I've made a new version of SRFI 113, Sets.  There are many editorial
changes, and two major substantive ones.  SRFI 14 character sets are
now incorporated into this SRFI.  Implementations that provide both
SRFI 14 and this SRFI are required to use the same disjoint type to
implement both.  Most of the names are the same, but not all, and the
preallocated character sets like char:set-digit are not provided in
this SRFI.  If you want them you can add them with selective import.

In addition, all the sets are now linear-update rather than mutable.
That means that the implementation of mutation operations may be
either pure or impure at the discretion of the implementation, and
all such operations return the new set.  This does not mean that the
implementations are *persistent*; after a mutation operation, the old
set may or may not be unchanged, and you cannot count on its value.
This is already true for SRFI 14 character sets.

Unfortunately, the implementation has not yet been updated.

The SRFI is temporarily at <http://ccil.org/~cowan/temp/srfi-113.html>.
SRFI editors, please migrate it to its proper place.

Everyone: please review.  I plan to recommend that WG2 make this a
optional part of R7RS-large.

--
John Cowan    xxxxxx@ccil.org    http://ccil.org/~cowan
Nobody expects the RESTifarian Inquisition!  Our chief weapon is
surprise ... surprise and tedium  ... tedium and surprise ....
Our two weapons are tedium and surprise ... and ruthless disregard
for unpleasant facts....  Our three weapons are tedium, surprise, and
ruthless disregard ... and an almost fanatical devotion to Roy Fielding....