Recursive function to evaluate whether a phrase is a palindrome

palindrome.xqy

xquery version "3.0";

(: Recursive function to evaluate whether a phrase is a palindrome :)

declare function local:test-palindrome($palindrome as xs:string?) as xs:boolean {
    switch (fn:string-length($palindrome))
        case 0 return fn:true()
        case 1 return fn:true()
        default return
            let $first := fn:substring($palindrome, 1, 1)
            let $last := fn:substring($palindrome, fn:string-length($palindrome), 1)
            let $rest := fn:replace($palindrome, "^.", "")
            let $rest := fn:replace($rest, ".$", "") 
            return 
                if ($first = $last) then local:test-palindrome($rest)
                else fn:false()
};

let $palindrome := "شکر بترازوی وزارت برکش"
let $palindrome := fn:lower-case($palindrome)
let $palindrome := fn:replace($palindrome, " ", "")
return local:test-palindrome($palindrome)