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Re: Evaluation of macro arguments


From: Pascal J. Bourguignon
Subject: Re: Evaluation of macro arguments
Date: Tue, 05 Jan 2016 20:22:17 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Marcin Borkowski <address@hidden> writes:

> Hi all,
>
> continuing my quest to grok macro argument evaluation issues, I'd like
> (again) to make sure that I get it correctly.  So I have this simple
> macro generating a list of consecutive numbers (which is not without
> problems - I am aware of those, namely (i) it uses hard-coded symbols
> instead of generating them on the fly, and (ii) it has no error
> checking):
>
> (defmacro range (from dir to)
>   `(let ((delta (cond ((eq ',dir 'upto) 1)
>                       ((eq ',dir 'downto) -1)))
>          (i ,from)
>          (list nil))
>      (while (not (= i ,to))
>        (push i list)
>        (setq i (+ i delta)))
>      (nreverse list)))

(let ((i 0))
   (list (range  i 'upto (incf i 10))  ; bam!
         i))

I hope you may debug it well.


-- 
__Pascal Bourguignon__                 http://www.informatimago.com/
“The factory of the future will have only two employees, a man and a
dog. The man will be there to feed the dog. The dog will be there to
keep the man from touching the equipment.” -- Carl Bass CEO Autodesk




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