Re: dynamic scope

[Miroslav Silovic <silovic@zesoi.fer.hr>]

Sascha Ziemann <szi@aibon.ping.de> writes:

> Hi,
> 
> "load" works globally even if it was called in a procedure:
> 
> szi@olivia:~/scheme$ cat dynamic-load.scm
> (define a 1)
> (define (dynamic)
>   (load "dynamic-load-define.scm")
>   a)
> (display (dynamic)) (newline)
> (display a) (newline)
> szi@olivia:~/scheme$ cat dynamic-load-define.scm 
> (define a 2)
> szi@olivia:~/scheme$ guile -s dynamic-load.scm
> 2
> 2
> 
> R4RS does not define that this is necessary. I think it would be better
> to have a local "load". And together with this a local
> "load-from-string" or "load-from-list". This would make configuration
> tasks really easy.
> 
> Example: You have a Scheme tree with HTML tags like this one:
> 
> (define example-mini-html-document
>   '(html
>     (head )
>     (body "moin")))
> 
> With a dynamic load you can write transformation filters without parsing
> the HTML code by simply defining a function for every HTML tag without
> defining the HTML functions in the translator function. This would make
> transformations much faster, because it is not necessary to navigate
> through the tree. 
> 
> Instead of this:
> 
> (define $ string-append)
> (define (translate-to-html sml-document)
>   (letrec ((<> (lambda (name) ($ "<" name ">")))
>            (<>nl (lambda (name) ($ "<" name ">\n")))
>            (</> (lambda (name) ($ "<" name ">")))
>            (</>nl (lambda (name) ($ "<" name ">\n")))
>            (html (lambda (. args) ($ (<>nl "HTML") args (</>nl
> "HTML"))))
>            (head (lambda (. args) ($ (<>nl "HEAD") args (</>nl
> "HEAD"))))
>            (body (lambda (. args) ($ (<>nl "BODY") args (</>nl
> "BODY"))))
>            )
>     (if (sml:html? sml-document)
>         (catch #t
>                (lambda () (eval sml-document))
>                (lambda (key . args)
>                  (display key)
>                  (display args)
>                  (newline)
>                  (backtrace)
>                  'error-during-eval))
>         'no-html)))
> 
> I would like to be able to write something like this:
> 
> (define (translate to-html sml-document)
>   (if (sml:html? sml-document)
>       (catch #t
> 	     (lambda ()
> 	       (load-from-list to-html)    ; <--
> 	       (eval sml-document))

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