Opening a File and Selecting a Format Handler

The function mred:edit-file takes a filename and dispatches it to an appropriate format handler. A format handler takes a filename and opens a frame for the user to view or edit the file. If no handler is found for a particular format, then the file is opened as a text file (and an appropriate mode is installed in the editing buffer; see section for more information on modes).

The function mred:open-file lets the user select a filename using mred:get-file, and then passes the name to mred:edit-file.

Both mred:open-file and mred:edit-file return a frame on success or #f otherwise. Both procedures take optional arguments for working with frame groups:

• (mred:edit-file filename group group-handles? make-frame) -- If group is not #f (the default is #f) and group-handles? is not #f (the default is #t), then group's open-file method is called to get a frame for the filename. Otherwise, if a format handler can be found for filename, the handler is invoked to get a frame (passing filename and group to the handler). If no format handler is found, then make-frame is invoked with filename and group; the default make-frame creates an instance of mred:frame%.
• (mred:open-file group) -- Queries the user for a filename and passes it on to mred:edit-file. The group argument is passed on to mred:edit-file; it defaults to #f.

A new format handler is installed with

  (mred:insert-format-handler name ext handler) 

The name argument is a string that names the format handler; e.g. ``Text'' or ``Picture''. The ext argument specifies when the handler should be invoked. It can be either:

• A string specifying a file type/extension; e.g. "txt" or "gif".
• A list of types/extensions; e.g. '("gif" "jpg").
• A predicate procedure that takes a filename and returns a boolean. This predicate can perform arbitrary tests on the filename.

The handler argument is a procedure that takes one argument: a filename. The return value is a frame opened to edit or display the file or #f if there was an error.

  (mred:find-format-handler filename) 

returns a format handler procedure for filename, or #f if no handler can be found.

  (mred:find-named-format-handler name) 

returns a format handler with the name name (a format name, not a filename) or #f if no format by that name exists.