David A. Wheeler scripsit:

> >   In particular, the abbreviations #', #`, #, and #,@
> >   are widely used by the syntax-case macro system.
>
> A fair point.  I didn't include them as requirements because
> R7RS drafts (currently draft 9) don't include them, but
> some sort of discussion does seem appropriate.

They ought to be included.  Not only does R6RS require them, but many
non-R6RS Schemes also provide syntax-case, often in the form of the
portable syntax expander.  However, Gauche, Chicken, STklos, and RScheme
provide SRFI-10, which conflicts with the syntax-case meaning of #,.
None of my other Schemes have any conflicts: they either implement
syntax-case or treat #, as an error.

> Perhaps something like "An implementation MAY support
> additional abbreviations, such as ..." and then listing those four.

Plausible.

--
De plichten van een docent zijn divers,         John Cowan
die van het gehoor ook.                         xxxxxx@ccil.org
      --Edsger Dijkstra                         http://www.ccil.org/~cowan