XQuery3.0: Higher-Order functions (Filtering)

	(:
	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>
	:)

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