diff --git a/LICENSE.txt b/LICENSE.txt
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--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
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+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<http://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<http://www.gnu.org/philosophy/why-not-lgpl.html>.
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,33 @@
+# Robin
+
+Robin is a build daemon for Haskell development.
+
+## Usage
+
+    robin (start | stop | build | watch | debug)
+
+This daemon rebuilds a cabalized Haskell project whenever a source file
+changes. It runs one of the following commands:
+
+* `./robin.sh`, if that file exists, or
+* `stack build`, if `stack.yaml` exists, or
+* `cabal build`, otherwise.
+
+## Commands
+
+* start - if the current project doesn't already have a daemon, start one
+* stop - stop the daemon for the current project
+* build - show the output of the last build, or if a build is in progress, wait
+  for completion and then show its output
+* watch - take over the console, always showing the latest build output
+* debug - like _start_, but doesn't daemonize
+
+The default command is _build_.
+
+Note: the _current project_ is assumed to be the root of the git working copy
+which contains the current directory.  definition.
+
+
+## Vim integration
+
+    echo 'setlocal makeprg=robin' >> ~/.vim/ftplugin/haskell.vim
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/robin.cabal b/robin.cabal
new file mode 100644
--- /dev/null
+++ b/robin.cabal
@@ -0,0 +1,66 @@
+
+name:           robin
+version:        0.1.0.0
+cabal-version:  >= 1.10
+build-type:     Simple
+license:        GPL-3
+license-file:   LICENSE.txt
+copyright:      (c) 2013-2015 Karl Voelker
+author:         Karl Voelker
+maintainer:     robin@karlv.net
+stability:      experimental
+homepage:       https://www.github.com/ktvoelker/robin
+bug-reports:    https://www.github.com/ktvoelker/robin/issues
+synopsis:       A build daemon for Haskell development
+description:
+  Robin is a daemon for Haskell developers. It runs a build whenever a source
+  file changes. Cabal, Stack, and custom builds are all supported.
+category:       Development
+tested-with:    GHC == 7.10.2
+extra-source-files:
+  stack.yaml,
+  README.md
+
+Source-repository head
+  type: git
+  location: https://github.com/ktvoelker/robin.git
+
+Executable robin
+  main-is: Main.hs
+  default-language: Haskell2010
+  hs-source-dirs: src
+  other-modules:
+    Command
+    Lock
+    PidFile
+    Types
+    Util
+    Watch
+  ghc-options:
+    -Wall
+    -fno-warn-missing-signatures
+    -fno-warn-name-shadowing
+    -fno-warn-orphans
+  build-depends:
+    Cabal,
+    base >= 4 && < 5,
+    directory,
+    filepath,
+    fsnotify,
+    hdaemonize,
+    lens,
+    lifted-base,
+    monad-control,
+    mtl,
+    process,
+    resourcet,
+    text,
+    time,
+    unix
+  default-extensions:
+    FlexibleContexts
+    LambdaCase
+  other-extensions:
+    OverloadedStrings
+    TemplateHaskell
+
diff --git a/src/Command.hs b/src/Command.hs
new file mode 100644
--- /dev/null
+++ b/src/Command.hs
@@ -0,0 +1,16 @@
+
+module Command where
+
+import Control.Monad.Trans
+import System.Directory
+import System.FilePath
+import System.Process
+
+buildCommand :: (MonadIO m) => FilePath -> m CreateProcess
+buildCommand dir = liftIO $
+  doesFileExist (dir </> "robin.sh") >>= \case
+    True -> return $ proc "./robin.sh" []
+    False -> doesFileExist (dir </> "stack.yaml") >>= \case
+      True -> return $ proc "stack" ["build"]
+      False -> return $ proc "cabal" ["build"]
+
diff --git a/src/Lock.hs b/src/Lock.hs
new file mode 100644
--- /dev/null
+++ b/src/Lock.hs
@@ -0,0 +1,21 @@
+
+module Lock (ensureLock, withLock) where
+
+import Control.Exception.Lifted
+import Control.Monad.Trans
+import Control.Monad.Trans.Resource
+import System.Posix.Semaphore
+
+name :: String
+name = "/robin-xRBVe8IB7Z"
+
+ensureLock :: (MonadIO m) => m Semaphore
+ensureLock = liftIO $ semOpen name flags 0x700 1
+  where
+    flags = OpenSemFlags { semCreate = True, semExclusive = False }
+
+withLock :: (MonadBaseControl IO m, MonadIO m) => m a -> m a
+withLock m =
+  liftIO ensureLock
+  >>= \sem -> bracket_ (liftIO $ semWait sem) (liftIO $ semPost sem) m
+
diff --git a/src/Main.hs b/src/Main.hs
new file mode 100644
--- /dev/null
+++ b/src/Main.hs
@@ -0,0 +1,190 @@
+
+{-# LANGUAGE OverloadedStrings #-}
+module Main (main) where
+
+import Control.Concurrent
+import Control.Lens
+import Control.Monad
+import Control.Monad.Except
+import Control.Monad.Reader
+import Control.Monad.Trans.Resource
+import System.Environment
+import System.Exit
+import System.FilePath
+import System.IO
+import System.Posix.Daemonize
+import System.Posix.Directory
+import System.Posix.IO
+import System.Posix.Process
+import System.Posix.Signals
+import System.Process
+
+import Command
+import Lock
+import PidFile
+import Types
+import Watch
+import Util
+
+check :: Either Err a -> IO ()
+check = maybe (return ()) print . leftMaybe
+
+startDaemon :: IO ()
+startDaemon = do
+  wd <- getWorkingDirectory
+  -- Fork before calling daemonize, because it calls exit after forking the daemon.
+  void $ forkProcess $ daemonize $ do
+    changeWorkingDirectory wd
+    (check =<<) . runI $ do
+      logFileString <- view envLogFile
+      let
+      { openLog = do
+          (hKey, logHandle) <- allocate (openFile logFileString AppendMode) hClose
+          (fdKey, logFd) <- allocate (handleToFd logHandle) closeFd
+          void $ unprotect hKey
+          void $ allocate (dupTo logFd stdOutput) closeFd
+          release fdKey
+      }
+      openLog
+      debug "Daemon started; log opened."
+      start
+
+usage :: IO ()
+usage = hPutStrLn stderr
+  "Usage: cabal-build-daemon (start | stop | build | watch | debug)"
+
+commands :: [(String, IO ())]
+commands =
+  [ ("start" , startDaemon)
+  , ("debug" , runI start >>= check)
+  , ("stop"  , runI stop >>= check)
+  , ("build" , startDaemon >> runM waitForBuild >>= check)
+  , ("watch" , startDaemon >> runM watchBuilds >>= check)
+  , ("help"  , usage)
+  ]
+
+errExit :: IO ()
+errExit = usage >> exitFailure
+
+command :: [String] -> IO ()
+command []     = command ["build"]
+command [name] = maybe errExit id $ lookup name commands
+command _      = errExit
+
+main :: IO ()
+main = getArgs >>= command
+
+exts :: [String]
+exts = ["hs", "lhs", "cabal", "yaml"]
+
+srcPred :: WatchPred
+srcPred = PredDisj $ map PredExtension exts
+
+start :: I ()
+start = do
+  repoRoot <- view envRepoRoot
+  readPidFile >>= \pid -> case pid of
+    Just pid -> do
+      debugs $ "Daemon already running: pid " ++ show pid
+    Nothing -> do
+      debug "Creating lock..."
+      void ensureLock
+      debug "Starting notification manager..."
+      do
+        mainThread <- liftIO myThreadId
+        liftIO $ do
+          let
+          { handler = Catch $ do
+              debug "Caught signal; throwing ExitSuccess to main thread"
+              throwTo mainThread $ ExitSuccess
+          }
+          let exitOn sig = void $ installHandler sig handler Nothing
+          debug "Installing signal handlers..."
+          exitOn sigTERM
+          exitOn sigINT
+        debug "Writing pidfile..."
+        writePidFile
+        debug "Starting event loop..."
+        let
+        { w = (emptyWatch $ repoRoot)
+          { wRecurse  = True
+          , wPred     = srcPred
+          }
+        }
+        watchForever [w] build
+
+-- TODO use ResourceT to be safer about the handle
+runBuildProcess :: CreateProcess -> I ExitCode
+runBuildProcess p = do
+  repoRoot <- view envRepoRoot
+  outHandle <- view envOutputFile >>= liftIO . flip openFile WriteMode
+  liftIO $ do
+    (_, _, _, ph) <- createProcess $ p
+      { cwd = Just repoRoot
+      , std_in = Inherit
+      , std_out = Inherit
+      , std_err = UseHandle outHandle
+      }
+    code <- waitForProcess ph
+    hClose outHandle
+    return code
+
+build :: I ()
+build = withLock $ view envRepoRoot >>= buildCommand >>= runBuildProcess >>= \case
+  ExitSuccess -> writeCode 0
+  ExitFailure n -> writeCode n
+
+writeCode :: (MonadReader Env m, MonadIO m) => Int -> m ()
+writeCode n = view envStatusFile >>= liftIO . flip writeFile (show n)
+
+stop :: I ()
+stop = do
+  pid <- readPidFile
+  case pid of
+    Nothing -> return ()
+    Just pid -> liftIO $ signalProcess sigTERM pid
+
+waitForBuild :: M ()
+waitForBuild = do
+  (liftIO . exitWith =<<) . withLock $ do
+    view envOutputFile >>= liftIO . readFile >>= liftIO . putStr
+    statusStr <- view envStatusFile >>= liftIO . readFile
+    return $ case readMaybe statusStr of
+      Nothing -> ExitFailure 42
+      Just 0  -> ExitSuccess
+      Just n  -> ExitFailure n
+
+watchBuilds :: M ()
+watchBuilds = do
+  statusFile <- view envStatusFile
+  let
+  { w = (emptyWatch $ takeDirectory statusFile)
+    { wPred = PredConj [PredPath statusFile, PredInverse PredRemoved]
+    }
+  }
+  watchForever [w] lessDump
+
+lessDump :: M ()
+lessDump = void $
+  use stLessProcess >>= maybe (return ()) (liftIO . terminateProcess)
+  >> dump >>= assign stLessProcess . Just
+
+clearTerminal :: (MonadIO m) => m ProcessHandle
+clearTerminal = liftIO $ runProcess "clear" [] Nothing Nothing Nothing Nothing Nothing
+
+dump :: M ProcessHandle
+dump = do
+  clearProc <- clearTerminal
+  lessFileString <- view envLessFile
+  withLock
+    $ view envOutputFile
+      >>= liftIO . readFile
+      >>= liftIO . writeFile lessFileString
+  outHandle <- liftIO $ openFile lessFileString ReadMode
+  void $ liftIO $ waitForProcess clearProc
+  lessProc <-
+    liftIO
+    $ runProcess "less" [] Nothing Nothing (Just outHandle) Nothing Nothing
+  liftIO $ hClose outHandle
+  return lessProc
+
diff --git a/src/PidFile.hs b/src/PidFile.hs
new file mode 100644
--- /dev/null
+++ b/src/PidFile.hs
@@ -0,0 +1,32 @@
+
+module PidFile where
+
+import Control.Lens
+import Control.Monad.Except
+import Control.Monad.Reader
+import Control.Monad.Trans.Resource
+import System.Directory
+import System.Posix.Process
+import System.Posix.Types
+
+import Types
+import Util
+
+readPidFile :: (MonadIO m, MonadReader Env m) => m (Maybe CPid)
+readPidFile = do
+  view envPidFile
+  >>= \fp -> liftIO (doesFileExist fp)
+  >>= \ex -> case ex of
+    False -> return Nothing
+    True  -> liftIO (readFile fp) >>= return . readMaybe
+
+requirePidFile :: (MonadIO m, MonadReader Env m, MonadError Err m) => m CPid
+requirePidFile = readPidFile >>= maybe (throwError Err) return
+
+writePidFile :: (MonadIO m, MonadReader Env m, MonadResource m) => m ()
+writePidFile = do
+  fp  <- view envPidFile
+  pid <- liftIO getProcessID
+  _   <- allocate (writeFile fp $ show pid) (const $ removeFile fp)
+  return ()
+
diff --git a/src/Types.hs b/src/Types.hs
new file mode 100644
--- /dev/null
+++ b/src/Types.hs
@@ -0,0 +1,83 @@
+
+{-# LANGUAGE OverloadedStrings, TemplateHaskell #-}
+module Types where
+
+import Prelude hiding (FilePath, putStrLn)
+
+import Control.Lens
+import Control.Monad.Except
+import Control.Monad.Reader
+import Control.Monad.State
+import Control.Monad.Trans.Resource
+import Data.Text (Text(), pack)
+import Data.Text.IO (putStrLn)
+import System.Directory
+import System.IO (hFlush, stdout)
+import System.FilePath
+import System.Process
+
+import Util
+
+data St =
+  St
+  { _stLessProcess :: Maybe ProcessHandle
+  }
+
+makeLenses ''St
+
+emptySt :: St
+emptySt = St Nothing
+
+data Env =
+  Env
+  { _envRepoRoot   :: FilePath
+  , _envRobinRoot  :: FilePath
+  , _envStatusFile :: FilePath
+  , _envOutputFile :: FilePath
+  , _envLessFile   :: FilePath
+  , _envPidFile    :: FilePath
+  , _envLogFile    :: FilePath
+  }
+  deriving (Show)
+
+makeLenses ''Env
+
+emptyEnv :: String -> Env
+emptyEnv rr =
+  Env
+  { _envRepoRoot   = rr
+  , _envRobinRoot  = robinRoot
+  , _envStatusFile = specialFile "status"
+  , _envOutputFile = specialFile "output"
+  , _envLessFile   = specialFile "less"
+  , _envPidFile    = specialFile "pid"
+  , _envLogFile    = specialFile "log"
+  }
+  where
+    robinRoot = rr </> ".robin"
+    specialFile n = robinRoot </> n
+
+data Err = Err
+  deriving (Show)
+
+type I = ReaderT Env (ExceptT Err (ResourceT IO))
+
+type M = StateT St I
+
+runI :: I a -> IO (Either Err a)
+runI m = getRepoRoot >>= runResourceT . runExceptT . runReaderT m' . emptyEnv
+  where
+    m' = view envRobinRoot >>= ensureDir >> m
+
+ensureDir :: (MonadIO m) => FilePath -> m ()
+ensureDir = liftIO . createDirectoryIfMissing False
+
+runM :: M a -> IO (Either Err a)
+runM = runI . flip evalStateT emptySt
+
+debug :: (MonadIO m) => Text -> m ()
+debug text = liftIO $ putStrLn text >> hFlush stdout
+
+debugs :: (MonadIO m) => [Char] -> m ()
+debugs = debug . pack
+
diff --git a/src/Util.hs b/src/Util.hs
new file mode 100644
--- /dev/null
+++ b/src/Util.hs
@@ -0,0 +1,23 @@
+
+module Util (todo, leftMaybe, readMaybe, getRepoRoot) where
+
+import Data.Char
+import System.Process
+
+todo :: a
+todo = error "Not implemented"
+
+leftMaybe :: Either a b -> Maybe a
+leftMaybe = either Just $ const Nothing
+
+readMaybe :: (Read a) => String -> Maybe a
+readMaybe xs = case reads xs of
+  [(x, "")] -> Just x
+  _ -> Nothing
+
+trim :: String -> String
+trim = let f = reverse . dropWhile isSpace in f . f
+
+getRepoRoot :: IO String
+getRepoRoot = readProcess "git" ["rev-parse", "--show-toplevel"] "" >>= return . trim
+
diff --git a/src/Watch.hs b/src/Watch.hs
new file mode 100644
--- /dev/null
+++ b/src/Watch.hs
@@ -0,0 +1,96 @@
+
+{-# LANGUAGE OverloadedStrings #-}
+module Watch
+  ( WatchPred(..)
+  , Watch(..)
+  , emptyWatch
+  , watchOnce
+  , watchForever
+  ) where
+
+import Prelude hiding (FilePath)
+
+import Control.Concurrent.Chan hiding (isEmptyChan)
+import Control.Exception.Lifted
+import Control.Monad.Reader
+import Control.Monad.Trans.Control
+import Data.Time.Clock
+import System.FilePath
+import System.FSNotify
+
+import Types
+
+data WatchPred =
+    PredPath FilePath
+  | PredName String
+  | PredExtension String
+  | PredAdded
+  | PredModified
+  | PredRemoved
+  | PredConst Bool
+  | PredConj [WatchPred]
+  | PredDisj [WatchPred]
+  | PredInverse WatchPred
+  deriving (Show)
+
+data Watch =
+  Watch
+  { wRecurse   :: Bool
+  , wRootDir   :: FilePath
+  , wPred      :: WatchPred
+  } deriving (Show)
+
+emptyWatch fp = Watch False fp (PredConst True)
+
+eventFile :: Event -> FilePath
+eventFile (Added fp _) = fp
+eventFile (Modified fp _) = fp
+eventFile (Removed fp _) = fp
+
+wEvalPred :: Event -> WatchPred -> Bool
+wEvalPred e (PredPath fp) = fp == eventFile e
+wEvalPred e (PredName xs) = xs == takeFileName (eventFile e)
+wEvalPred e (PredExtension xs) = '.' : xs == takeExtension (eventFile e)
+wEvalPred (Added _ _) PredAdded = True
+wEvalPred (Modified _ _) PredModified = True
+wEvalPred (Removed _ _) PredRemoved = True
+wEvalPred _ (PredConst b) = b
+wEvalPred e (PredConj ps) = all (wEvalPred e) ps
+wEvalPred e (PredDisj ps) = any (wEvalPred e) ps
+wEvalPred e (PredInverse p) = not $ wEvalPred e p
+wEvalPred _ _ = False
+
+watchPrim
+  :: (MonadBaseControl IO m, MonadIO m)
+  => [Watch] -> (Chan Event -> m a) -> m a
+watchPrim xs f = bracket (liftIO startManager) (liftIO . stopManager) $ \mgr -> do
+  chan <- liftIO newChan
+  let r x = if wRecurse x then watchTreeChan else watchDirChan
+  let w x = r x mgr (wRootDir x) (\e -> wEvalPred e $ wPred x) chan
+  liftIO $ mapM_ w xs
+  f chan
+
+readEvent :: (MonadIO m) => Chan Event -> m Event
+readEvent chan = do
+  event <- liftIO $ readChan chan
+  debugs $ show event
+  return event
+
+watchOnce
+  :: (MonadBaseControl IO m, MonadIO m)
+  => [Watch] -> m a -> m a
+watchOnce xs m = watchPrim xs $ \chan -> void (readEvent chan) >> m
+
+watchForever
+  :: (MonadBaseControl IO m, MonadIO m)
+  => [Watch] -> m () -> m ()
+watchForever xs m = watchPrim xs $ \chan -> forever $ do
+  t <- liftIO $ getCurrentTime
+  m
+  void $ readEventNewerThan chan t
+
+readEventNewerThan :: (MonadIO m) => Chan Event -> UTCTime -> m ()
+readEventNewerThan chan t =
+  readEvent chan
+  >>= \e -> if eventTime e > t then return () else readEventNewerThan chan t
+
diff --git a/stack.yaml b/stack.yaml
new file mode 100644
--- /dev/null
+++ b/stack.yaml
@@ -0,0 +1,5 @@
+flags: {}
+packages:
+- '.'
+extra-deps: []
+resolver: lts-3.4