rowdy is DSL for defining web application routes. Check out the examples!
Servant has a cool DSL for routes. It is embedded into the type system, and type level programming in Haskell isn't nearly as pleasant as value-level programming. As a result, there can be a lot of complexity with common combinators, and you must be familiar with advanced type-level techniques to work with it.
Yesod has a cool DSL for routes. It uses a Template Haskell quasiquoter to parse a non-Haskell DSL into a data structure, which is then used to generate routes. Since it isn't Haskell, you don't get good error messages, syntax highlighting, or the ability to define your own combinators.
rowdy is a value level DSL for defining routes. A Template Haskell splice can
then interpret the value at compile-time and provide a Yesod representation, or a
Servant representation, or whatever else you'd like!
rowdy supports Yesod-style routes concretely and completely. The
Servant support is limited and not ready for publish yet -- if you have ideas
for providing an extensible design for this, please let me know!