Last week, I posted a message to this list looking for people interested in joining projects using my domain-specific language Ur/Web. Some responses rightly chastised me for the lack of documentation on the core Ur language's novel type system features. I'm sure many Haskellers have had the experience of quickly grokking the interfaces of new libraries by reading their type signatures, and I think the same is true for Ur. So, to provide that initial bump of background that should help folks get started, I've begun an Ur tutorial: http://www.impredicative.com/ur/tutorial/ The chapters that are already there are intended to be sufficient to help any experienced Haskell programmer get started quickly with Ur/Web. In particular the second chapter on type-level programming may be of interest as a mind expander, even for folks who don't want to use Ur/Web. I'd love feedback about weaknesses in the tutorial! I also want to attach a challenge to this tutorial, as an expansion to an answer I gave earlier about why Ur/Web needs a new programming language and can't just be implemented as a Haskell library. Consider this online Ur/Web demo: http://www.impredicative.com/ur/demo/crud1.html The example involves a library component encapsulating functionality like that of Ruby on Rails's scaffolding: automatic generation of a standard web-based "admin interface" to an SQL database table. The Ur/Web version uses static typing to guarantee that any applications generated by this component are free of injection attacks and other generic problems. The guarantees apply both to app communication with server-side pieces (e.g., static type-checking of SQL) and client-side pieces (e.g., static type-checking of HTML). This is not done by type-checking individual invocations of the admin-interface component. Rather, the component is checked at a static type which guarantees correct operation for _any_specialization_parameters_. So, the challenge is, can this functionality be implemented in Haskell (GHC extensions fair game, any web framework allowed)? If so, how pretty is it? :)