RFC: Unpacking sum types

[Johan Tibell]

After some discussions with SPJ I've now rewritten the proposal in terms of
unboxed sums (which should suffer from the extra seq problem you mention
above).

On Tue, Sep 1, 2015 at 11:31 AM, Dan Doel <dan.doel at gmail.com> wrote:

> I wonder: are there issues with strict/unpacked fields in the sum
> type, with regard to the 'fill in stuff' behavior?
>
> For example:
>
>     data C = C1 !Int | C2 ![Int]
>
>     data D = D1 !Double {-# UNPACK #-} !C
>
> Naively we might think:
>
>     data D' = D1 !Double !Tag !Int ![Int]
>
> But this is obviously not going to work at the
> Haskell-implemented-level. Since we're at a lower level, we could just
> not seq the things from the opposite constructor, but are there
> problems that arise from that? Also of course the !Int will probably
> also be unpacked, so such prim types need different handling (fill
> with 0, I guess).
>
> --
>
> Also, I guess this is orthogonal, but having primitive, unboxed sums
> (analogous to unboxed tuples) would be nice as well. Conceivably they
> could be used as part of the specification of unpacked sums, since we
> can apparently put unboxed tuples in data types now. I'm not certain
> if they would cover all cases, though (like the strictness concerns
> above).
>
> -- Dan
>
>
> On Tue, Sep 1, 2015 at 1:23 PM, Johan Tibell <johan.tibell at gmail.com>
> wrote:
> > I have a draft design for unpacking sum types that I'd like some feedback
> > on. In particular feedback both on:
> >
> >  * the writing and clarity of the proposal and
> >  * the proposal itself.
> >
> > https://ghc.haskell.org/trac/ghc/wiki/UnpackedSumTypes
> >
> > -- Johan
> >
> >
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> >
>
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