Add a DevelMain file for use in GHCi

.dir-locals.el

@@ -1,2 +1,3 @@
 ((haskell-mode . ((haskell-process-type . cabal-repl)
-                  (haskell-indent-spaces . 4))))
+                  (haskell-indent-spaces . 4)
+                  (haskell-process-use-ghci . t))))

DevelMain.hs

@@ -0,0 +1,52 @@
+{-# LANGUAGE ImplicitPrelude #-}
+
+-- | Devel web server.
+--
+-- > :l DevelMain
+-- > DevelMain.update
+--
+-- To start/restart the server.
+
+module DevelMain where
+
+import Application (getApplicationDev)
+
+import Control.Concurrent
+import Data.IORef
+import Foreign.Store
+import Network.Wai.Handler.Warp
+import Yesod
+import Yesod.Static
+
+-- | Start the web server.
+main :: IO (Store (IORef Application))
+main =
+  do s <- static "static"
+     c <- newChan
+     (port,app) <- getApplicationDev
+     ref <- newIORef app
+     tid <- forkIO
+              (runSettings
+                 (setPort port defaultSettings)
+                 (\req ->
+                    do handler <- readIORef ref
+                       handler req))
+     _ <- newStore tid
+     ref' <- newStore ref
+     _ <- newStore c
+     return ref'
+
+-- | Update the server, start it if not running.
+update :: IO (Store (IORef Application))
+update =
+  do m <- lookupStore 1
+     case m of
+       Nothing -> main
+       Just store ->
+         do ref <- readStore store
+            c <- readStore (Store 2)
+            writeChan c ()
+            s <- static "static"
+            (port,app) <- getApplicationDev
+            writeIORef ref app
+            return store