Path: utzoo!attcan!uunet!husc6!bloom-beacon!IBM.COM!ALBERGA
From: ALBERGA@IBM.COM (Cyril Alberga)
Newsgroups: comp.lang.scheme
Subject: Self replicating code
Message-ID: <101088.090653.alberga@ibm.com>
Date: 10 Oct 88 13:06:52 GMT
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 29

Here is a brute-force expression which prints itself.  This was in LISP370,
circa 1978.

 (PRINT
   ( (LAMBDA (X Y)
       (SEQ
         (RPLACA (CDAR (CDDADR X)) (COPY Y))
         (RPLACA (CDADR (CADADR X)) (COPY Y))
         (EXIT X) ) )
     (COPY
       "(PRINT
         ( (LAMBDA (X Y)
             (SEQ
               (RPLACA (CDAR (CDDADR X)) (COPY Y))
               (RPLACA (CDADR (CADADR X)) (COPY Y))
               (EXIT X) ) ) (COPY "NIL) "NIL ) ) )
     "(PRINT
       ( (LAMBDA (X Y)
           (SEQ
             (RPLACA (CDAR (CDDADR X)) (COPY Y))
             (RPLACA (CDADR (CADADR X)) (COPY Y))
             (EXIT X) ) ) (COPY "NIL) "NIL ) ) ) )


The uses of copy were to keep it from modifying itself.
Obviously, shared sub-structure could be used to shorten the
representation.

Cyril N. Alberga