GHC for Plugins

[Matt Walker]

Hello,

I am developing a game and would like to write the core in haskell with
haskell also for scripting.  I like haskell.

I have the following file to help me do this.

>>> BEGIN FILE

{-# LANGUAGE ScopedTypeVariables #-}

module Plugin.Load where

import Data.Functor
import System.Directory
import GHC
import GHC.Paths
import DynFlags
import Unsafe.Coerce

type ModName = String
type ValName = String

loadPlugin :: FilePath -> ModName -> ValName -> IO a
loadPlugin dir modName value = do
  withCurrentDirectory dir $
    defaultErrorHandler defaultFatalMessager defaultFlushOut $
    runGhc (Just libdir) $ do

    dynFlags <- getSessionDynFlags
    setSessionDynFlags $ dynamicTooMkDynamicDynFlags $ dynFlags
      { importPaths = [modName] ++ importPaths dynFlags
      , hscTarget = HscAsm
      , ghcLink = LinkInMemory
      , ghcMode = CompManager
      }
    sequence [guessTarget modName Nothing] >>= setTargets
    load LoadAllTargets
    setContext [IIDecl $ simpleImportDecl $ mkModuleName modName]
    fetched <- compileExpr (modName ++ "." ++ value)
    return (unsafeCoerce fetched :: a)

<<< END FILE

The problem is that if I run the function loadPlugin on the same input more
than once, GHC barfs.  The error I get is:

/usr/bin/ld.gold: error: cannot find -lghc_5
collect2: error: ld returned 1 exit status
`gcc' failed in phase `Linker'. (Exit code: 1)
*** Exception: ExitFailure 1

sometimes it's -lghc_2 or -lghc_13 above.  Anyways, it seems like I and/or
ghc isn't cleaning up properly after themself and then wants to try to
append numbers.  Any idea what is causing this and how to fix it?

Thanks,
Matt

PS. is there a better way of doing this using Typeable?  I'd rather not
unsafeCoerce.
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