "-module(supervisor).
+   start_link(Mod, Args) ->
+     spawn(fun () ->
+       process_flag(trap_exit, true),
+       case Mod:init(Args) of
+         {ok, ChildSpecs} ->
+           Children = lists:map(
+             fun (Spec) -> supervisor:start_child(Spec) end,
+             ChildSpecs),
+           supervisor:loop(Children)
+       end
+     end).
+   start_child({Id, StartFn}) ->
+     P = StartFn(),
+     link(P),
+     {Id, StartFn, P}.
+   which_children(Sup) ->
+     Sup ! {'$sup_which', self()},
+     receive {'$sup_children', Cs} -> Cs end.
+   stop(Sup) ->
+     Sup ! '$sup_stop',
+     ok.
+   loop(Children) ->
+     receive
+       {'EXIT', Dead, _Reason} ->
+         supervisor:loop(supervisor:restart(Children, Dead));
+       {'$sup_which', From} ->
+         From ! {'$sup_children', Children},
+         supervisor:loop(Children);
+       '$sup_stop' ->
+         ok
+     end.
+   restart([], _) -> [];
+   restart([{Id, SF, P} | T], Dead) ->
+     case P =:= Dead of
+       true ->
+         NewP = SF(),
+         link(NewP),
+         [{Id, SF, NewP} | T];
+       false ->
+         [{Id, SF, P} | supervisor:restart(T, Dead)]
+     end.")
+
+(define
+  er-load-supervisor!
+  (fn () (erlang-load-module er-supervisor-source)))