[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [r6rs] probably bad syntax expansion
From: |
Andy Wingo |
Subject: |
Re: [r6rs] probably bad syntax expansion |
Date: |
Mon, 21 Jun 2010 21:24:10 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.0.92 (gnu/linux) |
Hello,
On Mon 21 Jun 2010 09:59, Marco Maggi <address@hidden> writes:
> (define A <function-using-macro-B>)
> (define-syntax B <>)
> (A)
I have abbreviated your illuminating example. I don't really know what
to think of it, except to say that for top-level programs Guile
implements "REPL semantics".
It would seem that both for toplevel programs and for libraries --
because Guile expands the `library' form to toplevel definitions -- that
these REPL semantics do diverge from lexically-nested semantics.
It's the difference between:
(let ()
(define even?
(lambda (x)
(or (= x 0) (odd? (- x 1)))))
(define-syntax odd?
(syntax-rules ()
((odd? x) (not (even? x)))))
(even? 10))
=> #t
and
(begin
(define even?
(lambda (x)
(or (= x 0) (odd? (- x 1)))))
(define-syntax odd?
(syntax-rules ()
((odd? x) (not (even? x)))))
(even? 10))
ERROR: In procedure vm-debug-engine:
ERROR: Wrong type to apply: #<syntax-transformer odd?>
It is unfortunate for users that expect R6RS semantics for toplevel and
library definitions. I would be happy to accept a well-reasoned patch to
letrec-compile the first forms from a file that prove to be definitions,
though we cannot remove support for mixed definitions and expressions at
the toplevel. However, I don't have the motivation to work on this in
the foreseeable future.
Thank you for the report, though, and I will document the
incompatibility.
Andy
--
http://wingolog.org/