that (if I recall) was documented.... many moons ago and it was used in something like this:
;; carga una aplicacion
(defun appload (app / ext app1)
(setq ext (strcase (vl-filename-extension app))
app1 (strcase (vl-filename-base app)))
(if (or (= ext ".EXE") (= ext ".EXP"))
(if
(vl-some
'(lambda (afn) (= (strcase (vl-filename-base afn)) app1))
(ads))
T
(xload app nil))
(if
(vl-some
'(lambda (afn) (= (strcase (vl-filename-base afn)) app1))
(arx))
T
(arxload app nil))))