permutations.xqm

permutations.xqm

declare function local:permutations($list as array(*)) as array(array(*))  {
  if (array:size($list) eq 0)
  then
    array {}

  else if (array:size($list) eq 1)
  then
    array { $list }

  else
      array:fold-left($list, array {}, function($a as array(array(*)), $x) {
        array:join(($a, array {
            array:for-each(local:permutations(array:filter($list, function($y){ $x ne $y })), function($p as array(*)) {
              array:insert-before($p, 1, $x)
            })?*
        }))
      }) 
};

local:permutations(["a","b","c"])