[Haskell-cafe] Correct parsers for bounded integral values

[Akhra Gannon]

I believe it's not that integers must wrap, but that Read behavior must
match compiler behavior (and GHC's behavior is to wrap).

On Sun, Aug 3, 2025, 12:17 PM Stefan Klinger <haskell at stefan-klinger.de>
wrote:

> Pierre Thierry (2025-Jul-21, excerpt):
> > Well, IIUC, it conforms to the Haskell 98 specification.
>
> Hm.  Maybe I keep missing something here.  After all it's beeing
> pointed out repeatedly by you guys (and yes, I do listen), but I fail
> to verify that claim.
>
> I don't think the Haskell Spec really *requires* the `read` function
> for a bounded integral type to wrap around.
>
> Jeff Clites via Haskell-Cafe (2025-Jul-21, excerpt):
> > I think you will find, though, that `read @Word8` is intended to
> > match the behavior of `(fromInteger @Word8) . (read @Integer)`. At
> > least, the `Int` case is specified in the Haskell Report (in the
> > Prelude implementation).
>
> Sorry, I cannot find this.  Would you have a URL and a line number for
> me?  I'm really sorry my google-foo seems to be insufficient.
>
> I have found in the 98 report [4], similar in 2010 [5]:
>
>     The results of exceptional conditions (such as overflow or
>     underflow) on the fixed-precision numeric types are undefined; an
>     implementation may choose error (_|_, semantically), a truncated
>     value, or a special value such as infinity, indefinite, etc.
>
> So, not violating the report, but the implementation might choose to
> do better.
>
> Cheers
> Stefan
>
>
> [1]: https://mail.haskell.org/pipermail/haskell-cafe/2025-July/137156.html
> [2]: https://mail.haskell.org/pipermail/haskell-cafe/2025-July/137155.html
> [3]: https://mail.haskell.org/pipermail/haskell-cafe/2025-July/137162.html
> [4]: https://www.haskell.org/onlinereport/basic.html#sect6.4
> [5]:
> https://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1350006.4
>
>
> --
> Stefan Klinger, Ph.D. -- computer scientist              o/X
> http://stefan-klinger.de                                 /\/
> https://github.com/s5k6                                    \
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