[plt-scheme] to define, or to let

From: Eli Barzilay (eli at barzilay.org)
Date: Sat Mar 20 23:49:53 EST 2004

On Mar 20, Bradd W. Szonye wrote:
> Eli Barzilay wrote:
> > I don't know (and certainly don't care) about C/C++ standards,
> > their gurus, and their quiet or noisy changes.
> What's up with the parochial tone?

I'm just tired of this.  I obviously didn't say anything you didn't
know about, you didn't say anything I didn't know about (except fot
that C/C++ stuff, which I *really* don't care about).  My opinion is
not surprising given the fact that there was a time where I had to
choose an implementation, and I went with PLT.  Your opinion is also
quite known by now.  This is now at the beginning of an opinion
festival -- lots of texts, almost zero content.  Do you want to do

> Quiet changes are a major risk factor for language implementors and
> users. While you may reasonably not care about C/C++ stuff, and you
> may not have heard about "quiet changes" before, it's quite foolish
> to ignore wisdom from another community just because it's another
> community.

My community uses a standard that leaves important things open for
implementations.  It is a standard that forces implementations to do
such things, and indeed implementations do them and they usually do a
very good job documenting such changes.

> > Having said that, I don't see any quitness problem -- open up the
> > MzScheme manual, and all places that have some extensions are
> > clearly specified.
> Just because it's documented doesn't mean that it isn't quiet.
> Indeed, quiet changes normally *are* documented. A feature is
> "quiet" when you can't tell whether it exists at compile time.  If
> you don't notice it in the docs, you won't know about the problem
> until it breaks at runtime.

Strictly speaking, the following:

  (defun foo (x) x)

is valid at Scheme's compile time.

> > It's easy -- search the help-desk for `foo', and if it is found in
> > the R5RS and in the MzScheme manual, then this is probably an
> > instance of standard behavior in R5RS and an extension discussed
> > in MzScheme.  `letrec' will get you to where the extensions are
> > defined.
> That's missing the point. How will a user even know to look for the
> extension?

Because it is a user of *Scheme*.

> > Is there anything "less quiet" that is needed? Is there any
> > implementation that doesn't change things in a well-advertised
> > way?
> First, I wouldn't call the letrec extension "well-advertised." The
> compiler doesn't report it at all,

What should the compiler do?  Spit a warning?  That'll be as good as
forbidding it, which is the whole point of an *extension*.

> and the docs don't make any special note of it.

It's under "local binding".  It is the only place where `letrec' is
indexed.  What more do you want?

> > Is there any implementation that does *exactly* R5RS, nothing
> > more, nothing less? And the most important question: Is there any
> > point in continuing this thread?
> Definitely not, if you're only going to contribute this kind of
> rant.  You obviously did not understand what "quiet change" means,
> yet you went on for a screenful spewing bile at the idea, apparently
> just because it came from the C/C++ community.

You have things completely confused.  The reason I don't like this
discussion is that it will lead nowhere.  When I wrote my reply I
didn't care for the C/C++ community, and it might be surprising, but I
still don't care about them -- yet this has nothing to do with the
fact that this thread is leading nowhere.  You are talking in a forum
that is dedicated to an implementation that has some intentional
design decisions like the specified evaluation order and like this
behavior of letrec.  By speaking in this forum against these
intentional features you should expect similar reaction as posting a
"Scheme is stupid, use Python" on c.l.l.

Now, please don't refer to my posts as "bile", and to me typing as
"spewing", unless you really want this discussion to deteriorate at
such a high speed.

          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                  http://www.barzilay.org/                 Maze is Life!

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