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Lossages in CMUA MACLISP

We are using an internal LISP editor here until such time as we can get an
EMACS/LEDIT system running.  In such a system it is inconvenient to have
displace do its thing, since it puts out the expanded form into the edited
source.  I can think of other situations in which DISPLACE wants to be 
inhibited as well.  How about having DISPLACE be a no-op unless the variable
displace is NON-NIL.  Most of the old hand-written displace functions had this

A number of errors punt the user out of LISP and back to the TOPS-10 system.
Two examples are typing alt-P to the PDL-OVERFLOW error handler, which
causes an IRREPARABLE-PDL-OVERFLOW (I know it's stupid, but it's easy to do
by accident) and setting T or NIL, which causes an attempt to write into
read-only memory error, and exits to the system with no intervening break.
When this happens, it should be easy to get back to the top-level of the
existing LISP.  It turns out that START does this, but REE or CONTIN flame
out destructively.  Is this easy to correct?  It is particularly tragic to
flame out a LISP when editing internally, since fuction definitions
representing a lot of work may be lost.

Aside from such minor lossages, we are winning.  The active MACLISP
community now stands at four members, Dave McDonald has adapted the
UCI-Lisp editor for MACLISP, and Dave Touretzky has created an init
file and some IO functions which move around nicely through the 
cretinous CMU directory structure.

Scott Fahlman