RE: [emacs-lisp newbie] print-something() -> clipboard?

[Drew Adams]

> > (defun foo (&optional arg)
> >  "..."
> >  (interactive "P")
> >  (let ((bn ...))
> >    (if arg
> >      (insert bn)
> >      (kill-new bn))))
> 
> Thanks! I probably should `let`,

Yes, you should.

> but this works:
> 
> (defun print-buffer-name (&optional arg)
>   "..."
>   (interactive "P")
>   (setq bn ...)
>   (if arg
>     (kill-new bn)
>     (insert bn)))

`bn' is a free variable here - by default a global, dynamically scoped variable.

If you or some code that you use defines another variable named `bn' then your
code will suffer from variable capture: You could end up changing the other
variable.

There is NO reason to use `setq' here, and NO reason not to use `let'.

When you suffer from variable capture you don't necessarily realize it, and
debugging the problem (with perhaps farflung symptoms) can be a headache.  A
self-imposed headache in this case, for no benefit.