# Re: [NTG-context] Getting the width of an expression inside lua

Hi Hans,

thanks for the instant reply :-) I haven't tried your suggestion yet, but I've
got a few questions first.

> \startluacode
> function document.step_one(str)
>     tex.sprint("\\setbox0\\hbox{",str,"}")
Would there be any danger of overwriting an existing box by doing this? I'm
not quite sure how this boxing thing works...

>     tex.sprint("\\ctxlua{document.step_two(0)}")
I guess this indirection is needed to force the \setbox command to be
expanded? I guess tex.sprint doesn't expand its arguments immediately, so just
putting document.step_two(0) instead of the entire tex.sprint("\\ctxlua...
won't work...

I'm using this from inside a pretty printer, so I'd have to think a bit about
how to set this up so things run inside the right context and stuff, but I
guess that should work out. Still slightly more complicated that a direct "How
wide is this thing" function, though.

> function document.step_two(n)
>     tex.sprint("width: ",tex.wd[0])
> end
I gues you mean tex.wd[n] here, but whatever :-)

> \ctxlua{document.step_one("test {\\bf test} test")}
>
> \box0
Why is this \box0 needed? Just to show the test test test output? AFAICS, the
width of the box will be displayed always, even without this?

Gr.

Matthijs


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