servant-router
servant-router routes a URI given a Servant API and an appropriate handler.
In web applications,
this is used to make single page applications (SPAs) with front-end routing,
letting you share portions of your Servant APIs between the client and server.
servant-router does not depend on reflex or any GHCJS packages.
It's intended to be a general purpose URI router on any platform.
Combined with reflex-dom, servant-reflex, and reflex-dom-contrib,
this makes for a very satisfactory front-end Haskell experience.
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeOperators #-}
module Main where
import Control.Monad.Except
import Data.Proxy
import Reflex.Dom
import Reflex.Dom.Contrib.Router
import Servant.API
import Servant.Router
type MyApi = "books" :> Capture "id" Int :> View
:<|> "search" :> QueryParam "keywords" String :> View
myApi :: Proxy MyApi
myApi = Proxy
main :: IO ()
-- reflex-dom-contrib provides a 'routeSite' function
-- for routing single page applications with reflex.
-- servant-router uses the provided uri String to perform the routing.
main = routeSite $ \uri -> do
let handler = books :<|> search
books i = do
-- Here, you would get and display a book.
-- Return a Reflex event for changing the browser location.
return never
search Nothing = do
-- Here, you would display a search bar.
return never
search (Just keywords) = do
-- Here you would display the search bar plus results.
return never
-- With the handler constructed, run the router with the uri.
result <- runExceptT $ runRoute uri myApi handler
case result of
-- If 'Left', there was no correct route for the uri.
Left _ -> do
el "div" $ text "No such page"
return never
-- If 'Right', the result of the route is returned.
Right e -> return e
Serving
When using servant-router on the front-end in Single Page Applications (SPAs),
you still need to serve the application from the back-end.
To share the routing layout between the front-end and back-end,
the View endpoints need to be converted to a verb like Get.
Plus, with an SPA,
all the end-points should serve the same HTML on the back-end.
To do this, use the ViewTransform type family, and constHandler function.
type Views = "books" :> View
:<|> "search" :> QueryParam "query" String :> View
-- Equivalent to:
--
-- type ViewsServer = "books" :> Get '[HTML] Blaze.Html
-- :<|> "search" :> QueryParam "query" String :> Get '[HTML] Blaze.Html
type ViewsServer = ViewTransform Views (Get '[HTML] Blaze.Html)
viewsServer :: Server ViewsServer
viewsServer = constHandler
(Proxy :: Proxy Views)
(Proxy :: Proxy Handler) $
docTypeHtml $ do
H.head $ return ()
body $
script ! src "app.js" $ return ()
