On Wed, Sep 19, 2012 at 10:22 AM, John Cowan <xxxxxx@mercury.ccil.org> wrote:
>> For Scheme as of R6RS, [x ...] means (x ...), so that's what SRFI-105
>> (which is specific to Scheme) says.
>
> R6RS imposes this requirement, but R7RS does not.  See
> http://trac.sacrideo.us/wg/wiki/BracketsBraces for details of which
> Schemes do what with brackets.  You can't just say "Brackets mean what
> they mean in Scheme", because there is and will be no unified meaning.
>
> Since you're providing a full implementation modulo the change to
> the readtable, you need to make some decision for the purposes of that
> implementation, and it's not clear to me what it should be.  The advantage
> of Kawa's $bracket-list$ convention is that it can be mapped to treating
> [] like (), but it can be mapped to something else too, at the will of
> the user.
>

Hmm, how about "unprefixed square brackets mean whatever they mean
normally in the Scheme implementation; if the Scheme implementation
does not have any particular intended meaning, it should use the R6RS
meaning."?

I don't really see "we need a unified meaning for unprefixed [ ]" to be an
important requirement; basically, the intent is that unprefixed [ ] means
the same as [ ] outside of n-expr syntax.

After all, it seems that currently portable Scheme code can't depend on
any particular interpretation for [ ] anyway, so it's not really being worse
off - and I dunno, maybe it'll help adoption a bit?

I'll let David consider this first, in any case the above is what is intended
for unprefixed [ ] in the general syntax of n-expressions.

Sincerely,
AmkG