Presents your  
JAVA E-NEWSLETTER for August 14, 2003 
 
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CREATE MINI-LANGUAGES USING ANTLR   
  
In the life of a complicated system, it may become crucial at some point
to change the system's behavior without recompiling and redeploying it. 
You can achieve this functionality by creating a domain or mini-language
specifically for manipulating system components. (Domain languages are 
small languages that allow an application's programmer or administrator to
change how components interact with each other, and even to decide what 
components will exist when the system is running.) After you decide that
you need a domain language, you'll have to design its syntax; this means
determining the language's capabilities and what it will look like.   

Once you've decided on the language's syntax, the next step is to create
a parser for the language, which can be quite a large, arduous task. If 
you've ever built a parser by hand, then you know that the complexity of
the parser grows exponentially in relation to the complexity of the language.   
  
One of the tools at your disposal is ANTLR (ANother Tool for Language 
Recognition), which allows you to describe your language in a text file.
If you point ANTLR at this file, it will generate a Lexer and a Parser that
are capable of processing your new language. A Lexer translates 
characters into language tokens, and a Parser uses these tokens to perform work. 
Once ANTLR has generated these classes for your mini-language, you can 
use them in your applications to manipulate your system.   
  
Even with the help of ANTLR, creating your first mini-language can be 
quite complicated and require a lot of work. The good news is that the 
folks who maintain ANTLR provide a number of resources to get you started. 
Visit ANTLR's site and take a look for yourself.   
http://ct.com.com/click?q=94-rOTNQaIYkZMFbBqW9PRW8W990Qz2   
  
David Petersheim is a Senior Java Developer with Genscape, Inc. He 
designs and develops server-side applications to acquire and process
real-time energy data.   
  
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