What's your favorite Domain Specific Language?

[This was originally posted at http://timstall.dotnetdevelopersjournal.com/whats_your_favorite_domain_specific_language.htm]

I love domain specific languages (DSL). The idea is that instead of programming at a low level (i.e. tedious and error-prone), you program at a higher level of abstraction. This means coding with a language (or even class library) that closely maps to the problem domain. For example, here are several domain specific languages. While you could try to do without, it just becomes so much easier with them:

 

DSL	Purpose	Example	Manually doing without:
Regular Expressions	Find and replace patterns in text	Find all numeric decimals in a file	You could use core string methods like SubString and IndexOf
SQL	Manage database data	Select all employees that meet a certain criteria	You could do selects by getting the entire dataset and cycling through the object model
XPath	Query xml data	Get the custom order xml nodes where price is less than $100	You could step through the xml with a reader, or loop through an XmlDocument
MSBuild	Microsoft's build engine to automate your processes	Compile your application on a build server, run unit tests, and then produce MSI outputs	You could use System.Diagnostics to manually run a bunch of commands, and keep track of error conditions and logging output yourself.
String Format Expressions	Format a string using var.ToString("myPattern")	Format the number 12.3456 to only two decimal places	You could use core string methods, and pick apart the variable, and re-assemble it.

 

The point is that while someone could get by without knowing the appropriate domain language, it's just not practical to tackle the domain without it. Each of these has tons of tutorials and quickstarts, so there's no reason to avoid them. An application developer should probably be comfortable with most of these.

 

So, what's your favorite domain specific language?