Editing Quine (computing) (section)

==Ouroboros programs==
The quine concept can be extended to multiple levels of recursion, giving rise to  "[[ouroboros]] programs", or quine-relays. This should not be confused with [[#Multiquines|multiquines]].

===Example===
This Java program outputs the source for a C++ program that outputs the original Java code.
<!--
NOTE TO EDITORS: The following code is very fragile. If you edit it, be very careful not to break it -- verify that the output of the Java program is identical to the C++ program, and that the output of the C++ program is identical to the Java program.
-->
<div style="width: 49%; overflow: auto; float: right; padding-left: 1%;" >
<syntaxhighlight lang="cpp">
#include <iostream>
#include <string>
using namespace std;

int main(int argc, char* argv[])
{
    char q = 34;
    string l[] = {
    "    ",
    "=============<<<<<<<< C++ Code >>>>>>>>=============",
    "#include <iostream>",
    "#include <string>",
    "using namespace std;",
    "",
    "int main(int argc, char* argv[])",
    "{",
    "    char q = 34;",
    "    string l[] = {",
    "    };",
    "    for(int i = 20; i <= 25; i++)",
    "        cout << l[i] << endl;",
    "    for(int i = 0; i <= 34; i++)",
    "        cout << l[0] + q + l[i] + q + ',' << endl;",
    "    for(int i = 26; i <= 34; i++)",
    "        cout << l[i] << endl;",
    "    return 0;",
    "}",
    "=============<<<<<<<< Java Code >>>>>>>>=============",
    "public class Quine",
    "{",
    "  public static void main(String[] args)",
    "  {",
    "    char q = 34;",
    "    String[] l = {",
    "    };",
    "    for(int i = 2; i <= 9; i++)",
    "        System.out.println(l[i]);",
    "    for(int i = 0; i < l.length; i++)",
    "        System.out.println(l[0] + q + l[i] + q + ',');",
    "    for(int i = 10; i <= 18; i++)",
    "        System.out.println(l[i]);",
    "  }",
    "}",
    };
    for(int i = 20; i <= 25; i++)
        cout << l[i] << endl;
    for(int i = 0; i <= 34; i++)
        cout << l[0] + q + l[i] + q + ',' << endl;
    for(int i = 26; i <= 34; i++)
        cout << l[i] << endl;
    return 0;
}</syntaxhighlight>
</div><div style="width: 49%; overflow: auto; float: left; padding-right: 1%;" >
<syntaxhighlight lang="java">public class Quine
{
  public static void main(String[] args)
  {
    char q = 34;
    String[] l = {
    "    ",
    "=============<<<<<<<< C++ Code >>>>>>>>=============",
    "#include <iostream>",
    "#include <string>",
    "using namespace std;",
    "",
    "int main(int argc, char* argv[])",
    "{",
    "    char q = 34;",
    "    string l[] = {",
    "    };",
    "    for(int i = 20; i <= 25; i++)",
    "        cout << l[i] << endl;",
    "    for(int i = 0; i <= 34; i++)",
    "        cout << l[0] + q + l[i] + q + ',' << endl;",
    "    for(int i = 26; i <= 34; i++)",
    "        cout << l[i] << endl;",
    "    return 0;",
    "}",
    "=============<<<<<<<< Java Code >>>>>>>>=============",
    "public class Quine",
    "{",
    "  public static void main(String[] args)",
    "  {",
    "    char q = 34;",
    "    String[] l = {",
    "    };",
    "    for(int i = 2; i <= 9; i++)",
    "        System.out.println(l[i]);",
    "    for(int i = 0; i < l.length; i++)",
    "        System.out.println(l[0] + q + l[i] + q + ',');",
    "    for(int i = 10; i <= 18; i++)",
    "        System.out.println(l[i]);",
    "  }",
    "}",
    };
    for(int i = 2; i <= 9; i++)
        System.out.println(l[i]);
    for(int i = 0; i < l.length; i++)
        System.out.println(l[0] + q + l[i] + q + ',');
    for(int i = 10; i <= 18; i++)
        System.out.println(l[i]);
  }
}</syntaxhighlight></div>

Such programs have been produced with various cycle lengths:

* [[Haskell (programming language)|Haskell]] → [[Python (programming language)|Python]] → [[Ruby (programming language)|Ruby]]<ref>{{cite web
   |url = http://blog.sigfpe.com/2008/02/third-order-quine-in-three-languages.html
   |title = A Third Order Quine in Three Languages
   |author = Dan Piponi
   |date = 5 February 2008
  }}</ref>
* [[Python (programming language)|Python]] → [[Bash (Unix shell)|Bash]] → [[Perl]]<ref>{{cite web
   |url = http://www.stratigery.com/source.html#Ouroboros
   |title = Ask and ye shall receive: Self-replicating program that goes through three generations, Python, Bash, Perl
   |author = Bruce Ediger
   |access-date = 2011-03-17
   |archive-date = 2011-02-23
   |archive-url = https://web.archive.org/web/20110223164033/http://www.stratigery.com/source.html#Ouroboros
   |url-status = dead
   }}</ref>
* [[C (programming language)|C]] → [[Haskell (programming language)|Haskell]] → [[Python (programming language)|Python]] → [[Perl]]<ref>{{cite web
 |url         = http://hpaste.org/43501/multiquine
 |title       = multiquine
 |author      = b.m.
 |date        = 1 February 2011
 |archive-url  = https://archive.today/20130415050710/http://hpaste.org/43501/multiquine
 |archive-date = 2013-04-15
 |url-status     = dead
}}</ref>
* [[Haskell (programming language)|Haskell]] → [[Perl]] → [[Python (programming language)|Python]] → [[Ruby (programming language)|Ruby]] → [[C (programming language)|C]] → [[Java (programming language)|Java]]<ref>{{cite web
   |url = http://blog.sigfpe.com/2011/01/quine-central.html
   |title = Quine Central
   |author = Dan Piponi
   |date = 30 January 2011
  }}</ref>
* [[Ruby (programming language)|Ruby]] → [[Java (programming language)|Java]] → [[C Sharp (programming language)|C#]] → [[Python (programming language)|Python]]<ref>{{cite web
   |url = http://ruslan.ibragimov.by/20-04-2013.quine-ruby-java-c-python
   |title = Quine Ruby -> Java -> C# -> Python
   |author = Ruslan Ibragimov
   |date = 20 April 2013
   |language = ru
   |access-date = 20 April 2013
   |archive-date = 4 March 2016
   |archive-url = https://web.archive.org/web/20160304040341/http://ruslan.ibragimov.by/20-04-2013.quine-ruby-java-c-python
   |url-status = dead
   }}</ref>
* [[C (programming language)|C]] → [[C++]] → [[Ruby (programming language)|Ruby]] → [[Python (programming language)|Python]] → [[PHP]] → [[Perl]]<ref>{{cite web
   |url = http://golf.shinh.org/reveal.rb?Quine/shinh+%28C+C%2B%2B+Ruby+Python+PHP+Perl%29_1194650418&rb
   |title = Quine by shinh (C C++ Ruby Python PHP Perl)
   |author = Shinichiro Hamaji
   |date = 10 November 2007
  }} (this one is also a [[Polyglot (computing)|polyglot]])</ref>
* [[Ruby (programming language)|Ruby]] → [[Python (programming language)|Python]] → [[Perl]] → [[Lua (programming language)|Lua]] → [[OCaml]] → [[Haskell (programming language)|Haskell]] → [[C (programming language)|C]] → [[Java (programming language)|Java]] → [[Brainfuck]] → [[Whitespace (programming language)|Whitespace]] → [[Unlambda]]<ref>{{cite web
   |url = http://asiajin.com/blog/2009/09/22/uroboros-programming-with-11-programming-languages/
   |title = Uroboros Programming With 11 Programming Languages
   |author = Ku-ma-me
   |date = 22 September 2009
   |access-date = 17 March 2011
   |archive-date = 29 August 2011
   |archive-url = https://web.archive.org/web/20110829204605/http://asiajin.com/blog/2009/09/22/uroboros-programming-with-11-programming-languages/
   |url-status = dead
   }}</ref>
* [[Ruby (programming language)|Ruby]] → [[Scala (programming language)|Scala]] → [[Scheme (programming language)|Scheme]] → [[Scilab]] → [[Bash (Unix shell)|Shell (bash)]] → [[S (programming language)|S-Lang]] → [[Smalltalk]] → [[Squirrel (programming language)|Squirrel3]] → [[Standard ML]] → ... → [[Rexx]] (128 (and formerly 50) programming languages)<ref>{{cite web
   |url = https://github.com/mame/quine-relay
   |title = Quine Relay - An uroboros program with 100+ programming languages
   |author = Yusuke Endoh
  |website = [[GitHub]]
 |date = 2 November 2021
 }}</ref>
* Web application → [[C (programming language)|C]] (web application source code consists of [[HTML]], [[JavaScript]], and [[CSS]])<ref>{{cite web
   |url = http://michaelwehar.com/quines/c_prints_javascript.html
   |title = C Prints JavaScript
   |author = Michael Wehar
   |date = 10 November 2019
   |language = en
  }}</ref>