Adds the actor to the top of the actor list, so that commands will be passed to the actor first.
outputs all the actors; the first object in the list is the topmost actor that gets first chance at commands.
f removeactor(interp, the_actor=None) ...
Remove the actor from the actor list. If the actor does not appear on the list, it will be an error. If the actor is None or  then the most recent actor added with ACTOR will be removed.
command. Sets a prefix that will be used as the implicit beginning of filenames in OPENREAD, OPENWRITE, OPENAPPEND, OPENUPDATE, LOAD, and SAVE commands. Logo will put the appropriate separator character (slash for Unix, backslash for DOS/Windows, colon for MacOS) between the prefix and the filename entered by the user. The input to SETPREFIX must be a word, unless it is the empty list, to indicate that there should be no prefix.
@@ Note: LOAD and SAVE don't use this
outputs the current file prefix, or None if there is no prefix. See SETPREFIX.
@@ Note: None instead of  like in ucblogo
command. Opens the named file for reading. The read position is initially at the beginning of the file.
Use ACTOR OPENREAD filename to take all input from the given file.
command. Opens the named file for writing. If the file already existed, the old version is deleted and a new, empty file created.
Use ACTOR OPENWRITE filename to put all output to the given file.
f openappend(filename) ...
command. Opens the named file for writing. If the file already exists, the write position is initially set to the end of the old file, so that newly written data will be appended to it.
Use ACTOR OPENAPPEND filename to put all output to the given file.
outputs a list whose members are the file objects currently open. This list does not include the dribble file, if any.
command. Closes all open files. Abbreviates FOREACH ALLOPEN [CLOSE ?]
ERASEFILE filename ERF filename
command. Erases (deletes, removes) the named file, which should not currently be open.
FILEP filename FILE? filename
predicate, outputs TRUE if a file of the specified name exists and can be read, FALSE otherwise.
See the source for more information.