A Quine Program with a Twist

March 26th, 2010

From Wikipedia:

In computing, a quine is a computer program which produces a copy of its own source code as its only output.

Quines like that are known to exist in every Turing-complete language. Examples can be found in the Wikipedia article linked above and elsewhere on the net.

Then there are the programmers who are not satisfied with just regular exceptionality.

About six months ago, ku-ma-me, a japanese blogger, published this Ruby code:

# ruby
l=92.chr;eval s="s=s.dump[r=1..-2].gsub(/("+l*4+"){4,}(?!\\")/){|t|'\\"+l*%d+\\"'%(t
.size/2)};5.times{s=s.dump[r]};puts\\"# python\\\\nprint(\\\\\\"# perl\\\\\\\\nprint(\\\\\\\\\\\\
\\"# lua"+l*4+"nprint("+l*7+"\\"(* ocaml *)"+l*8+"nprint_endline"+l*15+"\\"-- haskel
l"+l*16+"nimport Data.List;import Data.Bits;import Data.Char;main=putStrLn("+l*31
+"\\"/* C */"+l*32+"n#include<stdio.h>"+l*32+"nint main(void){char*s[501]={"+l*31+
"\\"++intercalate"+l*31+"\\","+l*31+"\\"(c(tail(init(show("+l*31+"\\"/* Java */"+l*32
+"npublic class QuineRelay{public static void main(String[]a){String[]s={"+l*31+"
\\"++intercalate"+l*31+"\\","+l*31+"\\"(c("+l*31+"\\"brainfuck"+l*64+"n++++++++[>++++
<-]+++++++++>>++++++++++"+l*31+"\\"++(concat(snd(mapAccumL h 2("+l*31+"\\"110"+l*31
+"\\"++g(length s)++"+l*31+"\\"22111211100111112021111102011112120012"+l*31+"\\"++co
ncatMap("+l*32+"c->let d=ord c in if d<11then"+l*31+"\\"21002"+l*31+"\\"else"+l*31+
"\\"111"+l*31+"\\"++g d++"+l*31+"\\"22102"+l*31+"\\")s++"+l*31+"\\"2100211101012021122
2211211101000120211021120221102111000110120211202"+l*31+"\\"))))))++"+l*31+"\\","+l
*63+"\\""+l*64+"n"+l*63+"\\"};int i=0;for(;i<94;i++)System.out.print(s[i]);}}"+l*31
+"\\")))))++"+l*31+"\\",0};int i=0;for(;s[i];i++)printf("+l*63+"\\"%s"+l*63+"\\",s[i]
);puts("+l*63+"\\""+l*63+"\\");return 0;}"+l*31+"\\");c s=map("+l*32+"s->"+l*31+"\\""
+l*63+"\\""+l*31+"\\"++s++"+l*31+"\\""+l*63+"\\""+l*31+"\\")(unfoldr t s);t[]=Nothing;
t s=Just(splitAt(if length s>w&&s!!w=='"+l*31+"\\"'then 501else w)s);w=500;f 0=Not
hing;f x=Just((if x`mod`2>0then '0'else '1'),x`div`2);g x= reverse (unfoldr f x);
h p c=let d=ord c-48in(d,replicate(abs(p-d))(if d<p then '<'else '>')++"+l*31+"\\"
."+l*31+"\\");s="+l*31+"\\"# ruby"+l*32+"n"+l*31+"\\"++"+l*31+"\\"l=92.chr;eval s=\\"+
(z=l*31)+\\"\\\\\\"\\"+s+z+\\"\\\\\\""+l*31+"\\"++"+l*31+"\\""+l*32+"n"+l*31+"\\""+l*15+"\\""+
l*7+"\\")"+l*4+"n\\\\\\\\\\\\\\")\\\\\\")\\"########### (c) Yusuke Endoh, 2009 ###########\\n"

(Apparently it has to be saved without line breaks.)

So what will happen if you run that code? The shell output very much speaks for itself:

$ ruby QuineRelay.rb > QuineRelay.py
$ python QuineRelay.py > QuineRelay.pl
$ perl QuineRelay.pl > QuineRelay.lua
$ lua QuineRelay.lua > QuineRelay.ml
$ ocaml QuineRelay.ml > QuineRelay.hs
$ runghc QuineRelay.hs > QuineRelay.c
$ gcc -Wall -o QuineRelay QuineRelay.c && ./QuineRelay > QuineRelay.java
$ javac QuineRelay.java && java QuineRelay > QuineRelay.bf
$ beef QuineRelay.bf > QuineRelay.ws
$ wspace QuineRelay.ws > QuineRelay.unl
$ unlambda QuineRelay.unl > QuineRelay2.rb
$ diff QuineRelay.rb QuineRelay2.rb
$

The original article clarifies the employed versions of the involved compilers and interpreters.

According to the author of this piece of code, creating it was “easier than it looks,” he says he finished it in under three hours. The result is truly fascinating regardless.