# Lua function to see if a macro is defined or not

I need to determine if a TeX macro is already defined or not via a Lua function. Any ideas?

function IsTeXMacroDefined(macroname)
if defined(macroname) then return true end
return false
end

-

I don't know how robust it is but the following seems to work.

\documentclass{standalone}
\def\test{}

\begin{document}

\directlua{%
function is_defined(s)
local undef = 'undefined_cs'
if token.command_name(token.create(s)) == undef then
return false
else
return true
end
end
if is_defined('test') then tex.sprint('test is defined\noexpand\\par') else
tex.sprint('test is not defined\noexpand\\par') end
if is_defined('testa') then tex.sprint('testa is defined\noexpand\\par') else
tex.sprint('testa is not defined\noexpand\\par') end}

\end{document}


Updated

I added a TeX wrapper. It takes as an argument the name of the control sequence to be tested or the control sequence itself (this is done by removing the backslash at lua level with the help of lpeg). The TeX wrapper uses the expandability of \directlua to define on the fly a TeX \iftrue or \iffalse statement inside a \csname.

As pointed out in comments, one should always write lua code in a separate lua file.

First the lua file (save it as is_def.lua).

local lpeg = require('lpeg')
local P, C, Cs, V, match = lpeg.P, lpeg.C, lpeg.Cs, lpeg.V, lpeg.match

function is_cs_defined (s)
s = match(Cs(P({(C('\\') / '' + 1) * V(1) + true})),s)
local undef = 'undefined_cs'
return not(token.command_name(token.create(s)) == undef)
end


Then the .tex file.

\documentclass{standalone}

\directlua{dofile('is_def.lua')}

\def\iscsdefined#1{%
\texttt{\string#1}
\csname if\directlua{if is_cs_defined('\luatexluaescapestring{#1}')
then tex.sprint('true') else tex.sprint('false') end}\endcsname
is defined
\else
is not defined
\fi}

\def\test{}

\begin{document}

\iscsdefined{test}

\iscsdefined{\test}

\iscsdefined{testa}

\end{document}


-
Thanks. This will probably work good enough. You'll need to use no expand on the \\par for the example to work though. – Uiy Apr 10 '12 at 12:21
... Or better put it into a Lua file :-) – topskip Apr 10 '12 at 14:03