Changing GHCMod as a library.

Language/Haskell/GhcMod/List.hs

@@ -0,0 +1,23 @@
+module Language.Haskell.GhcMod.List (listModules) where
+
+import Control.Applicative
+import Data.List
+import GHC
+import Language.Haskell.GhcMod.GHCApi
+import Language.Haskell.GhcMod.Types
+import Packages
+import UniqFM
+
+----------------------------------------------------------------
+
+listModules :: Options -> IO String
+listModules opt = convert opt . nub . sort <$> list opt
+
+list :: Options -> IO [String]
+list opt = withGHCDummyFile $ do
+    initializeFlags opt
+    getExposedModules <$> getSessionDynFlags
+  where
+    getExposedModules = map moduleNameString
+                      . concatMap exposedModules
+                      . eltsUFM . pkgIdMap . pkgState