Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!sun-barr!apple!agate!shelby!rutgers!bellcore!att!cbnewsl!dfp
From: dfp@cbnewsl.ATT.COM (david.f.prosser)
Newsgroups: comp.lang.c
Subject: Re: Recursive Definitions: Trouble or Bad news?
Message-ID: <2246@cbnewsl.ATT.COM>
Date: 12 Oct 89 19:37:36 GMT
References: <7657@cdis-1.uucp>
Reply-To: dfp@cbnewsl.ATT.COM (david.f.prosser)
Organization: AT&T Bell Laboratories
Lines: 20

In article <7657@cdis-1.uucp> tanner@cdis-1.uucp (Dr. T. Andrews) writes:
>I should be interested to know the latest ANSI wisdom on a construct
>requesting that token BLUNGE be replaced by itself:
>	#define BLUNGE BLUNGE

When BLUNGE is replaced, the attempted recursion is detected and
the macro is left unchanged.  A more complicated example would be

	#define A B
	#define B A
	A

in which A is replaced by B and during the rescan B is replaced by A.
The next rescan detects the recursion, and this A is unreplaced and
is the result.

Yes, this implies that the macro replacement algorithm must keep track
of potentially lots of information.

Dave Prosser	...not an official X3J11 answer...