> 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?
Yes, that's right.
> Could ForeignPtr be generalised so that its ForeignObj# could
> represent any type, rather than just a Ptr?
Unfortunately no. The ForeignObj# type is unlifted, which means it
doesn't have _|_ as a possible value. The same restrictions as for
unboxed types apply: you can't instantiate a polymorphic type variable
with ForeignObj#, or indeed any primitive type.
Cheers,
Simon
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