Thompson's self-reproducing program

[Alex Colvin]

"What is the point of a self-duplicating program?"

Well ... For one thing, you never have to keep the source code around.

Seriously, it's mildly interesting as a bit-banging (character-banging)
challenge to those who don't worry about the fixed-point combinator.
For those who do, here's a different version in SCHEME (or, with slight
syntax changes, in LISP).

(labels (f (lambda () f)) f)

This one simply returns itself -- not necessarily its source code.  It gets
printed by the read-eval-print loop.  A C analogue is 

f() { return f; };