SFA Lossage

[JONL at MIT-MC (Jon L White)]

    Date: 26 Jan 1981 1529-PST
    From: Lisp files <LSP at SU-AI>
    Subject: SFA Loss 
    Jonl, the following makes the reader lose. In particular, when it tries to
    put together OXYZY it gets two nulls in a row. 
    The problem centers around the (ascii (car sfa-buffer)) in that changing 
    that to () or to (ascii 101) does not cause the lossage, which happens at 
    MC as well.
    .  .  . | P O OXYZY OXYZT OXYZT |  .  .  .
Indeed, there are a number of "screws" that we have been finding out as
the SFA feature gets more usage -- this one is due to the fact that the
ASCII function will ocasionally clobber a word of the PNBUF (a 10 word
vector which is READ's buffer for words of a forming pname).  As it
happens, READLIST also has this side effect, so I put in a little code
to preserve-and-restore the portion of the PNBUF which is clobbered.
Your conjecture that some "register" was getting clobbered by the
sfa function was correct -- it's just that the "register" was this
writeable vector of words.  Do a SRCCOM on the latest version of
MC:L;READER >  to see how I fixed it.