Fix warnings

src/Network/MPD/Applicative/Internal.hs

@@ -45,14 +45,13 @@ newtype Parser a
       deriving Functor
 
 instance Monad Parser where
-    return a  = Parser $ \input -> Right (a, input)
     p1 >>= p2 = Parser $ \input -> runParser p1 input >>= uncurry (runParser . p2)
 
 instance Fail.MonadFail Parser where
     fail = Prelude.fail
 
 instance Applicative Parser where
-    pure  = return
+    pure  a = Parser $ \input -> Right (a, input)
     (<*>) = ap
 
 -- | Convert a regular parser.

src/Network/MPD/Commands/Query.hs

@@ -77,15 +77,15 @@ toExpr (m:ms) = ExprAnd (Exact m) (toExpr ms)
 
 instance Monoid Query where
     mempty  = Query []
-    Query  a  `mappend` Query    b  = Query (a ++ b)
-    Query  [] `mappend` Filter   b  = Filter b
-    Filter a  `mappend` Query    [] = Filter a
-    Query  a  `mappend` Filter   b  = Filter (ExprAnd (toExpr a) b)
-    Filter a  `mappend` Query    b  = Filter (ExprAnd a (toExpr b))
-    Filter a  `mappend` Filter   b  = Filter (a <> b)
 
 instance Semigroup Query where
-    (<>) = mappend
+    Query  a  <> Query    b  = Query (a ++ b)
+    Query  [] <> Filter   b  = Filter b
+    Filter a  <> Query    [] = Filter a
+    Query  a  <> Filter   b  = Filter (ExprAnd (toExpr a) b)
+    Filter a  <> Query    b  = Filter (ExprAnd a (toExpr b))
+    Filter a  <> Filter   b  = Filter (a <> b)
+
 instance Semigroup Expr where
   ex1 <> ex2 = ExprAnd ex1 ex2
 

src/Network/MPD/Core.hs

@@ -28,7 +28,7 @@ import           Network.MPD.Core.Error
 import           Data.Char (isDigit)
 import qualified Control.Exception as E
 import           Control.Exception.Safe (catch, catchAny)
-import           Control.Monad (ap, unless)
+import           Control.Monad (unless)
 import           Control.Monad.Except (ExceptT(..),runExceptT, MonadError(..))
 import           Control.Monad.Reader (ReaderT(..), ask)
 import           Control.Monad.State (StateT, MonadIO(..), modify, gets, evalStateT)
@@ -54,7 +54,6 @@ import           System.IO.Error (isEOFError, tryIOError, ioeGetErrorType)
 import           Text.Printf (printf)
 import qualified GHC.IO.Exception as GE
 
-import qualified Prelude
 import           Prelude hiding (break, drop, dropWhile, read)
 import           Data.ByteString.Char8 (ByteString, isPrefixOf, break, drop, dropWhile)
 import qualified Data.ByteString.Char8 as B
@@ -85,11 +84,7 @@ newtype MPD a =
     MPD { runMPD :: ExceptT MPDError
                     (StateT MPDState
                      (ReaderT (Host, Port) IO)) a
-        } deriving (Functor, Monad, MonadIO, MonadError MPDError)
-
-instance Applicative MPD where
-    (<*>) = ap
-    pure  = return
+        } deriving (Functor, Applicative, Monad, MonadIO, MonadError MPDError)
 
 instance MonadMPD MPD where
     open  = mpdOpen
@@ -140,10 +135,9 @@ mpdOpen = MPD $ do
             `catchAny` const (return Nothing)
         checkConn = do
             singleMsg <- send ""
-            let [msg] = singleMsg
-            if "OK MPD" `isPrefixOf` msg
-                then MPD $ checkVersion $ parseVersion msg
-                else return False
+            case singleMsg of
+                [msg] | "OK MPD" `isPrefixOf` msg -> MPD $ checkVersion $ parseVersion msg
+                _                                 -> pure False
 
         checkVersion Nothing = throwError $ Custom "Couldn't determine MPD version"
         checkVersion (Just version)
@@ -234,12 +228,10 @@ getResponse cmd = (send cmd >>= parseResponse) `catchError` sendpw
 
 -- Consume response and return a Response.
 parseResponse :: (MonadError MPDError m) => [ByteString] -> m [ByteString]
-parseResponse xs
-    | null xs                    = throwError $ NoMPD
+parseResponse [] = throwError $ NoMPD
+parseResponse xs@(x : _)
     | "ACK" `isPrefixOf` x       = throwError $ parseAck x
     | otherwise                  = return $ Prelude.takeWhile ("OK" /=) xs
-    where
-        x = head xs
 
 -- Turn MPD ACK into the corresponding 'MPDError'
 parseAck :: ByteString -> MPDError

tests/StringConn.hs

@@ -14,6 +14,7 @@ module StringConn where
 import           Control.Applicative
 import           Prelude hiding (exp)
 import           Control.Monad.Except
+import           Control.Monad
 import           Control.Monad.Identity
 import           Control.Monad.Reader
 import           Control.Monad.State