sharp plus question

[David C. Plummer <DCP@QUABBIN.SCRC.Symbolics.COM>]

    Date: Fri, 19 Dec 86 11:59 EST
    From: Don Morrison <dfm@JASPER.Palladian.COM>

    What should the second form in the following read as?

	    (push :mumble *features*)
	    '(#-mumble #+mumble 1 2 3)

    I would expect '(2 3).  Both implementations I've tried read '(3), which
    is completely unintuitive to me.  Such a thing can easily come up in real
    life (e.g. commenting out with #+(or) something that's already under
    #+mumble).

					      Don Morrison
					      Palladian Software, Inc.

This is curious.  In the Symbolics 7.0 implementation,
	'(#+non-existent-feature #-non-existent-feature 1 2 3)
	'(#-non-existent-feature #+non-existent-feature 1 2 3)
	'(#+LISPM #-LISPM 1 2 3)
each read as '(2 3) but
	'(#-LISPM #+LISPM 1 2 3)
does read as '(3).  This does seem wrong on the following grounds:
	#-LISPM goes into the mode "read me a form, and ignore it."  It
	recursively invokes the reader.
	    The reader gets #+LISPM.  #+LISPM goes into the mode "read
	    me a form and don't ignore it."  This recursively invokes
	    the reader. 
		The reader reads 1.
            #+LISPM does not ignore the 1, so it returns it as the thing
	    read.
	#-LISPM is given 1 as the result of the read, and ignores it.
	2 and 3 are still in the input stream, so I don't know how both
	of them manage to get ignored.


    [I'm not sure what the current state of our mailer is, but I think mail
    addressed to DFM%JASPER@LIVE-OAK.LCS.MIT.EDU will eventually get to me.]