(rx (|))

[Peter Wang <tjaden@users.sourceforge.net>]

Hello,

I've found that (rx (|)) doesn't work (I wanted to use it to easily
kill off certain "branches" of a regexp while maintaining submatches).
I traced it as far as compile-regexp in re-high.scm, which was calling
regexp->posix-string (which returns [#f #f #f #f]), then calling
(new-cre #f #f).

Here's a log of the error:

  Welcome to scsh 0.6.4 (Olin Shivers)
  Type ,? for help.
  > (rx (|))

  Error: exception
         (vector-length #f)
  1> re-empty
  '#{re-char-set}
  1> (regexp-search re-empty "test")

  Error: exception
         (vector-length #f)
  2> 


BTW, minor corrections for the manual:
- make-re-seq, re-seq, make-re-choice, re-choice aren't [any longer?]
  n-ary procedures.
- regexp->posix-string returns 4 values, not 1.