When calling remote-host on a closed socket, we get an unrelated type error (on ECL, about NIL not being a FIXNUM).

By analogy to CL:CLOSE, I think it would be better if it returned the remote-host of the last connection, or either return NIL or a specific condition (which would be guaranted to be the same on all implementations).

(let ((s (open "/etc/passwd"))) (close s) (pathname s)) --> #P"/etc/passwd"