This document explains how to use abbreviations with JED.

Overview
========

   Abbreviations are possible only when `abbrev' mode is enabled.  It can be
   toggled on and off on a buffer by buffer basis using the `abbrev_mode'
   command.  If it is on, the word `abbrev' will appear on the status line.
   
   Each buffer can have its own abbreviation table or use the ``Global''
   abbreviation table.  If a table has not been defined for a given buffer,
   the ``Global'' table will be used.  Typically, abbreviation tables are
   mode dependent and are usually assigned to the buffer when a mode is
   selected.
   
   An abbreviation table consists of abbreviations as well as a definition
   of characters that are allowed to appear in an abbreviation.  By default,
   the characters that comprise a word are used.  However, this is not
   always what is desired.  For example, one might like to use abbreviations
   like `\be' for `\begin{equation}' in TeX mode.  For this to happen, the
   `\' character should be included in the definition of a word.  The
   examples below should shed more light on this concept.
   
Using Abbreviations
===================

   Once abbreviations have been loaded into the editor (the mechanism is
   explained below), they can be used only if abbrev mode is turned on. This
   mode can be turned on or off by pressing `ESC X' and entering
   `abbrev_mode' at the prompt.  It can also be turned on in a mode hook.

   After entering an abbreviation into the buffer, the abbreviation will be
   expanded if the next character inserted into the buffer immediately after
   the position of the abbreviation is NOT a member of the set of characters
   that is allowed in an abbreviation.  Then the editor scans backward
   across the text until it finds a character that is NOT part of the set of
   special characters.  Finally it attempts to expand the resulting
   abbreviation.

   For example, consider an abbreviation for TeX mode and assume that, when
   the abbreviation table was created, the characters `\', `a-z', `A-Z', and
   `0-9' were specified as the special set of characters that may be used in
   an abbreviation.  This means that `\be' is a valid abbreviation but `@be'
   is not since `@' is not part of the above set.  Suppose that `\be' is the
   abbreviation for `\begin{equation}' and `\be' is entered on a line as

      This is an equation.\be

   At this point nothing happens.  However, if a SPACE is inserted, the
   editor will realize that the space is not part of the special
   abbreviation character set and scan back until another character NOT in
   the set is found.  In this case, it will find a `.'.  From this
   information, it looks up `\be' in the table, finds `\begin{equation}' and
   expands the line to look like:

      This is an equation.\begin{equation}
      
   However, if the line had looked like:
   
      This is an equation\be

   the expansion would have failed because the editor would have scanned
   back to the space character between `an' and `equation' and tried to expand
   `equation\be'.

   Although this sounds complex, it is trivial in practice.
   
The Abbreviation File
======================

   An abbreviation file is simply a file that contains the approrite S-Lang
   function calls to create abbreviation tables and assign abbreviations to
   the tables.  It is loaded like any other S-Lang file, via `evalfile'.
   Simply turning abbreviations on via `abbrev_mode' is sufficient to cause
   JED to load the file.
   
   The variable `Abbrev_File' may be used to specify the name of the
   abbreviation file.  If this variable is undefined, the file name defaults
   to `abbrevs.sl' on non-Unix systems and `.abbrevs.sl' on Unix.  It is
   assumed to reside in the HOME directory.  To specify a different name,
   e.g., `/usr/lib/jed/abbrev.sl', put 
   
      variable Abbrev_File = "/usr/lib/jed/abbrev.sl";
      
   in the JED startup file.
   
   Here is a simple file that is sufficient to create a global abbreviation
   table and a local table for TeX mode:
   
       % abbrevs.sl
       create_abbrev_table ("Global", "");
       define_abbrev ("Global", "adn",    "and");
       define_abbrev ("Global", "amy",    "amy.tch.harvard.edu");
       
       create_abbrev_table ("TeX", "\\A-Za-z0-9");
       define_abbrev ("TeX", "\\be", "\\begin{equation}");
       define_abbrev ("TeX", "\\ee", "\\end{equation}");
       
   Note that `create_abbrev_table' takes 2 parameters.  The first parameter
   is simply the name of the table to be created and the second parameter
   represents the list of characters that are allowed to be in an
   abbreviation.  If the second parameter is the empty string, JED's word
   definition willbe used.  Also note that the backslash character must be
   typed twice for S-Lang to interpret it properly as a backslash character.
   
   The `define_abbrev' function takes 3 parameters: the name of the table,
   the abbreviation, and the expansion for the abbreviation.
   
   If the last character of the expansion is the backspace character
   (\010), then the character that triggered the expansion (e.g., a
   space) will not get inserted.  For example,

       define_abbrev ("TeX", "\\s", "\\section{\010");
     
   is preferable to
   
       define_abbrev ("TeX", "\\s", "\\section{");

   There is really nothing special about an abbreviation file.  The code
   that appears in it can also appear in the JED startup file.
   
   Usually the abbreviation mode is enabled in a hook.  For example, to
   enable abbreviations for TeX mode, use a mode hook of the form:
   
         define tex_mode_hook ()
	 {
	    set_abbrev_mode (1);
	 }

   This way, when TeX mode is enabled, the abbreviation file will be
   automatically loaded if not already loaded and abbrev mode will be turned
   on.  
   

Creating Abbreviations
======================
       
    There are two ways to create abbreviations:
    
       1.  Simply create an abbreviation file by hand.
       2.  Use the `define_abbreviation' function call.
       
    Here the latter method is explained.

    The `define_abbreviation' function uses the abbreviation table
    associated with the current buffer.  If there is none explicitly
    associated with the buffer, the Global table will be used.  If the table
    does not exist, it will be created.  This function will prompt for an
    abbreviation.  It may or may not prompt for an expansion.  If a region
    is defined when `define_abbreviation' is called, the region will be
    taken as the expansion.  This is useful if the expansion consists of of
    more than one word. If a region is not defined, the expansion will
    consist of the previous word as defined by the table.  Only if that
    fails will the user be prompted for an expansion, e.g., this could
    happen if the Point is at the beginning of a line.

    Note that simply using `define_abbreviation' by itself does not
    save the abbreviation for future use.  To save the abbreviations to the
    abbreviation file, use the function `save_abbrevs'.   That is, press
    `ESC X' and enter `save_abbrevs' at the prompt.  The editor will then
    prompt for a file name.  Simply hitting RETURN at the prompt means that
    the `Abbrev_File' definition will be used.  Enter a different filename
    to save them elsewhere.  Note that entering a new file name will not
    change the value of `Abbrev_File'.  Also, this function saves ALL
    currently defined abbreviation tables.