One day, several years ago, I came across an
article in an old Byte on "self-reproducing
programs". I was a curious lad, and looked to see what the article
was about. It said, "Listing 1 is a C program which duplicates itself.
When the program is run it produces (on the standard output) a file containing
an exact copy of its own source code". I was hooked immediately--these
guys must be
geniuses! I copied the article at once, and tried
to figure it out, but I didn't know C at the time. Soon after, I
found another article, this one in Creative
Computing. It had listings in BASIC, and I was ecstatic.
I soon realized that anyone could write self-reproducing programs, and
made a few in BASIC, Pascal, and Forth.
Later that year I finally got a PC, and quickly
forgot about the programs I had written on my old TI-994/A. Then,
last year, as I was skimming through the Jargon file, I saw an entry I
had not noticed before:
:quine: /kwi:n/ /n./ [from the name of the logician Willard van Orman Quine, via Douglas Hofstadter] A program that generates a copy of its own source text as its complete output. Devising the shortest possible quine in some given programming language is a common hackish amusement. Here is one classic quine:
((lambda (x) (list x (list (quote quote) x))) (quote (lambda (x) (list x (list (quote quote) x)))))This one works in LISP or Scheme. It's relatively easy to write quines in other languages such as Postscript which readily handle programs as data; much harder (and thus more challenging!) in languages like C which do not. Here is a classic C quine for ASCII machines:
char*f="char*f=%c%s%c;main()
{printf(f,34,f,34,10);}%c";
main(){printf(f,34,f,34,10);}
For excruciatingly exact quinishness, remove the interior line breaks.
Some infamous
Obfuscated C Contest
entries have been quines that reproduced in exotic ways.
"Wow. A 'common hackish amusement'. I've
seen the Beer List, and the Hello World page, there must be a Quine Page.
I'll have to look around, that should be pretty neat to see what must be
hundreds of quines."
I was half right. There were hundreds of quines,
just no quine page. Admittedly, there were a few attempts, but none
had more than ten or so. I had found over fifty by the time I came
across any of these pages.
ABC
Ada
Algol
APL
Assembly
Awk
BASIC
BeFunge
BlooP
BrainF***
C
C++
Objective CAML
dBASE
Emacs Lisp
False
Forth
Fortran
Haskell
HP 48 RPL
Icon
Inform
Intercal
Interpol
J
Java
More Java
Javascript
LISP
Logo
Lpc
Lua
Miranda
ML
Modula-2
MUMPS
Oberon
Pascal
Perl
More Perl
Postscript
POV-Ray
Prolog
Python
Rexx
Scheme
SGML
Smalltalk
Snack
SNOBOL 4
Tcl
TeX
TSE
Unix Shell
Vi
Multiple Languages(polyglots)
Iterating Quines
Quine Generating Programs
Kimian Self Reproduction
Bratley, Paul and Jean Millo. "Computer Recreations; Self-Reproducing Automata", Software -- Practice & Experience, Vol. 2 (1972). pp. 397-400.
Burger, John, David Brill, and Filip Machi. "Self-Reproducing programs", Byte. August 1980. pp. 74-75.
Hay, Louise. "Self-Reproducing Programs", Creative Computing. July, 1980. pp. 134-136.
Hofstadter, Douglas R. Godel, Escher, and Bach: an Eternal Golden Braid. Basic Books, Inc. New York, New York. pp. 498-504 (et al.).
Wetherell, Charles. Etudes for Programmers. Prentice-Hall, Inc.,
Englewood Cliffs, New Jersey. 1978. pp. 34-35.