Re: t and nil in pure memory?

[Sam Steingold]

> * Chong Yidong <address@hidden> [2009-11-20 00:47:18 -0500]:
>
> FWIW, in CLISP and CMUCL (unintern nil) and (unintern t) are no-ops
> returning nil.  Presumably the other CL implementations do likewise.

This is not true about CLISP (and presumably other CL implementations).

[1]> (unintern cl:t)
NIL

This is indeed a noop because the default package is CL-USER and T lived
in CL.

[2]> (unintern cl:t :cl)

** - Continuable Error
UNINTERN(T): #<PACKAGE COMMON-LISP> is locked
If you continue (by typing 'continue'): Ignore the lock and proceed
The following restarts are also available:
ABORT          :R1      Abort main loop
Break 1 [3]> continue
#:T
USER[4]> (find-symbol "T" "CL")
NIL ;
NIL

i.e., it IS possible to remove the T symbol (with all the trouble this
entails).

As a CLISP maintainer, I don't think T & NIL are special enough.
We lock entire packages.
Please see <http://clisp.cons.org/impnotes/pack-lock.html>.

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