A hypothetical use of "walkros", macros that don't fire on a call but rather on a code pattern

example.p6

intercept (Q::Infix::Add $op) {
    quasi {
        {{{ $op.right }}} + {{{ $op.left }}} ~ ", lol"    # let's ignore the possible infinite regress from defining + with +
    }
}

say 40 + 2;    # '42, lol'

sub pause {}

intercept (Q::Sub $sub where { #`[the sub has a trait "is cps"; handwave] }) {
    #`[ we split the sub up and do lots of funky things to it ]
}

sub foo() is cps {
    loop {
        say "one";
        pause;
        say "two";
        pause;
    }
}

foo();  # 'one'