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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. (We ignore some variants of BASIC
in which a program consisting of a single empty string literal
reproduces itself trivially.) 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. Here is another elegant quine in ANSI C:
#define q(k)main(){return!puts(#k"\nq("#k")");}
q(#define q(k)main(){return!puts(#k"\nq("#k")");})
Some infamous Obfuscated C Contest entries have been quines that reproduced in exotic ways. There is an amusing Quine Home Page.
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