Re: SXML example showing diff between node-reduce and node-join

[Ricardo Wurmus]

Hi Matt,

> I'm going through the (sxml xpath) low-level routines to try to get a
> solid understanding of what they do.  I just can't come up with an example
> to show how node-reduce and node-join differ.   If someone could provide
> such an example I would really appreciate it.  Takers?

Here’s an example:

--8<---------------cut here---------------start------------->8---
(define sxml
  (xml->sxml "\
<foo>
  <bar>baz</bar>
  <wow>great</wow>
  <boo>
    <wow>
      <b>superb</b>
    </wow>
  </boo>
  <bye>
    <hello>
      <world>
        <excellent>
          <wow>today</wow>
        </excellent>
      </world>
   </hello>
  </bye>
  <greet>
    <hello>
      <world>
        <wow>yesterday</wow>
      </world>
    </hello>
  </greet>
</foo>"
             #:trim-whitespace? #true))

(define wow-converter
  (lambda (node-or-nodeset)
    (if (and (string? node-or-nodeset)
             (string=? "yesterday" node-or-nodeset))
        '(new "WOW!")
        node-or-nodeset)))

(define joined
  ((node-join (sxpath '(//))
              (node-trace "visiting")
              wow-converter
              (sxpath '(*text*)))
   sxml))

(define reduced
  ((node-reduce (sxpath '(//))
                (node-trace "visiting")
                wow-converter
                (sxpath '(*text*)))
   sxml))
--8<---------------cut here---------------end--------------->8---

The node-trace converter already shows that they behave differently.
The wow-converter only gets to see the plain string “yesterday” when it
is used with node-join.

Clearly, this is not the best example one could come up with, but I hope
it’s a start.

-- 
Ricardo