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<CHAPTER><HEADER>
<TITLE> The Erlang editing mode for Emacs </TITLE>

<PREPARED>Anders Lindgren
    <RESPONSIBLE>
    <DOCNO>
    <APPROVED>
    <CHECKED>
    <DATE>1998-04-20
    <REV>C
    <FILE>emacs-user.sgml</HEADER>

<SECTION>
<TITLE> Introduction </TITLE>


<p>
If you want to get started immediately, the chapters
"<SEEALSO MARKER="#unix_dotemacs">An Example for UNIX</SEEALSO>"
and
"<SEEALSO MARKER="#win_dotemacs">An Example for Windows</SEEALSO>" 
gives you examples of the configurations you need to make to use the
Erlang Editing mode for Emacs.
</P>


<P>
Emacs has been the text editor of choice for programmers in the UNIX
community for many years.  Thanks to a continuing development process,
Emacs is the most powerful editor available.  Today, Emacs runs under
most operating systems including MS-Windows, OS/2, Macintosh, and
several dialects of UNIX.
</P>

<P>
Emacs has editing support for all major programming languages and
quite a lot of minor and unknown languages are supported as well.
</P>

<P>
Emacs is designed to be extendible.  In the unlikely event that you
would miss a feature in Emacs you can add it yourself, or you might
find it in the large number of add-on packages that people all over
the world have written.
</P>

<P>
This book is the documentation to the Emacs package <C> erlang.el</C>.
It provides support for the programming language Erlang.  The package
provides an editing mode with lots of bells and whistles, compilation
support, and it makes it possible for the user to start Erlang shells
that run inside Emacs.
</P>

<P>
Emacs is written by the Free Software Foundation and is part of the
GNU project.  Emacs, including the source code and documentation, is
released under the GNU General Public License.
</P>

<SECTION>

<TITLE>Overview of this Book</TITLE>


<P>This book can be divided into the following sections:

<LIST>
<ITEM><EM> Introduction. </EM>  This part introduces Emacs, the Erlang
editing mode, and this book.  In fact, this is the section you
currently are reading.

<ITEM><EM> The editing mode. </EM> Here the editing mode is described.
The editing mode contains a whole series of features including
indentation, syntax highlighting, electric commands, module name
verification, comment support including paragraph filling, skeletons,
tags support, and much more.

<ITEM><EM> Erlang shells. </EM> How to start and use an Erlang shell
that runs inside Emacs is described in this section.

<ITEM><EM> Compilation support. </EM> This package is capable of
starting compilations of Erlang module.  Should compilation errors
occur Emacs is capable of placing the cursor on the erroneous lines.

<ITEM><EM> Customization. </EM> The Erlang editing mode, like most
Emacs packages, supports extensive customization.  In this chapter we
demonstrate how you can bind your favorite functions to the hotkeys
on the keyboard.  It also introduces the concept of "hooks", a general
method for the user to add code that will be executed when a specific
situation occur, for example when an Erlang file is loaded into Emacs.

</LIST>

<P>
The terminology used in this book is the terminology used in the
documentation to Emacs.  The chapter "<SEEALSO
MARKER="#notation">Notation</SEEALSO>" contains a list of commonly
used words and their meaning in the Emacs world.
</P>

<P>
The intended readers of this book are Emacs users.  The book contains
some examples on how to customize this package using the Emacs
extension language Emacs Lisp.  You can safely skip those sections.
</P>

</SECTION>
</SECTION>

<SECTION>
<TITLE>Emacs</TITLE>

<P>
The first component needed to get this package up and running is, of
course, an Emacs editor.  You can use either the standard Emacs
distribution from FSF or XEmacs, an alternative distribution.  Both
brands have their advantages and disadvantages.
</P>

<P>
Regardless of the brand, it is recommended to use a modern version.
If an old version is used it is possible that some of the features
provided by the editing mode cannot be used.
</P>

<P>
The chapter "<SEEALSO MARKER="#distributions">Emacs
Distributions</SEEALSO>" below contains a short summary on the
differences between the Emacs brands, as well as instructions where to
get the distributions and how to install them.
</P>

</SECTION>

<SECTION>
<TITLE>Installing the Erlang Support Packages</TITLE>

<P>
Once Emacs has been installed, it must be informed about the presence
of the Erlang support packages.
</P>

<P>
If you do not know if the packages have been installed open, an Erlang
source file.  The mode line should contain the word "Erlang".  You can
check the version of the installed package by selecting the "version"
entry in the Erlang menu in Emacs.  Should no Erlang menu be present,
or if the menu does not contain a "Version" item, you are using an old
version.
</P>

<P>
The packages can either be installed for all users by the system
administrator, or each individual user can install it in their own
Emacs setup.  The chapter "<SEEALSO
MARKER="#installation">Installation of the Erlang Editing Mode</SEEALSO>"
 contains a description
on how to install the packages.
</P>

</SECTION>


<SECTION>
<TITLE> The Editing Mode </TITLE>

<P>
The Erlang editing for Emacs provides a number of features described
in this and the following chapters.  The editing mode can work with
either Erlang source mode or Mnesia database rules.  The Erlang
editing mode for Emacs is in Emacs terminology a <EM> Major mode </EM>.
</P>

<P>
When Erlang mode is correctly installed, it is automatically activated
when a file ending in <C>.erl</C> or <C>.hrl</C> is opened in Emacs.
It is possible to activate Erlang mode for other buffers as well.
</P>

<P>
The editing mode provides a menu containing a selection of commands
structured into logical subgroups.  The menu is designed to help new
users get an overview of the features provided by the Erlang packages
while still giving full power to more advanced users.
</P>

<P>
Erlang mode has got a local key map that contains keyboard bindings
for a number of commands.  In the chapter 
"<SEEALSO MARKER="#key_bindings">Custom Key Bindings</SEEALSO>" below,
we will demonstrate how the users can bind their favorite commands to
the local Erlang key map.
</P>

<P>
It is possible for the users to perform advanced customizations by
adding their own functions to the "hook" variables provided by this
package.  This will be described in the "<SEEALSO
MARKER="#customization">Customization</SEEALSO>" chapter below.
</P>


<SECTION>
<TITLE>The Mode</TITLE>

<LIST>
<ITEM><C>M-x erlang-mode RET</C><BR>

<P>
This command activates the Erlang major mode for the current buffer.
When this mode is active the mode line contain the word "Erlang".
</P>

</LIST>
</SECTION>

<SECTION>
<TITLE>The Version</TITLE>

<LIST>
<ITEM><C>M-x erlang-version RET</C><BR>

<P>
This command displays the version number of the Erlang editing mode.
Remember to always supply the version number when asking questions
about Erlang mode.
</P>

<P>
Should this command not be present in your setup (after Erlang mode
has been activated) you probably have a very old version of the Erlang
editing mode.
</P>

</LIST>
</SECTION>

<SECTION>
<TITLE>Module Name Check</TITLE>

<P>
When a file is saved the name in the <C>-module().</C> line is checked
against the file name.  Should they mismatch Emacs can change the
module specifier so that it matches the file name.  By default, the user
is asked before the change is performed.
</P>


<LIST>
<ITEM> <EM> Variable: </EM> <C>erlang-check-module-name</C> (default <C>ask</C>)<BR>

<P>
This variable controls the behavior of the module name check system.
When it is <C>t</C> Emacs changes the module specifier without asking
the user, when it is bound to the atom <C>ask</C> the user is asked.
Should it be <C>nil</C> the module name check mechanism is
deactivated.
</P>

</LIST>
</SECTION>

<SECTION>
<TITLE>Variables</TITLE>

<P>
There are several variables that control the behavior of the
Erlang Editing mode.
</P>

<LIST>
  <ITEM><EM> Variable: </EM> <C>erlang-mode-hook</C><BR>

<P>
Functions to run when the Erlang mode is activated.  See chapter
"<SEEALSO MARKER="#customization">Customization</SEEALSO>" below for
examples.
</P>


  <ITEM><EM> Variable: </EM> <C>erlang-new-file-hook</C><BR>

<P>
Functions to run when a new file is created.  See chapter "<SEEALSO
MARKER="#customization">Customization</SEEALSO>" below for examples.
</P>


  <ITEM><EM> Variable: </EM> <C>erlang-mode-load-hook</C><BR>

<P>
Functions to run when the <C>erlang</C> package is loaded into Emacs.
See chapter "<SEEALSO MARKER="#customization">Customization</SEEALSO>"
below for examples.
</P>

</LIST>

</SECTION>
</SECTION>

<!-- Chapter -->

<SECTION>
<TITLE>Indentation</TITLE>

<P>
The "Oxford Advanced Learners Dictionary of Current English" says the
following about the word "indent":
</P>

<QUOTE>
<P>
   "start (a line of print or writing) farther from
    the margin than the others".
</P>
</QUOTE>

<P>
Possibly the most important feature of an editor designed for
programmers is the ability to indent a line of code in accordance
with the structure of the programming language.
</P>

<P>
The Erlang mode does, of course, provide this feature.  The layout
used is based on the common use of the language.
</P>

<P>
It is strongly recommend to use this feature and avoid to indent lines
in a nonstandard way.  Some motivations are:
</P>

<LIST>

  <ITEM> Code using the same layout is easy to read and maintain.

  <ITEM> The indentation features can be used to reindent large sections of a
file.  If some lines use nonstandard indentation they will be
reindented.

  <ITEM> Since several features of Erlang mode is based on the
standard layout they might not work correctly if a nonstandard layout
is used.  For example, the movement commands (described in chapter
"<SEEALSO MARKER="#func_cmds">Function and clause commands</SEEALSO>"
below) will not work unless the function headers start in the first
column.

</LIST>

<SECTION>
<TITLE>The Layout</TITLE>

<P>
The basic layout is that the clause headers start in the first column,
and the bodies of clauses and complex expressions (e.g. "case" and
"if") are indented more that the surrounding code.  For example:
</P>

<CODE>
remove_bugs([]) ->
    [];
remove_bugs([X | Xs])
    case X of
        bug ->
            test(Xs);
        _ ->
            [X | test(Xs)]
    end.
</CODE>


<LIST>

<ITEM> <EM> Variable: </EM> <C>erlang-indent-level</C><BR>

<P>
The depth of the indentation is controlled by the variable
"erlang-indent-level", see section "<SEEALSO
MARKER="#customization">Customization</SEEALSO>" below.
</P>

</LIST>

</SECTION>

<SECTION>
<TITLE>Indentation of comments</TITLE>

<P>
Lines containing comment are indented differently depending on the
number of %-characters used:
</P>

<LIST>
<ITEM> Lines with one %-character is indented to the right of the
code.  The column is specified by the variable <C>comment-column</C>,
by default column 48 is used.

<ITEM> Lines with two %-characters will be indented to the same depth
as code would have been in the same situation.

<ITEM> Lines with three of more %-characters are indented to the left
margin.

</LIST>

<P>
<EM> Example: </EM>
</P>

<CODE>
%%%
%%% Function: remove_bugs
%%%

remove_bugs([]) ->
    [];
remove_bugs([X | Xs])
    case X of
        bug ->                                  % Oh no, a bug!
                                                % Remove it.
            test(Xs);
        %% This element is not a bug, let's keep it.
        _ ->
            [X | test(Xs)]
    end.
</CODE>
</SECTION>

<SECTION>

<TITLE>Indentation commands</TITLE>

<P>The following command are directly available for indentation.</P>

<LIST>
<ITEM><C>TAB</C> (<C>erlang-indent-command</C>)<BR>

<P>Indent the current line of code.</P>


<ITEM><C>M-C-\</C> (<C>indent-region</C>)<BR>

<P>Indent all lines in the region.</P>


<ITEM><C>M-l</C> (<C>indent-for-comment</C>)<BR>

<P>
Insert a comment character to the right of the code on the line (if
any).  The comment character is placed in the column specified by the
variable "comment-column", by default column 48 is used.
</P>


<ITEM><C>C-c C-q</C> (<C>erlang-indent-function</C>)<BR>

<P>
Indent the current Erlang function.
</P>


<ITEM><C> M-x erlang-indent-clause RET</C><BR>

<P>
Indent the current Erlang clause.</P>


<ITEM><C>M-x erlang-indent-current-buffer RET</C><BR>

<P>
Indent the entire buffer.
</P>

</LIST>

</SECTION>
<SECTION>
<MARKER ID="customization">
<TITLE>Customization</TITLE>

<P>
The most common customization of the indentation system is to bind the
return key to <C>newline-and-indent</C>.  Please see the chapter
"<SEEALSO MARKER="#key_bindings">Custom Key Bindings</SEEALSO>"
below for an example.
</P>

<P>
There are several Emacs variables that control the indentation system.
</P>

<LIST>

<ITEM><EM> Variable: </EM> <C>erlang-indent-level</C>  (default 4)<BR>

<P>
The amount of indentation for normal Erlang functions and complex
expressions.  Should, for example, the value of this variable be 2 the
example above would be indented like:
</P>

<CODE>
remove_bugs([]) ->
  [];
remove_bugs([X | Xs])
  case X of
    bug ->
      test(Xs);
    _ ->
      [X | test(Xs)]
  end.
</CODE>


<ITEM><EM> Variable: </EM> <C>erlang-indent-guard</C> (default 2)<BR>

<P>The amount of indentation for Erlang guards.</P>


<ITEM><EM> Variable: </EM> <C>erlang-argument-indent</C> (default 2)<BR>

<P>The amount of indentation for function calls that span several lines.</P>

<P>
<EM> Example: </EM>
</P>

<CODE>
foo() ->
    a_very_long_function_name(
      AVeryLongVariableName),
</CODE>


<ITEM><EM> Variable: </EM> <C>erlang-tab-always-indent</C>
(default <C>t</C>)<BR>

<P>
When non-<C>nil</C> the <C>TAB</C> command always indents the line
(this is the default).  When <C>nil</C>, the line will be indented
only when the point is in the beginning of any text on the line,
otherwise it will insert a tab character into the buffer.
</P>

</LIST>

</SECTION>
</SECTION>


<!-- CHAPTER -->

<SECTION>

<TITLE> General Commands </TITLE>

<P>
This chapter contains a group of commands that are not found in any
other category.  Unlike most other books we do not have a chapter named
"Miscellaneous xxx" found at the end of most books.  This chapter is
placed near the beginning to reflect the importance and usefulness of
the commands.
</P>

<SECTION>

<TITLE>Filling comments</TITLE>

<P>
How many times have you edited a section of text in a comment only to
wind up with a unevenly formatted paragraph?  Or even worse, have you
ever decided not to edit a comment just because the formatting would
look bad?
</P>

<P>
When editing normal text in text mode you can let Emacs reformat the
text by the <C>fill-paragraph</C> command.  This command will not work
for comments since it will treat the comment characters as words.
</P>

<P>
The Erlang editing mode provides a command that known about the Erlang
comment structure and can be used to fill text paragraphs in comments.
</P>


<LIST>
<ITEM><C>M-q</C>  (<C>erlang-fill-paragraph</C>)<BR>

Fill the text in an Erlang comment.  This command known about the
Erlang comment characters.  The column to perform the word wrap is
defined by the variable <C>fill-column</C>.

</LIST>

<P>
<EM> Example: </EM>
</P>

<P>
For the sake of this example, let's assume that <C>fill-column</C> is set
to column 30.  Assume that we have an Erlang comment paragraph on the
following form:
</P>

<CODE>
%% This is just a test to show
%% how the Erlang fill 
%% paragraph command works.
</CODE>

<P>
Assume that you would add the words "very simple" before the word
"test":
</P>

<CODE>
%% This is just a very simple test to show
%% how the Erlang fill
%% paragraph command works.
</CODE>

<P>
Clearly, the text is badly formatted.  Instead of formatting this
paragraph line by line, let's try <C>erlang-fill-paragraph</C> by
pressing <C>M-q</C>.  The result is:
</P>

<CODE>
%% This is just a very simple
%% test to show how the Erlang
%% fill paragraph command
%% works.
</CODE>

<P>
As you can see the paragraph is now evenly formatted.
</P>

</SECTION>

<SECTION>
<TITLE> Creating Comments </TITLE>

<P>
In Erlang it is possible to write comments to the right of the code.
The indentation system described in the chapter "Indentation" above is
able to indent lines containing only comments, and gives support for
end-of-the-line comments.
</P>

<LIST>

<ITEM><C>M-;</C> (<C>indent-for-comment</C>)<BR>

This command will create, or reindent, a comment to the right of the
code.  The variable <C>comment-column</C> controls the placement of the
comment character.

</LIST>
</SECTION>

<SECTION>

<TITLE> Comment Region </TITLE>

<P>
The standard command <C>comment-region</C> can be used to comment out
all lines in a region.  To uncomment the lines in a region precede
this command with <C>C-u</C>.
</P>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Syntax Highlighting</TITLE>

<P>
It is possible for Emacs to use colors when displaying a buffer.  By
"syntax highlighting", we mean that syntactic components, for example
keywords and function names, will be colored.
</P>

<P>
The basic idea of syntax highlighting is to make the structure of a
program clearer.  For example, the highlighting will make it easier to
spot simple bugs.  Have not you ever written a variable in lower-case
only?  With syntax highlighting a variable will colored while atoms
will be shown with the normal text color.
</P>

<P>
The syntax highlighting can be activated from the Erlang menu.  There
are four different alternatives:
</P>

<LIST>

<ITEM> Off: Normal black and white display.

<ITEM> Level 1: Function headers, reserved words, comments, strings, quoted
atoms, and character constants will be colored.

<ITEM> Level 2: The above, attributes, Erlang bif:s, guards, and words
in comments enclosed in single quotes will be colored.

<ITEM> Level 3: The above, variables, records, and macros will be colored.
(This level is also known as the Christmas tree level.)

</LIST>


<P>
The syntax highlighting is based on the standard Emacs package
"font-lock".  It is possible to use the font-lock commands and
variables to enable syntax highlighting.  The commands in question
are:
</P>

<LIST>
<ITEM><C>M-x font-lock-mode RET</C><BR>

<P>
This command activates syntax highlighting for the current buffer.
</P>


<ITEM><C>M-x global-font-lock-mode RET</C><BR>

<P>
Activate syntax highlighting for all buffers.
</P>

</LIST>

<P>
The variable <C>font-lock-maximum-decoration</C> is used to specify
the level of highlighting.  If the variable is bound to an integer,
that level is used; if it is bound to <C>t</C> the highest possible
level is used.  (It is possible to set different levels for different
editing modes; please see the font-lock documentation for more
information.)
</P>

<P>
It is possible to change the color used.  It is even possible to use
bold, underlined, and italic fonts in combination with colors.
However, the method to do this differs between Emacs and XEmacs; and
between different versions of Emacs.  For Emacs 19.34, the variable
<C>font-lock-face-attributes</C> controls the colors.  For version 20 of
Emacs and XEmacs, the faces can be defined in the interactive custom
system.
</P>

<SECTION>
<MARKER ID="font-lock">
<TITLE>Customization</TITLE>

<P>
Font-lock mode is activated in different ways in different versions of
Emacs.  For modern versions of GNU Emacs place the following lines in
your <C>~/.emacs</C> file:
</P>

<CODE>
(setq font-lock-maximum-decoration t)
(global-font-lock-mode 1)
</CODE>

<!-- TODO: Check this -->
<P>
For modern versions of XEmacs the following code can be used:
</P>

<CODE>
(setq auto-font-lock-mode 1)
</CODE>

<P>
For older versions of Emacs and XEmacs, font-lock mode must be
activated individually for each buffer.  The following will add a
function to the Erlang mode hook that activates font-lock mode for all
Erlang buffers.
</P>

<CODE>
(defun my-erlang-font-lock-hook ()
  (font-lock-mode 1))

(add-hook 'erlang-mode-hook 'my-erlang-font-lock-hook)
</CODE>

</SECTION>

<SECTION>
<TITLE>Known Problems</TITLE>

<P>
Emacs has one problem with the syntactic structure of Erlang, namely
the <C>$</C> character.  The normal Erlang use of the $ character is
to denote the ASCII value of a character, for example:
</P>

<CODE>
ascii_value_of_a() -> $a.
</CODE>

<P>
In order to get the font-lock mechanism to work for the next example,
the $ character must be marked as an "escape" character that changes
the ordinary Emacs interpretation of the following double-quote
character.
</P>

<CODE>
ascii_value_of_quote() -> $".
</CODE>


<P>
The problem is that Emacs will also treat the <C>$</C> character as an
"escape" character at the end of strings and quoted atoms.
Practically, this means that Emacs will not detect the end of the
following string:
</P>
      
<CODE>
the_id() -> "$id: $".
</CODE>

<P>
Fortunately, there are ways around this.  From Erlang's point of view
the following two strings are equal: <C>"test$"</C> and
<C>"test\$"</C>.  The <C>\</C>-character is also marked as an Emacs "escape"
character, hence it will change the Emacs interpretation of the
<C>$</C>-character.
</P>

<P>
This work-around cannot always be used. For example, when the string is
used by an external version control program.  In this situation we can
try to avoid placing the <C>$</C>-character at the end of the string, for
example:
</P>

<CODE>
-vsn(" $Revision: 1.1 $ ").
</CODE>

<P>
Should this not be possible we can try to create an artificial end of
the string by placing an extra quote sign in the file. We do this as a
comment:
</P>

<CODE>
-vsn("$Revision: 1.1 $").    % "
</CODE>


<P>
The comment will be ignored by Erlang since it is a comment.  From
Emacs point of view the comment character is part of the string.
</P>

<P>
This problem is a generic problem for languages with similar syntax.
For example, the major mode for Perl suffers from the same problem.
</P>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Electric Commands</TITLE>

<P>
An "electric" command is a character that in addition to just
inserting the character performs some type of action.  For example the
";" character is typed in a situation where is ends a function clause
a new function header is generated.
</P>

<P>
Since some people find electric commands annoying they can be
deactivated, see section "<SEEALSO MARKER="#unplug_elec">Unplugging
the Electric Commands</SEEALSO>" below.
</P>

<SECTION>

<TITLE>The Commands</TITLE>

<LIST>
<ITEM><C> ; </C> (<C>erlang-electric-semicolon</C>)<BR>

<P>
Insert a semicolon.  When ending a function or the body of a
case clause, and the next few lines are empty, the special action will
be performed.  For functions, a new function header will be generated
and the point will be placed between the parentheses.  (See the
command <C>erlang-clone-arguments</C>.)  For other clauses the string
"<C> -&gt;</C>" will be inserted and the point will be placed in from of
the arrow.
</P>

<ITEM><C> , </C> (<C>erlang-electric-comma</C>)<BR>

<P>
Insert a comma. If the point is at the end of the line
and the next few lines are empty, a new indented line is created.
</P>

<ITEM><C> > </C> (<C>erlang-electric-arrow</C>)<BR>

<P>
Insert a <C>></C> character.  If it is inserted at the end of a line
after a <C>-</C> character so that an arrow "<C>-></C>" is being
formed, a new indented line is created. This requires that the next
few lines are empty.

<ITEM><C> RET </C> (<C>erlang-electric-newline</C>)<BR>

<P>
The special action of this command is normally off by default.  When
bound to the return key the following line will be indented.  Should
the current line contain a comment the initial comment characters will
be copied to the new line.  For example, assume that the point is at
the end of a line (denoted by "<C>&lt;point&gt</C>" below).
</P>

<CODE>
    %% A comment<point>
</CODE>

<P>
When pressing return (and <C>erlang-electric-newline</C> is active)
the result will be:
</P>

<CODE>
    %% A comment
    %% <point>
</CODE>

<P>
This command has a second feature.  When issued directly after another
electric command that created a new line this command does nothing.
The motivation is that it is in the fingers of many programmers to hit
the return key just when they have, for example, finished a function
clause with the <C>;</C> character.  Without this feature both the
electric semicolon and this command would insert one line each which
is probably not what the user wants.
</P>

</LIST>

</SECTION>

<SECTION>
<TITLE> Undo </TITLE>

<P>
All electric command will set an undo marker after the initial
character has been inserted but before the special action has been
performed.  By executing the undo command (<C>C-x u</C>) the effect of
the special action will be undone while leaving the character.
Execute undo a second time to remove the character itself.
</P>

</SECTION>

<SECTION>
<TITLE> Variables </TITLE>

<P>
The electric commands are controlled by a number of variables.
</P>

<LIST>
  <ITEM><C>erlang-electric-commands</C><BR>

<P>
This variable controls if an electric command is active or not.  This
variable should contain a list of electric commands to be active.  To
activate all electric commands bind this variable to the atom
<C>t</C>.
</P>


  <ITEM><C>erlang-electric-newline-inhibit</C><BR>

<P>
When non-<C>nil</C> when <C>erlang-electric-newline</C> should do
nothing when preceded by a electric command that is member of the
list <C>erlang-electric-newline-inhibit-list</C>.
</P>


  <ITEM><C>erlang-electric-newline-inhibit-list</C><BR>

<P>
A list of electric commands.  The command
<C>erlang-electric-newline</C> will do nothing when preceded by a
command in this list, and the variable
<C>erlang-electric-newline-inhibit</C> is non-<C>nil</C>.
</P>

  <ITEM><C>erlang-electric-X-criteria</C><BR>

<P>
There is one variable of this form for each electric command.  The
variable is used to decide if the special action of an electric
command should be used.  The variable contains a list of criteria
functions that are called in the order they appear in the list.
			</p>
<p>
If a criteria function returns the atom <C>stop</C> the special
action is not performed.

If it returns a non-<C>nil</C> value the action is taken.

If it returns <C>nil</C> the next function in the list is called.

Should no function in the list return
a non-<C>nil</C> value the special action will not be executed.

Should the list contain the atom <C>t</C> the special action is performed
(unless a previous function returned the atom <C>stop</C>).
</P>


  <ITEM><C>erlang-next-lines-empty-threshold</C> (default 2)<BR>

<P>
Should the function <C>erlang-next-lines-empty-p</C> be part of a
criteria list of an electric command (currently semicolon, comma, and
arrow), this variable controls the number of blank lines required.
</P>

</LIST>

</SECTION>

<SECTION>
<MARKER ID="unplug_elec">
<TITLE> Unplugging the Electric Commands </TITLE>

<P>
To disable all electric commands set the variable
<C>erlang-electric-commands</C> to the empty list.  In short, place the
following line in your <C>~/.emacs</C> file:
</P>

<CODE>
(setq erlang-electric-commands '())
</CODE>

</SECTION>

<SECTION>

<TITLE> Customizing the Electric Commands </TITLE>

<P>
To activate all electric commands, including
<C>erlang-electric-newline</C>, add the following line to your
<C>~/.emacs</C> file:
</P>

<CODE>
(setq erlang-electric-commands t)
</CODE>

</SECTION>
</SECTION>


<!-- CHAPTER -->

<SECTION>
<MARKER ID="func_cmds">
<TITLE> Function and Clause Commands </TITLE>

<P>
The Erlang editing mode has a set of commands that are aware of the
Erlang functions and function clauses.  The commands can be used to
move the point (cursor) to the end of, or to the beginning of Erlang
functions, or to jump between functions.  The region can be placed
around a function. Function headers can be cloned (copied).
</P>


<SECTION>
<TITLE> Movement Commands </TITLE>

<P>
There is a set of commands that can be used to move the point to
the beginning or the end of an Erlang clause or function.  The
commands are also designed for movement between Erlang functions and
clauses.
</P>

<LIST>

  <ITEM><C> C-a M-a </C> (<C>erlang-beginning-of-function</C>)<BR>

<P>
Move the point to the beginning of the current or preceding Erlang
function.  With an argument skip backwards over this many Erlang
functions.  Should the argument be negative the point is moved to the
beginning of a function below the current function.
</P>

<P>
This function returns <C>t</C> if a function was found, <C>nil</C>
otherwise.
</P>


  <ITEM><C> M-C-a </C>  (<C>erlang-beginning-of-clause</C>)<BR>

<P>
As above but move point to the beginning of the current or preceding
Erlang clause.
</P>

<P>
This function returns <c>t</c> if a clause was found, <C>nil</C> otherwise.
</P>

  <ITEM><C> C-a M-e </C> (<C>erlang-end-of-function</C>)<BR>

<P>
Move to the end of the current or following Erlang function.  With an
argument to it that many times.  Should the argument be negative move
to the end of a function above the current functions.
</P>


  <ITEM><C> M-C-e </C>  (<C>erlang-end-of-clause</C>)<BR>

<P>
As above but move point to the end of the current or following Erlang
clause.
</P>

</LIST>

<P>
When one of the movement commands is executed and the point is already
placed at the beginning or end of a function or clause, the point is
moved to the previous/following function or clause.
</P>

<P>
When the point is above the first or below the last function in the
buffer, and an <c>erlang-beginning-of-</c>, or <c>erlang-end-of-</c>
command is issued, the point is moved to the beginning or to the end
of the buffer, respectively.
<P>


<SECTION>
<TITLE> Development Tips </TITLE>

<P>
The functions described above can be used both as user commands and
called as functions in programs written in Emacs Lisp.
</P>

<P>
<EM> Example: </EM>
</P>

<P>
The sequence below will move the point to the beginning of the current
function even if the point should already be positioned at the
beginning of the function:
</P>

<CODE>
    (end-of-line)
    (erlang-beginning-of-function)
</CODE>


<P>
<EM> Example: </EM>
</P>

<P>
To repeat over all the function in a buffer the following code can be
used.  It will first move the point to the beginning of the buffer,
then it will locate the first Erlang function.  Should the buffer
contain no functions at all the call to
<C>erlang-beginning-of-function</C> will return <C>nil</C> and hence
the loop will never be entered.
</P>

<CODE>
    (goto-char (point-min))
    (erlang-end-of-function 1)
    (let ((found-func (erlang-beginning-of-function 1)))
       (while found-func
         ;; Do something with this function.
         ;; Go to the beginning of the next function.
         (setq found-func (erlang-beginning-of-function -1))))
</CODE>

</SECTION>
</SECTION>

<SECTION>

<TITLE>Region Commands</TITLE>

<LIST>

  <ITEM><C> C-c M-h </C> (<C>erlang-mark-function</C>)<BR>

<P>
Put the region around the current Erlang function.  The point is
placed in the beginning and the mark at the end of the function.
</P>

  <ITEM><C> M-C-h </C>  (<C>erlang-mark-clause</C>)<BR>

<P>
Put the region around the current Erlang clause.  The point is
placed in the beginning and the mark at the end of the function.
</P>

</LIST>
</SECTION>

<SECTION>

<TITLE>Function Header Commands</TITLE>

<LIST>
  <ITEM><C> C-c C-j </C> (<C>erlang-generate-new-clause</C>)<BR>

<P>
Create a new clause in the current Erlang function.  The point is
placed between the parentheses of the argument list.
</P>

  <ITEM><C> C-c C-y </C> (<C>erlang-clone-arguments</C>)<BR>

<P>
Copy the function arguments of the preceding Erlang clause.  This
command is useful when defining a new clause with almost the same
argument as the preceding.
</P>

</LIST>

</SECTION>

<SECTION>
<TITLE>Limitations</TITLE>

<P>
Several clauses are considered to be part of the same Erlang function
if they have the same name.  It is possible that in the future the
arity of the function also will be checked.

To avoid to perform a full parse of the entire buffer the functions
described in the chapter only look at lines where the function starts
in the first column.  This means that the commands does not work
properly if the source code contain non-standardized indentation.

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>

<TITLE>Skeletons</TITLE>

<P>
A skeleton is a piece of pre-written code that can be inserted into
the buffer.  Erlang mode comes with a set of predefined skeletons
ranging from simple <C>if</C> expressions to stand-alone applications.
</P>

<P>
The skeletons can be accessed either from the Erlang menu of from
commands named <C>tempo-template-erlang-</C>X.
</P>

<P>
The skeletons is defined using the standard Emacs package "tempo".  It
is possible to define new skeletons for your favorite erlang
constructions.
</P>

<SECTION>

<TITLE>Commands</TITLE>

<LIST>

  <ITEM><C> C-c M-f </C> (<C>tempo-forward-mark</C>)
  <ITEM><C> C-c M-b </C> (<C>tempo-backward-mark</C>)

<P>
In a skeleton certain positions are marked.  These two commands
move the point between such positions.
</P>

</LIST>
</SECTION>

<SECTION>

<TITLE>Predefined Skeletons</TITLE>

<LIST>

  <ITEM>Simple skeletons: If, Case, Receive, Receive After, Receive Loop.

  <ITEM>Header elements: Module, Author.

<P>
These commands inserts lines on the form <C>-module(</C>xxx<C>).</C> and
<C>-author('my@home').</C>.  They can be used directly, but are also used
as part of the full headers described below:
</P>


  <ITEM>Full Headers: Small, Medium, and Large Headers

<P>
These commands generate three variants of file headers.
</P>

</LIST>

<P>
The following skeletons will complete almost ready-to-run modules.

<LIST>

  <ITEM>Small Server

  <ITEM>application

  <ITEM>Supervisor

  <ITEM>Supervisor Bridge

  <ITEM>gen_server

  <ITEM>gen_event

  <ITEM>gen_fsm

</LIST>
</SECTION>

<SECTION>
<TITLE>Defining New Skeletons</TITLE>

<P>
It is possible to define new Erlang skeletons.  The skeletons are
defined using the standard package "tempo".  The skeleton is described
using the following variables:
</P>

<LIST>

  <ITEM><C>erlang-skel-</C>X  (Where X is the name of this skeleton.)<BR>

<P>
Each skeleton is described by a variable.  It contains a list of Tempo
rules.  See below for two examples of skeleton definitions.  See the
Tempo Reference Manual for a complete description of tempo rules.
</P>

  <ITEM><C>erlang-skel</C><BR>

<P>
This variable describes all Erlang skeletons.  It is used to define
the skeletons and to add them to the Erlang menu.  The variable is a
list where is each entry is either the empty list, representing a
vertical bar in the menu, or a list on the form:
</P>

<CODE>
   (Menu-name tempo-name erlang-skel-X)
</CODE>

<P>
The Menu-name is name to use in the menu.  A named function is created
for each skeleton, it is <C>tempo-template-erlang-</C>tempo-name.
Finally, <C>erlang-skel-</C>X is the name of the variable describing the
skeleton.
</P>

<P>
The best time to change this variable is right after the Erlang mode
has been loaded but before it has been activated.  See the "Example"
section below.
</P>

</LIST>

<SECTION>

<TITLE>Examples</TITLE>

<P>
Below is two example on skeletons and one example on how to add an
entry to the <C>erlang-skel</C> variable.  Please see the Tempo
reference manual for details about the format.
</P>


<P>
<EM> Example 1: </EM>
</P>

<P>
The "If" skeleton is defined by the following variable
(slightly rearranged for pedagogical reasons):
</P>

<CODE>
(defvar erlang-skel-if
  '((erlang-skel-skip-blank)   ;;  1
    o                          ;;  2
    >                          ;;  3
    "if"                       ;;  4
    n>                         ;;  5
    p                          ;;  6
    " ->"                      ;;  7
    n>                         ;;  8
    p                          ;;  9
    "ok"                       ;; 10
    n>                         ;; 11
    "end"                      ;; 12
    p))                        ;; 13
</CODE>

<P>
Each line describes an action to perform:
</P>

<LIST>

  <ITEM> 1:  This is a normal function call.  Here we skip over any space
characters after the point.  (If we do not they will end up after the
skeleton.)

  <ITEM> 2:  This means "Open Line", i.e. split the current line at the
point, but leave the point on the end of the first line.

  <ITEM> 3:  Indent Line.  This indents the current line.

  <ITEM> 4:  Here we insert the string <C>if</C> into the buffer

  <ITEM> 5, 8, 11:  Newline and indent.

  <ITEM> 6, 9, 13: Mark these positions as special.  The point will be
placed at the position of the first <C>p</C>.  The point can later be
moved to the other by the <C>tempo-forward-mark</C> and
<C>tempo-backward-mark</C> described above.

  <ITEM> 7, 10, 12: These insert the strings "<C> -></C>",
"<C>ok</C>", and "<C>end</C>", respectively.

</LIST>

<P>
<EM> Example 2: </EM>
</P>

<P>
This example contains very few entries.  Basically, what it does is to
include other skeletons in the correct place.
</P>

<CODE>
(defvar erlang-skel-small-header
  '(o                                         ;; 1
    (erlang-skel-include erlang-skel-module   ;; 2
                         erlang-skel-author)
    n                                         ;; 3
    (erlang-skel-include erlang-skel-compile  ;; 4
			 erlang-skel-export   ;; 5
			 erlang-skel-vc)))    ;; 6
</CODE>

<P>
The lines performs the following actions:
</P>

<LIST>
  <ITEM> 1: "Open Line" (see example 1 above).

  <ITEM> 2: Insert the skeletons <C>erlang-skel-module</C> and
<C>erlang-skel-compile</C> into the buffer.

  <ITEM> 3: Insert one empty line.

  <ITEM> 4: Insert three more skeletons.

</LIST>

<P>
<EM> Example 3: </EM>
</P>

<P>
Here we assume that we have defined a new skeleton named
<C>erlang-skel-example</C>.  The best time to add this skeleton to the
variable <C>erlang-skel</C> is when Erlang mode has been loaded but
before it has been activated.  We define a function that adds two
entries to <C>erlang-skel</C>, the first is <C>()</C> that represent a
divisor in the menu, the second is the entry for the <C>Example</C>
skeleton.  We then add the function to the <C>erlang-load-hook</C>, a
hook that is called when Erlang mode is loaded into Emacs.

<CODE>
(defun my-erlang-skel-hook ()
  (setq erlang-skel
	(append erlang-skel
                '(()
                  ("Example" "example" erlang-skel-example)))))

(add-hook 'erlang-load-hook 'my-erlang-skel-hook)
</CODE>

</SECTION>
</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>

<TITLE>Manual Pages</TITLE>

<P>
The UNIX version of Erlang tools contain a set of manual pages that
can be accessed by the standard UNIX command "man".  The Erlang mode
place a list of all available manual pages in the "Erlang" menu.
</P>

<P>
Unfortunately this feature is not available in the Windows version of
the Erlang editing mode since the Erlang tools are not delivered with
the manual pages.
</P>

<SECTION>
<TITLE> The Menu </TITLE>

<P>
In the Erlang menu a list of all Erlang manual pages can be found.
The menu item "Man Pages".  The sub-menu to this menu item contains a
list of categories, normally "Man - Commands" and "Man - Modules".
Under these is a menu containing the names of the man pages.
Should this menu be to large it is split alphabetically into a number
of sub-menus.
</P>

<P>
The menu item "Man - Function" is capable of finding the man page of a
named Erlang function.  This commands understands the
<C>module:function</C> notation.  This command defaults to the name under
the point.  Should the name not contain a module name the list of
imported modules is searched.
</P>

</SECTION>

<SECTION>
<TITLE>Customization</TITLE>

<P>
The following variables control the manual page feature.
</P>

<LIST>

  <ITEM><C>erlang-man-dirs</C><BR>

<P>
This variable is a list representing the sub-menu to the "Man Pages"
menu item in the Erlang menu.  Each element is a list with three
elements.  The first is the name of the menu, e.g. "Man - Modules" or
"Man - Local Stuff".  The second is the name of a directory.  The
third is a flag that control the interpretation of the directory.
When <C>nil</C> the directory is treated as an absolute path, when
non-<C>nil</C> it is taken as relative to the directory named in the
variable <C>erlang-root-dir</C>.
</P>


  <ITEM><C>erlang-man-max-menu-size</C><BR>

<P>
The maximum number of menu items in a manual page menu.  If the number
of manual pages would be more than this variable the menu will be
split alphabetically into chunks each not larger than the value of
this variable.
</P>

</LIST>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Tags</TITLE>

<P>
Tags is a standard Emacs package used to record information about
source files in large development projects.  In addition to listing
the files of a project, a tags file normally contains information
about all functions and variables that are defined.  By far, the most
useful command of the tags system is its ability to find the
definition of functions in any file in the project.  However the Tags
system is not limited to this feature, for example, it is possible to
do a text search in all files in a project, or to perform a
project-wide search and replace.
</P>

<SECTION>
<TITLE>Creating a TAGS file</TITLE>

<P>
In order to use the Tags system a file named <C>TAGS</C> must be created.
The file can be seen as a database over all functions, records, and
macros in all files in the project.  The <C>TAGS</C> file can be created
using to different methods for Erlang.  The first is the standard
Emacs utility "etags", the second is by using the Erlang module
<C>tags</C>.
</P>

</SECTION>

<SECTION>
<TITLE>The etags utility</TITLE>
<!-- <TITLE>The <C>etags</C> utility</TITLE> -->

<P>
The <C>etags</C> is a program that is part of the Emacs distribution.  It
is normally executed from a command line, like a unix shell or a DOS
box.
</P>

<P>
The <C>etags</C> program of fairly modern versions of Emacs and XEmacs
has native support for Erlang.  To check if your version does include
this support, issue the command <C>etags --help</C> at a the command
line prompt.  At the end of the help text there is a list of supported
languages.  Unless Erlang is a member of this list I suggest that you
should upgrade to a newer version of Emacs.
</P>

<P>
As seen in the help text -- unless you have not upgraded your Emacs yet
(well, what are you waiting around here for?  Off you go and upgrade!)
-- <C>etags</C> associate the file extensions <C>.erl</C> and
<C>.hrl</C> with Erlang.
</P>

<P>
Basically, the <C>etags</C> utility is runed using the following form:
</P>

<CODE>
    etags file1.erl file2.erl
</CODE>

<P>
This will create a file named <C>TAGS</C> in the current directory.
</P>

<P>
The <C>etags</C> utility can also read a list of files from its standard
input by supplying a single dash in place of the file names.  This
feature is useful when a project consists of a large number of files.
The standard UNIX command <C>find</C> can be used to generate the list of
files, e.g:
</P>

<CODE>
    file . -name "*.[he]rl" -print | etags -
</CODE>

<P>
The above line will create a <C>TAGS</C> file covering all the Erlang
source files in the current directory, and in the subdirectories
below.
</P>

<P>
Please see the GNU Emacs Manual and the etags man page for more info.
</P>


<P>
The code implementing the Erlang support for the <C>etags</C> program has
been donated to the Free Software Foundation by the company Anders
Lindgren Development.
</P>

</SECTION>

<SECTION>
<TITLE>The tags Erlang module</TITLE>
<!-- <TITLE>The <C>tags</C> Erlang module</TITLE> -->

<P>
One of the tools in the Erlang distribution is a module named
<C>tags</C>.  This tool can create a <C>TAGS</C> file from Erlang
source files.
</P>

<P>
The following are examples of useful functions in this module.  Please
see the reference manual on tags for details.
</P>

<LIST>

  <ITEM><C>tags:file('foo.erl').</C><BR>

<P>
Create a <C>TAGS</C> file for the file "foo.erl".
</P>

  <ITEM><C>tags:subdir('src/project/', [{outfile, 'project.TAGS'}]).</C><BR>

<P>
Create a tags file containing all Erlang source files in the directory
<C>"src/project/"</C>.  The option <C>outfile</C> specify the name of
the created <C>TAGS</C> file.
</P>

  <ITEM><C>tags:root([{outdir, 'bar'}]).</C><BR>

<P>
Create a <C>TAGS</C> file of all the Erlang files in the Erlang
distribution.  The <C>TAGS</C> file will be placed in the the directory
<C>bar</C>.
</P>

</LIST>

</SECTION>

<SECTION>
<TITLE>Additional Erlang support</TITLE>

<P>
The standard Tags system has only support for simple names.  The
naming convention <C>module:function</C> used by Erlang is not supported.
</P>

<P>
The Erlang mode supplies an alternative set of Tags functions that is
aware of the format <C>module:function</C>.  When selecting a the
default search string for the commands the name under the point is
first selected.  Should the name not contain a module name the
<C>-import</C> list at the beginning of the buffer is scanned.
</P>

<SECTION>

<TITLE>Limitations</TITLE>

<P>
Currently, the additional Erlang module name support is not compatible
with the <C>etags.el</C> package that is part of XEmacs.
</P>

</SECTION>
</SECTION>

<SECTION>
<TITLE>Useful Tags Commands</TITLE>

<LIST>

  <ITEM><C> M-. </C> (<C>erlang-find-tag</C>)<BR>

<P>
Find a function definition.  The default value is the function name
under the point.  Should the function name lack the module specifier
the <C>-import</C> list is searched for an appropriate candidate.
</P>


  <ITEM><C> C-u M-. </C> (<C>erlang-find-tag</C> with an argument)<BR>

<P>
The <C>find-tag</C> commands place the point on the first occurrence of
a function that match the tag.  This command move the point to the
next match.
</P>


  <ITEM><C> C-x 4 . </C> (<C>erlang-find-tag-other-window</C>)<BR>

<P>
As above, but the new file will be shown in another window in the same
frame.
</P>


  <ITEM><C> C-x 5 . </C> (<C>erlang-find-tag-other-frame</C>)<BR>

<P>
As <C>erlang-find-tag</C> but the new file will be shown in a new frame.
</P>

  <ITEM><C> M-TAB </C> (<C>erlang-complete-tag</C>)<BR>

<P>
This command is used to fill in the end of a partially written
function name.  For example, assume that the point is at the end of
the string <C>a_long</C>, and the Tags file contain the function
<C>a_long_function_name</C>.  By executing this command the string
<C>a_long</C> will be expanded into <C>a_long_function_name</C>.
</P>


  <ITEM><C> M-x tags-search RET </C><BR>

<P>
This command will search through all the files in a project for a
string.  (Actually, it search for a pattern described by a regular
expression.)
</P>


  <ITEM><C> M-, </C> (<C>tags-loop-continue</C>)<BR>

<P>
Move the point to the next search match.
</P>

</LIST>

</SECTION>
</SECTION>

<SECTION>
<TITLE>IMenu</TITLE>

<P>
IMenu is a standard package of GNU Emacs.  With IMenu it is possible
to get a menu in the menu bar containing all the functions in the
buffer.  Erlang mode provides support for Erlang source files.
</P>

<!-- TODO
<P>
Unfortunately the IMenu package is not part of XEmacs.  In the future
Erlang mode might get support for the XEmacs package "funcmenu" that
provides similar support for XEmacs.
</P>
-->

<SECTION>
<TITLE>Starting IMenu</TITLE>

<LIST>

  <ITEM><C> M-x imenu-add-to-menubar RET</C><BR>

<P>
This command will create the IMenu menu containing all the functions
in the current buffer.  The command will ask you for a suitable name
for the menu.
</P>

</LIST>
</SECTION>

<SECTION>
<TITLE>Customization</TITLE>

<P>
See chapter "<SEEALSO MARKER="#customization">Customization</SEEALSO>"
below for a general description on how to customize the Erlang mode.
</P>

<P>
To automatically create the IMenu menu for all Erlang buffers, place
the lines below into the appropriate init file (e.g. ~/.emacs).  The
function <C>my-erlang-imenu-hook</C> will be called each time an
Erlang source file is read.  It will call the
<C>imenu-add-to-menubar</C> function.  The menu will be named
"Functions".
</P>

<CODE>
(add-hook 'erlang-mode-hook 'my-erlang-imenu-hook)

(defun my-erlang-imenu-hook ()
  (if (and window-system (fboundp 'imenu-add-to-menubar))
      (imenu-add-to-menubar "Functions")))
</CODE>

</SECTION>
</SECTION>

<!-- ---------------------------- Inferior Erlang -->

<!-- - CHAPTER -->

<SECTION>
<TITLE>Running Erlang from Emacs</TITLE>

<P>
One of the strengths of Emacs is its ability to start slave processes.
Since Emacs is extendible it is possible let Emacs be a part of a
large application.  For example, Emacs could be used as the user
interface for Erlang applications.
</P>

<P>
The Erlang editing mode provides two simple, yet very useful,
applications.  The first is to start an Erlang shell and use an Emacs
buffer for input and output.  The second is a compile commands that
makes it possible to compile Erlang modules and to locate the lines
containing the compilation errors.
</P>

<P>
The actual communication between Emacs and Erlang can be performed by
different low-level techniques.  The Erlang editing mode provides a
technique called "inferior" processes.  The add on package Erl'em
supplies a technically much more advanced communication technique
known as an Erl'em link.  All the commands that are provided by the
editing mode can use either technique.  However, more advanced
packages will probably need features only provided by the Erl'em
package.
</P>

<SECTION>
<TITLE>Inferior Erlang</TITLE>

<P>
The editing mode is capable of starting a so called "inferior" Erlang
process.  This is a normal subprocess that use one Emacs buffer for
input and output.  The effect is that a command line shell, or an
Erlang shell, can be displayed inside Emacs.
</P>

<P>
The big drawback with an inferior process is that the communication
between Emacs and the process is limited to commands issued at the
command line.  Since this is the interface that is used by the user it
is difficult, to say the least, to write an Emacs application that
communicate with the inferior process.  For example, the
<C>erlang-compile</C> command described in the section "Compilation"
below really stretch the capabilities of the inferior Erlang process.
In fact, should the user have issued a command that would take some
time to complete it is impossible for Emacs to perform the
<C>erlang-compile</C> command.
</P>

</SECTION>


<SECTION>
<TITLE>The Erl'em Link</TITLE>

<P>
The Erl'em package established a low-level communication channel
between Emacs and an Erlang node.  This communication channel can be
used by Emacs to issue several independent Erlang commands, to start
Erlang processes and to open several Erlang IO streams.  It is also
possible for Erlang to call Emacs functions.
</P>

<P>
In short the Erl'em package is designed to be the base of complex
application that is partially implemented in Emacs and partially in
Erlang.
</P>

<P>
It is the hope of the author that the Erl'em link in the future will
be used as the base for porting the user interface of the Erlang
debugger to Emacs.  If this could be possible, Emacs could be used as
an Integrated Debugger Environment (IDE) for Erlang.
</P>

<P>
The structure of the Erl'em link and its programming interface is
described in the text "Erl'em Developers Manual".
</P>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Erlang Shell</TITLE>

<P>
It is possible to start an Erlang shell inside Emacs.  The shell will
use an Emacs buffer for input and output.  Normal Emacs commands can
be used to edit the command line and to recall lines from the command
line history.
</P>

<P>
The output will never be erased from the buffer so you will never risk
letting important output fall over the top edge of the display.
</P>

<P>
As discussed in the previous chapter there are two low-level
methods for Emacs to communicate with Erlang.  The first is by
starting an inferior process, the second is by using an Erl'em link.
When using inferior processes each new shell will start a new Erlang
node.  Should the Erl'em link be used it is possible to start several
shells on the same node, a feature not normally available.
</P>

<SECTION>
<TITLE>The shell</TITLE>

<P>
In this section we describe how to start a shell. In the next we cover
how to use it once it has been started.
</P>

<LIST>
  <ITEM><C> M-x erlang-shell RET </C><BR>

<P>
Start a new Erlang shell.  When an inferior process is used a new
Erlang node is started for each shell.  Should the Erl'em link package
be installed several shells can be started on the same Erlang node.
</P>

<P>
A word of warning.  The Erlang function <C>halt().</C> will kill the
current Erlang node, including all shells running on it.
</P>


  <ITEM><C> M-x erlang-shell-display RET </C><BR>

<P>
Display one Erlang shell.  If there are no Erlang shells active a new
will be started.
</P>

</LIST>

</SECTION>

<SECTION>

<TITLE>Command line history</TITLE>

<P>
The look and feel on an Erlang shell inside Emacs should be the same
as in a normal Erlang shell.  There is just one major difference, the
cursor keys will actually move the cursor around just like in any
normal Emacs buffer.  The command line history can be accessed by the
following commands:
</P>

<LIST>

  <ITEM><C> C-up </C>  or <C> M-p </C>  (<C>comint-previous-input</C>)<BR>

<P>
Move to the previous line in the input history.
</P>


  <ITEM><C> C-down </C> or <C> M-n </C>  (<C>comint-next-input</C>)<BR>

<P>
Move to the next line in the input history.
</P>

</LIST>

<P>
If the Erlang shell buffer would be killed the command line history is
saved to a file.  The command line history is automatically retrieved
when a new Erlang shell is started.
</P>

</SECTION>

<SECTION>

<TITLE>The Erlang Shell Mode</TITLE>

<P>
The buffers that are used to run Erlang shells use the major mode
<C>erlang-shell-mode</C>.  This major mode is based on the standard
mode <C>comint-mode</C>.
</P>

<LIST>
  <ITEM><C> erlang-shell-mode </C><BR>

<P>
Enter Erlang shell mode.  To operate correctly the buffer should be in
Comint mode when this command is called. 
</P>

</LIST>

</SECTION>

<SECTION>

<TITLE>Variables</TITLE>

<P>
In this section we present the variables that control the behavior of
the Erlang shell.  See also the next section "Inferior Erlang
Variables".
</P>

<LIST>

<ITEM> <EM>Variable: </EM> <C>erlang-shell-mode-hook</C>
(default <C>()</C>)<BR>

<P>
Function to run when this mode is activated.  See chapter "<SEEALSO
MARKER="#customization">Customization</SEEALSO>" below for examples.
</P>


<ITEM> <EM>Variable: </EM> <C>erlang-input-ring-file-name</C>
(default "~/.erlang_history")<BR>

<P>
The file name used to save the command line history.
</P>


<ITEM> <EM>Variable: </EM> <C>erlang-shell-function</C>
(default <C>inferior-erlang</C>)<BR>

<P>
This variable contain the low-level function to call to start an
Erlang shell.  This variable will be changed by the Erl'em
installation.
</P>


<ITEM> <EM>Variable: </EM> <C>erlang-shell-display-function</C>
(default <C>inferior-erlang-run-or-select</C>)<BR>

<P>
This variable contain the low-level function to call when the
<C>erlang-shell-display</C> is issued.  This variable will be changed by
the Erl'em installation.
</P>

</LIST>

</SECTION>

<SECTION>
<TITLE>Inferior Erlang Variables</TITLE>

<P>
The variables described in this chapter are only used when inferior
Erlang processes are used.  They do not affect the behavior of the
shell when using an Erl'em link.
</P>

<LIST>

  <ITEM> <EM>Variable: </EM> 
<C>inferior-erlang-display-buffer-any-frame</C> (default
<C>nil</C>)<BR>

<P>
When this variable is <C>nil</C> the command
<C>erlang-shell-display</C> will display the inferior process in the
current frame.  When <C>t</C>, it will do nothing when it already is
visible in another frame.  When it is bound to the atom <C>raise</C>
the frame displaying the buffer will be raised.
</P>

  <ITEM> <EM>Variable: </EM> <C>inferior-erlang-shell-type</C>
(default <C>newshell</C>)<BR>

<P>
There are two different variants of the Erlang shell, named the old
and the new shell.  The old is a simple variant that does not provide
command line editing facilities.  The new, on the other hand, provide
full edition features.  Apart from this major difference, they differ
on some subtle points.  Since Emacs itself takes care of the command
line edition features you can switch between the two shell types if
your shell behaves strange.
</P>

<P>
To use the new or the old shell bind this variable to <C>newshell</C> or
<C>oldshell</C>, respectively.
</P>

  <ITEM> <EM>Variable: </EM> <C>inferior-erlang-machine</C>
(default <C>"erl"</C>)<BR>

<P>
The command name of the Erlang runtime system.
</P>


  <ITEM> <EM>Variable: </EM> <C>inferior-erlang-machine-options</C>
(default <C>()</C>)<BR>

<P>
A list of strings containing command line options that is used when
starting an inferior Erlang.
</P>


  <ITEM> <EM>Variable: </EM> <C>inferior-erlang-buffer-name</C>
(default <C>"*erlang*"</C>)<BR>

<P>
The base name of the Erlang shell buffer.  Should several Erlang shell
buffers be used they will be named <C>*erlang*<2></C>,
<C>*erlang*<3></C> etc.
</P>

</LIST>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Compilation</TITLE>

<P>
The classic edit-compile-bugfix cycle for Erlang is to edit the source
file in an editor, save it to a file and switch to an Erlang shell.
In the shell the compilation command is given.  Should the compilation
fail you have to bring out the editor and locate the correct line.
</P>

<P>
With the Erlang editing mode the entire edit-compile-bugfix cycle can
be performed without leaving Emacs.  Emacs can order Erlang to compile
a file and it can parse the error messages to automatically place the
point on the erroneous lines.
</P>

<SECTION>

<TITLE>Commands</TITLE>

<LIST>

  <ITEM><C>C-c C-k</C> (<C>erlang-compile</C>)<BR>

<P>
This command compiles the file in the current buffer.
</P>

<P>
The action performed by this command depend on the low-level
communication method used.  Should an inferior Erlang process be used
Emacs tries to issue a compile command at the Erlang shell prompt.
The compilation output will be sent to the shell buffer.
This command will fail if it is not possible to issue a command at the
Erlang shell prompt.
</P>

<P>
Should an Erl'em link be used the compile command sent to Erlang will
be independent of any active shell.  The output will be sent to a
dedicated buffer.
</P>


  <ITEM><C>C-x ` </C>  (<C>erlang-next-error</C>)<BR>

<P>
This command will place the point on the line where the first error
was found.  Each successive use of this command will move the point to
the next error.  The buffer displaying the compilation errors will be
updated so that the current error will be visible.
</P>

<P>
You can reparse the compiler output from the beginning by preceding
this command by <C> C-u </C>.
</P>

  <ITEM><C>erlang-compile-display</C><BR>

<P>
Show the output generated by the compile command.
</P>

</LIST>
</SECTION>

<SECTION>
<TITLE>Variables</TITLE>

<LIST>

  <ITEM> <EM>Variable: </EM> <C>erlang-compile-use-outdir</C>
(default <C>t</C>)<BR>

<P>
In some versions of Erlang the <C>outdir</C> options contains a bug.
Should the directory not be present in the current Erlang load path
the object file will not be loaded.
</P>

<P>
Should this variable be set to <C>nil</C> the <C>erlang-compile</C>
command will use a workaround by change current directory, compile the
file, and change back.
</P>


  <ITEM> <EM>Variable: </EM> <C>erlang-compile-function</C>
(default <C>inferior-erlang-compile</C>)<BR>

<P>
The low-level function to use to compile an Erlang module.
</P>


  <ITEM> <EM>Variable: </EM> <C>erlang-compile-display-function</C>
(default <C>inferior-erlang-run-or-select</C>)<BR>

<P>
The low-level function to call when the result of a compilation should
be shown.
</P>


  <ITEM> <EM>Variable: </EM> <C>erlang-next-error-function</C>
(default <C>inferior-erlang-next-error</C>)<BR>

<P>
The low-level function to use when <C>erlang-next-error</C> is used.
</P>

</LIST>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE>Customization</TITLE>

<P>
One of the strengths of Emacs is that users can fairly easy customize
the behavior of almost every detail.  The Erlang editing mode is not
an exception to this rule.
</P>

<P>
Normally, Emacs is customized through the user and system init files,
<C>~/.emacs</C> and <C>site-start.el</C>, respectively.  The content
of the files are expressions written in the Emacs extension language
Emacs Lisp.  The semantics of Lisp is fairly similar Erlang's.
However, the syntax is very different.  Fortunately, most
customizations require only very minor knowledge of the language.
</P>

<SECTION>

<TITLE>Emacs Lisp</TITLE>

<P>
In this section we show the basic constructions of Emacs Lisp needed to
perform customizations.
</P>

<P>
In addition to placing the expressions in the init file, they can be
evaluated while Emacs is started.  One method is to use the <C> M-:
</C> (On older versions of Emacs this is bound to <C> ESC ESC</C>)
function that evaluates Emacs Lisp expressions in the minibuffer.
Another method is to write the expressions in the <C> *scratch* </C> buffer,
place the point at the end of the line and press <C>C-j</C>.
</P>

<P>
Below is a series of example that we use to demonstrate simple Emacs
Lisp constructions.
</P>

<LIST>


  <ITEM> <EM>Example 1:</EM> <BR>

<P>
In this example we set the variable <C>foo</C> to the value 10 added
to the value of the variable <C>a</C>.  As we can see by this example,
Emacs Lisp use prefix form for all function calls, including simple
functions like <C>+</C>.
</P>

<CODE>
(setq foo (+ 10 a))
</CODE>


  <ITEM> <EM>Example 2:</EM> <BR>

<P>
In this example we first define a function <C>bar</C> that sums the value
of its four parameters.  Then we evaluated an expression that first
calls <C>bar</C> then calls the standard Emacs function <C>message</C>.
</P>

<CODE>
(defun bar (a b c d)
  (+ a b c d))

(message "The sum becomes %d" (bar 1 2 3 4))
</CODE>


  <ITEM> <EM>Example 3:</EM><BR>

<P>
Among the Emacs Lisp data types we have atoms.  However, in
the following expressions we assign the variable <C>foo</C> the value of
the variable <C>bar</C>.
</P>

<CODE>
(setq foo bar)
</CODE>

<P>
To assign the variable <C>foo</C> the atom <C>bar</C> we must quote
the atom with a <C>'</C>-character.  Note the syntax, we should precede the
expression (in this case <C>bar</C>) with the quote, not surround it.
</P>

<CODE>
(setq foo 'bar)
</CODE>

</LIST>

</SECTION>


<SECTION>
<TITLE>Hooks</TITLE>

<P>
A hook variable is a variable that contain a list of functions to
run.  In Emacs there is a large number of hook variables, each is
runed at a special situation.  By adding functions to hooks the user
make Emacs automatically perform anything (well, almost).
</P>

<P>
To add a function to a hook you must use the function <C>add-hook</C>.
To remove it use <C>remove-hook</C>.
</P>

<P>
See chapter "The Editing Mode" above for a list of hooks defined by
the Erlang editing mode.
</P>

<LIST>
  <ITEM> <EM> Example: </EM> <BR>

<P>
In this example we add <C>tempo-template-erlang-large-header</C> to
the hook <C>erlang-new-file-hook</C>.  The effect is that whenever a
new Erlang file is created a file header is immediately inserted.
</P>

<CODE>
  (add-hook 'erlang-new-file-hook 'tempo-template-erlang-large-header)
</CODE>

<ITEM> <EM> Example: </EM> <BR>

<P>
Here we define a new function that sets a few variables when it is
called.  We then add the function to the hook <C>erlang-mode-hook</C> that
gets called every time Erlang mode is activated.
</P>

<CODE>
(defun my-erlang-mode-hook ()
  (setq erlang-electric-commands t))

(add-hook 'erlang-mode-hook 'my-erlang-mode-hook)
</CODE>

</LIST>

</SECTION>

<SECTION>
<MARKER ID="key_bindings">
<TITLE>Custom Key Bindings</TITLE>

<P>
It is possible to bind keys to your favorite commands.  Emacs use a
number of key-maps: the global key-map defines the default value of
keys, local maps are used by the individual major modes, minor modes
can have their own key map etc.
</P>

<P>
The commands <C>global-set-key</C> and <C>local-set-key</C> defines
keys in the global and in the current local key-map, respectively.
</P>

<P>
If we would like to redefine a key in the Erlang editing mode we can
do that by activating Erlang mode and call <C>local-set-key</C>.  To
automate this we must define a function that calls
<C>local-set-key</C>.  This function can then be added to the Erlang
mode hook so that the correct local key map is active when the key is
defined.
</P>

<P>
<EM> Example: </EM>
</P>

<P>
Here we bind <C> C-c C-c </C> to the command <C>erlang-compile</C>,
the function key <C>f1</C> to <C>erlang-shell</C>, and <C> M-f1 </C>
to <C> erlang-shell-display </C>.  The calls to <C> local-set-key </C>
will not be performed when the init file is loaded, they will be
called first when the functions in the hook <C>erlang-mode-hook</C> is
called, i.e. when Erlang mode is started.
</P>

<CODE>
(defun my-erlang-keymap-hook ()
  (local-set-key (read-kbd-macro "C-c C-c") 'erlang-compile)
  (local-set-key (read-kbd-macro "<f1>")    'erlang-shell)
  (local-set-key (read-kbd-macro "M-<f1>")  'erlang-shell-display))
(add-hook 'erlang-mode-hook 'my-erlang-keymap-hook)
</CODE>

<P>
The function <C>read-kbd-macro</C> used in the above example converts
a string of readable keystrokes into Emacs internal representation.
</P>

<P>
<EM> Example: </EM>
</P>

<P>
In Erlang mode the tags commands understand the Erlang module naming
convention.  However, the normal tags commands does not.  This line
will bind <C> M-. </C> in the global map to <C>erlang-find-tag</C>.
</P>

<CODE>
(global-set-key (read-kbd-macro "M-." 'erlang-find-tag))
</CODE>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<MARKER ID="distributions">
<TITLE>Emacs Distributions</TITLE>

<P>
Today there are two major Emacs development streams.  The first is
GNU Emacs from Free Software Foundation and the second is XEmacs.
Both have advantages and disadvantages, you have to decide for
yourself which Emacs you prefer.
</P>

<SECTION>

<TITLE> GNU Emacs </TITLE>

<P>
This is the standard distribution from The Free Software Foundation,
an organization lead by the original author of Emacs, Richard
M. Stallman.
</P>

<P>
The source code for the latest version of Emacs can be fetched from
<C>http://www.gnu.org</C>.  A binary distribution for Window NT and 95
can be found at
<C>http://www.cs.washington.edu/homes/voelker/ntemacs.html</C>.
</P>

</SECTION>

<SECTION>

<TITLE> XEmacs </TITLE>

<P>
This is an alternative version of Emacs.  Historically XEmacs is based
on Lucid Emacs that in turn was based on an early version of Emacs 19.
The big advantage of XEmacs is that it can handle graphics much
better.  One difference is a list of icons that contains a number of
commonly used commands.  Another is the ability to display graphical
images in the buffer.
</P>

<P>
The major drawback is that when a new feature turns up in GNU Emacs,
it will often take quite a long time before it will be incorporated
into XEmacs.
</P>

<P>
The latest distribution can be fetched from <C>http://www.xemacs.org</C>.
</P>

</SECTION>

<SECTION>
<TITLE> Installing Emacs </TITLE>

<P>
The source distributions usually comes in a tared and gzipped format.
Unpack this with the following command:
</P>

<CODE>
    tar zxvf <file>.tar.gz
</CODE>

<P>
If your tar command do not know how to handle the "z" (unpack) option
you can unpack it separately:
</P>

<CODE>
    gunzip <file>.tar.gz
    tar xvf <file>.tar
</CODE>

<P>
The program <C>gunzip</C> is part of the <C>gzip</C> package that can
be found on the <C>http://www.gnu.org</C> site.
</P>

<P>
Next, read the file named <C>INSTALL</C>.  The build process is
normally performed in three steps: in the first the build system
performs a number of tests on your system, the next step is to
actually build the Emacs executable, finally Emacs is installed.
</P>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<MARKER ID="installation">
<TITLE> Installation of the Erlang Editing Mode</TITLE>

<P>
In the OTP installation, the Erlang editing mode is already
installed. All that is needed is that the system administrator or the
individual user configures their Emacs Init files to use it.

<P>
If we assume that OTP has been installed in
<em>OTP_ROOT</em>, the editing mode can be found in
<em>OTP_ROOT</em><c>/misc/emacs</C>.

<P>
The <C>erlang.el</C> file found in the installation directory is already
compiled. If it needs to be recompiled, the following command line
should create a new <C>erlang.elc</C> file:

<CODE>
    emacs -batch -q -no-site-file -f batch-byte-compile erlang.el
</CODE>

<P>

<SECTION>
<TITLE>Editing the right Emacs Init file</TITLE>
<P>
System administrators edit <C>site-start.el</C>, individuals edit
their <C>.emacs</C> files.

<p>
On UNIX systems, individuals should edit/create the file <c>.emacs</c>
in their home directories.

<p>
On Windows NT/95, individuals should also edit/create their
<c>.emacs</c> file, but the location of the file depends on the
configuration of the system. 

<p>
<list>
<item>
If the <em>HOME</em> environment variable
is set, Emacs will look for the <c>.emacs</c> file in the directory
indicated by the <em>HOME</em> variable.

			  
<item>
If <em>HOME</em> is not set,
Emacs will look for the <c>.emacs</c> file in <c>C:\</c>.  
</list>
</section>


<SECTION>
<TITLE> Extending the load path</TITLE>
<P>		
The directory with the editing mode,
<em>OTP_ROOT</em><c>/misc/emacs</C>, must be in the load path for Emacs.

<P>
Add the following line to the selected initialization file (replace
<C> OTP_ROOT </C> with the name of the installation
directory for OTP, keep the quote characters):
</P>
<CODE>
	(setq load-path (cons "OTP_ROOT/misc/emacs" load-path))
</CODE>


<P>
Note: When running under Windows, use <C> / </C> or <C> \\ </C> as
separator in pathnames in the Emacs configuration files.  Using a single
<C> \ </C> in strings does not work, as it is interpreted by Emacs as
an escape character.
</P>


</section>

<section>
<TITLE> Specifying the OTP installation directory</TITLE>

<P>
Some functions in the Erlang editing mode require that the OTP
installation directory is known.  The following is an example where we
assume that they are installed in the directory <C>OTP_ROOT</C>,
change this to reflect the location on your system.
</P>

<CODE>
	(setq erlang-root-dir "OTP_ROOT")
</CODE>

</section>

<section>
<title>Extending the execution path</title>

<p>
To use inferior Erlang Shells, you need to do the following
configuration. If your <em>PATH</em> environment variable already
includes the location of the <c>erl</c> or <c>erl.exe</c> executable
this configuration is not necessary.

<p>
You can either extend the <em>PATH</em> environment variable with the
location of the  <c>erl</c>/<c>erl.exe</c> executable. Please refer to
instructions for setting environment variables on your particular
platform for details.	    

<p>
You can also extend the execution path for Emacs as described
below. If the executable is located in <c>OTP_ROOT/bin</c> then you
add the following line to you Emacs Init file:

<code>
	(setq exec-path (cons "OTP_ROOT/bin" exec-path))

</code>
</section>

<section>
<TITLE>Final setup</TITLE>
<P>
Finally, add the following line to the init file:
</P>

<CODE>
	(require 'erlang-start)
</CODE>

<P>
This will inform Emacs that the Erlang editing mode is available.  It
will associate the file extensions <C> .erl </C> and <C> .hrl </C>
with Erlang mode.  Also it will make sure that files with the
extension <C> .beam </C> will be ignored when using file name
completion.
</P>

</SECTION>

<SECTION>
<MARKER ID="unix_dotemacs">
<TITLE> An Example for UNIX </TITLE>

<P>
Below is a complete example of what should be added to a user's
<c>.emacs</c> provided that OTP is installed in the directory
<C>/usr/local/otp</C>:

<CODE>
(setq load-path (cons  "/usr/local/otp/misc/emacs"
                       load-path))
(setq erlang-root-dir "/usr/local/otp")
(setq exec-path (cons "/usr/local/otp/bin" exec-path))
(require 'erlang-start)
</CODE>

<P>
Any additional user configurations can be added after this.  See for
instance section "<SEEALSO
MARKER="#font-lock">Customization</SEEALSO>" for some useful
customizations.
		    

</section>

<SECTION>
<MARKER ID="win_dotemacs">
<TITLE> An Example for Windows </TITLE>

<P>
Below is a complete example of what should be added to a user's
<c>.emacs</c> provided that OTP is installed in the directory
<C>C:\Program Files\erl-4.7</C>:

<CODE>
(setq load-path (cons  "C:/Program Files/erl-4.7/misc/emacs"
                       load-path))
(setq erlang-root-dir "C:/Program Files/erl-4.7")
(setq exec-path (cons "C:/Program Files/erl-4.7/bin" exec-path))
(require 'erlang-start)
</CODE>

<P>
Any additional user configurations can be added after this.  See for
instance section "<SEEALSO
MARKER="#font-lock">Customization</SEEALSO>" for some useful
customizations.



</section>


<SECTION>
<TITLE> Check the Installation </TITLE>

<P>
Restart the Emacs and load or create an Erlang file (with the <C>.erl</C>
extension).  If the installation was performed correctly the mode line
should contain the word "Erlang".  Select the "Version" menu item in
the "Erlang" menu, check that the version number matches the version in
found in the files in <c>OTP_ROOT/misc/emacs</c>.
</P>

</SECTION>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<MARKER ID="notation">
<TITLE> Notation </TITLE>

<P>
In this book we use the same terminology used in the Emacs
documentation.  This chapter contain a short glossary of words and
their meaning in the Emacs world.
</P>

<LIST>

  <ITEM><EM> Buffer </EM> 

<P>
A buffer is used by Emacs to handle text.  When editing a file the
content is loaded into a buffer.  However buffers can contain other
things as well.  For example, a buffer can contain a list of files in
a directory, it can contain generated help texts, or it is possible to
start processes that use a buffer in Emacs for input and output.  A
buffer need not be visible, but if it is, it is shown in a window.
</P>

  <ITEM><EM> Emacs Lisp </EM>

<P>
Emacs is written in two languages.  The Emacs core is written in C.
The major part, as well as most add-on packages, are written in Emacs
Lisp.  This is also the language used by the init files.
</P>

  <ITEM><EM> Frame  </EM>

<P>
This is what most other systems refer to as a <EM> window </EM>.
Emacs use frame since the word window was used for another feature
long before window systems were invented.
</P>

  <ITEM><EM> init file  </EM>

<P>
Files read by Emacs at startup.  The user startup file is named
<C>~/.emacs</C>.  The init files are used to customize Emacs, for
example to add new packages like <C>erlang</C>.  The language used in
the startup files is Emacs Lisp.
</P>

  <ITEM><EM> Major mode </EM>

<P>
A major mode provides support for edit text of a particular sort.  For
example, the Erlang editing mode is a major mode.  Each buffer have
exactly one major mode active.
</P>

  <ITEM><EM> Minor mode  </EM>

<P>
A minor mode provides some additional support.  Each buffer can have
several minor modes active at the same time.  One example is
<C>font-lock-mode</C> that activates syntax highlighting, another is
<C>follow-mode</C> that make two side-by-side windows act like one
tall window.
</P>

  <ITEM><EM> Mode line  </EM>

<P>
The line at the bottom of each Emacs window that contain information
about the buffer.  E.g. the name of the buffer, the line number, and
the name of the the current major mode.
</P>

  <ITEM><C> nil </C> 

<P>
The value used in Emacs Lisp to represent false.  True can be
represented by any non-<C>nil</C> value, but it is preferred to use
<C>t</C>.
</P>

  <ITEM><EM> Point </EM> 
<P>
The point can be seen as the position of the cursor.  More precisely,
the point is the position between two characters while the cursor is
drawn over the character following the point.
</P>

  <ITEM><C> t </C>

<P>
The value <C>t</C> is used by flags in Emacs Lisp to represent true.
See also <C>nil</C>.
</P>

  <ITEM><EM> Window </EM>

<P>
An area where text is visible in Emacs.  A <EM>frame</EM> (which is a
window in non-Emacs terminology) can contain one or more windows.  New
windows can be created by splitting windows either vertically or
horizontally.
</P>

</LIST>
</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE> Keys </TITLE>

<LIST>

  <ITEM><C> C- </C> The control key.

  <ITEM><C> M- </C> The meta key.  Normally this is the left ALT key.
Alternatively the escape key can be used (with the difference that the
escape key should be pressed and released while the ALT key work just
like the control key.)

  <ITEM><C> M-C- </C> Press both meta and control at the same time.  (Or press the
escape key, release it, and then press the control key.)

  <ITEM><C> RET  </C> The return key.

</LIST>

<P>
All commands in Emacs have names.  A named command can be executed by
pressing <C> M-x</C>, typing the name of the command, and hitting <C>
RET </C>.
</P>

</SECTION>

<!-- CHAPTER -->

<SECTION>
<TITLE> Further reading </TITLE>

<P>
In this chapter I present some references to material on Emacs.  They
are divided into the two categories "Usage" and "Development".  The
first is for normal Emacs users who would like to know how to get more
power out of their editor.  The second is for people who would like
to develop their own applications in Emacs Lisp.
</P>

<P>
Personally, I would recommend the series of books from the Free
Software Foundation, they are written by the people that wrote Emacs
and they form a coherent series useful for everyone from beginners to
experienced Emacs Lisp developers.
</P>

<SECTION>
<TITLE> Usage </TITLE>

<LIST>


  <ITEM> Richard M. Stallman. GNU Emacs Manual.  Free Software
Foundation, 1995. <BR>

<P>
This is the Bible on using Emacs.  It is written by the principle
author of Emacs.  An on-line version of this manual is part of the
standard Emacs distribution, see the "Help->Browse Manuals" menu.
</P>


  <ITEM> "comp.emacs", News Group on Usenet. <BR>

<P>
General Emacs group, everything is discussed here from beginners to
complex development issues.
</P>


  <ITEM> "comp.emacs.xemacs", News Group on Usenet. <BR>

<P>
This group cover XEmacs only.
</P>


  <ITEM> "gnu.emacs.help", News Group on Usenet.  <BR>

<P>
This group is like "comp.emacs" except that the topic only should
cover GNU Emacs, not XEmacs or any other Emacs derivate.
</P>


  <ITEM> "gnu.emacs.sources", News Group on Usenet. <BR>

<P>
In this group a lot of interesting Emacs packages are posted.  In fact
only source code is permitted, questions should be redirected to one of
the other Emacs groups.
</P>


  <ITEM> "gnu.emacs.bugs", News Group on Usenet. <BR>

<P>
If you have found a bug in Emacs you should post it here.  Do not post
bug reports on packages that are nor part of the standard Emacs
distribution, they should be sent to the maintainer of the package.
</P>

</LIST>
</SECTION>


<SECTION>
<TITLE> Development </TITLE>

<LIST>

  <ITEM> Robert J. Chassell.  Programming in Emacs Lisp: an Introduction.
Free Software Foundation, 1995. <BR>

<P>
This a good introduction to Lisp in general and Emacs Lisp in
particular.  Just like the other books form FSF, this book is free and
can be downloaded from <C> http://www.gnu.org </C>.
</P>


  <ITEM> Bil Lewis et.al. The GNU Emacs Lisp Reference Manual. Free Software
Foundation, 1995. <BR>

<P>
This is the main source of information for any serious Emacs
developer.  This manual covers every aspect of Emacs Lisp.  This
manual, like Emacs itself, is free.  The manuscript can be downloaded
from <C> http://www.gnu.org </C> and can either be converted into printable
form or be converted into a hypertext on-line manual.
</P>


  <ITEM> Bob Glickstein.  Writing GNU Emacs Extensions. O'Reilly, 1997. <BR>

<P>
This is a good tutorial on how to write Emacs packages.
</P>


  <ITEM> Anders Lindgren. Erl'em Developers Manual. Ericsson, 1998. <BR>

<P>
This text covers the architecture of the Erl'em communication link and
the application programmers interface to it.
</P>

<!--  <ITEM> David K&aring;gedal. Tempo Manual. -->

<!-- TODO: the url -->

<P>
The tempo package is presented in this manual.  The latest version can
be found at <C> http://www.lysator.liu.se </C>.
</P>

</LIST>

</SECTION>
</SECTION>


<!-- TODO -->
<!-- Known Bugs -->

<!-- Arity -->

<SECTION>

<TITLE> Reporting Bugs </TITLE>

<P>
Please send bug reports to the following email address:
</P>

<CODE>
     [email protected]
</CODE>

<P>
Please state as accurate as possible:
</P>

<LIST>
  <ITEM> Version number of the Erlang editing mode (see the menu), Emacs,
Erlang, and of any other relevant software.

  <ITEM> What the expected result was.

  <ITEM> What you did, preferably in a repeatable step-by-step form.

  <ITEM> A description of the unexpected result.

  <ITEM> Relevant pieces of Erlang code causing the problem.

  <ITEM> Personal Emacs customizations, if any.
</LIST>

<P>
Should the Emacs generate an error, please set the emacs variable
<C>debug-on-error</C> to <C>t</C>.  Repeat the error and enclose the
debug information in your bug-report.
</P>

<P>
To set the variable you can use the following command:
</P>

<CODE>
    M-x set-variable RET debug-on-error RET t RET
</CODE>

</SECTION>

</CHAPTER>