Selecting a Mode for a Text File

The same format handler is used for all text files. Specialization for a certain kind of text file (e.g., a Scheme file or C++ file) is provided through a mode. Different modes provide different key bindings and menus within the same basic editor frame.

A mode is implemented by a class derived from mred:basic-mode%. A mode object is attached to a mred:edit% buffer (see section ). Each buffer has only one mode, and each mode object is attached to only one buffer. A mode gets the first opportunity to handle input events from the user, and it is notified about all changes to the buffer. The mode for a buffer can be changed by the user at any time. In mred:frame%, a mode is automatically selected for a new buffer based on the buffer's filename.

A new mode handler is installed with

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

The name argument is a string that names the mode handler; e.g. ``Scheme'' or ``C++''. The ext argument specifies when the handler should be invoked. It can be either:

• A string specifying a file type/extension; e.g. "ss" or "cc".
• A list of types/extensions; e.g. '("ss" "scm").
• 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 buffer argument and returns a mode object. (This mode object will then be installed into the buffer.)

  (mred:find-mode-handler filename) 

returns the mode handler procedure for filename or #f if no handler is found.

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

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