# Datastar Haskell SDK
[](https://github.com/starfederation/datastar-haskell/actions/workflows/test.yml)
A Haskell implementation of the [Datastar](https://data-star.dev/) SDK for building real-time hypermedia applications with server-sent events (SSE).
Live examples:
## License
This package is licensed for free under the [MIT License](LICENSE).
## Design
The SDK is built on [WAI](https://github.com/yesodweb/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`, and `wai`.
- **WAI streaming** -- SSE responses use WAI's native `responseStream`, giving
you a `ServerSentEventGenerator` callback with `sendPatchElements`,
`sendPatchSignals`, and `sendExecuteScript`.
- **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)`.
## API Overview
```haskell
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)
```
## Quick Start
Add `datastar-hs` to your `build-depends`, then:
```haskell
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 "Hello!
")
_ ->
respond $ responseLBS status404 [] "Not found"
main :: IO ()
main = Warp.run 3000 app
```