sub asynchronize(Supply $s) {
    #"asynchronize".say;
    supply {
        whenever Promise.kept {
            #"asynchronize whenever".say;
            whenever $s { "asynchronize whenever emit".say;.emit }
        }
    }
}

react {
    my $i = 0;
    my $supply1 = supply { loop { await Promise.in(3); done if $i++> 5; emit("1") } }
    my $supply2 = supply { loop { await Promise.in(1); done if $i++> 5; emit("2") } }

    whenever asynchronize $supply2 -> $x { $x.print }
    whenever asynchronize $supply1 -> $x { $x.print }
}