Dump original source code on failure

See #10

2 files changed, 18 insertions, 8 deletions

diff --git a/src/Main.hs b/src/Main.hs
index 40c801e..f880f1d 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -11,6 +11,7 @@ import           Data.List              (intercalate)
 import           Data.Version           (Version(..))
 import           Prelude                hiding (readFile)
 import           System.Console.CmdArgs
+import           System.IO              (hPutStrLn, stderr)
 import           System.IO.Strict       (readFile)
 
 
@@ -74,7 +75,11 @@ stylishHaskell sa
 file :: StylishArgs -> Config -> Maybe FilePath -> IO ()
 file sa conf mfp = do
     contents <- maybe getContents readFile mfp
-    write $ unlines $ runSteps (configLanguageExtensions conf)
-        mfp (configSteps conf) $ lines contents
+    let result = runSteps (configLanguageExtensions conf)
+            mfp (configSteps conf) $ lines contents
+
+    case result of
+        Left  err -> hPutStrLn stderr err >> write contents
+        Right ok  -> write $ unlines ok
   where
     write = maybe putStr (if inPlace sa then writeFile else const putStr) mfp
diff --git a/src/StylishHaskell.hs b/src/StylishHaskell.hs
index 7705d3a..e588655 100644
--- a/src/StylishHaskell.hs
+++ b/src/StylishHaskell.hs
@@ -6,18 +6,23 @@ module StylishHaskell
 
 
 --------------------------------------------------------------------------------
+import           Control.Applicative   ((<$>))
+import           Control.Monad         (foldM)
+
+
+--------------------------------------------------------------------------------
 import           StylishHaskell.Config
 import           StylishHaskell.Parse
 import           StylishHaskell.Step
 
 
 --------------------------------------------------------------------------------
-runStep :: Extensions -> Maybe FilePath -> Step -> Lines -> Lines
-runStep exts mfp step ls = case parseModule exts mfp (unlines ls) of
-    Left err      -> error err  -- TODO: maybe return original lines?
-    Right module' -> stepFilter step ls module'
+runStep :: Extensions -> Maybe FilePath -> Lines -> Step -> Either String Lines
+runStep exts mfp ls step =
+    stepFilter step ls <$> parseModule exts mfp (unlines ls)
 
 
 --------------------------------------------------------------------------------
-runSteps :: Extensions -> Maybe FilePath -> [Step] -> Lines -> Lines
-runSteps exts mfp = foldr (flip (.)) id . map (runStep exts mfp)
+runSteps :: Extensions -> Maybe FilePath -> [Step] -> Lines
+         -> Either String Lines
+runSteps exts mfp steps ls = foldM (runStep exts mfp) ls steps