Python and Ruby, 39 characters

This Python snippet

s='puts %%q{s=%r;print s%%s}';print s%s

generates this Ruby snippet

puts %q{s='puts %%q{s=%r;print s%%s}';print s%s}

which then generates the inital Python snippet again:

$ diff -s mutualquine.py <(ruby <(python mutualquine.py))
Files mutualquine.py and /dev/fd/63 are identical

Note that this is similar to J B's answer.

C and Perl, 73

This C:

main(s){printf(s="print q<main(s){printf(s=%c%s%c,34,s,34);}>",34,s,34);}

...outputs the following Perl:

print q<main(s){printf(s="print q<main(s){printf(s=%c%s%c,34,s,34);}>",34,s,34);}>

...that outputs the C back.

• 3
  \$\begingroup\$ Save 4 bytes: main(s){printf(s="print q<main(s){printf(s=%c%s%1$c,34,s);}>",34,s);} \$\endgroup\$

  MD XF

  – MD XF

  2017年09月22日 16:21:04 +00:00

  Commented Sep 22, 2017 at 16:21

C and C++, 123 chars

This C (compilable with gcc v4.3.4):

#include <stdio.h>
main(){char *c="#include <stdio.h>%cmain(){char *c=%c%s%c;printf(c,10,34,c,34);}";printf(c,10,34,c,34);}

outputs this (identical) C++ (compilable with g++ 4.3.4, one warning):

#include <stdio.h>
main(){char *c="#include <stdio.h>%cmain(){char *c=%c%s%c;printf(c,10,34,c,34);}";printf(c,10,34,c,34);}

This is within the rules as posted. :P And, like Ventero's, this is based on J B's answer.

• 1
  \$\begingroup\$ OK, so it was within the rules as posted until the edit saying the sources can't be the same. A minor change could fix that, but I'm disinclined to encourage such late edits. \$\endgroup\$

  Matthew Read

  – Matthew Read

  2011年06月08日 21:22:01 +00:00

  Commented Jun 8, 2011 at 21:22

><> (Fish) and Python - 26 characters

"00gr00g:a9*2+$' tnirp'>o<

Generates this Python

print "\"00gr00g:a9*2+$' tnirp'>o<"

• \$\begingroup\$ You have an issue with the ><> code because " and ' enable string parsing, so the entire program is just pushed onto the stack and never displayed. \$\endgroup\$

  Kevin Brown-Silva

  – Kevin Brown-Silva

  2011年05月16日 22:44:29 +00:00

  Commented May 16, 2011 at 22:44
• 2
  \$\begingroup\$ @Bass5098 That's precisely how the whole thing works. The first " enables string parsing. It reads.the whole program and then wraps back around to.the first " and runs the program with itself on the stack \$\endgroup\$

  cthom06

  – cthom06

  2011年05月17日 10:22:34 +00:00

  Commented May 17, 2011 at 10:22
• \$\begingroup\$ Fixed the issue in my interpreter. Your ><> code outputs print 00円gr00g:a9*2+$' tnirp'>o< after timing out. I'm pretty sure this is because g copies the actual cell contents, but o outputs the ASCII version of the character, and " isnt a valid ASCII character code. ideone.com/kaM0r \$\endgroup\$

  Kevin Brown-Silva

  – Kevin Brown-Silva

  2011年05月17日 22:38:48 +00:00

  Commented May 17, 2011 at 22:38
• 6
  \$\begingroup\$ @Bass5098 " is ASCII 34. Your interpreter must be off. \$\endgroup\$

  cthom06

  – cthom06

  2011年05月18日 00:11:44 +00:00

  Commented May 18, 2011 at 0:11

Python + Piet one-liners: 417 chars + (削除) 7391 (削除ここまで) 7107 executing codels

This Python script produces a 7393 x 2 image; the rightmost 2x2 block of which is a "sentinel" which terminates the program; so I'm not counting those; and the second row is otherwise white. I can probably golf the piet code down further by using addition/subtraction/multiplication chains instead of the naive binary algorithm... but I don't want to give away a solution to a future puzzle.

I'm not going to post the image here, because of its ridiculous dimensions. If you want to see it, run the python code, and pipe the output to a .ppm file. Then, convert the .ppm to a .gif, and run the output at Rapapaing. (alternately, use a non-web Piet interpreter that groks .ppm)

A='P=lambda A:reduce(lambda(D,H,B),P:(D[P/3:]+D[:P/3],H[P%3*2:]+H[:P%3*2],B+"".join("%i "%H[(D[0]/P)%2]for P in[1,2,4])),map(" A ! @ B".find,A),([1,3,2,6,4,5],[0,192,192,255,0,255],"P3 %i 2 255 "%(len(A)+2)))[2]+"255 "*4+"0 0 "+"255 "*len(A)*3+"255 0 0 "*2;B=lambda D:["@!%s","@@!%s!"][D%2]%B(D/2)if 1<D else"";print P("".join("A%sB"%B(ord(D))for D in"A=%s;exec A[:-13]"%`A`)+" ");exec A[:-13]';exec A[:-13]

edit: golfed the piet a bit by reducing Hamming weight of variable names.

less golfed pre-quine:

This is a previous version, before I realized I could make it a one-liner. It's marginally easier to understand. The function P translates a special instruction set into Piet; and the function p takes an integer and produces a sequence of instructions to create that integer on the stack. I'm only using the instructions =,+,:,|, so this could probably be made more efficient... but I kinda like having a fullblown Piet compiler (of sorts) in the source.

s="""def P(s):
 l=len(s)+1;R="P3 %i 2 255 "%(l+2);C=[1,3,2,6,4,5];V=[0,192,192,255,0,255]
 for x in map("=|^+-*/%~>.,:@$?#!".find,"="+s):
 C=C[x//3:]+C[:x//3];V=V[x%3*2:]+V[:x%3*2]
 for i in [1,2,4]:R+="%i "%V[(C[0]//i)%2]
 return R+"255 "*4+"0 0 "+"255 "*l*3+"255 0 0 "*2
p=lambda x:[":+%s","::+%s+"][x%2]%p(x/2)if x/2 else""
print P("".join("|%s!"%k(ord(c))for c in "s="+`s`+";exec s[:-13]"))
exec s[:-13]"""
exec s[:-13]

• \$\begingroup\$ Piet Creator is a much nicer (and far less buggy) Piet IDE. Written by a user of this site, by the way :) \$\endgroup\$

  Joey

  – Joey

  2011年07月17日 22:02:50 +00:00

  Commented Jul 17, 2011 at 22:02
• \$\begingroup\$ I've used Piet Creator before; it's a great tool. Rapapaing is nice for people who are lazy, like me, and don't want to bother. FWIW, I'd use Piet Creator if you ran it through github.com/kripken/emscripten/wiki, and put that up on your page. \$\endgroup\$

  boothby

  – boothby

  2011年07月17日 23:52:32 +00:00

  Commented Jul 17, 2011 at 23:52
• \$\begingroup\$ I couldn't even get the Qt version to compile here ;) \$\endgroup\$

  Joey

  – Joey

  2011年07月18日 07:33:35 +00:00

  Commented Jul 18, 2011 at 7:33
• \$\begingroup\$ ;) Thanks for trying, anyway. I wrote you a fuzz tester: codegolf.stackexchange.com/questions/2922/… \$\endgroup\$

  boothby

  – boothby

  2011年07月20日 21:38:25 +00:00

  Commented Jul 20, 2011 at 21:38
• \$\begingroup\$ Well, you could poke Casey in chat and point him to it ;-) \$\endgroup\$

  Joey

  – Joey

  2011年07月20日 21:40:21 +00:00

  Commented Jul 20, 2011 at 21:40

Java to Python - 219

Java:

class Q{public static void main(String[]a){char q=34,c=39;String s="print%sclass Q{public static void main(String[]a){char q=34,c=39;String s=%s%s%s;System.out.printf(s,c,q,s,q,c);}}%s";System.out.printf(s,c,q,s,q,c);}}

Python:

print'class Q{public static void main(String[]a){char q=34,c=39;String s="print%sclass Q{public static void main(String[]a){char q=34,c=39;String s=%s%s%s;System.out.printf(s,c,q,s,q,c);}}%s";System.out.printf(s,c,q,s,q,c);}}'

Makes use of the fact that python allows ' for strings; this makes it much easier to write the java program's source in the python program.

• 4
  \$\begingroup\$ +1 for doing the dirty work in the worst golfing language ever. :P \$\endgroup\$

  cjfaure

  – cjfaure

  2014年03月10日 21:09:19 +00:00

  Commented Mar 10, 2014 at 21:09

/Brainf..k/, 6988 bytes

Brainfuck

++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>+++++++++++>>>++++++>>>+++++++>>>++++++++++>>>+>>>++++++++>>>+>>>++++++++++>>>+++++++++++>>>++>>>+++++++++>>>+>>>++>>>++++++>>>+>>>+>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>+>>>++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++>>>++++++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>++>>>+++++++>>>++>>>++++++++++>>>+>>>++++++>>>++++++++++>>>+++++++++++>>>+>>>++++++++++>>>+++++++++++>>>+>>>++>>>+>>>++>>>++>>>+++++++>>>++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+++++++>>>++>>>+>>>++++++>>>+++++++>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++++>>>+>>>++>>>+++++++++>>>++>>>++++++>>>+++++++>>>+>>>+>>>+>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>++>>>++++++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>++++++>>>+++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>+>>>+>>>+>>>+>>>++++++++++>>>+++++++++++>>>++>>>+>>>+>>>+>>>+>>>++>>>+>>>++>>>+>>>++>>>++>>>++>>>++++++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++>>>++++++++++>>>+++++++++++>>>+>>>++>>>++>>>++>>>++>>>++++++>>>+++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+>>>++++++++>>>+++++++++>>>++>>>++++++++++>>>+>>>+>>>+>>>++++++++++>>>+++++++++++>>>++++++++>>>+>>>++>>>+++++++++>>>++>>>++++++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++++>>>+>>>++>>>+++++++++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>++++++>>>+++++++>>>+++++++>>>++>>>+++++++>>>++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+++++++>>>++>>>++++++>>>++++++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++++>>>+>>>++>>>+++++++++>>>++++++>>>++++++>>>+++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>+++++++>>>++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+++++++>>>++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++++++++++>>>++++++>>>+++++++>>>+>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>+>>>++++++>>>+++++++>>>++>>>++++++++++>>>++++++>>>++++++>>>++++++>>>++++++++>>>++++++>>>++++++>>>++++++>>>+++++++++>>>+++++++>>>+++++++>>>+++++++>>>++++++++>>>+++++++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++++>>>++++++>>>++++++++>>>++++>>>+++++++>>>+++++>>>+++>>>+++++>>>++++>>>+++++++>>>+++>>>++++++>>>++++++>>>+++++++++>>>+++++++>>>+++>>>+++++>>>++++++++>>>++++>>>+++++++++>>>+++++++>>>+++++++>>>+++++++++>>>++++++>>>++++++++>>>++++++>>>++++++>>>++++++>>>+++++++++>>>+++++++>>>+++++++>>>+++++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++>>>+++++++>>>++++>>>++++++++>>>++++++>>>+++>>>+++>>>+++++++>>>++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>+++++++++>>>++++++>>>+++++>>>+++++++>>>+++++++>>>+++++++>>>+++++++>>>+++++++++>>>+++++++++++>>>++++++++++>>>+++++++++++>>>++++++>>>+++++++>>>{({}<>)<>}<>{([({})]()<((((()()()()()){}){}){})>){({}()<({}())>){({}()<({}()())>){({}()<({}()())>){({}()<({}())>){({}()<({}((()()()){}()){})>){({}()<({}()())>){({}()<({}(((()()()){}()){}){}())>){({}()<({}()())>){({}()<({}(((()()()()())){}{}){})>){(<{}({}()())>)}}}}}}}}}}{}({}<(<>)<>{({}<>)<>}{}>)(<><>)<>{({}<>)<>}{}<>{({}[()])<>(((((()()()){}())){}{}){}())<>}{}<>(((({})(((()()())){}{}){}())))<>}{}([]){((({}[()])<{({}[()]<({}<({}<>)<>>)>)}{}>)<{({}[()]<<>({}<>)>)}{}>)}{}{<>({}<>)}{}(<>){<<<[<<<]>>>[>++++++++++++++++++++++++++++++++++++++++.<[->.+.->+<<]>+.[-]>>]<[<<<]>>>[<++++++++++++++++++++++++++++++++++++++++>-[<+>-[<++>-[<++>-[<+>-[<++++++++++++++>-[<++>-[<+++++++++++++++++++++++++++++>-[<++>-[<++++++++++++++++++++++++++++++>-[<++>-]]]]]]]]]]<.>>>>]}{}<>

Try it online!

Brain-Flak

(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()()()()()()()()()())(())(()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()())(())(()())(()()()()()())(())(())(())(())(())(()())(())(()())(())(()())(())(()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(())(())(()())(())(()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(())(())(())(()())(())(()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(())(())(())(()())(())(()())(())(()())(())(()())(())(()())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()())(()())(()()()()()()()()()())(())(()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(())(()())(()())(()()()()()()())(()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()())(()())(())(()()()()()())(()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()())(())(()())(()()()()()()()()())(()())(()()()()()())(()()()()()()())(())(())(())(())(())(())(()())(())(()())(())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(())(())(())(())(()()()()()()()()()())(()()()()()()()()()()())(()())(())(())(())(())(()())(())(()())(())(()())(()())(()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()())(()()()()()()()()()())(()()()()()()()()()()())(())(()())(()())(()())(()())(()()()()()())(()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(())(()()()()()()()())(()()()()()()()()())(()())(()()()()()()()()()())(())(())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()())(())(()())(()()()()()()()()())(()())(()()()()()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()())(())(()())(()()()()()()()()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()())(()()()()()()())(()())(()()()()()()())(()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()())(()())(()()()()()())(()()()()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()())(())(()())(()()()()()()()()())(()()()()()())(()()()()()())(()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()()())(()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()())(()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()())(()()()()()()())(())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()())(()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(())(()()()()()())(()()()()()()())(()())(()()()()()()()()()())(()()()()()())(()()()()()())(()()()()()())(()()()()()()()())(()()()()()())(()()()()()())(()()()()()())(()()()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()()())(()()()()()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()()()())(()()()()()())(()()()()()()()())(()()()())(()()()()()()())(()()()()())(()()())(()()()()())(()()()())(()()()()()()())(()()())(()()()()()())(()()()()()())(()()()()()()()()())(()()()()()()())(()()())(()()()()())(()()()()()()()())(()()()())(()()()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()()()())(()()()()()())(()()()()()()()())(()()()()()())(()()()()()())(()()()()()())(()()()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()())(()()()()()())(()()())(()()())(()()()()()()())(()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()()()()())(()()()()()())(()()()()())(()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()())(()()()()()()()()())(()()()()()()()()()()())(()()()()()()()()()())(()()()()()()()()()()())(()()()()()())(()()()()()()()){({}<>)<>}<>{([({})]()<((((()()()()()){}){}){})>){({}()<({}())>){({}()<({}()())>){({}()<({}()())>){({}()<({}())>){({}()<({}((()()()){}()){})>){({}()<({}()())>){({}()<({}(((()()()){}()){}){}())>){({}()<({}()())>){({}()<({}(((()()()()())){}{}){})>){(<{}({}()())>)}}}}}}}}}}{}({}<(<>)<>{({}<>)<>}{}>)(<><>)<>{({}<>)<>}{}<>{({}[()])<>(((((()()()){}())){}{}){}())<>}{}<>(((({})(((()()())){}{}){}())))<>}{}([]){((({}[()])<{({}[()]<({}<({}<>)<>>)>)}{}>)<{({}[()]<<>({}<>)>)}{}>)}{}{<>({}<>)}{}(<>){<<<[<<<]>>>[>++++++++++++++++++++++++++++++++++++++++.<[->.+.->+<<]>+.[-]>>]<[<<<]>>>[<++++++++++++++++++++++++++++++++++++++++>-[<+>-[<++>-[<++>-[<+>-[<++++++++++++++>-[<++>-[<+++++++++++++++++++++++++++++>-[<++>-[<++++++++++++++++++++++++++++++>-[<++>-]]]]]]]]]]<.>>>>]}{}<>

Try it online!

The Brain-Flak might time out on TIO.

Explanation

Coming soon.

• \$\begingroup\$ That polyglot at the end is quite impressive... \$\endgroup\$

  ETHproductions

  – ETHproductions

  2017年05月22日 20:21:07 +00:00

  Commented May 22, 2017 at 20:21
• 6
  \$\begingroup\$ Explanation coming soon -> Jan 27 \$\endgroup\$

  MD XF

  – MD XF

  2017年09月22日 16:22:03 +00:00

  Commented Sep 22, 2017 at 16:22
• 3
  \$\begingroup\$ @MDXF Explanation coming soon checks date \$\endgroup\$

  caird coinheringaahing

  – caird coinheringaahing ♦

  2020年08月11日 00:09:47 +00:00

  Commented Aug 11, 2020 at 0:09
• \$\begingroup\$ When you'll add an explanation? \$\endgroup\$

  Fmbalbuena

  – Fmbalbuena

  2022年12月16日 19:55:42 +00:00

  Commented Dec 16, 2022 at 19:55
• 1
  \$\begingroup\$ @Fmbalbuena Soon. \$\endgroup\$

  Wheat Wizard

  – Wheat Wizard ♦

  2022年12月17日 04:04:51 +00:00

  Commented Dec 17, 2022 at 4:04

Ruby and Python (393 + 413 = 806 chars)

Slight change of this answer of mine. Could definitely be reduced since I just hard-coded the input without any optimisation.

Ruby (393 chars)

require 'json';s=%q[{"ruby":[" %q[","require 'json';s=##;j=JSON.load s;puts j[l='python'][1].sub('##',j[l][0].delete(' ')+s+j[l][2].delete(' '))"," ]"],"python":["' ''","import json,re;s=##;j=json.loads(s);l='ruby';print(re.sub('##',j[l][0].replace(' ','')+s+j[l][2].replace(' ',''),j[l][1],1))","' ''"]}];j=JSON.load s;puts j[l='python'][1].sub('##',j[l][0].delete(' ')+s+j[l][2].delete(' '))

Python (413 chars)

import json,re;s='''{"ruby":[" %q[","require 'json';s=##;j=JSON.load s;puts j[l='python'][1].sub('##',j[l][0].delete(' ')+s+j[l][2].delete(' '))"," ]"],"python":["' ''","import json,re;s=##;j=json.loads(s);l='ruby';print(re.sub('##',j[l][0].replace(' ','')+s+j[l][2].replace(' ',''),j[l][1],1))","' ''"]}''';j=json.loads(s);l='ruby';print(re.sub('##',j[l][0].replace(' ','')+s+j[l][2].replace(' ',''),j[l][1],1))

Python 2 to Befunge 98, (削除) 94 (削除ここまで) 78

Again, making use of Python's two ways of making strings:

Python:

s='<@,kM%c%cs=%c%s%c;print s%%(39,34,39,s,39,34)%c';print s%(39,34,39,s,39,34)

Befunge 98:

<@,kM'"s='<@,kM%c%cs=%c%s%c;print s%%(39,34,39,s,39,34)%c';print s%(39,34,39,s,39,34)"

The python program formats the string to include itself and the characters for the single and double quote.

The Befunge program works like this:

• <: move to the left, and wrap around. So now we execute the commands from right to left

• ": make it so that every char we encounter is pushed to the stack until we encounter another ", so we push:

  )43,93,s,93,43,93(%s tnirp;'c%)43,93,s,93,43,93(%%s tnirp;c%s%c%=sc%c%Mk,@<'=s
  

  Which is actually just the python program, reversed because of the way Befunge prints (which is a pop+print loop)

• 'M: push M to the stack. M is also the number 77, which is one less than the number of chars pushed to the stack by the "s.
• k: pop the top value off the stack (M) and do the next operation that many times, plus one.
• ,: pop the top value off the stack and print the char.
• @: end the program.

• \$\begingroup\$ Good grief, and in a notoriously difficult esoteric language too. Thats..... terrifying. \$\endgroup\$

  Shayne

  – Shayne

  2017年10月17日 05:24:30 +00:00

  Commented Oct 17, 2017 at 5:24

Gol><> and APL, 10 bytes and 13 bytes

'r3d*:::}H

Try it online! Which outputs:

'''r3d*:::}H'

Try APL online!

Which simple prints the code as a string (with the ' escaped with another ')

Clipper and C (111 + 108 = 219 chars)

Clipper (111)

?'char*f="%c%cchar*f=%c%s%c;main(){printf(f,63,39,34,f,34,39,10);}%c%c";main(){printf(f,63,39,34,f,34,39,10);}'

C (108)

char*f="%c%cchar*f=%c%s%c;main(){printf(f,63,39,34,f,34,39,10);}%c%c";main(){printf(f,63,39,34,f,34,39,10);}

This is a bit of a cop-out because:

1. the "print" command in Clipper is really simple: ?'foo' :-)
2. I based it on the "classic C" quine from http://www.nyx.net/~gthompso/quine.htm, with some modification to squeeze in the ? and 's.
3. I didn't #include <stdio.h>, so it gives a compiler warning
4. The C code output by the Clipper version had to be prodded to remove a line break that had been introduced by an 80-character column limit in either my terminal or the Harbour printing routine or something.

• \$\begingroup\$ Well, the BASIC PRINT command could be abbreviated ? as well :-) \$\endgroup\$

  Joey

  – Joey

  2011年07月20日 21:41:16 +00:00

  Commented Jul 20, 2011 at 21:41

Jelly, 13 bytes

"Ṿ;)v`+/ŒṘ"v`

Try it online!

RAD

'"Ṿ;)v`+/ŒṘ"v`'

Try it online!

A Jelly quine that wraps itself in single quotes, such that the resultant RAD program simply prints the original Jelly program back out.

Underload and Betaload, 16 bytes

Underload:

(a(:^)*a(S)*S):^

Betaload:

((a(:^)*a(S)*S):^)S

Betaload is a superset of Underload, so this could be two Underload answers.

Vyxal, 10 bytes

`:qpq`:qpq

Try it Online!

Vyxal V

`\`:qpq\`:qpq`

Try it Online!

The V flag does nothing, the first is a quine that unevaluates itself, and the second is a string.

Or...

Vyxal DrV, 16 bytes

`q\`:Ė\`p1→ip`:Ė

Try it Online!

Vyxal Dr

0`q\`:Ė\`p1→ip`:Ė

Try it Online!

The 0 at the start is a NOP - Vyxal pads the stack with 0s anyway, so the two programs are functionally identical.

`q\`:Ė\`p `:Ė # Standard eval quine
 1→ip # If `V` (single-char variable names) is off, this stores 1 to the variable ip.
 # If it's on, this stores 1 to the variable i and prepends a 0 to the current program.

Javascript and Windows .bat, 71 bytes and 81 bytes

f=()=>{console.log('echo f='+(f+';f()').replace(/(?=[>^\\])/g,'^'))};f()

and

echo f=()=^>{console.log('echo f='+(f+';f()').replace(/(?=[^>^^^\^\])/g,'^^'))};f()

Guile, 114 bytes

((lambda(v)(format #t".\\~s"(format #f" (~a~s)"v v)))"(lambda(v)(format #t\".\\\\~s\"(format #f\" (~a~s)\"v v)))")

Try it online!

Forth (gforth), 139 bytes

.\" ((lambda(v)(format #t\".\\\\~s\"(format #f\" (~a~s)\"v v)))\"(lambda(v)(format #t\\\".\\\\\\\\~s\\\"(format #f\\\" (~a~s)\\\"v v)))\")"

Try it online!

Python and ~-~! - 77 and 81 = 158

This Python code:

q=chr(124);s='@%sq=chr(124);s=%s;print(s%%repr(s))%s:';print(s%(q,repr(s),q))

outputs this ~-~! code:

@|q=chr(124);s='@%sq=chr(124);s=%s;print(s%%repr(s))%s:';print(s%(q,repr(s),q))|:

Can definitely be improved a lot, and adopts a whole bunch from the other answers.

• code-golf
• quine
• polyglot