(dir-open) begin
(dir-open) mkdir "xyzzy"
(dir-open) open "xyzzy"
(dir-open) open returned -1 -- ok
(dir-open) end
--OR--
(dir-open) begin
(dir-open) mkdir "xyzzy"
(dir-open) open "xyzzy"
(dir-open) write "xyzzy" (must return -1, actually -1)
(dir-open) end