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Re: problems with syntax-case and with-syntax
From: |
Chris Vine |
Subject: |
Re: problems with syntax-case and with-syntax |
Date: |
Mon, 28 Aug 2017 12:38:32 +0100 |
On Sun, 27 Aug 2017 20:36:53 -0400
Mark H Weaver <address@hidden> wrote:
> Matt Wette <address@hidden> writes:
>
> > Q1) The code below creates two macros. One called `define-foo'
> > which generates a new identifier and then defines that to #t. The
> > other, `define-foo/p', generates the same identifier (lexical
> > issue?) and another identifier, then "calls" define-foo and then
> > uses both identifiers in a `define'. When executed I get this
> > error:
> >
> > scheme@(guile-user)> (define-foo/p abc)
> > ;;; <stdin>:2:0: warning: possibly unbound variable `wrap-abc'
> > <unnamed port>:2:0: <unnamed port>:2:0: In procedure module-lookup:
> > Unbound variable: wrap-abc
> >
> > What am I doing wrong here?
>
> The problem is that in Guile 2.2, whenever (define <id> ...) is found
> in the expanded code, where <id> was introduced by a macro (i.e. not
> passed as an explicit argument to the macro), Guile will rewrite the
> <id> into a new name based on the hash of the entire definition form.
>
> I don't know of any way to make this work without passing 'wrap-abc'
> explicitly as an argument to the 'define-foo' macro.
>
> FWIW, I've always been opposed to these non-standard semantics, but
> they were included in Guile 2.2 over my strenuous objections:
>
> https://lists.gnu.org/archive/html/guile-devel/2014-01/msg00061.html
> https://lists.gnu.org/archive/html/guile-devel/2011-11/msg00021.html
> https://lists.gnu.org/archive/html/guile-devel/2011-11/msg00042.html
How interesting.
There seems very little uniformity in how the different schemes which I
happen to have available deal with the issue of top level hygiene with
nested macros. Given the example in paragraph 6.10.10 of the guile-2.2
manual, after the definitions of both 'foo' and 'bar' have both been
made the following schemes evaluate '(foo)' as 37:
guile-2.0, chicken;
and the following evaluate it as 42:
guile-2.2, chez, kawa.
Chris