Merge pull request 'Linting integration' (#17) from Hecate/Hash2Pub:hlint-configuration into master

Introduce some code formatting guidelines and enforce them with hlint and stylish:

- End-of-line extra spaces removal;
- Import lines ordering;
- Redundant ($) removal;
- Generalisation of (++) and map to (<>) and fmap;
- Preferring pure over return;
- Removing extraenous extensions.

.hlint.yaml

@@ -0,0 +1,8 @@
+- group: {name: generalise, enabled: true}
+
+- warn: { name: Use DerivingStrategies }
+
+- error: { lhs: return, rhs: pure }
+
+- ignore: {name: "Avoid lambda using `infix`"}
+          

default.nix

@@ -23,6 +23,7 @@ in
         haddock
         cabal-install
         hlint
+        stylish-haskell
         pkgs.python3Packages.asn1ate
       ];
   };

src/CacheEdgeCases.hs

@@ -1,9 +1,9 @@
-import Hash2Pub.FediChord
 import           Data.Map.Internal.Debug (showTree)
 import qualified Data.Map.Strict         as Map
+import           Hash2Pub.FediChord
 
 giebMalCache :: [Integer] -> Map.Map NodeID ()
-giebMalCache = Map.fromList . map (mkCacheEntry . fromInteger)
+giebMalCache = Map.fromList . fmap (mkCacheEntry . fromInteger)
   where
     mkCacheEntry nodeid = (nodeid, ())
 
@@ -22,7 +22,7 @@ edgeCase1 = do
     putStrLn "\nWhile (NodeID 2^255+2^254+3) > (NodeID 2^254 + 14) …"
     print $ toNodeID (2^255+2^254+3) > toNodeID (2^254+14)
     putStrLn "… and 2^255+2^254+3 is an element of the map…"
-    print $ Map.member (fromInteger 2^255+2^254+3) testOverlap
+    print $ Map.member (fromInteger (2^255+2^254+3)) testOverlap
     putStrLn "… looking for an element larger than 2^254 + 14 doesn't yield any."
     print $ nidLookupGT testOverlap (2^254+14)
     putStrLn "\nThat's the tree of the map:"

src/Hash2Pub/ASN1Coding.hs

@@ -2,23 +2,23 @@
 
 module Hash2Pub.ASN1Coding where
 
-import Data.ASN1.Encoding -- asn1-encoding package
-import Data.ASN1.BinaryEncoding
-import Data.ASN1.Error()
-import Data.ASN1.Types -- asn1-types package
-import Data.ASN1.Parse
-import Data.Maybe (fromMaybe, mapMaybe, isNothing)
-import Data.Time.Clock.POSIX()
-import qualified Data.ByteString as BS
-import qualified Data.Set as Set
-import qualified Data.Map.Strict as Map
-import Data.Bifunctor (first)
 import           Control.Exception        (displayException)
+import           Data.ASN1.BinaryEncoding
+import           Data.ASN1.Encoding
+import           Data.ASN1.Error          ()
+import           Data.ASN1.Parse
+import           Data.ASN1.Types
+import           Data.Bifunctor           (first)
+import qualified Data.ByteString          as BS
+import qualified Data.Map.Strict          as Map
+import           Data.Maybe               (fromMaybe, isNothing, mapMaybe)
+import qualified Data.Set                 as Set
+import           Data.Time.Clock.POSIX    ()
 import           Safe
 
+import           Hash2Pub.DHTProtocol
 import           Hash2Pub.FediChord
 import           Hash2Pub.Utils
-import Hash2Pub.DHTProtocol
 
 import           Debug.Trace
 
@@ -107,7 +107,7 @@ serialiseMessage maxBytesLength msg =
         payloadParts i = zip [1..] . splitPayload i <$> actionPayload
         actionPayload = payload msg
         encodedMsgs i = Map.map encodeMsg $ messageParts i
-        maxMsgLength = maximum . map BS.length . Map.elems
+        maxMsgLength = maximum . fmap BS.length . Map.elems
 
 -- | encode a 'FediChordMessage' to a bytestring without further modification
 encodeMsg :: FediChordMessage -> BS.ByteString
@@ -127,21 +127,21 @@ encodePayload LeaveResponsePayload = [Null]
 encodePayload payload'@LeaveRequestPayload{} =
     Start Sequence
   : Start Sequence
-  : map (IntVal . getNodeID) (leaveSuccessors payload')
+  : fmap (IntVal . getNodeID) (leaveSuccessors payload')
-  ++ [End Sequence
+  <> [End Sequence
   , Start Sequence]
-  ++ map (IntVal . getNodeID) (leavePredecessors payload')
+  <> fmap (IntVal . getNodeID) (leavePredecessors payload')
-  ++ [End Sequence
+  <> [End Sequence
   , End Sequence]
 -- currently StabiliseResponsePayload and LeaveRequestPayload are equal
 encodePayload payload'@StabiliseResponsePayload{} =
     Start Sequence
   : Start Sequence
-  : map (IntVal . getNodeID) (stabiliseSuccessors payload')
+  : fmap (IntVal . getNodeID) (stabiliseSuccessors payload')
-  ++ [End Sequence
+  <> [End Sequence
   , Start Sequence]
-  ++ map (IntVal . getNodeID) (stabilisePredecessors payload')
+  <> fmap (IntVal . getNodeID) (stabilisePredecessors payload')
-  ++ [End Sequence
+  <> [End Sequence
   , End Sequence]
 encodePayload payload'@StabiliseRequestPayload = [Null]
 encodePayload payload'@QueryIDResponsePayload{} =
@@ -151,12 +151,12 @@ encodePayload payload'@QueryIDResponsePayload{} =
     Start Sequence
   : encodeQueryResult resp
   : case resp of
-      FOUND ns -> encodeNodeState $ ns
+      FOUND ns -> encodeNodeState ns
       FORWARD entrySet ->
             Start Sequence
           : (concatMap encodeCacheEntry . Set.elems $ entrySet)
-          ++ [End Sequence]
+          <> [End Sequence]
-  ++ [End Sequence]
+  <> [End Sequence]
 encodePayload payload'@QueryIDRequestPayload{} = [
     Start Sequence
   , IntVal . getNodeID $ queryTargetID payload'
@@ -167,21 +167,21 @@ encodePayload payload'@QueryIDRequestPayload{} = [
 encodePayload payload'@JoinResponsePayload{} =
     Start Sequence
   : Start Sequence
-  : map (IntVal . getNodeID) (joinSuccessors payload')
+  : fmap (IntVal . getNodeID) (joinSuccessors payload')
-  ++ [End Sequence
+  <> [End Sequence
   , Start Sequence]
-  ++ map (IntVal . getNodeID) (joinPredecessors payload')
+  <> fmap (IntVal . getNodeID) (joinPredecessors payload')
-  ++ [End Sequence
+  <> [End Sequence
     , Start Sequence]
-  ++ concatMap encodeCacheEntry (joinCache payload')
+  <> concatMap encodeCacheEntry (joinCache payload')
-  ++ [End Sequence
+  <> [End Sequence
     , End Sequence]
 encodePayload payload'@JoinRequestPayload{} = [Null]
 encodePayload PingRequestPayload{} = [Null]
 encodePayload payload'@PingResponsePayload{} =
     Start Sequence
   : concatMap encodeNodeState (pingNodeStates payload')
-  ++ [End Sequence]
+  <> [End Sequence]
 
 encodeNodeState :: NodeState -> [ASN1]
 encodeNodeState ns = [
@@ -200,7 +200,7 @@ encodeCacheEntry (RemoteCacheEntry ns timestamp) =
     Start Sequence
   : encodeNodeState ns
   -- ToDo: possibly optimise this by using dlists
-  ++ [
+  <> [
     IntVal . fromIntegral . fromEnum $ timestamp
   , End Sequence]
 encodeCacheEntry _ = []
@@ -218,11 +218,11 @@ encodeMessage
       : (Enumerated . fromIntegral . fromEnum $ action)
       : IntVal requestID
       : encodeNodeState sender
-      ++ [
+      <> [
         IntVal parts
       , IntVal part ]
-      ++ maybe [] encodePayload requestPayload
+      <> maybe [] encodePayload requestPayload
-      ++ [End Sequence]
+      <> [End Sequence]
 encodeMessage
     (Response responseTo senderID parts part action responsePayload) = [
         Start Sequence
@@ -231,8 +231,8 @@ encodeMessage
       , IntVal parts
       , IntVal part
       , Enumerated . fromIntegral . fromEnum $ action]
-      ++ maybe [] encodePayload responsePayload
+      <> maybe [] encodePayload responsePayload
-      ++ [End Sequence]
+      <> [End Sequence]
 
 -- ===== parser combinators =====
 
@@ -240,21 +240,21 @@ parseMessage :: ParseASN1 FediChordMessage
 parseMessage = do
     begin <- getNext
     case begin of
-      Start Sequence -> return ()
+      Start Sequence -> pure ()
-      x -> throwParseError $ "unexpected ASN.1 element " ++ show x
+      x -> throwParseError $ "unexpected ASN.1 element " <> show x
 -- request and response messages are distiguishable by their structure,
 -- see ASN.1 schema
     firstElem <- getNext
     message <- case firstElem of
       Enumerated a -> parseRequest . toEnum . fromIntegral $ a
       IntVal i -> parseResponse i
-      other -> throwParseError $ "unexpected first ASN1 element: " ++ show other
+      other -> throwParseError $ "unexpected first ASN1 element: " <> show other
     -- consume sequence end
     end <- getNext
     case end of
-      End Sequence -> return ()
+      End Sequence -> pure ()
-      x -> throwParseError $ "unexpected ASN.1 element " ++ show x
+      x            -> throwParseError $ "unexpected ASN.1 element " <> show x
-    return message
+    pure message
 
 
 
@@ -265,14 +265,14 @@ parseRequest action = do
     parts <- parseInteger
     part <- parseInteger
     hasPayload <- hasNext
-    payload <- if not hasPayload then return Nothing else Just <$> case action of
+    payload <- if not hasPayload then pure Nothing else Just <$> case action of
                  QueryID   -> parseQueryIDRequest
                  Join      -> parseJoinRequest
                  Leave     -> parseLeaveRequest
                  Stabilise -> parseStabiliseRequest
                  Ping      -> parsePingRequest
 
-    return $ Request requestID sender parts part action payload
+    pure $ Request requestID sender parts part action payload
 
 parseResponse :: Integer -> ParseASN1 FediChordMessage
 parseResponse responseTo = do
@@ -281,49 +281,49 @@ parseResponse responseTo = do
     part <- parseInteger
     action <- parseEnum :: ParseASN1 Action
     hasPayload <- hasNext
-    payload <- if not hasPayload then return Nothing else Just <$> case action of
+    payload <- if not hasPayload then pure Nothing else Just <$> case action of
                  QueryID   -> parseQueryIDResponse
                  Join      -> parseJoinResponse
                  Leave     -> parseLeaveResponse
                  Stabilise -> parseStabiliseResponse
                  Ping      -> parsePingResponse
 
-    return $ Response responseTo senderID parts part action payload
+    pure $ Response responseTo senderID parts part action payload
 
 parseInteger :: ParseASN1 Integer
 parseInteger = do
     i <- getNext
     case i of
-        IntVal parsed -> return parsed
+        IntVal parsed -> pure parsed
-        x -> throwParseError $ "Expected IntVal but got " ++ show x
+        x -> throwParseError $ "Expected IntVal but got " <> show x
 
 parseEnum :: Enum a => ParseASN1 a
 parseEnum = do
     e <- getNext
     case e of
-        Enumerated en -> return $ toEnum . fromIntegral $ en
+        Enumerated en -> pure $ toEnum . fromIntegral $ en
-        x -> throwParseError $ "Expected Enumerated but got " ++ show x
+        x -> throwParseError $ "Expected Enumerated but got " <> show x
 
 parseString :: ParseASN1 String
 parseString = do
     s <- getNext
     case s of
-        ASN1String toBeParsed -> maybe (throwParseError "string parsing failed") return $ asn1CharacterToString toBeParsed
+        ASN1String toBeParsed -> maybe (throwParseError "string parsing failed") pure $ asn1CharacterToString toBeParsed
-        x -> throwParseError $ "Expected a ASN1String but got " ++ show x
+        x -> throwParseError $ "Expected a ASN1String but got " <> show x
 
 parseOctets :: ParseASN1 BS.ByteString
 parseOctets = do
     os <- getNext
     case os of
-        OctetString bs -> return bs
+        OctetString bs -> pure bs
-        x -> throwParseError $ "Expected an OctetString but got " ++ show x
+        x -> throwParseError $ "Expected an OctetString but got " <> show x
 
 parseNull :: ParseASN1 ()
 parseNull = do
     n <- getNext
     case n of
-        Null -> return ()
+        Null -> pure ()
-        x -> throwParseError $ "Expected Null but got " ++ show x
+        x    -> throwParseError $ "Expected Null but got " <> show x
 
 parseNodeState :: ParseASN1 NodeState
 parseNodeState = onNextContainer Sequence $ do
@@ -333,7 +333,7 @@ parseNodeState = onNextContainer Sequence $ do
     dhtPort' <- fromInteger <$> parseInteger
     apPort' <- fromInteger <$> parseInteger
     vServer' <- parseInteger
-    return NodeState {
+    pure NodeState {
         nid = nid'
       , domain = domain'
       , dhtPort = dhtPort'
@@ -348,7 +348,7 @@ parseCacheEntry :: ParseASN1 RemoteCacheEntry
 parseCacheEntry = onNextContainer Sequence $ do
     node <- parseNodeState
     timestamp <- toEnum . fromIntegral <$> parseInteger
-    return $ RemoteCacheEntry node timestamp
+    pure $ RemoteCacheEntry node timestamp
 
 parseNodeCache :: ParseASN1 [RemoteCacheEntry]
 parseNodeCache = onNextContainer Sequence $ getMany parseCacheEntry
@@ -356,14 +356,14 @@ parseNodeCache = onNextContainer Sequence $ getMany parseCacheEntry
 parseJoinRequest :: ParseASN1 ActionPayload
 parseJoinRequest = do
     parseNull
-    return JoinRequestPayload
+    pure JoinRequestPayload
 
 parseJoinResponse :: ParseASN1 ActionPayload
 parseJoinResponse = onNextContainer Sequence $ do
-    succ' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    succ' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
-    pred' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    pred' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
     cache <- parseNodeCache
-    return $ JoinResponsePayload {
+    pure $ JoinResponsePayload {
         joinSuccessors = succ'
       , joinPredecessors = pred'
       , joinCache = cache
@@ -373,7 +373,7 @@ parseQueryIDRequest :: ParseASN1 ActionPayload
 parseQueryIDRequest = onNextContainer Sequence $ do
     targetID <- fromInteger <$> parseInteger
     lBestNodes <- parseInteger
-    return $ QueryIDRequestPayload {
+    pure $ QueryIDRequestPayload {
         queryTargetID = targetID
       , queryLBestNodes = lBestNodes
                                    }
@@ -385,29 +385,29 @@ parseQueryIDResponse = onNextContainer Sequence $ do
                   0 -> FOUND <$> parseNodeState
                   1 -> FORWARD . Set.fromList <$> parseNodeCache
                   _ -> throwParseError "invalid QueryIDResponse type"
-    return $ QueryIDResponsePayload {
+    pure $ QueryIDResponsePayload {
         queryResult = result
                            }
 
 parseStabiliseRequest :: ParseASN1 ActionPayload
 parseStabiliseRequest = do
     parseNull
-    return StabiliseRequestPayload
+    pure StabiliseRequestPayload
 
 parseStabiliseResponse :: ParseASN1 ActionPayload
 parseStabiliseResponse = onNextContainer Sequence $ do
-    succ' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    succ' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
-    pred' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    pred' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
-    return $ StabiliseResponsePayload {
+    pure $ StabiliseResponsePayload {
         stabiliseSuccessors = succ'
       , stabilisePredecessors = pred'
                                       }
 
 parseLeaveRequest :: ParseASN1 ActionPayload
 parseLeaveRequest = onNextContainer Sequence $ do
-    succ' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    succ' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
-    pred' <- map fromInteger <$> onNextContainer Sequence (getMany parseInteger)
+    pred' <- fmap fromInteger <$> onNextContainer Sequence (getMany parseInteger)
-    return $ LeaveRequestPayload {
+    pure $ LeaveRequestPayload {
         leaveSuccessors = succ'
       , leavePredecessors = pred'
                                       }
@@ -415,16 +415,16 @@ parseLeaveRequest = onNextContainer Sequence $ do
 parseLeaveResponse :: ParseASN1 ActionPayload
 parseLeaveResponse = do
     parseNull
-    return LeaveResponsePayload
+    pure LeaveResponsePayload
 
 parsePingRequest :: ParseASN1 ActionPayload
 parsePingRequest = do
     parseNull
-    return PingRequestPayload
+    pure PingRequestPayload
 
 parsePingResponse :: ParseASN1 ActionPayload
 parsePingResponse = onNextContainer Sequence $ do
     handledNodes <- getMany parseNodeState
-    return $ PingResponsePayload {
+    pure $ PingResponsePayload {
         pingNodeStates = handledNodes
                                  }

src/Hash2Pub/DHTProtocol.hs

@@ -1,5 +1,3 @@
-{-# LANGUAGE OverloadedStrings #-}
-
 module Hash2Pub.DHTProtocol
     ( QueryResponse (..)
     , queryLocalCache
@@ -17,28 +15,20 @@ module Hash2Pub.DHTProtocol
     )
         where
 
-import Data.Maybe (maybe, fromMaybe)
-import qualified Data.Set as Set
 import qualified Data.Map                  as Map
+import           Data.Maybe                (fromMaybe, maybe)
+import qualified Data.Set                  as Set
 import           Data.Time.Clock.POSIX
-import Network.Socket hiding (send, sendTo, recv, recvFrom)
+import           Network.Socket            hiding (recv, recvFrom, send, sendTo)
 import           Network.Socket.ByteString
 
-import Hash2Pub.FediChord
+import           Hash2Pub.FediChord        (CacheEntry (..), NodeCache, NodeID,
-  ( NodeID
+                                            NodeState (..),
-  , NodeState (..)
+                                            cacheGetNodeStateUnvalidated,
-  , getSuccessors
+                                            cacheLookup, cacheLookupPred,
-  , putSuccessors
+                                            cacheLookupSucc, getPredecessors,
-  , getPredecessors
+                                            getSuccessors, localCompare,
-  , putPredecessors
+                                            putPredecessors, putSuccessors)
-  , cacheGetNodeStateUnvalidated
-  , NodeCache
-  , CacheEntry(..)
-  , cacheLookup
-  , cacheLookupSucc
-  , cacheLookupPred
-  , localCompare
-  )
 
 import           Debug.Trace               (trace)
 
@@ -170,7 +160,7 @@ addCacheEntry :: RemoteCacheEntry   -- ^ a remote cache entry received from netw
               -> IO NodeCache       -- ^ new node cache with the element inserted
 addCacheEntry entry cache = do
     now <- getPOSIXTime
-    return $ addCacheEntryPure now entry cache
+    pure $ addCacheEntryPure now entry cache
 
 -- | pure version of 'addCacheEntry' with current time explicitly specified as argument
 addCacheEntryPure :: POSIXTime      -- ^ current time
@@ -214,9 +204,9 @@ markCacheEntryAsVerified timestamp = Map.adjust adjustFunc
 attempts :: Int             -- ^ number of retries *i*
          -> IO (Maybe a)    -- ^ action to retry
          -> IO (Maybe a)    -- ^ result after at most *i* retries
-attempts 0 _ = return Nothing
+attempts 0 _ = pure Nothing
 attempts i action = do
     actionResult <- action
     case actionResult of
       Nothing  -> attempts (i-1) action
-      Just res -> return $ Just res
+      Just res -> pure $ Just res

src/Hash2Pub/FediChord.hs

@@ -1,4 +1,6 @@
-{-# LANGUAGE GeneralizedNewtypeDeriving, DataKinds, OverloadedStrings #-}
+{-# LANGUAGE DataKinds                  #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE OverloadedStrings          #-}
 {- |
 Module      : FediChord
 Description : An opinionated implementation of the EpiChord DHT by Leong et al.
@@ -45,25 +47,26 @@ module Hash2Pub.FediChord (
   , cacheWriter
                            ) where
 
-import qualified Data.Map.Strict as Map
-import Network.Socket
-import Data.Time.Clock.POSIX
 import           Control.Exception
-import Data.Maybe (isJust, fromMaybe, mapMaybe)
+import qualified Data.Map.Strict               as Map
+import           Data.Maybe                    (fromMaybe, isJust, mapMaybe)
+import           Data.Time.Clock.POSIX
+import           Network.Socket
 
 -- for hashing and ID conversion
-import Crypto.Hash
-import Data.Word
-import qualified Data.ByteString as BS
-import qualified Data.ByteString.UTF8 as BSU
-import qualified Data.ByteArray as BA
-import qualified Network.ByteOrder as NetworkBytes
-import Data.IP (IPv6, fromHostAddress6, toHostAddress6)
-import Data.IORef
 import           Control.Concurrent.STM
 import           Control.Concurrent.STM.TQueue
 import           Control.Monad                 (forever)
+import           Crypto.Hash
+import qualified Data.ByteArray                as BA
+import qualified Data.ByteString               as BS
+import qualified Data.ByteString.UTF8          as BSU
+import           Data.IORef
+import           Data.IP                       (IPv6, fromHostAddress6,
+                                                toHostAddress6)
 import           Data.Typeable                 (Typeable (..), typeOf)
+import           Data.Word
+import qualified Network.ByteOrder             as NetworkBytes
 
 import           Hash2Pub.Utils
 
@@ -280,12 +283,12 @@ lookupWrapper :: (NodeID -> NodeCache -> Maybe (NodeID, CacheEntry)) -> (NodeID
 lookupWrapper f fRepeat direction key cache =
     case f key cache of
         -- the proxy entry found holds a
-        Just (_, (ProxyEntry _ (Just entry@NodeEntry{}))) -> Just entry
+        Just (_, ProxyEntry _ (Just entry@NodeEntry{})) -> Just entry
         -- proxy entry holds another proxy entry, this should not happen
-        Just (_, (ProxyEntry _ (Just (ProxyEntry _ _)))) -> Nothing
+        Just (_, ProxyEntry _ (Just (ProxyEntry _ _))) -> Nothing
         -- proxy entry without own entry is a pointer on where to continue
         -- if lookup direction is the same as pointer direction: follow pointer
-        Just (foundKey, (ProxyEntry (pointerID, pointerDirection) Nothing)) ->
+        Just (foundKey, ProxyEntry (pointerID, pointerDirection) Nothing) ->
             let newKey = if pointerDirection == direction
                             then pointerID
                             else foundKey + (fromInteger . toInteger . fromEnum $ direction)
@@ -322,17 +325,17 @@ cacheLookupPred = lookupWrapper Map.lookupLT Map.lookupLE Backwards
 cacheGetNodeStateUnvalidated :: CacheEntry -> NodeState
 cacheGetNodeStateUnvalidated (NodeEntry _ nState _) = nState
 cacheGetNodeStateUnvalidated (ProxyEntry _ (Just entry)) = cacheGetNodeStateUnvalidated entry
-cacheGetNodeStateUnvalidated _ = error "trying to return empty node state, please report a bug"
+cacheGetNodeStateUnvalidated _ = error "trying to pure empty node state, please report a bug"
 
 -- | converts a 'HostAddress6' IP address to a big-endian strict ByteString
 ipAddrAsBS :: HostAddress6 -> BS.ByteString
-ipAddrAsBS (a, b, c, d) = mconcat $ map NetworkBytes.bytestring32 [a, b, c, d]
+ipAddrAsBS (a, b, c, d) = mconcat $ fmap NetworkBytes.bytestring32 [a, b, c, d]
 
 -- | converts a ByteString in big endian order to an IPv6 address 'HostAddress6'
 bsAsIpAddr :: BS.ByteString -> HostAddress6
 bsAsIpAddr bytes = (a,b,c,d)
     where
-        a:b:c:d:_ = map NetworkBytes.word32 . chunkBytes 4 $ bytes 
+        a:b:c:d:_ = fmap NetworkBytes.word32 . chunkBytes 4 $ bytes
 
 
 -- | generates a 256 bit long NodeID using SHAKE128, represented as ByteString
@@ -344,7 +347,7 @@ genNodeIDBS ip nodeDomain vserver =
     hashIpaddrUpper `BS.append` hashID nodeDomain' `BS.append` hashIpaddLower
         where
             vsBS = BS.pack [vserver] -- attention: only works for vserver IDs up to 255
-            ipaddrNet = (BS.take 8 $ ipAddrAsBS ip) `BS.append` vsBS
+            ipaddrNet = BS.take 8 (ipAddrAsBS ip) `BS.append` vsBS
             nodeDomain' = BSU.fromString nodeDomain `BS.append` vsBS
             hashID bstr = BS.pack . BA.unpack $ (hash bstr :: Digest (SHAKE128 128))
             (hashIpaddrUpper, hashIpaddLower) = BS.splitAt 64 $ hashID ipaddrNet
@@ -391,7 +394,7 @@ byteStringToUInteger bs = sum $ parsedBytes 0 bs
 --checkCacheSlices :: NodeState -> IO [()]
 --checkCacheSlices state = case getNodeCache state of
 --    -- don't do anything on nodes without a cache
---    Nothing -> return [()]
+--    Nothing -> pure [()]
 --    Just cache' -> checkSlice jEntries (nid state) startBound lastSucc =<< readIORef cache'
 --    -- TODO: do the same for predecessors
 --    where
@@ -415,10 +418,10 @@ byteStringToUInteger bs = sum $ parsedBytes 0 bs
 --                   -- TODO: replace empty IO actions with actual lookups to middle of slice
 --                   -- TODO: validate ID before adding to cache
 --                   case Map.lookupLT upperBound cache of
---                       Nothing -> return () : checkSlice j ownID lowerBound (Just lastSuccNode) cache
+--                       Nothing -> pure () : checkSlice j ownID lowerBound (Just lastSuccNode) cache
 --                       Just (matchID, _) ->
 --                           if
---                               matchID <= lowerBound then return () : checkSlice j ownID lowerBound (Just lastSuccNode) cache
+--                               matchID <= lowerBound then pure () : checkSlice j ownID lowerBound (Just lastSuccNode) cache
 --                           else
 --                               checkSlice j ownID lowerBound (Just lastSuccNode) cache
 
@@ -439,7 +442,7 @@ fediChordInit :: FediChordConf -> IO (Socket, NodeState)
 fediChordInit conf = do
     initialState <- nodeStateInit conf
     serverSock <- mkServerSocket (ipAddr initialState) (dhtPort initialState)
-    return (serverSock, initialState)
+    pure (serverSock, initialState)
 
 -- | initialises the 'NodeState' for this local node.
 -- Separated from 'fediChordInit' to be usable in tests.
@@ -467,7 +470,7 @@ nodeStateInit conf = do
           , pNumParallelQueries = 2
           , jEntriesPerSlice = 2
                                            }
-    return initialState
+    pure initialState
 
 --fediChordJoin :: NodeState              -- ^ the local 'NodeState'
 --              -> (String, PortNumber)   -- ^ domain and port of a bootstrapping node
@@ -486,13 +489,13 @@ cacheWriter :: NodeState -> IO ()
 cacheWriter ns = do
     let writeQueue' = getCacheWriteQueue ns
     case writeQueue' of
-      Nothing -> return ()
+      Nothing -> pure ()
       Just writeQueue -> forever $ do
         f <- atomically $ readTQueue writeQueue
         let
             refModifier :: NodeCache -> (NodeCache, ())
             refModifier nc = (f nc, ())
-        maybe (return ()) (
+        maybe (pure ()) (
             \ref -> atomicModifyIORef' ref refModifier
                  ) $ getNodeCacheRef ns
 
@@ -518,7 +521,7 @@ mkServerSocket ip port = do
     sock <- socket AF_INET6 Datagram defaultProtocol
     setSocketOption sock IPv6Only 1
     bind sock sockAddr
-    return sock
+    pure sock
 
 -- | create a UDP datagram socket, connected to a destination.
 -- The socket gets an arbitrary free local port assigned.
@@ -529,4 +532,4 @@ mkSendSocket dest destPort = do
     destAddr <- addrAddress <$> resolve (Just dest) (Just destPort)
     sendSock <- socket AF_INET6 Datagram defaultProtocol
     setSocketOption sendSock IPv6Only 1
-    return sendSock
+    pure sendSock

src/Hash2Pub/Main.hs

@@ -1,8 +1,8 @@
 module Main where
 
-import System.Environment
-import Data.IP (IPv6, toHostAddress6) -- iproute, just for IPv6 string parsing
 import           Control.Concurrent
+import           Data.IP            (IPv6, toHostAddress6)
+import           System.Environment
 
 import           Hash2Pub.FediChord
 
@@ -20,12 +20,12 @@ main = do
     -- idea: list of bootstrapping nodes, try joining within a timeout
     -- stop main thread from terminating during development
     getChar
-    return ()
+    pure ()
 
 readConfig :: IO FediChordConf
 readConfig = do
     confDomainString : ipString : portString : _ <- getArgs
-    return $ FediChordConf {
+    pure $ FediChordConf {
         confDomain = confDomainString
       , confIP = toHostAddress6 . read $ ipString
       , confDhtPort = read portString

src/asn1test.hs

@@ -1,11 +1,11 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Main where
 
-import qualified Data.ASN1.Encoding as ASN1 -- asn1-encoding package
 import qualified Data.ASN1.BinaryEncoding as ASN1
+import qualified Data.ASN1.Encoding       as ASN1
 import qualified Data.ASN1.Error          as ASN1
-import qualified Data.ASN1.Types as ASN1 -- asn1-types package
 import qualified Data.ASN1.Parse          as ASN1P
+import qualified Data.ASN1.Types          as ASN1
 import qualified Data.ByteString          as BS
 import           Data.Maybe               (fromMaybe)
 import           Debug.Trace              (trace)
@@ -14,7 +14,7 @@ import Debug.Trace (trace)
 
 -- encoding values as ASN.1 types is done using Data.ASN1.Prim
 someASN1 :: [ASN1.ASN1]
-someASN1 = ASN1.Start ASN1.Sequence : ASN1.ASN1String (ASN1.asn1CharacterString ASN1.Visible domain) : ASN1.ASN1String (ASN1.asn1CharacterString ASN1.UTF8 unicode) : map ASN1.IntVal xs ++ [ASN1.End ASN1.Sequence]
+someASN1 = ASN1.Start ASN1.Sequence : ASN1.ASN1String (ASN1.asn1CharacterString ASN1.Visible domain) : ASN1.ASN1String (ASN1.asn1CharacterString ASN1.UTF8 unicode) : fmap ASN1.IntVal xs <> [ASN1.End ASN1.Sequence]
   where
     domain = "domains.are.ascii.on.ly"
     unicode = "Hähä, but unicode string!"
@@ -27,12 +27,12 @@ derToAsn1 :: BS.ByteString -> Either ASN1.ASN1Error [ASN1.ASN1]
 derToAsn1 = ASN1.decodeASN1' ASN1.DER
 
 getUnicodeField :: [ASN1.ASN1] -> String
-getUnicodeField ((ASN1.Start ASN1.Sequence) : _ : (ASN1.ASN1String strASN1) : _) = fromMaybe "" $ ASN1.asn1CharacterToString strASN1
+getUnicodeField (ASN1.Start ASN1.Sequence : _ : ASN1.ASN1String strASN1 : _) = fromMaybe "" $ ASN1.asn1CharacterToString strASN1
 
 testParser :: ASN1P.ParseASN1 String
 testParser = do
     foo <- ASN1P.onNextContainer ASN1.Sequence getAll
-    return $ show foo
+    pure $ show foo
 
 getAll :: ASN1P.ParseASN1 [ASN1.ASN1]
 getAll = ASN1P.getMany ASN1P.getNext

stylish.sh

@@ -0,0 +1,32 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+function ls-source-files {
+  git ls-files "app/*.hs" "src/*.hs" "test/*.hs"
+}
+
+function check-git-status {
+  [ "$(git status -s '*.hs' | wc -l)" == "0" ]
+}
+
+function stylish {
+  stylish-haskell -i $(ls-source-files)
+}
+
+if check-git-status
+then
+  echo "Running stylish-haskell..."
+  stylish
+  echo "Done."
+  if check-git-status
+  then
+    echo "OK, impeccable style."
+  else
+    echo "KO! Lack of style on those files:"
+    git status -sb
+    exit 1
+  fi
+else
+  echo "git status not clean, aborting"
+fi

test/FediChordSpec.hs

@@ -1,20 +1,20 @@
 {-# LANGUAGE OverloadedStrings #-}
 module FediChordSpec where
 
-import Test.Hspec
 import           Control.Exception
-import Network.Socket
-import Data.Maybe (fromJust)
-import qualified Data.Map.Strict as Map
-import qualified Data.ByteString as BS
-import qualified Data.Set as Set
 import           Data.ASN1.Parse       (runParseASN1)
-import Data.Time.Clock.POSIX
+import qualified Data.ByteString       as BS
 import           Data.IORef
+import qualified Data.Map.Strict       as Map
+import           Data.Maybe            (fromJust)
+import qualified Data.Set              as Set
+import           Data.Time.Clock.POSIX
+import           Network.Socket
+import           Test.Hspec
 
-import Hash2Pub.FediChord
-import Hash2Pub.DHTProtocol
 import           Hash2Pub.ASN1Coding
+import           Hash2Pub.DHTProtocol
+import           Hash2Pub.FediChord
 
 spec :: Spec
 spec = do
@@ -123,7 +123,7 @@ spec = do
             nid1 = toNodeID 2^(23::Integer)+1
             node1 = do
                 eln <- exampleLocalNode -- is at 2^23.00000017198264 = 8388609
-                return $ putPredecessors [nid4] $ eln {nid = nid1}
+                pure $ putPredecessors [nid4] $ eln {nid = nid1}
             nid2 = toNodeID 2^(230::Integer)+12
             node2 = exampleNodeState { nid = nid2}
             nid3 = toNodeID 2^(25::Integer)+10
@@ -156,7 +156,7 @@ spec = do
     describe "Messages can be encoded to and decoded from ASN.1" $ do
         -- define test messages
         let
-            someNodeIDs = map fromInteger [3..12]
+            someNodeIDs = fmap fromInteger [3..12]
             qidReqPayload = QueryIDRequestPayload {
                 queryTargetID = nid exampleNodeState
               , queryLBestNodes = 3

test/Specs.hs

@@ -1,8 +1,8 @@
 module Main (main) where
 
-import Test.Hspec
 import qualified FediChordSpec
+import           Test.Hspec
 
 main :: IO ()
-main = hspec $ do
+main = hspec $
     describe "FediChord tests" FediChordSpec.spec