[Ecls-list] Common-Lisp question

[Juan Jose Garcia Ripoll]

On Wed, 2006-05-03 at 11:14 +0200, Julian Stecklina wrote:
> "Goffioul Michael" <goffioul at imec.be> writes:
> > I have a common-lisp question, maybe someone here has an answer.
> > I'm trying to implement a macro character ($), but I'd like different
> > expansion when the associated form is at the beginning of a cons or not.
> > So, ($f1 a b) would get me one expansion, and (func $f1 a) would get me
> > a different expansion. Is it possible to detect such cases in the 
> > macro reader function?
> 
> With ANSI CL this is not possible. Of course you could enclose
> occurences of $ within [ ] or something, much like ` and , work.

Why not? Just redefine the reader for () as well as the reader for $. A
special variable can be used to transmit the information to $, or
otherwise you can make $ expand into something like (#:%symbol-marker
value) and make the reader for lists replace these occurences with the
right value.

Juanjo
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