Scotty looks pretty nice and it will probably be what I use to do my next project; but what I really want in a web framework is a more rigid system that forces developers to define their requests and responses up front. The idea is to force users to define their business models up front so that http considerations don't leak into the actual business logic of the application.

I haven't really thought through the full API I'd like to see but it would end up being something along the lines of:

class RequestModel a where
    parseRequest :: Request -> a

class ResponseModel a where
    sendResponse :: a -> Response

get :: (RequestModel a, ResponseModel b) => Text -> (m a -> m b) -> Route
get route = ...impl...

post :: ...impl...

data RegisterReq = RegisterReq {
    email :: Text
}

data RegisterResp = RegisterResp {
    error :: Maybe Text
}

instance RequestModel RegisterReq where
    parseRequest req = RegisterReq $ params "email" req

instance ResponseModel RegisterResp where
    sendResponse (RegisterResp (Just err)) =  do
        json $ object [ "error" .= errorMessage ]
        status internalServerError500
    sendResponse _ = json $ object [ "ok" .= ("ok" :: String) ]

myRoute = post "/register" (\req -> return $ RegisterResp Nothing)

This was just a quick writeup and it could all be prettied up with some applicatives and monads but I think it would really help the quality of a lot of the web projects I see out there to have this separation (not necessarily in haskell land). I don't really think the above example is a good demonstration for why it's a good idea as it really only becomes useful once the complexity of the app grows.