Re: `StablePtr` in `ST`
Our use case is unsafeCoercing a mutable reference to use as a key in an IntMap. Our reasoning is that coercing an IORef/STRef is unsuitable because the underlying MutVar# may move, invalidating the key (i.e., you cannot safely coerce back if a GC has happened between insertion and reading). (If that’s incorrect, do enlighten us!) This is a “very nice to have” for our purposes—with the understanding that it’s wicked unsafe. ;) On Tue, Aug 20, 2019, 18:09 David Feuer wrote: > You also need to avoid inspecting the StablePtr itself, which is just a > number, to maintain purity. The whole thing is a bit weird. Why do you want > this anyway? > > On Wed, Aug 21, 2019, 7:39 AM David Feuer wrote: > >> So something like >> >> newtype StablePtr a = StablePtr (StablePtrST RealWorld a)? >> >> I suppose that could work with some discipline. You have to assume that >> foreign code doesn't pick its address out of a hat and so something silly, >> but I guess you pretty much have to assume that anyway. >> >> On Wed, Aug 21, 2019, 5:00 AM Matthew Farkas-Dyck >> wrote: >> >>> I have been doing some work where i want `StablePtr`, but also to not >>> be confined to `IO`. I saw the following comment in >>> "compiler/prelude/PrimOp.hs": >>> >>> Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? >>> [ADR] >>> >>> It has been there for 20 years. What is the answer? If it is safe i'll >>> send the patch generalizing these operations. >>> ___ >>> Glasgow-haskell-users mailing list >>> Glasgow-haskell-users@haskell.org >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users >>> >> ___ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users > ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: `StablePtr` in `ST`
You also need to avoid inspecting the StablePtr itself, which is just a number, to maintain purity. The whole thing is a bit weird. Why do you want this anyway? On Wed, Aug 21, 2019, 7:39 AM David Feuer wrote: > So something like > > newtype StablePtr a = StablePtr (StablePtrST RealWorld a)? > > I suppose that could work with some discipline. You have to assume that > foreign code doesn't pick its address out of a hat and so something silly, > but I guess you pretty much have to assume that anyway. > > On Wed, Aug 21, 2019, 5:00 AM Matthew Farkas-Dyck > wrote: > >> I have been doing some work where i want `StablePtr`, but also to not >> be confined to `IO`. I saw the following comment in >> "compiler/prelude/PrimOp.hs": >> >> Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR] >> >> It has been there for 20 years. What is the answer? If it is safe i'll >> send the patch generalizing these operations. >> ___ >> Glasgow-haskell-users mailing list >> Glasgow-haskell-users@haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users >> > ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
Re: `StablePtr` in `ST`
So something like newtype StablePtr a = StablePtr (StablePtrST RealWorld a)? I suppose that could work with some discipline. You have to assume that foreign code doesn't pick its address out of a hat and so something silly, but I guess you pretty much have to assume that anyway. On Wed, Aug 21, 2019, 5:00 AM Matthew Farkas-Dyck wrote: > I have been doing some work where i want `StablePtr`, but also to not > be confined to `IO`. I saw the following comment in > "compiler/prelude/PrimOp.hs": > > Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR] > > It has been there for 20 years. What is the answer? If it is safe i'll > send the patch generalizing these operations. > ___ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users > ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
`StablePtr` in `ST`
I have been doing some work where i want `StablePtr`, but also to not be confined to `IO`. I saw the following comment in "compiler/prelude/PrimOp.hs": Question: Why @RealWorld@ - won't any instance of @_ST@ do the job? [ADR] It has been there for 20 years. What is the answer? If it is safe i'll send the patch generalizing these operations. ___ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/glasgow-haskell-users
