Re: How to put this in a macro

[José A . Romero L .]

On 17 Kwi, 08:38, Cecil Westerhof <Ce...@decebal.nl> wrote:
> Barry Margolin <bar...@alum.mit.edu> writes:
> > (defmacro canonicalize-start-end (start-var end-var)
> >   `(if (equal ,start-var ,end-var)
> >        (setq ,start-var (point-min)
> >              ,end-var (point-max))
> >      (setq ,start-var (or ,start-var (point-min))
> >            ,end-var (or ,end-var (point-max))))
>
> This gives an error:
>     Debugger entered--Lisp error: (void-variable start-var)
>       (list (quote equal) start-var end-var)
(...)

Makes  sense.  In general writing things like `(setq ,foo bar) is (if
possible at all) asking for trouble -- what would happen when foo  is
nil, or 5?

Maybe you could do something like this:

    (defmacro cw/set-bounds (start-sym end-sym)
      `(if (equal (symbol-value ,start-sym) (symbol-value ,end-sym))
           (progn
             (set ,start-sym (point-min))
             (set ,end-sym (point-max)))
         (progn
           (set ,start-sym (or start (point-min)))
           (set ,end-sym (or end (point-max))))))

and use it as:

    (cw/set-bounds 'start 'end)

i.e. passing the symbols of the variables you want to set.

Cheers,
--
José A. Romero L.
escherdragon at gmail
"We who cut mere stones must always be envisioning cathedrals."
(Quarry worker's creed)