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.
>
>
>
>