Quasi-macros ?

Quasi-macros ?

[Joris van der Hoeven]

Hi,

Consider the following piece of code:

  (define (define-table-decls name l)
    (if (null? l) l
        (cons `(hash-set! ,name ',(caar l) ',(cadar l))
  	      (define-table-decls name (cdr l)))))

  (define-macro (define-table name . l)
    `(begin 
       (define ,name (make-hash-table ,(+ (* (length l) 2) 1)))
       ,@(define-table-decls name l)))

  (define-table test
    (hello hoi)
    (joke grapje)
    (gnu blauwbilgorgel))

This allows you to define many tables in a nice way.
Sometimes however, it would be nice to write things like

  (define-table the-question
    (two ,(+ 1 1))
    (four ,(* 2 2)))

Someone has an idea of how to do this *without* explicitly
using 'eval', which might result in loosing the context?

Thanks, Joris


-----------------------------------------------------------
Joris van der Hoeven <vdhoeven@texmacs.org>
http://www.texmacs.org: GNU TeXmacs scientific text editor
http://www.math.u-psud.fr/~vdhoeven: personal homepage
-----------------------------------------------------------



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Re: Quasi-macros ?

[david]

On Sun, Feb 09, 2003 at 08:23:23PM +0100, Joris van der Hoeven wrote:
> 
>   (define (define-table-decls name l)
>     (if (null? l) l
>         (cons `(hash-set! ,name ',(caar l) ',(cadar l))
>   	      (define-table-decls name (cdr l)))))
> 
>   (define-macro (define-table name . l)
>     `(begin 
>        (define ,name (make-hash-table ,(+ (* (length l) 2) 1)))
>        ,@(define-table-decls name l)))
> 
>   (define-table test
>     (hello hoi)
>     (joke grapje)
>     (gnu blauwbilgorgel))
> 
> This allows you to define many tables in a nice way.
> Sometimes however, it would be nice to write things like
> 
>   (define-table the-question
>     (two ,(+ 1 1))
>     (four ,(* 2 2)))
> 
> Someone has an idea of how to do this *without* explicitly
> using 'eval', which might result in loosing the context?

It looks like quasiquote has special behaviour when it comes to
quoting himself... However, with a bit of hacking you can do what you
want.

  (define (define-table-decls h l)
    (define (sub ll) (hash-set! h (car ll) (cadr ll)))
    (for-each sub l))

  (define-macro (define-table name . l)
    `(begin
       (define ,name (make-hash-table ,(+ (* (length l) 2) 1)))
       (define-table-decls ,name ,(list 'quasiquote l))))

  (define-table the-question
    (two ,(+ 1 1))
    (four ,(* 2 2)))

-- 
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