Vincent Manis scripsit:
> I really hope we don't go down this path; if implementation A implements
> features x, y, and z, while implementation B implements features u,
> v, and w, you end up with essentially no portability. Cobol did that,
> with its subsets, and the results weren't very good: vendors ended up
> implementing a common core of subsets, and the ones that only a few
> (or no) implementations provided merely ended up vanishing from the
> language.
That's perhaps not such a bad thing: it allows less useful parts to be
omitted in later revisions. We have already seen this happening on a
small scale in the evolution from R2RS to R4RS. Provided the rule laid
down by the standard is "our way or not at all", I can live with a fair
amount of optionality. That is, implementation X can conformantly omit
dynamic-wind, or even cons, but it *cannot* bind those names to different
procedures. Or as Aaron put it on #scheme, "Any feature, if provided,
must be provided in at least the way that the standard specifies."
Indeed, the WG1 charter actually suggests this:
Features of the [small Scheme] language should be marked as
optional if their implementation is likely to be burdensome
for some target uses (for example, floating point arithmetic,
file I/O, "load", "eval", and read/eval/print loops may not make
sense for small or embedded systems).
> But if an implementation claims to implement R7RS Super-Dooper Scheme,
> that should be a full implementation, not merely the set of features
> the implementer felt like providing.
In practice it will be anyhow.
--
John Cowan [email protected] http://ccil.org/~cowan
And now here I was, in a country where a right to say how the country should
be governed was restricted to six persons in each thousand of its population.
For the nine hundred and ninety-four to express dissatisfaction with the
regnant system and propose to change it, would have made the whole six
shudder as one man, it would have been so disloyal, so dishonorable, such
putrid black treason. --Mark Twain's Connecticut Yankee
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