sub my-grep(@list, &block) { gather { for @list.batch: &block.count -> @part { my Bool() @resps = block |@part; for @resps.kv -> $i, $b { take @part[$i] if $b } } } } say (^6).&my-grep: -> $a { $a %% 2 } say (^6).&my-grep: -> $a, $b { $a %% 2, $b >= 3 } say (^7).&my-grep: -> $a, $b? { !$b.defined, $b.defined } say (^12).&my-grep: -> $a, $b { $b %% 3 } say <a b c d>.kv.&my-grep: -> $i, $l { $i %% 2 } say <a b c d>.kv.&my-grep: -> $i, $l { False, $i %% 2 }