HELP ISCLOSED                                            John Gibson, July 83

    isclosed(<device>) -> <boolean>;
or
    isclosed(<character_repeater>) -> <boolean>;

Given a device record, or a character-repeater for a device produced by
*DISCIN or *DISCOUT, this procedure returns TRUE if the device (or underlying
device in the procedure case) is closed, e.g.

    discin("myfile") -> char_rep;
    isclosed(char_rep) =>
    ** <false>

    ... (read characters from char_rep until *TERMIN produced)

    isclosed(char_rep) =>
    ** <true>

See also
HELP *ISDEVICE  - recogniser procedure for a device record NOT DONE
HELP *DEVICE    - on I/O device descriptors in POP-11
HELP *DEVNAME   - returns name of file for which device was created
HELP *DISCIN    - creates a character repeater for a file or device
HELP *DISCOUT   - creates a character consumer for a file or device
HELP *POPDEVERR - returns the device for the standard error channel
HELP *POPDEVIN  - returns the device for the standard input channel
HELP *POPDEVOUT - returns the device for the standard output channel
HELP *POPDEVRAW - returns the device for 'raw' terminal input/output
