fully generalized recursion with Y-combinator in xquery 3.0 ... recursion via 'deferred execution'

gistfile1.xquery

xquery version "3.0";
 
let $makeFactorialFunc := function($givenFactFunc) {
let $fact := function($n) {
if( $n lt 2 )
then 1
else $n * $givenFactFunc($n - 1)
}
return $fact
}
 
let $y := function($le) {
   function($f) { 
		 $f($f) 
	}( function($f) {
		  $le(
			function($x) {  ($f($f))($x) }
		)
	})
}
 
let $factorial := $y($makeFactorialFunc)
return $factorial(5)