per jnthn++ https://irclog.perlgeek.de/perl6-dev/2017-01-04#i_13854591
Turns out this is not a bug, but a consequence of arrays itemizing their contents. You can still use the array, but you need to ».list on it it to de-itemize the contents; same with `zip`: <ZoffixW> m: my @l = (0,1,2),(3,4,5),(6,7); say zip @l».list.Slip; <camelia> rakudo-moar 40d7de: OUTPUT«((0 3 6) (1 4 7))» <ZoffixW> m: my @l = (0,1,2),(3,4,5),(6,7); say roundrobin @l».list.Slip; <camelia> rakudo-moar 40d7de: OUTPUT«((0 3 6) (1 4 7) (2 5))»