permutations-dimitre.xq

let $permArray := function($myAr as array(*))   
{  
  let $extend := function($ar as array(*), $mem as item()*) 
   {
     array{     
             for $i in 1 to (array:size($ar) +1)
               return                     
                  array:insert-before($ar, $i, $mem)
           }   
   } 
   return
     array:fold-left($myAr, [[]], 
                      function($zero as array(*), $mem as item()*)
                      {
                         array:join(for $i in 1 to array:size($zero)
                                      return $extend($zero($i), $mem) )
                       }
                     )  
}
return $permArray([<a/>, 2, 3])