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<?xml version="1.0" encoding="latin1" ?>
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<!DOCTYPE chapter SYSTEM "chapter.dtd">
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<holder>Ericsson AB, All Rights Reserved</holder>
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The contents of this file are subject to the Erlang Public License,
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Version 1.1, (the "License"); you may not use this file except in
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compliance with the License. You should have received a copy of the
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Erlang Public License along with this software. If not, it can be
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retrieved online at http://www.erlang.org/.
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Software distributed under the License is distributed on an "AS IS"
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basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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the License for the specific language governing rights and limitations
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The Initial Developer of the Original Code is Ericsson AB.
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<title>The Erlang mode for Emacs</title>
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<title>Purpose</title>
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<p>The purpose of this user guide is to introduce you to the
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Erlang mode for Emacs and gives some relevant background
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information of the functions and features. See also <seealso marker="erlang_mode">Erlang mode reference manual</seealso> The
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purpose of the Erlang mode itself is to facilitate the developing
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process for the Erlang programmer.</p>
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<title>Pre-requisites</title>
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<p>Basic knowledge of Emacs and Erlang/OTP. </p>
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<p>There are two Elsip modules include in this tool package
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for Emacs. There is erlang.el that defines the actual erlang mode
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and there is erlang-start.el that makes some nice initializations.</p>
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<title>Setup on UNIX</title>
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<p>To set up the Erlang Emacs mode on a UNIX systems, edit/create
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the file <c>.emacs</c> in the your home directory.</p>
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<p>Below is a complete example of what should be added to a user's
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<c>.emacs</c> provided that OTP is installed in the directory
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<c>/usr/local/otp </c>: </p>
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<code type="none"><![CDATA[
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(setq load-path (cons "/usr/local/otp/lib/tools-<ToolsVer>/emacs"
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(setq erlang-root-dir "/usr/local/otp")
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(setq exec-path (cons "/usr/local/otp/bin" exec-path))
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(require 'erlang-start)
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<title>Setup on Windows </title>
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<p>To set up the Erlang Emacs mode on a Windows systems,
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edit/create the file <c>.emacs</c>, the location of the file
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depends on the configuration of the system. If the <em>HOME</em>
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environment variable is set, Emacs will look for the
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<c>.emacs</c> file in the directory indicated by the
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<em>HOME</em> variable. If <em>HOME</em> is not set, Emacs
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will look for the <c>.emacs</c> file in <c>C:\\ </c>.</p>
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<p>Below is a complete example of what should be added to a user's
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<c>.emacs</c> provided that OTP is installed in the directory
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<c><![CDATA[C:\\Program Files\\erl<Ver>]]></c>: </p>
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<code type="none"><![CDATA[
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(setq load-path (cons "C:/Program Files/erl<Ver>/lib/tools-<ToolsVer>/emacs"
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(setq erlang-root-dir "C:/Program Files/erl<Ver>")
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(setq exec-path (cons "C:/Program Files/erl<Ver>/bin" exec-path))
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(require 'erlang-start)
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<p>In .emacs, the slash character "/" can be used as path
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separator. But if you decide to use the backslash character "\\",
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please not that you must use double backslashes, since they are
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treated as escape characters by Emacs.</p>
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<title>Indentation</title>
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<p>The "Oxford Advanced Learners Dictionary of Current English" says the
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following about the word "indent":</p>
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<p>"start (a line of print or writing) farther from
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the margin than the others".</p>
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<p>The Erlang mode does, of course, provide this feature. The layout
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used is based on the common use of the language.</p>
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<p>It is strongly recommend to use this feature and avoid to indent lines
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in a nonstandard way. Some motivations are:</p>
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<list type="bulleted">
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<item>Code using the same layout is easy to read and maintain. </item>
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<item>Since several features of Erlang mode is based on the
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standard layout they might not work correctly if a nonstandard layout
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<p>The indentation features can be used to reindent large sections
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of a file. If some lines use nonstandard indentation they will
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<title>Editing</title>
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<list type="bulleted">
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<item><em><c>M-x erlang-mode RET</c></em> - This command activates
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the Erlang major mode for the current buffer. When this
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mode is active the mode line contain the word "Erlang".</item>
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<p>When the Erlang mode is correctly installed, it is
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automatically activated when a file ending in <c>.erl</c> or
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<c>.hrl</c> is opened in Emacs.</p>
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<p>When a file is saved the name in the <c>-module().</c> line is
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checked against the file name. Should they mismatch Emacs can
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change the module specifier so that it matches the file name.
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By default, the user is asked before the change is performed.</p>
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<p>An "electric" command is a character that in addition to just
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inserting the character performs some type of action. For
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example the ";" character is typed in a situation where is ends
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a function clause a new function header is generated. The electric
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commands are as follows: </p>
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<list type="bulleted">
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<item><em><c>erlang-electric-comma</c></em> - Insert a comma
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character and possibly a new indented line. </item>
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<item><em><c>erlang-electric-semicolon</c></em> - Insert a
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semicolon character and possibly a prototype for the next line.</item>
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<item><em><c>erlang-electric-gt</c></em> - "Insert a '>'-sign
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and possible a new indented line.</item>
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<p>To disable all electric commands set the variable
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<c>erlang-electric-commands</c> to the empty list. In short,
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place the following line in your <c>.emacs</c>-file:</p>
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(setq erlang-electric-commands '())</code>
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<title>Syntax highlighting</title>
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<p>It is possible for Emacs to use colors when displaying a buffer. By
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"syntax highlighting", we mean that syntactic components, for example
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keywords and function names, will be colored.</p>
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<p>The basic idea of syntax highlighting is to make the structure of a
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program clearer. For example, the highlighting will make it easier to
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spot simple bugs. Have not you ever written a variable in lower-case
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only? With syntax highlighting a variable will colored while atoms
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will be shown with the normal text color.</p>
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<marker id="tags"></marker>
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<p>Tags is a standard Emacs package used to record information
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about source files in large development projects. In addition to
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listing the files of a project, a tags file normally contains
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information about all functions and variables that are defined.
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By far, the most useful command of the tags system is its ability
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to find the definition of functions in any file in the project.
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However the Tags system is not limited to this feature, for
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example, it is possible to do a text search in all files in a
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project, or to perform a project-wide search and replace.</p>
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<p>In order to use the Tags system a file named <c>TAGS</c> must be
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created. The file can be seen as a database over all functions,
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records, and macros in all files in the project. The
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<c>TAGS</c> file can be created using two different methods for
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Erlang. The first is the standard Emacs utility "etags", the
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second is by using the Erlang module <c>tags</c>.</p>
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<p><c>etags</c> is a program that is part of the Emacs
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distribution. It is normally executed from a command line, like
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a unix shell or a DOS box.</p>
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<p>The <c>etags</c> program of fairly modern versions of Emacs and XEmacs
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has native support for Erlang. To check if your version does include
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this support, issue the command <c>etags --help</c> at a the command
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line prompt. At the end of the help text there is a list of supported
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languages. Unless Erlang is a member of this list I suggest that you
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should upgrade to a newer version of Emacs.</p>
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<p>As seen in the help text -- unless you have not upgraded your
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Emacs yet (well, what are you waiting around here for? Off you go and
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upgrade!) -- <c>etags</c> associate the file extensions <c>.erl</c>
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and <c>.hrl</c> with Erlang.</p>
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<p>Basically, the <c>etags</c> utility is runed using the following form:</p>
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etags file1.erl file2.erl</code>
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<p>This will create a file named <c>TAGS</c> in the current directory.</p>
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<p>The <c>etags</c> utility can also read a list of files from its
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standard input by supplying a single dash in place of the file
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names. This feature is useful when a project consists of a
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large number of files. The standard UNIX command <c>find</c>
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can be used to generate the list of files, e.g:</p>
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find . -name "*.[he]rl" -print | etags -</code>
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<p>The above line will create a <c>TAGS</c> file covering all the
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Erlang source files in the current directory, and in the
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subdirectories below.</p>
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<p>Please see the GNU Emacs Manual and the etags man page for more
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<p>The look and feel on an Erlang shell inside Emacs should be the
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same as in a normal Erlang shell. There is just one major
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difference, the cursor keys will actually move the cursor around
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just like in any normal Emacs buffer. The command line history
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can be accessed by the following commands: </p>
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<list type="bulleted">
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<item><em><c>C-up </c></em> or <em><c>M-p </c></em>
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(<c>comint-previous-input</c>) -
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Move to the previous line in the input history.</item>
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<item><em><c>C-down </c></em> or <em><c>M-n </c></em>
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(<c>comint-next-input</c>) - Move to the next line in the
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input history.</item>
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<p>If the Erlang shell buffer would be killed the command line
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history is saved to a file. The command line history is
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automatically retrieved when a new Erlang shell is started.</p>
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<title>Compilation</title>
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<p>The classic edit-compile-bugfix cycle for Erlang is to edit the
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source file in an editor, save it to a file and switch to an
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Erlang shell. In the shell the compilation command is given.
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Should the compilation fail you have to bring out the editor and
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locate the correct line.</p>
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<p>With the Erlang editing mode the entire edit-compile-bugfix cycle can
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be performed without leaving Emacs. Emacs can order Erlang to compile
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a file and it can parse the error messages to automatically place the
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point on the erroneous lines.</p>
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