Most Lisp implementations (at least Allegro, CCL, CMUCL, CLISP, ECL, LispWorks, MKCL) agree that #p"", which has NIL slots for DIRECTORY, FILENAME, TYPE and DEVICE (but the current HOST), represents the current directory (on the current HOST), since overriding the DIRECTORY, FILENAME or TYPE behaves just like looking things up in the current directory.
On the other hand, ABCL agrees with SBCL that this is an error.
Most Lisp implementations (at least Allegro, CCL, CMUCL, CLISP, ECL, LispWorks, MKCL) agree that #p"", which has NIL slots for DIRECTORY, FILENAME, TYPE and DEVICE (but the current HOST), represents the current directory (on the current HOST), since overriding the DIRECTORY, FILENAME or TYPE behaves just like looking things up in the current directory.
On the other hand, ABCL agrees with SBCL that this is an error.