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From: brown@vidiot.UUCP (Vidiot)
Newsgroups: comp.text
Subject: Re: troff string register interpolation if strange char
Message-ID: <523@vidiot.UUCP>
Date: 8 Jun 90 02:05:27 GMT
References: <16321@smunews.UUCP>
Reply-To: brown@vidiot.UUCP (Vidiot)
Organization: Vidiot's Hangout
Lines: 57

In article <16321@smunews.UUCP> leff@.seas.smu.edu (leff) writes:
<A strange control character is being inserted on character interpolations
<before a closing \} of an if statement.
<
<In the example below, there are two operations involving interpolation of a
<string register before a \} of an if.  In the first operation, the output of 
<the "tm" inside of the macro, M1, includes both an X and a control character.
<
<The second operation shows that the string register X2 receives both an X
<and a control character.  
<
<I have experienced this problem with both nroff and ditroff.
<
<nroff inserts an octal 36 (^^) while ditroff inserts a control-Q.
<
<The obvious workaround is to insert a dummy statement just before the \}
<but I would like to understand what is happening.  Any ideas?
<
<.de M1
<.if X\\n(R1X1X \{\
<.tm \\*(U1\}
<.if X\\n(R1X1X \{\
<.ds X2 \\*(U1\}
<..
<.ds U1 X
<.nr R1 1
<.M1
<.tm \*(X2X

I have read somewhere that doing what you do is incorrect.  I too ran into
and problem and have solved it by doing:

.de M1
.if X\\n(R1X1X \{\
.tm \\*(U1
.\}
.if X\\n(R1X1X \{\
.ds X2 \\*(U1
.\}
..

The . in front of the \} makes it look like a n/troff command.  But since it
isn't, it is ignored, ie, a blank line isn't put into the output.  The \}
is still seen and operated on.

Your examples can best be re-written as:

.de M1
.if X\\n(R1X1X .tm \\*(U1
.if X\\n(R1X1X .ds X2 \\*(U1
..

The \{\ and \} are best used for multi-line if continuations.
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