Merge pull request #45 from PaulJohnson/master

Provide help message.

app/Main.hs

@@ -9,7 +9,9 @@ import Hie.Locate
 import Hie.Yaml
 import System.Directory
 import System.Environment
+import System.Exit
 import System.FilePath.Posix
+import System.IO
 
 main :: IO ()
 main = do
@@ -19,8 +21,8 @@ main = do
     "cabal" -> cabalPkgs pwd
     _ -> stackYamlPkgs pwd
   when (null cfs) $
-    error $
-      "Used" <> name
+    die $
+      "Used " <> name
         <> "\n No .cabal files found under"
         <> pwd
         <> "\n You may need to run stack build."
@@ -31,6 +33,16 @@ resolveName :: FilePath -> IO String
 resolveName pwd = do
   args <- getArgs
   files <- listDirectory pwd
+  when ("--help" `elem` args || "-h" `elem` args) $ do
+    progName <- getProgName
+    hPutStrLn stderr $
+      "Usage: " <> progName
+        <> " [ --cabal | --stack ]\n\n\
+           \If neither argument is given then "
+        <> progName
+        <> " will infer the type by\n\
+           \looking for dist-newstyle, .stack-work, cabal.project and stack.yaml in that order."
+    exitSuccess
   let fileNames = map takeFileName files
       name =
         if