Attempt to mimic Java's @OverRide

override.pl

use v6;

multi trait_mod:<is>(Routine:D $m, Mu $interface, :$declared-in!) {
    my $name = $m.name;
    unless $interface.^can($name) {
        die "Method $name clames to be declared in {$interface.^name}, but there's no such method in {$interface.^name}!\n";
    }
}

role R {
    method m1() { ... };
}

class C {
    method m1() is declared-in(R) {
        # all fine here
    }
    method m2() is declared-in(R) {
        # should bomb
    }
}