Quine (computing)

This is an article about a kind of computer program. For a biography of the logician and philosopher see Willard Van Orman Quine.

In computing, a quine is a program (a form of metaprogram) that produces its complete source code as its only output. For amusement, hackers sometimes attempt to develop the shortest possible quine in any given programming language.

Note that programs which take input are not considered quines. This would allow the source code to be fed to the program via keyboard input, opening the source file of the program, and similar mechanisms. Also, a quine which contains no code is ruled out as trivial; in many programming languages executing such a program will output the code (i.e. nothing). Such an empty program once won the "worst abuse of the rules" prize in the Obfuscated C contest (indeed, an empty program is not legal ISO C since it has no main() function, so many compilers will reject it).

Quines are named after philosopher Willard Van Orman Quine (1908–2000), who made an extensive study of indirect self-reference: he coined, among others, the paradox-producing expression, "yields falsehood when appended to its own quotation."

History

This hackish phenomenon was first described in Bratley, Paul and Jean Millo. "Computer Recreations; Self-Reproducing Automata", Software -- Practice & Experience, Vol. 2 (1972). pp. 397-400.

Paul Bratley first became interested in self-reproducing programs after seeing the first known such program written in Atlas Autocode at Edinburgh in the 1960s by the University of Edinburgh lecturer and researcher Hamish Dewar.

This seminal program has been found and is reproduced here:

%BEGIN
!THIS IS A SELF-REPRODUCING PROGRAM
%ROUTINESPEC R
R
PRINT SYMBOL(39)
R
PRINT SYMBOL(39)
NEWLINE
%CAPTION %END~
%CAPTION %ENDOFPROGRAM~
%ROUTINE R
%PRINTTEXT '
%BEGIN
!THIS IS A SELF-REPRODUCING PROGRAM
%ROUTINESPEC R
R
PRINT SYMBOL(39)
R
PRINT SYMBOL(39)
NEWLINE
%CAPTION %END~
%CAPTION %ENDOFPROGRAM~
%ROUTINE R
%PRINTTEXT '
%END
%ENDOFPROGRAM

Examples

For more examples, see Wikisource:Quines

C

#include<stdio.h>
char*i="\\#include<stdio.h>",n='\n',q='"',*p=
"%s%cchar*i=%c%c%s%c,n='%cn',q='%c',*p=%c%c%s%c,*m=%c%c%s%c%c;%s%c",*m=
"int main(){return!printf(p,i+1,n,q,*i,i,q,*i,q,n,q,p,q,n,q,m,q,n,m,n);}"
;int main(){return!printf(p,i+1,n,q,*i,i,q,*i,q,n,q,p,q,n,q,m,q,n,m,n);}

Haskell

main=putStr$q++show q;q="main=putStr$q++show q;q="

Python

a='a=%r;print a%%a';print a%a

Scheme

   ((lambda (x)
           (list x (list (quote quote) x)))
       (quote
           (lambda (x)
               (list x (list (quote quote) x)))))

Unix shell scripting

#!/bin/cat
any text here

HQ9+

External links

The Quine Page (by Gary P. Thompson)
QuineProgram at the Portland Pattern Repository Wiki
David Madore's Discussion of Quines
JavaScript Quine Contest Entries
Quines.tk (click link at top to skip the ad)

Quine (computing)

History

Examples

See also

Further reading

External links