diff --git a/Language/Haskell/GhcMod/CabalApi.hs b/Language/Haskell/GhcMod/CabalApi.hs
index d545bec..6d3aecf 100644
--- a/Language/Haskell/GhcMod/CabalApi.hs
+++ b/Language/Haskell/GhcMod/CabalApi.hs
@@ -3,9 +3,9 @@
 module Language.Haskell.GhcMod.CabalApi (
     fromCabalFile
   , parseCabalFile
-  , cabalAllDependPackages
-  , cabalAllSourceDirs
   , cabalAllBuildInfo
+  , cabalDependPackages
+  , cabalSourceDirs
   , getGHCVersion
   ) where
 
@@ -32,6 +32,9 @@ import System.FilePath
 
 ----------------------------------------------------------------
 
+-- | Parsing a cabal file in 'Cradle' and returns
+--   options for GHC, include directories for modules and
+--   package names of dependency.
 fromCabalFile :: [GHCOption]
               -> Cradle
               -> IO ([GHCOption],[IncludeDir],[Package])
@@ -50,8 +53,8 @@ cookInfo ghcOptions cradle cabal = (gopts,idirs,depPkgs)
     Just cfile = cradleCabalFile  cradle
     buildInfos = cabalAllBuildInfo cabal
     gopts      = getGHCOptions ghcOptions $ head buildInfos
-    idirs      = includeDirectories cdir wdir $ cabalAllSourceDirs buildInfos
-    depPkgs    = removeThem problematicPackages $ removeMe cfile $ cabalAllDependPackages buildInfos
+    idirs      = includeDirectories cdir wdir $ cabalSourceDirs buildInfos
+    depPkgs    = removeThem problematicPackages $ removeMe cfile $ cabalDependPackages buildInfos
 
 removeMe :: FilePath -> [String] -> [String]
 removeMe cabalfile = filter (/= me)
@@ -72,6 +75,8 @@ includeDirectories cdir wdir dirs = uniqueAndSort (map (cdir </>) dirs ++ [cdir,
 
 ----------------------------------------------------------------
 
+-- | Parsing a cabal file and returns 'PackageDescription'.
+--   'IOException' is thrown if parsing fails.
 parseCabalFile :: FilePath -> IO PackageDescription
 parseCabalFile file = do
     cid <- getGHCId
@@ -99,6 +104,7 @@ getGHCOptions ghcOptions binfo = ghcOptions ++ exts ++ [lang] ++ libs ++ libDirs
 
 ----------------------------------------------------------------
 
+-- | Extracting all 'BuildInfo' for libraries, executables, tests and benchmarks.
 cabalAllBuildInfo :: PackageDescription -> [BuildInfo]
 cabalAllBuildInfo pd = libBI ++ execBI ++ testBI ++ benchBI
   where
@@ -109,19 +115,21 @@ cabalAllBuildInfo pd = libBI ++ execBI ++ testBI ++ benchBI
 
 ----------------------------------------------------------------
 
-cabalAllSourceDirs :: [BuildInfo] -> [FilePath]
-cabalAllSourceDirs bis = uniqueAndSort $ concatMap hsSourceDirs bis
-
-----------------------------------------------------------------
-
-cabalAllDependPackages :: [BuildInfo] -> [Package]
-cabalAllDependPackages bis = uniqueAndSort $ pkgs
+-- | Extracting package names of dependency.
+cabalDependPackages :: [BuildInfo] -> [Package]
+cabalDependPackages bis = uniqueAndSort $ pkgs
   where
     pkgs = map getDependencyPackageName $ concatMap targetBuildDepends bis
     getDependencyPackageName (Dependency (PackageName nm) _) = nm
 
 ----------------------------------------------------------------
 
+-- | Extracting include directories for modules.
+cabalSourceDirs :: [BuildInfo] -> [IncludeDir]
+cabalSourceDirs bis = uniqueAndSort $ concatMap hsSourceDirs bis
+
+----------------------------------------------------------------
+
 uniqueAndSort :: [String] -> [String]
 uniqueAndSort = toList . fromList
 
diff --git a/Language/Haskell/GhcMod/GHCApi.hs b/Language/Haskell/GhcMod/GHCApi.hs
index 91d47c0..2e259b3 100644
--- a/Language/Haskell/GhcMod/GHCApi.hs
+++ b/Language/Haskell/GhcMod/GHCApi.hs
@@ -96,6 +96,8 @@ initSession build opt cmdOpts idirs mDepPkgs logging = do
 
 ----------------------------------------------------------------
 
+-- | Initialize the 'DynFlags' relating to the compilation of a single
+-- file or GHC session.
 initializeFlags :: GhcMonad m => Options -> m ()
 initializeFlags opt = do
     dflags0 <- getSessionDynFlags
@@ -167,6 +169,8 @@ setTargetFiles files = do
 getDynamicFlags :: IO DynFlags
 getDynamicFlags = runGhc (Just libdir) getSessionDynFlags
 
+-- | Checking if Template Haskell or quasi quotes are used.
+--   If not, the process can be faster.
 canCheckFast :: ModuleGraph -> Bool
 canCheckFast = not . any (hasTHorQQ . ms_hspp_opts)
   where
diff --git a/Language/Haskell/GhcMod/GHCChoice.hs b/Language/Haskell/GhcMod/GHCChoice.hs
index 4bad3f0..6f0677d 100644
--- a/Language/Haskell/GhcMod/GHCChoice.hs
+++ b/Language/Haskell/GhcMod/GHCChoice.hs
@@ -9,20 +9,22 @@ import GHC
 
 ----------------------------------------------------------------
 
+-- | Try the left 'Ghc' action. If 'IOException' occurs, try
+--   the right 'Ghc' action.
 (||>) :: Ghc a -> Ghc a -> Ghc a
 x ||> y = x `gcatch` (\(_ :: IOException) -> y)
 
-(|||>) :: GhcMonad m => m a -> m a -> m a
-x |||> y = x `gcatch` (\(_ :: IOException) -> y)
-
-----------------------------------------------------------------
-
-{-| Go to the next 'Ghc' monad by throwing 'AltGhcgoNext'.
--}
+-- | Go to the next 'Ghc' monad by throwing 'AltGhcgoNext'.
 goNext :: Ghc a
 goNext = liftIO . throwIO $ userError "goNext"
 
-{-| Run any one 'Ghc' monad.
--}
+-- | Run any one 'Ghc' monad.
 runAnyOne :: [Ghc a] -> Ghc a
 runAnyOne = foldr (||>) goNext
+
+----------------------------------------------------------------
+
+-- | Try the left 'GhcMonad' action. If 'IOException' occurs, try
+--   the right 'GhcMonad' action.
+(|||>) :: GhcMonad m => m a -> m a -> m a
+x |||> y = x `gcatch` (\(_ :: IOException) -> y)
diff --git a/Language/Haskell/GhcMod/Internal.hs b/Language/Haskell/GhcMod/Internal.hs
index 151035a..069b8ea 100644
--- a/Language/Haskell/GhcMod/Internal.hs
+++ b/Language/Haskell/GhcMod/Internal.hs
@@ -1,16 +1,37 @@
 -- | Low level access to the ghc-mod library.
 
 module Language.Haskell.GhcMod.Internal (
-  -- * Low level access
+  -- * Types
     LogReader
   , GHCOption
+  , Package
+  , IncludeDir
+  -- * Cabal API
+  , fromCabalFile
+  , parseCabalFile
+  , cabalAllBuildInfo
+  , cabalDependPackages
+  , cabalSourceDirs
+  -- * GHC API
+  , canCheckFast
+  -- * Getting 'DynFlags'
+  , getDynamicFlags
+  -- * Initializing 'DynFlags'
+  , initializeFlags
   , initializeFlagsWithCradle
+  -- * 'GhcMonad'
   , setTargetFiles
   , checkSlowAndSet
-  , getDynamicFlags
+  -- * 'Ghc' Choice
+  , (||>)
+  , goNext
+  , runAnyOne
+  -- * 'GhcMonad' Choice
+  , (|||>)
   ) where
 
+import Language.Haskell.GhcMod.CabalApi
 import Language.Haskell.GhcMod.ErrMsg
 import Language.Haskell.GhcMod.GHCApi
+import Language.Haskell.GhcMod.GHCChoice
 import Language.Haskell.GhcMod.Types
-
diff --git a/Language/Haskell/GhcMod/Types.hs b/Language/Haskell/GhcMod/Types.hs
index f69d562..b8cbebf 100644
--- a/Language/Haskell/GhcMod/Types.hs
+++ b/Language/Haskell/GhcMod/Types.hs
@@ -94,7 +94,10 @@ data Cradle = Cradle {
 -- | A single GHC option, as it would appear on the command line.
 type GHCOption  = String
 
+-- | Include directories for modules
 type IncludeDir = FilePath
+
+-- | Package names
 type Package    = String
 
 -- | GHC version in 'String'.