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<h2>Book on Domain-Specific Languages with Groovy</h2>

<p>You can have a look at our <a class="confluence-link" href="/display/GROOVY/Books" data-linked-resource-id="73818" data-linked-resource-type="page" data-linked-resource-default-alias="Books" data-base-url="http://docs.codehaus.org">books section</a> listing Fergal Dearle's book titled &quot;<a href="https://www.packtpub.com/groovy-for-domain-specific-languages-dsl/book">Groovy for Domain-Specific Languages</a>&quot; published by Packt Publishing.</p>

<h2>Tutorial on DSLs </h2>

<p>Guillaume Laforge and Paul King presented a <a href="http://glaforge.appspot.com/article/groovy-domain-specific-languages-in-chicago">session at SpringOne2GX on the various techniques for authoring DSLs</a>, and integrating them in your applications.</p>

<p>Guillaume Laforge and John Wilson presented a <a href="http://glaforge.free.fr/groovy/QCon-Tutorial-Groovy-DSL-2-colour.pdf">tutorial on Groovy DSLs</a> at the QCon 2007 conference in London.</p>

<p>Matt Secoske presented a session on <a href="http://blog.secosoft.net/wp-content/oscon2007/groovy_dsl_oscon.ppt">Implementing DSLs in Groovy</a> at the OSCON 2007 conference.</p>

<h2>Groovy features enabling DSLs </h2>

<p>Groovy is particularly well suited for writing a DSL: <a href="http://en.wikipedia.org/wiki/Domain-specific_programming_language">Domain-Specific Language</a>. A DSL is a mini-language aiming at representing constructs for a given domain. Groovy provides various features to let you easily embed DSLs in your Groovy code:</p>
<ul>
	<li>the <a class="confluence-link" href="/display/GROOVY/BuilderSupport" data-linked-resource-id="10594" data-linked-resource-type="page" data-linked-resource-default-alias="BuilderSupport" data-base-url="http://docs.codehaus.org">builder</a> concept lets you write tree structured languages</li>
	<li>you can add new methods and properties on arbitrary classes through <a class="confluence-link" href="/display/GROOVY/TMPGroovy+Categories" data-linked-resource-id="27920" data-linked-resource-type="page" data-linked-resource-default-alias="TMPGroovy Categories" data-base-url="http://docs.codehaus.org">categories</a> or custom metaclasses, even numbers: 3.euros, 5.days, etc, as shown in this <a href="http://groovy.dzone.com/news/domain-specific-language-unit%2d">article explaining how to write a unit handling mini-DSL</a></li>
	<li>most <a class="confluence-link" href="/display/GROOVY/Operator+Overloading" data-linked-resource-id="2764" data-linked-resource-type="page" data-linked-resource-default-alias="Operator Overloading" data-base-url="http://docs.codehaus.org">operators can be overloaded</a>: 5.days + 6.hours, myAccount += 400.euros</li>
	<li>passing maps to methods makes your code look like methods have named parameters: move( x: 500.meters, y: 1.kilometer )</li>
	<li>you can also create your own control structures by passing <a class="confluence-link" href="/display/GROOVY/Closures+-+Informal+Guide" data-linked-resource-id="2729" data-linked-resource-type="page" data-linked-resource-default-alias="Closures - Informal Guide" data-base-url="http://docs.codehaus.org">closures</a> as the last argument of a method call: ifOnce( condition )<br />
{ ... }; inTransaction { ... }</li>
	<li>it is also possible to add dynamic methods or properties (methods or properties which don't really exist but that can be intercepted and acted upon) by implementing <a href="http://groovy.codehaus.org/apidocs/groovy/lang/GroovyObject.html">GroovyObject</a> or creating a custom <a href="http://groovy.codehaus.org/apidocs/groovy/lang/MetaClass.html">MetaClass</a></li>
</ul>

<p>Guillaume Laforge gave some <a href="http://glaforge.free.fr/weblog/index.php?itemid=187">thoughts and examples</a> on that topic on his blog. John Wilson has implemented a DSL in his <a href="http://docs.codehaus.org/display/GROOVY/Google+Data+support">Google Data Support</a> to make operations on dates easier.</p>

<p>Joachim Baumann wrote an article showing how to <a href="http://joesgroovyblog.blogspot.com/2007/09/and-miles-to-go-before-i-sleep.html">implement a small DSL for measurement calculation</a>, which uses some of the techniques like adding properties to numbers, or overloading operators. Guillaume Laforge also wrote an article on <a href="http://groovy.dzone.com/news/domain-specific-language-unit-">representing units using the JScience library</a>.</p>

<p>Andy Glover also plays with internal DSLs in Groovy by producing a <a href="http://thediscoblog.com/2007/11/05/internal-dsls-groovy-style/">behavior testing DSL</a>.</p>

<p>Inspired by an article from Bruce Tate <a href="http://www-128.ibm.com/developerworks/java/library/j-cb03137/index.html">IBMs Alphaworks</a> a couple of samples were written in groovy.</p>
<ul>
	<li><a href="http://www.bytemycode.com/snippets/snippet/639/">Chris vanBuskirk</a> uses arrays and maps to model the injection of the state transitions.</li>
	<li><a href="http://www.bytemycode.com/snippets/snippet/640/">Edward Sumerfield</a> uses closures to inject the state transitions.</li>
</ul>

<p>Inspired by <a href="http://rspec.rubyforge.org/">RSpec</a> (and also by random episodes of Family Guy) <a href="http://codeforfun.wordpress.com/2007/04/09/gspec-for-java-bdd/">an example</a> of a unit testing DSL using Groovy</p>
<ul>
	<li><a href="http://codeforfun.wordpress.com">Clifton Craig</a> uses Builders in Groovy to create <a href="http://codeforfun.wordpress.com/gspec/">GSpec.</a></li>
</ul>

<h3>When Groovy's not enough </h3>

<p>If you have the need to write your own language completely, consider using a compiler compiler. There are many to choose from, e.g. Antlr, JavaCC, SableCC, Coco/R, Cup/JLex/JFl;ex, BYacc/J, Beaver, etc.  See <a href="http://en.wikipedia.org/wiki/List_of_compiler-compilers">wikipedia</a> for an interesting list. Some of these can even benefit from Groovy. Here is a groovy example for <a href="http://jparsec.codehaus.org/Groovy+Parser">JParsec</a>.</p>