path: root/src/Text/Pandoc/Writers/Markdown.hs

{-# LANGUAGE OverloadedStrings, TupleSections #-}
{-
Copyright (C) 2006-2010 John MacFarlane <jgm@berkeley.edu>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-}

{- |
   Module      : Text.Pandoc.Writers.Markdown
   Copyright   : Copyright (C) 2006-2010 John MacFarlane
   License     : GNU GPL, version 2 or above

   Maintainer  : John MacFarlane <jgm@berkeley.edu>
   Stability   : alpha
   Portability : portable

Conversion of 'Pandoc' documents to markdown-formatted plain text.

Markdown:  <http://daringfireball.net/projects/markdown/>
-}
module Text.Pandoc.Writers.Markdown (writeMarkdown, writePlain) where
import Text.Pandoc.Definition
import Text.Pandoc.Generic
import Text.Pandoc.Templates (renderTemplate)
import Text.Pandoc.Shared
import Text.Pandoc.Options
import Text.Pandoc.Parsing hiding (blankline, char, space)
import Data.List ( group, isPrefixOf, find, intersperse, transpose )
import Text.Pandoc.Pretty
import Control.Monad.State
import qualified Data.Set as Set
import Text.Pandoc.Writers.HTML (writeHtmlString)
import Text.Pandoc.Readers.TeXMath (readTeXMath)
import Text.HTML.TagSoup (renderTags, parseTags, isTagText, Tag(..))

type Notes = [[Block]]
type Refs = [([Inline], Target)]
data WriterState = WriterState { stNotes :: Notes
                               , stRefs :: Refs
                               , stPlain :: Bool }

-- | Convert Pandoc to Markdown.
writeMarkdown :: WriterOptions -> Pandoc -> String
writeMarkdown opts document =
  evalState (pandocToMarkdown opts document) WriterState{ stNotes = []
                                                        , stRefs  = []
                                                        , stPlain = False }

-- | Convert Pandoc to plain text (like markdown, but without links,
-- pictures, or inline formatting).
writePlain :: WriterOptions -> Pandoc -> String
writePlain opts document =
  evalState (pandocToMarkdown opts{
                 writerExtensions = Set.delete Ext_escaped_line_breaks $
                                    writerExtensions opts }
              document') WriterState{ stNotes = []
                                    , stRefs  = []
                                    , stPlain = True }
    where document' = plainify document

plainify :: Pandoc -> Pandoc
plainify = bottomUp go
  where go :: Inline -> Inline
        go (Emph xs) = SmallCaps xs
        go (Strong xs) = SmallCaps xs
        go (Strikeout xs) = SmallCaps xs
        go (Superscript xs) = SmallCaps xs
        go (Subscript xs) = SmallCaps xs
        go (SmallCaps xs) = SmallCaps xs
        go (Code _ s) = Str s
        go (Math _ s) = Str s
        go (RawInline _ _) = Str ""
        go (Link xs _) = SmallCaps xs
        go (Image xs _) = SmallCaps $ [Str "["] ++ xs ++ [Str "]"]
        go (Cite _ cits) = SmallCaps cits
        go x = x

pandocTitleBlock :: Doc -> [Doc] -> Doc -> Doc
pandocTitleBlock tit auths dat =
  hang 2 (text "% ") tit <> cr <>
  hang 2 (text "% ") (hcat (intersperse (text "; ") auths)) <> cr <>
  hang 2 (text "% ") dat <> cr

mmdTitleBlock :: Doc -> [Doc] -> Doc -> Doc
mmdTitleBlock tit auths dat =
  hang 8 (text "Title:  ") tit <> cr <>
  hang 8 (text "Author: ") (hcat (intersperse (text "; ") auths)) <> cr <>
  hang 8 (text "Date:   ") dat <> cr

plainTitleBlock :: Doc -> [Doc] -> Doc -> Doc
plainTitleBlock tit auths dat =
  tit <> cr <>
  (hcat (intersperse (text "; ") auths)) <> cr <>
  dat <> cr

-- | Return markdown representation of document.
pandocToMarkdown :: WriterOptions -> Pandoc -> State WriterState String
pandocToMarkdown opts (Pandoc (Meta title authors date) blocks) = do
  title' <- inlineListToMarkdown opts title
  authors' <- mapM (inlineListToMarkdown opts) authors
  date' <- inlineListToMarkdown opts date
  isPlain <- gets stPlain
  let titleblock = case True of
                        _ | isPlain ->
                              plainTitleBlock title' authors' date'
                          | isEnabled Ext_pandoc_title_block opts ->
                              pandocTitleBlock title' authors' date'
                          | isEnabled Ext_mmd_title_block opts ->
                              mmdTitleBlock title' authors' date'
                          | otherwise -> empty
  let headerBlocks = filter isHeaderBlock blocks
  let toc = if writerTableOfContents opts
               then tableOfContents opts headerBlocks
               else empty
  body <- blockListToMarkdown opts blocks
  st <- get
  notes' <- notesToMarkdown opts (reverse $ stNotes st)
  st' <- get  -- note that the notes may contain refs
  refs' <- refsToMarkdown opts (reverse $ stRefs st')
  let colwidth = if writerWrapText opts
                    then Just $ writerColumns opts
                    else Nothing
  let main = render colwidth $ body <>
               (if isEmpty notes' then empty else blankline <> notes') <>
               (if isEmpty refs' then empty else blankline <> refs')
  let context  = writerVariables opts ++
                 [ ("toc", render colwidth toc)
                 , ("body", main)
                 ] ++
                 [ ("titleblock", render colwidth titleblock)
                   | not (null title && null authors && null date) ]
  if writerStandalone opts
     then return $ renderTemplate context $ writerTemplate opts
     else return main

-- | Return markdown representation of reference key table.
refsToMarkdown :: WriterOptions -> Refs -> State WriterState Doc
refsToMarkdown opts refs = mapM (keyToMarkdown opts) refs >>= return . vcat

-- | Return markdown representation of a reference key.
keyToMarkdown :: WriterOptions
              -> ([Inline], (String, String))
              -> State WriterState Doc
keyToMarkdown opts (label, (src, tit)) = do
  label' <- inlineListToMarkdown opts label
  let tit' = if null tit
                then empty
                else space <> "\"" <> text tit <> "\""
  return $ nest 2 $ hang 2
            ("[" <> label' <> "]:" <> space) (text src <> tit')

-- | Return markdown representation of notes.
notesToMarkdown :: WriterOptions -> [[Block]] -> State WriterState Doc
notesToMarkdown opts notes =
  mapM (\(num, note) -> noteToMarkdown opts num note) (zip [1..] notes) >>=
  return . vsep

-- | Return markdown representation of a note.
noteToMarkdown :: WriterOptions -> Int -> [Block] -> State WriterState Doc
noteToMarkdown opts num blocks = do
  contents  <- blockListToMarkdown opts blocks
  let num' = text $ show num
  let marker = if isEnabled Ext_footnotes opts
                  then text "[^" <> num' <> text "]:"
                  else text "[" <> num' <> text "]"
  let markerSize = 4 + offset num'
  let spacer = case writerTabStop opts - markerSize of
                     n | n > 0  -> text $ replicate n ' '
                     _          -> text " "
  return $ if isEnabled Ext_footnotes opts
              then hang (writerTabStop opts) (marker <> spacer) contents
              else marker <> spacer <> contents

-- | Escape special characters for Markdown.
escapeString :: String -> String
escapeString = escapeStringUsing markdownEscapes
  where markdownEscapes = backslashEscapes "\\`*_$<>#~^"

-- | Construct table of contents from list of header blocks.
tableOfContents :: WriterOptions -> [Block] -> Doc
tableOfContents opts headers =
  let opts' = opts { writerIgnoreNotes = True }
      contents = BulletList $ map elementToListItem $ hierarchicalize headers
  in  evalState (blockToMarkdown opts' contents) WriterState{ stNotes = []
                                                            , stRefs  = []
                                                            , stPlain = False }

-- | Converts an Element to a list item for a table of contents,
elementToListItem :: Element -> [Block]
elementToListItem (Blk _) = []
elementToListItem (Sec _ _ _ headerText subsecs) = [Plain headerText] ++
  if null subsecs
     then []
     else [BulletList $ map elementToListItem subsecs]

attrsToMarkdown :: Attr -> Doc
attrsToMarkdown attribs = braces $ hsep [attribId, attribClasses, attribKeys]
        where attribId = case attribs of
                                ([],_,_) -> empty
                                (i,_,_)  -> "#" <> text i
              attribClasses = case attribs of
                                (_,[],_) -> empty
                                (_,cs,_) -> hsep $
                                            map (text . ('.':))
                                            cs
              attribKeys = case attribs of
                                (_,_,[]) -> empty
                                (_,_,ks) -> hsep $
                                            map (\(k,v) -> text k
                                              <> "=\"" <> text v <> "\"") ks

-- | Ordered list start parser for use in Para below.
olMarker :: Parser [Char] ParserState Char
olMarker = do (start, style', delim) <- anyOrderedListMarker
              if delim == Period &&
                          (style' == UpperAlpha || (style' == UpperRoman &&
                          start `elem` [1, 5, 10, 50, 100, 500, 1000]))
                          then spaceChar >> spaceChar
                          else spaceChar

-- | True if string begins with an ordered list marker
beginsWithOrderedListMarker :: String -> Bool
beginsWithOrderedListMarker str =
  case runParser olMarker defaultParserState "para start" (take 10 str) of
         Left  _  -> False
         Right _  -> True

-- | Convert Pandoc block element to markdown.
blockToMarkdown :: WriterOptions -- ^ Options
                -> Block         -- ^ Block element
                -> State WriterState Doc
blockToMarkdown _ Null = return empty
blockToMarkdown opts (Plain inlines) = do
  contents <- inlineListToMarkdown opts inlines
  return $ contents <> cr
blockToMarkdown opts (Para inlines) = do
  contents <- inlineListToMarkdown opts inlines
  -- escape if para starts with ordered list marker
  st <- get
  let esc = if isEnabled Ext_all_symbols_escapable opts &&
               not (stPlain st) &&
               beginsWithOrderedListMarker (render Nothing contents)
               then text "\x200B" -- zero-width space, a hack
               else empty
  return $ esc <> contents <> blankline
blockToMarkdown opts (RawBlock f str)
  | f == "html" = do
    st <- get
    if stPlain st
       then return empty
       else return $ if isEnabled Ext_markdown_attribute opts
                        then text (addMarkdownAttribute str) <> text "\n"
                        else text str <> text "\n"
  | f == "latex" || f == "tex" || f == "markdown" = do
    st <- get
    if stPlain st
       then return empty
       else return $ text str <> text "\n"
blockToMarkdown _ (RawBlock _ _) = return empty
blockToMarkdown _ HorizontalRule =
  return $ blankline <> text "* * * * *" <> blankline
blockToMarkdown opts (Header level inlines) = do
  contents <- inlineListToMarkdown opts inlines
  st <- get
  let setext = writerSetextHeaders opts
  return $ nowrap
         $ case level of
            1 | setext ->
                  contents <> cr <> text (replicate (offset contents) '=') <>
                  blankline
            2 | setext ->
                  contents <> cr <> text (replicate (offset contents) '-') <>
                  blankline
            -- ghc interprets '#' characters in column 1 as linenum specifiers.
            _ | stPlain st || isEnabled Ext_literate_haskell opts ->
                contents <> blankline
            _ -> text (replicate level '#') <> space <> contents <> blankline
blockToMarkdown opts (CodeBlock (_,classes,_) str)
  | "haskell" `elem` classes && "literate" `elem` classes &&
    isEnabled Ext_literate_haskell opts =
  return $ prefixed "> " (text str) <> blankline
blockToMarkdown opts (CodeBlock attribs str) = return $
  if isEnabled Ext_delimited_code_blocks opts && attribs /= nullAttr
     then -- use delimited code block
          (tildes <> space <> attrs <> cr <> text str <>
                  cr <> tildes) <> blankline
     else nest (writerTabStop opts) (text str) <> blankline
   where tildes  = text "~~~~"
         attrs = attrsToMarkdown attribs
blockToMarkdown opts (BlockQuote blocks) = do
  st <- get
  -- if we're writing literate haskell, put a space before the bird tracks
  -- so they won't be interpreted as lhs...
  let leader = if isEnabled Ext_literate_haskell opts
                  then " > "
                  else if stPlain st
                          then "  "
                          else "> "
  contents <- blockListToMarkdown opts blocks
  return $ (prefixed leader contents) <> blankline
blockToMarkdown opts t@(Table caption aligns widths headers rows) =  do
  caption' <- inlineListToMarkdown opts caption
  let caption'' = if null caption || not (isEnabled Ext_table_captions opts)
                     then empty
                     else blankline <> ": " <> caption' <> blankline
  rawHeaders <- mapM (blockListToMarkdown opts) headers
  rawRows <- mapM (mapM (blockListToMarkdown opts)) rows
  let isSimple = all (==0) widths
  (nst,tbl) <- case isSimple of
                True  | isEnabled Ext_simple_tables opts -> fmap (nest 2,) $
                         pandocTable opts (all null headers) aligns widths
                             rawHeaders rawRows
                      | isEnabled Ext_pipe_tables opts -> fmap (id,) $
                         pipeTable (all null headers) aligns rawHeaders rawRows
                      | otherwise -> fmap (id,) $
                         return $ text $ writeHtmlString def
                                $ Pandoc (Meta [] [] []) [t]
                False | isEnabled Ext_multiline_tables opts -> fmap (nest 2,) $
                         pandocTable opts (all null headers) aligns widths
                             rawHeaders rawRows
                      | otherwise -> fmap (id,) $
                         return $ text $ writeHtmlString def
                                $ Pandoc (Meta [] [] []) [t]
  return $ nst $ tbl $$ blankline $$ caption'' $$ blankline
blockToMarkdown opts (BulletList items) = do
  contents <- mapM (bulletListItemToMarkdown opts) items
  return $ cat contents <> blankline
blockToMarkdown opts (OrderedList (start,sty,delim) items) = do
  let start' = if isEnabled Ext_startnum opts then start else 1
  let sty'   = if isEnabled Ext_fancy_lists opts then sty else DefaultStyle
  let delim' = if isEnabled Ext_fancy_lists opts then delim else DefaultDelim
  let attribs = (start', sty', delim')
  let markers  = orderedListMarkers attribs
  let markers' = map (\m -> if length m < 3
                               then m ++ replicate (3 - length m) ' '
                               else m) markers
  contents <- mapM (\(item, num) -> orderedListItemToMarkdown opts item num) $
              zip markers' items
  return $ cat contents <> blankline
blockToMarkdown opts (DefinitionList items) = do
  contents <- mapM (definitionListItemToMarkdown opts) items
  return $ cat contents <> blankline

addMarkdownAttribute :: String -> String
addMarkdownAttribute s =
  case span isTagText $ reverse $ parseTags s of
       (xs,(TagOpen t attrs:rest)) ->
            renderTags $ reverse rest ++ (TagOpen t attrs' : reverse xs)
              where attrs' = ("markdown","1"):[(x,y) | (x,y) <- attrs,
                                 x /= "markdown"]
       _ -> s

pipeTable :: Bool -> [Alignment] -> [Doc] -> [[Doc]] -> State WriterState Doc
pipeTable headless aligns rawHeaders rawRows = do
  let torow cs = nowrap $ text "|" <>
                 hcat (intersperse (text "|") $ map chomp cs) <> text "|"
  let toborder (a, h) = let wid = max (offset h) 3
                        in  text $ case a of
                             AlignLeft    -> ':':replicate (wid - 1) '-'
                             AlignCenter  -> ':':replicate (wid - 2) '-' ++ ":"
                             AlignRight   -> replicate (wid - 1) '-' ++ ":"
                             AlignDefault -> replicate wid '-'
  let header = if headless then empty else torow rawHeaders
  let border = torow $ map toborder $ zip aligns rawHeaders
  let body   = vcat $ map torow rawRows
  return $ header $$ border $$ body

pandocTable :: WriterOptions -> Bool -> [Alignment] -> [Double]
            -> [Doc] -> [[Doc]] -> State WriterState Doc
pandocTable opts headless aligns widths rawHeaders rawRows =  do
  let isSimple = all (==0) widths
  let alignHeader alignment = case alignment of
                                AlignLeft    -> lblock
                                AlignCenter  -> cblock
                                AlignRight   -> rblock
                                AlignDefault -> lblock
  let numChars = maximum . map offset
  let widthsInChars = if isSimple
                         then map ((+2) . numChars)
                              $ transpose (rawHeaders : rawRows)
                         else map
                              (floor . (fromIntegral (writerColumns opts) *))
                              widths
  let makeRow = hcat . intersperse (lblock 1 (text " ")) .
                   (zipWith3 alignHeader aligns widthsInChars)
  let rows' = map makeRow rawRows
  let head' = makeRow rawHeaders
  let maxRowHeight = maximum $ map height (head':rows')
  let underline = cat $ intersperse (text " ") $
                  map (\width -> text (replicate width '-')) widthsInChars
  let border = if maxRowHeight > 1
                  then text (replicate (sum widthsInChars +
                          length widthsInChars - 1) '-')
                  else if headless
                          then underline
                          else empty
  let head'' = if headless
                  then empty
                  else border <> cr <> head'
  let body = if maxRowHeight > 1
                then vsep rows'
                else vcat rows'
  let bottom = if headless
                  then underline
                  else border
  return $ head'' $$ underline $$ body $$ bottom

-- | Convert bullet list item (list of blocks) to markdown.
bulletListItemToMarkdown :: WriterOptions -> [Block] -> State WriterState Doc
bulletListItemToMarkdown opts items = do
  contents <- blockListToMarkdown opts items
  let sps = replicate (writerTabStop opts - 2) ' '
  let start = text ('-' : ' ' : sps)
  return $ hang (writerTabStop opts) start $ contents <> cr

-- | Convert ordered list item (a list of blocks) to markdown.
orderedListItemToMarkdown :: WriterOptions -- ^ options
                          -> String        -- ^ list item marker
                          -> [Block]       -- ^ list item (list of blocks)
                          -> State WriterState Doc
orderedListItemToMarkdown opts marker items = do
  contents <- blockListToMarkdown opts items
  let sps = case length marker - writerTabStop opts of
                   n | n > 0 -> text $ replicate n ' '
                   _         -> text " "
  let start = text marker <> sps
  return $ hang (writerTabStop opts) start $ contents <> cr

-- | Convert definition list item (label, list of blocks) to markdown.
definitionListItemToMarkdown :: WriterOptions
                             -> ([Inline],[[Block]])
                             -> State WriterState Doc
definitionListItemToMarkdown opts (label, defs) = do
  labelText <- inlineListToMarkdown opts label
  defs' <- mapM (mapM (blockToMarkdown opts)) defs
  if isEnabled Ext_definition_lists opts
     then do
       let tabStop = writerTabStop opts
       st <- get
       let leader  = if stPlain st then "   " else ":  "
       let sps = case writerTabStop opts - 3 of
                      n | n > 0   -> text $ replicate n ' '
                      _           -> text " "
       let contents = vcat $ map (\d -> hang tabStop (leader <> sps) $ vcat d <> cr) defs'
       return $ nowrap labelText <> cr <> contents <> cr
     else do
       return $ nowrap labelText <> text "  " <> cr <>
                vsep (map vsep defs') <> blankline

-- | Convert list of Pandoc block elements to markdown.
blockListToMarkdown :: WriterOptions -- ^ Options
                    -> [Block]       -- ^ List of block elements
                    -> State WriterState Doc
blockListToMarkdown opts blocks =
  mapM (blockToMarkdown opts) (fixBlocks blocks) >>= return . cat
    -- insert comment between list and indented code block, or the
    -- code block will be treated as a list continuation paragraph
    where fixBlocks (b : CodeBlock attr x : rest)
            | (not (isEnabled Ext_delimited_code_blocks opts) || attr == nullAttr)
                && isListBlock b =
               b : RawBlock "html" "<!-- -->\n" : CodeBlock attr x :
                   fixBlocks rest
          fixBlocks (x : xs)             = x : fixBlocks xs
          fixBlocks []                   = []
          isListBlock (BulletList _)     = True
          isListBlock (OrderedList _ _)  = True
          isListBlock (DefinitionList _) = True
          isListBlock _                  = False

-- | Get reference for target; if none exists, create unique one and return.
--   Prefer label if possible; otherwise, generate a unique key.
getReference :: [Inline] -> Target -> State WriterState [Inline]
getReference label (src, tit) = do
  st <- get
  case find ((== (src, tit)) . snd) (stRefs st) of
    Just (ref, _) -> return ref
    Nothing       -> do
      let label' = case find ((== label) . fst) (stRefs st) of
                      Just _ -> -- label is used; generate numerical label
                                 case find (\n -> not (any (== [Str (show n)])
                                           (map fst (stRefs st)))) [1..(10000 :: Integer)] of
                                      Just x  -> [Str (show x)]
                                      Nothing -> error "no unique label"
                      Nothing -> label
      modify (\s -> s{ stRefs = (label', (src,tit)) : stRefs st })
      return label'

-- | Convert list of Pandoc inline elements to markdown.
inlineListToMarkdown :: WriterOptions -> [Inline] -> State WriterState Doc
inlineListToMarkdown opts lst =
  mapM (inlineToMarkdown opts) lst >>= return . cat

escapeSpaces :: Inline -> Inline
escapeSpaces (Str s) = Str $ substitute " " "\\ " s
escapeSpaces Space = Str "\\ "
escapeSpaces x = x

-- | Convert Pandoc inline element to markdown.
inlineToMarkdown :: WriterOptions -> Inline -> State WriterState Doc
inlineToMarkdown opts (Emph lst) = do
  contents <- inlineListToMarkdown opts lst
  return $ "*" <> contents <> "*"
inlineToMarkdown opts (Strong lst) = do
  contents <- inlineListToMarkdown opts lst
  return $ "**" <> contents <> "**"
inlineToMarkdown opts (Strikeout lst) = do
  contents <- inlineListToMarkdown opts lst
  return $ if isEnabled Ext_strikeout opts
              then "~~" <> contents <> "~~"
              else "<s>" <> contents <> "</s>"
inlineToMarkdown opts (Superscript lst) = do
  let lst' = bottomUp escapeSpaces lst
  contents <- inlineListToMarkdown opts lst'
  return $ if isEnabled Ext_superscript opts
              then "^" <> contents <> "^"
              else "<sup>" <> contents <> "</sup>"
inlineToMarkdown opts (Subscript lst) = do
  let lst' = bottomUp escapeSpaces lst
  contents <- inlineListToMarkdown opts lst'
  return $ if isEnabled Ext_subscript opts
              then "~" <> contents <> "~"
              else "<sub>" <> contents <> "</sub>"
inlineToMarkdown opts (SmallCaps lst) = inlineListToMarkdown opts lst
inlineToMarkdown opts (Quoted SingleQuote lst) = do
  contents <- inlineListToMarkdown opts lst
  return $ "‘" <> contents <> "’"
inlineToMarkdown opts (Quoted DoubleQuote lst) = do
  contents <- inlineListToMarkdown opts lst
  return $ "“" <> contents <> "”"
inlineToMarkdown opts (Code attr str) =
  let tickGroups = filter (\s -> '`' `elem` s) $ group str
      longest    = if null tickGroups
                     then 0
                     else maximum $ map length tickGroups
      marker     = replicate (longest + 1) '`'
      spacer     = if (longest == 0) then "" else " "
      attrs      = if isEnabled Ext_inline_code_attributes opts && attr /= nullAttr
                      then attrsToMarkdown attr
                      else empty
  in  return $ text (marker ++ spacer ++ str ++ spacer ++ marker) <> attrs
inlineToMarkdown _ (Str str) = do
  st <- get
  if stPlain st
     then return $ text str
     else return $ text $ escapeString str
inlineToMarkdown opts (Math InlineMath str)
  | isEnabled Ext_tex_math_dollars opts =
      return $ "$" <> text str <> "$"
  | isEnabled Ext_tex_math_single_backslash opts =
      return $ "\\(" <> text str <> "\\)"
  | isEnabled Ext_tex_math_double_backslash opts =
      return $ "\\\\(" <> text str <> "\\\\)"
  | otherwise = inlineListToMarkdown opts $ readTeXMath str
inlineToMarkdown opts (Math DisplayMath str)
  | isEnabled Ext_tex_math_dollars opts =
      return $ "$$" <> text str <> "$$"
  | isEnabled Ext_tex_math_single_backslash opts =
      return $ "\\[" <> text str <> "\\]"
  | isEnabled Ext_tex_math_double_backslash opts =
      return $ "\\\\[" <> text str <> "\\\\]"
  | otherwise = (\x -> cr <> x <> cr) `fmap`
        inlineListToMarkdown opts (readTeXMath str)
inlineToMarkdown opts (RawInline f str)
  | f == "html" || f == "markdown" ||
    (isEnabled Ext_raw_tex opts && (f == "latex" || f == "tex")) =
    return $ text str
inlineToMarkdown _ (RawInline _ _) = return empty
inlineToMarkdown opts (LineBreak)
  | isEnabled Ext_escaped_line_breaks opts = return $ "\\" <> cr
  | otherwise                            = return $ "  " <> cr
inlineToMarkdown _ Space = return space
inlineToMarkdown opts (Cite (c:cs) lst)
  | writerCiteMethod opts == Citeproc = inlineListToMarkdown opts lst
  | citationMode c == AuthorInText = do
    suffs <- inlineListToMarkdown opts $ citationSuffix c
    rest <- mapM convertOne cs
    let inbr = suffs <+> joincits rest
        br   = if isEmpty inbr then empty else char '[' <> inbr <> char ']'
    return $ text ("@" ++ citationId c) <+> br
  | otherwise = do
    cits <- mapM convertOne (c:cs)
    return $ text "[" <> joincits cits <> text "]"
  where
        joincits = hcat . intersperse (text "; ") . filter (not . isEmpty)
        convertOne Citation { citationId      = k
                            , citationPrefix  = pinlines
                            , citationSuffix  = sinlines
                            , citationMode    = m }
                               = do
           pdoc <- inlineListToMarkdown opts pinlines
           sdoc <- inlineListToMarkdown opts sinlines
           let k' = text (modekey m ++ "@" ++ k)
               r = case sinlines of
                        Str (y:_):_ | y `elem` ",;]@" -> k' <> sdoc
                        _                             -> k' <+> sdoc
           return $ pdoc <+> r
        modekey SuppressAuthor = "-"
        modekey _              = ""
inlineToMarkdown _ (Cite _ _) = return $ text ""
inlineToMarkdown opts (Link txt (src, tit)) = do
  linktext <- inlineListToMarkdown opts txt
  let linktitle = if null tit
                     then empty
                     else text $ " \"" ++ tit ++ "\""
  let srcSuffix = if isPrefixOf "mailto:" src then drop 7 src else src
  let useAuto = case (tit,txt) of
                      ("", [Code _ s]) | s == srcSuffix -> True
                      _                                 -> False
  let useRefLinks = writerReferenceLinks opts && not useAuto
  ref <- if useRefLinks then getReference txt (src, tit) else return []
  reftext <- inlineListToMarkdown opts ref
  return $ if useAuto
              then "<" <> text srcSuffix <> ">"
              else if useRefLinks
                      then let first  = "[" <> linktext <> "]"
                               second = if txt == ref
                                           then "[]"
                                           else "[" <> reftext <> "]"
                           in  first <> second
                      else "[" <> linktext <> "](" <>
                           text src <> linktitle <> ")"
inlineToMarkdown opts (Image alternate (source, tit)) = do
  let txt = if null alternate || alternate == [Str source]
                                 -- to prevent autolinks
               then [Str ""]
               else alternate
  linkPart <- inlineToMarkdown opts (Link txt (source, tit))
  return $ "!" <> linkPart
inlineToMarkdown opts (Note contents) = do
  modify (\st -> st{ stNotes = contents : stNotes st })
  st <- get
  let ref = show $ (length $ stNotes st)
  if isEnabled Ext_footnotes opts
     then return $ "[^" <> text ref <> "]"
     else return $ "[" <> text ref <> "]"