?? !! is the ternary operator. It works as its counterpart ? : in Perl 5. The characters are doubled to avoid the mixture with infix operators ? and !, which change the context of their operands.
say rand < 0.5 ?? 'Yes' !! 'No';
📘 Ternary operator ?? !! in Raku
N. B. Perl 6 has been renamed to Raku. Click to read more.