Lua module: add readers submodule

Plain text readers are exposed to lua scripts via the `pandoc.reader`
submodule, which is further subdivided by format.  Converting e.g. a
markdown string into a pandoc document is possible from within lua:

    doc = pandoc.reader.markdown.read_doc("Hello, World!")

A `read_block` convenience function is provided for all formats,
although it will still parse the whole string but return only the first
block as the result.

Custom reader options are not supported yet, default options are used
for all parsing operations.

3 files changed, 150 insertions, 30 deletions

diff --git a/src/Text/Pandoc/Lua.hs b/src/Text/Pandoc/Lua.hs
index 6fa6b2020..d754b43b8 100644
--- a/src/Text/Pandoc/Lua.hs
+++ b/src/Text/Pandoc/Lua.hs
@@ -15,11 +15,7 @@ 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
 -}
-{-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE ScopedTypeVariables #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
 {- |
    Module      : Text.Pandoc.Lua
    Copyright   : Copyright © 2017 Albert Krewinkel
@@ -34,24 +30,23 @@ module Text.Pandoc.Lua ( runLuaFilter ) where
 
 import Control.Monad ( (>=>), when )
 import Control.Monad.Trans ( MonadIO(..) )
-import Data.Aeson ( FromJSON(..), ToJSON(..), Result(..), Value, fromJSON )
 import Data.HashMap.Lazy ( HashMap )
 import Data.Text ( Text, pack, unpack )
 import Data.Text.Encoding ( decodeUtf8 )
 import Scripting.Lua ( LuaState, StackValue(..) )
-import Scripting.Lua.Aeson ()
+import Scripting.Lua.Aeson ( newstate )
 import Text.Pandoc.Definition ( Block(..), Inline(..), Pandoc(..) )
 import Text.Pandoc.Lua.PandocModule
+import Text.Pandoc.Lua.StackInstances ()
 import Text.Pandoc.Walk
 
 import qualified Data.HashMap.Lazy as HashMap
 import qualified Scripting.Lua as Lua
-import qualified Scripting.Lua as LuaAeson
 
 runLuaFilter :: (MonadIO m)
              => FilePath -> [String] -> Pandoc -> m Pandoc
 runLuaFilter filterPath args pd = liftIO $ do
-  lua <- LuaAeson.newstate
+  lua <- newstate
   Lua.openlibs lua
   Lua.newtable lua
   Lua.setglobal lua "PANDOC_FILTER_FUNCTIONS"  -- hack, store functions here
@@ -204,23 +199,3 @@ isLuaFunction lua fnName = do
   res <- Lua.isfunction lua (-1)
   Lua.pop lua (-1)
   return res
-
-maybeFromJson :: (FromJSON a) => Maybe Value -> Maybe a
-maybeFromJson mv = fromJSON <$> mv >>= \case
-  Success x -> Just x
-  _         -> Nothing
-
-instance StackValue Pandoc where
-  push lua = Lua.push lua . toJSON
-  peek lua i = maybeFromJson <$> peek lua i
-  valuetype _ = Lua.TTABLE
-
-instance StackValue Block where
-  push lua = Lua.push lua . toJSON
-  peek lua i = maybeFromJson <$> peek lua i
-  valuetype _ = Lua.TTABLE
-
-instance StackValue Inline where
-  push lua = Lua.push lua . toJSON
-  peek lua i = maybeFromJson <$> peek lua i
-  valuetype _ = Lua.TTABLE
diff --git a/src/Text/Pandoc/Lua/PandocModule.hs b/src/Text/Pandoc/Lua/PandocModule.hs
index 87d1fa6b9..d0c78f562 100644
--- a/src/Text/Pandoc/Lua/PandocModule.hs
+++ b/src/Text/Pandoc/Lua/PandocModule.hs
@@ -28,11 +28,25 @@ Pandoc module for lua.
 module Text.Pandoc.Lua.PandocModule ( pushPandocModule ) where
 
 import Data.ByteString.Char8 ( unpack )
-import Scripting.Lua ( LuaState, call)
+import Data.Default ( Default(..) )
+import Scripting.Lua ( LuaState, call, newtable, push, pushhsfunction, rawset)
+import Text.Pandoc.Class hiding ( readDataFile )
+import Text.Pandoc.Definition ( Pandoc(..), Block(..) )
 import Text.Pandoc.Lua.Compat ( loadstring )
+import Text.Pandoc.Lua.StackInstances ()
+import Text.Pandoc.Readers.DocBook ( readDocBook )
+import Text.Pandoc.Readers.HTML ( readHtml )
+import Text.Pandoc.Readers.LaTeX ( readLaTeX )
+import Text.Pandoc.Readers.Native ( readNative )
+import Text.Pandoc.Readers.Markdown ( readMarkdown )
+import Text.Pandoc.Readers.MediaWiki ( readMediaWiki )
+import Text.Pandoc.Readers.Org ( readOrg )
+import Text.Pandoc.Readers.RST ( readRST )
+import Text.Pandoc.Readers.Textile ( readTextile )
+import Text.Pandoc.Readers.TWiki ( readTWiki )
+import Text.Pandoc.Readers.Txt2Tags ( readTxt2Tags )
 import Text.Pandoc.Shared ( readDataFile )
 
-
 -- | Push the "pandoc" on the lua stack.
 pushPandocModule :: LuaState -> IO ()
 pushPandocModule lua = do
@@ -42,7 +56,63 @@ pushPandocModule lua = do
     then return ()
     else do
       call lua 0 1
+  push lua "reader"
+  pushReadersModule lua readers
+  rawset lua (-3)
+
+readers :: [(String, String -> PandocIO Pandoc)]
+readers =
+  [ ("docbook", readDocBook def)
+  , ("html", readHtml def)
+  , ("latex", readLaTeX def)
+  , ("native", readNative def)
+  , ("markdown", readMarkdown def)
+  , ("mediawiki", readMediaWiki def)
+  , ("org", readOrg def)
+  , ("rst", readRST def)
+  , ("textile", readTextile def)
+  , ("twiki", readTWiki def)
+  , ("txt2tags", readTxt2Tags def)
+  ]
 
 -- | Get the string representation of the pandoc module
 pandocModuleScript :: IO String
 pandocModuleScript = unpack <$> readDataFile Nothing "pandoc.lua"
+
+-- | Push a lua table containing readers of the given formats.
+pushReadersModule :: LuaState
+                 -> [(String, String -> PandocIO Pandoc)]
+                 -> IO ()
+pushReadersModule lua readerFns = do
+  newtable lua
+  mapM_ (uncurry $ addReaderTable) readerFns
+ where
+   addReaderTable :: String
+                  -> (String -> PandocIO Pandoc)
+                  -> IO ()
+   addReaderTable formatName readerFn = do
+     let readDoc :: String -> IO Pandoc
+         readDoc s = do
+           res <- runIO $ readerFn s
+           case res of
+             (Left x) -> error (show x)
+             (Right x) -> return x
+     let readBlock :: String -> IO Block
+         readBlock s = do
+           Pandoc _ blks <- readDoc s
+           return $ case blks of
+             x:_ -> x
+             _   -> Null
+     -- Push table containing all functions for this format
+     push lua formatName
+     newtable lua
+     -- set document-reading function
+     push lua "read_doc"
+     pushhsfunction lua readDoc
+     rawset lua (-3)
+     -- set block-reading function
+     push lua "read_block"
+     pushhsfunction lua readBlock
+     rawset lua (-3)
+     -- store table in readers module
+     rawset lua (-3)
diff --git a/src/Text/Pandoc/Lua/StackInstances.hs b/src/Text/Pandoc/Lua/StackInstances.hs
new file mode 100644
index 000000000..0c9addc23
--- /dev/null
+++ b/src/Text/Pandoc/Lua/StackInstances.hs
@@ -0,0 +1,75 @@
+{-
+Copyright © 2012-2015 John MacFarlane <jgm@berkeley.edu>
+            2017 Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+
+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
+-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
+#if !MIN_VERSION_base(4,8,0)
+{-# LANGUAGE OverlappingInstances #-}
+#endif
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{- |
+   Module      : Text.Pandoc.Lua.StackInstances
+   Copyright   : Copyright © 2017 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+StackValue instances for pandoc types.
+-}
+module Text.Pandoc.Lua.StackInstances () where
+
+import Data.Aeson ( FromJSON(..), ToJSON(..), Result(..), Value, fromJSON )
+import Scripting.Lua ( StackValue(..) )
+import Scripting.Lua.Aeson ()
+import Text.Pandoc.Definition ( Block(..), Inline(..), Pandoc(..) )
+
+import qualified Scripting.Lua as Lua
+import qualified Text.Pandoc.UTF8 as UTF8
+
+maybeFromJson :: (FromJSON a) => Maybe Value -> Maybe a
+maybeFromJson mv = fromJSON <$> mv >>= \case
+  Success x -> Just x
+  _         -> Nothing
+
+instance StackValue Pandoc where
+  push lua = Lua.push lua . toJSON
+  peek lua i = maybeFromJson <$> peek lua i
+  valuetype _ = Lua.TTABLE
+
+instance StackValue Block where
+  push lua = Lua.push lua . toJSON
+  peek lua i = maybeFromJson <$> peek lua i
+  valuetype _ = Lua.TTABLE
+
+instance StackValue Inline where
+  push lua = Lua.push lua . toJSON
+  peek lua i = maybeFromJson <$> peek lua i
+  valuetype _ = Lua.TTABLE
+
+#if MIN_VERSION_base(4,8,0)
+instance {-# OVERLAPS #-} StackValue [Char] where
+#else
+instance StackValue [Char] where
+#endif
+  push lua cs = Lua.push lua (UTF8.fromString cs)
+  peek lua i = do
+                 res <- Lua.peek lua i
+                 return $ UTF8.toString `fmap` res
+  valuetype _ = Lua.TSTRING