Date: Thu, 14 Sep 89 20:29:28 -0400
To: NeWS-makers@brillig.umd.edu
Subject: A PostScript Quine
From: spectral!sjs@bellcore.com  (Stan Switzer)

   "'Yields falsehood when preceded by itself in quotes" yields
   falsehood when preceded by itself in quotes." -- W. V. O. Quine
   (paraphrase)

A "quine" is a program which when evaluated yields its own
representation.  A quine can be formally described as a fixed point of
a language's denotation function.  Trivial evaluations (e.g.:
literals) are excluded and the program cannot require any input data
(e.g.: "cat cat.c").

In my experience, the merit of a language is inversely related to the
length of its shortest quine.  (Though I _am_ prejudiced toward
reflective semantics.)

For the heck of it, let's say a PostScript quine is a procedure
"{...}" which when followed by "n { exec } repeat" yields the same (or
equivalent) value for any non-negative integer value of "n"
(including 0).

The shortest I have found for PostScript is

  {{[ exch /dup load /exec load ] cvx} dup exec}

Compare to Lisp:

  ((lambda(f)(list f (list 'quote f))) '(lambda(f)(list f (list 'quote f))))

or (ASCII) C:

  char*f="char*f=%c%s%c;main(){printf(f,042,f,042,012);}%c";main(){printf(f,042,f,042,012);}

Not that it'll change your life or anything...

Enjoy,

Stan Switzer  sjs@bellcore.com