[NTG-context] Passing macro parameters to lua

5 Aug 2013

      Hello, good people--

I've encountered what appears to be a bug in either the TeX->Lua
interface or the documentation thereof (I have the latest stable
ConTeXt standalone from contextgarden.net).

I'm trying to create a macro that will insert different text depending
on whether one of the arguments is empty or not. My initial test
implementation (following the wiki section entitled "Passing arguments
and buffers: ConTeXt commands that hook into Lua") looked like this:

\startluacode
    userdata = userdata or {}

    function userdata.empty_or_not(str)
        if str == "" or str == nil then
            context("{\\sc Empty}")
        else
            context(str)
        end
    end
\stopluacode

\def\emptyOrNot#1{%
    \ctxlua{userdata.empty_or_not(#1)}%
}

\starttext

    \emptyOrNot{Amazing Text!}

    \emptyOrNot{}

\stoptext

This did not work. I determined that even when I passed a non-empty
string, the Lua interpreter detected it as nil. It turns out the fix
was simple--I had to quote the string, as follows.

\def\emptyOrNot#1{%
    \ctxlua{userdata.empty_or_not("#1")}%
}

It took me a while to figure that out, though, since the wiki example
does not show quotes.

--
Matt Gushee