Saturday, May 15, 2004

Quine = Self-Reproducing Code

Metamagical Themas: Questing for the Essence of Mind and PatternI received a note from AG regarding self-reproducing code. "I presume by now you have seen a kazillions of these"...

...quine: /kwi:n/ /n./ [from the name of the logician Willard van Orman Quine, via Douglas Hofstadter] A program that generates a copy of its own source text as its complete output. Devising the shortest possible quine in some given programming language is a common hackish amusement. Here is one classic quine:

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

This one works in LISP or Scheme. It's relatively easy to write quines in other languages such as Postscript which readily handle programs as data; much harder (and thus more challenging!) in languages like C which do not. Here is a classic C quine for ASCII machines:


For excruciatingly exact quinishness, remove the interior line breaks...

The Quine Page

No comments: