diff --git a/CmdDB.hs b/CmdDB.hs
--- a/CmdDB.hs
+++ b/CmdDB.hs
@@ -205,6 +205,14 @@
        , manual = Nothing
        }
   , CommandSpec {
+         command = Ghci
+       , commandNames = ["ghci"]
+       , document = "Run GHCi within a sandbox"
+       , routing = RouteFunc ghci
+       , switches = [(SwSandbox, Just "--sandbox")]
+       , manual = Nothing
+       }
+  , CommandSpec {
          command = Help
        , commandNames = ["help"]
        , document = "Display the help message of the command"
diff --git a/Commands.hs b/Commands.hs
--- a/Commands.hs
+++ b/Commands.hs
@@ -1,6 +1,6 @@
 module Commands (
     deps, revdeps, installed, outdated, uninstall, search, env
-  , genpaths, check, add
+  , genpaths, check, add, ghci
   ) where
 
 import Control.Applicative hiding (many)
@@ -86,7 +86,7 @@
     if doit then do
         putStrLn $ "Deleting " ++ name ++ " " ++ ver
         pkgconf <- pkgConfOpt opts
-        when doit $ system (script pkgconf) >> return ()
+        when doit $ void . system $ script pkgconf
       else
         putStrLn $ name ++ " " ++ ver
   where
@@ -109,8 +109,7 @@
 check :: FunctionCommand
 check _ _ opts = do
     pkgconf <- pkgConfOpt opts
-    system (script pkgconf)
-    return ()
+    void . system $ script pkgconf
   where
    script pkgconf = "ghc-pkg check -v " ++ pkgconf
 
@@ -190,7 +189,14 @@
 add _ params opts = case getSandbox opts of
     Nothing -> hPutStrLn stderr "A sandbox must be specified with \"-s\" option."
     Just sbox -> case params of
-        [src] -> do
-            system $ "cabal-dev add-source " ++ src ++ " -s " ++ sbox
-            return ()
-        _ -> hPutStrLn stderr "A source path be specified."
+        [src] -> void . system $ "cabal-dev add-source " ++ src ++ " -s " ++ sbox
+        _     -> hPutStrLn stderr "A source path be specified."
+
+----------------------------------------------------------------
+
+ghci :: FunctionCommand
+ghci _ _ opts = case getSandbox opts of
+    Nothing -> hPutStrLn stderr "A sandbox must be specified with \"-s\" option."
+    Just sbox -> do
+      _ <- system $ "cabal-dev -s " ++ sbox ++ " ghci"
+      return ()
diff --git a/Main.hs b/Main.hs
--- a/Main.hs
+++ b/Main.hs
@@ -85,7 +85,7 @@
     sws = switches cmdspec
 
 callProcess :: String -> [String] -> [Arg] -> [Option] -> [SwitchSpec] -> IO ()
-callProcess pro args0 args1 opts sws = system script >> return ()
+callProcess pro args0 args1 opts sws = void . system $ script
   where
     swchs = optionsToString opts sws
     script = joinBy " " $ pro : args0 ++ cat args1 ++ swchs
diff --git a/PkgDB.hs b/PkgDB.hs
--- a/PkgDB.hs
+++ b/PkgDB.hs
@@ -1,12 +1,11 @@
-{-# LANGUAGE CPP #-}
-
 module PkgDB where
 
-import Control.Applicative
 import Control.Monad
+import Data.Function
 import Data.List
 import Data.Map (Map)
 import qualified Data.Map as M
+import Data.Maybe (isNothing)
 import Distribution.Compiler
     (CompilerId(..))
 import Distribution.License
@@ -30,7 +29,6 @@
 import Distribution.Verbosity
     (normal)
 import System.FilePath
-import System.Directory
 import Utils
 
 type PkgDB = PackageIndex
@@ -46,6 +44,11 @@
             Just path -> SpecificPackageDB $ packageConf path com
     getInstalledPackages normal [GlobalPackageDB,userDB] pro
 
+getGlobalPkgDB :: IO PkgDB
+getGlobalPkgDB = do
+    (_,pro) <- configure normal Nothing Nothing defaultProgramDb
+    getInstalledPackages normal [GlobalPackageDB] pro
+
 getPackageConf :: FilePath -> IO FilePath
 getPackageConf path = do
     (com,_) <- configure normal Nothing Nothing defaultProgramDb
@@ -85,15 +88,8 @@
 
 userPkgs :: IO (PkgInfo -> Bool)
 userPkgs = do
-#ifdef darwin_HOST_OS
-    -- drop "/."
-    userDirPref <- takeDirectory <$> getAppUserDataDirectory ""
-#else
-    userDirPref <- getAppUserDataDirectory ""
-#endif
-    return $ \pkgi -> case libraryDirs pkgi of
-        [] -> False -- haskell-platform for example
-        xs -> any (userDirPref `isPrefixOf`) xs
+    gDB <- getGlobalPkgDB
+    return$ \pkgi -> isNothing$ lookupInstalledPackageId gDB (installedPackageId pkgi)
 
 allPkgs :: IO (PkgInfo -> Bool)
 allPkgs = return (const True)
@@ -133,7 +129,7 @@
 
 printDep :: Bool -> Bool -> PkgDB -> Int -> InstalledPackageId -> IO ()
 printDep rec info db n pid = case lookupInstalledPackageId db pid of
-    Nothing -> return ()
+    Nothing   -> return ()
     Just pkgi -> do
         putStr $ prefix ++ fullNameOfPkgInfo pkgi
         extraInfo info pkgi
@@ -166,7 +162,7 @@
 
 printRevDep' :: Bool -> Bool -> PkgDB -> RevDB -> Int -> InstalledPackageId -> IO ()
 printRevDep' rec info db revdb n pid = case lookupInstalledPackageId db pid of
-    Nothing -> return ()
+    Nothing   -> return ()
     Just pkgi -> do
         putStr $ prefix ++ fullNameOfPkgInfo pkgi
         extraInfo info pkgi
@@ -187,7 +183,7 @@
     idDeps pkg = (installedPackageId pkg, depends pkg)
     kvs = sort $ concatMap decomp deps
     decomp (k,vs) = map (\v -> (v,k)) vs
-    kvss = groupBy (\x y -> fst x == fst y) kvs
+    kvss = groupBy ((==) `on` fst) kvs
     comp xs = (fst (head xs), map snd xs)
     revdeps = map comp kvss
 
diff --git a/Types.hs b/Types.hs
--- a/Types.hs
+++ b/Types.hs
@@ -80,6 +80,7 @@
              | Search
              | Env
              | Add
+             | Ghci
              | Test
              | Doc
              | Help
diff --git a/VerDB.hs b/VerDB.hs
--- a/VerDB.hs
+++ b/VerDB.hs
@@ -51,7 +51,7 @@
     name <- string "* " *> nonEols <* endOfLine
     synpsis
     lat <- latestLabel *> latest <* endOfLine
-    many skip
+    _ <- many skip
     endOfLine
     return (name, lat)
   where
diff --git a/cab.cabal b/cab.cabal
--- a/cab.cabal
+++ b/cab.cabal
@@ -1,5 +1,5 @@
 Name:                   cab
-Version:                0.1.13
+Version:                0.1.14
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -19,10 +19,7 @@
 
 Executable cab
   Main-Is:              Main.hs
-  if impl(ghc >= 6.12)
-    GHC-Options:        -Wall -fno-warn-unused-do-bind
-  else
-    GHC-Options:        -Wall
+  GHC-Options:          -Wall
   Build-Depends:        base >= 4.0 && < 5
                       , Cabal
                       , attoparsec >= 0.10