Powerpoint writer: Refactor into separate modules.

There are two steps in the conversion: a conversion from pandoc to a
Presentation datatype modeling pptx, and a conversion from
Presentation to a pptx archive. The two steps were sharing the same
state and environment, and the code was getting a bit
spaghetti-ish. This separates the conversion into separate
modules (T.P.W.Powerpoint.Presentation, which defineds the
Presentation datatype and goes Pandoc->Presentation)
and (T.P.W.Pandoc.Output, which goes Presentation->Archive).
Text.Pandoc.Writers.Powerpoint a thin wrapper around the two modules.

pandoc.cabal

@@ -527,6 +527,8 @@ library
                    Text.Pandoc.Readers.Org.ParserState,
                    Text.Pandoc.Readers.Org.Parsing,
                    Text.Pandoc.Readers.Org.Shared,
+                   Text.Pandoc.Writers.Powerpoint.Presentation,
+                   Text.Pandoc.Writers.Powerpoint.Output,
                    Text.Pandoc.Lua.Filter,
                    Text.Pandoc.Lua.Init,
                    Text.Pandoc.Lua.Module.MediaBag,

src/Text/Pandoc/Writers/Powerpoint/Presentation.hs

@@ -0,0 +1,701 @@
+{-# LANGUAGE PatternGuards #-}
+
+{-
+Copyright (C) 2017-2018 Jesse Rosenthal <jrosenthal@jhu.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.Powerpoint.Presentation
+   Copyright   : Copyright (C) 2017-2018 Jesse Rosenthal
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Jesse Rosenthal <jrosenthal@jhu.edu>
+   Stability   : alpha
+   Portability : portable
+
+Definition of Presentation datatype, modeling a MS Powerpoint (pptx)
+document, and functions for converting a Pandoc document to
+Presentation.
+-}
+
+module Text.Pandoc.Writers.Powerpoint.Presentation ( documentToPresentation
+                                                   , Presentation(..)
+                                                   , Slide(..)
+                                                   , SlideElement(..)
+                                                   , Shape(..)
+                                                   , Graphic(..)
+                                                   , BulletType(..)
+                                                   , Algnment(..)
+                                                   , Paragraph(..)
+                                                   , ParaElem(..)
+                                                   , ParaProps(..)
+                                                   , RunProps(..)
+                                                   , TableProps(..)
+                                                   , Strikethrough(..)
+                                                   , Capitals(..)
+                                                   , PicProps(..)
+                                                   , URL
+                                                   , TeXString(..)
+                                                   ) where
+
+
+import Control.Monad.Reader
+import Control.Monad.State
+import Data.List (intercalate)
+import Data.Default
+import Text.Pandoc.Definition
+import Text.Pandoc.Class (PandocMonad)
+import Text.Pandoc.Slides (getSlideLevel)
+import qualified Text.Pandoc.Class as P
+import Text.Pandoc.Options
+import Text.Pandoc.Logging
+import Text.Pandoc.Walk
+import qualified Text.Pandoc.Shared as Shared -- so we don't overlap "Element"
+import Text.Pandoc.Writers.Shared (metaValueToInlines)
+import qualified Data.Map as M
+import Data.Maybe (maybeToList)
+
+data WriterEnv = WriterEnv { envMetadata :: Meta
+                           , envRunProps :: RunProps
+                           , envParaProps :: ParaProps
+                           , envSlideLevel :: Int
+                           , envOpts :: WriterOptions
+                           , envSlideHasHeader :: Bool
+                           , envInList :: Bool
+                           , envInNoteSlide :: Bool
+                           , envCurSlideId :: Int
+                           -- the difference between the number at
+                           -- the end of the slide file name and
+                           -- the rId number
+                           , envSlideIdOffset :: Int
+                           }
+                 deriving (Show)
+
+instance Default WriterEnv where
+  def = WriterEnv { envMetadata = mempty
+                  , envRunProps = def
+                  , envParaProps = def
+                  , envSlideLevel = 2
+                  , envOpts = def
+                  , envSlideHasHeader = False
+                  , envInList = False
+                  , envInNoteSlide = False
+                  , envCurSlideId = 1
+                  , envSlideIdOffset = 1
+                  }
+
+
+data WriterState = WriterState { stNoteIds :: M.Map Int [Block]
+                               -- associate anchors with slide id
+                               , stAnchorMap :: M.Map String Int
+                               } deriving (Show, Eq)
+
+instance Default WriterState where
+  def = WriterState { stNoteIds = mempty
+                    , stAnchorMap= mempty
+                    }
+
+type Pres m = ReaderT WriterEnv (StateT WriterState m)
+
+runPres :: Monad m => WriterEnv -> WriterState -> Pres m a -> m a
+runPres env st p = evalStateT (runReaderT p env) st
+
+-- GHC 7.8 will still complain about concat <$> mapM unless we specify
+-- Functor. We can get rid of this when we stop supporting GHC 7.8.
+concatMapM        :: (Monad m) => (a -> m [b]) -> [a] -> m [b]
+concatMapM f xs   =  liftM concat (mapM f xs)
+
+type Pixels = Integer
+
+data Presentation = Presentation [Slide]
+  deriving (Show)
+
+data Slide = MetadataSlide { metadataSlideTitle :: [ParaElem]
+                            , metadataSlideSubtitle :: [ParaElem]
+                            , metadataSlideAuthors :: [[ParaElem]]
+                            , metadataSlideDate :: [ParaElem]
+                            }
+           | TitleSlide { titleSlideHeader :: [ParaElem]}
+           | ContentSlide { contentSlideHeader :: [ParaElem]
+                          , contentSlideContent :: [Shape]
+                          }
+           | TwoColumnSlide { twoColumnSlideHeader :: [ParaElem]
+                            , twoColumnSlideLeft   :: [Shape]
+                            , twoColumnSlideRight  :: [Shape]
+                            }
+           deriving (Show, Eq)
+
+data SlideElement = SlideElement Pixels Pixels Pixels Pixels Shape
+  deriving (Show, Eq)
+
+data Shape = Pic PicProps FilePath Text.Pandoc.Definition.Attr [ParaElem]
+           | GraphicFrame [Graphic] [ParaElem]
+           | TextBox [Paragraph]
+  deriving (Show, Eq)
+
+type Cell = [Paragraph]
+
+data TableProps = TableProps { tblPrFirstRow :: Bool
+                             , tblPrBandRow :: Bool
+                             } deriving (Show, Eq)
+
+data Graphic = Tbl TableProps [Cell] [[Cell]]
+  deriving (Show, Eq)
+
+
+data Paragraph = Paragraph { paraProps :: ParaProps
+                           , paraElems  :: [ParaElem]
+                           } deriving (Show, Eq)
+
+
+data BulletType = Bullet
+                | AutoNumbering ListAttributes
+  deriving (Show, Eq)
+
+data Algnment = AlgnLeft | AlgnRight | AlgnCenter
+  deriving (Show, Eq)
+
+data ParaProps = ParaProps { pPropMarginLeft :: Maybe Pixels
+                           , pPropMarginRight :: Maybe Pixels
+                           , pPropLevel :: Int
+                           , pPropBullet :: Maybe BulletType
+                           , pPropAlign :: Maybe Algnment
+                           , pPropSpaceBefore :: Maybe Pixels
+                           } deriving (Show, Eq)
+
+instance Default ParaProps where
+  def = ParaProps { pPropMarginLeft = Just 0
+                  , pPropMarginRight = Just 0
+                  , pPropLevel = 0
+                  , pPropBullet = Nothing
+                  , pPropAlign = Nothing
+                  , pPropSpaceBefore = Nothing
+                  }
+
+newtype TeXString = TeXString {unTeXString :: String}
+  deriving (Eq, Show)
+
+data ParaElem = Break
+              | Run RunProps String
+              -- It would be more elegant to have native TeXMath
+              -- Expressions here, but this allows us to use
+              -- `convertmath` from T.P.Writers.Math. Will perhaps
+              -- revisit in the future.
+              | MathElem MathType TeXString
+              deriving (Show, Eq)
+
+data Strikethrough = NoStrike | SingleStrike | DoubleStrike
+  deriving (Show, Eq)
+
+data Capitals = NoCapitals | SmallCapitals | AllCapitals
+  deriving (Show, Eq)
+
+type URL = String
+
+data RunProps = RunProps { rPropBold :: Bool
+                         , rPropItalics :: Bool
+                         , rStrikethrough :: Maybe Strikethrough
+                         , rBaseline :: Maybe Int
+                         , rCap :: Maybe Capitals
+                         , rLink :: Maybe (URL, String)
+                         , rPropCode :: Bool
+                         , rPropBlockQuote :: Bool
+                         , rPropForceSize :: Maybe Pixels
+                         } deriving (Show, Eq)
+
+instance Default RunProps where
+  def = RunProps { rPropBold = False
+                 , rPropItalics = False
+                 , rStrikethrough = Nothing
+                 , rBaseline = Nothing
+                 , rCap = Nothing
+                 , rLink = Nothing
+                 , rPropCode = False
+                 , rPropBlockQuote = False
+                 , rPropForceSize = Nothing
+                 }
+
+data PicProps = PicProps { picPropLink :: Maybe (URL, String)
+                         } deriving (Show, Eq)
+
+instance Default PicProps where
+  def = PicProps { picPropLink = Nothing
+                 }
+
+--------------------------------------------------
+
+inlinesToParElems :: Monad m => [Inline] -> Pres m [ParaElem]
+inlinesToParElems ils = concatMapM inlineToParElems ils
+
+inlineToParElems :: Monad m => Inline -> Pres m [ParaElem]
+inlineToParElems (Str s) = do
+  pr <- asks envRunProps
+  return [Run pr s]
+inlineToParElems (Emph ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rPropItalics=True}}) $
+  inlinesToParElems ils
+inlineToParElems (Strong ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rPropBold=True}}) $
+  inlinesToParElems ils
+inlineToParElems (Strikeout ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rStrikethrough=Just SingleStrike}}) $
+  inlinesToParElems ils
+inlineToParElems (Superscript ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rBaseline=Just 30000}}) $
+  inlinesToParElems ils
+inlineToParElems (Subscript ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rBaseline=Just (-25000)}}) $
+  inlinesToParElems ils
+inlineToParElems (SmallCaps ils) =
+  local (\r -> r{envRunProps = (envRunProps r){rCap = Just SmallCapitals}}) $
+  inlinesToParElems ils
+inlineToParElems Space = inlineToParElems (Str " ")
+inlineToParElems SoftBreak = inlineToParElems (Str " ")
+inlineToParElems LineBreak = return [Break]
+inlineToParElems (Link _ ils (url, title)) = do
+  local (\r ->r{envRunProps = (envRunProps r){rLink = Just (url, title)}}) $
+    inlinesToParElems ils
+inlineToParElems (Code _ str) = do
+  local (\r ->r{envRunProps = (envRunProps r){rPropCode = True}}) $
+    inlineToParElems $ Str str
+inlineToParElems (Math mathtype str) =
+  return [MathElem mathtype (TeXString str)]
+inlineToParElems (Note blks) = do
+  notes <- gets stNoteIds
+  let maxNoteId = case M.keys notes of
+        [] -> 0
+        lst -> maximum lst
+      curNoteId = maxNoteId + 1
+  modify $ \st -> st { stNoteIds = M.insert curNoteId blks notes }
+  inlineToParElems $ Superscript [Str $ show curNoteId]
+inlineToParElems (Span _ ils) = concatMapM inlineToParElems ils
+inlineToParElems (RawInline _ _) = return []
+inlineToParElems _ = return []
+
+isListType :: Block -> Bool
+isListType (OrderedList _ _) = True
+isListType (BulletList _) = True
+isListType (DefinitionList _) = True
+isListType _ = False
+
+registerAnchorId :: PandocMonad m => String -> Pres m ()
+registerAnchorId anchor = do
+  anchorMap <- gets stAnchorMap
+  slideId <- asks envCurSlideId
+  unless (null anchor) $
+    modify $ \st -> st {stAnchorMap = M.insert anchor slideId anchorMap}
+
+-- Currently hardcoded, until I figure out how to make it dynamic.
+blockQuoteSize :: Pixels
+blockQuoteSize = 20
+
+noteSize :: Pixels
+noteSize = 18
+
+blockToParagraphs :: PandocMonad m => Block -> Pres m [Paragraph]
+blockToParagraphs (Plain ils) = do
+  parElems <- inlinesToParElems ils
+  pProps <- asks envParaProps
+  return [Paragraph pProps parElems]
+blockToParagraphs (Para ils) = do
+  parElems <- inlinesToParElems ils
+  pProps <- asks envParaProps
+  return [Paragraph pProps parElems]
+blockToParagraphs (LineBlock ilsList) = do
+  parElems <- inlinesToParElems $ intercalate [LineBreak] ilsList
+  pProps <- asks envParaProps
+  return [Paragraph pProps parElems]
+-- TODO: work out the attributes
+blockToParagraphs (CodeBlock attr str) =
+  local (\r -> r{envParaProps = def{pPropMarginLeft = Just 100}}) $
+  blockToParagraphs $ Para [Code attr str]
+-- We can't yet do incremental lists, but we should render a
+-- (BlockQuote List) as a list to maintain compatibility with other
+-- formats.
+blockToParagraphs (BlockQuote (blk : blks)) | isListType blk = do
+  ps  <- blockToParagraphs blk
+  ps' <- blockToParagraphs $ BlockQuote blks
+  return $ ps ++ ps'
+blockToParagraphs (BlockQuote blks) =
+  local (\r -> r{ envParaProps = (envParaProps r){pPropMarginLeft = Just 100}
+                , envRunProps = (envRunProps r){rPropForceSize = Just blockQuoteSize}})$
+  concatMapM blockToParagraphs blks
+-- TODO: work out the format
+blockToParagraphs (RawBlock _ _) = return []
+blockToParagraphs (Header _ (ident, _, _) ils) = do
+  -- Note that this function only deals with content blocks, so it
+  -- will only touch headers that are above the current slide level --
+  -- slides at or below the slidelevel will be taken care of by
+  -- `blocksToSlide'`. We have the register anchors in both of them.
+  registerAnchorId ident
+  -- we set the subeader to bold
+  parElems <- local (\e->e{envRunProps = (envRunProps e){rPropBold=True}}) $
+              inlinesToParElems ils
+  -- and give it a bit of space before it.
+  return [Paragraph def{pPropSpaceBefore = Just 30} parElems]
+blockToParagraphs (BulletList blksLst) = do
+  pProps <- asks envParaProps
+  let lvl = pPropLevel pProps
+  local (\env -> env{ envInList = True
+                    , envParaProps = pProps{ pPropLevel = lvl + 1
+                                           , pPropBullet = Just Bullet
+                                           , pPropMarginLeft = Nothing
+                                           }}) $
+    concatMapM multiParBullet blksLst
+blockToParagraphs (OrderedList listAttr blksLst) = do
+  pProps <- asks envParaProps
+  let lvl = pPropLevel pProps
+  local (\env -> env{ envInList = True
+                    , envParaProps = pProps{ pPropLevel = lvl + 1
+                                           , pPropBullet = Just (AutoNumbering listAttr)
+                                           , pPropMarginLeft = Nothing
+                                           }}) $
+    concatMapM multiParBullet blksLst
+blockToParagraphs (DefinitionList entries) = do
+  let go :: PandocMonad m => ([Inline], [[Block]]) -> Pres m [Paragraph]
+      go (ils, blksLst) = do
+        term <-blockToParagraphs $ Para [Strong ils]
+        -- For now, we'll treat each definition term as a
+        -- blockquote. We can extend this further later.
+        definition <- concatMapM (blockToParagraphs . BlockQuote) blksLst
+        return $ term ++ definition
+  concatMapM go entries
+blockToParagraphs (Div (_, ("notes" : []), _) _) = return []
+blockToParagraphs (Div _ blks)  = concatMapM blockToParagraphs blks
+blockToParagraphs blk = do
+  P.report $ BlockNotRendered blk
+  return []
+
+-- Make sure the bullet env gets turned off after the first para.
+multiParBullet :: PandocMonad m => [Block] -> Pres m [Paragraph]
+multiParBullet [] = return []
+multiParBullet (b:bs) = do
+  pProps <- asks envParaProps
+  p <- blockToParagraphs b
+  ps <- local (\env -> env{envParaProps = pProps{pPropBullet = Nothing}}) $
+    concatMapM blockToParagraphs bs
+  return $ p ++ ps
+
+cellToParagraphs :: PandocMonad m => Alignment -> TableCell -> Pres m [Paragraph]
+cellToParagraphs algn tblCell = do
+  paras <- mapM (blockToParagraphs) tblCell
+  let alignment = case algn of
+        AlignLeft -> Just AlgnLeft
+        AlignRight -> Just AlgnRight
+        AlignCenter -> Just AlgnCenter
+        AlignDefault -> Nothing
+      paras' = map (map (\p -> p{paraProps = (paraProps p){pPropAlign = alignment}})) paras
+  return $ concat paras'
+
+rowToParagraphs :: PandocMonad m => [Alignment] -> [TableCell] -> Pres m [[Paragraph]]
+rowToParagraphs algns tblCells = do
+  -- We have to make sure we have the right number of alignments
+  let pairs = zip (algns ++ repeat AlignDefault) tblCells
+  mapM (\(a, tc) -> cellToParagraphs a tc) pairs
+
+blockToShape :: PandocMonad m => Block -> Pres m Shape
+blockToShape (Plain (il:_)) | Image attr ils (url, _) <- il =
+      Pic def url attr <$> (inlinesToParElems ils)
+blockToShape (Para (il:_))  | Image attr ils (url, _) <- il =
+      Pic def url attr <$> (inlinesToParElems ils)
+blockToShape (Plain (il:_)) | Link _ (il':_) target <- il
+                            , Image attr ils (url, _) <- il' =
+      Pic def{picPropLink = Just target} url attr <$> (inlinesToParElems ils)
+blockToShape (Para (il:_))  | Link _ (il':_) target <- il
+                            , Image attr ils (url, _) <- il' =
+      Pic def{picPropLink = Just target} url attr <$> (inlinesToParElems ils)
+blockToShape (Table caption algn _ hdrCells rows) = do
+  caption' <- inlinesToParElems caption
+  hdrCells' <- rowToParagraphs algn hdrCells
+  rows' <- mapM (rowToParagraphs algn) rows
+  let tblPr = if null hdrCells
+              then TableProps { tblPrFirstRow = False
+                              , tblPrBandRow = True
+                              }
+              else TableProps { tblPrFirstRow = True
+                              , tblPrBandRow = True
+                              }
+
+  return $ GraphicFrame [Tbl tblPr hdrCells' rows'] caption'
+blockToShape blk = do paras <- blockToParagraphs blk
+                      let paras' = map (\par -> par{paraElems = combineParaElems $ paraElems par}) paras
+                      return $ TextBox paras'
+
+combineShapes :: [Shape] -> [Shape]
+combineShapes [] = []
+combineShapes (s : []) = [s]
+combineShapes (pic@(Pic _ _ _ _) : ss) = pic : combineShapes ss
+combineShapes ((TextBox []) : ss) = combineShapes ss
+combineShapes (s : TextBox [] : ss) = combineShapes (s : ss)
+combineShapes ((TextBox (p:ps)) : (TextBox (p':ps')) : ss) =
+  combineShapes $ TextBox ((p:ps) ++ (p':ps')) : ss
+combineShapes (s:ss) = s : combineShapes ss
+
+blocksToShapes :: PandocMonad m => [Block] -> Pres m [Shape]
+blocksToShapes blks = combineShapes <$> mapM blockToShape blks
+
+isImage :: Inline -> Bool
+isImage (Image _ _ _) = True
+isImage (Link _ ((Image _ _ _) : _) _) = True
+isImage _ = False
+
+splitBlocks' :: Monad m => [Block] -> [[Block]] -> [Block] -> Pres m [[Block]]
+splitBlocks' cur acc [] = return $ acc ++ (if null cur then [] else [cur])
+splitBlocks' cur acc (HorizontalRule : blks) =
+  splitBlocks' [] (acc ++ (if null cur then [] else [cur])) blks
+splitBlocks' cur acc (h@(Header n _ _) : blks) = do
+  slideLevel <- asks envSlideLevel
+  case compare n slideLevel of
+    LT -> splitBlocks' [] (acc ++ (if null cur then [] else [cur]) ++ [[h]]) blks
+    EQ -> splitBlocks' [h] (acc ++ (if null cur then [] else [cur])) blks
+    GT -> splitBlocks' (cur ++ [h]) acc blks
+-- `blockToParagraphs` treats Plain and Para the same, so we can save
+-- some code duplication by treating them the same here.
+splitBlocks' cur acc ((Plain ils) : blks) = splitBlocks' cur acc ((Para ils) : blks)
+splitBlocks' cur acc ((Para (il:ils)) : blks) | isImage il = do
+  slideLevel <- asks envSlideLevel
+  case cur of
+    (Header n _ _) : [] | n == slideLevel ->
+                            splitBlocks' []
+                            (acc ++ [cur ++ [Para [il]]])
+                            (if null ils then blks else (Para ils) : blks)
+    _ -> splitBlocks' []
+         (acc ++ (if null cur then [] else [cur]) ++ [[Para [il]]])
+         (if null ils then blks else (Para ils) : blks)
+splitBlocks' cur acc (tbl@(Table _ _ _ _ _) : blks) = do
+  slideLevel <- asks envSlideLevel
+  case cur of
+    (Header n _ _) : [] | n == slideLevel ->
+                            splitBlocks' [] (acc ++ [cur ++ [tbl]]) blks
+    _ ->  splitBlocks' [] (acc ++ (if null cur then [] else [cur]) ++ [[tbl]]) blks
+splitBlocks' cur acc (d@(Div (_, classes, _) _): blks) | "columns" `elem` classes =  do
+  slideLevel <- asks envSlideLevel
+  case cur of
+    (Header n _ _) : [] | n == slideLevel ->
+                            splitBlocks' [] (acc ++ [cur ++ [d]]) blks
+    _ ->  splitBlocks' [] (acc ++ (if null cur then [] else [cur]) ++ [[d]]) blks
+splitBlocks' cur acc (blk : blks) = splitBlocks' (cur ++ [blk]) acc blks
+
+splitBlocks :: Monad m => [Block] -> Pres m [[Block]]
+splitBlocks = splitBlocks' [] []
+
+blocksToSlide' :: PandocMonad m => Int -> [Block] -> Pres m Slide
+blocksToSlide' lvl ((Header n (ident, _, _) ils) : blks)
+  | n < lvl = do
+      registerAnchorId ident
+      hdr <- inlinesToParElems ils
+      return $ TitleSlide {titleSlideHeader = hdr}
+  | n == lvl = do
+      registerAnchorId ident
+      hdr <- inlinesToParElems ils
+      -- Now get the slide without the header, and then add the header
+      -- in.
+      slide <- blocksToSlide' lvl blks
+      return $ case slide of
+        ContentSlide _ cont          -> ContentSlide hdr cont
+        TwoColumnSlide _ contL contR -> TwoColumnSlide hdr contL contR
+        slide'                       -> slide'
+blocksToSlide' _ (blk : blks)
+  | Div (_, classes, _) divBlks <- blk
+  , "columns" `elem` classes
+  , (Div (_, clsL, _) blksL) : (Div (_, clsR, _) blksR) : remaining <- divBlks
+  , "column" `elem` clsL, "column" `elem` clsR = do
+      unless (null blks)
+        (mapM (P.report . BlockNotRendered) blks >> return ())
+      unless (null remaining)
+        (mapM (P.report . BlockNotRendered) remaining >> return ())
+      mbSplitBlksL <- splitBlocks blksL
+      mbSplitBlksR <- splitBlocks blksR
+      let blksL' = case mbSplitBlksL of
+            bs : _ -> bs
+            []     -> []
+      let blksR' = case mbSplitBlksR of
+            bs : _ -> bs
+            []     -> []
+      shapesL <- blocksToShapes blksL'
+      shapesR <- blocksToShapes blksR'
+      return $ TwoColumnSlide { twoColumnSlideHeader = []
+                              , twoColumnSlideLeft = shapesL
+                              , twoColumnSlideRight = shapesR
+                              }
+blocksToSlide' _ (blk : blks) = do
+      inNoteSlide <- asks envInNoteSlide
+      shapes <- if inNoteSlide
+                then forceFontSize noteSize $ blocksToShapes (blk : blks)
+                else blocksToShapes (blk : blks)
+      return $ ContentSlide { contentSlideHeader = []
+                            , contentSlideContent = shapes
+                            }
+blocksToSlide' _ [] = return $ ContentSlide { contentSlideHeader = []
+                                            , contentSlideContent = []
+                                            }
+
+blocksToSlide :: PandocMonad m => [Block] -> Pres m Slide
+blocksToSlide blks = do
+  slideLevel <- asks envSlideLevel
+  blocksToSlide' slideLevel blks
+
+makeNoteEntry :: Int -> [Block] -> [Block]
+makeNoteEntry n blks =
+  let enum = Str (show n ++ ".")
+  in
+    case blks of
+      (Para ils : blks') -> (Para $ enum : Space : ils) : blks'
+      _ -> (Para [enum]) : blks
+
+forceFontSize :: PandocMonad m => Pixels -> Pres m a -> Pres m a
+forceFontSize px x = do
+  rpr <- asks envRunProps
+  local (\r -> r {envRunProps = rpr{rPropForceSize = Just px}}) x
+
+-- We leave these as blocks because we will want to include them in
+-- the TOC.
+makeNotesSlideBlocks :: PandocMonad m => Pres m [Block]
+makeNotesSlideBlocks = do
+  noteIds <- gets stNoteIds
+  slideLevel <- asks envSlideLevel
+  meta <- asks envMetadata
+  -- Get identifiers so we can give the notes section a unique ident.
+  anchorSet <- M.keysSet <$> gets stAnchorMap
+  if M.null noteIds
+    then return []
+    else do let title = case lookupMeta "notes-title" meta of
+                  Just val -> metaValueToInlines val
+                  Nothing  -> [Str "Notes"]
+                ident = Shared.uniqueIdent title anchorSet
+                hdr = Header slideLevel (ident, [], []) title
+            blks <- return $
+                    concatMap (\(n, bs) -> makeNoteEntry n bs) $
+                    M.toList noteIds
+            return $ hdr : blks
+
+getMetaSlide :: PandocMonad m => Pres m (Maybe Slide)
+getMetaSlide  = do
+  meta <- asks envMetadata
+  title <- inlinesToParElems $ docTitle meta
+  subtitle <- inlinesToParElems $
+    case lookupMeta "subtitle" meta of
+      Just (MetaString s)           -> [Str s]
+      Just (MetaInlines ils)        -> ils
+      Just (MetaBlocks [Plain ils]) -> ils
+      Just (MetaBlocks [Para ils])  -> ils
+      _                             -> []
+  authors <- mapM inlinesToParElems $ docAuthors meta
+  date <- inlinesToParElems $ docDate meta
+  if null title && null subtitle && null authors && null date
+    then return Nothing
+    else return $ Just $ MetadataSlide { metadataSlideTitle = title
+                                       , metadataSlideSubtitle = subtitle
+                                       , metadataSlideAuthors = authors
+                                       , metadataSlideDate = date
+                                       }
+-- adapted from the markdown writer
+elementToListItem :: PandocMonad m => Shared.Element -> Pres m [Block]
+elementToListItem (Shared.Sec lev _nums (ident,_,_) headerText subsecs) = do
+  opts <- asks envOpts
+  let headerLink = if null ident
+                   then walk Shared.deNote headerText
+                   else [Link nullAttr (walk Shared.deNote headerText)
+                          ('#':ident, "")]
+  listContents <- if null subsecs || lev >= writerTOCDepth opts
+                  then return []
+                  else mapM elementToListItem subsecs
+  return [Plain headerLink, BulletList listContents]
+elementToListItem (Shared.Blk _) = return []
+
+makeTOCSlide :: PandocMonad m => [Block] -> Pres m Slide
+makeTOCSlide blks = do
+  contents <- BulletList <$> mapM elementToListItem (Shared.hierarchicalize blks)
+  meta <- asks envMetadata
+  slideLevel <- asks envSlideLevel
+  let tocTitle = case lookupMeta "toc-title" meta of
+                   Just val -> metaValueToInlines val
+                   Nothing  -> [Str "Table of Contents"]
+      hdr = Header slideLevel nullAttr tocTitle
+  sld <- blocksToSlide [hdr, contents]
+  return sld
+
+combineParaElems' :: Maybe ParaElem -> [ParaElem] -> [ParaElem]
+combineParaElems' mbPElem [] = maybeToList mbPElem
+combineParaElems' Nothing (pElem : pElems) =
+  combineParaElems' (Just pElem) pElems
+combineParaElems' (Just pElem') (pElem : pElems)
+  | Run rPr' s' <- pElem'
+  , Run rPr s <- pElem
+  , rPr == rPr' =
+    combineParaElems' (Just $ Run rPr' $ s' ++ s) pElems
+  | otherwise =
+    pElem' : combineParaElems' (Just pElem) pElems
+
+combineParaElems :: [ParaElem] -> [ParaElem]
+combineParaElems = combineParaElems' Nothing
+
+blocksToPresentation :: PandocMonad m => [Block] -> Pres m Presentation
+blocksToPresentation blks = do
+  opts <- asks envOpts
+  let metadataStartNum = 1
+  metadataslides <- maybeToList <$> getMetaSlide
+  let tocStartNum = metadataStartNum + length metadataslides
+  -- As far as I can tell, if we want to have a variable-length toc in
+  -- the future, we'll have to make it twice. Once to get the length,
+  -- and a second time to include the notes slide. We can't make the
+  -- notes slide before the body slides because we need to know if
+  -- there are notes, and we can't make either before the toc slide,
+  -- because we need to know its length to get slide numbers right.
+  --
+  -- For now, though, since the TOC slide is only length 1, if it
+  -- exists, we'll just get the length, and then come back to make the
+  -- slide later
+  let tocSlidesLength = if writerTableOfContents opts then 1 else 0
+  let bodyStartNum = tocStartNum + tocSlidesLength
+  blksLst <- splitBlocks blks
+  bodyslides <- mapM
+                (\(bs, n) -> local (\st -> st{envCurSlideId = n}) (blocksToSlide bs))
+                (zip blksLst [bodyStartNum..])
+  let noteStartNum = bodyStartNum + length bodyslides
+  notesSlideBlocks <- makeNotesSlideBlocks
+  -- now we come back and make the real toc...
+  tocSlides <- if writerTableOfContents opts
+               then do toc <- makeTOCSlide $ blks ++ notesSlideBlocks
+                       return [toc]
+               else return []
+  -- ... and the notes slide. We test to see if the blocks are empty,
+  -- because we don't want to make an empty slide.
+  notesSlides <- if null notesSlideBlocks
+                 then return []
+                 else do notesSlide <- local
+                           (\env -> env { envCurSlideId = noteStartNum
+                                        , envInNoteSlide = True
+                                        })
+                           (blocksToSlide $ notesSlideBlocks)
+                         return [notesSlide]
+  return $
+    Presentation $
+    metadataslides ++ tocSlides ++ bodyslides ++ notesSlides
+
+documentToPresentation :: PandocMonad m
+                       => WriterOptions
+                       -> Pandoc
+                       -> m Presentation
+documentToPresentation opts (Pandoc meta blks) = do
+  let env = def { envOpts = opts
+                , envMetadata = meta
+                , envSlideLevel = case writerSlideLevel opts of
+                                    Just lvl -> lvl
+                                    Nothing  -> getSlideLevel blks
+                }
+  runPres env def $ blocksToPresentation blks