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Re: "Backquote constructs" to "splice" values without "eval".
From: |
Oleksandr Gavenko |
Subject: |
Re: "Backquote constructs" to "splice" values without "eval". |
Date: |
Mon, 07 Jan 2013 23:47:06 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.2 (gnu/linux) |
On 2013-01-07, Jambunathan K wrote:
>> 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.
Your trick work because + is associative operation.
I just start from example from 'apply' doc-string.
Consider example when 'some' func return region and 'another' require beg/end
pair:
(defun some () ... (list beg end))
(defun another (x beg end y) ...)
I think that this code ugly:
(another x (car (some)) (cdr (some)) y)
If 'some' is complicated you need:
(let* ( (region some) (beg (car region)) (end (cdr region)) )
(another x beg end y)
)
--
Best regards!
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