How to check for Lua definitions

Question

When there is \directlua{x = 25} one can say \edef\rgf{\directlua{tex.sprint(x)}}, but when x was never created by \directlua{x = 25}, \directlua{tex.sprint(x)} will fail. Thus something like \@ifundefined{x}{x undefined}{x defined} would be nice. How does one "say this in Lua", please?

May be you 'd try reading some general lua programming documentation first. — خالد حسني, Nov 03 '11 at 14:28
@KhaledHosny: I tried but did not find it there. Any suggestion for better lua-documentation? — Stephen, Nov 03 '11 at 17:56

score 12 · Accepted Answer · answered Nov 03 '11 at 12:30

12

You can do this:

\directlua{tex.sprint( x or 42 ) }

or perhaps

\directlua{
  if x then
    tex.sprint(x)
  % else
    % do something else
  end
}

answered Nov 03 '11 at 12:30

topskip

37,020

1

But see also the question about using luacode and \directlua{} – topskip Nov 03 '11 at 12:31
Thanks, it works! (Upvoted & accepted.) Also your answer to the other question is enlightening, but unfortunately with that question title one does not find it without being told that it is there. – Stephen Nov 03 '11 at 17:52

How to check for Lua definitions

1 Answers1