From 2e52c2b56a2bccb2f06c90a081e27f0fe35cf814 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:11 -0500
Subject: [PATCH 01/17] Use notElem instead of not on the result of elem

---
 src/ShellCheck/Analytics.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 582b8cd..64a71a3 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -3169,7 +3169,7 @@ checkSplittingInArrays params t =
         T_DollarBraced id _ str |
             not (isCountingReference part)
             && not (isQuotedAlternativeReference part)
-            && not (getBracedReference (bracedString part) `elem` variablesWithoutSpaces)
+            && getBracedReference (bracedString part) `notElem` variablesWithoutSpaces
             -> warn id 2206 $
                 if shellType params == Ksh
                 then "Quote to prevent word splitting/globbing, or split robustly with read -A or while read."

From 3449e6be215dc3d2ec05032dcfc282897a49e836 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:13 -0500
Subject: [PATCH 02/17] Get rid of our getOpt, as it already exists as lookup

---
 src/ShellCheck/Analytics.hs   | 2 +-
 src/ShellCheck/AnalyzerLib.hs | 2 --
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 64a71a3..e8bee4f 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -2840,7 +2840,7 @@ checkReadWithoutR _ t@T_SimpleCommand {} | t `isUnqualifiedCommand` "read" =
     flags = getAllFlags t
     has_t0 = fromMaybe False $ do
         parsed <- getOpts flagsForRead flags
-        t <- getOpt "t" parsed
+        t <- lookup "t" parsed
         str <- getLiteralString t
         return $ str == "0"
 
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 590889c..e93758f 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -960,8 +960,6 @@ getOpts string flags = process flags
                 more <- process rest2
                 return $ (flag1, token1) : more
 
-getOpt str flags = snd <$> (listToMaybe $ filter (\(f, _) -> f == str) $ flags)
-
 supportsArrays shell = shell == Bash || shell == Ksh
 
 -- Returns true if the shell is Bash or Ksh (sorry for the name, Ksh)

From 93be86f988e17b6228a23924966da3d6e827bc1b Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:14 -0500
Subject: [PATCH 03/17] Use "drop 1" instead of clumsily rewriting it

---
 src/ShellCheck/AnalyzerLib.hs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index e93758f..563f8ea 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -612,8 +612,7 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
         _ -> []
   where
     flags = map snd $ getAllFlags base
-    stripEquals s = let rest = dropWhile (/= '=') s in
-        if rest == "" then "" else tail rest
+    stripEquals s = drop 1 $ dropWhile (/= '=') s
     stripEqualsFrom (T_NormalWord id1 (T_Literal id2 s:rs)) =
         T_NormalWord id1 (T_Literal id2 (stripEquals s):rs)
     stripEqualsFrom (T_NormalWord id1 [T_DoubleQuoted id2 [T_Literal id3 s]]) =

From 0f48bb78a50d4b76b2d1838ee22e3f00d5e8bf1f Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:14 -0500
Subject: [PATCH 04/17] Remove incorrect otherwise

You're supposed to use otherwise where you need a Boolean, not a pattern
match. This is misleadingly shadowing the real otherwise. Use _ instead.
---
 src/ShellCheck/Checks/ShellSupport.hs | 2 +-
 src/ShellCheck/Data.hs                | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/ShellCheck/Checks/ShellSupport.hs b/src/ShellCheck/Checks/ShellSupport.hs
index 07dfdda..e340d41 100644
--- a/src/ShellCheck/Checks/ShellSupport.hs
+++ b/src/ShellCheck/Checks/ShellSupport.hs
@@ -487,7 +487,7 @@ checkBraceExpansionVars = ForShell [Bash] f
             T_DollarBraced {} -> return "$"
             T_DollarExpansion {} -> return "$"
             T_DollarArithmetic {} -> return "$"
-            otherwise -> return "-"
+            _ -> return "-"
     toString t = fromJust $ getLiteralStringExt literalExt t
     isEvaled t = do
         cmd <- getClosestCommandM t
diff --git a/src/ShellCheck/Data.hs b/src/ShellCheck/Data.hs
index 732619d..fb4a1e4 100644
--- a/src/ShellCheck/Data.hs
+++ b/src/ShellCheck/Data.hs
@@ -135,6 +135,6 @@ shellForExecutable name =
         "ksh"   -> return Ksh
         "ksh88" -> return Ksh
         "ksh93" -> return Ksh
-        otherwise -> Nothing
+        _ -> Nothing
 
 flagsForRead = "sreu:n:N:i:p:a:t:"

From f5c6771016e396b8a0c11f8f2c6e58cb967c8356 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:16 -0500
Subject: [PATCH 05/17] Use find instead of listToMaybe and filter

---
 src/ShellCheck/Analytics.hs           | 6 +++---
 src/ShellCheck/Checks/ShellSupport.hs | 4 ++--
 src/ShellCheck/Parser.hs              | 4 ++--
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index e8bee4f..e33d873 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -1234,10 +1234,10 @@ checkLiteralBreakingTest _ t = potentially $
         return ()
 
     comparisonWarning list = do
-        token <- listToMaybe $ filter hasEquals list
+        token <- find hasEquals list
         return $ err (getId token) 2077 "You need spaces around the comparison operator."
     tautologyWarning t s = do
-        token <- listToMaybe $ filter isNonEmpty $ getWordParts t
+        token <- find isNonEmpty $ getWordParts t
         return $ err (getId token) 2157 s
 
 prop_checkConstantNullary = verify checkConstantNullary "[[ '$(foo)' ]]"
@@ -2910,7 +2910,7 @@ checkLoopVariableReassignment params token =
   where
     check = do
         str <- loopVariable token
-        next <- listToMaybe $ filter (\x -> loopVariable x == Just str) path
+        next <- find (\x -> loopVariable x == Just str) path
         return $ do
             warn (getId token) 2165 "This nested loop overrides the index variable of its parent."
             warn (getId next)  2167 "This parent loop has its index variable overridden."
diff --git a/src/ShellCheck/Checks/ShellSupport.hs b/src/ShellCheck/Checks/ShellSupport.hs
index e340d41..742cfa5 100644
--- a/src/ShellCheck/Checks/ShellSupport.hs
+++ b/src/ShellCheck/Checks/ShellSupport.hs
@@ -340,8 +340,8 @@ checkBashisms = ForShell [Sh, Dash] $ \t -> do
             potentially $ do
                 allowed' <- Map.lookup name allowedFlags
                 allowed <- allowed'
-                (word, flag) <- listToMaybe $
-                    filter (\x -> (not . null . snd $ x) && snd x `notElem` allowed) flags
+                (word, flag) <- find
+                    (\x -> (not . null . snd $ x) && snd x `notElem` allowed) flags
                 return . warnMsg (getId word) $ name ++ " -" ++ flag ++ " is"
 
             when (name == "source") $ warnMsg id "'source' in place of '.' is"
diff --git a/src/ShellCheck/Parser.hs b/src/ShellCheck/Parser.hs
index 339b50b..f295560 100644
--- a/src/ShellCheck/Parser.hs
+++ b/src/ShellCheck/Parser.hs
@@ -34,7 +34,7 @@ import Control.Monad.Identity
 import Control.Monad.Trans
 import Data.Char
 import Data.Functor
-import Data.List (isPrefixOf, isInfixOf, isSuffixOf, partition, sortBy, intercalate, nub)
+import Data.List (isPrefixOf, isInfixOf, isSuffixOf, partition, sortBy, intercalate, nub, find)
 import Data.Maybe
 import Data.Monoid
 import Debug.Trace
@@ -589,7 +589,7 @@ readConditionContents single =
 
     checkTrailingOp x = fromMaybe (return ()) $ do
         (T_Literal id str) <- getTrailingUnquotedLiteral x
-        trailingOp <- listToMaybe (filter (`isSuffixOf` str) binaryTestOps)
+        trailingOp <- find (`isSuffixOf` str) binaryTestOps
         return $ parseProblemAtId id ErrorC 1108 $
             "You need a space before and after the " ++ trailingOp ++ " ."
 

From 28978a8b65b303143b2251bc286527b3095c3622 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:17 -0500
Subject: [PATCH 06/17] Use maybe instead of fromMaybe and fmap

---
 src/ShellCheck/Analytics.hs   | 10 +++++-----
 src/ShellCheck/AnalyzerLib.hs |  4 ++--
 src/ShellCheck/Checker.hs     |  4 ++--
 3 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index e33d873..8d10a02 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -409,7 +409,7 @@ prop_checkArithmeticOpCommand1 = verify checkArithmeticOpCommand "i=i + 1"
 prop_checkArithmeticOpCommand2 = verify checkArithmeticOpCommand "foo=bar * 2"
 prop_checkArithmeticOpCommand3 = verifyNot checkArithmeticOpCommand "foo + opts"
 checkArithmeticOpCommand _ (T_SimpleCommand id [T_Assignment {}] (firstWord:_)) =
-    fromMaybe (return ()) $ check <$> getGlobOrLiteralString firstWord
+    maybe (return ()) check $ getGlobOrLiteralString firstWord
   where
     check op =
         when (op `elem` ["+", "-", "*", "/"]) $
@@ -493,8 +493,8 @@ checkPipePitfalls _ (T_Pipeline id _ commands) = do
 
     for ["grep", "wc"] $
         \(grep:wc:_) ->
-            let flagsGrep = fromMaybe [] $ map snd . getAllFlags <$> getCommand grep
-                flagsWc = fromMaybe [] $ map snd . getAllFlags <$> getCommand wc
+            let flagsGrep = maybe [] (map snd . getAllFlags) $ getCommand grep
+                flagsWc = maybe [] (map snd . getAllFlags) $ getCommand wc
             in
                 unless (any (`elem` ["o", "only-matching", "r", "R", "recursive"]) flagsGrep || any (`elem` ["m", "chars", "w", "words", "c", "bytes", "L", "max-line-length"]) flagsWc || null flagsWc) $
                     style (getId grep) 2126 "Consider using grep -c instead of grep|wc -l."
@@ -3140,9 +3140,9 @@ checkSubshellAsTest _ t =
 
 
     checkParams id first second = do
-        when (fromMaybe False $ (`elem` unaryTestOps) <$> getLiteralString first) $
+        when (maybe False (`elem` unaryTestOps) $ getLiteralString first) $
             err id 2204 "(..) is a subshell. Did you mean [ .. ], a test expression?"
-        when (fromMaybe False $ (`elem` binaryTestOps) <$> getLiteralString second) $
+        when (maybe False (`elem` binaryTestOps) $ getLiteralString second) $
             warn id 2205 "(..) is a subshell. Did you mean [ .. ], a test expression?"
 
 
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 563f8ea..4dd3f9d 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -784,8 +784,8 @@ isCommand token str = isCommandMatch token (\cmd -> cmd  == str || ('/' : str) `
 -- Compare a command to a literal. Like above, but checks full path.
 isUnqualifiedCommand token str = isCommandMatch token (== str)
 
-isCommandMatch token matcher = fromMaybe False $
-    fmap matcher (getCommandName token)
+isCommandMatch token matcher = maybe False
+    matcher (getCommandName token)
 
 -- Does this regex look like it was intended as a glob?
 -- True:  *foo*
diff --git a/src/ShellCheck/Checker.hs b/src/ShellCheck/Checker.hs
index 2ea950d..2837d9a 100644
--- a/src/ShellCheck/Checker.hs
+++ b/src/ShellCheck/Checker.hs
@@ -88,9 +88,9 @@ checkScript sys spec = do
                     asOptionalChecks = csOptionalChecks spec
                 } where as = newAnalysisSpec root
         let analysisMessages =
-                fromMaybe [] $
+                maybe []
                     (arComments . analyzeScript . analysisSpec)
-                        <$> prRoot result
+                        $ prRoot result
         let translator = tokenToPosition tokenPositions
         return . nub . sortMessages . filter shouldInclude $
             (parseMessages ++ map translator analysisMessages)

From 5487b3f229fa3ce56f105733caff6a707c39e7bb Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:18 -0500
Subject: [PATCH 07/17] Use sortOn instead of sortBy and comparing

---
 src/ShellCheck/Checker.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellCheck/Checker.hs b/src/ShellCheck/Checker.hs
index 2837d9a..b423f2d 100644
--- a/src/ShellCheck/Checker.hs
+++ b/src/ShellCheck/Checker.hs
@@ -104,7 +104,7 @@ checkScript sys spec = do
             code     = cCode (pcComment pc)
             severity = cSeverity (pcComment pc)
 
-    sortMessages = sortBy (comparing order)
+    sortMessages = sortOn order
     order pc =
         let pos = pcStartPos pc
             comment = pcComment pc in

From d7278b95f2c840a5a764838d23a32008aaeb6168 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:19 -0500
Subject: [PATCH 08/17] Remove unnecessary "map snd"

---
 src/ShellCheck/Checks/Commands.hs | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/ShellCheck/Checks/Commands.hs b/src/ShellCheck/Checks/Commands.hs
index eb0c434..7841089 100644
--- a/src/ShellCheck/Checks/Commands.hs
+++ b/src/ShellCheck/Checks/Commands.hs
@@ -997,8 +997,7 @@ missingDestination handler token = do
     args = getAllFlags token
     params = map fst $ filter (\(_,x) -> x == "") args
     hasTarget =
-        any (\x -> x /= "" && x `isPrefixOf` "target-directory") $
-            map snd args
+        any (\(_,x) -> x /= "" && x `isPrefixOf` "target-directory") args
 
 prop_checkMvArguments1 = verify    checkMvArguments "mv 'foo bar'"
 prop_checkMvArguments2 = verifyNot checkMvArguments "mv foo bar"

From f25b8bd03af4997df3572973a09da025f417422c Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:20 -0500
Subject: [PATCH 09/17] Use gets instead of fmapping the result of get

---
 src/ShellCheck/Analytics.hs | 2 +-
 src/ShellCheck/Parser.hs    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 8d10a02..ae8e81d 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -1961,7 +1961,7 @@ prop_checkQuotesInLiterals9 = verifyNotTree checkQuotesInLiterals "param=\"/foo/
 checkQuotesInLiterals params t =
     doVariableFlowAnalysis readF writeF Map.empty (variableFlow params)
   where
-    getQuotes name = fmap (Map.lookup name) get
+    getQuotes name = gets (Map.lookup name)
     setQuotes name ref = modify $ Map.insert name ref
     deleteQuotes = modify . Map.delete
     parents = parentMap params
diff --git a/src/ShellCheck/Parser.hs b/src/ShellCheck/Parser.hs
index f295560..fa9084e 100644
--- a/src/ShellCheck/Parser.hs
+++ b/src/ShellCheck/Parser.hs
@@ -325,7 +325,7 @@ parseProblem level code msg = do
     parseProblemAt pos level code msg
 
 setCurrentContexts c = Ms.modify (\state -> state { contextStack = c })
-getCurrentContexts = contextStack <$> Ms.get
+getCurrentContexts = Ms.gets contextStack
 
 popContext = do
     v <- getCurrentContexts

From e6e89d68fdda2fb1f8f7ec2e4485ab7a5584db15 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:20 -0500
Subject: [PATCH 10/17] Use list comprehensions instead of clunky combinations
 of map and filter

---
 src/ShellCheck/Checks/Commands.hs | 6 +++---
 src/ShellCheck/Fixer.hs           | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/ShellCheck/Checks/Commands.hs b/src/ShellCheck/Checks/Commands.hs
index 7841089..21c6cb7 100644
--- a/src/ShellCheck/Checks/Commands.hs
+++ b/src/ShellCheck/Checks/Commands.hs
@@ -706,7 +706,7 @@ checkReadExpansions = CommandCheck (Exactly "read") check
     options = getGnuOpts flagsForRead
     getVars cmd = fromMaybe [] $ do
         opts <- options cmd
-        return . map snd $ filter (\(x,_) -> x == "" || x == "a") opts
+        return [y | (x,y) <- opts, x == "" || x == "a"]
 
     check cmd = mapM_ warning $ getVars cmd
     warning t = potentially $ do
@@ -995,7 +995,7 @@ missingDestination handler token = do
         _ -> return ()
   where
     args = getAllFlags token
-    params = map fst $ filter (\(_,x) -> x == "") args
+    params = [x | (x,"") <- args]
     hasTarget =
         any (\(_,x) -> x /= "" && x `isPrefixOf` "target-directory") args
 
@@ -1083,7 +1083,7 @@ checkSudoArgs = CommandCheck (Basename "sudo") f
   where
     f t = potentially $ do
         opts <- parseOpts t
-        let nonFlags = map snd $ filter (\(flag, _) -> flag == "") opts
+        let nonFlags = [x | ("",x) <- opts]
         commandArg <- nonFlags !!! 0
         command <- getLiteralString commandArg
         guard $ command `elem` builtins
diff --git a/src/ShellCheck/Fixer.hs b/src/ShellCheck/Fixer.hs
index 12de3c2..a69616e 100644
--- a/src/ShellCheck/Fixer.hs
+++ b/src/ShellCheck/Fixer.hs
@@ -295,7 +295,7 @@ prop_pstreeSumsCorrectly kvs targets =
     -- Trivial O(n * m) implementation
     dumbPrefixSums :: [(Int, Int)] -> [Int] -> [Int]
     dumbPrefixSums kvs targets =
-        let prefixSum target = sum . map snd . filter (\(k,v) -> k <= target) $ kvs
+        let prefixSum target = sum [v | (k,v) <- kvs, k <= target]
         in map prefixSum targets
     -- PSTree O(n * log m) implementation
     smartPrefixSums :: [(Int, Int)] -> [Int] -> [Int]

From c29b6afa5600d68ff3dced9259ff0b5f59822864 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 22:50:21 -0500
Subject: [PATCH 11/17] Use null instead of comparing with empty lists

---
 src/ShellCheck/Analytics.hs       |  4 ++--
 src/ShellCheck/AnalyzerLib.hs     |  4 ++--
 src/ShellCheck/Checker.hs         | 12 ++++++------
 src/ShellCheck/Checks/Commands.hs |  6 +++---
 src/ShellCheck/Parser.hs          |  2 +-
 5 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index ae8e81d..2888047 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -563,7 +563,7 @@ checkShebang params (T_Annotation _ list t) =
     isOverride _ = False
 checkShebang params (T_Script _ (T_Literal id sb) _) = execWriter $ do
     unless (shellTypeSpecified params) $ do
-        when (sb == "") $
+        when (null sb) $
             err id 2148 "Tips depend on target shell and yours is unknown. Add a shebang."
         when (executableFromShebang sb == "ash") $
             warn id 2187 "Ash scripts will be checked as Dash. Add '# shellcheck shell=dash' to silence."
@@ -2332,7 +2332,7 @@ checkWhileReadPitfalls _ (T_WhileExpression id [command] contents)
     checkMuncher _ = return ()
 
     stdinRedirect (T_FdRedirect _ fd _)
-        | fd == "" || fd == "0" = True
+        | null fd || fd == "0" = True
     stdinRedirect _ = False
 checkWhileReadPitfalls _ _ = return ()
 
diff --git a/src/ShellCheck/AnalyzerLib.hs b/src/ShellCheck/AnalyzerLib.hs
index 4dd3f9d..e4640e7 100644
--- a/src/ShellCheck/AnalyzerLib.hs
+++ b/src/ShellCheck/AnalyzerLib.hs
@@ -643,7 +643,7 @@ getModifiedVariableCommand base@(T_SimpleCommand id cmdPrefix (T_NormalWord _ (T
     getModifierParam _ _ = []
 
     letParamToLiteral token =
-          if var == ""
+          if null var
             then []
             else [(base, token, var, DataString $ SourceFrom [stripEqualsFrom token])]
         where var = takeWhile isVariableChar $ dropWhile (`elem` "+-") $ concat $ oversimplify token
@@ -952,7 +952,7 @@ getOpts string flags = process flags
         takesArg <- Map.lookup flag1 flagMap
         if takesArg
             then do
-                guard $ flag2 == ""
+                guard $ null flag2
                 more <- process rest
                 return $ (flag1, token2) : more
             else do
diff --git a/src/ShellCheck/Checker.hs b/src/ShellCheck/Checker.hs
index b423f2d..6370f75 100644
--- a/src/ShellCheck/Checker.hs
+++ b/src/ShellCheck/Checker.hs
@@ -198,11 +198,11 @@ prop_optionDisablesBadShebang =
                 }
 
 prop_annotationDisablesBadShebang =
-    [] == check "#!/usr/bin/python\n# shellcheck shell=sh\ntrue\n"
+    null $ check "#!/usr/bin/python\n# shellcheck shell=sh\ntrue\n"
 
 
 prop_canParseDevNull =
-    [] == check "source /dev/null"
+    null $ check "source /dev/null"
 
 prop_failsWhenNotSourcing =
     [1091, 2154] == check "source lol; echo \"$bar\""
@@ -218,7 +218,7 @@ prop_worksWhenDotting =
 
 -- FIXME: This should really be giving [1093], "recursively sourced"
 prop_noInfiniteSourcing =
-    [] == checkWithIncludes  [("lib", "source lib")] "source lib"
+    null $ checkWithIncludes  [("lib", "source lib")] "source lib"
 
 prop_canSourceBadSyntax =
     [1094, 2086] == checkWithIncludes [("lib", "for f; do")] "source lib; echo $1"
@@ -239,10 +239,10 @@ prop_recursiveParsing =
     [1037] == checkRecursive [("lib", "echo \"$10\"")] "source lib"
 
 prop_nonRecursiveAnalysis =
-    [] == checkWithIncludes [("lib", "echo $1")] "source lib"
+    null $ checkWithIncludes [("lib", "echo $1")] "source lib"
 
 prop_nonRecursiveParsing =
-    [] == checkWithIncludes [("lib", "echo \"$10\"")] "source lib"
+    null $ checkWithIncludes [("lib", "echo \"$10\"")] "source lib"
 
 prop_sourceDirectiveDoesntFollowFile =
     null $ checkWithIncludes
@@ -328,7 +328,7 @@ prop_optionIncludes4 =
     [2154] == checkOptionIncludes (Just [2154]) "#!/bin/sh\n var='a b'\n echo $var\n echo $bar"
 
 
-prop_readsRcFile = result == []
+prop_readsRcFile = null result
   where
     result = checkWithRc "disable=2086" emptyCheckSpec {
         csScript = "#!/bin/sh\necho $1",
diff --git a/src/ShellCheck/Checks/Commands.hs b/src/ShellCheck/Checks/Commands.hs
index 21c6cb7..299a335 100644
--- a/src/ShellCheck/Checks/Commands.hs
+++ b/src/ShellCheck/Checks/Commands.hs
@@ -345,7 +345,7 @@ returnOrExit multi invalid = (f . arguments)
             invalid (getId value)
     f _ = return ()
 
-    isInvalid s = s == "" || any (not . isDigit) s || length s > 5
+    isInvalid s = null s || any (not . isDigit) s || length s > 5
         || let value = (read s :: Integer) in value > 255
 
     literal token = fromJust $ getLiteralStringExt lit token
@@ -706,7 +706,7 @@ checkReadExpansions = CommandCheck (Exactly "read") check
     options = getGnuOpts flagsForRead
     getVars cmd = fromMaybe [] $ do
         opts <- options cmd
-        return [y | (x,y) <- opts, x == "" || x == "a"]
+        return [y | (x,y) <- opts, null x || x == "a"]
 
     check cmd = mapM_ warning $ getVars cmd
     warning t = potentially $ do
@@ -1057,7 +1057,7 @@ checkSudoRedirect = CommandCheck (Basename "sudo") f
             Just (T_Redirecting _ redirs _) ->
                 mapM_ warnAbout redirs
     warnAbout (T_FdRedirect _ s (T_IoFile id op file))
-        | (s == "" || s == "&") && not (special file) =
+        | (null s || s == "&") && not (special file) =
         case op of
             T_Less _ ->
               info (getId op) 2024
diff --git a/src/ShellCheck/Parser.hs b/src/ShellCheck/Parser.hs
index fa9084e..727572d 100644
--- a/src/ShellCheck/Parser.hs
+++ b/src/ShellCheck/Parser.hs
@@ -3169,7 +3169,7 @@ readScriptFile sourced = do
             Nothing -> parseProblemAt pos ErrorC 1008 "This shebang was unrecognized. ShellCheck only supports sh/bash/dash/ksh. Add a 'shell' directive to specify."
 
     isValidShell s =
-        let good = s == "" || any (`isPrefixOf` s) goodShells
+        let good = null s || any (`isPrefixOf` s) goodShells
             bad = any (`isPrefixOf` s) badShells
         in
             if good

From 8a005526cc5b1379b0c651a0505f7110c6bf0d8e Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 23:02:10 -0500
Subject: [PATCH 12/17] Use drop instead of splitAt since we only use the
 second half

---
 src/ShellCheck/Fixer.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellCheck/Fixer.hs b/src/ShellCheck/Fixer.hs
index a69616e..16bdd98 100644
--- a/src/ShellCheck/Fixer.hs
+++ b/src/ShellCheck/Fixer.hs
@@ -200,7 +200,7 @@ doReplace start end o r =
     let si = fromIntegral (start-1)
         ei = fromIntegral (end-1)
         (x, xs) = splitAt si o
-        (y, z) = splitAt (ei - si) xs
+        z = drop (ei - si) xs
     in
     x ++ r ++ z
 

From 76b798394f18307677b44e231d6922db251955be Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sat, 1 Feb 2020 23:07:16 -0500
Subject: [PATCH 13/17] Use case matching instead of null

Using null followed by a head, tail, or a partial pattern match is
an anti-pattern. Use case matching instead.
---
 src/ShellCheck/Parser.hs | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/src/ShellCheck/Parser.hs b/src/ShellCheck/Parser.hs
index 727572d..025fa98 100644
--- a/src/ShellCheck/Parser.hs
+++ b/src/ShellCheck/Parser.hs
@@ -329,12 +329,11 @@ getCurrentContexts = Ms.gets contextStack
 
 popContext = do
     v <- getCurrentContexts
-    if not $ null v
-        then do
-            let (a:r) = v
+    case v of
+        (a:r) -> do
             setCurrentContexts r
             return $ Just a
-        else
+        [] ->
             return Nothing
 
 pushContext c = do

From 115ef290798d8d4b046d2a57470c461ce3b26d6f Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sun, 2 Feb 2020 00:13:16 -0500
Subject: [PATCH 14/17] Use pattern matching instead of head

---
 src/ShellCheck/Analytics.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index 2888047..cf8015b 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -1298,7 +1298,7 @@ checkArithmeticDeref params t@(TA_Expansion _ [b@(T_DollarBraced id _ _)]) =
     unless (isException $ bracedString b) getWarning
   where
     isException [] = True
-    isException s = any (`elem` "/.:#%?*@$-!+=^,") s || isDigit (head s)
+    isException s@(h:_) = any (`elem` "/.:#%?*@$-!+=^,") s || isDigit h
     getWarning = fromMaybe noWarning . msum . map warningFor $ parents params t
     warningFor t =
         case t of

From 6595e14d25deed617b4c8a9c7d2162ee29d77198 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sun, 2 Feb 2020 00:22:52 -0500
Subject: [PATCH 15/17] Adjust a pattern to avoid tail

---
 src/ShellCheck/Analytics.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index cf8015b..ddc3b43 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -1644,9 +1644,9 @@ checkSpuriousExec _ = doLists
     doList = doList' . stripCleanup
     -- The second parameter is True if we are in a loop
     -- In that case we should emit the warning also if `exec' is the last statement
-    doList' t@(current:following:_) False = do
+    doList' (current:t@(following:_)) False = do
         commentIfExec current
-        doList (tail t) False
+        doList t False
     doList' (current:tail) True = do
         commentIfExec current
         doList tail True

From 392b57b8e848a3008a0851d3212a4657870230a1 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sun, 2 Feb 2020 00:27:05 -0500
Subject: [PATCH 16/17] Use maybe instead of isJust and fromJust

---
 src/ShellCheck/Checks/ShellSupport.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ShellCheck/Checks/ShellSupport.hs b/src/ShellCheck/Checks/ShellSupport.hs
index 742cfa5..b643525 100644
--- a/src/ShellCheck/Checks/ShellSupport.hs
+++ b/src/ShellCheck/Checks/ShellSupport.hs
@@ -491,7 +491,7 @@ checkBraceExpansionVars = ForShell [Bash] f
     toString t = fromJust $ getLiteralStringExt literalExt t
     isEvaled t = do
         cmd <- getClosestCommandM t
-        return $ isJust cmd && fromJust cmd `isUnqualifiedCommand` "eval"
+        return $ maybe False (`isUnqualifiedCommand` "eval") cmd
 
 
 prop_checkMultiDimensionalArrays1 = verify checkMultiDimensionalArrays "foo[a][b]=3"

From e820a5642b4029e3bfe793f59b4cd23dd22b7c20 Mon Sep 17 00:00:00 2001
From: "Joseph C. Sible" <josephcsible@users.noreply.github.com>
Date: Sun, 2 Feb 2020 00:34:54 -0500
Subject: [PATCH 17/17] Adjust a pattern to get rid of a fromJust

---
 src/ShellCheck/Analytics.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/ShellCheck/Analytics.hs b/src/ShellCheck/Analytics.hs
index ddc3b43..501847a 100644
--- a/src/ShellCheck/Analytics.hs
+++ b/src/ShellCheck/Analytics.hs
@@ -2635,8 +2635,8 @@ checkMultipleAppends params t =
   where
     checkList list =
         mapM_ checkGroup (groupWith (fmap fst) $ map getTarget list)
-    checkGroup (f:_:_:_) | isJust f =
-        style (snd $ fromJust f) 2129
+    checkGroup (Just (_,id):_:_:_) =
+        style id 2129
             "Consider using { cmd1; cmd2; } >> file instead of individual redirects."
     checkGroup _ = return ()
     getTarget (T_Annotation _ _ t) = getTarget t