Re: setupinteraction and macroexpansion

[Wolfgang Schuster <schuster.wolfgang@googlemail.com>]

Am 19.06.2012 um 10:59 schrieb Andreas Schneider:

> On Tuesday, June 19, 2012, at 10:42 Wolfgang Schuster wrote:
> 
>> Am 19.06.2012 um 10:39 schrieb Andreas Schneider:
> 
>>> Hello,
>>> 
>>> I'm  a bit lost with macro expansion here. I try to use some macros to
>>> set  the title (and subject) of the PDF document. The attached minimal
>>> example shows what I want to achieve.
>>> 
>>> I tried def, edef, gdef, define, explicit expand, expandoneafter, etc.
>>> etc.  without  any  success. Whatever I do, the title field in the PDF
>>> metadata  always  contains  the  raw "\date..." command instead of the
>>> formatted date.
>>> 
>>> Any suggestions?
> 
>> You can’t use \date (or any other unexpandable command) in an expandable context.
> 
>> Wolfgang
> 
> Hmm  I  see, so \date is simply not possible for that case. Ok, thanks
> for  explaining  that  I wasn't aware (until now) that commands can be
> unexpandable.

To explain it in a simple way: Commands which can be used in \edef\comecommand{…}
are expandable and commands which fail in \edef are unexpandable. It’s also important
to know that commands with optional arguments are always unexpandable because
the underlying mechanism to check for the optional bracket, brace etc. can’t be used
in \edef, you can also make a expandable command (e.g. \def\foo{FOO}) unexpandable
by adding \unexpanded in front of the \def (e.g. \unexpanded\def\bar{BAR}).

Wolfgang
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