[Haskell-cafe] Integer representation

[Oleg Grenrus]

Hi David,

you could  check http://hackage.haskell.org/package/integer-logarithms

I don't use different source-dirs (I could), the implementation isn't
that different so  CPP didn't felt too intrusive.

The
http://cabal.readthedocs.io/en/latest/developing-packages.html#resolution-of-conditions-and-flags
section speaks about automatic flags.
TL;DR cabal solver will toggle _automatic_ flags (manual flags are set
to defaults). It's recommended to make flag assignment disjoint, e.g.
note how bytestring version ranges are disjoint.

    if flag(bytestring-builder)
      build-depends: bytestring >= 0.9.2 && < 0.10.4,
                     bytestring-builder >= 0.10.4 && < 1
    else
      build-depends: bytestring >= 0.10.4 && < 0.11

Similarly, in `integer-logarithms` we have

    flag integer-gmp
      description:  integer-gmp or integer-simple
      default:      True
      manual:       False

    library
    ...
     if flag(integer-gmp)
        build-depends:
          integer-gmp < 1.1
     else
        build-depends:
          integer-simple
          -- here we could have hs-source-dirs

relying that there aren't install plan with both integer-gmp and
integer-simple

For very complicated example see: functor-classes-compat
http://hackage.haskell.org/package/functor-classes-compat-1/functor-classes-compat.cabal


Hopefully these help

Cheers, Oleg.


On 19.04.2018 23:05, David Feuer wrote:
> I'm not familiar with automatic cabal flags. Could you point me to
> documentation?
>
> On Thu, Apr 19, 2018 at 3:01 PM, Claude Heiland-Allen
> <claude at mathr.co.uk> wrote:
>> Hi David,
>>
>> On 19/04/18 18:13, David Feuer wrote:
>>> Is there any way to determine whether Integer comes from integer-gmp
>>> or integer-simple? I'm playing with the idea of using the underlying
>>> representation to get more compact/efficient tries, but I need to be
>>> able to find out what that representation is.
>> One way could be to use an automatic cabal flag.  With it enabled,
>> depend on integer-gmp and add hs-source-dirs to a directory containing
>> your integer-gmp implementation, with it disabled, depend on
>> integer-simple and add hs-source dirs to a directory containing your
>> integer-simple implementation.  This gives module-level control.  With
>> automatic flag I think cabal will try both and choose the setting that
>> gives the best build plan (likely corresponding to the Integer
>> implementation of your ghc).
>>
>>
>> Claude
>> --
>> https://mathr.co.uk
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