Ad-hoc associativity

sub as-left(&f) {
    sub infix:<@>(|xs) is assoc<left> {
        &f(|xs);
    }
    &infix:<@>;
}

sub as-right(&f) {
    sub infix:<@>(|xs) is assoc<right> {
        &f(|xs);
    }
    &infix:<@>;
}

say (|("a" .. "f"), "Unit").reduce(as-right({"Tuple $^a ($^b)"}));