On Jun 11, 2004, at 1:06 PM, Jacques B. Siboni wrote:
>
> Hi all,
>
> Could someone give me a suggestion to avoid evaluation in parameters
> in a
> defun?
>
>
> (defun foo (bbb)
> ...
> )
>
> (foo bar)
> with this defun and this call bar is evaluated
>
> to avoid evaluation i need to call with (foo 'bar)
>
> What modification to the (defun foo ...) do I have to make to have
> bar not
> evaluated in
> (foo bar) ?
>
>
The parameters are evaluated before the function is called. There is
nothing
you can do in foo to avoid evaluation of bar.
The solution is to make foo a macro instead. Something like this:
* (defun %foo (bar)
(format t "bar is \"~s\"~%" bar))
%FOO
* (defmacro foo (bar)
`(%foo (quote ,bar)))
FOO
* (foo (format t "hello~%"))
bar is "(FORMAT T "hello~%")"
NIL
*
Macros are covered very well in Paul Graham's On Lisp,
http://www.paulgraham.com/onlisp.html
and they're a fairly advanced topic in Lisp programming.
Regards,
Craig Ludington
--
Craig Ludington __o
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