Tests for the presence of a directory.
file-directory-p pathname => bool
A pathname, string, or file-stream.
t, the pathname represented by pathname exists and is a directory. If
nil, it either does not exist, or it is not a directory.
file-directory-p tests whether the pathname represents a directory.
CL-USER 70 > (file-directory-p "~")
CL-USER 71 > (file-directory-p ".login")
LispWorks User Guide and Reference Manual - 20 Sep 2017