Text.Pandoc.Lua: throw LuaException instead of using 'error'.

Text.Pandoc.App: trap LuaException and issue a PandocFilterError.

src/Text/Pandoc/App.hs

@@ -78,7 +78,7 @@ import Text.Pandoc.Builder (setMeta)
 import Text.Pandoc.Class (PandocIO, extractMedia, fillMediaBag, getLog,
                           setResourcePath, withMediaBag, setTrace)
 import Text.Pandoc.Highlighting (highlightingStyles)
-import Text.Pandoc.Lua (runLuaFilter)
+import Text.Pandoc.Lua (runLuaFilter, LuaException(..))
 import Text.Pandoc.Writers.Math (defaultMathJaxURL, defaultKaTeXURL)
 import Text.Pandoc.PDF (makePDF)
 import Text.Pandoc.Process (pipeProcess)
@@ -782,10 +782,16 @@ expandFilterPath mbDatadir fp = liftIO $ do
                _ -> return fp
 
 applyLuaFilters :: MonadIO m
-                => Maybe FilePath -> [FilePath] -> [String] -> Pandoc -> m Pandoc
+                => Maybe FilePath -> [FilePath] -> [String] -> Pandoc
+                -> m Pandoc
 applyLuaFilters mbDatadir filters args d = do
   expandedFilters <- mapM (expandFilterPath mbDatadir) filters
-  foldrM ($) d $ map (flip runLuaFilter args) expandedFilters
+  let go f d' = liftIO $ do
+        res <- E.try (runLuaFilter f args d')
+        case res of
+             Right x -> return x
+             Left (LuaException s) -> E.throw (PandocFilterError f s)
+  foldrM ($) d $ map go expandedFilters
 
 applyFilters :: MonadIO m
              => Maybe FilePath -> [FilePath] -> [String] -> Pandoc -> m Pandoc

src/Text/Pandoc/Lua.hs

@@ -28,11 +28,15 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 
 Pandoc lua utils.
 -}
-module Text.Pandoc.Lua ( runLuaFilter, pushPandocModule ) where
+module Text.Pandoc.Lua ( LuaException(..),
+                         runLuaFilter,
+                         pushPandocModule ) where
 
+import Control.Exception
 import Control.Monad (unless, when, (>=>))
 import Control.Monad.Trans (MonadIO (..))
 import Data.Map (Map)
+import Data.Typeable (Typeable)
 import Scripting.Lua (LuaState, StackValue (..))
 import Text.Pandoc.Definition
 import Text.Pandoc.Lua.PandocModule (pushPandocModule)
@@ -42,6 +46,11 @@ import Text.Pandoc.Walk
 import qualified Data.Map as Map
 import qualified Scripting.Lua as Lua
 
+data LuaException = LuaException String
+  deriving (Show, Typeable)
+
+instance Exception LuaException
+
 runLuaFilter :: (MonadIO m)
              => FilePath -> [String] -> Pandoc -> m Pandoc
 runLuaFilter filterPath args pd = liftIO $ do
@@ -59,7 +68,7 @@ runLuaFilter filterPath args pd = liftIO $ do
   if (status /= 0)
     then do
       Just luaErrMsg <- Lua.peek lua 1
-      error luaErrMsg
+      throwIO (LuaException luaErrMsg)
     else do
       Lua.call lua 0 Lua.multret
       newtop <- Lua.gettop lua
@@ -195,8 +204,9 @@ instance StackValue a => PushViaFilterFunction (IO a) where
     Lua.call lua num 1
     mbres <- Lua.peek lua (-1)
     case mbres of
-      Nothing -> error $ "Error while trying to get a filter's return "
-                 ++ "value from lua stack."
+      Nothing -> throwIO $ LuaException
+                  ("Error while trying to get a filter's return "
+                   ++ "value from lua stack.")
       Just res -> res <$ Lua.pop lua 1
 
 instance (StackValue a, PushViaFilterFunction b) =>
@@ -225,7 +235,8 @@ instance StackValue LuaFilterFunction where
   push lua v = pushFilterFunction lua v
   peek lua i = do
     isFn <- Lua.isfunction lua i
-    unless isFn (error $ "Not a function at index " ++ (show i))
+    unless isFn (throwIO $ LuaException $
+        "Not a function at index " ++ (show i))
     Lua.pushvalue lua i
     push lua ("PANDOC_FILTER_FUNCTIONS"::String)
     Lua.rawget lua Lua.registryindex