Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!ucbvax!TAMVM1.BITNET!X066TR
From: X066TR@TAMVM1.BITNET ("Thomas J. Reid")
Newsgroups: comp.text.tex
Subject: Re: \the \baselineskip
Message-ID: <97DCDB12A000E084@post-office.uh.edu>
Date: 17 Feb 91 09:36:03 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: Texas A&M University Computing Services Center
Lines: 38

On Sun, 17 Feb 91 03:05:17 EST xiaofei@acsu.buffalo.edu said:
>If I say
>``
>\the\baselineskip
>\baselineskip=2.0\baselineskip
>\the\baselineskip
>''
>
>I expect the first \the\baselineskip gives me a ``12.0pt'' and the
>second one goves me a ``24.0pt''. But it is not the case, they both
>give me ``12.0pt'' which I find it difficult to understand.
 
The point which you are not understanding is the difference between TeX's
parsing tokens, and executing commands.  TeX processes the sequence by
first expanding "\the\baselineskip" into its current value of "12.0pt".
It then begins parsing the tokens "\baselineskip", "=", "2", ".", "0",
"\baselineskip".  At this point, TeX does not yet realize that it has a
complete command which it can execute, so it continues parsing.  It then
finds "\the" which causes it to immediately expand the "\baselineskip"
which follows it.  This generates a new set of tokens: "1", "2", ".",
"0", "p", and "t" which TeX stacks.  Finally, TeX executes the assignment
command and changes the value of \baselineskip to 24pt.  Thus, it is
the look-ahead action of the token parser which is causing your problem.
 
To work around this problem, it is merely necessary to insert a token
between the assignment and the second expansion of \the\baselineskip
to cause TeX to actually make the assignment.  Your test of inserting
\par at this point would do the trick; however, if you didn't want a
paragraph break there, it would have a bad side-effect.  The best thing
to do is to insert \relax after the assignment.
 
The processing of dimensional arguments is one of the more confused
aspects of TeX but is better understood when one realizes the two phases
of parsing tokens and actually processing the commands.
 
Regards,
 
Tom Reid