diff --git a/shellcheck.hs b/shellcheck.hs
index f1757ef..d7e818d 100644
--- a/shellcheck.hs
+++ b/shellcheck.hs
@@ -507,7 +507,7 @@ ioInterface options files = do
       where
         find filename deflt = do
             sources <- findM ((allowable inputs) `andM` doesFileExist) $
-                        (adjustPath filename):(map (</> filename) $ map adjustPath $ sourcePathFlag ++ sourcePathAnnotation)
+                        (adjustPath filename):(map ((</> filename) . adjustPath) $ sourcePathFlag ++ sourcePathAnnotation)
             case sources of
                 Nothing -> return deflt
                 Just first -> return first
diff --git a/src/ShellCheck/ASTLib.hs b/src/ShellCheck/ASTLib.hs
index d9ee8b1..c5f1735 100644
--- a/src/ShellCheck/ASTLib.hs
+++ b/src/ShellCheck/ASTLib.hs
@@ -178,7 +178,7 @@ getOpts (gnu, arbitraryLongOpts) string longopts args = process args
     process [] = return []
     process (token:rest) = do
         case getLiteralStringDef "\0" token of
-            '-':'-':[] -> return $ listToArgs rest
+            "--" -> return $ listToArgs rest
             '-':'-':word -> do
                 let (name, arg) = span (/= '=') word
                 needsArg <-
@@ -466,7 +466,7 @@ getCommandNameAndToken direct t = fromMaybe (Nothing, t) $ do
                 "run" -> firstArg -- Used by bats
                 "exec" -> do
                     opts <- getBsdOpts "cla:" args
-                    (_, (t, _)) <- listToMaybe $ filter (null . fst) opts
+                    (_, (t, _)) <- find (null . fst) opts
                     return t
                 _ -> fail ""
 
diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 8ab7f12..8500a7b 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -417,7 +417,7 @@ prop_checkAssignAteCommand4 = verifyNot checkAssignAteCommand "A=foo ls -l"
 prop_checkAssignAteCommand5 = verify checkAssignAteCommand "PAGER=cat grep bar"
 prop_checkAssignAteCommand6 = verifyNot checkAssignAteCommand "PAGER=\"cat\" grep bar"
 prop_checkAssignAteCommand7 = verify checkAssignAteCommand "here=pwd"
-checkAssignAteCommand _ (T_SimpleCommand id (T_Assignment _ _ _ _ assignmentTerm:[]) list) =
+checkAssignAteCommand _ (T_SimpleCommand id [T_Assignment _ _ _ _ assignmentTerm] list) =
     -- Check if first word is intended as an argument (flag or glob).
     if firstWordIsArg list
     then
@@ -449,7 +449,7 @@ checkArithmeticOpCommand _ _ = return ()
 
 prop_checkWrongArit = verify checkWrongArithmeticAssignment "i=i+1"
 prop_checkWrongArit2 = verify checkWrongArithmeticAssignment "n=2; i=n*2"
-checkWrongArithmeticAssignment params (T_SimpleCommand id (T_Assignment _ _ _ _ val:[]) []) =
+checkWrongArithmeticAssignment params (T_SimpleCommand id [T_Assignment _ _ _ _ val] []) =
   sequence_ $ do
     str <- getNormalString val
     match <- matchRegex regex str
@@ -2518,7 +2518,7 @@ checkCharRangeGlob p t@(T_Glob id str) |
   where
     isCharClass str = "[" `isPrefixOf` str && "]" `isSuffixOf` str
     contents = dropNegation . drop 1 . take (length str - 1) $ str
-    hasDupes = any (>1) . map length . group . sort . filter (/= '-') $ contents
+    hasDupes = any ((>1) . length) . group . sort . filter (/= '-') $ contents
     dropNegation s =
         case s of
             '!':rest -> rest
@@ -2881,7 +2881,7 @@ checkTestArgumentSplitting params t =
                 then
                     -- Ksh appears to stop processing after unrecognized tokens, so operators
                     -- will effectively work with globs, but only the first match.
-                    when (op `elem` ['-':c:[] | c <- "bcdfgkprsuwxLhNOGRS" ]) $
+                    when (op `elem` [['-', c] | c <- "bcdfgkprsuwxLhNOGRS" ]) $
                         warn (getId token) 2245 $
                             op ++ " only applies to the first expansion of this glob. Use a loop to check any/all."
                 else
@@ -3408,7 +3408,7 @@ checkPipeToNowhere params t =
 
         sequence_ $ do
             T_Redirecting _ redirs cmd <- return stage
-            fds <- sequence $ map getRedirectionFds redirs
+            fds <- mapM getRedirectionFds redirs
 
             let fdAndToken :: [(Integer, Token)]
                 fdAndToken =
@@ -3441,7 +3441,7 @@ checkPipeToNowhere params t =
 
     commandSpecificException name cmd =
         case name of
-            "du" -> any (`elem` ["exclude-from", "files0-from"]) $ map snd $ getAllFlags cmd
+            "du" -> any ((`elem` ["exclude-from", "files0-from"]) . snd) $ getAllFlags cmd
             _ -> False
 
     warnAboutDupes (n, list@(_:_:_)) =
@@ -3845,7 +3845,7 @@ checkAliasUsedInSameParsingUnit params root =
         -- Group them by whether they start on the same line where the previous one ended
         units = groupByLink followsOnLine commands
     in
-        execWriter $ sequence_ $ map checkUnit units
+        execWriter $ mapM_ checkUnit units
   where
     lineSpan t =
         let m = tokenPositions params in do
@@ -3895,13 +3895,13 @@ groupByLink :: (a -> a -> Bool) -> [a] -> [[a]]
 groupByLink f list =
     case list of
         [] -> []
-        (x:xs) -> g x [] xs
+        (x:xs) -> foldr c n xs x []
   where
-    g current span (next:rest) =
+    c next rest current span =
         if f current next
-        then g next (current:span) rest
-        else (reverse $ current:span) : g next [] rest
-    g current span [] = [reverse (current:span)]
+        then rest next (current:span)
+        else (reverse $ current:span) : rest next []
+    n current span = [reverse (current:span)]
 
 
 prop_checkBlatantRecursion1 = verify checkBlatantRecursion ":(){ :|:& };:"
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index bc8bc3d..d3b1134 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -258,9 +258,9 @@ determineShell fallbackShell t = fromMaybe Bash $
 executableFromShebang :: String -> String
 executableFromShebang = shellFor
   where
-    shellFor s | "/env " `isInfixOf` s = fromMaybe "" $ do
-        [flag, shell] <- matchRegex re s
-        return shell
+    shellFor s | "/env " `isInfixOf` s = case matchRegex re s of
+        Just [flag, shell] -> shell
+        _ -> ""
     shellFor s | ' ' `elem` s = shellFor $ takeWhile (/= ' ') s
     shellFor s = reverse . takeWhile (/= '/') . reverse $ s
     re = mkRegex "/env +(-S|--split-string=?)? *([^ ]*)"
@@ -270,7 +270,7 @@ executableFromShebang = shellFor
 -- This is used to populate parentMap in Parameters
 getParentTree :: Token -> Map.Map Id Token
 getParentTree t =
-    snd . snd $ runState (doStackAnalysis pre post t) ([], Map.empty)
+    snd $ execState (doStackAnalysis pre post t) ([], Map.empty)
   where
     pre t = modify (first ((:) t))
     post t = do
@@ -687,12 +687,10 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
         parseArgs :: Maybe (Token, Token, String, DataType)
         parseArgs = do
             args <- getGnuOpts "d:n:O:s:u:C:c:t" rest
-            let names = map snd $ filter (\(x,y) -> null x) args
-            if null names
-                then
+            case [y | ("",(_,y)) <- args] of
+                [] ->
                     return (base, base, "MAPFILE", DataArray SourceExternal)
-                else do
-                    (_, first) <- listToMaybe names
+                first:_ -> do
                     name <- getLiteralString first
                     guard $ isVariableName name
                     return (base, first, name, DataArray SourceExternal)
diff --git a/src/ShellCheck/Checks/Commands.hs b/src/ShellCheck/Checks/Commands.hs
index 36f32a5..b3e81a1 100644
--- a/src/ShellCheck/Checks/Commands.hs
+++ b/src/ShellCheck/Checks/Commands.hs
@@ -122,7 +122,7 @@ checkGetOpts str flags args f =
     toTokens = map (T_Literal (Id 0)) . words
     opts = fromMaybe [] $ f (toTokens str)
     actualFlags = filter (not . null) $ map fst opts
-    actualArgs = map (\(_, (_, x)) -> onlyLiteralString x) $ filter (null . fst) opts
+    actualArgs = [onlyLiteralString x | ("", (_, x)) <- opts]
 
 -- Short options
 prop_checkGetOptsS1 = checkGetOpts "-f x" ["f"] [] $ getOpts (True, True) "f:" []
@@ -916,7 +916,7 @@ checkWhileGetoptsCase = CommandCheck (Exactly "getopts") f
 
     fromGlob t =
         case t of
-            T_Glob _ ('[':c:']':[]) -> return [c]
+            T_Glob _ ['[', c, ']'] -> return [c]
             T_Glob _ "*" -> return "*"
             T_Glob _ "?" -> return "?"
             _ -> Nothing
@@ -951,7 +951,7 @@ checkCatastrophicRm = CommandCheck (Basename "rm") $ \t ->
     when (isRecursive t) $
         mapM_ (mapM_ checkWord . braceExpand) $ arguments t
   where
-    isRecursive = any (`elem` ["r", "R", "recursive"]) . map snd . getAllFlags
+    isRecursive = any ((`elem` ["r", "R", "recursive"]) . snd) . getAllFlags
 
     checkWord token =
         case getLiteralString token of
diff --git a/src/ShellCheck/Parser.hs b/src/ShellCheck/Parser.hs
index afe6262..03865af 100644
--- a/src/ShellCheck/Parser.hs
+++ b/src/ShellCheck/Parser.hs
@@ -211,8 +211,7 @@ startSpan = IncompleteInterval <$> getPosition
 
 endSpan (IncompleteInterval start) = do
     endPos <- getPosition
-    id <- getNextIdBetween start endPos
-    return id
+    getNextIdBetween start endPos
 
 getSpanPositionsFor m = do
     start <- getPosition
@@ -394,7 +393,7 @@ unexpecting s p = try $
 
 notFollowedBy2 = unexpecting ""
 
-isFollowedBy p = (lookAhead . try $ p *> return True) <|> return False
+isFollowedBy p = (lookAhead . try $ p $> True) <|> return False
 
 reluctantlyTill p end =
     (lookAhead (void (try end) <|> eof) >> return []) <|> do
@@ -2095,10 +2094,6 @@ readSimpleCommand = called "simple command" $ do
         then action
         else getParser def cmd rest
 
-    cStyleComment cmd =
-        case cmd of
-            _ -> False
-
     validateCommand cmd =
         case cmd of
             (T_NormalWord _ [T_Literal _ "//"]) -> commentWarning (getId cmd)
@@ -2721,7 +2716,7 @@ readConditionCommand = do
 
     pos <- getPosition
     hasDashAo <- isFollowedBy $ do
-        c <- choice $ map (\s -> try $ string s) ["-o", "-a", "or", "and"]
+        c <- choice $ try . string <$> ["-o", "-a", "or", "and"]
         posEnd <- getPosition
         parseProblemAtWithEnd pos posEnd ErrorC 1139 $
             "Use " ++ alt c ++ " instead of '" ++ c ++ "' between test commands."