Detect C or Lua function?

["J. Perkins" <jason@...>]

Is there any way to determine if a function reference stored on the 
stack points to a Lua or a C function? It appears that the only way 
I can differentiate the two is to store my C functions as userdata 
and attach an event table with a "call" tag to actually make the 
call. I'd like to avoid this approach as it must incur a (small I'm 
sure) performance hit. It also seems like it would use more memory 
but I'm not sure about that.

Thanks,
Jason
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