Added `Text.Pandoc.Writers.Custom`, `--print-custom-lua-writer`.

    pandoc -t data/sample.lua

will load the script sample.lua and use it as a custom writer.
data/sample.lua is provided as an example.

Added `--print-custom-lua-writer` option to print the sample
script.

2 files changed, 237 insertions, 2 deletions

diff --git a/src/Text/Pandoc.hs b/src/Text/Pandoc.hs
index cd2aa0fd3..0d1d6375e 100644
--- a/src/Text/Pandoc.hs
+++ b/src/Text/Pandoc.hs
@@ -99,6 +99,7 @@ module Text.Pandoc
                , writeFB2
                , writeOrg
                , writeAsciiDoc
+               , writeCustom
                -- * Rendering templates and default templates
                , module Text.Pandoc.Templates
                -- * Version
@@ -142,11 +143,12 @@ import Text.Pandoc.Writers.MediaWiki
 import Text.Pandoc.Writers.Textile
 import Text.Pandoc.Writers.Org
 import Text.Pandoc.Writers.AsciiDoc
+import Text.Pandoc.Writers.Custom
 import Text.Pandoc.Templates
 import Text.Pandoc.Options
 import Text.Pandoc.Shared (safeRead, warn)
 import Data.ByteString.Lazy (ByteString)
-import Data.List (intercalate)
+import Data.List (intercalate, isSuffixOf)
 import Data.Version (showVersion)
 import Text.JSON.Generic
 import Data.Set (Set)
@@ -286,7 +288,10 @@ getWriter s =
        Left e  -> Left $ intercalate "\n" $ [m | Message m <- errorMessages e]
        Right (writerName, setExts) ->
            case lookup writerName writers of
-                   Nothing  -> Left $ "Unknown writer: " ++ writerName
+                   Nothing
+                     | ".lua" `isSuffixOf` s ->
+                       Right $ IOStringWriter $ writeCustom s
+                     | otherwise -> Left $ "Unknown writer: " ++ writerName
                    Just (PureStringWriter r) -> Right $ PureStringWriter $
                            \o -> r o{ writerExtensions = setExts $
                                             getDefaultExtensions writerName }
diff --git a/src/Text/Pandoc/Writers/Custom.hs b/src/Text/Pandoc/Writers/Custom.hs
new file mode 100644
index 000000000..fc16a057e
--- /dev/null
+++ b/src/Text/Pandoc/Writers/Custom.hs
@@ -0,0 +1,230 @@
+{-# LANGUAGE OverlappingInstances, FlexibleInstances, OverloadedStrings #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{- Copyright (C) 2012 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.Custom
+   Copyright   : Copyright (C) 2012 John MacFarlane
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : John MacFarlane <jgm@berkeley.edu>
+   Stability   : alpha
+   Portability : portable
+
+Conversion of 'Pandoc' documents to custom markup using
+a lua writer.
+-}
+module Text.Pandoc.Writers.Custom ( writeCustom ) where
+import Text.Pandoc.Definition
+import Text.Pandoc.Options
+import Data.List ( intersperse )
+import Scripting.Lua (LuaState, StackValue, callfunc)
+import qualified Scripting.Lua as Lua
+import Text.Pandoc.UTF8 (fromString, toString)
+import Data.ByteString (ByteString)
+import qualified Data.ByteString.Char8 as C8
+import Data.Monoid
+import qualified Data.Map as M
+
+attrToMap :: Attr -> M.Map ByteString ByteString
+attrToMap (id',classes,keyvals) = M.fromList
+    $ ("id", fromString id')
+    : ("class", fromString $ unwords classes)
+    : map (\(x,y) -> (fromString x, fromString y)) keyvals
+
+getList :: StackValue a => LuaState -> Int -> IO [a]
+getList lua i' = do
+  continue <- Lua.next lua i'
+  if continue
+     then do
+       next <- Lua.peek lua (-1)
+       Lua.pop lua 1
+       x <- maybe (fail "peek returned Nothing") return next
+       rest <- getList lua i'
+       return (x : rest)
+     else return []
+
+instance StackValue ByteString where
+    push l x = Lua.push l $ C8.unpack x
+    peek l n = (fmap . fmap) C8.pack (Lua.peek l n)
+    valuetype _ = Lua.TSTRING
+
+instance StackValue a => StackValue [a] where
+  push lua xs = do
+    Lua.createtable lua (length xs + 1) 0
+    let addValue (i, x) = Lua.push lua x >> Lua.rawseti lua (-2) i
+    mapM_ addValue $ zip [1..] xs
+  peek lua i = do
+    top <- Lua.gettop lua
+    let i' = if i < 0 then top + i + 1 else i
+    Lua.pushnil lua
+    lst <- getList lua i'
+    Lua.pop lua 1
+    return (Just lst)
+  valuetype _ = Lua.TTABLE
+
+instance (StackValue a, StackValue b) => StackValue (M.Map a b) where
+  push lua m = do
+    let xs = M.toList m
+    Lua.createtable lua (length xs + 1) 0
+    let addValue (k, v) = Lua.push lua k >> Lua.push lua v >>
+                          Lua.rawset lua (-3)
+    mapM_ addValue xs
+  peek _ _ = undefined -- not needed for our purposes
+  valuetype _ = Lua.TTABLE
+
+instance (StackValue a, StackValue b) => StackValue (a,b) where
+  push lua (k,v) = do
+    Lua.createtable lua 2 0
+    Lua.push lua k
+    Lua.push lua v
+    Lua.rawset lua (-3)
+  peek _ _ = undefined -- not needed for our purposes
+  valuetype _ = Lua.TTABLE
+
+instance StackValue [Inline] where
+  push l ils = Lua.push l . C8.unpack =<< inlineListToCustom l ils
+  peek _ _ = undefined
+  valuetype _ = Lua.TSTRING
+
+instance StackValue [Block] where
+  push l ils = Lua.push l . C8.unpack =<< blockListToCustom l ils
+  peek _ _ = undefined
+  valuetype _ = Lua.TSTRING
+
+-- | Convert Pandoc to custom markup.
+writeCustom :: FilePath -> WriterOptions -> Pandoc -> IO String
+writeCustom luaFile opts doc = do
+  luaScript <- readFile luaFile
+  lua <- Lua.newstate
+  Lua.openlibs lua
+  Lua.loadstring lua luaScript "custom"
+  Lua.call lua 0 0
+  -- TODO - call hierarchicalize, so we have that info
+  rendered <- docToCustom lua opts doc
+  Lua.close lua
+  return $ toString rendered
+
+docToCustom :: LuaState -> WriterOptions -> Pandoc -> IO ByteString
+docToCustom lua opts (Pandoc (Meta title authors date) blocks) = do
+  title' <- inlineListToCustom lua title
+  authors' <- mapM (inlineListToCustom lua) authors
+  date' <- inlineListToCustom lua date
+  body <- blockListToCustom lua blocks
+  callfunc lua "Doc" body title' authors' date' (writerVariables opts)
+
+-- | Convert Pandoc block element to Custom.
+blockToCustom :: LuaState      -- ^ Lua state
+              -> Block         -- ^ Block element
+              -> IO ByteString
+
+blockToCustom _ Null = return ""
+
+blockToCustom lua (Plain inlines) = callfunc lua "Plain" inlines
+
+blockToCustom lua (Para [Image txt (src,tit)]) =
+  callfunc lua "CaptionedImage" src tit txt
+
+blockToCustom lua (Para inlines) = callfunc lua "Para" inlines
+
+blockToCustom lua (RawBlock format str) =
+  callfunc lua "RawBlock" format (fromString str)
+
+blockToCustom lua HorizontalRule = callfunc lua "HorizontalRule"
+
+blockToCustom lua (Header level attr inlines) =
+  callfunc lua "Header" level inlines (attrToMap attr)
+
+blockToCustom lua (CodeBlock attr str) =
+  callfunc lua "CodeBlock" (fromString str) (attrToMap attr)
+
+blockToCustom lua (BlockQuote blocks) = callfunc lua "BlockQuote" blocks
+
+blockToCustom lua (Table capt aligns widths headers rows') =
+  callfunc lua "Table" capt (map show aligns) widths headers rows'
+
+blockToCustom lua (BulletList items) = callfunc lua "BulletList" items
+
+blockToCustom lua (OrderedList (num,sty,delim) items) =
+  callfunc lua "OrderedList" items num (show sty) (show delim)
+
+blockToCustom lua (DefinitionList items) =
+  callfunc lua "DefinitionList" items
+
+-- | Convert list of Pandoc block elements to Custom.
+blockListToCustom :: LuaState -- ^ Options
+                  -> [Block]       -- ^ List of block elements
+                  -> IO ByteString
+blockListToCustom lua xs = do
+  blocksep <- callfunc lua "Blocksep"
+  bs <- mapM (blockToCustom lua) xs
+  return $ mconcat $ intersperse blocksep bs
+
+-- | Convert list of Pandoc inline elements to Custom.
+inlineListToCustom :: LuaState -> [Inline] -> IO ByteString
+inlineListToCustom lua lst = do
+  xs <- mapM (inlineToCustom lua) lst
+  return $ C8.concat xs
+
+-- | Convert Pandoc inline element to Custom.
+inlineToCustom :: LuaState -> Inline -> IO ByteString
+
+inlineToCustom lua (Str str) = callfunc lua "Str" $ fromString str
+
+inlineToCustom lua Space = callfunc lua "Space"
+
+inlineToCustom lua (Emph lst) = callfunc lua "Emph" lst
+
+inlineToCustom lua (Strong lst) = callfunc lua "Strong" lst
+
+inlineToCustom lua (Strikeout lst) = callfunc lua "Strikeout" lst
+
+inlineToCustom lua (Superscript lst) = callfunc lua "Superscript" lst
+
+inlineToCustom lua (Subscript lst) = callfunc lua "Subscript" lst
+
+inlineToCustom lua (SmallCaps lst) = callfunc lua "SmallCaps" lst
+
+inlineToCustom lua (Quoted SingleQuote lst) = callfunc lua "SingleQuoted" lst
+
+inlineToCustom lua (Quoted DoubleQuote lst) = callfunc lua "DoubleQuoted" lst
+
+inlineToCustom lua (Cite _  lst) = callfunc lua "Cite" lst
+
+inlineToCustom lua (Code attr str) =
+  callfunc lua "Code" (fromString str) (attrToMap attr)
+
+inlineToCustom lua (Math DisplayMath str) =
+  callfunc lua "DisplayMath" (fromString str)
+
+inlineToCustom lua (Math InlineMath str) =
+  callfunc lua "InlineMath" (fromString str)
+
+inlineToCustom lua (RawInline format str) =
+  callfunc lua "RawInline" format (fromString str)
+
+inlineToCustom lua (LineBreak) = callfunc lua "LineBreak"
+
+inlineToCustom lua (Link txt (src,tit)) =
+  callfunc lua "Link" txt (fromString src) (fromString tit)
+
+inlineToCustom lua (Image alt (src,tit)) =
+  callfunc lua "Image" alt (fromString src) (fromString tit)
+
+inlineToCustom lua (Note contents) = callfunc lua "Note" contents
+