last() in spawned functions

Question

Why would the fn:last() function not work while spawning?

This failed:

xquery version "1.0-ml";
let $items := (1, 2, 3)
return xdmp:spawn-function(function () {
   $items[3 to fn:last()] 
}) 

After some time I cancel the job because it does nothing.

Output: Cancelling fails with message indication function must be stopped manually.

This works just fine:

xquery version "1.0-ml";
let $items := (1, 2, 3)[3 to fn:last()] 
return xdmp:spawn-function(function () {
   $items
}) 

Output: Query completed successfully

Answer 1

The example for the docs of fn:last() is showing a very similar usage of this function. The downside for using functions in predicates is though that they are evaluated for each item in the sequence. Using fn:subsequence and optionally fn:count should both be more efficient, and by-pass your issue:

let $items := (1, 2, 3)
return xdmp:spawn-function(function () {
   xdmp:log(subsequence($items, 3, count($items))) (: you can omit 3rd param with same effect :)
})

HTH!