PROPOSAL: Add 'Natural' type to base:Data.Word

[David Feuer]

I'm definitely in favor of this idea. How (if at all) would you like these
term-level natural numbers to relate to the type-level ones?

On Tue, Nov 11, 2014 at 4:35 AM, Herbert Valerio Riedel <hvr at gnu.org> wrote:

> Hello CLC et al.,
>
> I hereby suggest to add a type for encoding term-level naturals
>
>   data Natural = <opaque/hidden>
>        deriving (...the usual standard classes...)
>
> to `base:Data.Word` module
>
> Motivation
> ==========
>
>  - GHC 7.10 is planned to ship with integer-gmp2[2] as its default
>    `Integer` lib, whose low-level primitives are based on *unsigned*
>    BigNums. And 'Natural' type for integer-gmp2 can be implemented
>    directly w/o the overhead of wrapping an `Integer` via
>
>      data Natural = NatS# Word# | NatJ# !PrimBigNat#
>
>    as well as having a twice as large domain handled via the small-word
>    constructor and thus avoiding FFI calls into GMP.
>
>  - GHC/`base` already provides type-level naturals, but no term-level
>    naturals
>
>  - Remove the asymmetry of having an unbounded signed `Integer` but no
>    unbounded /unsigned/ integral type.
>
>    Also, `Data.Word` has been carrying the following note[1] for some
>    time now:
>
>    > It would be very natural to add a type Natural providing an
>    > unbounded size unsigned integer, just as Integer provides unbounded
>    > size signed integers. We do not do that yet since there is no
>    > demand for it.
>
>
>
> Discussion period: ~10 days (GHC 7.10 RC freeze is scheduled for Nov 21st)
>
> Cheers,
>   hvr
>
>  [1]:
> http://hackage.haskell.org/package/base-4.7.0.1/docs/Data-Word.html#g:3
>
>  [2]: https://phabricator.haskell.org/D82
>       https://ghc.haskell.org/trac/ghc/wiki/Design/IntegerGmp2
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