[gambit-list] macro tricks
Marc Feeley
feeley at iro.umontreal.ca
Thu Aug 13 08:56:54 EDT 2009
On 13-Aug-09, at 7:22 AM, lowly coder wrote:
> it looks like the stuff in lib/_eval.scm , especially with ##eval and
> the ##*cte* stuff seems like it might work; but I can't quite get it;
> anyone have experience?
>
> On Thu, Aug 13, 2009 at 4:09 AM, lowly
> coder<lowlycoder at huoyanjinjing.com> wrote:
>> (define-macro (foo)
>> (define x 20)
>> (define (magic-func var-name)
>> ...)
>>
>> (pp (magic-func 'x)))
>>
>> (foo)
>>
>>
>> Is there anyway I can define magic-func so that 20 is outputted?
>
With the code attached below, do:
(define (magic-func var-name)
(env-ref (the-env) var-name))
Marc
(include "~~lib/_gambit#.scm")
(define (the-env) ;; get the environment at the call site
(##continuation-capture
(lambda (cont)
(if (##interp-continuation? cont)
(let (($code (##interp-continuation-code cont))
(rte (##interp-continuation-rte cont)))
(cons (macro-code-cte $code) rte))
(error "the-env must be called from interpreted code")))))
(define (env-ref env var) ;; fetch variable from an environment
(let loop1 ((c (car env))
(r (cdr env)))
(cond ((##cte-top? c)
(##global-var-ref (##make-global-var var)))
((##cte-frame? c)
(let loop2 ((vars (##cte-frame-vars c))
(i 1))
(if (pair? vars)
(if (eq? var (##car vars))
(vector-ref r i)
(loop2 (cdr vars)
(+ i 1)))
(loop1 (##cte-parent-cte c)
(macro-rte-up r)))))
(else
(loop1 (##cte-parent-cte c)
r)))))
(define (env-set! env var val) ;; modify variable in an environment
(let loop1 ((c (car env))
(r (cdr env)))
(cond ((##cte-top? c)
(##global-var-set! (##make-global-var var) val))
((##cte-frame? c)
(let loop2 ((vars (##cte-frame-vars c))
(i 1))
(if (pair? vars)
(if (eq? var (##car vars))
(vector-set! r i val)
(loop2 (cdr vars)
(+ i 1)))
(loop1 (##cte-parent-cte c)
(macro-rte-up r)))))
(else
(loop1 (##cte-parent-cte c)
r)))))
;; test:
(define (f var)
(let ((x 11))
(define (g y) (* y y))
(pp (env-ref (the-env) 'g))
(pp (env-ref (the-env) var))
(env-set! (the-env) var 22)
(pp (env-ref (the-env) var))
(pp (g x))))
(f 'x)
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