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diff --git a/lambda-calcul/haskell/src/Minilang/Server.hs b/lambda-calcul/haskell/src/Minilang/Server.hs
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+{-# LANGUAGE TypeApplications #-}
+
+-- | An HTTP server providing a basic REPL and text editor to work
+-- collaboratively on Minilang code.
+module Minilang.Server where
+
+import Control.Concurrent.Async
+import Control.Concurrent.STM.TVar
+import Data.Aeson
+  ( Value,
+    decode,
+    object,
+    (.=),
+  )
+import Data.ByteString.Lazy (fromStrict)
+import Data.Default
+import Data.Text (Text)
+import Minilang.Log
+import Minilang.REPL.Net
+import Network.Wai
+import Network.Wai.Application.Static
+import Network.Wai.Handler.Warp as Warp
+import Network.Wai.Middleware.RequestLogger
+import Network.Wai.Middleware.RequestLogger.JSON
+import System.Log.FastLogger (fromLogStr)
+import           Control.Concurrent.Async
+
+data Server = Server
+    { serverThread :: Maybe (Async ())
+    -- ^If the server is running, this will contain the underlying
+    , serverPort   :: Int
+    -- ^The actual port this server is listening on. Useful when
+    }
+
+-- | Starts HTTP server on given port.
+--  This server serves static files from public/ directory and also
+--  exposes a WebSocket-based REPL under `/repl` path.
+startServer :: Int -> IO Server
+startServer serverPort = do
+  envs <- newTVarIO mempty
+  logger <- newLog "minilang"
+  loggerMiddleware <- runHTTPLog logger
+  let app = loggerMiddleware $ runNetREPL logger envs staticResources
+  (port, action) <- startWarp serverPort app
+  thread <- async action
+  logInfo logger $ object ["action" .= ("Started" :: Text), "port" .= port]
+  pure $ Server (Just thread) port
+  where
+    startWarp 0 app = do
+      (port, socket) <- openFreePort
+      pure (port, Warp.runSettingsSocket defaultSettings socket app)
+    startWarp port app = pure (port, Warp.run port app)
+
+    runHTTPLog logger =
+      mkRequestLogger $
+        def
+          { outputFormat = CustomOutputFormatWithDetails formatAsJSON,
+            destination = Callback (\str -> logInfo logger (decode @Value $ fromStrict $ fromLogStr str))
+          }
+
+stopServer :: Server -> IO ()
+stopServer (Server (Just th) _) = cancel th
+stopServer _ = pure ()
+
+waitServer :: Server -> IO ()
+waitServer (Server (Just th) _) = wait th
+waitServer _ = pure ()
+
+-- | Serve static resources under `public/` directory
+staticResources :: Application
+staticResources = staticApp (defaultFileServerSettings "public")