Infix "in"

infix.pl

proto infix:<in>(|) is equiv<==> is assoc<non> { * }
multi infix:<in>($a, $b) { so $b ~~ / $a /  }
multi infix:<in>($a, @b) { so $a eqv any @b }
multi infix:<in>($a, %b) {    %b{$a}:exists }

say 2 in 22;
say 2 !in (1, 22, 23);
say 22 in (1, 22, 23);
say "a" in {a => "b"};
say "a" !in {aa => "b"};