Exceptions from "wrapper" functions

bug.hs

-- ghc bug.hs c.c && bug

module Main(main) where

import Control.Concurrent
import Control.Monad
import Foreign.C
import Foreign.Ptr

foreign import ccall apply :: FunPtr (CString -> IO CString) -> CString -> IO CString
foreign import ccall "wrapper" wrapper :: (CString -> IO CString) -> IO (FunPtr (CString -> IO CString))

main :: IO ()
main = do
    putStrLn "starting"
    main <- myThreadId
    threads <- replicateM 100 $ forkIO $
        withCString "hello" $ \ptr -> do
            let f x = do
                    error "die"
                    return x
            ff <- wrapper f
            res <- apply ff ptr
            print =<< peekCString res
    threadDelay 10000000

c.c

char* apply(char*(*f)(char*), char* x)
{
    return f(x);
}