[Scheme-reports] R7RS-small draft ratified by Steering Committee

[John Cowan]

The final draft of R7RS-small has been ratified by a unanimous vote of
the Scheme Language Steering Committee. A formal announcement will be
made by the SLSC at the Scheme 2013 workshop.

The final draft, post-final errata, and the TeX source of the draft
are available at:

<http://trac.sacrideo.us/wg/raw-attachment/wiki/WikiStart/r7rs.pdf>
<http://trac.sacrideo.us/wg/wiki/R7RSSmallErrata>
<http://trac.sacrideo.us/wg/raw-attachment/wiki/WikiStart/r7rs-small-spec.zip>

Comments and discussion are encouraged on the scheme-***@scheme-reports.org
mailing list, as always.

[ceving]

Post by John Cowan
The final draft of R7RS-small has been ratified by a unanimous vote of
the Scheme Language Steering Committee.
<http://trac.sacrideo.us/wg/raw-attachment/wiki/WikiStart/r7rs.pdf>

The new standard seems to ban Guile's 1+ operator. It must be quoted in
R7RS |1+|.

[John Cowan]

Post by ceving
The new standard seems to ban Guile's 1+ operator. It must be quoted in
R7RS |1+|.

True. Then again, it wasn't valid R5RS either, or R4RS or even R3RS;
R2RS was the only Scheme standard to explicitly allow it, almost thirty
years ago.

The theory of R7RS identifiers is that they can't have a prefix which
is a valid number. In practice, many Schemes simply attempt to parse
an alphanumeric sequence as a number, and if that fails, accept it as
an identifier.

[Sanel Zukan]

Hi,

Is this means that we are no longer allowed to write and support
someting like:

(define (1+x x) (+ 1 x))

?

Best,
Sanel

Post by John Cowan

Post by ceving
The new standard seems to ban Guile's 1+ operator. It must be
quoted in R7RS |1+|.

True. Then again, it wasn't valid R5RS either, or R4RS or even R3RS;
R2RS was the only Scheme standard to explicitly allow it, almost
thirty years ago.
The theory of R7RS identifiers is that they can't have a prefix which
is a valid number. In practice, many Schemes simply attempt to parse
an alphanumeric sequence as a number, and if that fails, accept it as
an identifier.

[John Cowan]

Post by Sanel Zukan
Is this means that we are no longer allowed to write and support
(define (1+x x) (+ 1 x))
?

If you are an implementer, you certainly can provide such a procedure.

If you are a user, and you care about standards conformance,
you should choose a different identifier, as 1+x has never been a
standards-conformant identifier under *any* version of the Scheme
standard. However, most Scheme implementations will accept 1+x as a
valid identifier.

[Alex Shinn]

Post by John Cowan

Post by Sanel Zukan
Is this means that we are no longer allowed to write and support
(define (1+x x) (+ 1 x))
?

If you are an implementer, you certainly can provide such a procedure.
If you are a user, and you care about standards conformance,
you should choose a different identifier, as 1+x has never been a
standards-conformant identifier under *any* version of the Scheme
standard. However, most Scheme implementations will accept 1+x as a
valid identifier.

There are actually many implementations for which this
is an error. Notably R6RS requires it to be an error.

Schemes typically use the name `add1' for this.

[John Cowan]

There are actually many implementations for which this is an error.
Notably R6RS requires it to be an error.

Not too many outside R6RS, actually: only RScheme, SXM, SigScheme, UMB,
Dfsch, Foment, Chibi.

Schemes typically use the name `add1' for this.

This is only available (at least at the REPL) in Racket, Chicken, SISC,
Sizzle, Vicare, IronScheme, RScheme, SXM.

See <http://trac.sacrideo.us/wg/wiki/PlusOneEx> for details.

[Alex Shinn]

Post by John Cowan

There are actually many implementations for which this is an error.
Notably R6RS requires it to be an error.

Not too many outside R6RS, actually: only RScheme, SXM, SigScheme, UMB,
Dfsch, Foment, Chibi.

Schemes typically use the name `add1' for this.

This is only available (at least at the REPL) in Racket, Chicken, SISC,
Sizzle, Vicare, IronScheme, RScheme, SXM.

That's still a lot more than provide 1+ out of the box (do any
other than Guile?).

See <http://trac.sacrideo.us/wg/wiki/PlusOneEx> for details.
You tested the wrong thing - the original question was about
1+, then 1+x was brought up, not +1x.

[John Cowan]

That's still a lot more than provide 1+ out of the box (do any other
than Guile?).

Provide `1+` but not `add1`: MIT, Guile, SCM, XLisp, Rep, Elk, FemtoLisp,
Inlab.

Provide `add1` but not `1+`: Racket, Chicken, SISC, Vicare, IronScheme,
RScheme, SXM.

Provide both: Chez, Sizzle.

So as far as counting Schemes go, it's a wash; but since almost the
beginning of this process I have adopted the rule "witnesses should be
weighed, not counted."

Post by John Cowan
See <http://trac.sacrideo.us/wg/wiki/PlusOneEx> for details.

You tested the wrong thing - the original question was about
1+, then 1+x was brought up, not +1x.

I actually tested the right thing, but reported it wrongly. (Post in
haste, repent at leisure.) In any case, the tests for 1+ are now merged
in and some errors corrected. We are stuck with the wrong page name,
though.

[John Boyle]

I'm guessing you're looking at section "2.1. Identifiers", specifically
this quote:

"An identifier is any sequence of letters, digits, and “extended identifier
characters” provided that it does not have a prefix which is a valid
number."

Since "1+" has the prefix "1", which is a valid number, I would agree that
R7RS does not require implementations to parse "1+" as an identifier, and
if you wrote a program using an un-escaped 1+, you could not be sure it
would run on all implementations. However, I think it is *permitted* for
implementations to recognize additional tokens as identifiers. R7RS does
not say that 1+ is a number, or anything else, and I don't think it
requires the reader to raise an exception, so if Guile accepts it as an
identifier, that doesn't seem to disqualify Guile as a conforming
implementation.

--John Boyle
*Science is what we understand well enough to explain to a computer. Art is
everything else we do.* --Knuth

Post by ceving

Post by John Cowan
The final draft of R7RS-small has been ratified by a unanimous vote of
the Scheme Language Steering Committee.
<http://trac.sacrideo.us/wg/raw-attachment/wiki/WikiStart/r7rs.pdf>

The new standard seems to ban Guile's 1+ operator. It must be quoted in
R7RS |1+|.
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[Peter Bex]

Post by ceving

Post by John Cowan
The final draft of R7RS-small has been ratified by a unanimous vote of
the Scheme Language Steering Committee.
<http://trac.sacrideo.us/wg/raw-attachment/wiki/WikiStart/r7rs.pdf>

The new standard seems to ban Guile's 1+ operator. It must be quoted in
R7RS |1+|.

Could you please refrain from CCing this many mailinglists? This thread
exploded into my mailbox: I got three copies of your mail, plus each
reply in this thread!

I don't think this is very relevant to chicken-users, and not very much
for chicken-hackers either. Same goes for the chibi-scheme list.

Cheers,
Peter