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Re: Evaluation of macro arguments


From: Marcin Borkowski
Subject: Re: Evaluation of macro arguments
Date: Tue, 05 Jan 2016 20:39:28 +0100
User-agent: mu4e 0.9.13; emacs 25.1.50.1


On 2016-01-05, at 20:22, Pascal J. Bourguignon <address@hidden> wrote:

> 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.

That's unfair, Pascal; I wrote that I'm aware of this, I know how to
make it work, and wasn't asking about it.

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University



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