Thursday, July 12, 2007

Using CodeSmith to create your own Domain-Specific-Language

[This was originally posted at]

Using CodeSmith to create your own Domain-Specific-Language

Yesterday I mentioned about software factories and domain-specific languages (DSL). A DSL is just that - working at a higher level language that maps to a specific problem domain instead of constantly re-inventing the wheel with a lower-level language. Some common examples of DSLs are:

  • SQL
  • Regular Expressions
  • XPath

Each of these could be achieved by coding in a "low level" language like C#, but you wouldn't think of doing that because it'd be too slow and error prone. It's so easy to use each language because it maps naturally to what you're trying to do in that domain.

This same concept applies to application development. For example, an application has different domains:

  • Initial data for your application (like security settings, roles, out-of-the-box dropdown values, etc...) - usually achieved with lots of custom SQL scripts.
  • UI formatting - usually achieved with tons of table or CSS references, or highly-refactored controls
  • Validation
  • Data access code

Each of these can have their own DSL, which you could easily create using a code-generator like CodeSmith. You could abstract the concepts to an XML schema, and then use CodeSmith as a "Compiler" to transform that xml into the appropriate output (sql, html, or C# code files). CodeSmith's out-of-the-box XmlProperty feature, along with text based templates and huge online community make it very easy to do.

For example, instead of having tons of custom SQL scripts for your security data, you may have a hierarchal XML file that (1) is completely refactored and maps directly to the business needs (something potentially impossible with a procedural language like SQL), (2) can be easily validated via the XML schema and CodeSmith checks, and (3) is much easier to track version history on.

Microsoft offers their own DSL toolkit, but I think it doesn't yet compete with CodeSmith because the MS DSL toolkit: (1) requires you to learn a whole new GUI syntax (whereas CodeSmith is intuitive C# and Xml templates), (2) seems limited in what it can generate, and (3) screws up Visual Studio by inserting a new reference (or something like that) into every project.

Once you start code-generating tedious stuff, such as using your own DSL, you'll never go back.

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