Re: my latest blog post

[Mark H Weaver <mhw@netris.org>]

Hi Catonano,

Thank you for your email.  I don't have time to make a proper response
yet, but for now I will respond to just one point:

Catonano <catonano@gmail.com> writes:
> On my side, I was a bit adversary because I feel that a macro stepper
> is a fundamental feature of a scheme system and in Guile it's less
> than an afterthought

As far as I know, Racket is the only Scheme implementation with a macro
stepper for hygienic macros.  Do you know of any others?

So, I strongly disagree that a macro stepper is a "fundamental feature
of a scheme system".  In fact, Scheme first appeared in 1975, and first
gained hygienic macros in 1986, but it was not until ~2007 that a macro
stepper for Scheme appeared, for Racket (called PLT Scheme at the time).
The paper, <https://www2.ccs.neu.edu/racket/pubs/gpce07-cf.pdf>,
described it as "the first macro stepper for Scheme".

> I understand that implementing it is too much work

It's not that it's too much work; it just hasn't yet been done.

> But I think that the manual should at least mention macro stepping as
> a missing feature,

If it were part of a Scheme standard, or even a very commonly
implemented extension, then I would agree that we should document its
absence.  However, as far as I know, Racket is the only Scheme
implementation that has a macro stepper.  So, this is not a feature that
users generally expect to have in a Scheme implementation.

I disagree that the Guile manual should specifically call attention to a
missing feature that almost no other Scheme implementation includes.

Whenever people switch from one Scheme implementation to another, they
will notice many missing features and APIs, and some new ones.  In your
case, you noticed that Guile lacks Racket's macro stepper, but there are
a great many other things in Racket which Guile lacks.

If we were to start documenting all of the features that exist in at
least one Scheme implementation as missing features, that's quite a
slippery slope.  I don't want to go down that slope.

If this were a common confusion among our users, then there would be
some justification for this, but it's not a common confusion.  In the
decade since the first Scheme macro stepper was invented, you are the
_only_ person who has reported confusion from the absence of this
feature in Guile.

That's not to say that you're unreasonable; it's simply due to your
particular experience of being acquainted with this feature of Racket
and perhaps being surprised that Guile didn't have it.  This same thing
could happen with _any_ feature of _any_ Scheme implementation.

Does that make sense?

     Regards,
       Mark