def u: ['a', 'b'];
def v: ['A', 'B', 'C'];
def w: [1];

templates transpose2
  @: [];
  $... -> \[i](
    when <?($i <..$@transpose2::length>)> do ..|@transpose2($i): $;
    otherwise ..|@transpose2: [$];\) -> !VOID
  $@ !
end transpose2

[$x, $y, $z] -> transpose2... -> '$...;
' -> !OUT::write

'
' -> !OUT::write

[$u,$v,$w] -> transpose2... -> '$...;
' -> !OUT::write