# A Neighborhood of Infinity

## Tuesday, February 05, 2008

### A Third Order Quine in Three Languages

Suppose Fnxy is a program, written in language x, that takes as input n string arguments as input, G1,...,Gn and outputs a program in language y that is the application of the function whose source code is G2 to the strings G2,G3,...,Gn,G1. Then F3xy(F3xy,F3yz,F3zx) will be a program in language x that that outputs a program in y that computes F3yz(F3yz,F3zx,F3xy).

We can put this into practice:

q a b c=putStrLn $b ++ [toEnum 10,'q','('] ++ show b ++ [','] ++ show c ++ [','] ++ show a ++ [')']main=q "q a b c=putStrLn$ b ++ [toEnum 10,'q','('] ++ show b ++ [','] ++ show c ++ [','] ++ show a ++ [')']" "def q(a,b,c):print b+chr(10)+'q('+repr(b)+','+repr(c)+','+repr(a)+')'" "def e(x) return 34.chr+x+34.chr end;def q(a,b,c) print b+10.chr+'main=q '+e(b)+' '+e(c)+' '+e(a)+' '+10.chr end"

This is a Haskell program that outputs a Python program that outputs a Ruby program that outputs the original Haskell program.

Apologies for the lack of line breaks. If it's not readable, it should be possible to copy and paste that source. Also, you may need to tweak it if your OS doesn't treat character 10 as a new line.

cypher said...

That is awesome.

Nikolay said...

[15:27 /]$ghci ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Prelude> q a b c=putStrLn$ b ++ [toEnum 10,'q','('] ++ show b ++ [','] ++ show c ++ [','] ++ show a ++ [')']
< interactive >:1:7: parse error on input `='

Anonymous said...

Impressive O_O

Brent said...

nice!

Nikolay: you won't be able to just paste it into ghci like that, you'll have to put it in a file and then load the file into ghci.

mzz said...

nikolay:
Write it into .hs file and use runhaskell to execute it.
ghci expects let before name bindings to distinguish them from expressions.

Nikolay said...

Ooh, I see. Thanks! It is really awesome!

jk said...

Wow! That is really awesome.

Anonymous said...

Wow! You're all dorks

Anonymous said...

Amazing :)

Anonymous said...

paurullan said...

Gorgeous!

Paul Hobbs said...

This is so fascinating! You are awesome =]

What this really needs is a recursive function

Anonymous said...

it formatted my pr0n.

Anonymous said...