(vl-file-directory-p name)
The vl-file-directory-p function verifies whether the specified name is an existing folder name.
name specifies a folder name as string. If not a full path is specified, the function searches only the default drawing directory.
The function returns T, if name refers to a folder; nil if it does not.
Examples
: (vl-file-directory-p "sample")
T
: (vl-file-directory-p "mysample")
nil