Added a plugin system, based on hint.

+ In Text.Pandoc.Definition, added processIn, processInM,
  and queryIn, and deprecated processPandoc and queryPandoc
  for these more general functions, which are useful in writing
  plugins.

+ Added module Text.Pandoc.Plugins.

+ Added a --plugins option to Main, and code to run the parsed pandoc
  document through all the plugins.

+ Provided five sample plugin files in the plugins/ directory.

+ Documented --plugin in the pandoc man page and README.


git-svn-id: https://pandoc.googlecode.com/svn/trunk@1519 788f1e2b-df1e-0410-8736-df70ead52e1b

2 files changed, 88 insertions, 6 deletions

diff --git a/Text/Pandoc/Definition.hs b/Text/Pandoc/Definition.hs
index 3c783b1b9..ed58f6b75 100644
--- a/Text/Pandoc/Definition.hs
+++ b/Text/Pandoc/Definition.hs
@@ -128,10 +128,23 @@ data Inline
     | Note [Block]          -- ^ Footnote or endnote 
     deriving (Show, Eq, Read, Typeable, Data)
 
--- | Applies a transformation to matching elements in a Pandoc document.
-processPandoc :: Typeable a => (a -> a) -> Pandoc -> Pandoc
-processPandoc f = everywhere (mkT f)
+-- | Applies a transformation on @a@s to matching elements in a @b@.
+processIn :: (Data a, Data b) => (a -> a) -> b -> b
+processIn f = everywhere (mkT f)
+
+-- | Like 'processIn', but with monadic transformations.
+processInM :: (Monad m, Data a, Data b) => (a -> m a) -> b -> m b
+processInM f = everywhereM (mkM f)
+
+-- | Runs a query on matching @a@ elements in a @c@.
+queryIn :: (Data a, Data c) => (a -> [b]) -> c -> [b]
+queryIn f = everything (++) ([] `mkQ` f)
+
+{-# DEPRECATED processPandoc "Use processIn instead" #-}
+processPandoc :: Data a => (a -> a) -> Pandoc -> Pandoc
+processPandoc = processIn
+
+{-# DEPRECATED queryPandoc "Use queryIn instead" #-}
+queryPandoc :: Data a => (a -> [b]) -> Pandoc -> [b]
+queryPandoc = queryIn
 
--- | Runs a query on matching elements in a Pandoc document. 
-queryPandoc :: Typeable a => (a -> [b]) -> Pandoc -> [b]
-queryPandoc f = everything (++) ([] `mkQ` f)
diff --git a/Text/Pandoc/Plugins.hs b/Text/Pandoc/Plugins.hs
new file mode 100644
index 000000000..5ba333faa
--- /dev/null
+++ b/Text/Pandoc/Plugins.hs
@@ -0,0 +1,69 @@
+{-
+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 "processInM transform" (as :: Pandoc -> IO Pandoc)
+     else interpret "return . (processIn transform)" (as :: Pandoc -> IO Pandoc)