Re: [Jscheme-user] Re: modules?

[Timothy H. <tim...@ma...>]

On Friday, March 7, 2003, at 11:35 AM, Timothy Hickey wrote:
> We could easily write a little macro which implements this style
> of export:
>
>>   (export (future future? ...)
>>     (define (future x) ...)
>>     (define (future? x) ...)
>>     ...
>>   )
>>
>

;; Here is a version of the macro that implements "export"
;; I create the "bigsym" symbol to strictly include all other symbols
;; and hence be different from them, kind of a gensym....

(define (export Symbols . Body)
   ; this bigsymbol is guaranteed to be different from all individual 
symbols
   (define bigsym (string->symbol (apply string-append (cons "R_" (map 
.toString Symbols)))))
   (define (make-defines N S)
      (if (null? S) ()
          (cons `(set! ,(first S) (list-ref ,bigsym ,N))
                 (make-defines (+ N 1) (rest S)))))
   `((lambda (,bigsym)
        ,@(make-defines 0 Symbols))
     (let () ,@Body ,(cons 'list Symbols))
    ))

e.g.

(export '(R S) (set! R 1) (set! S 2))

  -->

(  (lambda (R_RS)
          (set! R (list-ref R_RS 0))
          (set! S (list-ref R_RS 1)))

     (let () 1 2 (list R S))
)

Oh... but this will still have problems if list-ref is one of the symbols
being exported.... This is why hygeniec macros are nice....

---Tim---



>
> Similarly, we could wriite a macro to import just a few values from a 
> file
>> (import "elf/future.scm" (future future?  ...))
>
> which could expand to
>>  (import "elf/future.scm" "HIDDEN:")
>>  (define future HIDDEN:future)
>>  (define future? HIDDEN:future?)
>>  ...
>
> Other variations could be implemented as well (import-all-but ....) etc.
>
> ---Tim---
>
>
>
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