Various minor cleanups and refactoring (#6117)

* Use concatMap instead of reimplementing it

* Replace an unnecessary multi-way if with a regular if

* Use sortOn instead of sortBy and comparing

* Use guards instead of lots of indents for if and else

* Remove redundant do blocks

* Extract common functions from both branches of maybe

Whenever both the Nothing and the Just branch of maybe do the same
function, do that function on the result of maybe instead.

* Use fmap instead of reimplementing it from maybe

* Use negative forms instead of negating the positive forms

* Use mapMaybe instead of mapping and then using catMaybes

* Use zipWith instead of mapping over the result of zip

* Use unwords instead of reimplementing it

* Use <$ instead of <$> and const

* Replace case of Bool with if and else

* Use find instead of listToMaybe and filter

* Use zipWithM instead of mapM and zip

* Inline lambda wrappers into the real functions

* We get zipWithM from Text.Pandoc.Writers.Shared

* Use maybe instead of fromMaybe and fmap

I'm not sure how this one slipped past me.

* Increase a bit of indentation

15 files changed, 56 insertions, 63 deletions

diff --git a/src/Text/Pandoc/PDF.hs b/src/Text/Pandoc/PDF.hs
index bd36f0d33..5ef2bd80c 100644
--- a/src/Text/Pandoc/PDF.hs
+++ b/src/Text/Pandoc/PDF.hs
@@ -440,10 +440,7 @@ html2pdf verbosity program args source = do
                 -- We read PDF as a strict bytestring to make sure that the
                 -- temp directory is removed on Windows.
                 -- See https://github.com/jgm/pandoc/issues/1192.
-                then do
-                  res <- Just . BL.fromChunks . (:[]) <$>
-                            BS.readFile pdfFile
-                  return res
+                then Just . BL.fromChunks . (:[]) <$> BS.readFile pdfFile
                 else return Nothing
       return $ case (exit, mbPdf) of
                  (ExitFailure _, _)      -> Left out
diff --git a/src/Text/Pandoc/Readers/CommonMark.hs b/src/Text/Pandoc/Readers/CommonMark.hs
index 40b6f77c9..f4daabc57 100644
--- a/src/Text/Pandoc/Readers/CommonMark.hs
+++ b/src/Text/Pandoc/Readers/CommonMark.hs
@@ -177,7 +177,7 @@ addInlines :: ReaderOptions -> [Node] -> [Inline]
 addInlines opts = foldr (addInline opts) []
 
 addInline :: ReaderOptions -> Node -> [Inline] -> [Inline]
-addInline opts (Node _ (TEXT t) _) = (foldr ((++) . toinl) [] clumps ++)
+addInline opts (Node _ (TEXT t) _) = (concatMap toinl clumps ++)
   where clumps = T.groupBy samekind t
         samekind ' ' ' ' = True
         samekind ' ' _   = False
diff --git a/src/Text/Pandoc/Readers/DocBook.hs b/src/Text/Pandoc/Readers/DocBook.hs
index ade9d27a3..fbd9d595d 100644
--- a/src/Text/Pandoc/Readers/DocBook.hs
+++ b/src/Text/Pandoc/Readers/DocBook.hs
@@ -941,7 +941,7 @@ elementToStr x = x
 parseInline :: PandocMonad m => Content -> DB m Inlines
 parseInline (Text (CData _ s _)) = return $ text $ T.pack s
 parseInline (CRef ref) =
-  return $ maybe (text $ T.toUpper $ T.pack ref) (text . T.pack) $ lookupEntity ref
+  return $ text $ maybe (T.toUpper $ T.pack ref) T.pack $ lookupEntity ref
 parseInline (Elem e) =
   case qName (elName e) of
         "equation" -> equation e displayMath
diff --git a/src/Text/Pandoc/Readers/Docx.hs b/src/Text/Pandoc/Readers/Docx.hs
index 80fd6285c..c4bb16ec6 100644
--- a/src/Text/Pandoc/Readers/Docx.hs
+++ b/src/Text/Pandoc/Readers/Docx.hs
@@ -528,9 +528,9 @@ extraInfo :: (Eq (StyleName a), PandocMonad m, HasStyleName a)
           => (Attr -> i -> i) -> a -> DocxContext m (i -> i)
 extraInfo f s = do
   opts <- asks docxOptions
-  return $ if | isEnabled Ext_styles opts
-              -> f ("", [], [("custom-style", fromStyleName $ getStyleName s)])
-              | otherwise -> id
+  return $ if isEnabled Ext_styles opts
+              then f ("", [], [("custom-style", fromStyleName $ getStyleName s)])
+              else id
 
 parStyleToTransform :: PandocMonad m => ParagraphStyle -> DocxContext m (Blocks -> Blocks)
 parStyleToTransform pPr
diff --git a/src/Text/Pandoc/Readers/Docx/Parse.hs b/src/Text/Pandoc/Readers/Docx/Parse.hs
index 8598ada6f..b4a0c1ac9 100644
--- a/src/Text/Pandoc/Readers/Docx/Parse.hs
+++ b/src/Text/Pandoc/Readers/Docx/Parse.hs
@@ -347,8 +347,7 @@ getDocumentXmlPath zf = do
   entry <- findEntryByPath "_rels/.rels" zf
   relsElem <- (parseXMLDoc . UTF8.toStringLazy . fromEntry) entry
   let rels = filterChildrenName (\n -> qName n == "Relationship") relsElem
-  rel <- listToMaybe $
-         filter (\e -> findAttr (QName "Type" Nothing Nothing) e ==
+  rel <- find (\e -> findAttr (QName "Type" Nothing Nothing) e ==
                        Just "http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument")
          rels
   fp <- findAttr (QName "Target" Nothing Nothing) rel
diff --git a/src/Text/Pandoc/Readers/DokuWiki.hs b/src/Text/Pandoc/Readers/DokuWiki.hs
index da6e7df64..727dd1ecc 100644
--- a/src/Text/Pandoc/Readers/DokuWiki.hs
+++ b/src/Text/Pandoc/Readers/DokuWiki.hs
@@ -472,7 +472,7 @@ table = do
   let (headerRow, body) = if firstSeparator == '^'
                             then (head rows, tail rows)
                             else ([], rows)
-  let attrs = const (AlignDefault, 0.0) <$> transpose rows
+  let attrs = (AlignDefault, 0.0) <$ transpose rows
   pure $ B.table mempty attrs headerRow body
 
 tableRows :: PandocMonad m => DWParser m [[B.Blocks]]
diff --git a/src/Text/Pandoc/Readers/JATS.hs b/src/Text/Pandoc/Readers/JATS.hs
index 320b9c1dd..4b8eb9098 100644
--- a/src/Text/Pandoc/Readers/JATS.hs
+++ b/src/Text/Pandoc/Readers/JATS.hs
@@ -443,7 +443,7 @@ elementToStr x = x
 parseInline :: PandocMonad m => Content -> JATS m Inlines
 parseInline (Text (CData _ s _)) = return $ text $ T.pack s
 parseInline (CRef ref) =
-  return $ maybe (text $ T.toUpper $ T.pack ref) text $ T.pack <$> lookupEntity ref
+  return . text . maybe (T.toUpper $ T.pack ref) T.pack $ lookupEntity ref
 parseInline (Elem e) =
   case qName (elName e) of
         "italic" -> emph <$> innerInlines
diff --git a/src/Text/Pandoc/Readers/Man.hs b/src/Text/Pandoc/Readers/Man.hs
index feacb8450..314643621 100644
--- a/src/Text/Pandoc/Readers/Man.hs
+++ b/src/Text/Pandoc/Readers/Man.hs
@@ -234,22 +234,22 @@ linePartsToInlines = go False
   go mono (RoffStr s : xs)
     | mono      = code s <> go mono xs
     | otherwise = text s <> go mono xs
-  go mono (Font fs: xs) =
-    if litals > 0 && litals >= lbolds && litals >= lmonos
-       then emph (go mono (Font fs{ fontItalic = False } :
+  go mono (Font fs: xs)
+    | litals > 0 && litals >= lbolds && litals >= lmonos
+       = emph (go mono (Font fs{ fontItalic = False } :
                    map (adjustFontSpec (\s -> s{ fontItalic = False }))
                    itals)) <>
             go mono italsrest
-       else if lbolds > 0 && lbolds >= lmonos
-            then strong (go mono (Font fs{ fontBold = False } :
-                   map (adjustFontSpec (\s -> s{ fontBold = False }))
-                   bolds)) <>
-                 go mono boldsrest
-            else if lmonos > 0
-                 then go True (Font fs{ fontMonospace = False } :
-                    map (adjustFontSpec (\s -> s { fontMonospace = False }))
-                    monos) <> go mono monosrest
-                 else go mono xs
+    | lbolds > 0 && lbolds >= lmonos
+       = strong (go mono (Font fs{ fontBold = False } :
+              map (adjustFontSpec (\s -> s{ fontBold = False }))
+              bolds)) <>
+            go mono boldsrest
+    | lmonos > 0
+       = go True (Font fs{ fontMonospace = False } :
+          map (adjustFontSpec (\s -> s { fontMonospace = False }))
+          monos) <> go mono monosrest
+    | otherwise = go mono xs
     where
       adjustFontSpec f (Font fspec) = Font (f fspec)
       adjustFontSpec _ x            = x
diff --git a/src/Text/Pandoc/Readers/RST.hs b/src/Text/Pandoc/Readers/RST.hs
index d2fba4449..68b853ca5 100644
--- a/src/Text/Pandoc/Readers/RST.hs
+++ b/src/Text/Pandoc/Readers/RST.hs
@@ -952,7 +952,7 @@ unicodeTransform t
                      $ extractUnicodeChar zs
 
 extractUnicodeChar :: Text -> Maybe (Char, Text)
-extractUnicodeChar s = maybe Nothing (\c -> Just (c,rest)) mbc
+extractUnicodeChar s = fmap (\c -> (c,rest)) mbc
   where (ds,rest) = T.span isHexDigit s
         mbc = safeRead ("'\\x" <> ds <> "'")
 
diff --git a/src/Text/Pandoc/Readers/Vimwiki.hs b/src/Text/Pandoc/Readers/Vimwiki.hs
index f7edabc48..d641df8a5 100644
--- a/src/Text/Pandoc/Readers/Vimwiki.hs
+++ b/src/Text/Pandoc/Readers/Vimwiki.hs
@@ -546,21 +546,21 @@ link :: PandocMonad m => VwParser m Inlines
 link = try $ do
   string "[["
   contents <- lookAhead $ manyTillChar anyChar (string "]]")
-  case T.any (== '|') contents of
-                  False -> do
-                    manyTill anyChar (string "]]")
--- not using try here because [[hell]o]] is not rendered as a link in vimwiki
-                    let tit = if isURI contents
-                                 then ""
-                                 else "wikilink"
-                    return $ B.link (procLink contents) tit (B.str contents)
-                  True  -> do
+  if T.any (== '|') contents
+                  then do
                     url <- manyTillChar anyChar $ char '|'
                     lab <- mconcat <$> manyTill inline (string "]]")
                     let tit = if isURI url
                                  then ""
                                  else "wikilink"
                     return $ B.link (procLink url) tit lab
+                  else do
+                    manyTill anyChar (string "]]")
+-- not using try here because [[hell]o]] is not rendered as a link in vimwiki
+                    let tit = if isURI contents
+                                 then ""
+                                 else "wikilink"
+                    return $ B.link (procLink contents) tit (B.str contents)
 
 image :: PandocMonad m => VwParser m Inlines
 image = try $ do
diff --git a/src/Text/Pandoc/Shared.hs b/src/Text/Pandoc/Shared.hs
index 69ade7e95..933798534 100644
--- a/src/Text/Pandoc/Shared.hs
+++ b/src/Text/Pandoc/Shared.hs
@@ -115,8 +115,7 @@ import qualified Data.Bifunctor as Bifunctor
 import Data.Char (isAlpha, isLower, isSpace, isUpper, toLower, isAlphaNum,
                   generalCategory, GeneralCategory(NonSpacingMark,
                   SpacingCombiningMark, EnclosingMark, ConnectorPunctuation))
-import Data.List (find, intercalate, intersperse, stripPrefix, sortBy)
-import Data.Ord (comparing)
+import Data.List (find, intercalate, intersperse, stripPrefix, sortOn)
 import qualified Data.Map as M
 import Data.Maybe (mapMaybe, fromMaybe)
 import Data.Monoid (Any (..))
@@ -621,7 +620,7 @@ headerLtEq _ _                   = False
 uniqueIdent :: Extensions -> [Inline] -> Set.Set T.Text -> T.Text
 uniqueIdent exts title' usedIdents =
   if baseIdent `Set.member` usedIdents
-     then case find (\x -> not $ numIdent x `Set.member` usedIdents)
+     then case find (\x -> numIdent x `Set.notMember` usedIdents)
                ([1..60000] :: [Int]) of
             Just x  -> numIdent x
             Nothing -> baseIdent
@@ -799,7 +798,7 @@ filterIpynbOutput mode = walk go
                           -> Div (ident, ("output":os), kvs) bs
               | otherwise -> Div (ident, ("output":os), kvs) $
                               walk removeANSI $
-                              take 1 $ sortBy (comparing rank) bs
+                              take 1 $ sortOn rank bs
                  where
                   rank (RawBlock (Format "html") _)
                     | fmt == Format "html" = (1 :: Int)
diff --git a/src/Text/Pandoc/Writers/Markdown.hs b/src/Text/Pandoc/Writers/Markdown.hs
index 10ab3dfe1..87e41b766 100644
--- a/src/Text/Pandoc/Writers/Markdown.hs
+++ b/src/Text/Pandoc/Writers/Markdown.hs
@@ -25,7 +25,7 @@ import Data.Char (isAlphaNum)
 import Data.Default
 import Data.List (find, intersperse, sortBy, transpose)
 import qualified Data.Map as M
-import Data.Maybe (fromMaybe, catMaybes)
+import Data.Maybe (fromMaybe, mapMaybe)
 import Data.Ord (comparing)
 import qualified Data.Set as Set
 import Data.Text (Text)
@@ -121,7 +121,7 @@ mmdTitleBlock (Context hashmap) =
                  | null xs        -> empty
                  | otherwise      -> k' <> ":" <> space <>
                                       hcat (intersperse "; " $
-                                          catMaybes $ map fromVal xs)
+                                            mapMaybe fromVal xs)
                (k', SimpleVal x)
                       | isEmpty x -> empty
                       | otherwise -> k' <> ":" <> space <>
@@ -256,7 +256,7 @@ keyToMarkdown opts (label', (src, tit), attr) = do
 notesToMarkdown :: PandocMonad m => WriterOptions -> [[Block]] -> MD m (Doc Text)
 notesToMarkdown opts notes = do
   n <- gets stNoteNum
-  notes' <- mapM (\(num, note) -> noteToMarkdown opts num note) (zip [n..] notes)
+  notes' <- zipWithM (noteToMarkdown opts) [n..] notes
   modify $ \st -> st { stNoteNum = stNoteNum st + length notes }
   return $ vsep notes'
 
@@ -647,8 +647,7 @@ blockToMarkdown' opts (OrderedList (start,sty,delim) items) = do
                                then m <> T.replicate (3 - T.length m) " "
                                else m) markers
   contents <- inList $
-              mapM (\(item, num) -> orderedListItemToMarkdown opts item num) $
-              zip markers' items
+              zipWithM (orderedListItemToMarkdown opts) markers' items
   return $ (if isTightList items then vcat else vsep) contents <> blankline
 blockToMarkdown' opts (DefinitionList items) = do
   contents <- inList $ mapM (definitionListItemToMarkdown opts) items
@@ -680,11 +679,11 @@ pipeTable headless aligns rawHeaders rawRows = do
                     hcat (intersperse (literal "|") $
                           zipWith3 blockFor aligns widths (map chomp cs))
                     <> literal "|"
-  let toborder (a, w) = literal $ case a of
-                             AlignLeft    -> ":" <> T.replicate (w + 1) "-"
-                             AlignCenter  -> ":" <> T.replicate w "-" <> ":"
-                             AlignRight   -> T.replicate (w + 1) "-" <> ":"
-                             AlignDefault -> T.replicate (w + 2) "-"
+  let toborder a w = literal $ case a of
+                          AlignLeft    -> ":" <> T.replicate (w + 1) "-"
+                          AlignCenter  -> ":" <> T.replicate w "-" <> ":"
+                          AlignRight   -> T.replicate (w + 1) "-" <> ":"
+                          AlignDefault -> T.replicate (w + 2) "-"
   -- note:  pipe tables can't completely lack a
   -- header; for a headerless table, we need a header of empty cells.
   -- see jgm/pandoc#1996.
@@ -692,7 +691,7 @@ pipeTable headless aligns rawHeaders rawRows = do
                   then torow (replicate (length aligns) empty)
                   else torow rawHeaders
   let border = nowrap $ literal "|" <> hcat (intersperse (literal "|") $
-                        map toborder $ zip aligns widths) <> literal "|"
+                        zipWith toborder aligns widths) <> literal "|"
   let body   = vcat $ map torow rawRows
   return $ header $$ border $$ body
 
diff --git a/src/Text/Pandoc/Writers/Powerpoint/Output.hs b/src/Text/Pandoc/Writers/Powerpoint/Output.hs
index 344a5564a..856dbfcd0 100644
--- a/src/Text/Pandoc/Writers/Powerpoint/Output.hs
+++ b/src/Text/Pandoc/Writers/Powerpoint/Output.hs
@@ -249,7 +249,7 @@ presentationToArchiveP p@(Presentation docProps slides) = do
   filePaths <- patternsToFilePaths $ inheritedPatterns p
 
   -- make sure all required files are available:
-  let missingFiles = filter (\fp -> not (fp `elem` filePaths)) requiredFiles
+  let missingFiles = filter (`notElem` filePaths) requiredFiles
   unless (null missingFiles)
     (throwError $
       PandocSomeError $
@@ -1539,15 +1539,15 @@ slideToSlideRelEntry slide = do
   element <- slideToSlideRelElement slide
   elemToEntry ("ppt/slides/_rels/" <> idNumToFilePath idNum <> ".rels") element
 
-linkRelElement :: PandocMonad m => Int -> LinkTarget -> P m Element
-linkRelElement rIdNum (InternalTarget targetId) = do
+linkRelElement :: PandocMonad m => (Int, LinkTarget) -> P m Element
+linkRelElement (rIdNum, InternalTarget targetId) = do
   targetIdNum <- getSlideIdNum targetId
   return $
     mknode "Relationship" [ ("Id", "rId" <> show rIdNum)
                           , ("Type", "http://schemas.openxmlformats.org/officeDocument/2006/relationships/slide")
                           , ("Target", "slide" <> show targetIdNum <> ".xml")
                           ] ()
-linkRelElement rIdNum (ExternalTarget (url, _)) = do
+linkRelElement (rIdNum, ExternalTarget (url, _)) = do
   return $
     mknode "Relationship" [ ("Id", "rId" <> show rIdNum)
                           , ("Type", "http://schemas.openxmlformats.org/officeDocument/2006/relationships/hyperlink")
@@ -1556,7 +1556,7 @@ linkRelElement rIdNum (ExternalTarget (url, _)) = do
                           ] ()
 
 linkRelElements :: PandocMonad m => M.Map Int LinkTarget -> P m [Element]
-linkRelElements mp = mapM (\(n, lnk) -> linkRelElement n lnk) (M.toList mp)
+linkRelElements mp = mapM linkRelElement (M.toList mp)
 
 mediaRelElement :: MediaInfo -> Element
 mediaRelElement mInfo =
diff --git a/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs b/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
index 75ce0dd4e..d36c92fa3 100644
--- a/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
+++ b/src/Text/Pandoc/Writers/Powerpoint/Presentation.hs
@@ -712,8 +712,8 @@ blocksToSlide blks = do
   slideLevel <- asks envSlideLevel
   blocksToSlide' slideLevel blks' spkNotes
 
-makeNoteEntry :: Int -> [Block] -> [Block]
-makeNoteEntry n blks =
+makeNoteEntry :: (Int, [Block]) -> [Block]
+makeNoteEntry (n, blks) =
   let enum = Str (tshow n <> ".")
   in
     case blks of
@@ -742,7 +742,7 @@ makeEndNotesSlideBlocks = do
                        ls -> ls
              ident = Shared.uniqueIdent exts title anchorSet
              hdr = Header slideLevel (ident, [], []) title
-             blks = concatMap (\(n, bs) -> makeNoteEntry n bs) $
+             blks = concatMap makeNoteEntry $
                     M.toList noteIds
          in return $ hdr : blks
 
diff --git a/src/Text/Pandoc/Writers/XWiki.hs b/src/Text/Pandoc/Writers/XWiki.hs
index 7afe845c7..4f9494933 100644
--- a/src/Text/Pandoc/Writers/XWiki.hs
+++ b/src/Text/Pandoc/Writers/XWiki.hs
@@ -54,10 +54,9 @@ type XWikiReader m = ReaderT WriterState m
 
 -- | Convert Pandoc to XWiki.
 writeXWiki :: PandocMonad m => WriterOptions -> Pandoc -> m Text
-writeXWiki _ (Pandoc _ blocks) = do
+writeXWiki _ (Pandoc _ blocks) =
   let env = WriterState { listLevel = "" }
-  body <- runReaderT (blockListToXWiki blocks) env
-  return $ body
+  in runReaderT (blockListToXWiki blocks) env
 
 -- | Concatenates strings with line breaks between them.
 vcat :: [Text] -> Text
@@ -219,7 +218,7 @@ inlineToXWiki (Link (id', _, _) txt (src, _)) = do
 inlineToXWiki (Image _ alt (source, tit)) = do
   alt' <- inlineListToXWiki alt
   let
-    params = intercalate " " $ filter (not . Text.null) [
+    params = Text.unwords $ filter (not . Text.null) [
         if Text.null alt' then "" else "alt=\"" <> alt' <> "\"",
           if Text.null tit then "" else "title=\"" <> tit <> "\""
         ]