Jon Wilson <[EMAIL PROTECTED]> writes:
> (define-macro (dyn-set! var val)
> `(begin (if (not (defined? (quote ,var)))
> (primitive-eval `(define ,(quote ,var) #f)))
> (set! ,var ,val)))
>
> (defined? 'undefined-symbol) ; => #f
> ;(set! undefined-symbol #t) Gives an error.
> (dyn-set! undefined-symbol #t) ; No error.
> (defined? 'undefined-symbol) ; => #t
I think this mostly does what you want, but
- isn't ,(quote xxx) equivalent to just xxx?
- as you kind of said, it will go wrong if ,var is defined locally:
defined? will be #f for a local variable, so a top-level variable
with the same name will be created, but the set! will then set the
local variable.
Regards,
Neil
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