templates permutations
  when <=1> do [1] !
  otherwise
    def n: $;
    templates expand
      def p: $;
      1..$n -> \(def k: $;
        [$p(1..$k-1)..., $n, $p($k..last)...] !\) !
    end expand
    $n - 1 -> permutations -> expand !
end permutations

def alpha: ['ABCD'...];
[ $alpha::length -> permutations -> '$alpha($)...;' ] -> !OUT::write