OK, thanks to Luite Stegeman I've found the solution and I think I'll post it here in case someone else stumbles upon the same problem. The solution is the following: you have to change 'log_action' parameter in dynFlags. For example, one can do this: ----------------------------------------------------------------------------------------------------------------------- initGhc = do .. ref <- liftIO $ newIORef "" dfs <- getSessionDynFlags setSessionDynFlags $ dfs { hscTarget = HscInterpreted , ghcLink = LinkInMemory , log_action = logHandler ref} logHandler :: IORef String -> LogAction logHandler ref dflags severity srcSpan style msg = case severity of SevError -> modifyIORef' ref (++ printDoc) SevFatal -> modifyIORef' ref (++ printDoc) _ -> return () where cntx = initSDocContext dflags style locMsg = mkLocMessage severity srcSpan msg printDoc = show (runSDoc locMsg cntx) -- LogAction == DynFlags -> Severity -> SrcSpan -> PprStyle -> MsgDoc -> IO () ----------------------------------------------------------------------------------------------------------------------- On Sat, Jun 15, 2013 at 1:26 PM, Daniel F wrote:

Hello, everyone.

I am in need of setting up custom exception handlers when using GHC API to compile modules. Right now I have the following piece of code:

* Main.hs: -------------------------------------------------------------------------------------------------- import GHC import GHC.Paths import MonadUtils import Exception import Panic import Unsafe.Coerce import System.IO.Unsafe

handleException :: (ExceptionMonad m, MonadIO m) => m a -> m (Either String a) handleException m = ghandle (\(ex :: SomeException) -> return (Left (show ex))) $ handleGhcException (\ge -> return (Left (showGhcException ge ""))) $ flip gfinally (liftIO restoreHandlers) $ m >>= return . Right

initGhc :: Ghc () initGhc = do dfs <- getSessionDynFlags setSessionDynFlags $ dfs { hscTarget = HscInterpreted , ghcLink = LinkInMemory } return ()

test :: IO (Either String Int) test = handleException $ runGhc (Just libdir) $ do initGhc setTargets =<< sequence [ guessTarget "./test/file1.hs" Nothing ] graph <- depanal [] False loaded <- load LoadAllTargets -- when (failed loaded) $ throw LoadingException setContext (map (IIModule . moduleName . ms_mod) graph) let expr = "main" ty <- exprType expr -- throws exception if doesn't typecheck output ty res <- unsafePerformIO . unsafeCoerce <$> compileExpr expr return res

--------------------------------------------------------------------------------------------------

* file1.hs:

---------------------------- module Main where

main = do return x

----------------------------

The problem is when I run the 'test' function above I receive the following output:

h> test

test/file1.hs:4:10: Not in scope: `x'

Left "Cannot add module Main to context: not a home module" it :: Either String Int

So, if I understand this correctly, my exception handler does indeed catch an exception correctly, however, I still receive some output which I want to be captured. Is there a way to do this?

-- Sincerely yours, -- Daniil Frumin

-- Sincerely yours, -- Daniil