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Re: Fixing the slib mess

From: Stefan Israelsson Tampe
Subject: Re: Fixing the slib mess
Date: Mon, 22 Oct 2012 21:33:04 +0200

Yes in that case this stands on it's own!

On Mon, Oct 22, 2012 at 9:11 PM, Mikael Djurfeldt <address@hidden> wrote:
On Mon, Oct 22, 2012 at 8:31 PM, Stefan Israelsson Tampe
<address@hidden> wrote:
>> Comments?  Can I add syntax-toplevel? to psyntax.scm and (system
>> syntax)?
> [...]
> I can answer with some kind of suggestion here.
> in (system syntax) there is syntax-local-binding which you can use for
> example as
> (define-syntax f
>   (lambda (x)
>     (syntax-case x ()
>       ((_ x)
>         (call-with-values (lambda () (syntax-local-binding #'x))
>                                 (lambda (x y) (pk x) (pk y))) #'#t))))
> Then,
> scheme@(guile-user) [1]> (f +)
> ;;; (global)
> ;;; ((+ guile-user))
> And,
> scheme@(guile-user) [1]> (let ((s 1)) (f s))
> ;;; (lexical)
> ;;; (s-490)
> (let ((s 1)) (define-syntax g (lambda (x) #'#f)) (f g))
> ;;; (displaced-lexical)
> ;;; (#f)
> I'm not sure what exactly syntax-toplevel? does, but can you base it on
> syntax-local-binding?
> And if not is it possible to change syntax-local-binding so that you can use
> it?

Thanks, Stefan.

(syntax-toplevel?) expands to #t if occurs in a context (position in
the code if you prefer) where a (define x #f) would create/set! a
global binding for x.  It expands to #f otherwise.

I had a look at syntax-local-binding, but decided that
syntax-toplevel? was needed since the latter is not trying to
determine the nature of an existing binding but rather the nature of
the context.  Of course oncould probe the context by first creating a
new binding (with some random name) and then use syntax-local-binding
to determine the nature of the context by looking at the new binding,
but that seems somewhat invasive. :-)

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