Add support for the abs builtin

[meadori]

Implement the abs as defined here:

• https://docs.python.org/2.7/library/functions.html#abs

[trotterdylan]

Thanks for putting this together! Please just confirm that the command "make precommit" succeeds.

[meadori]

make precommit passed.

[trotterdylan]

I realized that the right way to implement this is with an __abs__ slot that's implemented by int, float etc.

…

On Wed, Jan 4, 2017 at 9:32 PM Meador Inge ***@***.***> wrote: make precommit passed. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#28 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAHLeyFSeiDK6fywFbiqDAM9au_QFFCaks5rPIBRgaJpZM4LbVqk> .

[meadori]

Thanks for catching that! I reworked the patch to use the __abs__ slot instead.

[trotterdylan]

Couple more small suggestions. Also a friendly reminder to make precommit (I will get Travis doing that soon...)

[trotterdylan]

This can overflow if z == MinInt so check for that case and promote to Long.

[trotterdylan]

To avoid an unnecessary allocation in the positive case, how about:

z := toIntUnsafe(o)
if z.Value() > 0 {
  return z.ToObject(), nil
}
// .. check for overflow as mentioned below
return NewInt(-x).ToObject(), nil

[meadori]

Thanks for the review. I address the copy for > 0 and overflow issues.

[trotterdylan]

This is great! Thanks for getting this done.