libraries.xml

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<!DOCTYPE chapter SYSTEM "chapter.dtd">
<chapter>
  <header>
    <title>Erlang Libraries</title>
    <prepared>Matthias Lang</prepared>
<docno></docno>
<date>2007-09-12</date>
    <rev>1.0</rev>
    <file>libraries.xml</file>
  </header>

<section><title> What's in the OTP libraries?</title>
<p>
	The full library descriptions are included with the open-source
	distribution and also 
	<url href="http://www.erlang.org/doc/">
	on line</url>. The highlights are:
</p>

	<section>
	<title>O&amp;M Support</title>
        <p>
		SASL, EVA, INETS and SNMP provide
		Operations- and maintenance-related functionality:
		release handling, alarm and event handling,
		administration via web browser and SNMP.
        </p>

	</section><section>
	<title>CORBA</title>
        <p>
		ORBER, CosEvent, CosTransactions and IC
		contain support for everything CORBA related.
        </p>
	</section><section>
	<title>Database</title>
        <p>
		Mnesia and Mnemosyne provide a real-time distributed 
		database which can be both in-RAM and on-disk.
		There is also a standard ODBC client driver.
        </p>
	</section><section>
	<title>ASN.1</title>
        <p>
		There is an ASN.1 compiler which produces Erlang code.
        </p>
	</section><section>
	<title>Standard Library</title>
        <p>
		A rich collection of modules provides
		everything from string, list and regular expression
		manipulation to	random number generation and calendar 
		lookups.
        </p>
	</section><section>
	<title>Structural Components</title>
	<p>
		gen_server, gen_fsm, 
		and supervision trees provide standard ways of implementing
		client/server subsystems, state machines and 
		supervised fault-tolerant systems.
        </p>
	</section><section>
	<title>GUI and Graphics</title>
	<p>
		wx, gs and webtool provide ways to build a gui.
        </p>
	</section>

<p>
	Among other things, there are also HTTP, SSH and FTP servers.

</p></section>
<section><title> Is there a collection of data structures, e.g. balanced trees?</title>
<p>
	Linked lists are a fundamental part of Erlang, as are tuples.
	The other standard data structures are:
	</p>

	<table>
	<row><cell>Module</cell><cell>Description</cell></row>
	<row><cell>sets</cell>
              <cell>sets, i.e. a collection of unique elements.</cell>
        </row>
	<row><cell>gb_sets</cell>
              <cell>sets, but based on a general balanced data structure</cell>
        </row>
	<row><cell>gb_tree</cell>
              <cell>a general balanced tree</cell>
        </row>
	<row><cell>dict</cell>
              <cell>maps, also called associative arrays</cell>
        </row>
	<row><cell>ets</cell>
              <cell>hash tables and ordered sets (trees)</cell>
        </row>
	<row><cell>dets</cell>
              <cell>on-disk hash tables</cell>
        </row>
        <tcaption>Standard data structures</tcaption>
	</table>
	
<p>

	The <url href="http://www.erlang.org/user.html">
	contributions area</url>
	at the erlang.org site includes	modules for
	double-ended queues and balanced trees.
	</p>

        <p>
	<c>ordset</c> and <c>orddict</c> are 
	not really suitable for large amounts of data: they are no 
	better that lists for many common operations, e.g.
	inserting an element is O(n) for both. <c>dict</c>
	and <c>sets</c> are usually preferred.
	</p><p>

	In practice, Erlang programs use lists (either natively or
	via <c>dict</c>) for data structures involving 
	up to a few hundred elements and use <c>ETS</c> 
	(the Erlang Term Store) or mnesia 
	for anything larger. ETS uses hashing to allow near 
	constant-time access to almost arbitrarily large amounts of data.
	</p><p>
	
	For a collection of data consisting of a few (tens or
	hundreds) items, lists often outperform both ETS and
	trees. For large numbers of small items, ETS tends to 
	work best. For larger items, balanced trees can outperform
	ETS because they avoid copying the data.

</p></section>
<section><title>Is there a serial port driver for Erlang?</title>
<p>
	Johan Bevemyr wrote one which works for unix machines. The
	code is freely available at 
	<url href="http://www.erlang.org/user.html"> the contributions
	area</url> as <em>serial-1.0</em>.
	</p><p>

	There have been discussions on the mailing list about writing
	a more general driver which also works on windows machines.
	Nothing much has come of this (lack of interest?).

</p></section>
<section><title>Is there a toolkit for building GUIs?</title>
<p>

	There are several. 
</p><p>

	The <url
	href="http://www.erlang.org/doc/apps/wx/">wxErlang</url>
	application lets you make GUIs with 
	<url href="http://www.wxwidgets.org">wxWidgets</url>, a
	cross-platform toolkit. wxErlang is part of the OTP
	distribution.
</p><p>

	The older <url
	href="http://www.erlang.org/doc/apps/gs/">gs</url> application
	uses TK as a backend. Some people prefer to work with TK
	through <url href="http://sourceforge.net/projects/erlgtk/">
	etk</url>. ETK is a fairly direct binding to the TK toolkit.
	</p><p>

	Other graphics-related items on 
	<url href="http://jungerl.sourceforge.net/">sourceforge</url>
	are gtkNode (a C node which gives access to a large subset of GTK2) and
	gd1_drv (a driver which dynamically creates JPEG and PNG images).

	There are a few projects involving experimental graphics
	interfaces, including a binding to gtk (Ed: can someone 
	send me some more information about this!), an <url
	href="http://www.wings3d.com/">OpenGL modeller</url>
	and some <url href="http://www.sics.se/~joe/ex11/">
	interesting work</url> to directly access the X protocol.
	</p><p>

</p></section>
<section><title>I've written a library to handle XYZ. How do I get it into the standard Erlang distribution?</title>
<p>

        This takes more work and patience than most people
        have. Kent Boortz described many of the hurdles 
        <url href="http://erlang.org/pipermail/erlang-questions/2004-May/012327.html">on the mailing list</url>.
</p><p>
        There are other ways to spread your code, including
        distributing it from your own website or adding it to
        the <url href="http://jungerl.sourceforge.net/">jungerl</url>.

</p>
</section>        
</chapter>