[texhax] Question about \setbox

[Heiko Oberdiek]

On Fri, Sep 16, 2011 at 10:13:01AM +0100, Philip TAYLOR (Webmaster, Ret'd) wrote:

> Heiko Oberdiek wrote:
> > On Fri, Sep 16, 2011 at 06:13:27PM +1000, VAFA KHALIGHI wrote:
> > 
> >> Why this does not work:
> >>
> >>  \setbox0=\vbox{I am a vbox}
> >>
> >> \setbox1=\hbox{\unvbox0}
> > 
> > You are in restricted horizontal mode inside \hbox. There
> > a "vertical command" (\unvbox, \unvcopy, \halign, ...}
> > is forbidden ("The TeX book", Chapter 25 "Summary of Horizonal Mode).
> 
> Thank you : that has been puzzling me ever since Vafa first
> asked the question and I confirmed that he was correct !
> 
> In that case, presumably the answer will be to use something
> along the lines of the following :
> 
>     \setbox 0 = \vbox {I am a vbox}
>     \setbox 2 = \vbox {\unvbox 0 \global \setbox 4 = \lastbox}
>     \unhbox 4
>     \bye

I don't know/remember what Vafa wants in the first place.
\lastbox only gets the last box/last line. It is even empty
if there is something different at the end of the
\vbox (\kern, whatsit, ...).

Yours sincerely
  Heiko Oberdiek