use experimental :cached; proto collatz(Int) is cached { * } multi collatz(1) { 1 } multi collatz($n where * %% 2) { $n, |collatz Int($n / 2) } multi collatz($n where not * %% 2) { $n, |collatz Int(3*$n + 1) } say $_ => .&collatz for 1 .. 100