addForeignPtrFinalizer

[Alastair Reid]

> Still hoping ;-) The discussion seemed to stop without reaching a
> conclusion last time.

I thought it was concluded and the report changed such that all three
compilers which implement the ffi spec can implement it without
receiving a heart, lung and liver transplant.

> At least, I still don't think I fully understand why the current
> newForeignPtr is not implementable without concurrency, given that a
> form of context switching must already exist in order to implement
> foreign import that re-enters Haskell.

We've written a bunch about it.  I suspect that if we were to give a
full and complete list of all the changes required we'd have done most
of the work required to implement it (though not the work to debug and
maintain it which is probably more significant).  We're not going to
do that so you'll have to live with the explanations we've given so
far.

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A