Haskell library for the Microsoft Language Server Protocol. It currently implements all of the 3.15 specification.
It is split into two separate packages, lsp
and lsp-types
lsp-types
provides type-safe definitions that match up with the typescript definitions laid out in the specificationlsp
is a library for building language servers, handling:- JSON-RPC transport
- Keeping track of the document state in memory with the Virtual File System (VFS)
- Responding to notifications and requests via handlers
- Setting the server capabilities in the initialize request based on registered handlers
- Dynamic registration of capabilities
- Cancellable requests and progress notifications
- Publishing and flushing of diagnostics
There are two example language servers in the example/
folder. Simple.hs
provides a minimal example:
{-# LANGUAGE OverloadedStrings #-}
import Language.LSP.Server
import Language.LSP.Types
import Control.Monad.IO.Class
import qualified Data.Text as T
handlers :: Handlers (LspM ())
handlers = mconcat
[ notificationHandler SInitialized $ \_not -> do
let params = ShowMessageRequestParams MtInfo "Turn on code lenses?"
(Just [MessageActionItem "Turn on", MessageActionItem "Don't"])
_ <- sendRequest SWindowShowMessageRequest params $ \res ->
case res of
Right (Just (MessageActionItem "Turn on")) -> do
let regOpts = CodeLensRegistrationOptions Nothing Nothing (Just False)
_ <- registerCapability STextDocumentCodeLens regOpts $ \_req responder -> do
let cmd = Command "Say hello" "lsp-hello-command" Nothing
rsp = List [CodeLens (mkRange 0 0 0 100) (Just cmd) Nothing]
responder (Right rsp)
pure ()
Right _ ->
sendNotification SWindowShowMessage (ShowMessageParams MtInfo "Not turning on code lenses")
Left err ->
sendNotification SWindowShowMessage (ShowMessageParams MtError $ "Something went wrong!\n" <> T.pack (show err))
pure ()
, requestHandler STextDocumentHover $ \req responder -> do
let RequestMessage _ _ _ (HoverParams _doc pos _workDone) = req
Position _l _c' = pos
rsp = Hover ms (Just range)
ms = HoverContents $ markedUpContent "lsp-demo-simple-server" "Hello world"
range = Range pos pos
responder (Right $ Just rsp)
]
main :: IO Int
main = runServer $ ServerDefinition
{ onConfigurationChange = const $ pure $ Right ()
, doInitialize = \env _req -> pure $ Right env
, staticHandlers = handlers
, interpretHandler = \env -> Iso (runLspT env) liftIO
, options = defaultOptions
}
Whilst Reactor.hs
shows how a reactor design can be used to handle all
requests on a separate thread, such in a way that we could then execute them on
multiple threads without blocking server communication. They can be installed
from source with
cabal install lsp-demo-simple-server lsp-demo-reactor-server
stack install :lsp-demo-simple-server :lsp-demo-reactor-server --flag haskell-lsp:demo
See #haskell-ide-engine on IRC freenode