Org reader internals: disable some GHC extensions

The RecordWildCards and ViewPatterns language extensions can be used to
shorten code, but usually also makes it harder to read. The DocumentTree
module was hence refactored and no longer relies on these extensions.

src/Text/Pandoc/Readers/Org/DocumentTree.hs

@@ -1,4 +1,3 @@
-{-# LANGUAGE NoImplicitPrelude #-}
 {-
 Copyright (C) 2014-2018 Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
 
@@ -17,8 +16,7 @@ along with this program; if not, write to the Free Software
 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 -}
 {-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE RecordWildCards  #-}
-{-# LANGUAGE ViewPatterns     #-}
+{-# LANGUAGE NoImplicitPrelude #-}
 {- |
    Module      : Text.Pandoc.Readers.Org.DocumentTree
    Copyright   : Copyright (C) 2014-2018 Albert Krewinkel
@@ -167,14 +165,17 @@ headline blocks inline lvl = try $ do
 
 -- | Convert an Org mode headline (i.e. a document tree) into pandoc's Blocks
 headlineToBlocks :: Monad m => Headline -> OrgParser m Blocks
-headlineToBlocks hdln@Headline {..} = do
-  maxHeadlineLevels <- getExportSetting exportHeadlineLevels
+headlineToBlocks hdln = do
+  maxLevel <- getExportSetting exportHeadlineLevels
+  let tags = headlineTags hdln
+  let text = headlineText hdln
+  let level = headlineLevel hdln
   case () of
-    _ | any isNoExportTag headlineTags     -> return mempty
-    _ | any isArchiveTag  headlineTags     -> archivedHeadlineToBlocks hdln
-    _ | isCommentTitle headlineText        -> return mempty
-    _ | headlineLevel >= maxHeadlineLevels -> headlineToHeaderWithList hdln
-    _ | otherwise                          -> headlineToHeaderWithContents hdln
+    _ | any isNoExportTag tags -> return mempty
+    _ | any isArchiveTag  tags -> archivedHeadlineToBlocks hdln
+    _ | isCommentTitle text    -> return mempty
+    _ | maxLevel <= level      -> headlineToHeaderWithList hdln
+    _ | otherwise              -> headlineToHeaderWithContents hdln
 
 isNoExportTag :: Tag -> Bool
 isNoExportTag = (== toTag "noexport")
@@ -186,8 +187,9 @@ isArchiveTag = (== toTag "ARCHIVE")
 -- FIXME: This accesses builder internals not intended for use in situations
 -- like these.  Replace once keyword parsing is supported.
 isCommentTitle :: Inlines -> Bool
-isCommentTitle (B.toList -> (Str "COMMENT":_)) = True
-isCommentTitle _                               = False
+isCommentTitle inlns = case B.toList inlns of
+  (Str "COMMENT":_) -> True
+  _ -> False
 
 archivedHeadlineToBlocks :: Monad m => Headline -> OrgParser m Blocks
 archivedHeadlineToBlocks hdln = do
@@ -198,17 +200,21 @@ archivedHeadlineToBlocks hdln = do
     ArchivedTreesHeadlineOnly -> headlineToHeader hdln
 
 headlineToHeaderWithList :: Monad m => Headline -> OrgParser m Blocks
-headlineToHeaderWithList hdln@Headline {..} = do
+headlineToHeaderWithList hdln = do
   maxHeadlineLevels <- getExportSetting exportHeadlineLevels
   header        <- headlineToHeader hdln
-  listElements  <- mapM headlineToBlocks headlineChildren
+  listElements  <- mapM headlineToBlocks (headlineChildren hdln)
   let listBlock  = if null listElements
                    then mempty
                    else B.orderedList listElements
-  let headerText = if maxHeadlineLevels == headlineLevel
+  let headerText = if maxHeadlineLevels == headlineLevel hdln
                    then header
                    else flattenHeader header
-  return $ headerText <> headlineContents <> listBlock
+  return . mconcat $
+    [ headerText
+    , headlineContents hdln
+    , listBlock
+    ]
  where
    flattenHeader :: Blocks -> Blocks
    flattenHeader blks =
@@ -217,27 +223,27 @@ headlineToHeaderWithList hdln@Headline {..} = do
        _                    -> mempty
 
 headlineToHeaderWithContents :: Monad m => Headline -> OrgParser m Blocks
-headlineToHeaderWithContents hdln@Headline {..} = do
+headlineToHeaderWithContents hdln = do
   header         <- headlineToHeader hdln
-  childrenBlocks <- mconcat <$> mapM headlineToBlocks headlineChildren
-  return $ header <> headlineContents <> childrenBlocks
+  childrenBlocks <- mconcat <$> mapM headlineToBlocks (headlineChildren hdln)
+  return $ header <> headlineContents hdln <> childrenBlocks
 
 headlineToHeader :: Monad m => Headline -> OrgParser m Blocks
-headlineToHeader Headline {..} = do
+headlineToHeader hdln = do
   exportTodoKeyword <- getExportSetting exportWithTodoKeywords
   exportTags        <- getExportSetting exportWithTags
   let todoText    = if exportTodoKeyword
-                    then case headlineTodoMarker of
+                    then case headlineTodoMarker hdln of
                       Just kw -> todoKeywordToInlines kw <> B.space
                       Nothing -> mempty
                     else mempty
-  let text        = todoText <> headlineText <>
+  let text        = todoText <> headlineText hdln <>
                     if exportTags
-                    then tagsToInlines headlineTags
+                    then tagsToInlines (headlineTags hdln)
                     else mempty
-  let propAttr    = propertiesToAttr headlineProperties
-  attr           <- registerHeader propAttr headlineText
-  return $ B.headerWith attr headlineLevel text
+  let propAttr    = propertiesToAttr (headlineProperties hdln)
+  attr           <- registerHeader propAttr (headlineText hdln)
+  return $ B.headerWith attr (headlineLevel hdln) text
 
 todoKeyword :: Monad m => OrgParser m TodoMarker
 todoKeyword = try $ do