Merge pull request #6211 from tarleb/lua-pandocerror

API change: create PandocLua type, use PandocError for exceptions

20 files changed, 683 insertions, 430 deletions

diff --git a/src/Text/Pandoc/Class/IO.hs b/src/Text/Pandoc/Class/IO.hs
new file mode 100644
index 000000000..c38a37844
--- /dev/null
+++ b/src/Text/Pandoc/Class/IO.hs
@@ -0,0 +1,231 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{- |
+Module      : Text.Pandoc.Class.IO
+Copyright   : Copyright (C) 2016-2020 Jesse Rosenthal, John MacFarlane
+License     : GNU GPL, version 2 or above
+
+Maintainer  : Jesse Rosenthal <jrosenthal@jhu.edu>
+Stability   : alpha
+Portability : portable
+
+Default ways to perform @'PandocMonad'@ actions in a @'MonadIO'@ type.
+
+These functions are used to make the @'PandocIO'@ type an instance of
+@'PandocMonad'@, but can be reused for any other MonadIO-conforming
+types.
+-}
+module Text.Pandoc.Class.IO
+  ( fileExists
+  , getCurrentTime
+  , getCurrentTimeZone
+  , getDataFileName
+  , getModificationTime
+  , glob
+  , logOutput
+  , logIOError
+  , lookupEnv
+  , newStdGen
+  , newUniqueHash
+  , openURL
+  , readFileLazy
+  , readFileStrict
+  , extractMedia
+ ) where
+
+import Control.Monad.Except (throwError)
+import Control.Monad.IO.Class (MonadIO, liftIO)
+import Data.ByteString.Base64 (decodeLenient)
+import Data.ByteString.Lazy (toChunks)
+import Data.Text (Text, pack, unpack)
+import Data.Time (TimeZone, UTCTime)
+import Data.Unique (hashUnique)
+import Network.Connection (TLSSettings (TLSSettingsSimple))
+import Network.HTTP.Client
+       (httpLbs, responseBody, responseHeaders,
+        Request(port, host, requestHeaders), parseRequest, newManager)
+import Network.HTTP.Client.Internal (addProxy)
+import Network.HTTP.Client.TLS (mkManagerSettings)
+import Network.HTTP.Types.Header ( hContentType )
+import Network.Socket (withSocketsDo)
+import Network.URI (unEscapeString)
+import System.Directory (createDirectoryIfMissing)
+import System.Environment (getEnv)
+import System.FilePath ((</>), takeDirectory, normalise)
+import System.IO (stderr)
+import System.IO.Error
+import System.Random (StdGen)
+import Text.Pandoc.Class.CommonState (CommonState (..))
+import Text.Pandoc.Class.PandocMonad
+       (PandocMonad, getsCommonState, getMediaBag, report)
+import Text.Pandoc.Definition (Pandoc, Inline (Image))
+import Text.Pandoc.Error (PandocError (..))
+import Text.Pandoc.Logging (LogMessage (..), messageVerbosity, showLogMessage)
+import Text.Pandoc.MIME (MimeType)
+import Text.Pandoc.MediaBag (MediaBag, lookupMedia, mediaDirectory)
+import Text.Pandoc.Walk (walk)
+import qualified Control.Exception as E
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Lazy as BL
+import qualified Data.CaseInsensitive as CI
+import qualified Data.Text as T
+import qualified Data.Time
+import qualified Data.Time.LocalTime
+import qualified Data.Unique
+import qualified System.Directory
+import qualified System.Environment as Env
+import qualified System.FilePath.Glob
+import qualified System.Random
+import qualified Text.Pandoc.UTF8 as UTF8
+#ifndef EMBED_DATA_FILES
+import qualified Paths_pandoc as Paths
+#endif
+
+-- | Utility function to lift IO errors into 'PandocError's.
+liftIOError :: (PandocMonad m, MonadIO m) => (String -> IO a) -> String -> m a
+liftIOError f u = do
+  res <- liftIO $ tryIOError $ f u
+  case res of
+         Left e  -> throwError $ PandocIOError (pack u) e
+         Right r -> return r
+
+-- | Show potential IO errors to the user continuing execution anyway
+logIOError :: (PandocMonad m, MonadIO m) => IO () -> m ()
+logIOError f = do
+  res <- liftIO $ tryIOError f
+  case res of
+    Left e -> report $ IgnoredIOError $ pack $ E.displayException e
+    Right _ -> pure ()
+
+-- | Lookup an environment variable in the programs environment.
+lookupEnv :: MonadIO m => Text -> m (Maybe Text)
+lookupEnv = fmap (fmap pack) . liftIO . Env.lookupEnv . unpack
+
+-- | Get the current (UTC) time.
+getCurrentTime :: MonadIO m => m UTCTime
+getCurrentTime = liftIO Data.Time.getCurrentTime
+
+-- | Get the locale's time zone.
+getCurrentTimeZone :: MonadIO m => m TimeZone
+getCurrentTimeZone = liftIO Data.Time.LocalTime.getCurrentTimeZone
+
+-- | Return a new generator for random numbers.
+newStdGen :: MonadIO m => m StdGen
+newStdGen = liftIO System.Random.newStdGen
+
+-- | Return a new unique integer.
+newUniqueHash :: MonadIO m => m Int
+newUniqueHash = hashUnique <$> liftIO Data.Unique.newUnique
+
+openURL :: (PandocMonad m, MonadIO m) => Text -> m (B.ByteString, Maybe MimeType)
+openURL u
+ | Just u'' <- T.stripPrefix "data:" u = do
+     let mime     = T.takeWhile (/=',') u''
+     let contents = UTF8.fromString $
+                     unEscapeString $ T.unpack $ T.drop 1 $ T.dropWhile (/=',') u''
+     return (decodeLenient contents, Just mime)
+ | otherwise = do
+     let toReqHeader (n, v) = (CI.mk (UTF8.fromText n), UTF8.fromText v)
+     customHeaders <- map toReqHeader <$> getsCommonState stRequestHeaders
+     disableCertificateValidation <- getsCommonState stNoCheckCertificate
+     report $ Fetching u
+     res <- liftIO $ E.try $ withSocketsDo $ do
+       let parseReq = parseRequest
+       proxy <- tryIOError (getEnv "http_proxy")
+       let addProxy' x = case proxy of
+                            Left _ -> return x
+                            Right pr -> parseReq pr >>= \r ->
+                                return (addProxy (host r) (port r) x)
+       req <- parseReq (unpack u) >>= addProxy'
+       let req' = req{requestHeaders = customHeaders ++ requestHeaders req}
+       let tlsSimple = TLSSettingsSimple disableCertificateValidation False False
+       let tlsManagerSettings = mkManagerSettings tlsSimple  Nothing
+       resp <- newManager tlsManagerSettings >>= httpLbs req'
+       return (B.concat $ toChunks $ responseBody resp,
+               UTF8.toText `fmap` lookup hContentType (responseHeaders resp))
+
+     case res of
+          Right r -> return r
+          Left e  -> throwError $ PandocHttpError u e
+
+-- | Read the lazy ByteString contents from a file path, raising an error on
+-- failure.
+readFileLazy :: (PandocMonad m, MonadIO m) => FilePath -> m BL.ByteString
+readFileLazy s = liftIOError BL.readFile s
+
+-- | Read the strict ByteString contents from a file path,
+-- raising an error on failure.
+readFileStrict :: (PandocMonad m, MonadIO m) => FilePath -> m B.ByteString
+readFileStrict s = liftIOError B.readFile s
+
+-- | Return a list of paths that match a glob, relative to the working
+-- directory. See 'System.FilePath.Glob' for the glob syntax.
+glob :: (PandocMonad m, MonadIO m) => String -> m [FilePath]
+glob = liftIOError System.FilePath.Glob.glob
+
+-- | Returns True if file exists.
+fileExists :: (PandocMonad m, MonadIO m) => FilePath -> m Bool
+fileExists = liftIOError System.Directory.doesFileExist
+
+-- | Returns the path of data file.
+getDataFileName :: (PandocMonad m, MonadIO m) => FilePath -> m FilePath
+#ifdef EMBED_DATA_FILES
+getDataFileName = return
+#else
+getDataFileName = liftIOError Paths.getDataFileName
+#endif
+
+-- | Return the modification time of a file.
+getModificationTime :: (PandocMonad m, MonadIO m) => FilePath -> m UTCTime
+getModificationTime = liftIOError System.Directory.getModificationTime
+
+-- | Output a log message.
+logOutput :: (PandocMonad m, MonadIO m) => LogMessage -> m ()
+logOutput msg = liftIO $ do
+  UTF8.hPutStr stderr $
+      "[" ++ show (messageVerbosity msg) ++ "] "
+  alertIndent $ T.lines $ showLogMessage msg
+
+-- | Prints the list of lines to @stderr@, indenting every but the first
+-- line by two spaces.
+alertIndent :: [Text] -> IO ()
+alertIndent [] = return ()
+alertIndent (l:ls) = do
+  UTF8.hPutStrLn stderr $ unpack l
+  mapM_ go ls
+  where go l' = do UTF8.hPutStr stderr "  "
+                   UTF8.hPutStrLn stderr $ unpack l'
+
+-- | Extract media from the mediabag into a directory.
+extractMedia :: (PandocMonad m, MonadIO m) => FilePath -> Pandoc -> m Pandoc
+extractMedia dir d = do
+  media <- getMediaBag
+  case [fp | (fp, _, _) <- mediaDirectory media] of
+    []  -> return d
+    fps -> do
+      mapM_ (writeMedia dir media) fps
+      return $ walk (adjustImagePath dir fps) d
+
+-- | Write the contents of a media bag to a path.
+writeMedia :: (PandocMonad m, MonadIO m)
+           => FilePath -> MediaBag -> FilePath
+           -> m ()
+writeMedia dir mediabag subpath = do
+  -- we join and split to convert a/b/c to a\b\c on Windows;
+  -- in zip containers all paths use /
+  let fullpath = dir </> unEscapeString (normalise subpath)
+  let mbcontents = lookupMedia subpath mediabag
+  case mbcontents of
+       Nothing -> throwError $ PandocResourceNotFound $ pack subpath
+       Just (_, bs) -> do
+         report $ Extracting $ pack fullpath
+         liftIOError (createDirectoryIfMissing True) (takeDirectory fullpath)
+         logIOError $ BL.writeFile fullpath bs
+
+-- | If the given Inline element is an image with a @src@ path equal to
+-- one in the list of @paths@, then prepends @dir@ to the image source;
+-- returns the element unchanged otherwise.
+adjustImagePath :: FilePath -> [FilePath] -> Inline -> Inline
+adjustImagePath dir paths (Image attr lab (src, tit))
+   | unpack src `elem` paths = Image attr lab (pack dir <> "/" <> src, tit)
+adjustImagePath _ _ x = x
diff --git a/src/Text/Pandoc/Class/PandocIO.hs b/src/Text/Pandoc/Class/PandocIO.hs
index ee6a041ba..63cb94155 100644
--- a/src/Text/Pandoc/Class/PandocIO.hs
+++ b/src/Text/Pandoc/Class/PandocIO.hs
@@ -1,7 +1,5 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE OverloadedStrings #-}
 {- |
 Module      : Text.Pandoc.Class.PandocIO
 Copyright   : Copyright (C) 2016-2020 Jesse Rosenthal, John MacFarlane
@@ -16,79 +14,21 @@ This module defines @'PandocIO'@, an IO-based instance of the
 using IO operators.
 -}
 module Text.Pandoc.Class.PandocIO
-  ( getPOSIXTime
-  , getZonedTime
-  , readFileFromDirs
-  , report
-  , setTrace
-  , setRequestHeader
-  , getLog
-  , setVerbosity
-  , getVerbosity
-  , getMediaBag
-  , setMediaBag
-  , insertMedia
-  , setUserDataDir
-  , getUserDataDir
-  , fetchItem
-  , getInputFiles
-  , setInputFiles
-  , getOutputFile
-  , setOutputFile
-  , setResourcePath
-  , getResourcePath
-  , PandocIO(..)
+  ( PandocIO(..)
   , runIO
   , runIOorExplode
   , extractMedia
  ) where
 
-import Control.Monad.Except
-import Control.Monad.State.Strict
-import Data.ByteString.Base64 (decodeLenient)
-import Data.ByteString.Lazy (toChunks)
-import Data.Default
-import Data.Text (Text)
-import Data.Unique (hashUnique)
-import Network.HTTP.Client
-       (httpLbs, responseBody, responseHeaders,
-        Request(port, host, requestHeaders), parseRequest, newManager)
-import Network.HTTP.Client.Internal (addProxy)
-import Network.HTTP.Client.TLS (mkManagerSettings)
-import Network.Connection (TLSSettings (..))
-import Network.HTTP.Types.Header ( hContentType )
-import Network.Socket (withSocketsDo)
-import Network.URI ( unEscapeString )
-import Prelude
-import System.Directory (createDirectoryIfMissing)
-import System.Environment (getEnv)
-import System.FilePath ((</>), takeDirectory, normalise)
-import System.IO (stderr)
-import System.IO.Error
+import Control.Monad.Except (ExceptT, MonadError, runExceptT)
+import Control.Monad.IO.Class (MonadIO)
+import Control.Monad.State (StateT, evalStateT, lift, get, put)
+import Data.Default (Default (def))
 import Text.Pandoc.Class.CommonState (CommonState (..))
 import Text.Pandoc.Class.PandocMonad
 import Text.Pandoc.Definition
 import Text.Pandoc.Error
-import Text.Pandoc.Logging
-import Text.Pandoc.MediaBag (MediaBag, lookupMedia, mediaDirectory)
-import Text.Pandoc.Walk (walk)
-import qualified Control.Exception as E
-import qualified Data.ByteString as B
-import qualified Data.ByteString.Lazy as BL
-import qualified Data.CaseInsensitive as CI
-import qualified Data.Text as T
-import qualified Data.Time as IO (getCurrentTime)
-import qualified Data.Time.LocalTime as IO (getCurrentTimeZone)
-import qualified Data.Unique as IO (newUnique)
-import qualified System.Directory as Directory
-import qualified System.Directory as IO (getModificationTime)
-import qualified System.Environment as IO (lookupEnv)
-import qualified System.FilePath.Glob as IO (glob)
-import qualified System.Random as IO (newStdGen)
-import qualified Text.Pandoc.UTF8 as UTF8
-#ifndef EMBED_DATA_FILES
-import qualified Paths_pandoc as Paths
-#endif
+import qualified Text.Pandoc.Class.IO as IO
 
 -- | Evaluate a 'PandocIO' operation.
 runIO :: PandocIO a -> IO (Either PandocError a)
@@ -108,113 +48,27 @@ newtype PandocIO a = PandocIO {
              , MonadError PandocError
              )
 
--- | Utility function to lift IO errors into 'PandocError's.
-liftIOError :: (String -> IO a) -> String -> PandocIO a
-liftIOError f u = do
-  res <- liftIO $ tryIOError $ f u
-  case res of
-         Left e  -> throwError $ PandocIOError (T.pack u) e
-         Right r -> return r
-
--- | Show potential IO errors to the user continuing execution anyway
-logIOError :: IO () -> PandocIO ()
-logIOError f = do
-  res <- liftIO $ tryIOError f
-  case res of
-    Left e -> report $ IgnoredIOError $ T.pack $ E.displayException e
-    Right _ -> pure ()
-
 instance PandocMonad PandocIO where
-  lookupEnv = fmap (fmap T.pack) . liftIO . IO.lookupEnv . T.unpack
-  getCurrentTime = liftIO IO.getCurrentTime
-  getCurrentTimeZone = liftIO IO.getCurrentTimeZone
-  newStdGen = liftIO IO.newStdGen
-  newUniqueHash = hashUnique <$> liftIO IO.newUnique
-
-  openURL u
-   | Just u'' <- T.stripPrefix "data:" u = do
-       let mime     = T.takeWhile (/=',') u''
-       let contents = UTF8.fromString $
-                       unEscapeString $ T.unpack $ T.drop 1 $ T.dropWhile (/=',') u''
-       return (decodeLenient contents, Just mime)
-   | otherwise = do
-       let toReqHeader (n, v) = (CI.mk (UTF8.fromText n), UTF8.fromText v)
-       customHeaders <- map toReqHeader <$> getsCommonState stRequestHeaders
-       disableCertificateValidation <- getsCommonState stNoCheckCertificate
-       report $ Fetching u
-       res <- liftIO $ E.try $ withSocketsDo $ do
-         let parseReq = parseRequest
-         proxy <- tryIOError (getEnv "http_proxy")
-         let addProxy' x = case proxy of
-                              Left _ -> return x
-                              Right pr -> parseReq pr >>= \r ->
-                                  return (addProxy (host r) (port r) x)
-         req <- parseReq (T.unpack u) >>= addProxy'
-         let req' = req{requestHeaders = customHeaders ++ requestHeaders req}
-         resp <- newManager (mkManagerSettings  (TLSSettingsSimple disableCertificateValidation False False) Nothing) >>= httpLbs req'
-         return (B.concat $ toChunks $ responseBody resp,
-                 UTF8.toText `fmap` lookup hContentType (responseHeaders resp))
+  lookupEnv = IO.lookupEnv
+  getCurrentTime = IO.getCurrentTime
+  getCurrentTimeZone = IO.getCurrentTimeZone
+  newStdGen = IO.newStdGen
+  newUniqueHash = IO.newUniqueHash
 
-       case res of
-            Right r -> return r
-            Left e  -> throwError $ PandocHttpError u e
+  openURL = IO.openURL
+  readFileLazy = IO.readFileLazy
+  readFileStrict = IO.readFileStrict
 
-  readFileLazy s = liftIOError BL.readFile s
-  readFileStrict s = liftIOError B.readFile s
+  glob = IO.glob
+  fileExists = IO.fileExists
+  getDataFileName = IO.getDataFileName
+  getModificationTime = IO.getModificationTime
 
-  glob = liftIOError IO.glob
-  fileExists = liftIOError Directory.doesFileExist
-#ifdef EMBED_DATA_FILES
-  getDataFileName = return
-#else
-  getDataFileName = liftIOError Paths.getDataFileName
-#endif
-  getModificationTime = liftIOError IO.getModificationTime
   getCommonState = PandocIO $ lift get
-  putCommonState x = PandocIO $ lift $ put x
-  logOutput msg = liftIO $ do
-    UTF8.hPutStr stderr $
-        "[" ++ show (messageVerbosity msg) ++ "] "
-    alertIndent $ T.lines $ showLogMessage msg
+  putCommonState = PandocIO . lift . put
 
--- | Prints the list of lines to @stderr@, indenting every but the first
--- line by two spaces.
-alertIndent :: [Text] -> IO ()
-alertIndent [] = return ()
-alertIndent (l:ls) = do
-  UTF8.hPutStrLn stderr $ T.unpack l
-  mapM_ go ls
-  where go l' = do UTF8.hPutStr stderr "  "
-                   UTF8.hPutStrLn stderr $ T.unpack l'
+  logOutput = IO.logOutput
 
 -- | Extract media from the mediabag into a directory.
 extractMedia :: FilePath -> Pandoc -> PandocIO Pandoc
-extractMedia dir d = do
-  media <- getMediaBag
-  case [fp | (fp, _, _) <- mediaDirectory media] of
-        []  -> return d
-        fps -> do
-          mapM_ (writeMedia dir media) fps
-          return $ walk (adjustImagePath dir fps) d
-
--- | Write the contents of a media bag to a path.
-writeMedia :: FilePath -> MediaBag -> FilePath -> PandocIO ()
-writeMedia dir mediabag subpath = do
-  -- we join and split to convert a/b/c to a\b\c on Windows;
-  -- in zip containers all paths use /
-  let fullpath = dir </> unEscapeString (normalise subpath)
-  let mbcontents = lookupMedia subpath mediabag
-  case mbcontents of
-       Nothing -> throwError $ PandocResourceNotFound $ T.pack subpath
-       Just (_, bs) -> do
-         report $ Extracting $ T.pack fullpath
-         liftIOError (createDirectoryIfMissing True) (takeDirectory fullpath)
-         logIOError $ BL.writeFile fullpath bs
-
--- | If the given Inline element is an image with a @src@ path equal to
--- one in the list of @paths@, then prepends @dir@ to the image source;
--- returns the element unchanged otherwise.
-adjustImagePath :: FilePath -> [FilePath] -> Inline -> Inline
-adjustImagePath dir paths (Image attr lab (src, tit))
-   | T.unpack src `elem` paths = Image attr lab (T.pack dir <> "/" <> src, tit)
-adjustImagePath _ _ x = x
+extractMedia = IO.extractMedia
diff --git a/src/Text/Pandoc/Error.hs b/src/Text/Pandoc/Error.hs
index 977875907..4c3c1af79 100644
--- a/src/Text/Pandoc/Error.hs
+++ b/src/Text/Pandoc/Error.hs
@@ -47,6 +47,7 @@ data PandocError = PandocIOError Text IOError
                  | PandocPDFProgramNotFoundError Text
                  | PandocPDFError Text
                  | PandocFilterError Text Text
+                 | PandocLuaError Text
                  | PandocCouldNotFindDataFileError Text
                  | PandocResourceNotFound Text
                  | PandocTemplateError Text
@@ -100,6 +101,7 @@ handleError (Left e) =
     PandocPDFError logmsg -> err 43 $ "Error producing PDF.\n" <> logmsg
     PandocFilterError filtername msg -> err 83 $ "Error running filter " <>
         filtername <> ":\n" <> msg
+    PandocLuaError msg -> err 84 $ "Error running Lua:\n" <> msg
     PandocCouldNotFindDataFileError fn -> err 97 $
         "Could not find data file " <> fn
     PandocResourceNotFound fn -> err 99 $
diff --git a/src/Text/Pandoc/Filter/JSON.hs b/src/Text/Pandoc/Filter/JSON.hs
index 7e27f7d94..83ec9a97c 100644
--- a/src/Text/Pandoc/Filter/JSON.hs
+++ b/src/Text/Pandoc/Filter/JSON.hs
@@ -23,7 +23,6 @@ import System.Directory (executable, doesFileExist, findExecutable,
 import System.Environment (getEnvironment)
 import System.Exit (ExitCode (..))
 import System.FilePath ((</>), takeExtension)
-import Text.Pandoc.Class.PandocIO (PandocIO)
 import Text.Pandoc.Error (PandocError (PandocFilterError))
 import Text.Pandoc.Definition (Pandoc)
 import Text.Pandoc.Options (ReaderOptions)
@@ -32,11 +31,12 @@ import Text.Pandoc.Shared (pandocVersion, tshow)
 import qualified Control.Exception as E
 import qualified Text.Pandoc.UTF8 as UTF8
 
-apply :: ReaderOptions
+apply :: MonadIO m
+      => ReaderOptions
       -> [String]
       -> FilePath
       -> Pandoc
-      -> PandocIO Pandoc
+      -> m Pandoc
 apply ropts args f = liftIO . externalFilter ropts f args
 
 externalFilter :: MonadIO m
diff --git a/src/Text/Pandoc/Filter/Lua.hs b/src/Text/Pandoc/Filter/Lua.hs
index a50e5217d..8df057bfa 100644
--- a/src/Text/Pandoc/Filter/Lua.hs
+++ b/src/Text/Pandoc/Filter/Lua.hs
@@ -17,8 +17,7 @@ import qualified Data.Text as T
 import Text.Pandoc.Class.PandocIO (PandocIO)
 import Text.Pandoc.Definition (Pandoc)
 import Text.Pandoc.Error (PandocError (PandocFilterError))
-import Text.Pandoc.Lua (Global (..), LuaException (..),
-                        runLua, runFilterFile, setGlobals)
+import Text.Pandoc.Lua (Global (..), runLua, runFilterFile, setGlobals)
 import Text.Pandoc.Options (ReaderOptions)
 
 -- | Run the Lua filter in @filterPath@ for a transformation to the
@@ -40,7 +39,7 @@ apply ropts args fp doc = do
                ]
     runFilterFile fp doc
 
-forceResult :: FilePath -> Either LuaException Pandoc -> PandocIO Pandoc
+forceResult :: FilePath -> Either PandocError Pandoc -> PandocIO Pandoc
 forceResult fp eitherResult = case eitherResult of
-  Right x               -> return x
-  Left (LuaException s) -> throw (PandocFilterError (T.pack fp) s)
+  Right x  -> return x
+  Left err -> throw (PandocFilterError (T.pack fp) (T.pack $ show err))
diff --git a/src/Text/Pandoc/Lua.hs b/src/Text/Pandoc/Lua.hs
index 63a49596d..39db0074a 100644
--- a/src/Text/Pandoc/Lua.hs
+++ b/src/Text/Pandoc/Lua.hs
@@ -10,7 +10,6 @@ Running pandoc Lua filters.
 -}
 module Text.Pandoc.Lua
   ( runLua
-  , LuaException (..)
   -- * Lua globals
   , Global (..)
   , setGlobals
@@ -20,5 +19,5 @@ module Text.Pandoc.Lua
 
 import Text.Pandoc.Lua.Filter (runFilterFile)
 import Text.Pandoc.Lua.Global (Global (..), setGlobals)
-import Text.Pandoc.Lua.Init (LuaException (..), runLua)
+import Text.Pandoc.Lua.Init (runLua)
 import Text.Pandoc.Lua.Marshaling ()
diff --git a/src/Text/Pandoc/Lua/ErrorConversion.hs b/src/Text/Pandoc/Lua/ErrorConversion.hs
new file mode 100644
index 000000000..59c962723
--- /dev/null
+++ b/src/Text/Pandoc/Lua/ErrorConversion.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{- |
+   Module      : Text.Pandoc.Lua.ErrorConversion
+   Copyright   : © 2020 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Define how Lua errors are converted into @'PandocError'@ Haskell
+exceptions, and /vice versa/.
+-}
+module Text.Pandoc.Lua.ErrorConversion
+  ( errorConversion
+  ) where
+
+import Foreign.Lua (Lua (..), NumResults)
+import Text.Pandoc.Error (PandocError (PandocLuaError))
+import Text.Pandoc.Lua.Marshaling.PandocError (pushPandocError, peekPandocError)
+
+import qualified Control.Monad.Catch as Catch
+import qualified Data.Text as T
+import qualified Foreign.Lua as Lua
+
+-- | Conversions between Lua errors and Haskell exceptions, assuming
+-- that all exceptions are of type @'PandocError'@.
+errorConversion :: Lua.ErrorConversion
+errorConversion = Lua.ErrorConversion
+  { Lua.addContextToException = addContextToException
+  , Lua.alternative           = alternative
+  , Lua.errorToException      = errorToException
+  , Lua.exceptionToError      = exceptionToError
+  }
+
+-- | Convert a Lua error, which must be at the top of the stack, into a
+-- @'PandocError'@, popping the value from the stack.
+errorToException :: forall a . Lua.State -> IO a
+errorToException l = Lua.unsafeRunWith l $ do
+  err <- peekPandocError Lua.stackTop
+  Lua.pop 1
+  Catch.throwM err
+
+-- | Try the first op -- if it doesn't succeed, run the second.
+alternative :: forall a . Lua a -> Lua a -> Lua a
+alternative x y = Catch.try x >>= \case
+  Left (_ :: PandocError) -> y
+  Right x' -> return x'
+
+-- | Add more context to an error
+addContextToException :: forall a . String -> Lua a -> Lua a
+addContextToException ctx op = op `Catch.catch` \case
+  PandocLuaError msg -> Catch.throwM $ PandocLuaError (T.pack ctx <> msg)
+  e -> Catch.throwM e
+
+-- | Catch a @'PandocError'@ exception and raise it as a Lua error.
+exceptionToError :: Lua NumResults -> Lua NumResults
+exceptionToError op = op `Catch.catch` \e -> do
+  pushPandocError e
+  Lua.error
diff --git a/src/Text/Pandoc/Lua/Filter.hs b/src/Text/Pandoc/Lua/Filter.hs
index f6a0aea5b..e626356d5 100644
--- a/src/Text/Pandoc/Lua/Filter.hs
+++ b/src/Text/Pandoc/Lua/Filter.hs
@@ -18,14 +18,15 @@ module Text.Pandoc.Lua.Filter ( LuaFilterFunction
                               ) where
 import Control.Applicative ((<|>))
 import Control.Monad (mplus, (>=>))
-import Control.Monad.Catch (finally)
+import Control.Monad.Catch (finally, try)
 import Data.Data (Data, DataType, dataTypeConstrs, dataTypeName, dataTypeOf,
                   showConstr, toConstr, tyconUQname)
 import Data.Foldable (foldrM)
 import Data.Map (Map)
 import Data.Maybe (fromMaybe)
-import Foreign.Lua (Lua, Peekable, Pushable)
+import Foreign.Lua (Lua, Peekable, Pushable, StackIndex)
 import Text.Pandoc.Definition
+import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Marshaling ()
 import Text.Pandoc.Lua.Marshaling.List (List (..))
 import Text.Pandoc.Lua.Walk (SingletonsList (..))
@@ -102,7 +103,7 @@ elementOrList x = do
   if elementUnchanged
     then [x] <$ Lua.pop 1
     else do
-       mbres <- Lua.peekEither topOfStack
+       mbres <- peekEither topOfStack
        case mbres of
          Right res -> [res] <$ Lua.pop 1
          Left _    -> Lua.peekList topOfStack `finally` Lua.pop 1
@@ -234,11 +235,16 @@ singleElement x = do
   if elementUnchanged
     then x <$ Lua.pop 1
     else do
-    mbres <- Lua.peekEither (-1)
+    mbres <- peekEither (-1)
     case mbres of
       Right res -> res <$ Lua.pop 1
       Left err  -> do
         Lua.pop 1
-        Lua.throwException $
-          "Error while trying to get a filter's return " ++
-          "value from lua stack.\n" ++ err
+        Lua.throwMessage
+          ("Error while trying to get a filter's return " <>
+           "value from Lua stack.\n" <> show err)
+
+-- | Try to convert the value at the given stack index to a Haskell value.
+-- Returns @Left@ with an error message on failure.
+peekEither :: Peekable a => StackIndex -> Lua (Either PandocError a)
+peekEither = try . Lua.peek
diff --git a/src/Text/Pandoc/Lua/Init.hs b/src/Text/Pandoc/Lua/Init.hs
index 757d32898..a5e513a1f 100644
--- a/src/Text/Pandoc/Lua/Init.hs
+++ b/src/Text/Pandoc/Lua/Init.hs
@@ -9,96 +9,57 @@
 Functions to initialize the Lua interpreter.
 -}
 module Text.Pandoc.Lua.Init
-  ( LuaException (..)
-  , LuaPackageParams (..)
-  , runLua
-  , luaPackageParams
+  ( runLua
   ) where
 
+import Control.Monad.Catch (try)
 import Control.Monad.Trans (MonadIO (..))
 import Data.Data (Data, dataTypeConstrs, dataTypeOf, showConstr)
 import Foreign.Lua (Lua)
 import GHC.IO.Encoding (getForeignEncoding, setForeignEncoding, utf8)
 import Text.Pandoc.Class.PandocIO (PandocIO)
-import Text.Pandoc.Class.PandocMonad (getCommonState, getUserDataDir,
-                                      putCommonState)
-import Text.Pandoc.Lua.Global (Global (..), setGlobals)
-import Text.Pandoc.Lua.Packages (LuaPackageParams (..),
-                                 installPandocPackageSearcher)
-import Text.Pandoc.Lua.Util (loadScriptFromDataDir)
+import Text.Pandoc.Error (PandocError)
+import Text.Pandoc.Lua.Packages (installPandocPackageSearcher)
+import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua,
+                                  loadScriptFromDataDir, runPandocLua)
 
-import qualified Data.Text as Text
 import qualified Foreign.Lua as Lua
-import qualified Foreign.Lua.Module.Text as Lua
 import qualified Text.Pandoc.Definition as Pandoc
 import qualified Text.Pandoc.Lua.Module.Pandoc as ModulePandoc
 
--- | Lua error message
-newtype LuaException = LuaException Text.Text deriving (Show)
-
 -- | Run the lua interpreter, using pandoc's default way of environment
 -- initialization.
-runLua :: Lua a -> PandocIO (Either LuaException a)
+runLua :: Lua a -> PandocIO (Either PandocError a)
 runLua luaOp = do
-  luaPkgParams <- luaPackageParams
-  globals <- defaultGlobals
   enc <- liftIO $ getForeignEncoding <* setForeignEncoding utf8
-  res <- liftIO . Lua.runEither $ do
-    setGlobals globals
-    initLuaState luaPkgParams
-    -- run the given Lua operation
-    opResult <- luaOp
-    -- get the (possibly modified) state back
-    Lua.getglobal "PANDOC_STATE"
-    st <- Lua.peek Lua.stackTop
-    Lua.pop 1
-    -- done
-    return (opResult, st)
+  res <- runPandocLua . try $ do
+    initLuaState
+    liftPandocLua luaOp
   liftIO $ setForeignEncoding enc
-  case res of
-    Left (Lua.Exception msg) -> return $ Left (LuaException $ Text.pack msg)
-    Right (x, newState) -> do
-      putCommonState newState
-      return $ Right x
-
--- | Global variables which should always be set.
-defaultGlobals :: PandocIO [Global]
-defaultGlobals = do
-  commonState <- getCommonState
-  return
-    [ PANDOC_API_VERSION
-    , PANDOC_STATE commonState
-    , PANDOC_VERSION
-    ]
-
--- | Generate parameters required to setup pandoc's lua environment.
-luaPackageParams :: PandocIO LuaPackageParams
-luaPackageParams = do
-  datadir <- getUserDataDir
-  return LuaPackageParams { luaPkgDataDir = datadir }
+  return res
 
 -- | Initialize the lua state with all required values
-initLuaState :: LuaPackageParams -> Lua ()
-initLuaState pkgParams = do
-  Lua.openlibs
-  Lua.preloadTextModule "text"
-  installPandocPackageSearcher pkgParams
+initLuaState :: PandocLua ()
+initLuaState = do
+  liftPandocLua Lua.openlibs
+  installPandocPackageSearcher
   initPandocModule
-  loadScriptFromDataDir (luaPkgDataDir pkgParams) "init.lua"
+  loadScriptFromDataDir "init.lua"
  where
-  initPandocModule :: Lua ()
+  initPandocModule :: PandocLua ()
   initPandocModule = do
     -- Push module table
-    ModulePandoc.pushModule (luaPkgDataDir pkgParams)
+    ModulePandoc.pushModule
     -- register as loaded module
-    Lua.pushvalue Lua.stackTop
-    Lua.getfield Lua.registryindex Lua.loadedTableRegistryField
-    Lua.setfield (Lua.nthFromTop 2) "pandoc"
-    Lua.pop 1
+    liftPandocLua $ do
+      Lua.pushvalue Lua.stackTop
+      Lua.getfield Lua.registryindex Lua.loadedTableRegistryField
+      Lua.setfield (Lua.nthFromTop 2) "pandoc"
+      Lua.pop 1
     -- copy constructors into registry
     putConstructorsInRegistry
     -- assign module to global variable
-    Lua.setglobal "pandoc"
+    liftPandocLua $ Lua.setglobal "pandoc"
 
 -- | AST elements are marshaled via normal constructor functions in the
 -- @pandoc@ module. However, accessing Lua globals from Haskell is
@@ -108,8 +69,8 @@ initLuaState pkgParams = do
 --
 -- This function expects the @pandoc@ module to be at the top of the
 -- stack.
-putConstructorsInRegistry :: Lua ()
-putConstructorsInRegistry = do
+putConstructorsInRegistry :: PandocLua ()
+putConstructorsInRegistry = liftPandocLua $ do
   constrsToReg $ Pandoc.Pandoc mempty mempty
   constrsToReg $ Pandoc.Str mempty
   constrsToReg $ Pandoc.Para mempty
diff --git a/src/Text/Pandoc/Lua/Marshaling.hs b/src/Text/Pandoc/Lua/Marshaling.hs
index 624f8b917..1254402b6 100644
--- a/src/Text/Pandoc/Lua/Marshaling.hs
+++ b/src/Text/Pandoc/Lua/Marshaling.hs
@@ -13,6 +13,7 @@ module Text.Pandoc.Lua.Marshaling () where
 
 import Text.Pandoc.Lua.Marshaling.AST ()
 import Text.Pandoc.Lua.Marshaling.CommonState ()
-import Text.Pandoc.Lua.Marshaling.ReaderOptions ()
 import Text.Pandoc.Lua.Marshaling.Context ()
+import Text.Pandoc.Lua.Marshaling.PandocError()
+import Text.Pandoc.Lua.Marshaling.ReaderOptions ()
 import Text.Pandoc.Lua.Marshaling.Version ()
diff --git a/src/Text/Pandoc/Lua/Marshaling/AST.hs b/src/Text/Pandoc/Lua/Marshaling/AST.hs
index 81b206f67..8d7e83dc1 100644
--- a/src/Text/Pandoc/Lua/Marshaling/AST.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/AST.hs
@@ -19,9 +19,11 @@ module Text.Pandoc.Lua.Marshaling.AST
 import Control.Applicative ((<|>))
 import Foreign.Lua (Lua, Peekable, Pushable, StackIndex)
 import Text.Pandoc.Definition
+import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Util (defineHowTo, pushViaConstructor)
 import Text.Pandoc.Lua.Marshaling.CommonState ()
 
+import qualified Control.Monad.Catch as Catch
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.Lua.Util as LuaUtil
 
@@ -131,7 +133,7 @@ peekMetaValue idx = defineHowTo "get MetaValue" $ do
     Lua.TypeBoolean -> MetaBool <$> Lua.peek idx
     Lua.TypeString  -> MetaString <$> Lua.peek idx
     Lua.TypeTable   -> do
-      tag <- Lua.try $ LuaUtil.getTag idx
+      tag <- try $ LuaUtil.getTag idx
       case tag of
         Right "MetaBlocks"  -> MetaBlocks  <$> elementContent
         Right "MetaBool"    -> MetaBool    <$> elementContent
@@ -139,7 +141,7 @@ peekMetaValue idx = defineHowTo "get MetaValue" $ do
         Right "MetaInlines" -> MetaInlines <$> elementContent
         Right "MetaList"    -> MetaList    <$> elementContent
         Right "MetaString"  -> MetaString  <$> elementContent
-        Right t             -> Lua.throwException ("Unknown meta tag: " <> t)
+        Right t             -> Lua.throwMessage ("Unknown meta tag: " <> t)
         Left _ -> do
           -- no meta value tag given, try to guess.
           len <- Lua.rawlen idx
@@ -148,7 +150,7 @@ peekMetaValue idx = defineHowTo "get MetaValue" $ do
             else  (MetaInlines <$> Lua.peek idx)
                   <|> (MetaBlocks <$> Lua.peek idx)
                   <|> (MetaList <$> Lua.peek idx)
-    _        -> Lua.throwException "could not get meta value"
+    _        -> Lua.throwMessage "could not get meta value"
 
 -- | Push a block element to the top of the Lua stack.
 pushBlock :: Block -> Lua ()
@@ -199,7 +201,7 @@ peekBlock idx = defineHowTo "get Block value" $ do
                                     tbodies
                                     tfoot)
                           <$> elementContent
-      _ -> Lua.throwException ("Unknown block type: " <> tag)
+      _ -> Lua.throwMessage ("Unknown block type: " <> tag)
  where
    -- Get the contents of an AST element.
    elementContent :: Peekable a => Lua a
@@ -344,12 +346,15 @@ peekInline idx = defineHowTo "get Inline value" $ do
     "Strong"     -> Strong <$> elementContent
     "Subscript"  -> Subscript <$> elementContent
     "Superscript"-> Superscript <$> elementContent
-    _ -> Lua.throwException ("Unknown inline type: " <> tag)
+    _ -> Lua.throwMessage ("Unknown inline type: " <> tag)
  where
    -- Get the contents of an AST element.
    elementContent :: Peekable a => Lua a
    elementContent = LuaUtil.rawField idx "c"
 
+try :: Lua a -> Lua (Either PandocError a)
+try = Catch.try
+
 withAttr :: (Attr -> a -> b) -> (LuaAttr, a) -> b
 withAttr f (attributes, x) = f (fromLuaAttr attributes) x
 
diff --git a/src/Text/Pandoc/Lua/Marshaling/PandocError.hs b/src/Text/Pandoc/Lua/Marshaling/PandocError.hs
new file mode 100644
index 000000000..74537a1dd
--- /dev/null
+++ b/src/Text/Pandoc/Lua/Marshaling/PandocError.hs
@@ -0,0 +1,65 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# LANGUAGE LambdaCase           #-}
+{-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE ScopedTypeVariables  #-}
+{- |
+   Module      : Text.Pandoc.Lua.Marshaling.PandocError
+   Copyright   : © 2020 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+Marshaling of @'PandocError'@ values.
+-}
+module Text.Pandoc.Lua.Marshaling.PandocError
+  ( peekPandocError
+  , pushPandocError
+  )
+  where
+
+import Foreign.Lua (Lua, Peekable, Pushable, StackIndex)
+import Text.Pandoc.Error (PandocError (PandocLuaError))
+
+import qualified Foreign.Lua as Lua
+import qualified Foreign.Lua.Userdata as Lua
+import qualified Text.Pandoc.Lua.Util as LuaUtil
+import qualified Text.Pandoc.UTF8 as UTF8
+
+-- | Userdata name used by Lua for the @PandocError@ type.
+pandocErrorName :: String
+pandocErrorName = "pandoc error"
+
+-- | Peek a @'PandocError'@ element to the Lua stack.
+pushPandocError :: PandocError -> Lua ()
+pushPandocError = Lua.pushAnyWithMetatable pushPandocErrorMT
+  where
+    pushPandocErrorMT = Lua.ensureUserdataMetatable pandocErrorName $
+      LuaUtil.addFunction "__tostring" __tostring
+
+-- | Retrieve a @'PandocError'@ from the Lua stack.
+peekPandocError :: StackIndex -> Lua PandocError
+peekPandocError idx = Lua.ltype idx >>= \case
+  Lua.TypeUserdata -> do
+    errMb <- Lua.toAnyWithName idx pandocErrorName
+    return $ case errMb of
+      Just err -> err
+      Nothing  -> PandocLuaError "could not retrieve original error"
+  _ -> do
+    Lua.pushvalue idx
+    msg <- Lua.state >>= \l -> Lua.liftIO (Lua.errorMessage l)
+    return $ PandocLuaError (UTF8.toText msg)
+
+-- | Convert to string.
+__tostring :: PandocError -> Lua String
+__tostring = return . show
+
+--
+-- Instances
+--
+
+instance Pushable PandocError where
+  push = pushPandocError
+
+instance Peekable PandocError where
+  peek = peekPandocError
diff --git a/src/Text/Pandoc/Lua/Marshaling/Version.hs b/src/Text/Pandoc/Lua/Marshaling/Version.hs
index 090725afc..9adb1b763 100644
--- a/src/Text/Pandoc/Lua/Marshaling/Version.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/Version.hs
@@ -57,7 +57,7 @@ peekVersion idx = Lua.ltype idx >>= \case
     let parses = readP_to_S parseVersion versionStr
     case lastMay parses of
       Just (v, "") -> return v
-      _  -> Lua.throwException $ "could not parse as Version: " ++ versionStr
+      _  -> Lua.throwMessage $ "could not parse as Version: " ++ versionStr
 
   Lua.TypeUserdata ->
     reportValueOnFailure versionTypeName
@@ -71,7 +71,7 @@ peekVersion idx = Lua.ltype idx >>= \case
     makeVersion <$> Lua.peek idx
 
   _ ->
-    Lua.throwException "could not peek Version"
+    Lua.throwMessage "could not peek Version"
 
 instance Peekable Version where
   peek = peekVersion
diff --git a/src/Text/Pandoc/Lua/Module/MediaBag.hs b/src/Text/Pandoc/Lua/Module/MediaBag.hs
index 3a296ef46..e5a10217a 100644
--- a/src/Text/Pandoc/Lua/Module/MediaBag.hs
+++ b/src/Text/Pandoc/Lua/Module/MediaBag.hs
@@ -14,13 +14,13 @@ module Text.Pandoc.Lua.Module.MediaBag
   ) where
 
 import Control.Monad (zipWithM_)
-import Foreign.Lua (Lua, NumResults, Optional, liftIO)
+import Foreign.Lua (Lua, NumResults, Optional)
 import Text.Pandoc.Class.CommonState (CommonState (..))
-import Text.Pandoc.Class.PandocIO (runIOorExplode)
-import Text.Pandoc.Class.PandocMonad (fetchItem, putCommonState, setMediaBag)
+import Text.Pandoc.Class.PandocMonad (fetchItem, getMediaBag, modifyCommonState,
+                                      setMediaBag)
 import Text.Pandoc.Lua.Marshaling ()
 import Text.Pandoc.Lua.Marshaling.MediaBag (pushIterator)
-import Text.Pandoc.Lua.Util (addFunction)
+import Text.Pandoc.Lua.PandocLua (PandocLua (..), liftPandocLua, addFunction)
 import Text.Pandoc.MIME (MimeType)
 
 import qualified Data.ByteString.Lazy as BL
@@ -31,9 +31,9 @@ import qualified Text.Pandoc.MediaBag as MB
 --
 -- MediaBag submodule
 --
-pushModule :: Lua NumResults
+pushModule :: PandocLua NumResults
 pushModule = do
-  Lua.newtable
+  liftPandocLua Lua.newtable
   addFunction "delete" delete
   addFunction "empty" empty
   addFunction "insert" insertMediaFn
@@ -43,66 +43,46 @@ pushModule = do
   addFunction "fetch" fetch
   return 1
 
---
--- Port functions from Text.Pandoc.Class to the Lua monad.
--- TODO: reuse existing functions.
-
--- Get the current CommonState.
-getCommonState :: Lua CommonState
-getCommonState = do
-  Lua.getglobal "PANDOC_STATE"
-  Lua.peek Lua.stackTop
-
--- Replace MediaBag in CommonState.
-setCommonState :: CommonState -> Lua ()
-setCommonState st = do
-  Lua.push st
-  Lua.setglobal "PANDOC_STATE"
-
-modifyCommonState :: (CommonState -> CommonState) -> Lua ()
-modifyCommonState f = getCommonState >>= setCommonState . f
-
 -- | Delete a single item from the media bag.
-delete :: FilePath -> Lua NumResults
+delete :: FilePath -> PandocLua NumResults
 delete fp = 0 <$ modifyCommonState
   (\st -> st { stMediaBag = MB.deleteMedia fp (stMediaBag st) })
 
 -- | Delete all items from the media bag.
-empty :: Lua NumResults
+empty :: PandocLua NumResults
 empty = 0 <$ modifyCommonState (\st -> st { stMediaBag = mempty })
 
 -- | Insert a new item into the media bag.
 insertMediaFn :: FilePath
               -> Optional MimeType
               -> BL.ByteString
-              -> Lua NumResults
+              -> PandocLua NumResults
 insertMediaFn fp optionalMime contents = do
-  modifyCommonState $ \st ->
-    let mb = MB.insertMedia fp (Lua.fromOptional optionalMime) contents
-                               (stMediaBag st)
-    in st { stMediaBag = mb }
-  return 0
+  mb <- getMediaBag
+  setMediaBag $ MB.insertMedia fp (Lua.fromOptional optionalMime) contents mb
+  return (Lua.NumResults 0)
 
 -- | Returns iterator values to be used with a Lua @for@ loop.
-items :: Lua NumResults
-items = getCommonState >>= pushIterator . stMediaBag
+items :: PandocLua NumResults
+items = getMediaBag >>= liftPandocLua . pushIterator
 
 lookupMediaFn :: FilePath
-              -> Lua NumResults
+              -> PandocLua NumResults
 lookupMediaFn fp = do
-  res <- MB.lookupMedia fp . stMediaBag <$> getCommonState
-  case res of
+  res <- MB.lookupMedia fp <$> getMediaBag
+  liftPandocLua $ case res of
     Nothing -> 1 <$ Lua.pushnil
     Just (mimeType, contents) -> do
       Lua.push mimeType
       Lua.push contents
       return 2
 
-mediaDirectoryFn :: Lua NumResults
+mediaDirectoryFn :: PandocLua NumResults
 mediaDirectoryFn = do
-  dirContents <- MB.mediaDirectory . stMediaBag <$> getCommonState
-  Lua.newtable
-  zipWithM_ addEntry [1..] dirContents
+  dirContents <- MB.mediaDirectory <$> getMediaBag
+  liftPandocLua $ do
+    Lua.newtable
+    zipWithM_ addEntry [1..] dirContents
   return 1
  where
   addEntry :: Lua.Integer -> (FilePath, MimeType, Int) -> Lua ()
@@ -114,14 +94,9 @@ mediaDirectoryFn = do
     Lua.rawseti (-2) idx
 
 fetch :: T.Text
-      -> Lua NumResults
+      -> PandocLua NumResults
 fetch src = do
-  commonState <- getCommonState
-  let mediaBag = stMediaBag commonState
-  (bs, mimeType) <- liftIO . runIOorExplode $ do
-    putCommonState commonState
-    setMediaBag mediaBag
-    fetchItem src
-  Lua.push $ maybe "" T.unpack mimeType
-  Lua.push bs
+  (bs, mimeType) <- fetchItem src
+  liftPandocLua . Lua.push $ maybe "" T.unpack mimeType
+  liftPandocLua $ Lua.push bs
   return 2 -- returns 2 values: contents, mimetype
diff --git a/src/Text/Pandoc/Lua/Module/Pandoc.hs b/src/Text/Pandoc/Lua/Module/Pandoc.hs
index f376d0044..3886568b7 100644
--- a/src/Text/Pandoc/Lua/Module/Pandoc.hs
+++ b/src/Text/Pandoc/Lua/Module/Pandoc.hs
@@ -24,6 +24,8 @@ import Text.Pandoc.Class.PandocIO (runIO)
 import Text.Pandoc.Definition (Block, Inline)
 import Text.Pandoc.Lua.Filter (walkInlines, walkBlocks, LuaFilter, SingletonsList (..))
 import Text.Pandoc.Lua.Marshaling ()
+import Text.Pandoc.Lua.PandocLua (PandocLua, addFunction, liftPandocLua,
+                                  loadScriptFromDataDir)
 import Text.Pandoc.Walk (Walkable)
 import Text.Pandoc.Options (ReaderOptions (readerExtensions))
 import Text.Pandoc.Process (pipeProcess)
@@ -38,28 +40,28 @@ import Text.Pandoc.Error
 
 -- | Push the "pandoc" on the lua stack. Requires the `list` module to be
 -- loaded.
-pushModule :: Maybe FilePath -> Lua NumResults
-pushModule datadir = do
-  LuaUtil.loadScriptFromDataDir datadir "pandoc.lua"
-  LuaUtil.addFunction "read" readDoc
-  LuaUtil.addFunction "pipe" pipeFn
-  LuaUtil.addFunction "walk_block" walkBlock
-  LuaUtil.addFunction "walk_inline" walkInline
+pushModule :: PandocLua NumResults
+pushModule = do
+  loadScriptFromDataDir "pandoc.lua"
+  addFunction "read" readDoc
+  addFunction "pipe" pipeFn
+  addFunction "walk_block" walkBlock
+  addFunction "walk_inline" walkInline
   return 1
 
 walkElement :: (Walkable (SingletonsList Inline) a,
                 Walkable (SingletonsList Block) a)
-            => a -> LuaFilter -> Lua a
-walkElement x f = walkInlines f x >>= walkBlocks f
+            => a -> LuaFilter -> PandocLua a
+walkElement x f = liftPandocLua $ walkInlines f x >>= walkBlocks f
 
-walkInline :: Inline -> LuaFilter -> Lua Inline
+walkInline :: Inline -> LuaFilter -> PandocLua Inline
 walkInline = walkElement
 
-walkBlock :: Block -> LuaFilter -> Lua Block
+walkBlock :: Block -> LuaFilter -> PandocLua Block
 walkBlock = walkElement
 
-readDoc :: T.Text -> Optional T.Text -> Lua NumResults
-readDoc content formatSpecOrNil = do
+readDoc :: T.Text -> Optional T.Text -> PandocLua NumResults
+readDoc content formatSpecOrNil = liftPandocLua $ do
   let formatSpec = fromMaybe "markdown" (Lua.fromOptional formatSpecOrNil)
   res <- Lua.liftIO . runIO $
            getReader formatSpec >>= \(rdr,es) ->
@@ -80,8 +82,8 @@ readDoc content formatSpecOrNil = do
 pipeFn :: String
        -> [String]
        -> BL.ByteString
-       -> Lua NumResults
-pipeFn command args input = do
+       -> PandocLua NumResults
+pipeFn command args input = liftPandocLua $ do
   (ec, output) <- Lua.liftIO $ pipeProcess Nothing command args input
   case ec of
     ExitSuccess -> 1 <$ Lua.push output
diff --git a/src/Text/Pandoc/Lua/Module/Utils.hs b/src/Text/Pandoc/Lua/Module/Utils.hs
index 11a0bda84..4fe5e255d 100644
--- a/src/Text/Pandoc/Lua/Module/Utils.hs
+++ b/src/Text/Pandoc/Lua/Module/Utils.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE ScopedTypeVariables #-}
 {- |
    Module      : Text.Pandoc.Lua.Module.Utils
    Copyright   : Copyright © 2017-2020 Albert Krewinkel
@@ -13,15 +14,15 @@ module Text.Pandoc.Lua.Module.Utils
   ) where
 
 import Control.Applicative ((<|>))
+import Control.Monad.Catch (try)
 import Data.Default (def)
 import Data.Version (Version)
 import Foreign.Lua (Peekable, Lua, NumResults)
-import Text.Pandoc.Class.PandocIO (runIO)
-import Text.Pandoc.Class.PandocMonad (setUserDataDir)
 import Text.Pandoc.Definition ( Pandoc, Meta, MetaValue (..), Block, Inline
                               , Citation, Attr, ListAttributes)
+import Text.Pandoc.Error (PandocError)
 import Text.Pandoc.Lua.Marshaling ()
-import Text.Pandoc.Lua.Util (addFunction)
+import Text.Pandoc.Lua.PandocLua (PandocLua, addFunction, liftPandocLua)
 
 import qualified Data.Digest.Pure.SHA as SHA
 import qualified Data.ByteString.Lazy as BSL
@@ -32,14 +33,14 @@ import qualified Text.Pandoc.Filter.JSON as JSONFilter
 import qualified Text.Pandoc.Shared as Shared
 
 -- | Push the "pandoc.utils" module to the lua stack.
-pushModule :: Maybe FilePath -> Lua NumResults
-pushModule mbDatadir = do
-  Lua.newtable
+pushModule :: PandocLua NumResults
+pushModule = do
+  liftPandocLua Lua.newtable
   addFunction "blocks_to_inlines" blocksToInlines
   addFunction "equals" equals
   addFunction "make_sections" makeSections
   addFunction "normalize_date" normalizeDate
-  addFunction "run_json_filter" (runJSONFilter mbDatadir)
+  addFunction "run_json_filter" runJSONFilter
   addFunction "sha1" sha1
   addFunction "stringify" stringify
   addFunction "to_roman_numeral" toRomanNumeral
@@ -47,8 +48,8 @@ pushModule mbDatadir = do
   return 1
 
 -- | Squashes a list of blocks into inlines.
-blocksToInlines :: [Block] -> Lua.Optional [Inline] -> Lua [Inline]
-blocksToInlines blks optSep = do
+blocksToInlines :: [Block] -> Lua.Optional [Inline] -> PandocLua [Inline]
+blocksToInlines blks optSep = liftPandocLua $ do
   let sep = case Lua.fromOptional optSep of
               Just x -> B.fromList x
               Nothing -> Shared.defaultBlocksSeparator
@@ -67,23 +68,17 @@ normalizeDate :: T.Text -> Lua (Lua.Optional T.Text)
 normalizeDate = return . Lua.Optional . Shared.normalizeDate
 
 -- | Run a JSON filter on the given document.
-runJSONFilter :: Maybe FilePath
-              -> Pandoc
+runJSONFilter :: Pandoc
               -> FilePath
               -> Lua.Optional [String]
-              -> Lua NumResults
-runJSONFilter mbDatadir doc filterFile optArgs = do
+              -> PandocLua Pandoc
+runJSONFilter doc filterFile optArgs = do
   args <- case Lua.fromOptional optArgs of
             Just x -> return x
-            Nothing -> do
+            Nothing -> liftPandocLua $ do
               Lua.getglobal "FORMAT"
               (:[]) <$> Lua.popValue
-  filterRes <- Lua.liftIO . runIO $ do
-    setUserDataDir mbDatadir
-    JSONFilter.apply def args filterFile doc
-  case filterRes of
-    Left err -> Lua.raiseError (show err)
-    Right d -> (1 :: NumResults) <$ Lua.push d
+  JSONFilter.apply def args filterFile doc
 
 -- | Calculate the hash of the given contents.
 sha1 :: BSL.ByteString
@@ -93,7 +88,7 @@ sha1 = return . T.pack . SHA.showDigest . SHA.sha1
 -- | Convert pandoc structure to a string with formatting removed.
 -- Footnotes are skipped (since we don't want their contents in link
 -- labels).
-stringify :: AstElement -> Lua T.Text
+stringify :: AstElement -> PandocLua T.Text
 stringify el = return $ case el of
   PandocElement pd -> Shared.stringify pd
   InlineElement i  -> Shared.stringify i
@@ -109,7 +104,7 @@ stringifyMetaValue mv = case mv of
   MetaString s -> s
   _            -> Shared.stringify mv
 
-equals :: AstElement -> AstElement -> Lua Bool
+equals :: AstElement -> AstElement -> PandocLua Bool
 equals e1 e2 = return (e1 == e2)
 
 data AstElement
@@ -125,18 +120,18 @@ data AstElement
 
 instance Peekable AstElement where
   peek idx  = do
-    res <- Lua.try $  (PandocElement <$> Lua.peek idx)
-                  <|> (InlineElement <$> Lua.peek idx)
-                  <|> (BlockElement <$> Lua.peek idx)
-                  <|> (AttrElement <$> Lua.peek idx)
-                  <|> (ListAttributesElement <$> Lua.peek idx)
-                  <|> (MetaElement <$> Lua.peek idx)
-                  <|> (MetaValueElement <$> Lua.peek idx)
+    res <- try $  (PandocElement <$> Lua.peek idx)
+              <|> (InlineElement <$> Lua.peek idx)
+              <|> (BlockElement <$> Lua.peek idx)
+              <|> (AttrElement <$> Lua.peek idx)
+              <|> (ListAttributesElement <$> Lua.peek idx)
+              <|> (MetaElement <$> Lua.peek idx)
+              <|> (MetaValueElement <$> Lua.peek idx)
     case res of
       Right x -> return x
-      Left _ -> Lua.throwException
+      Left (_ :: PandocError) -> Lua.throwMessage
         "Expected an AST element, but could not parse value as such."
 
 -- | Convert a number < 4000 to uppercase roman numeral.
-toRomanNumeral :: Lua.Integer -> Lua T.Text
+toRomanNumeral :: Lua.Integer -> PandocLua T.Text
 toRomanNumeral = return . Shared.toRomanNumeral . fromIntegral
diff --git a/src/Text/Pandoc/Lua/Packages.hs b/src/Text/Pandoc/Lua/Packages.hs
index ad338f4bd..79d42a6d7 100644
--- a/src/Text/Pandoc/Lua/Packages.hs
+++ b/src/Text/Pandoc/Lua/Packages.hs
@@ -8,37 +8,32 @@
    Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
    Stability   : alpha
 
-Pandoc module for lua.
+Pandoc module for Lua.
 -}
 module Text.Pandoc.Lua.Packages
-  ( LuaPackageParams (..)
-  , installPandocPackageSearcher
+  ( installPandocPackageSearcher
   ) where
 
 import Control.Monad (forM_)
 import Data.ByteString (ByteString)
-import Foreign.Lua (Lua, NumResults, liftIO)
-import Text.Pandoc.Class.PandocIO (runIO)
-import Text.Pandoc.Class.PandocMonad (readDataFile, setUserDataDir)
+import Foreign.Lua (Lua, NumResults)
+import Text.Pandoc.Class.PandocMonad (readDataFile)
+import Text.Pandoc.Lua.PandocLua (PandocLua, liftPandocLua)
 
 import qualified Foreign.Lua as Lua
-import Text.Pandoc.Lua.Module.Pandoc as Pandoc
-import Text.Pandoc.Lua.Module.MediaBag as MediaBag
-import Text.Pandoc.Lua.Module.System as System
-import Text.Pandoc.Lua.Module.Types as Types
-import Text.Pandoc.Lua.Module.Utils as Utils
-
--- | Parameters used to create lua packages/modules.
-data LuaPackageParams = LuaPackageParams
-  { luaPkgDataDir :: Maybe FilePath
-  }
+import qualified Foreign.Lua.Module.Text as Text
+import qualified Text.Pandoc.Lua.Module.Pandoc as Pandoc
+import qualified Text.Pandoc.Lua.Module.MediaBag as MediaBag
+import qualified Text.Pandoc.Lua.Module.System as System
+import qualified Text.Pandoc.Lua.Module.Types as Types
+import qualified Text.Pandoc.Lua.Module.Utils as Utils
 
 -- | Insert pandoc's package loader as the first loader, making it the default.
-installPandocPackageSearcher :: LuaPackageParams -> Lua ()
-installPandocPackageSearcher luaPkgParams = do
+installPandocPackageSearcher :: PandocLua ()
+installPandocPackageSearcher = liftPandocLua $ do
   Lua.getglobal' "package.searchers"
   shiftArray
-  Lua.pushHaskellFunction (pandocPackageSearcher luaPkgParams)
+  Lua.pushHaskellFunction pandocPackageSearcher
   Lua.rawseti (Lua.nthFromTop 2) 1
   Lua.pop 1           -- remove 'package.searchers' from stack
  where
@@ -47,29 +42,24 @@ installPandocPackageSearcher luaPkgParams = do
     Lua.rawseti (-2) (i + 1)
 
 -- | Load a pandoc module.
-pandocPackageSearcher :: LuaPackageParams -> String -> Lua NumResults
-pandocPackageSearcher pkgParams pkgName =
+pandocPackageSearcher :: String -> PandocLua NumResults
+pandocPackageSearcher pkgName =
   case pkgName of
-    "pandoc"          -> let datadir = luaPkgDataDir pkgParams
-                         in pushWrappedHsFun (Pandoc.pushModule datadir)
+    "pandoc"          -> pushWrappedHsFun Pandoc.pushModule
     "pandoc.mediabag" -> pushWrappedHsFun MediaBag.pushModule
     "pandoc.system"   -> pushWrappedHsFun System.pushModule
     "pandoc.types"    -> pushWrappedHsFun Types.pushModule
-    "pandoc.utils"    -> let datadir = luaPkgDataDir pkgParams
-                         in pushWrappedHsFun (Utils.pushModule datadir)
-    _ -> searchPureLuaLoader
+    "pandoc.utils"    -> pushWrappedHsFun Utils.pushModule
+    "text"            -> pushWrappedHsFun Text.pushModule
+    _                 -> searchPureLuaLoader
  where
-  pushWrappedHsFun f = do
+  pushWrappedHsFun f = liftPandocLua $ do
     Lua.pushHaskellFunction f
     return 1
   searchPureLuaLoader = do
     let filename = pkgName ++ ".lua"
-    modScript <- liftIO (dataDirScript (luaPkgDataDir pkgParams) filename)
-    case modScript of
-      Just script -> pushWrappedHsFun (loadStringAsPackage pkgName script)
-      Nothing -> do
-        Lua.push ("\n\tno file '" ++ filename ++ "' in pandoc's datadir")
-        return 1
+    script <- readDataFile filename
+    pushWrappedHsFun (loadStringAsPackage pkgName script)
 
 loadStringAsPackage :: String -> ByteString -> Lua NumResults
 loadStringAsPackage pkgName script = do
@@ -79,11 +69,3 @@ loadStringAsPackage pkgName script = do
     else do
       msg <- Lua.popValue
       Lua.raiseError ("Error while loading `" <> pkgName <> "`.\n" <> msg)
-
--- | Get the ByteString representation of the pandoc module.
-dataDirScript :: Maybe FilePath -> FilePath -> IO (Maybe ByteString)
-dataDirScript datadir moduleFile = do
-  res <- runIO $ setUserDataDir datadir >> readDataFile moduleFile
-  return $ case res of
-    Left _ -> Nothing
-    Right s -> Just s
diff --git a/src/Text/Pandoc/Lua/PandocLua.hs b/src/Text/Pandoc/Lua/PandocLua.hs
new file mode 100644
index 000000000..6c3b410dd
--- /dev/null
+++ b/src/Text/Pandoc/Lua/PandocLua.hs
@@ -0,0 +1,134 @@
+{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+{- |
+   Module      : Text.Pandoc.Lua.PandocLua
+   Copyright   : Copyright © 2020 Albert Krewinkel
+   License     : GNU GPL, version 2 or above
+
+   Maintainer  : Albert Krewinkel <tarleb+pandoc@moltkeplatz.de>
+   Stability   : alpha
+
+PandocMonad instance which allows execution of Lua operations and which
+uses Lua to handle state.
+-}
+module Text.Pandoc.Lua.PandocLua
+  ( PandocLua (..)
+  , runPandocLua
+  , liftPandocLua
+  , addFunction
+  , loadScriptFromDataDir
+  ) where
+
+import Control.Monad (when)
+import Control.Monad.Catch (MonadCatch, MonadMask, MonadThrow)
+import Control.Monad.Except (MonadError (catchError, throwError))
+import Control.Monad.IO.Class (MonadIO (liftIO))
+import Foreign.Lua (Lua (..), NumResults, Pushable, ToHaskellFunction)
+import Text.Pandoc.Class.PandocIO (PandocIO)
+import Text.Pandoc.Class.PandocMonad (PandocMonad (..), readDataFile)
+import Text.Pandoc.Error (PandocError)
+import Text.Pandoc.Lua.Global (Global (..), setGlobals)
+import Text.Pandoc.Lua.ErrorConversion (errorConversion)
+
+import qualified Control.Monad.Catch as Catch
+import qualified Foreign.Lua as Lua
+import qualified Text.Pandoc.Class.IO as IO
+import qualified Text.Pandoc.Lua.Util as LuaUtil
+
+-- | Type providing access to both, pandoc and Lua operations.
+newtype PandocLua a = PandocLua { unPandocLua :: Lua a }
+  deriving
+    ( Applicative
+    , Functor
+    , Monad
+    , MonadCatch
+    , MonadIO
+    , MonadMask
+    , MonadThrow
+    )
+
+-- | Lift a @'Lua'@ operation into the @'PandocLua'@ type.
+liftPandocLua :: Lua a -> PandocLua a
+liftPandocLua = PandocLua
+
+-- | Evaluate a @'PandocLua'@ computation, running all contained Lua
+-- operations..
+runPandocLua :: PandocLua a -> PandocIO a
+runPandocLua pLua = do
+  origState <- getCommonState
+  globals <- defaultGlobals
+  (result, newState) <- liftIO . Lua.run' errorConversion . unPandocLua $ do
+    putCommonState origState
+    liftPandocLua $ setGlobals globals
+    r <- pLua
+    c <- getCommonState
+    return (r, c)
+  putCommonState newState
+  return result
+
+instance {-# OVERLAPPING #-} ToHaskellFunction (PandocLua NumResults) where
+  toHsFun _narg = unPandocLua
+
+instance Pushable a => ToHaskellFunction (PandocLua a) where
+  toHsFun _narg x = 1 <$ (unPandocLua x >>= Lua.push)
+
+-- | Add a function to the table at the top of the stack, using the given name.
+addFunction :: ToHaskellFunction a => String -> a -> PandocLua ()
+addFunction name fn = liftPandocLua $ do
+  Lua.push name
+  Lua.pushHaskellFunction fn
+  Lua.rawset (-3)
+
+-- | Load a file from pandoc's data directory.
+loadScriptFromDataDir :: FilePath -> PandocLua ()
+loadScriptFromDataDir scriptFile = do
+  script <- readDataFile scriptFile
+  status <- liftPandocLua $ Lua.dostring script
+  when (status /= Lua.OK) . liftPandocLua $
+    LuaUtil.throwTopMessageAsError'
+      (("Couldn't load '" ++ scriptFile ++ "'.\n") ++)
+
+-- | Global variables which should always be set.
+defaultGlobals :: PandocIO [Global]
+defaultGlobals = do
+  commonState <- getCommonState
+  return
+    [ PANDOC_API_VERSION
+    , PANDOC_STATE commonState
+    , PANDOC_VERSION
+    ]
+
+instance MonadError PandocError PandocLua where
+  catchError = Catch.catch
+  throwError = Catch.throwM
+
+instance PandocMonad PandocLua where
+  lookupEnv = IO.lookupEnv
+  getCurrentTime = IO.getCurrentTime
+  getCurrentTimeZone = IO.getCurrentTimeZone
+  newStdGen = IO.newStdGen
+  newUniqueHash = IO.newUniqueHash
+
+  openURL = IO.openURL
+
+  readFileLazy = IO.readFileLazy
+  readFileStrict = IO.readFileStrict
+
+  glob = IO.glob
+  fileExists = IO.fileExists
+  getDataFileName = IO.getDataFileName
+  getModificationTime = IO.getModificationTime
+
+  getCommonState = PandocLua $ do
+    Lua.getglobal "PANDOC_STATE"
+    Lua.peek Lua.stackTop
+  putCommonState = PandocLua . setGlobals . (:[]) . PANDOC_STATE
+
+  logOutput = IO.logOutput
diff --git a/src/Text/Pandoc/Lua/Util.hs b/src/Text/Pandoc/Lua/Util.hs
index d79fbb085..c6639e94c 100644
--- a/src/Text/Pandoc/Lua/Util.hs
+++ b/src/Text/Pandoc/Lua/Util.hs
@@ -19,7 +19,6 @@ module Text.Pandoc.Lua.Util
   , addFunction
   , addValue
   , pushViaConstructor
-  , loadScriptFromDataDir
   , defineHowTo
   , throwTopMessageAsError'
   , callWithTraceback
@@ -27,13 +26,11 @@ module Text.Pandoc.Lua.Util
   ) where
 
 import Control.Monad (unless, when)
+import Data.Text (Text)
 import Foreign.Lua ( Lua, NumArgs, NumResults, Peekable, Pushable, StackIndex
                    , Status, ToHaskellFunction )
-import Text.Pandoc.Class.PandocIO (runIOorExplode)
-import Text.Pandoc.Class.PandocMonad (readDataFile, setUserDataDir)
 import qualified Foreign.Lua as Lua
 import qualified Text.Pandoc.UTF8 as UTF8
-import Data.Text (Text)
 
 -- | Get value behind key from table at given index.
 rawField :: Peekable a => StackIndex -> String -> Lua a
@@ -87,15 +84,6 @@ pushViaCall fn = pushViaCall' fn (return ()) 0
 pushViaConstructor :: PushViaCall a => String -> a
 pushViaConstructor pandocFn = pushViaCall ("pandoc." ++ pandocFn)
 
--- | Load a file from pandoc's data directory.
-loadScriptFromDataDir :: Maybe FilePath -> FilePath -> Lua ()
-loadScriptFromDataDir datadir scriptFile = do
-  script <- Lua.liftIO . runIOorExplode $
-            setUserDataDir datadir >> readDataFile scriptFile
-  status <- Lua.dostring script
-  when (status /= Lua.OK) $
-    throwTopMessageAsError' (("Couldn't load '" ++ scriptFile ++ "'.\n") ++)
-
 -- | Get the tag of a value. This is an optimized and specialized version of
 -- @Lua.getfield idx "tag"@. It only checks for the field on the table at index
 -- @idx@ and on its metatable, also ignoring any @__index@ value on the
@@ -107,7 +95,7 @@ getTag idx = do
   Lua.push ("tag" :: Text)
   Lua.rawget (Lua.nthFromTop 2)
   Lua.tostring Lua.stackTop <* Lua.pop 2 >>= \case
-    Nothing -> Lua.throwException "untagged value"
+    Nothing -> Lua.throwMessage "untagged value"
     Just x -> return (UTF8.toString x)
 
 -- | Modify the message at the top of the stack before throwing it as an
@@ -116,11 +104,12 @@ throwTopMessageAsError' :: (String -> String) -> Lua a
 throwTopMessageAsError' modifier = do
   msg <- Lua.tostring' Lua.stackTop
   Lua.pop 2 -- remove error and error string pushed by tostring'
-  Lua.throwException (modifier (UTF8.toString msg))
+  Lua.throwMessage (modifier (UTF8.toString msg))
 
 -- | Mark the context of a Lua computation for better error reporting.
 defineHowTo :: String -> Lua a -> Lua a
-defineHowTo ctx = Lua.withExceptionMessage (("Could not " <> ctx <> ": ") <>)
+defineHowTo ctx op = Lua.errorConversion >>= \ec ->
+  Lua.addContextToException ec ("Could not " <> ctx <> ": ") op
 
 -- | Like @'Lua.pcall'@, but uses a predefined error handler which adds a
 -- traceback on error.
@@ -143,7 +132,8 @@ pcallWithTraceback nargs nresults = do
 callWithTraceback :: NumArgs -> NumResults -> Lua ()
 callWithTraceback nargs nresults = do
   result <- pcallWithTraceback nargs nresults
-  when (result /= Lua.OK) Lua.throwTopMessage
+  when (result /= Lua.OK)
+    Lua.throwTopMessage
 
 -- | Run the given string as a Lua program, while also adding a traceback to the
 -- error message if an error occurs.
diff --git a/src/Text/Pandoc/Writers/Custom.hs b/src/Text/Pandoc/Writers/Custom.hs
index 2be64d56f..50a013dfd 100644
--- a/src/Text/Pandoc/Writers/Custom.hs
+++ b/src/Text/Pandoc/Writers/Custom.hs
@@ -20,17 +20,14 @@ import Data.List (intersperse)
 import qualified Data.Map as M
 import qualified Data.Text as T
 import Data.Text (Text, pack)
-import Data.Typeable
 import Foreign.Lua (Lua, Pushable)
 import Text.DocLayout (render, literal)
 import Text.Pandoc.Class.PandocIO (PandocIO)
 import Text.Pandoc.Definition
-import Text.Pandoc.Lua (Global (..), LuaException (LuaException),
-                        runLua, setGlobals)
+import Text.Pandoc.Lua (Global (..), runLua, setGlobals)
 import Text.Pandoc.Lua.Util (addField, dofileWithTraceback)
 import Text.Pandoc.Options
 import Text.Pandoc.Templates (renderTemplate)
-import qualified Text.Pandoc.UTF8 as UTF8
 import Text.Pandoc.Writers.Shared
 
 import qualified Foreign.Lua as Lua
@@ -81,11 +78,6 @@ instance (Pushable a, Pushable b) => Pushable (KeyValue a b) where
     Lua.push v
     Lua.rawset (Lua.nthFromTop 3)
 
-data PandocLuaException = PandocLuaException Text
-    deriving (Show, Typeable)
-
-instance Exception PandocLuaException
-
 -- | Convert Pandoc to custom markup.
 writeCustom :: FilePath -> WriterOptions -> Pandoc -> PandocIO Text
 writeCustom luaFile opts doc@(Pandoc meta _) = do
@@ -97,21 +89,20 @@ writeCustom luaFile opts doc@(Pandoc meta _) = do
     stat <- dofileWithTraceback luaFile
     -- check for error in lua script (later we'll change the return type
     -- to handle this more gracefully):
-    when (stat /= Lua.OK) $
-      Lua.tostring' (-1) >>= throw . PandocLuaException . UTF8.toText
+    when (stat /= Lua.OK)
+      Lua.throwTopMessage
     rendered <- docToCustom opts doc
     context <- metaToContext opts
                (fmap (literal . pack) . blockListToCustom)
                (fmap (literal . pack) . inlineListToCustom)
                meta
     return (pack rendered, context)
-  let (body, context) = case res of
-        Left (LuaException msg) -> throw (PandocLuaException msg)
-        Right x -> x
-  return $
-    case writerTemplate opts of
-       Nothing  -> body
-       Just tpl -> render Nothing $
+  case res of
+    Left msg -> throw msg
+    Right (body, context) -> return $
+      case writerTemplate opts of
+        Nothing  -> body
+        Just tpl -> render Nothing $
                     renderTemplate tpl $ setField "body" body context
 
 docToCustom :: WriterOptions -> Pandoc -> Lua String