Thanks Michael,
so I was effectively building a stack in my first transform but it was a
stack of individual filenames as individual text parameters. Perhaps if I
build a stack as a node-set I might be able to crack this one!
I read a little on Turin completeness on Wikipedia would share the following
phrase: "Thus, a machine that can act as a universal Turing machine can, in
principle, perform any calculation that any other computer is capable of.
Note, however, that this says nothing about the effort required to write a
program for the machine."
Ain't that the truth! ;-)
Richard
-----Original Message-----
From: Michael Kay [mailto:mike(_at_)saxonica(_dot_)com]
Sent: 18 February 2008 13:36
To: xsl-list(_at_)lists(_dot_)mulberrytech(_dot_)com
Subject: RE: [xsl] Complex recursion in XSLT 1.0
Could you elucidate a little on the concept of a 'stack'. I can only
dream of such a thing. What mechanism would you use?
and... does that not sound like we need to have a list of all entries
first - is that another infinite loop?
OK. You're processing A, and it contains
<topic ref="X"/>
<topic ref="Y"/>
then when you make the call to process X, you pass it a $stack containing
<topic ref="Y"/>.
In X you find
<topic ref="P"/>
<topic ref="Q"/>
so you make a recursive call to process P, passing it a $stack containing
the previous $stack plus <topic ref="Q"/>
When you've finished processing P, you select the last thing on the stack
(which is Q), you process that, passing a stack from which Q has been
removed. Then when you finish processing Q, you select the last thing on the
stack (which is Y) and process that, passing a stack which is now empty.
When you finish processing Y you are done.
All these Catch 22's are piling up and I'm starting to think that this
is fundamentally impossible in XSLT 1.0 because we are not party to
essential information about what went before.
It's absolutely not fundamentally impossible because XSLT is
Turing-complete. I agree it might be a bit mind-bending when you're not used
to this style of coding.
One reason I published the knight's tour stylesheet in my XSLT Programmer's
Reference was to convince people that problems like this could be solved.
Michael Kay
http://www.saxonica.com/
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