On Sun, Apr 24, 2011 at 05:15:12PM +0200, Andy Wingo wrote:
> On Sun 24 Apr 2011 16:57, Peter Bex <Peter.Bex@xs4all.nl> writes:
>
> > Chicken doesn't support identifier syntax, so it would show an error :)
>
> Heh, cool.  Fortunately it's not central to my argument.  How about an
> accessor macro:
>
>       (begin
>         (define-syntax define-getter
>           (syntax-rules ()
>             ((_ var init)
>              (begin
>                (define val init)
>                (define-syntax var
>                  (syntax-rules ()
>                    ((_) val)))))))
>
>         (define-getter x 10)
>         (define-getter y 20))
>
> If I put that in a chicken module, import the module, then evaluate (x)
> and (y), does that evaluate to 10 and 20, respectively?

Yeah.  Each macro carries its syntactic information with it, like a
closure.  So "val" in the macro expansion would refer to the x that is
defined in that module.  The (x) macro simply expands to  a#x
which accesses the correct x.  (it does this through one extra layer of
gensym-indirection to prevent a bug with quote, but that's irrelevant to
the core idea)

Cheers,
Peter
--
http://sjamaan.ath.cx
--
"The process of preparing programs for a digital computer
 is especially attractive, not only because it can be economically
 and scientifically rewarding, but also because it can be an aesthetic
 experience much like composing poetry or music."
							-- Donald Knuth

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