General ⇒ detecting existence of directories

[scmal]

Is there a way to get LaTeX to detect directories?
\IfFileExists doesn't do it. Minimal example:

\documentclass{article}
\IfFileExists{tmp}{\typeout{*** found ***}}{\typeout{*** not found ***}}
\begin{document}
\end{document}

If tmp is an ordinary file, it is found. If it is a directory, it isn't found. \IfFileExists{tmp/.} isn't found either.
There doesn't appear to be a command \IfDirectoryExists.
Not worth busting a gut over how to do this, but if anyone happens to know, I'd be grateful.

Mike