uiop:directory-pathname-p
(uiop:directory-pathname-p pathname)
t when the pathname is in directory form -- non-wild, with no name and no
type, i.e. empty or ending in /. Does not check that the directory
exists (that is uiop:directory-exists-p).
Backend support
Works on all four backends (Lisp source, uiop-pathname.lisp).