[metapost] mpost or luamplib ?

[Olivier Péault]

Hello!
I'm looking for a way to know whether my metapost code is processed by
metapost itself or by luamplib in lualatex. Reading the luamplib code
(which I don't understand!!!) I found that the boolean mplib could do
the job. Is it right ? Can I be sure that if mplib exists and is true,
my code is processed by luamblib ?
Thank you in advance
-- 
Olivier