Introduce class HasLastStrPosition, generalize functions

Both `ParserState` and `OrgParserState` keep track of the parser position at
which the last string ended.  This patch introduces a new class
`HasLastStrPosition` and makes the above types instances of that class.  This
enables the generalization of functions updating the state or checking if one
is right after a string.

src/Text/Pandoc/Parsing.hs

@@ -54,7 +54,6 @@ module Text.Pandoc.Parsing ( (>>~),
                              withRaw,
                              escaped,
                              characterReference,
-                             updateLastStrPos,
                              anyOrderedListMarker,
                              orderedListMarker,
                              charRef,
@@ -66,11 +65,14 @@ module Text.Pandoc.Parsing ( (>>~),
                              testStringWith,
                              guardEnabled,
                              guardDisabled,
+                             updateLastStrPos,
+                             notAfterString,
                              ParserState (..),
                              HasReaderOptions (..),
                              HasHeaderMap (..),
                              HasIdentifierList (..),
                              HasMacros (..),
+                             HasLastStrPosition (..),
                              defaultParserState,
                              HeaderType (..),
                              ParserContext (..),
@@ -904,6 +906,14 @@ instance HasMacros ParserState where
   extractMacros        = stateMacros
   updateMacros f st    = st{ stateMacros = f $ stateMacros st }
 
+class HasLastStrPosition st where
+  setLastStrPos  :: SourcePos -> st -> st
+  getLastStrPos  :: st -> Maybe SourcePos
+
+instance HasLastStrPosition ParserState where
+  setLastStrPos pos st = st{ stateLastStrPos = Just pos }
+  getLastStrPos st     = stateLastStrPos st
+
 defaultParserState :: ParserState
 defaultParserState =
     ParserState { stateOptions         = def,
@@ -938,6 +948,17 @@ guardEnabled ext = getOption readerExtensions >>= guard . Set.member ext
 guardDisabled :: HasReaderOptions st => Extension -> Parser s st ()
 guardDisabled ext = getOption readerExtensions >>= guard . not . Set.member ext
 
+-- | Update the position on which the last string ended.
+updateLastStrPos :: HasLastStrPosition st => Parser s st ()
+updateLastStrPos = getPosition >>= updateState . setLastStrPos
+
+-- | Whether we are right after the end of a string.
+notAfterString :: HasLastStrPosition st => Parser s st Bool
+notAfterString = do
+  pos <- getPosition
+  st  <- getState
+  return $ getLastStrPos st /= Just pos
+
 data HeaderType
     = SingleHeader Char  -- ^ Single line of characters underneath
     | DoubleHeader Char  -- ^ Lines of characters above and below
@@ -1049,17 +1070,11 @@ charOrRef cs =
                        guard (c `elem` cs)
                        return c)
 
-updateLastStrPos :: Parser [Char] ParserState ()
-updateLastStrPos = getPosition >>= \p ->
-  updateState $ \s -> s{ stateLastStrPos = Just p }
-
 singleQuoteStart :: Parser [Char] ParserState ()
 singleQuoteStart = do
   failIfInQuoteContext InSingleQuote
-  pos <- getPosition
-  st <- getState
   -- single quote start can't be right after str
-  guard $ stateLastStrPos st /= Just pos
+  guard =<< notAfterString
   () <$ charOrRef "'\8216\145"
 
 singleQuoteEnd :: Parser [Char] st ()
@@ -1156,4 +1171,3 @@ applyMacros' target = do
      then do macros <- extractMacros `fmap` getState
              return $ applyMacros macros target
      else return target
-

src/Text/Pandoc/Readers/Markdown.hs

@@ -1474,9 +1474,7 @@ strongOrEmph =  enclosure '*' <|> (checkIntraword >> enclosure '_')
   where  checkIntraword = do
            exts <- getOption readerExtensions
            when (Ext_intraword_underscores `Set.member` exts) $ do
-             pos <- getPosition
-             lastStrPos <- stateLastStrPos <$> getState
-             guard $ lastStrPos /= Just pos
+             guard =<< notAfterString
 
 -- | Parses a list of inlines between start and end delimiters.
 inlinesBetween :: (Show b)
@@ -1518,8 +1516,7 @@ nonEndline = satisfy (/='\n')
 str :: MarkdownParser (F Inlines)
 str = do
   result <- many1 alphaNum
-  pos <- getPosition
-  updateState $ \s -> s{ stateLastStrPos = Just pos }
+  updateLastStrPos
   let spacesToNbr = map (\c -> if c == ' ' then '\160' else c)
   isSmart <- getOption readerSmart
   if isSmart
@@ -1821,9 +1818,7 @@ citeKey :: MarkdownParser (Bool, String)
 citeKey = try $ do
   -- make sure we're not right after an alphanumeric,
   -- since foo@bar.baz is probably an email address
-  lastStrPos <- stateLastStrPos <$> getState
-  pos <- getPosition
-  guard $ lastStrPos /= Just pos
+  guard =<< notAfterString
   suppress_author <- option False (char '-' >> return True)
   char '@'
   first <- letter <|> char '_'

src/Text/Pandoc/Readers/Org.hs

@@ -105,6 +105,10 @@ instance HasMeta OrgParserState where
   deleteMeta field st =
     st{ orgStateMeta = deleteMeta field $ orgStateMeta st }
 
+instance HasLastStrPosition OrgParserState where
+  getLastStrPos = orgStateLastStrPos
+  setLastStrPos pos st = st{ orgStateLastStrPos = Just pos }
+
 instance Default OrgParserState where
   def = defaultOrgParserState
 
@@ -1274,13 +1278,6 @@ afterEmphasisPreChar = do
   lastPrePos <- orgStateLastPreCharPos <$> getState
   return . fromMaybe True $ (== pos) <$> lastPrePos
 
--- | Whether we are right after the end of a string
-notAfterString :: OrgParser Bool
-notAfterString = do
-  pos <- getPosition
-  lastStrPos <- orgStateLastStrPos <$> getState
-  return $ lastStrPos /= Just pos
-
 -- | Whether the parser is right after a forbidden border char
 notAfterForbiddenBorderChar :: OrgParser Bool
 notAfterForbiddenBorderChar = do