Small introspective program

[Doug Gwyn]

In article <1991Mar16.163213.9794 at bingvaxu.cc.binghamton.edu> kym at bingvaxu.cc.binghamton.edu (R. Kym Horsell) writes:
>The following is a (probabalistic) example. It relies on fixpoint
>theory to guarantee finding the appropriate parameters (in fact the
>search for any self-replicating automaton can use this theory) and 
>terminates in several iterations.

I think it was Ken Thompson who tried the experiment of taking the
diagnostic output from a UNIX C compiler and feeding it back to
another invokation of the compiler as source code:

	echo foo bar > X	# initial invalid "program"
	while	:
	do	cp X x.c
		cc x.c > X 2>&1 || :
		if cmp -s X x.c
		then	cat X
			exit
		fi
	done