A Haskell implementation of the Datastar SDK for building real-time hypermedia applications with server-sent events (SSE).
Live examples: https://hamalainen.dev
This package is licensed for free under the MIT License.
The SDK is built on WAI (Web Application Interface), Haskell's standard interface for HTTP servers. This means it works with any WAI-compatible server (Warp, etc.) and any framework built on WAI (Yesod, Scotty, Servant, etc.) without framework-specific adapters.
Key design decisions:
- Minimal dependencies -- the library depends only on
aeson,bytestring,http-types,text, andwai. - WAI streaming -- SSE responses use WAI's native
responseStream, giving you aServerSentEventGeneratorcallback withsendPatchElements,sendPatchSignals, andsendExecuteScript. - No routing opinion -- the SDK provides request helpers (
readSignals,isDatastarRequest) but doesn't impose a routing framework. The examples use simple pattern matching on(requestMethod, pathInfo).
import Hypermedia.Datastar -- Create an SSE response sseResponse :: DatastarLogger -> (ServerSentEventGenerator -> IO ()) -> Response -- Send events sendPatchElements :: ServerSentEventGenerator -> PatchElements -> IO () sendPatchSignals :: ServerSentEventGenerator -> PatchSignals -> IO () sendExecuteScript :: ServerSentEventGenerator -> ExecuteScript -> IO () -- Read signals from a request (query string for GET, body for POST) readSignals :: FromJSON a => Request -> IO (Either String a)
Add datastar-hs to your build-depends, then:
import Hypermedia.Datastar import Network.Wai import Network.Wai.Handler.Warp qualified as Warp app :: Application app req respond = case (requestMethod req, pathInfo req) of ("GET", ["hello"]) -> do Right signals <- readSignals req respond $ sseResponse nullLogger $ \gen -> do sendPatchElements gen (patchElements "<div id=\"message\">Hello!</div>") _ -> respond $ responseLBS status404 [] "Not found" main :: IO () main = Warp.run 3000 app