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Re: "Backquote constructs" to "splice" values without "eval".
From: |
Jambunathan K |
Subject: |
Re: "Backquote constructs" to "splice" values without "eval". |
Date: |
Tue, 08 Jan 2013 02:40:29 +0530 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) |
Oleksandr Gavenko <gavenkoa@gmail.com> writes:
> On 2013-01-07, Barry Margolin wrote:
>
>>> I construct TLV (table-len-val) structs in string.
>>>
>>> Is it possible to omit "eval" from second line by using some sugar code:
>>>
>>> (setq binstr-len 4)
>>> (setq binstr (eval `(unibyte-string ?s binstr-len ,@(make-list binstr-len
>>> ?x))))
>>> (assert (eq (+ 2 binstr-len) (length binstr)))
>>>
>>> Another solution:
>>>
>>> (setq binstr (concat (unibyte-string ?s binstr-len) (make-list binstr-len
>>> ?x)))
>>>
>>> Or "apply" stands for this purpose(??):
>>>
>>> (setq binstr (apply 'unibyte-string ?s binstr-len (make-list binstr-len
>>> ?x)))
>>
>> The "apply" solution is usually the correct way to do it.
>
> I also start thinking about "apply" with several list inside it:
>
> (apply '+ 1 '(2) '(3 4))
>
> But above expression fail (only last arg expanded as list of args). To resolve
> this issue I use expression:
>
> (apply '+ 1 (append '(2) '(3 4)))
>
> But how about expression with atoms between (??):
>
> '(1) 2 '(3 4)
>
> I write non-linear code:
>
> (apply '+ (append '(1) (cons 2 '(3 4))))
>
> How to avoid call to "cons"?
(apply '+ (loop for x in '(1 (2) (3 4))
collect (if (numberp x) x (apply '+ x))))
There are also other predicates that you can use. For eg., atom, consp,
listp.
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