William D Clinger wrote:
>> 1. Denotational semantics, its "least fixpoint" approach,
>> is the best account we have of meaning, in programming
>> languages.
>>
>
> Not too many people would agree with that unqualified
> statement. Denotational and least fixpoint semantics
> may be the best accounts for some purposes, but SFAIK
> (and I used to know quite a bit about this) they don't
> work very well for languages with non-flat domains (e.g.
> higher order functions) and nondeterministic semantics.
>
Part of why the approach is good is that, in its accounts, it does
a good job of pointing out what we know we don't know, and
what we don't know if we can know, and other Rumsfeldian
permutations.
> In other words, they don't work very well for Scheme.
>
In what sense?
> To simplify the technical problem only slightly, it's
> hard to define an adequate ordering relation that
> won't conflate the possible results x and y with all
> possible results that lie between x and y in the
> ordering.
>
Is that a bug or a feature? Perhaps we should think more about
a distinction between "portable interpretations [with reliable,
operational effect]" and a larger class of "reasonable interpretations
[which characterize an implementor's/innovators degrees of freedom
and a programmer's list of cautions and opportunities]"
> You can work around that somewhat by using operational
> denotations, but that approach tends to have all of
> the disadvantages and none of the advantages of using
> an operational approach. That is why the editors
> asked Robby Findler and Jacob Matthews to write an
> operational semantics for R6RS, replacing the
> denotational semantics of previous reports.
>
>
Yes, well, at least I'm not picking on Cowan :-)
> As for the observably sequential functions, they
> form a proper subspace of the continuous function
> domains that are normally used in denotational
> semantics. They exclude things like parallel or,
> which have to do with the failure of the obvious
> denotational semantics for deterministic Lisp-like
> languages to be fully abstract. Robby and Matthias
> have been using observably sequential functions in
> their research, and may have some results or
> speculation that might bear on the problem; you'd
> have to ask them, as I have just told you almost
> all I know about observably sequential functions.
>
At first glance, that comment speaks poorly of the internal process
of the editors. (I do not mean the limits of your knowledge on that
particular topic -- I mean the dominance of some arbitrary ideas
that seems to emerge from the process for dubious reasons.)
(Disclosure: I'm 100% "speculation" in all of the conclusions I'm
suggesting in this thread. I do not mean to be claiming some new
fundamental results -- only to "problematize" some apparently
unquestioned assumptions in the draft that, pragmatically, cause
me to give up on R6RS, on its current course, being a language
I would want to call Scheme.)
-t
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://lists.r6rs.org/pipermail/r6rs-discuss/attachments/20070225/45fb531b/attachment.htm
Received on Sun Feb 25 2007 - 22:58:46 UTC