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

{-# LANGUAGE OverloadedStrings #-}
{-# OPTIONS_GHC -fno-warn-deprecations #-}
{-
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.HTML
   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 HTML.
-}
module Text.Pandoc.Writers.HTML ( writeHtml , writeHtmlString ) where
import Text.Pandoc.Definition
import Text.Pandoc.CharacterReferences ( decodeCharacterReferences )
import Text.Pandoc.Shared
import Text.Pandoc.Templates
import Text.Pandoc.Readers.TeXMath
import Text.Pandoc.Highlighting ( highlight, pygments, styleToHtml,
                                  formatHtmlInline, formatHtmlBlock )
import Text.Pandoc.XML (stripTags, escapeStringForXML)
import Network.HTTP ( urlEncode )
import Numeric ( showHex )
import Data.Char ( ord, toLower )
import Data.List ( isPrefixOf, intersperse )
import Data.String ( fromString )
import Data.Maybe ( catMaybes )
import Control.Monad.State
import Text.Blaze
import qualified Text.Blaze.Html5 as H5
import qualified Text.Blaze.XHtml1.Transitional as H
import qualified Text.Blaze.XHtml1.Transitional.Attributes as A
import Text.Blaze.Renderer.String (renderHtml)
import Text.TeXMath
import Text.XML.Light.Output
import System.FilePath (takeExtension)
import Data.Monoid (mempty, mconcat)

data WriterState = WriterState
    { stNotes            :: [Html]  -- ^ List of notes
    , stMath             :: Bool    -- ^ Math is used in document
    , stHighlighting     :: Bool    -- ^ Syntax highlighting is used
    , stSecNum           :: [Int]   -- ^ Number of current section
    }

defaultWriterState :: WriterState
defaultWriterState = WriterState {stNotes= [], stMath = False, stHighlighting = False, stSecNum = []}

-- Helpers to render HTML with the appropriate function.

strToHtml :: String -> Html
strToHtml = preEscapedString . escapeStringForXML
-- strToHtml = toHtml

-- | Hard linebreak.
nl :: WriterOptions -> Html
nl opts = if writerWrapText opts
             then preEscapedString "\n"
             else mempty

-- | Convert Pandoc document to Html string.
writeHtmlString :: WriterOptions -> Pandoc -> String
writeHtmlString opts d =
  let (tit, auths, date, toc, body', newvars) = evalState (pandocToHtml opts d)
                                                 defaultWriterState
  in  if writerStandalone opts
         then inTemplate opts tit auths date toc body' newvars
         else renderHtml body'

-- | Convert Pandoc document to Html structure.
writeHtml :: WriterOptions -> Pandoc -> Html
writeHtml opts d =
  let (tit, auths, date, toc, body', newvars) = evalState (pandocToHtml opts d)
                                                 defaultWriterState
  in  if writerStandalone opts
         then inTemplate opts tit auths date toc body' newvars
         else body'

-- result is (title, authors, date, toc, body, new variables)
pandocToHtml :: WriterOptions
             -> Pandoc
             -> State WriterState (Html, [Html], Html, Maybe Html, Html, [(String,String)])
pandocToHtml opts (Pandoc (Meta title' authors' date') blocks) = do
  let standalone = writerStandalone opts
  tit <- if standalone
            then inlineListToHtml opts title'
            else return mempty
  auths <- if standalone
              then mapM (inlineListToHtml opts) authors'
              else return []
  date <- if standalone
             then inlineListToHtml opts date'
             else return mempty
  let splitHrule (HorizontalRule : Header 1 xs : ys)
                                       = Header 1 xs : splitHrule ys
      splitHrule (HorizontalRule : xs) = Header 1 [] : splitHrule xs
      splitHrule (x : xs)              = x : splitHrule xs
      splitHrule []                    = []
  let ensureStartWithH1 bs@(Header 1 _:_) = bs
      ensureStartWithH1 bs                = Header 1 [] : bs
  let sects = hierarchicalize $
              if writerSlideVariant opts == NoSlides
                 then blocks
                 else ensureStartWithH1 $ splitHrule blocks
  toc <- if writerTableOfContents opts
            then tableOfContents opts sects
            else return Nothing
  blocks' <- liftM (mconcat . intersperse (nl opts)) $
                 mapM (elementToHtml opts) sects
  st <- get
  let notes = reverse (stNotes st)
  let thebody = blocks' >> footnoteSection opts notes
  let  math = if stMath st
                then case writerHTMLMathMethod opts of
                           LaTeXMathML (Just url) ->
                              H.script ! A.src (toValue url)
                                       ! A.type_ "text/javascript"
                                       $ mempty
                           MathML (Just url) ->
                              H.script ! A.src (toValue url)
                                       ! A.type_ "text/javascript"
                                       $ mempty
                           MathJax url ->
                              H.script ! A.src (toValue url)
                                       ! A.type_ "text/javascript"
                                       $ mempty
                           JsMath (Just url) ->
                              H.script ! A.src (toValue url)
                                       ! A.type_ "text/javascript"
                                       $ mempty
                           _ -> case lookup "mathml-script" (writerVariables opts) of
                                      Just s ->
                                        H.script ! A.type_ "text/javascript"
                                           $ preEscapedString
                                            ("/*<![CDATA[*/\n" ++ s ++ "/*]]>*/\n")
                                      Nothing -> mempty
                else mempty
  let newvars = [("highlighting-css", renderHtml $ styleToHtml pygments) |
                   stHighlighting st] ++
                [("math", renderHtml math) | stMath st]
  return (tit, auths, date, toc, thebody, newvars)

inTemplate :: TemplateTarget a
           => WriterOptions
           -> Html
           -> [Html]
           -> Html
           -> Maybe Html
           -> Html
           -> [(String,String)]
           -> a
inTemplate opts tit auths date toc body' newvars =
  let title'      = renderHtml tit
      authors     = map renderHtml auths
      date'       = renderHtml date
      variables   = writerVariables opts ++ newvars
      context     = variables ++
                    [ ("body", dropWhile (=='\n') $ renderHtml body')
                    , ("pagetitle", stripTags title')
                    , ("title", title')
                    , ("date", date')
                    , ("date-meta", stripTags date')
                    , ("idprefix", writerIdentifierPrefix opts)
                    , ("slidy-url", "http://www.w3.org/Talks/Tools/Slidy2")
                    , ("s5-url", "s5/default") ] ++
                    [ ("html5","true") | writerHtml5 opts ] ++
                    (case toc of
                         Just t  -> [ ("toc", renderHtml t)]
                         Nothing -> [])  ++
                    [ ("author", a) | a <- authors ] ++
                    [ ("author-meta", stripTags a) | a <- authors ]
  in  renderTemplate context $ writerTemplate opts

-- | Like Text.XHtml's identifier, but adds the writerIdentifierPrefix
prefixedId :: WriterOptions -> String -> Attribute
prefixedId opts s = A.id $ toValue $ writerIdentifierPrefix opts ++ s

-- | Replacement for Text.XHtml's unordList.
unordList :: WriterOptions -> ([Html] -> Html)
unordList opts items = H.ul $ mconcat $ toListItems opts items

-- | Replacement for Text.XHtml's ordList.
ordList :: WriterOptions -> ([Html] -> Html)
ordList opts items = H.ol $ mconcat $ toListItems opts items

-- | Construct table of contents from list of elements.
tableOfContents :: WriterOptions -> [Element] -> State WriterState (Maybe Html)
tableOfContents _ [] = return Nothing
tableOfContents opts sects = do
  let opts'        = opts { writerIgnoreNotes = True }
  contents  <- mapM (elementToListItem opts') sects
  let tocList = catMaybes contents
  return $ if null tocList
              then Nothing
              else Just $ unordList opts tocList

-- | Convert section number to string
showSecNum :: [Int] -> String
showSecNum = concat . intersperse "." . map show

-- | Converts an Element to a list item for a table of contents,
-- retrieving the appropriate identifier from state.
elementToListItem :: WriterOptions -> Element -> State WriterState (Maybe Html)
elementToListItem _ (Blk _) = return Nothing
elementToListItem opts (Sec _ num id' headerText subsecs) = do
  let sectnum = if writerNumberSections opts
                   then (H.span ! A.class_ "toc-section-number" $ toHtml $ showSecNum num) >>
                     preEscapedString " "
                   else mempty
  txt <- liftM (sectnum >>) $ inlineListToHtml opts headerText
  subHeads <- mapM (elementToListItem opts) subsecs >>= return . catMaybes
  let subList = if null subHeads
                   then mempty
                   else unordList opts subHeads
  return $ Just $ (H.a ! A.href (toValue $ "#" ++ writerIdentifierPrefix opts ++ id')
                       $ toHtml txt) >> subList

-- | Convert an Element to Html.
elementToHtml :: WriterOptions -> Element -> State WriterState Html
elementToHtml opts (Blk block) = blockToHtml opts block
elementToHtml opts (Sec level num id' title' elements) = do
  modify $ \st -> st{stSecNum = num}  -- update section number
  header' <- blockToHtml opts (Header level title')
  innerContents <- mapM (elementToHtml opts) elements
  let header'' = if (writerStrictMarkdown opts ||
                     writerSectionDivs opts ||
                     writerSlideVariant opts == S5Slides)
                    then header'
                    else header' ! prefixedId opts id'
  let stuff = header'' : innerContents
  let slide = writerSlideVariant opts /= NoSlides && level == 1
  let titleSlide = slide && null elements
  let classes = ["titleslide" | titleSlide] ++ ["slide" | slide] ++
                  ["level" ++ show level]
  let inNl x = mconcat $ nl opts : intersperse (nl opts) x ++ [nl opts]
  let secttag  = if writerHtml5 opts
                    then H5.section ! A.class_ (toValue $ unwords classes)
                    else H.div ! A.class_ (toValue $ unwords ("section":classes))
  return $ if writerSectionDivs opts || slide
              then secttag ! prefixedId opts id' $ inNl stuff
              else mconcat $ intersperse (nl opts) stuff

-- | Convert list of Note blocks to a footnote <div>.
-- Assumes notes are sorted.
footnoteSection :: WriterOptions -> [Html] -> Html
footnoteSection opts notes =
  if null notes
     then mempty
     else nl opts >> (container
          $ nl opts >> H.hr >> nl opts >>
            H.ol (mconcat notes >> nl opts) >> nl opts)
   where container x = if writerHtml5 opts
                          then H5.section ! A.class_ "footnotes" $ x
                          else if writerSlideVariant opts /= NoSlides
                               then H.div ! A.class_ "footnotes slide" $ x
                               else H.div ! A.class_ "footnotes" $ x

-- | Parse a mailto link; return Just (name, domain) or Nothing.
parseMailto :: String -> Maybe (String, String)
parseMailto ('m':'a':'i':'l':'t':'o':':':addr) =
  let (name', rest) = span (/='@') addr
      domain = drop 1 rest
  in  Just (name', domain)
parseMailto _ = Nothing

-- | Obfuscate a "mailto:" link.
obfuscateLink :: WriterOptions -> String -> String -> Html
obfuscateLink opts txt s | writerEmailObfuscation opts == NoObfuscation =
  H.a ! A.href (toValue s) $ toHtml txt
obfuscateLink opts txt s =
  let meth = writerEmailObfuscation opts
      s' = map toLower s
  in  case parseMailto s' of
        (Just (name', domain)) ->
          let domain'  = substitute "." " dot " domain
              at'      = obfuscateChar '@'
              (linkText, altText) =
                 if txt == drop 7 s' -- autolink
                    then ("'<code>'+e+'</code>'", name' ++ " at " ++ domain')
                    else ("'" ++ txt ++ "'", txt ++ " (" ++ name' ++ " at " ++
                          domain' ++ ")")
          in  case meth of
                ReferenceObfuscation ->
                     -- need to use preEscapedString or &'s are escaped to &amp; in URL
                     preEscapedString $ "<a href=\"" ++ (obfuscateString s')
                     ++ "\">" ++ (obfuscateString txt) ++ "</a>"
                JavascriptObfuscation ->
                     (H.script ! A.type_ "text/javascript" $
                     preEscapedString ("\n<!--\nh='" ++
                     obfuscateString domain ++ "';a='" ++ at' ++ "';n='" ++
                     obfuscateString name' ++ "';e=n+a+h;\n" ++
                     "document.write('<a h'+'ref'+'=\"ma'+'ilto'+':'+e+'\">'+" ++
                     linkText  ++ "+'<\\/'+'a'+'>');\n// -->\n")) >>
                     H.noscript (preEscapedString $ obfuscateString altText)
                _ -> error $ "Unknown obfuscation method: " ++ show meth
        _ -> H.a ! A.href (toValue s) $ toHtml txt  -- malformed email

-- | Obfuscate character as entity.
obfuscateChar :: Char -> String
obfuscateChar char =
  let num    = ord char
      numstr = if even num then show num else "x" ++ showHex num ""
  in  "&#" ++ numstr ++ ";"

-- | Obfuscate string using entities.
obfuscateString :: String -> String
obfuscateString = concatMap obfuscateChar . decodeCharacterReferences

attrsToHtml :: WriterOptions -> Attr -> [Attribute]
attrsToHtml opts (id',classes',keyvals) =
  [A.class_ (toValue $ unwords classes') | not (null classes')] ++
  [prefixedId opts id' | not (null id')] ++
  map (\(x,y) -> customAttribute (fromString x) (toValue y)) keyvals

imageExts :: [String]
imageExts = [ "art", "bmp", "cdr", "cdt", "cpt", "cr2", "crw", "djvu", "erf",
              "gif", "ico", "ief", "jng", "jpg", "jpeg", "nef", "orf", "pat", "pbm",
              "pcx", "pgm", "png", "pnm", "ppm", "psd", "ras", "rgb", "svg", "tiff",
              "wbmp", "xbm", "xpm", "xwd" ]

treatAsImage :: FilePath -> Bool
treatAsImage fp =
  let ext = map toLower $ drop 1 $ takeExtension fp
  in  null ext || ext `elem` imageExts

-- | Convert Pandoc block element to HTML.
blockToHtml :: WriterOptions -> Block -> State WriterState Html
blockToHtml _ Null = return mempty
blockToHtml opts (Plain lst) = inlineListToHtml opts lst
blockToHtml opts (Para [Image txt (s,tit)]) = do
  img <- inlineToHtml opts (Image txt (s,tit))
  capt <- inlineListToHtml opts txt
  return $ if writerHtml5 opts
              then H5.figure $ mconcat
                    [nl opts, img, H5.figcaption capt, nl opts]
              else H.div ! A.class_ "figure" $ mconcat
                    [nl opts, img, H.p ! A.class_ "caption" $ capt,
                    nl opts]
blockToHtml opts (Para lst) = do
  contents <- inlineListToHtml opts lst
  return $ H.p contents
blockToHtml _ (RawBlock "html" str) = return $ preEscapedString str
blockToHtml _ (RawBlock _ _) = return mempty
blockToHtml _ (HorizontalRule) = return H.hr
blockToHtml opts (CodeBlock (id',classes,keyvals) rawCode) = do
  let tolhs = writerLiterateHaskell opts &&
                any (\c -> map toLower c == "haskell") classes &&
                any (\c -> map toLower c == "literate") classes
      classes' = if tolhs
                    then map (\c -> if map toLower c == "haskell"
                                       then "literatehaskell"
                                       else c) classes
                    else filter (/= "literate") classes
      adjCode  = if tolhs
                    then unlines . map ("> " ++) . lines $ rawCode
                    else rawCode
  case highlight formatHtmlBlock (id',classes,keyvals) adjCode of
         Nothing -> let attrs = attrsToHtml opts (id', classes', keyvals)
                    in  return $ foldl (!) H.pre attrs $ H.code
                                         $ toHtml adjCode
         Just  h -> modify (\st -> st{ stHighlighting = True }) >>
                    return h
blockToHtml opts (BlockQuote blocks) =
  -- in S5, treat list in blockquote specially
  -- if default is incremental, make it nonincremental;
  -- otherwise incremental
  if writerSlideVariant opts /= NoSlides
     then let inc = not (writerIncremental opts) in
          case blocks of
             [BulletList lst]  -> blockToHtml (opts {writerIncremental = inc})
                                  (BulletList lst)
             [OrderedList attribs lst] ->
                                  blockToHtml (opts {writerIncremental = inc})
                                  (OrderedList attribs lst)
             _                 -> do contents <- blockListToHtml opts blocks
                                     return $ H.blockquote
                                            $ nl opts >> contents >> nl opts
     else do
       contents <- blockListToHtml opts blocks
       return $ H.blockquote $ nl opts >> contents >> nl opts
blockToHtml opts (Header level lst) = do
  contents <- inlineListToHtml opts lst
  secnum <- liftM stSecNum get
  let contents' = if writerNumberSections opts
                     then (H.span ! A.class_ "header-section-number" $ toHtml $ showSecNum secnum) >>
                            strToHtml " " >> contents
                     else contents
  let contents''  = if writerTableOfContents opts
                       then H.a ! A.href (toValue $ "#" ++ writerIdentifierPrefix opts ++ "TOC") $ contents'
                       else contents'
  return $ (case level of
              1 -> H.h1 contents''
              2 -> H.h2 contents''
              3 -> H.h3 contents''
              4 -> H.h4 contents''
              5 -> H.h5 contents''
              6 -> H.h6 contents''
              _ -> H.p contents'')
blockToHtml opts (BulletList lst) = do
  contents <- mapM (blockListToHtml opts) lst
  let lst' = unordList opts contents
  let lst'' = if writerIncremental opts
                 then lst' ! A.class_ "incremental"
                 else lst'
  return lst''
blockToHtml opts (OrderedList (startnum, numstyle, _) lst) = do
  contents <- mapM (blockListToHtml opts) lst
  let numstyle' = camelCaseToHyphenated $ show numstyle
  let attribs = (if writerIncremental opts
                   then [A.class_ "incremental"]
                   else []) ++
                (if startnum /= 1
                   then [A.start $ toValue startnum]
                   else []) ++
                (if numstyle /= DefaultStyle
                   then if writerHtml5 opts
                           then [A.type_ $
                                 case numstyle of
                                      Decimal    -> "1"
                                      LowerAlpha -> "a"
                                      UpperAlpha -> "A"
                                      LowerRoman -> "i"
                                      UpperRoman -> "I"
                                      _          -> "1"]
                           else [A.style $ toValue $ "list-style-type: " ++
                                   numstyle']
                   else [])
  return $ foldl (!) (ordList opts contents) attribs
blockToHtml opts (DefinitionList lst) = do
  contents <- mapM (\(term, defs) ->
                  do term' <- liftM (H.dt) $ inlineListToHtml opts term
                     defs' <- mapM ((liftM (\x -> H.dd $ (x >> nl opts))) .
                                    blockListToHtml opts) defs
                     return $ mconcat $ nl opts : term' : nl opts : defs') lst
  let lst' = H.dl $ mconcat contents >> nl opts
  let lst'' = if writerIncremental opts
                 then lst' ! A.class_ "incremental"
                 else lst'
  return lst''
blockToHtml opts (Table capt aligns widths headers rows') = do
  captionDoc <- if null capt
                   then return mempty
                   else do
                     cs <- inlineListToHtml opts capt
                     return $ H.caption cs >> nl opts
  let percent w = show (truncate (100*w) :: Integer) ++ "%"
  let coltags = if all (== 0.0) widths
                   then mempty
                   else mconcat $ map (\w ->
                          if writerHtml5 opts
                             then H.col ! A.style (toValue $ "width: " ++ percent w)
                             else H.col ! A.width (toValue $ percent w) >> nl opts)
                          widths
  head' <- if all null headers
              then return mempty
              else do
                contents <- tableRowToHtml opts aligns 0 headers
                return $ H.thead (nl opts >> contents) >> nl opts
  body' <- liftM (\x -> H.tbody (nl opts >> mconcat x)) $
               zipWithM (tableRowToHtml opts aligns) [1..] rows'
  return $ H.table $ nl opts >> captionDoc >> coltags >> head' >>
                   body' >> nl opts

tableRowToHtml :: WriterOptions
               -> [Alignment]
               -> Int
               -> [[Block]]
               -> State WriterState Html
tableRowToHtml opts aligns rownum cols' = do
  let mkcell = if rownum == 0 then H.th else H.td
  let rowclass = case rownum of
                      0                  -> "header"
                      x | x `rem` 2 == 1 -> "odd"
                      _                  -> "even"
  cols'' <- sequence $ zipWith
            (\alignment item -> tableItemToHtml opts mkcell alignment item)
            aligns cols'
  return $ (H.tr ! A.class_ rowclass $ nl opts >> mconcat cols'')
          >> nl opts

alignmentToString :: Alignment -> [Char]
alignmentToString alignment = case alignment of
                                 AlignLeft    -> "left"
                                 AlignRight   -> "right"
                                 AlignCenter  -> "center"
                                 AlignDefault -> "left"

tableItemToHtml :: WriterOptions
                -> (Html -> Html)
                -> Alignment
                -> [Block]
                -> State WriterState Html
tableItemToHtml opts tag' align' item = do
  contents <- blockListToHtml opts item
  let alignStr = alignmentToString align'
  let attribs = if writerHtml5 opts
                   then A.style (toValue $ "text-align: " ++ alignStr ++ ";")
                   else A.align (toValue alignStr)
  return $ (tag' ! attribs $ contents) >> nl opts

toListItems :: WriterOptions -> [Html] -> [Html]
toListItems opts items = map (toListItem opts) items ++ [nl opts]

toListItem :: WriterOptions -> Html -> Html
toListItem opts item = nl opts >> H.li item

blockListToHtml :: WriterOptions -> [Block] -> State WriterState Html
blockListToHtml opts lst =
  mapM (blockToHtml opts) lst >>=
  return . mconcat . intersperse (nl opts)

-- | Convert list of Pandoc inline elements to HTML.
inlineListToHtml :: WriterOptions -> [Inline] -> State WriterState Html
inlineListToHtml opts lst =
  mapM (inlineToHtml opts) lst >>= return . mconcat

-- | Convert Pandoc inline element to HTML.
inlineToHtml :: WriterOptions -> Inline -> State WriterState Html
inlineToHtml opts inline =
  case inline of
    (Str str)        -> return $ strToHtml str
    (Space)          -> return $ strToHtml " "
    (LineBreak)      -> return H.br
    (EmDash)         -> return $ strToHtml "—"
    (EnDash)         -> return $ strToHtml "–"
    (Ellipses)       -> return $ strToHtml "…"
    (Apostrophe)     -> return $ strToHtml "’"
    (Emph lst)       -> inlineListToHtml opts lst >>= return . H.em
    (Strong lst)     -> inlineListToHtml opts lst >>= return . H.strong
    (Code attr str)  -> case highlight formatHtmlInline attr str of
                             Nothing -> return
                                        $ foldl (!) H.code (attrsToHtml opts attr)
                                        $ strToHtml str
                             Just  h -> return h
    (Strikeout lst)  -> inlineListToHtml opts lst >>=
                        return . H.del
    (SmallCaps lst)   -> inlineListToHtml opts lst >>=
                         return . (H.span ! A.style "font-variant: small-caps;")
    (Superscript lst) -> inlineListToHtml opts lst >>= return . H.sup
    (Subscript lst)   -> inlineListToHtml opts lst >>= return . H.sub
    (Quoted quoteType lst) ->
                        let (leftQuote, rightQuote) = case quoteType of
                              SingleQuote -> (strToHtml "‘",
                                              strToHtml "’")
                              DoubleQuote -> (strToHtml "“",
                                              strToHtml "”")
                        in  do contents <- inlineListToHtml opts lst
                               return $ leftQuote >> contents >> rightQuote
    (Math t str) ->     modify (\st -> st {stMath = True}) >>
                        (case writerHTMLMathMethod opts of
                               LaTeXMathML _ ->
                                  -- putting LaTeXMathML in container with class "LaTeX" prevents
                                  -- non-math elements on the page from being treated as math by
                                  -- the javascript
                                  return $ H.span ! A.class_ "LaTeX" $
                                         case t of
                                           InlineMath  -> toHtml ("$" ++ str ++ "$")
                                           DisplayMath -> toHtml ("$$" ++ str ++ "$$")
                               JsMath _ -> do
                                  let m = preEscapedString str
                                  return $ case t of
                                           InlineMath -> H.span ! A.class_ "math" $ m
                                           DisplayMath -> H.div ! A.class_ "math" $ m
                               WebTeX url -> do
                                  let m = H.img ! A.style "vertical-align:middle"
                                                ! A.src (toValue $ url ++ urlEncode str)
                                                ! A.alt (toValue str)
                                                ! A.title (toValue str)
                                  return $ case t of
                                            InlineMath  -> m
                                            DisplayMath -> H.br >> m >> H.br
                               GladTeX ->
                                  return $ case t of
                                             InlineMath -> preEscapedString "<EQ ENV=\"math\">" >> toHtml str >> preEscapedString "</EQ>"
                                             DisplayMath -> preEscapedString "<EQ ENV=\"displaymath\">" >> toHtml str >> preEscapedString "</EQ>"
                               MathML _ -> do
                                  let dt = if t == InlineMath
                                              then DisplayInline
                                              else DisplayBlock
                                  let conf = useShortEmptyTags (const False)
                                               defaultConfigPP
                                  case texMathToMathML dt str of
                                        Right r -> return $ preEscapedString $
                                                    ppcElement conf r
                                        Left  _ -> inlineListToHtml opts
                                                   (readTeXMath str) >>= return .
                                                     (H.span ! A.class_ "math")
                               MathJax _ -> return $ toHtml $
                                  case t of
                                    InlineMath  -> "\\(" ++ str ++ "\\)"
                                    DisplayMath -> "\\[" ++ str ++ "\\]"
                               PlainMath -> do
                                  x <- inlineListToHtml opts (readTeXMath str)
                                  let m = H.span ! A.class_ "math" $ x
                                  return  $ case t of
                                             InlineMath  -> m
                                             DisplayMath -> H.br >> m >> H.br )
    (RawInline "latex" str) -> case writerHTMLMathMethod opts of
                               LaTeXMathML _ -> do modify (\st -> st {stMath = True})
                                                   return $ toHtml str
                               _             -> return mempty
    (RawInline "html" str) -> return $ preEscapedString str
    (RawInline _ _) -> return mempty
    (Link [Code _ str] (s,_)) | "mailto:" `isPrefixOf` s ->
                        return $ obfuscateLink opts str s
    (Link txt (s,_)) | "mailto:" `isPrefixOf` s -> do
                        linkText <- inlineListToHtml opts txt
                        return $ obfuscateLink opts (renderHtml linkText) s
    (Link txt (s,tit)) -> do
                        linkText <- inlineListToHtml opts txt
                        let link = H.a ! A.href (toValue s) $ linkText
                        return $ if null tit
                                    then link
                                    else link ! A.title (toValue tit)
    (Image txt (s,tit)) | treatAsImage s -> do
                        let alternate' = stringify txt
                        let attributes = [A.src $ toValue s] ++
                                         (if null tit
                                            then []
                                            else [A.title $ toValue tit]) ++
                                         if null txt
                                            then []
                                            else [A.alt $ toValue alternate']
                        return $ foldl (!) H.img attributes
                        -- note:  null title included, as in Markdown.pl
    (Image _ (s,tit)) -> do
                        let attributes = [A.src $ toValue s] ++
                                         (if null tit
                                            then []
                                            else [A.title $ toValue tit])
                        return $ foldl (!) H5.embed attributes
                        -- note:  null title included, as in Markdown.pl
    (Note contents)          -> do
                        st <- get
                        let notes = stNotes st
                        let number = (length notes) + 1
                        let ref = show number
                        htmlContents <- blockListToNote opts ref contents
                        -- push contents onto front of notes
                        put $ st {stNotes = (htmlContents:notes)}
                        return $ H.sup $
                                 H.a ! A.href (toValue $ "#" ++ writerIdentifierPrefix opts ++ "fn" ++ ref)
                                     ! A.class_ "footnoteRef"
                                     ! prefixedId opts ("fnref" ++ ref)
                                     $ toHtml ref
    (Cite _ il)  -> do contents <- inlineListToHtml opts il
                       return $ H.span ! A.class_ "citation" $ contents

blockListToNote :: WriterOptions -> String -> [Block] -> State WriterState Html
blockListToNote opts ref blocks =
  -- If last block is Para or Plain, include the backlink at the end of
  -- that block. Otherwise, insert a new Plain block with the backlink.
  let backlink = [RawInline "html" $ " <a href=\"#" ++ writerIdentifierPrefix opts ++ "fnref" ++ ref ++
                 "\" class=\"footnoteBackLink\">↩</a>"]
      blocks'  = if null blocks
                    then []
                    else let lastBlock   = last blocks
                             otherBlocks = init blocks
                         in  case lastBlock of
                                  (Para lst)  -> otherBlocks ++
                                                 [Para (lst ++ backlink)]
                                  (Plain lst) -> otherBlocks ++
                                                 [Plain (lst ++ backlink)]
                                  _           -> otherBlocks ++ [lastBlock,
                                                 Plain backlink]
  in  do contents <- blockListToHtml opts blocks'
         return $ nl opts >> (H.li ! (prefixedId opts ("fn" ++ ref)) $ contents)