Gah. We have no way to be polymorphic over all pointers (both lifted and unlifted) but not over Int# etc.
As you say, this is too much of a special case to make an invasive change. I’m quite dubious about making weak poitners to unlifted heap-allocated objects. I can’t say it’s wrong but it feels dodgy to me. Simon From: David Feuer <david.fe...@gmail.com> Sent: 22 August 2018 14:59 To: Ben Gamari <b...@smart-cactus.org> Cc: Simon Peyton Jones <simo...@microsoft.com>; David Feuer <da...@well-typed.com>; ghc-devs <ghc-devs@haskell.org> Subject: Re: Unlifted primop types The problem is that this also accepts things that aren't pointers at all! We could fix that *for primops* by changing RuntimeRep to something like data RuntimeRep = PtrRep Liftedness | ... But that would only work for primops (at least for now) so it may not be worth the breakage. On Wed, Aug 22, 2018, 7:45 AM Ben Gamari <b...@smart-cactus.org<mailto:b...@smart-cactus.org>> wrote: Simon Peyton Jones <simo...@microsoft.com<mailto:simo...@microsoft.com>> writes: > | Huh! It looks like what we currently do for some primops is just use a > | totally bogus kind. For example, mkWeak# will happily accept an Int# as > | its first argument. > > Well, I see > primop MkWeakOp "mkWeak#" GenPrimOp > o -> b -> (State# RealWorld -> (# State# RealWorld, c #)) > > and I believe (from Ben's message) that the "o" means "open type variable", > which is the old terminology for what we now call levity-polymorphic. > Right; currently (largely for historical reasons) we use `o` to accommodate cases that accept both lifted and unlifted pointers. Cheers, - Ben
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