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From: dahosek@biivax.dp.beckman.com
Newsgroups: comp.text.tex
Subject: Re: TeXbook question Appendix E getaddress macro
Message-ID: <1991May22.111014.324@biivax.dp.beckman.com>
Date: 22 May 91 18:10:14 GMT
References: <16505@leadsv.UUCP>
Distribution: usa
Organization: Beckman Instruments, Inc.
Lines: 49

In article <16505@leadsv.UUCP>, wurtz@sgi400.msd.lmsc.lockheed.com (Jeff Wurtz) writes:
> I need someone's help to understand the \getaddress macro in Appendix E,
> page 407 of the TeXbook.  Anything you can tell me to assist my understanding
> will be greatly appreciated.  I have the following specific questions:
> 1) What is parameter #1 used for?  My guess is that it is used only to "get
>    to the end of line", but if that is so, then why is it used in the
>    replacement text?  As best as I can determine, parameter #1 is blank!

Yep. It's pulled to get past the EOL after \address and its
contents are reinserted in the output to guarantee that no text
is lost (see also \closing).

> 2) In the line defining \getaddress, is the \obeylines included only for
>    purposes of the macro definition or is it used "outside" of the macro?

Yes. \obeylines is used to make sure that the catcode of ^^M is
correct when the definition takes place. In the execution,
\obeylines is handled by \beginlinemode in \address which calls
\getlinemode

> 3) When \getaddress is used (by \address), only one line (Prof.~Brian~K. Reid)
>    goes into parameter #2.  How does \getaddress read paremeter #2?  Does it
>    use a <CR> as a delimiter?  Does it use "end of paragraph" as a delimiter?
>    What determines the end of the argument for parameter #2?

It's the ^^M (which is active because of the \obeylines) which
indicates the end of parameter #2.

> 4) How do the three address lines get into box \theaddress?

The box isn't finished off until \endmode is called by \body so
everything from parm #2 on goes into the box. (You may want to
look up \bgroup and \egroup in the index for more insight on
that.)
 
> Macro \getaddress appears (to me) to be a sophisticated way of specifying
> arguments for a macro.  I really want to understand how it works.  The amount
> of explanation for this macro in the TeXbook seems woefully inadequate.

You may want to also examine the \closing/\getclosing macro to
see a similar parsing of text.

-dh

-- 
Don Hosek // Quixote Digital Typography   714-625-0147
     dhosek@ymir.claremont.edu
On contract to Beckman Instruments        714-961-4562
     dahosek@beckman.com