BoxedRep UNPACK pragma

[Mikolaj Konarski]

On Sat, Aug 12, 2023 at 5:20 PM Brandon Allbery <allbery.b at gmail.com> wrote:
>
> The warning sounds correct to me: `Maybe` has two constructors?

It says at https://downloads.haskell.org/ghc/latest/docs/users_guide/exts/pragmas.html#unpack-pragma

"Since 9.6.1, data types with multiple constructors can also be
unpacked, effectively transforming the field into an unboxed sum of
the unpackings of each constructor (see UnboxedSums)."

> On Sat, Aug 12, 2023 at 10:25 AM Alan & Kim Zimmerman
> <alan.zimm at gmail.com> wrote:
> >
> > I have seen the following warning on master for some time
> >
> > compiler/GHC/Core/TyCon.hs:1540:5: warning:
> >     • Ignoring unusable UNPACK pragma
> >         on the first argument of ‘BoxedRep’
> >     • In the definition of data constructor ‘BoxedRep’
> >       In the data type declaration for ‘PrimRep’
> >      |
> > 1540 |   | BoxedRep {-# UNPACK #-} !(Maybe Levity) -- ^ Boxed, heap value
> >      |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > Is it something that needs to be fixed? Can the code be updated to remove the warning?
> >
> > Alan
> > _______________________________________________
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>
>
>
> --
> brandon s allbery kf8nh
> allbery.b at gmail.com
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