[texhax] testing if a control sequence is primitive

[Philip TAYLOR (Webmaster, Ret'd)]

Vafa Khalighi wrote:

> How can you test if a control sequence is primitive or not?

"undefined" is \ifpdfprimitive \undefined \else not \fi a primitive \par
"foo" is \ifpdfprimitive \foo  \else not \fi a primitive \par
"csname" is \ifpdfprimitive \csname  \else not \fi a primitive \par
\end