-withForeignPtr :: ForeignPtr a -> (Ptr a -> IO b) -> IO b
--- ^This is a way to look at the pointer living inside a
--- foreign object. This function takes a function which is
--- applied to that pointer. The resulting 'IO' action is then
--- executed. The foreign object is kept alive at least during
--- the whole action, even if it is not used directly
--- inside. Note that it is not safe to return the pointer from
--- the action and use it after the action completes. All uses
--- of the pointer should be inside the
--- 'withForeignPtr' bracket. The reason for
--- this unsafety is the same as for
--- 'foreignPtrToPtr' below: the finalizer
--- may run earlier than expected, because the compiler can only
--- track usage of the 'ForeignPtr' object, not
--- a 'Ptr' object made from it.
---
--- This function is normally used for marshalling data to
--- or from the object pointed to by the
--- 'ForeignPtr', using the operations from the
--- 'Storable' class.
-withForeignPtr fo io
- = do r <- io (foreignPtrToPtr fo)
- touchForeignPtr fo
- return r
-
-foreignPtrToPtr :: ForeignPtr a -> Ptr a