[luatex] Getting the extra primitives?

[Joseph Wright]

Hello all,

I'm trying to build a simple format including the e-TeX primitives, etc. 
using LuaTeX in TeX Live 2009. Following the manual, I've got

\begingroup\expandafter\expandafter\expandafter\endgroup
\expandafter\ifx\csname directlua\endcsname\relax
\else
   \directlua{tex.enableprimitives('',tex.extraprimitives ())}
\fi

However, this dies horribly:

This is LuaTeX, Version beta-0.40.6-2009110118 (Web2C 2009)
(format.ltx
! LuaTeX error wrong number of arguments
stack traceback:
         [C]: in function 'enableprimitives'
         <\directlua >:1: in main chunk.
l.27   }

?
! Emergency stop.
l.27   }

What did I get wrong?
-- 
Joseph Wright