From: Luke Graham <spoooq@...>
Date: 2005-03-18T10:04:22+09:00
Subject: Re: tree transformation insight required

On Thu, 17 Mar 2005 17:27:17 +0900, Simon Strandgaard <neoneye@gmail.com> wrote:
> On Wed, 9 Mar 2005 19:00:46 +0900, Luke Graham <spoooq@gmail.com> wrote:
> [snip]
> > Can anyone suggest a good way to get the c++-producing code out
> > of recurse and into some sort of template language, or into functions
> > that get passed into simplified recurse? I figured those functions
> > would need to return functions (usually themselves) to simulate
> > some state changes, ala...
> [snip]
> 
> I have had good results with visitor design pattern and interpreter
> design pattern.
> 
> For instance have a look at the bottom most class in this file
> http://rubyforge.org/cgi-bin/viewcvs.cgi/projects/regexp_engine/source/scanner_nodes.rb?rev=1.22&cvsroot=aeditor&content-type=text/vnd.viewcvs-markup

Thats not a million miles from my first cut at an XSLT template. The
lightning bolt
was when I saw templates could take params.. in other words, they were
functions.
Everything fell into place then and I saw XSLT for what it really
is... a completely
average pure-functional programming language designed by committee. Its good
in the sense that its templating via XPath, but missing (IMHO) vital
things like I/O,
built-in higher-order functions and of course terse syntax. My little
language shows how
trivial the core ideas of XSLT really are, and how it is XPath that
does the real
heavy lifting.

My executive decision for the day is to finish the first version using
my big nasty
script, because its good enough to get something out there. Version 2 will have
better intermediate code because the templating style will suit the
problem better,
but I will just use XSLT from now on. Despite the ugly language, its
hard to write

<repeat for some vars>
class <varname> {
 <varname>();
 ~<varname>();

 <repeat for some other vars>
 int <varname>;
 </repeat>
};
</repeat>

better in any other style of programming.

Has anyone heard of an alternate syntax for XSLT? I used %< ... >%  for nesting,
%var% for attributes because they were the common case, and %% ... %% for
instructions like I/O.

Ok, enough non-Ruby talk now :D

-- 
spooq