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+{-
+Copyright (C) 2008 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.Pluigns
+ Copyright : Copyright (C) 2008 John MacFarlane
+ License : GNU GPL, version 2 or above
+
+ Maintainer : John MacFarlane <jgm@berkeley.edu>
+ Stability : alpha
+ Portability : portable
+
+Support for plugins.
+-}
+
+module Text.Pandoc.Plugins (getPlugin)
+where
+
+import Language.Haskell.Interpreter
+import Text.Pandoc
+import Control.Monad (unless, liftM)
+import Control.Monad.Error (throwError)
+import Data.List (isInfixOf)
+
+-- | Returns the function named @transform@ in the specified
+-- module. The module may be identified either by module name
+-- or by path name. The @transform@ function should have type
+-- @a -> a@ or @a -> IO a@, where @a@ is an instance of 'Data':
+-- for example, @Pandoc -> Pandoc@, @Inline -> IO Inline@,
+-- @Block -> Block@, or @[Inline] -> IO [Inline]@.
+getPlugin :: String -> IO (Pandoc -> IO Pandoc)
+getPlugin modsrc = do
+ res <- runInterpreter (evaluatePlugin modsrc)
+ case res of
+ Right func -> return func
+ Left (WontCompile xs) -> error $ "WontCompile error for plugin '" ++ modsrc ++ "'\n" ++ unlines (map errMsg xs)
+ Left (NotAllowed x) -> error $ "NotAllowed error for plugin '" ++ modsrc ++ "'\n" ++ x
+ Left (UnknownError x) -> error $ "UnknownError for plugin '" ++ modsrc ++ "'\n" ++ x
+ Left (GhcException x) -> error $ "GhcException for plugin '" ++ modsrc ++ "'\n" ++ x
+
+evaluatePlugin :: String -> Interpreter (Pandoc -> IO Pandoc)
+evaluatePlugin modsrc = do
+ set [installedModulesInScope := False]
+ loadModules [modsrc]
+ modnames <- getLoadedModules
+ setTopLevelModules modnames
+ setImports ["Prelude", "Text.Pandoc", "Text.Pandoc.Definition"]
+ exports <- liftM concat $ mapM getModuleExports modnames
+ unless ((Fun "transform") `elem` exports) $
+ throwError $ UnknownError $ "The plugin module must define a function 'transform'."
+ transformType <- typeOf "transform"
+ if "-> IO" `isInfixOf` transformType
+ then interpret "processWithM transform" (as :: Pandoc -> IO Pandoc)
+ else interpret "return . (processWith transform)" (as :: Pandoc -> IO Pandoc)