withStorableArray making IORefs

[Simon Marlow]

> I'm guessing it's not safe to use "newIORef" as the function=20
> argument to
> withStorableArray, but in a simple case [1], it seems to work okay.  I
> suppose the danger is if the RTS decides to move the array.  Does this
> happen IRL?

The danger is rather that the array might get freed.  A StorableArray
contains a ForeignPtr to the array, and the finalizer on the ForeignPtr
will free the array after the last use.  If you obtain a pointer to the
array by nefarious means (ie. 'withStorableArray return' would do it)
then the RTS might free the array while you still have a pointer to it.

Cheers,
	Simon