diff --git a/ChangeLog b/ChangeLog
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2014-09-12 v5.1.0.0
+        * GhcModError is now a recursive data type (`GMECabalConfigure`'s
+          type changed)
+        * GhcModT's MonadIO instance now converts IOError's to failures in
+          the ErrorT part of GhcModT on `liftIO`.
+        * Make `loadSymbolDb` polimorphic in the return types's monad.
+        * Add `hoistGhcModT` to Language.Haskell.GhcMod.Internal
+        * Fix `check` command for modules using `-XPatternSynonyms`
+        * Merge #364, Support cabal configuration flags
+
 2014-08-29 v5.0.1.2
         * Merge #345, Try fixing duplicate errors
         * Merge #344, elisp: Use advice to check syntax on save-buffer
diff --git a/Language/Haskell/GhcMod.hs b/Language/Haskell/GhcMod.hs
--- a/Language/Haskell/GhcMod.hs
+++ b/Language/Haskell/GhcMod.hs
@@ -60,7 +60,7 @@
 import Language.Haskell.GhcMod.Info
 import Language.Haskell.GhcMod.Lang
 import Language.Haskell.GhcMod.Lint
-import Language.Haskell.GhcMod.List
 import Language.Haskell.GhcMod.Monad
+import Language.Haskell.GhcMod.Modules
 import Language.Haskell.GhcMod.PkgDoc
 import Language.Haskell.GhcMod.Types
diff --git a/Language/Haskell/GhcMod/Boot.hs b/Language/Haskell/GhcMod/Boot.hs
--- a/Language/Haskell/GhcMod/Boot.hs
+++ b/Language/Haskell/GhcMod/Boot.hs
@@ -4,8 +4,8 @@
 import Language.Haskell.GhcMod.Browse
 import Language.Haskell.GhcMod.Flag
 import Language.Haskell.GhcMod.Lang
-import Language.Haskell.GhcMod.List
 import Language.Haskell.GhcMod.Monad
+import Language.Haskell.GhcMod.Modules
 
 -- | Printing necessary information for front-end booting.
 boot :: IOish m => GhcModT m String
diff --git a/Language/Haskell/GhcMod/Browse.hs b/Language/Haskell/GhcMod/Browse.hs
--- a/Language/Haskell/GhcMod/Browse.hs
+++ b/Language/Haskell/GhcMod/Browse.hs
@@ -14,7 +14,7 @@
 import Language.Haskell.GhcMod.Convert
 import Language.Haskell.GhcMod.Doc (showPage, styleUnqualified)
 import Language.Haskell.GhcMod.Gap
-import Language.Haskell.GhcMod.Monad (IOish, GhcModT, options)
+import Language.Haskell.GhcMod.Monad (GhcModT, options)
 import Language.Haskell.GhcMod.Target (setTargetFiles)
 import Language.Haskell.GhcMod.Types
 import Name (getOccString)
diff --git a/Language/Haskell/GhcMod/Cabal21.hs b/Language/Haskell/GhcMod/Cabal21.hs
new file mode 100644
--- /dev/null
+++ b/Language/Haskell/GhcMod/Cabal21.hs
@@ -0,0 +1,73 @@
+-- Copyright   :  Isaac Jones 2003-2004
+{- All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Isaac Jones nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. -}
+
+-- | ComponentLocalBuildInfo for Cabal >= 1.21
+module Language.Haskell.GhcMod.Cabal21 (
+    ComponentLocalBuildInfo
+  , PackageIdentifier(..)
+  , PackageName(..)
+  , componentPackageDeps
+  , componentLibraries
+  ) where
+
+import Distribution.Package (InstalledPackageId)
+import Data.Version (Version)
+
+data LibraryName = LibraryName String
+    deriving (Read, Show)
+
+newtype PackageName = PackageName { unPackageName :: String }
+  deriving (Read, Show)
+
+data PackageIdentifier
+  = PackageIdentifier {
+    pkgName :: PackageName,
+    pkgVersion :: Version
+  }
+  deriving (Read, Show)
+
+type PackageId = PackageIdentifier
+
+data ComponentLocalBuildInfo
+  = LibComponentLocalBuildInfo {
+    componentPackageDeps :: [(InstalledPackageId, PackageId)],
+    componentLibraries :: [LibraryName]
+  }
+  | ExeComponentLocalBuildInfo {
+    componentPackageDeps :: [(InstalledPackageId, PackageId)]
+  }
+  | TestComponentLocalBuildInfo {
+    componentPackageDeps :: [(InstalledPackageId, PackageId)]
+  }
+  | BenchComponentLocalBuildInfo {
+    componentPackageDeps :: [(InstalledPackageId, PackageId)]
+  }
+  deriving (Read, Show)
diff --git a/Language/Haskell/GhcMod/CabalApi.hs b/Language/Haskell/GhcMod/CabalApi.hs
--- a/Language/Haskell/GhcMod/CabalApi.hs
+++ b/Language/Haskell/GhcMod/CabalApi.hs
@@ -11,16 +11,16 @@
   ) where
 
 import Language.Haskell.GhcMod.CabalConfig
+import Language.Haskell.GhcMod.Error
 import Language.Haskell.GhcMod.Gap (benchmarkBuildInfo, benchmarkTargets,
                                     toModuleString)
 import Language.Haskell.GhcMod.GhcPkg
 import Language.Haskell.GhcMod.Types
 
-import MonadUtils (MonadIO, liftIO)
+import MonadUtils (liftIO)
 import Control.Applicative ((<$>))
 import qualified Control.Exception as E
 import Control.Monad (filterM)
-import Control.Monad.Error.Class (Error, MonadError(..))
 import Data.Maybe (maybeToList)
 import Data.Set (fromList, toList)
 import Distribution.Package (Dependency(Dependency)
@@ -42,7 +42,7 @@
 ----------------------------------------------------------------
 
 -- | Getting necessary 'CompilerOptions' from three information sources.
-getCompilerOptions :: (MonadIO m, MonadError GhcModError m, Functor m)
+getCompilerOptions :: (IOish m, MonadError GhcModError m)
                    => [GHCOption]
                    -> Cradle
                    -> PackageDescription
@@ -73,20 +73,22 @@
 ----------------------------------------------------------------
 
 -- | Parse a cabal file and return a 'PackageDescription'.
-parseCabalFile :: (MonadIO m, Error e,  MonadError e m)
-               => FilePath
+parseCabalFile :: (IOish m, MonadError GhcModError m)
+               => Cradle
+               -> FilePath
                -> m PackageDescription
-parseCabalFile file = do
+parseCabalFile cradle file = do
     cid <- liftIO getGHCId
     epgd <- liftIO $ readPackageDescription silent file
-    case toPkgDesc cid epgd of
+    flags <- cabalConfigFlags cradle
+    case toPkgDesc cid flags epgd of
         Left deps    -> fail $ show deps ++ " are not installed"
         Right (pd,_) -> if nullPkg pd
                         then fail $ file ++ " is broken"
                         else return pd
   where
-    toPkgDesc cid =
-        finalizePackageDescription [] (const True) buildPlatform cid []
+    toPkgDesc cid flags =
+        finalizePackageDescription flags (const True) buildPlatform cid []
     nullPkg pd = name == ""
       where
         PackageName name = C.pkgName (P.package pd)
@@ -155,6 +157,7 @@
 getGHC = do
     mv <- programFindVersion ghcProgram silent (programName ghcProgram)
     case mv of
+      -- TODO: MonadError it up
         Nothing -> E.throwIO $ userError "ghc not found"
         Just v  -> return v
 
diff --git a/Language/Haskell/GhcMod/CabalConfig.hs b/Language/Haskell/GhcMod/CabalConfig.hs
--- a/Language/Haskell/GhcMod/CabalConfig.hs
+++ b/Language/Haskell/GhcMod/CabalConfig.hs
@@ -5,8 +5,10 @@
 module Language.Haskell.GhcMod.CabalConfig (
     CabalConfig
   , cabalConfigDependencies
+  , cabalConfigFlags
   ) where
 
+import Language.Haskell.GhcMod.Error
 import Language.Haskell.GhcMod.GhcPkg
 import Language.Haskell.GhcMod.Utils
 import Language.Haskell.GhcMod.Read
@@ -14,28 +16,30 @@
 
 import qualified Language.Haskell.GhcMod.Cabal16 as C16
 import qualified Language.Haskell.GhcMod.Cabal18 as C18
+import qualified Language.Haskell.GhcMod.Cabal21 as C21
 
 #ifndef MIN_VERSION_mtl
 #define MIN_VERSION_mtl(x,y,z) 1
 #endif
 
 import Control.Applicative ((<$>))
-import Control.Monad (mplus,void)
+import Control.Monad (mplus)
 #if MIN_VERSION_mtl(2,2,1)
 import Control.Monad.Except ()
 #else
 import Control.Monad.Error ()
 #endif
-import Control.Monad.Error (MonadError(..))
 import Data.Maybe ()
 import Data.Set ()
 import Data.List (find,tails,isPrefixOf,isInfixOf,nub,stripPrefix)
 import Distribution.Package (InstalledPackageId(..)
-                           , PackageIdentifier)
+                           , PackageIdentifier(..)
+                           , PackageName(..))
+import Distribution.PackageDescription (FlagAssignment)
 import Distribution.Simple.BuildPaths (defaultDistPref)
 import Distribution.Simple.Configure (localBuildInfoFile)
 import Distribution.Simple.LocalBuildInfo (ComponentName)
-import MonadUtils (MonadIO)
+import MonadUtils (liftIO)
 import System.FilePath ((</>))
 
 ----------------------------------------------------------------
@@ -46,24 +50,26 @@
 -- | Get contents of the file containing 'LocalBuildInfo' data. If it doesn't
 -- exist run @cabal configure@ i.e. configure with default options like @cabal
 -- build@ would do.
-getConfig :: (MonadIO m, MonadError GhcModError m)
+getConfig :: (IOish m, MonadError GhcModError m)
           => Cradle
           -> m CabalConfig
-getConfig cradle = tryFix (liftIOExceptions (readFile path)) $ \_ ->
-    rethrowError (GMECabalConfigure . gmeMsg) configure
+getConfig cradle = liftIO (readFile path) `tryFix` \_ ->
+     configure `modifyError'` GMECabalConfigure
  where
    prjDir = cradleRootDir cradle
    path = prjDir </> configPath
-   configure = liftIOExceptions $ void $
-       withDirectory_ prjDir $ readProcess' "cabal" ["configure"]
 
+   configure :: (IOish m, MonadError GhcModError m) => m ()
+   configure =
+       withDirectory_ prjDir $ readProcess' "cabal" ["configure"] >> return ()
 
+
 -- | Path to 'LocalBuildInfo' file, usually @dist/setup-config@
 configPath :: FilePath
 configPath = localBuildInfoFile defaultDistPref
 
 -- | Get list of 'Package's needed by all components of the current package
-cabalConfigDependencies :: (MonadIO m, Functor m, MonadError GhcModError m)
+cabalConfigDependencies :: (IOish m, MonadError GhcModError m)
                         => Cradle
                         -> PackageIdentifier
                         -> m [Package]
@@ -75,7 +81,7 @@
 configDependencies thisPkg config = map fromInstalledPackageId deps
  where
     deps :: [InstalledPackageId]
-    deps = case deps18 `mplus` deps16 of
+    deps = case deps21 `mplus` deps18 `mplus` deps16 of
         Right ps -> ps
         Left msg -> error msg
 
@@ -83,7 +89,27 @@
     -- defined in the same package).
     internal pkgid = pkgid == thisPkg
 
-    -- Cabal >= 1.18
+    -- Cabal >= 1.21
+    deps21 :: Either String [InstalledPackageId]
+    deps21 =
+        map fst
+      <$> filterInternal21
+      <$> (readEither =<< extractField config "componentsConfigs")
+
+    filterInternal21
+        :: [(ComponentName, C21.ComponentLocalBuildInfo, [ComponentName])]
+        -> [(InstalledPackageId, C21.PackageIdentifier)]
+
+    filterInternal21 ccfg = [ (ipkgid, pkgid)
+                          | (_,clbi,_)      <- ccfg
+                          , (ipkgid, pkgid) <- C21.componentPackageDeps clbi
+                          , not (internal . packageIdentifierFrom21 $ pkgid) ]
+
+    packageIdentifierFrom21 :: C21.PackageIdentifier -> PackageIdentifier
+    packageIdentifierFrom21 (C21.PackageIdentifier (C21.PackageName myName) myVersion) =
+        PackageIdentifier (PackageName myName) myVersion
+
+    -- Cabal >= 1.18 && < 1.21
     deps18 :: Either String [InstalledPackageId]
     deps18 =
           map fst
@@ -127,6 +153,20 @@
        readConfigs f s = case readEither s of
            Right x -> x
            Left msg -> error $ "reading config " ++ f ++ " failed ("++msg++")"
+
+-- | Get the flag assignment from the local build info of the given cradle
+cabalConfigFlags :: (IOish m, MonadError GhcModError m)
+                 => Cradle
+                 -> m FlagAssignment
+cabalConfigFlags cradle = do
+  config <- getConfig cradle
+  case configFlags config of
+    Right x  -> return x
+    Left msg -> throwError (GMECabalFlags (GMEString msg))
+
+-- | Extract the cabal flags from the 'CabalConfig'
+configFlags :: CabalConfig -> Either String FlagAssignment
+configFlags config = readEither =<< flip extractField "configConfigurationsFlags" =<< extractField config "configFlags"
 
 -- | Find @field@ in 'CabalConfig'. Returns 'Left' containing a user readable
 -- error message with lots of context on failure.
diff --git a/Language/Haskell/GhcMod/Debug.hs b/Language/Haskell/GhcMod/Debug.hs
--- a/Language/Haskell/GhcMod/Debug.hs
+++ b/Language/Haskell/GhcMod/Debug.hs
@@ -31,7 +31,7 @@
     simpleCompilerOption = options >>= \op ->
         return $ CompilerOptions (ghcUserOptions op) [] []
     fromCabalFile c = options >>= \opts -> do
-        pkgDesc <- parseCabalFile $ fromJust $ cradleCabalFile c
+        pkgDesc <- parseCabalFile c $ fromJust $ cradleCabalFile c
         getCompilerOptions (ghcUserOptions opts) c pkgDesc
 
 ----------------------------------------------------------------
diff --git a/Language/Haskell/GhcMod/DynFlags.hs b/Language/Haskell/GhcMod/DynFlags.hs
--- a/Language/Haskell/GhcMod/DynFlags.hs
+++ b/Language/Haskell/GhcMod/DynFlags.hs
@@ -17,10 +17,10 @@
 setEmptyLogger :: DynFlags -> DynFlags
 setEmptyLogger df = Gap.setLogAction df $ \_ _ _ _ _ -> return ()
 
--- Fast
--- Friendly to foreign export
--- Not friendly to Template Haskell
--- Uses small memory
+-- * Fast
+-- * Friendly to foreign export
+-- * Not friendly to -XTemplateHaskell and -XPatternSynonyms
+-- * Uses little memory
 setModeSimple :: DynFlags -> DynFlags
 setModeSimple df = df {
     ghcMode   = CompManager
@@ -29,10 +29,10 @@
   , optLevel  = 0
   }
 
--- Slow
--- Not friendly to foreign export
--- Friendly to Template Haskell
--- Uses large memory
+-- * Slow
+-- * Not friendly to foreign export
+-- * Friendly to -XTemplateHaskell and -XPatternSynonyms
+-- * Uses lots of memory
 setModeIntelligent :: DynFlags -> DynFlags
 setModeIntelligent df = df {
     ghcMode   = CompManager
@@ -47,9 +47,9 @@
 setBuildEnv :: Build -> DynFlags -> DynFlags
 setBuildEnv build = setHideAllPackages build . setCabalPackage build
 
--- At the moment with this option set ghc only prints different error messages,
--- suggesting the user to add a hidden package to the build-depends in his cabal
--- file for example
+-- | With ghc-7.8 this option simply makes GHC print a message suggesting users
+-- add hiddend packages to the build-depends field in their cabal file when the
+-- user tries to import a module form a hidden package.
 setCabalPackage :: Build -> DynFlags -> DynFlags
 setCabalPackage CabalPkg df = Gap.setCabalPkg df
 setCabalPackage _ df = df
diff --git a/Language/Haskell/GhcMod/Error.hs b/Language/Haskell/GhcMod/Error.hs
new file mode 100644
--- /dev/null
+++ b/Language/Haskell/GhcMod/Error.hs
@@ -0,0 +1,41 @@
+{-# LANGUAGE TypeFamilies, ScopedTypeVariables #-}
+module Language.Haskell.GhcMod.Error (
+    GhcModError(..)
+  , modifyError
+  , modifyError'
+  , tryFix
+  , module Control.Monad.Error
+  , module Exception
+  ) where
+
+import Control.Monad.Error (MonadError(..), Error(..))
+import Exception
+
+data GhcModError = GMENoMsg
+                 -- ^ Unknown error
+                 | GMEString String
+                 -- ^ Some Error with a message. These are produced mostly by
+                 -- 'fail' calls on GhcModT.
+                 | GMECabalConfigure GhcModError
+                 -- ^ Configuring a cabal project failed.
+                 | GMECabalFlags GhcModError
+                 -- ^ Retrieval of the cabal configuration flags failed.
+                 | GMEProcess [String] GhcModError
+                 -- ^ Launching an operating system process failed. The first
+                 -- field is the command.
+                   deriving (Eq,Show)
+
+instance Error GhcModError where
+    noMsg = GMENoMsg
+    strMsg = GMEString
+
+modifyError :: MonadError e m => (e -> e) -> m a -> m a
+modifyError f action = action `catchError` \e -> throwError $ f e
+
+infixr 0 `modifyError'`
+modifyError' :: MonadError e m => m a -> (e -> e) -> m a
+modifyError' = flip modifyError
+
+tryFix :: MonadError e m => m a -> (e -> m ()) -> m a
+tryFix action fix = do
+  action `catchError` \e -> fix e >> action
diff --git a/Language/Haskell/GhcMod/Find.hs b/Language/Haskell/GhcMod/Find.hs
--- a/Language/Haskell/GhcMod/Find.hs
+++ b/Language/Haskell/GhcMod/Find.hs
@@ -16,7 +16,6 @@
 
 import Config (cProjectVersion,cTargetPlatformString)
 import Control.Applicative ((<$>))
-import Control.Exception (handle, SomeException(..))
 import Control.Monad (when, void)
 import Control.Monad.Error.Class
 import Data.Function (on)
@@ -78,7 +77,7 @@
 -- | Looking up 'SymbolDb' with 'Symbol' to \['ModuleString'\]
 --   which will be concatenated. 'loadSymbolDb' is called internally.
 findSymbol :: IOish m => Symbol -> GhcModT m String
-findSymbol sym = liftIO loadSymbolDb >>= lookupSymbol sym
+findSymbol sym = loadSymbolDb >>= lookupSymbol sym
 
 -- | Looking up 'SymbolDb' with 'Symbol' to \['ModuleString'\]
 --   which will be concatenated.
@@ -91,7 +90,7 @@
 ---------------------------------------------------------------
 
 -- | Loading a file and creates 'SymbolDb'.
-loadSymbolDb :: IO SymbolDb
+loadSymbolDb :: (IOish m, MonadError GhcModError m) => m SymbolDb
 loadSymbolDb = SymbolDb <$> readSymbolDb
 
 -- | Returns the path to the currently running ghc-mod executable. With ghc<7.6
@@ -102,7 +101,9 @@
     dir <- getExecutablePath'
     return $ dir </> "ghc-mod"
 #else
-ghcModExecutable = return "dist/build/ghc-mod/ghc-mod"
+ghcModExecutable = do _ <- getExecutablePath' -- get rid of unused warning when
+                                              -- compiling spec
+                      return "dist/build/ghc-mod/ghc-mod"
 #endif
  where
     getExecutablePath' :: IO FilePath
@@ -112,11 +113,11 @@
     getExecutablePath' = return ""
 # endif
 
-readSymbolDb :: IO (Map Symbol [ModuleString])
-readSymbolDb = handle (\(SomeException _) -> return M.empty) $ do
-    ghcMod <- ghcModExecutable
+readSymbolDb :: (IOish m, MonadError GhcModError m) => m (Map Symbol [ModuleString])
+readSymbolDb = do
+    ghcMod <- liftIO ghcModExecutable
     file <- chop <$> readProcess' ghcMod ["dumpsym"]
-    M.fromAscList . map conv . lines <$> readFile file
+    M.fromAscList . map conv . lines <$> liftIO (readFile file)
   where
     conv :: String -> (Symbol,[ModuleString])
     conv = read
diff --git a/Language/Haskell/GhcMod/GHCApi.hs b/Language/Haskell/GhcMod/GHCApi.hs
--- a/Language/Haskell/GhcMod/GHCApi.hs
+++ b/Language/Haskell/GhcMod/GHCApi.hs
@@ -11,7 +11,7 @@
   ) where
 
 import Language.Haskell.GhcMod.GhcPkg
-import Language.Haskell.GhcMod.Monad (IOish, GhcModT)
+import Language.Haskell.GhcMod.Monad (GhcModT)
 import Language.Haskell.GhcMod.Target (setTargetFiles)
 import Language.Haskell.GhcMod.Types
 
diff --git a/Language/Haskell/GhcMod/Internal.hs b/Language/Haskell/GhcMod/Internal.hs
--- a/Language/Haskell/GhcMod/Internal.hs
+++ b/Language/Haskell/GhcMod/Internal.hs
@@ -35,6 +35,7 @@
   , GhcModLog
   -- * Monad utilities
   , runGhcModT'
+  , hoistGhcModT
   -- ** Accessing 'GhcModEnv' and 'GhcModState'
   , options
   , cradle
diff --git a/Language/Haskell/GhcMod/List.hs b/Language/Haskell/GhcMod/List.hs
deleted file mode 100644
--- a/Language/Haskell/GhcMod/List.hs
+++ /dev/null
@@ -1,32 +0,0 @@
-module Language.Haskell.GhcMod.List (modules) where
-
-import Control.Applicative ((<$>))
-import Control.Exception (SomeException(..))
-import Data.List (nub, sort)
-import qualified GHC as G
-import Language.Haskell.GhcMod.Convert
-import Language.Haskell.GhcMod.Monad
-import Language.Haskell.GhcMod.Types
-import Packages (pkgIdMap, exposedModules, sourcePackageId, display)
-import UniqFM (eltsUFM)
-
-----------------------------------------------------------------
-
--- | Listing installed modules.
-modules :: IOish m => GhcModT m String
-modules = do
-    opt <- options
-    convert opt . arrange opt <$> (getModules `G.gcatch` handler)
-  where
-    getModules = getExposedModules <$> G.getSessionDynFlags
-    getExposedModules = concatMap exposedModules'
-                      . eltsUFM . pkgIdMap . G.pkgState
-    exposedModules' p =
-        map G.moduleNameString (exposedModules p)
-    	`zip`
-        repeat (display $ sourcePackageId p)
-    arrange opt = nub . sort . map (dropPkgs opt)
-    dropPkgs opt (name, pkg)
-      | detailed opt = name ++ " " ++ pkg
-      | otherwise = name
-    handler (SomeException _) = return []
diff --git a/Language/Haskell/GhcMod/Modules.hs b/Language/Haskell/GhcMod/Modules.hs
new file mode 100644
--- /dev/null
+++ b/Language/Haskell/GhcMod/Modules.hs
@@ -0,0 +1,32 @@
+module Language.Haskell.GhcMod.Modules (modules) where
+
+import Control.Applicative ((<$>))
+import Control.Exception (SomeException(..))
+import Data.List (nub, sort)
+import qualified GHC as G
+import Language.Haskell.GhcMod.Convert
+import Language.Haskell.GhcMod.Monad
+import Language.Haskell.GhcMod.Types
+import Packages (pkgIdMap, exposedModules, sourcePackageId, display)
+import UniqFM (eltsUFM)
+
+----------------------------------------------------------------
+
+-- | Listing installed modules.
+modules :: IOish m => GhcModT m String
+modules = do
+    opt <- options
+    convert opt . arrange opt <$> (getModules `G.gcatch` handler)
+  where
+    getModules = getExposedModules <$> G.getSessionDynFlags
+    getExposedModules = concatMap exposedModules'
+                      . eltsUFM . pkgIdMap . G.pkgState
+    exposedModules' p =
+        map G.moduleNameString (exposedModules p)
+    	`zip`
+        repeat (display $ sourcePackageId p)
+    arrange opt = nub . sort . map (dropPkgs opt)
+    dropPkgs opt (name, pkg)
+      | detailed opt = name ++ " " ++ pkg
+      | otherwise = name
+    handler (SomeException _) = return []
diff --git a/Language/Haskell/GhcMod/Monad.hs b/Language/Haskell/GhcMod/Monad.hs
--- a/Language/Haskell/GhcMod/Monad.hs
+++ b/Language/Haskell/GhcMod/Monad.hs
@@ -18,6 +18,7 @@
   -- * Monad utilities
   , runGhcModT
   , runGhcModT'
+  , hoistGhcModT
   -- ** Accessing 'GhcModEnv' and 'GhcModState'
   , gmsGet
   , gmsPut
@@ -45,6 +46,7 @@
 
 
 import Language.Haskell.GhcMod.Types
+import Language.Haskell.GhcMod.Error
 import Language.Haskell.GhcMod.Cradle
 import Language.Haskell.GhcMod.DynFlags
 import Language.Haskell.GhcMod.GhcPkg
@@ -52,7 +54,6 @@
 import qualified Language.Haskell.GhcMod.Gap as Gap
 
 import DynFlags
-import Exception
 import GHC
 import qualified GHC as G
 import GHC.Paths (libdir)
@@ -87,7 +88,7 @@
 import Control.Monad.Writer.Class (MonadWriter)
 import Control.Monad.State.Class (MonadState(..))
 
-import Control.Monad.Error (MonadError, ErrorT, runErrorT)
+import Control.Monad.Error (ErrorT, runErrorT)
 import Control.Monad.Reader (ReaderT, runReaderT)
 import Control.Monad.State.Strict (StateT, runStateT)
 import Control.Monad.Trans.Journal (JournalT, runJournalT)
@@ -100,6 +101,7 @@
 import Data.Maybe (fromJust, isJust)
 import Data.IORef (IORef, readIORef, writeIORef, newIORef)
 import System.Directory (getCurrentDirectory)
+import System.IO.Error (tryIOError)
 
 ----------------------------------------------------------------
 
@@ -122,21 +124,15 @@
 
 ----------------------------------------------------------------
 
--- | A constraint alias (-XConstraintKinds) to make functions dealing with
--- 'GhcModT' somewhat cleaner.
---
--- Basicially an @IOish m => m@ is a 'Monad' supporting arbitrary 'IO' and
--- exception handling. Usually this will simply be 'IO' but we parametrise it in
--- the exported API so users have the option to use a custom inner monad.
-type IOish m = (Functor m, MonadIO m, MonadBaseControl IO m)
-
--- | The GhcMod monad transformer data type. This is basically a newtype wrapper
--- around 'StateT', 'ErrorT', 'JournalT' and 'ReaderT' with custom instances for
--- 'GhcMonad' and it's constraints.
+-- | This is basically a newtype wrapper around 'StateT', 'ErrorT', 'JournalT'
+-- and 'ReaderT' with custom instances for 'GhcMonad' and it's constraints that
+-- means you can run (almost) all functions from the GHC API on top of 'GhcModT'
+-- transparently.
 --
--- The inner monad should have instances for 'MonadIO' and 'MonadBaseControl'
--- 'IO'. Most @mtl@ monads already have 'MonadBaseControl' 'IO' instances, see
--- the @monad-control@ package.
+-- The inner monad @m@ should have instances for 'MonadIO' and
+-- 'MonadBaseControl' 'IO', in the common case this is simply 'IO'. Most @mtl@
+-- monads already have 'MonadBaseControl' 'IO' instances, see the
+-- @monad-control@ package.
 newtype GhcModT m a = GhcModT {
       unGhcModT :: StateT GhcModState
                      (ErrorT GhcModError
@@ -147,7 +143,6 @@
                , Alternative
                , Monad
                , MonadPlus
-               , MonadIO
 #if DIFFERENT_MONADIO
                , Control.Monad.IO.Class.MonadIO
 #endif
@@ -157,7 +152,16 @@
                , MonadError GhcModError
                )
 
-instance MonadTrans GhcModT where
+instance MonadIO m => MonadIO (GhcModT m) where
+    liftIO action = do
+      res <- GhcModT . liftIO . liftIO . liftIO . liftIO $ tryIOError action
+      case res of
+        Right a -> return a
+        Left e -> case show e of
+          ""  -> throwError $ noMsg
+          msg -> throwError $ strMsg msg
+
+instance MonadTrans (GhcModT) where
     lift = GhcModT . lift . lift . lift . lift
 
 instance MonadState s m => MonadState s (GhcModT m) where
@@ -188,7 +192,7 @@
 -- | Initialize the 'DynFlags' relating to the compilation of a single
 -- file or GHC session according to the 'Cradle' and 'Options'
 -- provided.
-initializeFlagsWithCradle :: (GhcMonad m, MonadError GhcModError m)
+initializeFlagsWithCradle :: (IOish m, GhcMonad m, MonadError GhcModError m)
         => Options
         -> Cradle
         -> m ()
@@ -200,7 +204,7 @@
     cabal = isJust mCradleFile
     ghcopts = ghcUserOptions opt
     withCabal = do
-        pkgDesc <- parseCabalFile $ fromJust mCradleFile
+        pkgDesc <- parseCabalFile c $ fromJust mCradleFile
         compOpts <- getCompilerOptions ghcopts c pkgDesc
         initSession CabalPkg opt compOpts
     withSandbox = initSession SingleFile opt compOpts
@@ -253,6 +257,17 @@
             initializeFlagsWithCradle opt (gmCradle env)
             action)
 
+-- | @hoistGhcModT result@. Embed a GhcModT computation's result into a GhcModT
+-- computation. Note that if the computation that returned @result@ modified the
+-- state part of GhcModT this cannot be restored.
+hoistGhcModT :: IOish m
+             => (Either GhcModError a, GhcModLog)
+             -> GhcModT m a
+hoistGhcModT (r,l) = do
+  GhcModT (lift $ lift $ journal l) >> case r of
+    Left e -> throwError e
+    Right a -> return a
+
 -- | Run a computation inside @GhcModT@ providing the RWST environment and
 -- initial state. This is a low level function, use it only if you know what to
 -- do with 'GhcModEnv' and 'GhcModState'.
@@ -293,6 +308,9 @@
 
 ----------------------------------------------------------------
 
+gmeAsk :: IOish m => GhcModT m GhcModEnv
+gmeAsk = ask
+
 gmsGet :: IOish m => GhcModT m GhcModState
 gmsGet = GhcModT get
 
@@ -300,10 +318,10 @@
 gmsPut = GhcModT . put
 
 options :: IOish m => GhcModT m Options
-options = gmOptions <$> ask
+options = gmOptions <$> gmeAsk
 
 cradle :: IOish m => GhcModT m Cradle
-cradle = gmCradle <$> ask
+cradle = gmCradle <$> gmeAsk
 
 getCompilerMode :: IOish m => GhcModT m CompilerMode
 getCompilerMode = gmCompilerMode <$> gmsGet
diff --git a/Language/Haskell/GhcMod/PkgDoc.hs b/Language/Haskell/GhcMod/PkgDoc.hs
--- a/Language/Haskell/GhcMod/PkgDoc.hs
+++ b/Language/Haskell/GhcMod/PkgDoc.hs
@@ -3,18 +3,19 @@
 import Language.Haskell.GhcMod.Types
 import Language.Haskell.GhcMod.GhcPkg
 import Language.Haskell.GhcMod.Monad
+import Language.Haskell.GhcMod.Utils
 
 import Control.Applicative ((<$>))
-import System.Process (readProcess)
 
 -- | Obtaining the package name and the doc path of a module.
 pkgDoc :: IOish m => String -> GhcModT m String
-pkgDoc mdl = cradle >>= \c -> liftIO $ do
-    pkg <- trim <$> readProcess "ghc-pkg" (toModuleOpts c) []
+pkgDoc mdl = do
+    c <- cradle
+    pkg <- trim <$> readProcess' "ghc-pkg" (toModuleOpts c)
     if pkg == "" then
         return "\n"
       else do
-        htmlpath <- readProcess "ghc-pkg" (toDocDirOpts pkg c) []
+        htmlpath <- readProcess' "ghc-pkg" (toDocDirOpts pkg c)
         let ret = pkg ++ " " ++ drop 14 htmlpath
         return ret
   where
diff --git a/Language/Haskell/GhcMod/SrcUtils.hs b/Language/Haskell/GhcMod/SrcUtils.hs
--- a/Language/Haskell/GhcMod/SrcUtils.hs
+++ b/Language/Haskell/GhcMod/SrcUtils.hs
@@ -85,7 +85,10 @@
 
 ----------------------------------------------------------------
 
-inModuleContext :: IOish m => FilePath -> (DynFlags -> PprStyle -> GhcModT m a) -> GhcModT m a
+inModuleContext :: IOish m
+                => FilePath
+                -> (DynFlags -> PprStyle -> GhcModT m a)
+                -> GhcModT m a
 inModuleContext file action =
     withDynFlags (setWarnTypedHoles . setDeferTypeErrors . setNoWarningFlags) $ do
     setTargetFiles [file]
diff --git a/Language/Haskell/GhcMod/Target.hs b/Language/Haskell/GhcMod/Target.hs
--- a/Language/Haskell/GhcMod/Target.hs
+++ b/Language/Haskell/GhcMod/Target.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module Language.Haskell.GhcMod.Target (
     setTargetFiles
   ) where
@@ -5,7 +6,7 @@
 import Control.Applicative ((<$>))
 import Control.Monad (forM, void, (>=>))
 import DynFlags (ExtensionFlag(..), xopt)
-import GHC (DynFlags(..), LoadHowMuch(..))
+import GHC (LoadHowMuch(..))
 import qualified GHC as G
 import Language.Haskell.GhcMod.DynFlags
 import Language.Haskell.GhcMod.Monad
@@ -50,7 +51,10 @@
         setCompilerMode Intelligent
 
 needsFallback :: G.ModuleGraph -> Bool
-needsFallback = any (hasTHorQQ . G.ms_hspp_opts)
-  where
-    hasTHorQQ :: DynFlags -> Bool
-    hasTHorQQ dflags = any (`xopt` dflags) [Opt_TemplateHaskell, Opt_QuasiQuotes]
+needsFallback = any $ \ms ->
+                let df = G.ms_hspp_opts ms in
+                   Opt_TemplateHaskell `xopt` df
+                || Opt_QuasiQuotes     `xopt` df
+#if __GLASGOW_HASKELL__ >= 708
+                || (Opt_PatternSynonyms `xopt` df)
+#endif
diff --git a/Language/Haskell/GhcMod/Types.hs b/Language/Haskell/GhcMod/Types.hs
--- a/Language/Haskell/GhcMod/Types.hs
+++ b/Language/Haskell/GhcMod/Types.hs
@@ -1,23 +1,20 @@
 module Language.Haskell.GhcMod.Types where
 
+import Control.Monad.Trans.Control (MonadBaseControl)
 import Data.List (intercalate)
 import qualified Data.Map as M
-import Control.Monad.Error (Error(..))
+import Exception (ExceptionMonad)
+import MonadUtils (MonadIO)
 
 import PackageConfig (PackageConfig)
 
-data GhcModError = GMENoMsg
-                 -- ^ Unknown error
-                 | GMEString { gmeMsg :: String }
-                 -- ^ Some Error with a message. These are produced mostly by
-                 -- 'fail' calls on GhcModT.
-                 | GMECabalConfigure { gmeMsg :: String }
-                 -- ^ Configuring a cabal project failed.
-                   deriving (Eq,Show)
-
-instance Error GhcModError where
-    noMsg = GMENoMsg
-    strMsg = GMEString
+-- | A constraint alias (-XConstraintKinds) to make functions dealing with
+-- 'GhcModT' somewhat cleaner.
+--
+-- Basicially an @IOish m => m@ is a 'Monad' supporting arbitrary 'IO' and
+-- exception handling. Usually this will simply be 'IO' but we parametrise it in
+-- the exported API so users have the option to use a custom inner monad.
+type IOish m = (Functor m, MonadIO m, MonadBaseControl IO m, ExceptionMonad m)
 
 -- | Output style.
 data OutputStyle = LispStyle  -- ^ S expression style.
diff --git a/Language/Haskell/GhcMod/Utils.hs b/Language/Haskell/GhcMod/Utils.hs
--- a/Language/Haskell/GhcMod/Utils.hs
+++ b/Language/Haskell/GhcMod/Utils.hs
@@ -1,12 +1,10 @@
 module Language.Haskell.GhcMod.Utils where
 
 
-import Control.Exception
-import Control.Monad.Error (MonadError(..), Error(..))
+import Language.Haskell.GhcMod.Error
 import MonadUtils (MonadIO, liftIO)
 import System.Directory (getCurrentDirectory, setCurrentDirectory)
 import System.Exit (ExitCode(..))
-import System.IO.Error (tryIOError)
 import System.Process (readProcessWithExitCode)
 
 -- dropWhileEnd is not provided prior to base 4.5.0.0.
@@ -25,39 +23,22 @@
        | s `elem` "}])" = s : extractParens' ss (level-1)
        | otherwise = s : extractParens' ss level
 
-readProcess' :: (MonadIO m, Error e, MonadError e m)
+readProcess' :: (MonadIO m, MonadError GhcModError m)
              => String
              -> [String]
              -> m String
 readProcess' cmd opts = do
-  (rv,output,err) <- liftIO $ readProcessWithExitCode cmd opts ""
+  (rv,output,err) <- liftIO (readProcessWithExitCode cmd opts "")
+      `modifyError'` GMEProcess ([cmd] ++ opts)
   case rv of
     ExitFailure val -> do
-        throwError $ strMsg $
+        throwError $ GMEProcess ([cmd] ++ opts) $ strMsg $
           cmd ++ " " ++ unwords opts ++ " (exit " ++ show val ++ ")"
               ++ "\n" ++ err
     ExitSuccess ->
         return output
 
-withDirectory_ :: FilePath -> IO a -> IO a
+withDirectory_ :: (MonadIO m, ExceptionMonad m) => FilePath -> m a -> m a
 withDirectory_ dir action =
-    bracket getCurrentDirectory setCurrentDirectory
-                (\_ -> setCurrentDirectory dir >> action)
-
-rethrowError :: MonadError e m => (e -> e) -> m a -> m a
-rethrowError f action = action `catchError` \e -> throwError $ f e
-
-tryFix :: MonadError e m => m a -> (e -> m ()) -> m a
-tryFix action fix = do
-  action `catchError` \e -> fix e >> action
-
--- | 'IOException's thrown in the computation passed to this function will be
--- converted to 'MonadError' failures using 'throwError'.
-liftIOExceptions :: (MonadIO m, Error e, MonadError e m) => IO a -> m a
-liftIOExceptions action = do
-  res <- liftIO $ tryIOError action
-  case res of
-    Right a -> return a
-    Left e -> case show e of
-                ""  -> throwError $ noMsg
-                msg -> throwError $ strMsg msg
+    gbracket (liftIO getCurrentDirectory) (liftIO . setCurrentDirectory)
+                (\_ -> liftIO (setCurrentDirectory dir) >> action)
diff --git a/elisp/ghc.el b/elisp/ghc.el
--- a/elisp/ghc.el
+++ b/elisp/ghc.el
@@ -28,7 +28,7 @@
 	       (< emacs-minor-version minor)))
       (error "ghc-mod requires at least Emacs %d.%d" major minor)))
 
-(defconst ghc-version "5.0.1.2")
+(defconst ghc-version "5.1.0.0")
 
 ;; (eval-when-compile
 ;;  (require 'haskell-mode))
diff --git a/ghc-mod.cabal b/ghc-mod.cabal
--- a/ghc-mod.cabal
+++ b/ghc-mod.cabal
@@ -1,5 +1,5 @@
 Name:                   ghc-mod
-Version:                5.0.1.2
+Version:                5.1.0.0
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
                         Daniel Gröber <dxld@darkboxed.org>
                         Alejandro Serrano <trupill@gmail.com>
@@ -34,6 +34,7 @@
                         test/data/broken-cabal/cabal.sandbox.config.in
                         test/data/broken-sandbox/*.cabal
                         test/data/broken-sandbox/cabal.sandbox.config
+                        test/data/cabal-flags/*.cabal
                         test/data/check-test-subdir/*.cabal
                         test/data/check-test-subdir/src/Check/Test/*.hs
                         test/data/check-test-subdir/test/*.hs
@@ -45,6 +46,8 @@
                         test/data/duplicate-pkgver/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d/template-haskell-1.0-7c59d13f32294d1ef6dc6233c24df961.conf
                         test/data/duplicate-pkgver/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d/template-haskell-2.8.0.0-14e543bdae2da4d2aeff5386892c9112.conf
                         test/data/duplicate-pkgver/.cabal-sandbox/i386-osx-ghc-7.6.3-packages.conf.d/template-haskell-2.8.0.0-32d4f24abdbb6bf41272b183b2e23e9c.conf
+                        test/data/pattern-synonyms/*.cabal
+                        test/data/pattern-synonyms/*.hs
                         test/data/ghc-mod-check/*.cabal
                         test/data/ghc-mod-check/*.hs
                         test/data/ghc-mod-check/Data/*.hs
@@ -61,6 +64,7 @@
                         Language.Haskell.GhcMod.Browse
                         Language.Haskell.GhcMod.Cabal16
                         Language.Haskell.GhcMod.Cabal18
+                        Language.Haskell.GhcMod.Cabal21
                         Language.Haskell.GhcMod.CabalApi
                         Language.Haskell.GhcMod.CabalConfig
                         Language.Haskell.GhcMod.CaseSplit
@@ -70,6 +74,7 @@
                         Language.Haskell.GhcMod.Debug
                         Language.Haskell.GhcMod.Doc
                         Language.Haskell.GhcMod.DynFlags
+                        Language.Haskell.GhcMod.Error
                         Language.Haskell.GhcMod.FillSig
                         Language.Haskell.GhcMod.Find
                         Language.Haskell.GhcMod.Flag
@@ -80,9 +85,9 @@
                         Language.Haskell.GhcMod.Info
                         Language.Haskell.GhcMod.Lang
                         Language.Haskell.GhcMod.Lint
-                        Language.Haskell.GhcMod.List
                         Language.Haskell.GhcMod.Logger
                         Language.Haskell.GhcMod.Monad
+                        Language.Haskell.GhcMod.Modules
                         Language.Haskell.GhcMod.PkgDoc
                         Language.Haskell.GhcMod.Read
                         Language.Haskell.GhcMod.SrcUtils
@@ -99,7 +104,7 @@
                       , ghc-syb-utils
                       , hlint >= 1.8.61
                       , io-choice
-                      , monad-journal >= 0.2.2.0
+                      , monad-journal >= 0.2.2.0 && < 0.2.3.2
                       , old-time
                       , process
                       , syb
@@ -144,6 +149,7 @@
   Default-Extensions:   ConstraintKinds, FlexibleContexts
   HS-Source-Dirs:       src
   Build-Depends:        base >= 4.0 && < 5
+                      , async
                       , containers
                       , directory
                       , filepath
@@ -191,7 +197,7 @@
                       , ghc-syb-utils
                       , hlint >= 1.7.1
                       , io-choice
-                      , monad-journal >= 0.2.2.0
+                      , monad-journal >= 0.2.2.0 && < 0.2.3.2
                       , old-time
                       , process
                       , syb
diff --git a/src/GHCMod.hs b/src/GHCMod.hs
--- a/src/GHCMod.hs
+++ b/src/GHCMod.hs
@@ -113,6 +113,7 @@
         cmdArg4 = cmdArg !. 4
         cmdArg5 = cmdArg !. 5
         remainingArgs = tail cmdArg
+        nArgs :: Int -> a -> a
         nArgs n f = if length remainingArgs == n
                         then f
                         else E.throw (ArgumentsMismatch cmdArg0)
@@ -139,6 +140,7 @@
       "version" -> return progVersion
       "help"    -> return $ O.usageInfo usage argspec
       cmd       -> E.throw (NoSuchCommand cmd)
+
     case res of
       Right s -> putStr s
       Left (GMENoMsg) ->
@@ -146,7 +148,14 @@
       Left (GMEString msg) ->
           hPutStrLn stderr msg
       Left (GMECabalConfigure msg) ->
-          hPutStrLn stderr $ "cabal configure failed: " ++ msg
+          hPutStrLn stderr $ "cabal configure failed: " ++ show msg
+      Left (GMECabalFlags msg) ->
+          hPutStrLn stderr $ "retrieval of the cabal configuration flags failed: " ++ show msg
+      Left (GMEProcess cmd msg) ->
+          hPutStrLn stderr $
+            "launching operating system process `"++c++"` failed: " ++ show msg
+          where c = unwords cmd
+
   where
     handlers = [Handler (handleThenExit handler1), Handler (handleThenExit handler2)]
     handleThenExit handler e = handler e >> exitFailure
diff --git a/src/GHCModi.hs b/src/GHCModi.hs
--- a/src/GHCModi.hs
+++ b/src/GHCModi.hs
@@ -20,10 +20,10 @@
 
 import Config (cProjectVersion)
 import Control.Applicative ((<$>))
-import Control.Concurrent (forkIO, MVar, newEmptyMVar, putMVar, readMVar)
+import Control.Concurrent.Async (Async, async, wait)
 import Control.Exception (SomeException(..), Exception)
 import qualified Control.Exception as E
-import Control.Monad (when, void)
+import Control.Monad (when)
 import CoreMonad (liftIO)
 import Data.List (find, intercalate)
 import Data.List.Split (splitOn)
@@ -34,6 +34,7 @@
 import Data.Version (showVersion)
 import qualified GHC as G
 import Language.Haskell.GhcMod
+import Language.Haskell.GhcMod.Internal
 import Paths_ghc_mod
 import System.Console.GetOpt
 import System.Directory (setCurrentDirectory)
@@ -100,14 +101,13 @@
         let rootdir = cradleRootDir cradle0
 --            c = cradle0 { cradleCurrentDir = rootdir } TODO: ?????
         setCurrentDirectory rootdir
-        mvar <- liftIO newEmptyMVar
-        void $ forkIO $ setupDB mvar
-        (res, _) <- runGhcModT opt $ loop S.empty mvar
+        symDb <- async $ runGhcModT opt loadSymbolDb
+        (res, _) <- runGhcModT opt $ loop S.empty symDb
 
         case res of
           Right () -> return ()
           Left (GMECabalConfigure msg) -> do
-              putStrLn $ notGood $ "cabal configure failed: " ++ msg
+              putStrLn $ notGood $ "cabal configure failed: " ++ show msg
               exitFailure
           Left e -> bug $ show e
       where
@@ -132,19 +132,14 @@
 
 ----------------------------------------------------------------
 
-setupDB :: MVar SymbolDb -> IO ()
-setupDB mvar = loadSymbolDb >>= putMVar mvar
-
-----------------------------------------------------------------
-
-loop :: IOish m => Set FilePath -> MVar SymbolDb -> GhcModT m ()
-loop set mvar = do
+loop :: IOish m => Set FilePath -> SymDbReq -> GhcModT m ()
+loop set symDbReq = do
     cmdArg <- liftIO getLine
     let (cmd,arg') = break (== ' ') cmdArg
         arg = dropWhile (== ' ') arg'
     (ret,ok,set') <- case cmd of
         "check"  -> checkStx set arg
-        "find"   -> findSym set arg mvar
+        "find"   -> findSym set arg symDbReq
         "lint"   -> lintStx set arg
         "info"   -> showInfo set arg
         "type"   -> showType set arg
@@ -163,7 +158,7 @@
       else do
         liftIO $ putStrLn $ notGood ret
     liftIO $ hFlush stdout
-    when ok $ loop set' mvar
+    when ok $ loop set' symDbReq
 
 ----------------------------------------------------------------
 
@@ -207,10 +202,12 @@
 
 ----------------------------------------------------------------
 
-findSym :: IOish m => Set FilePath -> String -> MVar SymbolDb
+type SymDbReq = Async (Either GhcModError SymbolDb, GhcModLog)
+
+findSym :: IOish m => Set FilePath -> String -> SymDbReq
         -> GhcModT m (String, Bool, Set FilePath)
-findSym set sym mvar = do
-    db <- liftIO $ readMVar mvar
+findSym set sym dbReq = do
+    db <- hoistGhcModT =<< liftIO (wait dbReq)
     ret <- lookupSymbol sym db
     return (ret, True, set)
 
diff --git a/test/CabalApiSpec.hs b/test/CabalApiSpec.hs
--- a/test/CabalApiSpec.hs
+++ b/test/CabalApiSpec.hs
@@ -10,6 +10,7 @@
 import Test.Hspec
 import System.Directory
 import System.FilePath
+import System.Process (readProcess)
 
 import Dir
 import TestUtils
@@ -23,8 +24,10 @@
 spec = do
     describe "parseCabalFile" $ do
         it "throws an exception if the cabal file is broken" $ do
-            shouldReturnError $
-              runD' $ parseCabalFile "test/data/broken-cabal/broken.cabal"
+            shouldReturnError $ do
+              withDirectory_ "test/data/broken-cabal" $ do
+                  crdl <- findCradle
+                  runD' $ parseCabalFile crdl "broken.cabal"
 
 
     describe "getCompilerOptions" $ do
@@ -32,7 +35,7 @@
             cwd <- getCurrentDirectory
             withDirectory "test/data/subdir1/subdir2" $ \dir -> do
                 crdl <- findCradle
-                pkgDesc <- runD $ parseCabalFile $ fromJust $ cradleCabalFile crdl
+                pkgDesc <- runD $ parseCabalFile crdl $ fromJust $ cradleCabalFile crdl
                 res <- runD $ getCompilerOptions [] crdl pkgDesc
                 let res' = res {
                         ghcOptions  = ghcOptions res
@@ -47,18 +50,28 @@
 
     describe "cabalDependPackages" $ do
         it "extracts dependent packages" $ do
-            pkgs <- cabalDependPackages . cabalAllBuildInfo <$> runD (parseCabalFile "test/data/cabalapi.cabal")
+            crdl <- findCradle' "test/data/"
+            pkgs <- cabalDependPackages . cabalAllBuildInfo <$> runD (parseCabalFile crdl "test/data/cabalapi.cabal")
             pkgs `shouldBe` ["Cabal","base","template-haskell"]
+        it "uses non default flags" $ do
+            withDirectory_ "test/data/cabal-flags" $ do
+                crdl <- findCradle
+                _ <- readProcess "cabal" ["configure", "-ftest-flag"] ""
+                pkgs <- cabalDependPackages . cabalAllBuildInfo <$> runD (parseCabalFile crdl "cabal-flags.cabal")
+                pkgs `shouldBe` ["Cabal","base"]
 
     describe "cabalSourceDirs" $ do
         it "extracts all hs-source-dirs" $ do
-            dirs <- cabalSourceDirs . cabalAllBuildInfo <$> runD (parseCabalFile "test/data/check-test-subdir/check-test-subdir.cabal")
+            crdl <- findCradle' "test/data/check-test-subdir"
+            dirs <- cabalSourceDirs . cabalAllBuildInfo <$> runD (parseCabalFile crdl "test/data/check-test-subdir/check-test-subdir.cabal")
             dirs `shouldBe` ["src", "test"]
         it "extracts all hs-source-dirs including \".\"" $ do
-            dirs <- cabalSourceDirs . cabalAllBuildInfo <$> runD (parseCabalFile "test/data/cabalapi.cabal")
+            crdl <- findCradle' "test/data/"
+            dirs <- cabalSourceDirs . cabalAllBuildInfo <$> runD (parseCabalFile crdl "test/data/cabalapi.cabal")
             dirs `shouldBe` [".", "test"]
 
     describe "cabalAllBuildInfo" $ do
         it "extracts build info" $ do
-            info <- cabalAllBuildInfo <$> runD (parseCabalFile "test/data/cabalapi.cabal")
+            crdl <- findCradle' "test/data/"
+            info <- cabalAllBuildInfo <$> runD (parseCabalFile crdl "test/data/cabalapi.cabal")
             show info `shouldBe` "[BuildInfo {buildable = True, buildTools = [], cppOptions = [], ccOptions = [], ldOptions = [], pkgconfigDepends = [], frameworks = [], cSources = [], hsSourceDirs = [\".\"], otherModules = [ModuleName [\"Browse\"],ModuleName [\"CabalApi\"],ModuleName [\"Cabal\"],ModuleName [\"CabalDev\"],ModuleName [\"Check\"],ModuleName [\"ErrMsg\"],ModuleName [\"Flag\"],ModuleName [\"GHCApi\"],ModuleName [\"GHCChoice\"],ModuleName [\"Gap\"],ModuleName [\"Info\"],ModuleName [\"Lang\"],ModuleName [\"Lint\"],ModuleName [\"List\"],ModuleName [\"Paths_ghc_mod\"],ModuleName [\"Types\"]], defaultLanguage = Nothing, otherLanguages = [], defaultExtensions = [], otherExtensions = [], oldExtensions = [], extraLibs = [], extraLibDirs = [], includeDirs = [], includes = [], installIncludes = [], options = [(GHC,[\"-Wall\"])], ghcProfOptions = [], ghcSharedOptions = [], customFieldsBI = [], targetBuildDepends = [Dependency (PackageName \"Cabal\") (UnionVersionRanges (ThisVersion (Version {versionBranch = [1,10], versionTags = []})) (LaterVersion (Version {versionBranch = [1,10], versionTags = []}))),Dependency (PackageName \"base\") (IntersectVersionRanges (UnionVersionRanges (ThisVersion (Version {versionBranch = [4,0], versionTags = []})) (LaterVersion (Version {versionBranch = [4,0], versionTags = []}))) (EarlierVersion (Version {versionBranch = [5], versionTags = []}))),Dependency (PackageName \"template-haskell\") AnyVersion]},BuildInfo {buildable = True, buildTools = [], cppOptions = [], ccOptions = [], ldOptions = [], pkgconfigDepends = [], frameworks = [], cSources = [], hsSourceDirs = [\"test\",\".\"], otherModules = [ModuleName [\"Expectation\"],ModuleName [\"BrowseSpec\"],ModuleName [\"CabalApiSpec\"],ModuleName [\"FlagSpec\"],ModuleName [\"LangSpec\"],ModuleName [\"LintSpec\"],ModuleName [\"ListSpec\"]], defaultLanguage = Nothing, otherLanguages = [], defaultExtensions = [], otherExtensions = [], oldExtensions = [], extraLibs = [], extraLibDirs = [], includeDirs = [], includes = [], installIncludes = [], options = [], ghcProfOptions = [], ghcSharedOptions = [], customFieldsBI = [], targetBuildDepends = [Dependency (PackageName \"Cabal\") (UnionVersionRanges (ThisVersion (Version {versionBranch = [1,10], versionTags = []})) (LaterVersion (Version {versionBranch = [1,10], versionTags = []}))),Dependency (PackageName \"base\") (IntersectVersionRanges (UnionVersionRanges (ThisVersion (Version {versionBranch = [4,0], versionTags = []})) (LaterVersion (Version {versionBranch = [4,0], versionTags = []}))) (EarlierVersion (Version {versionBranch = [5], versionTags = []})))]}]"
diff --git a/test/CheckSpec.hs b/test/CheckSpec.hs
--- a/test/CheckSpec.hs
+++ b/test/CheckSpec.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module CheckSpec where
 
 import Data.List (isSuffixOf, isInfixOf, isPrefixOf)
@@ -30,6 +31,13 @@
             withDirectory_ "test/data" $ do
                 res <- runID $ checkSyntax ["Baz.hs"]
                 res `shouldSatisfy` ("Baz.hs:5:1:Warning:" `isPrefixOf`)
+
+#if __GLASGOW_HASKELL__ >= 708
+        it "works with modules using PatternSynonyms" $ do
+            withDirectory_ "test/data/pattern-synonyms" $ do
+                res <- runID $ checkSyntax ["B.hs"]
+                res `shouldSatisfy` ("B.hs:6:9:Warning:" `isPrefixOf`)
+#endif
 
         it "works with foreign exports" $ do
             withDirectory_ "test/data" $ do
diff --git a/test/MonadSpec.hs b/test/MonadSpec.hs
--- a/test/MonadSpec.hs
+++ b/test/MonadSpec.hs
@@ -5,6 +5,7 @@
 import Dir
 import TestUtils
 import Control.Applicative
+import Control.Exception
 import Control.Monad.Error.Class
 
 spec :: Spec
@@ -27,3 +28,12 @@
         it "work" $ do
           (runD $ gmsPut (GhcModState Intelligent) >> gmsGet)
             `shouldReturn` (GhcModState Intelligent)
+
+    describe "liftIO" $ do
+        it "converts user errors to GhcModError" $ do
+            shouldReturnError $
+                runD' $ liftIO $ throw (userError "hello") >> return ""
+
+        it "converts a file not found exception to GhcModError" $ do
+            shouldReturnError $
+                runD' $ liftIO $ readFile "/DOES_NOT_EXIST" >> return ""
diff --git a/test/data/cabal-flags/cabal-flags.cabal b/test/data/cabal-flags/cabal-flags.cabal
new file mode 100644
--- /dev/null
+++ b/test/data/cabal-flags/cabal-flags.cabal
@@ -0,0 +1,14 @@
+name: cabal-flags
+version: 0.1.0
+build-type: Simple
+cabal-version: >= 1.8
+
+flag test-flag
+  default: False
+
+library
+  build-depends: base == 4.*
+
+  if flag(test-flag)
+    build-depends: Cabal >= 1.10
+
diff --git a/test/data/pattern-synonyms/A.hs b/test/data/pattern-synonyms/A.hs
new file mode 100644
--- /dev/null
+++ b/test/data/pattern-synonyms/A.hs
@@ -0,0 +1,6 @@
+{-# LANGUAGE PatternSynonyms #-}
+module A where
+
+data SomeType a b = SomeType (a,b)
+
+pattern MyPat x y <- SomeType (x,y)
diff --git a/test/data/pattern-synonyms/B.hs b/test/data/pattern-synonyms/B.hs
new file mode 100644
--- /dev/null
+++ b/test/data/pattern-synonyms/B.hs
@@ -0,0 +1,7 @@
+{-# LANGUAGE PatternSynonyms #-}
+module B where
+import A
+
+foo :: SomeType Int Char -> String
+foo x = case x of
+          MyPat a b -> show a ++ " " ++ [b]
diff --git a/test/data/pattern-synonyms/Setup.hs b/test/data/pattern-synonyms/Setup.hs
new file mode 100644
--- /dev/null
+++ b/test/data/pattern-synonyms/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/test/data/pattern-synonyms/pattern-synonyms.cabal b/test/data/pattern-synonyms/pattern-synonyms.cabal
new file mode 100644
--- /dev/null
+++ b/test/data/pattern-synonyms/pattern-synonyms.cabal
@@ -0,0 +1,24 @@
+-- Initial pattern-synonyms.cabal generated by cabal init.  For further 
+-- documentation, see http://haskell.org/cabal/users-guide/
+
+name:                pattern-synonyms
+version:             0.1.0.0
+-- synopsis:            
+-- description:         
+-- license:             
+license-file:        LICENSE
+author:              Daniel Gröber
+maintainer:          dxld@darkboxed.org
+-- copyright:           
+-- category:            
+build-type:          Simple
+-- extra-source-files:  
+cabal-version:       >=1.10
+
+library
+  exposed-modules:     A, B
+  -- other-modules:       
+  other-extensions:    PatternSynonyms
+  build-depends:       base >=4.7 && <4.8
+  -- hs-source-dirs:      
+  default-language:    Haskell2010