gm2-libs-iso/SeqFile (The GNU Modula-2 Compiler)

#### 4.4.57 gm2-libs-iso/SeqFile ¶

    DEFINITION MODULE SeqFile;

      (* Rewindable sequential files *)

    IMPORT IOChan, ChanConsts;

    TYPE
      ChanId = IOChan.ChanId;
      FlagSet = ChanConsts.FlagSet;
      OpenResults = ChanConsts.OpenResults;

      (* Accepted singleton values of FlagSet *)

    CONST
      (* input operations are requested/available *)
      read = FlagSet{ChanConsts.readFlag};

      (* output operations are requested/available *)
      write = FlagSet{ChanConsts.writeFlag};

      (* a file may/must/did exist before the channel is opened *)
      old = FlagSet{ChanConsts.oldFlag};

      (* text operations are requested/available *)
      text = FlagSet{ChanConsts.textFlag};

      (* raw operations are requested/available *)
      raw = FlagSet{ChanConsts.rawFlag};

    PROCEDURE OpenWrite (VAR cid: ChanId; name: ARRAY OF CHAR;
                         flags: FlagSet; VAR res: OpenResults);
      (*
         Attempts to obtain and open a channel connected to a stored
         rewindable file of the given name.
         The write flag is implied; without the raw flag, text is
         implied.  If successful, assigns to cid the identity of
         the opened channel, assigns the value opened to res, and
         selects output mode, with the write position at the start
         of the file (i.e. the file is of zero length).
         If a channel cannot be opened as required, the value of
         res indicates the reason, and cid identifies the invalid
         channel.
      *)

    PROCEDURE OpenAppend (VAR cid: ChanId; name: ARRAY OF CHAR;
                          flags: FlagSet; VAR res: OpenResults);
      (*
         Attempts to obtain and open a channel connected to a stored
         rewindable file of the given name.  The write and old flags
         are implied; without the raw flag, text is implied.  If
         successful, assigns to cid the identity of the opened channel,
         assigns the value opened to res, and selects output mode,
         with the write position corresponding to the length of the
         file.  If a channel cannot be opened as required, the value
         of res indicates the reason, and cid identifies the invalid
         channel.
      *)

    PROCEDURE OpenRead (VAR cid: ChanId; name: ARRAY OF CHAR;
                        flags: FlagSet; VAR res: OpenResults);
      (* Attempts to obtain and open a channel connected to a stored
         rewindable file of the given name.
         The read and old flags are implied; without the raw flag,
         text is implied.  If successful, assigns to cid the
         identity of the opened channel, assigns the value opened to
         res, and selects input mode, with the read position
         corresponding to the start of the file.
         If a channel cannot be opened as required, the value of
         res indicates the reason, and cid identifies the invalid
         channel.
      *)

    PROCEDURE IsSeqFile (cid: ChanId): BOOLEAN;
      (* Tests if the channel identified by cid is open to a
         rewindable sequential file. *)

    PROCEDURE Reread (cid: ChanId);
      (* If the channel identified by cid is not open to a rewindable
         sequential file, the exception wrongDevice is raised;
         otherwise attempts to set the read position to the
         start of the file, and to select input mode.
         If the operation cannot be performed (perhaps because of
         insufficient permissions) neither input mode nor output
         mode is selected.
      *)

    PROCEDURE Rewrite (cid: ChanId);
      (* If the channel identified by cid is not open to a
         rewindable sequential file, the exception wrongDevice is
         raised; otherwise, attempts to truncate the file to zero
         length, and to select output mode.  If the operation
         cannot be performed (perhaps because of insufficient
         permissions) neither input mode nor output mode is selected.
      *)

    PROCEDURE Close (VAR cid: ChanId);
      (* If the channel identified by cid is not open to a rewindable
         sequential file, the exception wrongDevice is raised;
         otherwise closes the channel, and assigns the value
         identifying the invalid channel to cid.
      *)

    END SeqFile.