use Test; subset ChessPos of Str where /^<[a..h]><[1..8]>$/; my %a is Set = <a c e g>; sub chess(ChessPos $p) { my ($col, $row) = $p.comb; %a{$col}.&{ $row %% 2 ?? .so !! .not } } is "d3".&chess, True; is "g5".&chess, False; is "e6".&chess, True;