XQuery3.0: Higher-Order functions (Filtering)

gistfile1.xquery

(:
  Below I show 2 different ways of using the filter function. Both do exactly the same but one uses 
  an inline function expression while the other uses a named function reference
:)


(:  
*********************************************************************
Example of using filter with inline function expression
*********************************************************************
:)
return fn:filter(function($person) { $person/@gender = 'female'}, $persons/person)

(: 
*********************************************************************
Example of using filter with named function reference (predicate)
*********************************************************************
:)
declare function local:isFemale($person as element(person)) as xs:boolean {
    $person/@gender = 'female'
};

let $isFemale := local:isFemale#1

return fn:filter($isFemale, $persons/person)

(:
**********************************************
XQuery output:
**********************************************

<person gender="female">
  <country>Belgium</country>
  <name>Person C</name>
  <age>80</age>
</person>

<person gender="female">
  <country>Netherlands</country>
  <name>Person E</name>
  <age>30</age>
</person>
:)