Quine

This has been bugging me recently. Any quines or pointers to relevant articles or web pages is appreciated. Thanks!

Self-reproducing programs are commonly called quines. Do a web search, it should turn up lots of them. There was also a quine thread here in comp.lang.c just days ago, search deja.com (the thread's title was something about self-printing programs, I think).

A quine is a program that can print its own source code. Most quines are notoriously difficult (and fiendish) to write. Perl can cheat, though. :)

Why have a one-page chapter that doesn't say anything? At the least, you should present a quine program written in pure ISO C (I can send you one if you like); […] you might refer the interested reader to Ken Thompson's ACM lecture or to another good source of quine-related puzzles. Quines *are* a lot of fun, but why waste time with trivial ASCII-based examples when there are much more fundamental ways to create them?

A respectable quine—one that doesn't cheat—is not allowed to do anything as underhand or trivial as seeking the source file on the disk, opening it, and copying (or printing) its contents. Although writing a quine is not always easy, and in fact may seem impossible, it can always be done in any programming language that is Turing complete (see Turing machine), which includes every programming language actually in use.

SelfGOL can reproduce itself; it can turn other programs into a quine; it can display a scrolling banner; it plays the Game of Life; and it contains no (ordinary) loops, goto statements, or if statements. Control flow is done, well, interestingly.

Yet from a different perspective, it [the semantics of a program] describes the process of producing this very code; in other words, it is because object- and meta-language interrelate that makes a quine difficult; in less reflective programs, where means and ends are more separate, this difficulty is not so obvious.

Gee, last time I wrote a quine in Lisp it ended up being kind of difficult …