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From: eijkhout@s41.csrd.uiuc.edu (Victor Eijkhout)
Newsgroups: comp.text.tex
Subject: Re: letA=3 edefB{A} does not put 3 into B ?????
Message-ID: <1990Nov23.200527.17577@csrd.uiuc.edu>
Date: 23 Nov 90 20:05:27 GMT
References: <1990Nov22.001531.7022@zaphod.mps.ohio-state.edu>
Sender: news@csrd.uiuc.edu (news)
Organization: UIUC Center for Supercomputing Research and Development
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eao@shape.mps.ohio-state.edu (Ed Overman) writes:

>I want to do
>  \let\A=3 \edef\B{\A}
>and have \B contain 3.  

\let is a very strange thing. It makes a control sequence
to a synonym for a token, which can be a control sequence token,
or a character token. Note: a synonym, not a definition that
has to be expanded. Thus in \edef\B{\A} the \A is not expanded,
because there is nothing to expand; \A *is* already a charcter.
For instance \if 3\A is true! 

However, you cannot get at for instance the Ascii code of the
character that is \A: `\A is 65, which is Ascii for 'A'.

>The only solution I have found is to use  \meaning\A  since the third word
the output of \meaning\A is `the character 3'. I'm afraid I can't
do any better than this. 

But do you need to do it this way? What is wrong with
\def\GetOneLetter#1{ ... }
? This works at least for all letters and digits, tho' not
for things like braces, and unfortunately also not for spaces.
 
You can distinguish between a lot of tokens if you have \let\A,
using \ifcat. For instance, '\ifcat a\A' will be true if \A
has been let to a letter.

Victor.