improve n-ary continuation coercion

src/codegen/compile.ml

@@ -10590,8 +10590,7 @@ and compile_prim_invocation (env : E.t) ae p es at =
     let call_as_prim = match fun_sr, sort with
       | SR.Const (_, Const.Fun (mk_fi, Const.PrimWrapper prim)), _ ->
          begin match n_args, e2.it with
-         | 0, _ -> true
-         | 1, _ -> true
+         | (0 | 1), _ -> true
          | n, PrimE (TupPrim, es) when List.length es = n -> true
          | _, _ -> false
          end

src/ir_passes/async.ml

@@ -78,16 +78,9 @@ let new_nary_async_reply ts =
   (* construct the n-ary async value, coercing the continuation, if necessary *)
   let nary_async =
     let coerce u =
-      let v = fresh_var "v" u in
       let k = fresh_var "k" (contT u T.unit) in
-      let r = fresh_var "r" (err_contT T.unit) in
-      [k; r] -->* (
-        varE unary_async -*-
-          (tupE [
-             [v] -->* (varE k -*- varE v);
-             varE r
-          ])
-      )
+      varE (var "@coerce_and_cont" (unary_async --> ([k; fail] -->* (varE unary_async -*- tupE [varE unary_fulfill; varE fail])) |> typ))
+      -*- varE unary_async
     in
     match ts with
     | [t1] ->

src/ir_passes/await.ml

@@ -594,7 +594,7 @@ and t_comp_unit context = function
         let e = fresh_var "e" T.catch in
         ProgU [
           funcD throw e (assertE (falseE ()));
-          expD (c_block context' ds (tupE []) (meta (T.unit) (fun v1 -> tupE [])))
+          expD (c_block context' ds (tupE []) (meta T.unit (fun v1 -> tupE [])))
         ]
     end
   | ActorU (as_opt, ds, ids, { meta = m; preupgrade; postupgrade; heartbeat; timer; inspect}, t) ->
@@ -619,7 +619,7 @@ and t_ignore_throw context exp =
      { (blockE [
           funcD throw e (tupE[]);
         ]
-        (c_exp context' exp (meta (T.unit) (fun v1 -> tupE []))))
+        (c_exp context' exp (meta T.unit (fun v1 -> tupE []))))
        (* timer logic requires us to preserve any source location,
           or timer won't be initialized in compile.ml *)
        with at = exp.at

src/prelude/internals.mo

@@ -307,6 +307,13 @@ func @getSystemRefund() : @Refund {
   return (prim "cyclesRefunded" : () -> Nat) ();
 };
 
+func @coerce_and_cont(a : @Async<()>) :
+  (k : () -> (), r : @Cont<Error>) -> {
+                          #suspend;
+                          #schedule : () -> ()
+                      } =
+  func(k, r) = a(func() = k(), r);
+
 func @new_async<T <: Any>() : (@Async<T>, @Cont<T>, @Cont<Error>) {
   let w_null = func(r : @Refund, t : T) { };
   let r_null = func(_ : Error) {};