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Re: <xsl-script>

Subject: Re: <xsl-script>
From: Paul Prescod <paul@xxxxxxxxxxx>
Date: Wed, 12 May 1999 04:03:14 -0500
xsl script perl
David LeBlanc wrote:
> At 04:12 PM 5/11/99 -0500, you wrote:
> >David LeBlanc wrote:
> >>
> >> It seems to me that any extensible language can be made into a convenient
> >> tree manipulation language via an appropriate function library.
> >
> Based on your below example (even though I think you've shifted the focus
> of my issue which is the procedural elements (i.e. <xsl:if> etc.)), I
> *might* strike the word "convenient" from the above.

Great! That would end the argument.

> THIS is not what I object to! <xsl:if>, <xsl:when> etc. is what I 
> object to!

Do you have a proposal for keeping the containing structures of XSL and
the template description syntax of XSL but using the if/then/when
constructs of scripting languages?

<xsl:template match="p">

Is this that you are proposing?

> That's doable, even elegantly if that's important (A quick sketch in
> Smalltalk.):

This is close to how we are doing it in Python. Great minds think alike!

Yours hasn't handled all of the hard problems yet, though. The template
syntax is not correct. You haven't got an equivalent of apply-templates. I
also don't see how your "match" and "attribute" commands know what node
they are working on. Even so, your match syntax is more verbose and it
probably will not permit the extent of optimizations that XSL match
patterns will.

In Python we fixed these problems but by the time the template syntax was
as convenient as XSL's but still Python-integrated it was much more

> Where can XSL-extended Python be found?

Well, it is currently being reworked for compatibility with the latest
draft but:


Here is a flavor of it:

>>>p = PatternObject.CreateXSLPAtternObject('Chapter/Page','MatchExpr') 
>>>def DoSomethingWithChapterPage(node): 
...    print node.getNodeName()
...    e.apply_templates(node)
>>>e = PatternEngine() 
It isn't as optimized and minimized a syntax as the SmallTalk one because
we aren't trying to replace XSL. We're just making XSL idioms available to
Python programmers. (don't let the word "we" trick you into thinking that
I am doing any of the work...I influenced the original design to allow it
to be used this way but the implementors both work for a company called

> Errr.. aren't you making my original point here? If XSLT is going to be so
> marvelous what need is there for a pythonated xsl (or is it an xslated
> python?). 

No, I am not making your point. XSLT is marvelous because it is simple and
powerful. Python-with-an-XSL library is marvelous because it is more
powerful but still simpler than e.g. Java or Perl and cheaper than
Ominmark or Balise. If you take away the XSL part of my toolkit then I
lose that easy-to-use low-end. If I have to train people in a programming
language before they can start making stylesheets then you've increased
the ramp-up time for new hires. That's expensive.

In fact, I would rather let them cut their teeth on XSL and then let them
learn Python by showing them how their XSL idioms translate into Python.
One thing at a time.

> Is Python as a scripting language somehow less objectionable then
> some other well known language such as pearl or (my favorite) Tcl?

Sorry, I have to scratch an itch here: you mean Perl. Anyhow, you
certainly don't want to get me started on my objections to Perl and
(egad!) TCL. Luckily they are independently documented:


 Paul Prescod  - ISOGEN Consulting Engineer speaking for only himself

Diplomatic term: "Emerging Markets"
Translation: Poor countries. The great euphemism of the Asian financial
             meltdown. Investors got much more excited when they thought 
they could invest in up-and-comers than when they heard they could invest 
in the Third World.(Brills Content, Apr. 1999)

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