[texhax] A macro programming question

[Philipp Stephani]

Am 10.04.2010 um 07:11 schrieb Vafa Khalighi:

> I ask my question as an example
> 
> I can say \hbox to 10pt{This is a test.}
> 
> Now I want to define the macro \hboxR, so that when I say
> 
> \hboxR to 10pt{This is a test.}
> 
> it actually means
> 
> \hbox to 10pt{\beginR This is a test\endR}
> 
> Can \hboxR be defined like what I described?

Probably not with full generality.  The following is a partial solution with several issues:

\TeXXeTstate=1
\def\hboxR#1#{\hboxRR{#1}}
\def\hboxRR#1#2{\hbox#1{\beginR#2\endR}}
\setbox0=\hboxR to 40pt{abc\hfil def}
\box0
\bye

With this definition, \hboxR can presumably act as a <box>, and the syntax is similar to \hbox.  However, no braces must occur in the "to" part, and the braces enclosing the box contents must be explicit.