The following code generates the error "Stack Overflow: try tail recursion?" 

The code reads in bibliographic data using OAI-PMH and updates a database for each chunk of data. With OAI-PMH, only part of the data is available for each request, so the server returns a resumption token if there are more data available. 

The xquery function making the queries is implemented recursively preceded by a database update request (see the last two lines) for each call. Is it db:add() that causes the stack overflow? The recursion cannot be placed further towards the end!

declare %updating function local:getResumption($token) {

     if (empty($token)) then 

        ()

     else

        let $http-request := http:send-request($http-option, $URL || $token)

        let $result := 

            if ($http-request instance of node()) then

             $http-request

           else

             <http-err>{$http-request}</http-err>

        

        let $resume := $result//oai:resumptionToken/text()

        return  (

            db:add($database,element chunk {$result//oai:metadata}, $path) , 

            local:getResumption($resume)

        )

 };

Best,

Lars