OK, thanks, that answers my question, I think. I’ll have to look at how
syntax-rules interacts and where that problem is coming up.

As for syntactic closures, I’m fairly certain that it is possible to write
robust unhygienic macros in it. However, it’s by no means easy, which is why
I’ve been thinking for a long time about how to make a better solution.

I don’t much like syntax-case, or syntax-rules for that matter, because I’d
prefer to use Scheme as the underlying language rather than inventing a new
one. I made an attempt at using combinators but I’m not too happy with how it
turned out.

Thanks,
Chris

On Monday, August 29, 2022 8:42:08 AM PDT Marc Nieper-Wißkirchen wrote:
> Am Mo., 29. Aug. 2022 um 10:25 Uhr schrieb Chris Hanson <xxxxxx@chris-
hanson.org>:
> > I’m still having trouble understanding exactly what you mean about not
> > returning raw symbols in their output. Since there’s no code in the SRFI I
> > can’t read it to figure it out.
>
> The comment about returning raw symbols was about ER (without
> extensions), which doesn't have forms like `close-syntax'.
>
> > If I make the following change to foo, it takes care of the problem:
> >
> > (define-syntax foo
> >
> >   (er-macro-transformer
> >
> >    (lambda (x r c)
> >
> >      (capture-syntactic-environment
> >
> >       (lambda (use-env)
> >
> >         `(,(r 'loop) (exit ,(close-syntax (cadr x) use-env))))))))
> >
> > This captures the environment in which foo is used, then closes the
> > argument in that environment, ensuring that it gets the expected binding
> > of exit. But the raw symbol exit appearing in the output instead gets the
> > exit bound by loop’s expansion.
>
> Yes, this works, of course. But this is outside of what the note
> discusses as ER doesn't have `close-syntax'.
>
> > I’m pretty sure this isn’t what you are suggesting though. But in the
> > context of using syntactic closures it pretty clearly specifies what’s
> > supposed to happen.
>
> The issue I have is that it doesn't play well with syntax-rules. The
> `foo' macro should also work as expected when written with
> syntax-rules (which in turn is implemented with syntactic closures).
>
> In any case, this discussion shows that I should weaken the paragraph
> about syntactic closures added at the last minute to make it clear
> that I haven't yet found a satisfying way to write SC macros that are
> also robust in conjunction with syntax-rules. When we write every
> macro using an unhygienic one with the full power of SC (and not
> syntax-rules or the ER subset), the problem does not seem to occur, so
> I shouldn't say in isolation that I find SC broken.
>
> (There are still some robust unhygienic macros that can be formulated
> in syntax-case but not in syntactic closures, but these may not be too
> interesting.)
>
> Thanks,
>
> Marc
>
> > Thanks,
> > Chris
> >
> > On Sunday, August 21, 2022 11:16:50 PM PDT Marc Nieper-Wißkirchen wrote:
> > > Am Mo., 22. Aug. 2022 um 00:29 Uhr schrieb Chris Hanson <xxxxxx@chris-
> >
> > hanson.org>:
> > > > I’m not familiar with the term "robust unhygienic macros” and an
> > > > internet
> > > > search didn’t reveal any definitions.
> > >
> > > The term was coined by myself for the purpose of SRFI 211.
> > >
> > > > Is there a definition of this term, or better yet, a paper?
> > >
> > > Unfortunately no.
> > >
> > > What I mean by a "robust unhygienic macro" is an unhygienic macro that
> > > even works when the unhygienic macro becomes part of the body of a
> > > second macro expansion.
> > >
> > > Please see "Note 2" under "Explicit-renaming macro" for an example.
> > >
> > > > I’m a little confused because the SRFI claims that explicit-renaming
> > > > macros
> > > > can produce "robust unhygienic macros” yet syntactic-closure macros
> > > > cannot.
> > > > However, explicit-renaming is virtually identical to “reverse”
> > > > syntactic-
> > > > closure macros, which are syntactic-closure macros with the definition
> > > > and
> > > > use environments flipped.
> > >
> > > ER macros implemented with SC (syntactic closures) are indeed not
> > > "robust" (according to my findings). SRFI 211 describes a variation of
> > > ER (implemented with marks & substitutions) that can be used to define
> > > unhygienic macros that are "robust". The variation of ER is not 100%
> > > compatible with how ER is classically implemented.
> > >
> > > You can write down the example in Note 2 for SC as well.
> > >
> > > Does this help?
> > >
> > > Thanks,
> > >
> > > Marc
> > >
> > > PS My time this week is limited, so please excuse the rather brief
> > > reply.