At 2001-09-20 04:56, Simon Marlow wrote:

ForeignPtrs are defined like this

data ForeignPtr a = ForeignPtr ForeignObj#

where ForeignObj# is a *boxed* address, it corresponds to a real heap object. The heap object is primitive from the point of view of the compiler - it can't be optimised away. So it works to attach a finalizer to the ForeignObj# (but not to the ForeignPtr!).

OK, you are saying that the ForeignObj# is a representation of a 'Ptr a', but in a way such that the compiler can't optimise away the box. Is that correct? Could ForeignPtr be generalised so that its ForeignObj# could represent any type, rather than just a Ptr? -- Ashley Yakeley, Seattle WA