Zwaluw is a Haskell combinator library for specifying URL routers. The routers are bidirectional: they parse a URL into a sitemap and serialise sitemap values back to URLs. Because you specify such a router only once, the resulting parser and serialiser are each other's inverse by construction.

Zwaluw derives pure routers for all your constructors. You can either use pure Template Haskell to derive these routers (see ExampleTH.hs), or use the regular package (see ExampleRegular.hs). With those constructor routers, you can build your own router, combining them and producing/consuming URLs. Both files contain an example of this.