XPath 3.0 recursion with inline function and partial function application, adapted from http://www.xfront.com/Pearls-of-XSLT-and-XPath-3-0-Design.pdf and http://dnovatchev.wordpress.com/2012/10/15/recursion-with-anonymous-inline-functions-in-xpath-3-0-2/

gistfile1.xquery

let
  $isNegative := function($x as xs:integer) {$x lt 0},
  $decrement := function($x as xs:integer) {$x - 1},
  $until.r := 
    function(
      $p as function(item()*) as xs:boolean,
      $f as function(item()*) as item()*,
      $x as item()*,
      $r as function(function(), function(), item()*, function()) as item()*) as item()* {
        if ($p($x)) then $x else $helper($p, $f, $f($x), $r)
      },
  $until :=
    $helper(?,?,?,$until.r)
return $until($isNegative, $decrement, 20)