Re: How to put this in a macro

[Barry Margolin <barmar@alum.mit.edu>]

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In article 
<bf0039f9-f7eb-497d-bb74-88d3bb9c5077@u34g2000yqu.googlegroups.com>,
 José A. Romero L. <escherdragon@gmail.com> wrote:

> 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?

My macro requires that the parameters be variables, not expressions.

> 
> 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.

If you call it like that, it can be a function, not a macro.

-- 
Barry Margolin, barmar@alum.mit.edu
Arlington, MA
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