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Re: How do I remove "reference to free variable" warnings on buffer-loca


From: Pascal J. Bourguignon
Subject: Re: How do I remove "reference to free variable" warnings on buffer-local variables?
Date: Mon, 09 Nov 2009 18:40:42 +0100
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/22.3 (darwin)

rocky <address@hidden> writes:

> I have code that uses buffer local variables. I don't want to declare
> this variable global. So how can I remove messages of the form
> "reference to free variable `...' " when I byte compile a file?

A free variable is a variable that is used inside a function that is
not defined locally.  It must be considered a global variable.

As indicated in the other answers, if no such global variable is
declared, then you get this warning.

The point is that most often, you don't want a global variable
(otherwise you would have used defvar to define it), but you want a
local variable, and you used setq or setf instead of let.

Use let (or let*) to define local variables.  Instead of writing:

(defun equa2 (a b c)
   (setq delta (- (* b b) (* 4 a c)))
   (cond ((< delta 0)   '())
         ((= delta 0)   (list (/ (- b) 2 a)))
         (t             (list (/ (+ (- b) (sqrt delta)) 2 a)
                              (/ (- (- b) (sqrt delta)) 2 a)))))

write:

(defun equa2 (a b c)
   (let ((delta (- (* b b) (* 4 a c))))
       (cond ((< delta 0)   '())
             ((= delta 0)   (list (/ (- b) 2 a)))
             (t             (list (/ (+ (- b) (sqrt delta)) 2 a)
                                  (/ (- (- b) (sqrt delta)) 2 a))))))


In general, try to avoid setq or setf, and rather use the functional
programming style.


-- 
__Pascal Bourguignon__


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