    {-# OPTIONS_GHC -XNoImplicitPrelude #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Foreign.StablePtr
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  ffi@haskell.org
    -- Stability   :  provisional
    -- Portability :  portable
    --
    -- This module is part of the Foreign Function Interface (FFI) and will usually
    -- be imported via the module "Foreign".
    --
    -----------------------------------------------------------------------------

    module Foreign.StablePtr
            ( -- * Stable references to Haskell values
              StablePtr          -- abstract
            , newStablePtr       -- :: a -> IO (StablePtr a)
            , deRefStablePtr     -- :: StablePtr a -> IO a
            , freeStablePtr      -- :: StablePtr a -> IO ()
            , castStablePtrToPtr -- :: StablePtr a -> Ptr ()
            , castPtrToStablePtr -- :: Ptr () -> StablePtr a
            , -- ** The C-side interface

              -- $cinterface
            ) where

    #ifdef __GLASGOW_HASKELL__
    import GHC.Stable
    #endif

    #ifdef __HUGS__
    import Hugs.StablePtr
    #endif

    #ifdef __NHC__
    import NHC.FFI
      ( StablePtr
      , newStablePtr
      , deRefStablePtr
      , freeStablePtr
      , castStablePtrToPtr
      , castPtrToStablePtr
      )
    #endif

    -- $cinterface
    --
    -- The following definition is available to C programs inter-operating with
    -- Haskell code when including the header @HsFFI.h@.
    --
    -- > typedef void *HsStablePtr;  /* C representation of a StablePtr */
    --
    -- Note that no assumptions may be made about the values representing stable
    -- pointers.  In fact, they need not even be valid memory addresses.  The only
    -- guarantee provided is that if they are passed back to Haskell land, the
    -- function 'deRefStablePtr' will be able to reconstruct the
    -- Haskell value referred to by the stable pointer.