Euclidean division: emulating infix:</> and infix:<%> with only addition, subtraction, multiplication, conditionals, comparison, and recursion

euclidean-division.p6

multi MAIN {
    my $a = prompt "a (bigger number): ";
    my $b = prompt "b (smaller number): ";

    my ($q, $r) = euclidean($a, $b);
    say "q: $q";
    say "r: $r";
}

multi MAIN("test") {
    use Test;

    is euclidean(22, 5), [4, 2], "22 // 5 = 4, 22 % 5 = 2";
    is euclidean(15, 3), [5, 0], "15 // 3 = 5, 15 % 3 = 0";
    is euclidean(501, 5), [100, 1], "501 // 5 = 100, 501 % 5 = 1";

    done-testing;
}

sub euclidean($a is copy, $b) {
    my $q = 0;
    sub subtract($d) {
        if $d * $b * 2 <= $a {
            subtract($d * 2);
        }
        if $a >= $d * $b {
            $a -= $d * $b;
            $q += $d;
        }
    }(1);

    return $q, $a;
}