Re: [Sbcl-devel] RfC: backquote extension

[Kevin R. <kp...@ma...>]

On Jun 12, 2010, at 23:59, Tobias C Rittweiler wrote:

> I have just been asked in a private reply why not just use
>
> ,@(when (foop) `((something ,x ,y)))
>
> I'm responding to the list because a) I'm having trouble reaching
> my mail server, and b) it's a valid question!
>
> The above won't really work that well in case of
>
> ,?(when (foop) (generate-frobber x y))
>
> Without ,?, you must tie the return value of GENERATE-FROBBER to  
> whether
> you want to use it with ,@ or just , because in
>
> ,@(when (foop) (generate-frobber x y))
>
> it would have to return its expansion wrapped in a list, but in
>
> ,(generate-frobber x y)
>
> it would not.


(defmacro spleen (cond &body body)
  `(if ,cond
       (list (progn ,@body))
       '()))

,@(spleen (foop) (generate-frobber x y))

-- 
Kevin Reid                                  <http://switchb.org/kpreid/>