Introduce `HasSyntaxExtensions` typeclass (#4074)

+ Added new `HasSyntaxExtensions` typeclass for `ReaderOptions` and `WriterOptions`.
+ Reimplemented `isEnabled` function from `Options.hs` to accept both `ReaderOptions`
  and `WriterOptions`.
+ Replaced `enabled` from `CommonMark.hs` with new `isEnabled`.

2 files changed, 20 insertions, 15 deletions

diff --git a/src/Text/Pandoc/Options.hs b/src/Text/Pandoc/Options.hs
index 581f4c82a..03960b6b9 100644
--- a/src/Text/Pandoc/Options.hs
+++ b/src/Text/Pandoc/Options.hs
@@ -56,6 +56,9 @@ import Skylighting (SyntaxMap, defaultSyntaxMap)
 import Text.Pandoc.Extensions
 import Text.Pandoc.Highlighting (Style, pygments)
 
+class HasSyntaxExtensions a where
+  getExtensions :: a -> Extensions
+
 data ReaderOptions = ReaderOptions{
          readerExtensions            :: Extensions  -- ^ Syntax extensions
        , readerStandalone            :: Bool -- ^ Standalone document with header
@@ -69,6 +72,9 @@ data ReaderOptions = ReaderOptions{
        , readerStripComments         :: Bool -- ^ Strip HTML comments instead of parsing as raw HTML
 } deriving (Show, Read, Data, Typeable, Generic)
 
+instance HasSyntaxExtensions ReaderOptions where
+  getExtensions opts = readerExtensions opts
+
 instance ToJSON ReaderOptions where
   toEncoding = genericToEncoding defaultOptions
 instance FromJSON ReaderOptions
@@ -259,6 +265,9 @@ instance Default WriterOptions where
                       , writerSyntaxMap        = defaultSyntaxMap
                       }
 
+instance HasSyntaxExtensions WriterOptions where
+  getExtensions opts = writerExtensions opts
+
 -- | Returns True if the given extension is enabled.
-isEnabled :: Extension -> WriterOptions -> Bool
-isEnabled ext opts = ext `extensionEnabled` writerExtensions opts
+isEnabled :: HasSyntaxExtensions a => Extension -> a -> Bool
+isEnabled ext opts = ext `extensionEnabled` getExtensions opts
diff --git a/src/Text/Pandoc/Readers/CommonMark.hs b/src/Text/Pandoc/Readers/CommonMark.hs
index 47f4c4088..ea9747342 100644
--- a/src/Text/Pandoc/Readers/CommonMark.hs
+++ b/src/Text/Pandoc/Readers/CommonMark.hs
@@ -48,18 +48,14 @@ import Text.Pandoc.Walk (walkM)
 -- | Parse a CommonMark formatted string into a 'Pandoc' structure.
 readCommonMark :: PandocMonad m => ReaderOptions -> Text -> m Pandoc
 readCommonMark opts s = return $
-  (if enabled Ext_gfm_auto_identifiers opts
+  (if isEnabled Ext_gfm_auto_identifiers opts
       then addHeaderIdentifiers
       else id) $
   nodeToPandoc opts $ commonmarkToNode opts' exts s
-  where opts' = [ optSmart | enabled Ext_smart opts ]
-        exts = [ extStrikethrough | enabled Ext_strikeout opts ] ++
-               [ extTable | enabled Ext_pipe_tables opts ] ++
-               [ extAutolink | enabled Ext_autolink_bare_uris opts ]
-
--- | Returns True if the given extension is enabled.
-enabled :: Extension -> ReaderOptions -> Bool
-enabled ext opts = ext `extensionEnabled` readerExtensions opts
+  where opts' = [ optSmart | isEnabled Ext_smart opts ]
+        exts = [ extStrikethrough | isEnabled Ext_strikeout opts ] ++
+               [ extTable | isEnabled Ext_pipe_tables opts ] ++
+               [ extAutolink | isEnabled Ext_autolink_bare_uris opts ]
 
 convertEmojis :: String -> String
 convertEmojis (':':xs) =
@@ -112,7 +108,7 @@ addBlock _ (Node _ THEMATIC_BREAK _) =
 addBlock opts (Node _ BLOCK_QUOTE nodes) =
   (BlockQuote (addBlocks opts nodes) :)
 addBlock opts (Node _ (HTML_BLOCK t) _)
-  | enabled Ext_raw_html opts = (RawBlock (Format "html") (unpack t) :)
+  | isEnabled Ext_raw_html opts = (RawBlock (Format "html") (unpack t) :)
   | otherwise                 = id
 -- Note:  the cmark parser will never generate CUSTOM_BLOCK,
 -- so we don't need to handle it:
@@ -210,15 +206,15 @@ addInline opts (Node _ (TEXT t) _) = (map toinl clumps ++)
         samekind _   ' ' = False
         samekind _  _    = True
         toinl (' ':_) = Space
-        toinl xs      = Str $ if enabled Ext_emoji opts
+        toinl xs      = Str $ if isEnabled Ext_emoji opts
                                  then convertEmojis xs
                                  else xs
 addInline _ (Node _ LINEBREAK _) = (LineBreak :)
 addInline opts (Node _ SOFTBREAK _)
-  | enabled Ext_hard_line_breaks opts = (LineBreak :)
+  | isEnabled Ext_hard_line_breaks opts = (LineBreak :)
   | otherwise                           = (SoftBreak :)
 addInline opts (Node _ (HTML_INLINE t) _)
-  | enabled Ext_raw_html opts = (RawInline (Format "html") (unpack t) :)
+  | isEnabled Ext_raw_html opts = (RawInline (Format "html") (unpack t) :)
   | otherwise                 = id
 -- Note:  the cmark parser will never generate CUSTOM_BLOCK,
 -- so we don't need to handle it: