[R6RS] another glimpse into the abyss

Michael Sperber sperber at informatik.uni-tuebingen.de
Tue Mar 13 13:07:34 EDT 2007

William D Clinger <will at ccs.neu.edu> writes:

> Multiplying the amount of portable code I maintain by
> an estimated number of programmers who are maintaining
> portable subsystems as large or larger than Larceny's,
> I get a result that says backwards compatibility should
> be taken seriously.

That measure may or may not be correct.  The Scheme 48 byte-code
compiler/linker is also written (except for binary I/O) in
R5RS-compatible code, and probably amounts to around 10000 lines.
Yet, I consider this quite unusual.  (But, as I said, I recognize it's
just my own take.)

> What we have done so far is to *encourage* systems to
> hide their extensions "below the radar", by defining
> a brand-new concept of Scheme programs in which such
> extensions are forbidden, while allowing arbitrary
> extensions to be used in the kinds of Scheme programs
> that people have actually been writing and using for
> decades.

I disagree with that assessment.

> Mostly it entails an effort to design a language in
> which programmers will want to write applications,
> which should have started with an effort to identify
> the actual problems real-world application programmers
> face when trying to write their programs in R5RS Scheme.

I think we did that, if not particularly systematically or
exhaustively: At the Boston meeting, for example, the requirements we
formulated were based on the actual problems we perceived.

> The standard libraries of the draft R6RS won't even
> let you get a listing of the files within a directory,
> let alone register a Scheme procedure to be called in
> response to some asynchronous event.  Most applications
> will have to use external libraries.  That will require
> use of non-standard and non-portable features, so it is
> unrealistic to think that a conformant implementation
> could support "most applications" unless, of course,
> you adopt a rather arbitrary definition of that phrase.

Indeed, and I should have stated this more clearly.  What I meant is
an implementation that implements everything in R6RS as it's
specified, and where extensions are exlusively available through other

> A poll of potential implementors' intentions might
> shed some light, or at least heat, on this important
> subject.

I agree.

Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla

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