ENH make app puke if xcape isn't installed (good idea, right?)

app/Main.hs

@@ -42,6 +42,7 @@ import           Graphics.X11.Xlib.Types
 
 import           Text.Regex.TDFA
 
+import           System.Directory
 import           System.Environment
 import           System.Posix.IO
 import           System.Posix.Signals
@@ -96,12 +97,15 @@ parse ("-t":t:b:rs) = initXMan rs $ mkXcapeProcess (Just t) b
 parse (b:rs)        = initXMan rs $ mkXcapeProcess Nothing b
 parse _             = usage
 
+xcapeExe :: String
+xcapeExe = "xcape"
+
 -- | Given a timeout and bindings for xcape, return a process record. This will
 -- run xcape in debug mode (which will make it run as a foreground process,
 -- otherwise it will fork unnecessarily).
 mkXcapeProcess :: Timeout -> Bindings -> CreateProcess
-mkXcapeProcess (Just t) b =  proc "xcape" $ ["-t", t, "-d", "-e"] ++ [b]
-mkXcapeProcess Nothing b  =  proc "xcape" $ ["-d", "-e"] ++ [b]
+mkXcapeProcess (Just t) b =  proc xcapeExe $ ["-t", t, "-d", "-e"] ++ [b]
+mkXcapeProcess Nothing b  =  proc xcapeExe $ ["-d", "-e"] ++ [b]
 
 -- | Print the usage and exit
 usage :: IO ()
@@ -111,6 +115,10 @@ usage = putStrLn "xman [-t TIMEOUT] BINDINGS REGEXP [[REGEXP] ...]"
 -- titles we care about, initialize the XMan monad and run the main event loop
 initXMan :: Patterns -> CreateProcess -> IO ()
 initXMan rs cp = do
+  r <- checkXcape
+  if r then initX else putStrLn "could not find xcape binary"
+  where
+    initX = do
       -- ignore SIGCHLD so we don't produce zombie processes
       void $ installHandler sigCHLD Ignore Nothing
       dpy <- openDisplay ""
@@ -133,6 +141,10 @@ initXMan rs cp = do
           updateXCape -- set the initial state before entering main loop
           forever $ handle =<< io (nextEvent dpy e >> getEvent e)
 
+checkXcape :: IO Bool
+checkXcape = isJust <$> findExecutable xcapeExe
+
+
 
 -- | Lift an IO monad into the XMan context
 io :: MonadIO m => IO a -> m a

xman.cabal

@@ -33,5 +33,6 @@ executable xman
     , unix >= 2.7.2.2
     , regex-tdfa >= 1.2.3.2
     , process >= 1.6.5.0
+    , directory >= 1.3.3.0
   default-language: Haskell2010