fix

dune

@@ -12,6 +12,12 @@
     (:standard --enable effects))
    (build_runtime_flags
     (:standard --enable effects)))
+  (wasm_of_ocaml
+   (compilation_mode separate)
+   (flags
+    (:standard --enable effects))
+   (build_runtime_flags
+    (:standard --enable effects)))
   (binaries
    (tools/node_wrapper.exe as node)
    (tools/node_wrapper.exe as node.exe)))

runtime/js/effect.js

@@ -122,9 +122,10 @@ function caml_perform_effect(eff, cont, last, k0) {
   // Move to parent fiber and execute the effect handler there
   // The handler is defined in Stdlib.Effect, so we know that the arity matches
   var k1 = caml_pop_fiber();
+  var last_fiber = "last_fiber" // FIXME
   return caml_stack_check_depth()
-    ? handler(eff, cont, last, k1)
-    : caml_trampoline_return(handler, [eff, cont, last, k1]);
+    ? handler(eff, cont, last_fiber, k1)
+    : caml_trampoline_return(handler, [eff, cont, last_fiber, k1]);
 }
 
 //Provides: caml_alloc_stack

runtime/js/jslib.js

@@ -86,9 +86,9 @@ var caml_callback = caml_call_gen;
 //Requires:caml_stack_depth, caml_call_gen, caml_exn_stack, caml_fiber_stack, caml_wrap_exception, caml_resume_stack, caml_fresh_oo_id, caml_named_value, caml_raise_with_arg, caml_string_of_jsbytes
 //Requires: caml_raise_constant
 function caml_callback(f, args) {
-  function uncaught_effect_handler(eff, k, ms) {
+  function uncaught_effect_handler(eff, k, last, ms) {
     // Resumes the continuation k by raising exception Unhandled.
-    caml_resume_stack(k[1], 0, ms);
+    caml_resume_stack(k[1], last, ms);
     var exn = caml_named_value("Effect.Unhandled");
     if (exn) caml_raise_with_arg(exn, eff);
     else {

runtime/wasm/effect.wat

@@ -615,7 +615,7 @@
       (struct.get $cps_fiber $cont (local.get $top)))
 
    (func $caml_resume_stack (export "caml_resume_stack")
-      (param $vstack (ref eq)) (param $k (ref eq)) (result (ref eq))
+      (param $vstack (ref eq)) (param $last (ref eq)) (param $k (ref eq)) (result (ref eq))
       (local $stack (ref $cps_fiber))
       (drop (block $already_resumed (result (ref eq))
          (local.set $stack
@@ -645,7 +645,7 @@
       (ref.i31 (i32.const 0)))
 
    (func (export "caml_perform_effect")
-      (param $eff (ref eq)) (param $vcont (ref eq)) (param $k0 (ref eq))
+      (param $eff (ref eq)) (param $vcont (ref eq)) (param $last (ref eq)) (param $k0 (ref eq))
       (result (ref eq))
       (local $handlers (ref $handlers))
       (local $handler (ref eq)) (local $k1 (ref eq))
@@ -728,6 +728,7 @@
          (call $caml_resume_stack
             (array.get $block
                (ref.cast (ref $block) (local.get $k)) (i32.const 1))
+               (ref.i31 (i32.const 0))
             (local.get $ms)))
       (call $raise_unhandled (local.get $eff) (ref.i31 (i32.const 0))))