[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: "Backquote constructs" to "splice" values without "eval".
From: |
Barry Margolin |
Subject: |
Re: "Backquote constructs" to "splice" values without "eval". |
Date: |
Mon, 07 Jan 2013 15:51:26 -0500 |
User-agent: |
MT-NewsWatcher/3.5.3b3 (Intel Mac OS X) |
In article <mailman.16874.1357591009.855.help-gnu-emacs@gnu.org>,
Oleksandr Gavenko <gavenkoa@gmail.com> wrote:
> 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"?
Now you can go back to using backquote to construct the list:
(apply #'+ `(,@'(1) 2 ,@'(3 4)))
But you still don't need to use eval.
--
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
Message not available
- Re: "Backquote constructs" to "splice" values without "eval".,
Barry Margolin <=