Deep comparison of maps in XQuery

getDistinctMaps.xq

(: @see https://stackoverflow.com/questions/62844910/how-to-deep-compare-maps-to-filter-distinct-items-in-xquery :)
declare function local:getDistinctMaps($maps as map(*)*) as map(*)* {
  fold-left(
    $maps,
    (),
    function($distinct-maps, $new-map) {
      if (some $map in $distinct-maps satisfies deep-equal($map, $new-map))
      then $distinct-maps else ($distinct-maps, $new-map)
    }
  )
};

let $map1 := map{
  'a' : '1',
  'b' : '2'
}
let $map2 := map{
  'c' : '3',
  'd' : '4'
}
let $map3 := map{
  'a' : '1',
  'b' : '2'
}
return local:getDistinctMaps( ($map1, $map2, $map3) )