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From: jeff@itx.isc.com (Jeff Copeland)
Newsgroups: comp.text
Subject: Re: ISC 2.0.2 troff broke?
Message-ID: <1991Feb27.161113.22188@ism.isc.com>
Date: 27 Feb 91 16:11:13 GMT
References: <1434@vidiot.UUCP>
Sender: usenet@ism.isc.com (Ism Usenet News)
Followup-To: comp.text
Organization: Interactive Systems Corp., Austin, TX
Lines: 22

In article <1434@vidiot.UUCP> brown@vidiot.UUCP (Vidiot) writes:
>
>I am running ISC 2.0.2 Unix and ISC text processing package.  When I have
>the following line, with neither of the registers set on the command line:
>
>	.if \nG==1&\nI==0 \{\
>	.tm inside coverdef G=\nG I=\nI
>
>It gets past the if statement and shows that both registers are indeed zero.
>....
>What the Hell is going on here?  Is the ISC version of DWB 2.0 broke?

The secret is evaluation order:  if you add parentheses:
	.if (\nI==0)&(\nG==1) \{\
it works as you expect.  So the line in the DWB 2.0 docs that says:
	"Except where controlled by parentheses, evaluation of
	expressions is left-to-right."
is *really* true.

By the way, Interactive's DWB 2.0, IBM's DWB 2.0 on the RS/6000, DWB 1.0 on 
a VAX running BSD, and old troff as ported by BRL to BSD, all act the same 
on this fragment.