You want to perform a function on a sequence. You can one of the following functions: map, fold or filter.
Here is the structure of these three functions.
sequences:map($func as function, $seqA as item()*, $seqB as item()*) as item()*
sequences:fold($func as function, $seq as item()*, $start as item())
sequences:filter($func as function, $seq as item()*) as item()*
Each of them takes an XQuery function as the first argument.
The map function applies the function item $f to every item from the sequence $seq in turn, returning the concatenation of the resulting sequences in order.