NetNews Usenet Archive 1993 #1/NN_1993_1.iso/spool/comp/lang/lisp/3181

Text File | 1993-01-06 | 2.0 KB | 50 lines

Newsgroups: comp.lang.lisp
Path: sparky!uunet!zaphod.mps.ohio-state.edu!uwm.edu!linac!uchinews!uchinews.uchicago.edu!converse
From: [e-mail] (timoshenko)
Subject: Re: macro question
In-Reply-To: [e-mail]'s message of 7 Jan 93 04:05:52 GMT
Message-ID: <[e-mail]>
Sender: [e-mail] (News System)
Organization: University of Chicago Computer Science
References: <[e-mail]>
Date: Wed, 6 Jan 1993 04:52:05 GMT
Lines: 37

In article <[e-mail]> [e-mail] (Kardan Kaveh) writes:

>I would like to define a macro which in turn defines several functions.
>For example:

>(defmacro a (x y)
>  `(defun ,x () (+ 2 2))
>  `(defun ,y () (* 2 3)))

>As it stands, the macro only defines the second function, since that is the
>returned value.  How can I get both functions defined?

I suppose you could do something like

(defmacro a (x y)
   `(progn (defun ,x () (+ 2 2))
           (defun ,y () (* 2 3))))

This is a macro that expands to an expression that, when evaluated,
will cause both of the defun forms to be evaluated.  You're right
that the last form in the defmacro is returned as the expansion, and
so the first defun in your version above has no effect.

Why do you want to do this, though?  It's likely to be confusing,
both because it's unusual (though legal) to have defun forms that
aren't top-level, and because this will cause functions to be defined
without a corresponding explicit defun form in the code.  I suspect
that there is some better way to do whatever you're trying to do;
in particular, if you are defining functions that are used only once,
it would be better to use a lambda-expression than to automatically
define a named function before calling it.

    --Tim Converse

--
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Tim Converse  U. of Chicago CS Dept.  [e-mail]  [phone]