Working with sequences and the arrow operator I noticed that filter function cannot be used directly after the arrow operator. Tested in exist-db 4.1.0

arrows-and-sequences.xq

xquery version "3.1";

declare function local:plusOne ($a as xs:integer) { $a + 1 };
declare function local:greaterThanFive ($a as xs:integer) { $a > 5 };

declare function local:eachPlusOne ($s as xs:integer*) {
    for-each($s, local:plusOne#1)
};
declare function local:filterGreaterThanFive ($s as xs:integer*) {
    filter($s, local:greaterThanFive#1)
};

let $funcref1 := local:plusOne#1
let $funcref2 := local:greaterThanFive#1

let $funcref3 := local:eachPlusOne#1
let $funcref4 := local:filterGreaterThanFive#1

(: 
 : the following two ways to operate on sequences with the arrow operator do 
 : work but require to wrap the calls to for-each and filter in a function
 :)
return
(0 to 9)
    => local:eachPlusOne#1
    => local:filterGreaterThanFive#1

(: 
    => $funcref3(?)
    => $funcref4(?)
:)
    
(: nicer way of writing would be :)

(: 
    => for-each(?, local:plusOne#1)
    => filter(?, local:greaterThanFive#1)
:)

(: or :)

(: 
    => for-each(?, $funcref1(?))
    => filter(?, $funcref2(?))
:)