Re: [ssax-sxml] SXPath: high-level API modernization

[Kirill L. <lis...@ac...>]

Hello!

On Tue, 29 Jul 2003, David Allouche wrote:

> I am not sure this contribution is going to be relevant, but I had a
> similar issue in my work. That is handling dynamic environment in
> performant and referentially-transparent way.

Thank you very mach for very interesting message!

  I consider utilization of your "with-environment" in STX engine
for parameterization of template functions, but it looks like most peoples
consider explicit parameter passing as more clear for SXPath.
 It's a bit simpler and more concise also, so I think that's the way
to go for high-level API of SXPath, which has to be as friendly for XML people as
possible. Thus I think that your "environment" has to be passed explicitly to every
location function.

I really like your idea of convenience macro for access to environment
variable. As we are moving to R5RS macros now, I think that we'll employ
something like:
(define-syntax env-ref
  (syntax-rules  ()
		 ((env-ref env key)
		  (cond
		    ((assq (quote key) env)
		     => cdr)
		    (else (cerr "Unbound key " key " in environment:" env))))))

> It is "safer" performance-wise to use hash-tables (actually texmacs
> adaptative hash-tables) for variable look-up, but it may be
> preferrable in some context to use alists, or trees, to provide true
> referential transparence (thread safety).

In context of SXML we mostly have just a few vars in environment.
I think that for the sake of simplicity and portability we can use assq
here.

On 29 Jul 2003, Joerg F. Wittenberger wrote:

> Experience shows that you usually need not even a dozen XSLT variables
> and reference them a few times.  The penealty of a assoc seems
> bearable.
I do agree with Joerg, and my own experience shows that this holds for most
(any?) XPath/SXPath applications...

> (define (environment-ref* env key)
>   (let ((h (ahash-get-handle env key)))
>     (if h (cdr h)
> 	;; WARNING: guile-1.3.4 requires %S instead of ~S
> 	(texmacs-error "Unbound key in environment:" key))))
>
BTW: neither %S nor ~S here...

BTW#2: Please drop a look at sxml-tools.scm
I believe that you can reuse something in TexMacs convert/tools/sxml.scm ...

Thank you a lot for your feedback and ideas!

Best regards,
         Kirill.