Calculating sum of calculations is an example of a popular task with a poor XSLT solution. Let's demonstrate it on a quantity times price. A part of a source XML:
Example 19. Items with price and quantity
... <item price="20" qty="2"/> <item price="30" qty="1"/> <item price="40" qty="4"/> ...
The task is to calculate the sum of each (price*qty). XSLT FAQ provides a solution (section "Math", subsection "Quantity times price"), which takes 25 lines and uses recursion. As result, the code is hard to understand.
Compare the XSLT solution and the XSieve solution:
Example 20. XSieve solution for quantity times price
(apply +
(map (lambda (node)
(* (x:eval "number(@qty)" node)
(x:eval "number(@price)" node)))
(x:eval "//item")))
Code is easily read and understood by those who know Scheme. The "map" function takes list of all "item" elements, applies an anonymous lambda-function to each item, and returns the results as list, which in turn is processed by "+".