Documented instances of NominalDiffTime missing

[adambaker]

In particular, NominalDiffTime is missning (at least) Fractional and Num instances:

*Data.Thyme> 2::NominalDiffTime

<interactive>:3:1:
    No instance for (Num NominalDiffTime) arising from the literal `2'
    In the expression: 2 :: NominalDiffTime
    In an equation for `it': it = 2 :: NominalDiffTime

*Data.Thyme> 2.5::NominalDiffTime

<interactive>:4:1:
    No instance for (Fractional NominalDiffTime)
      arising from the literal `2.5'
    In the expression: 2.5 :: NominalDiffTime
    In an equation for `it': it = 2.5 :: NominalDiffTime

The hackage docs say NominalDiffTime has Fractional and Num instance.

I'm running this on Ubuntu 14.04, and I've tried it on MacOSX Yosemite and seen the same results.

$ cabal list thyme
* thyme
    Synopsis: A faster time library
    Default available version: 0.3.5.5
    Installed versions: 0.3.5.5
    Homepage: https://github.com/liyang/thyme
    License:  BSD3

I plan to work around this with fromSeconds and toSeconds for now.

[liyang]

The hackage docs say NominalDiffTime has Fractional and Num instance.

You'll get those instances by explicitly importing Data.Thyme.Time. I'll leave this ticket open until I get around to adding a word or two to the documentation along those lines.

I plan to work around this with fromSeconds and toSeconds for now.

Yes, please do. Because the result of NominalDiffTime multiplied/divided by NominalDiffTime is definitely not a NominalDiffTime.

PS: to avoid ambiguous types for literals, use fromSeconds'.

[adambaker]

I'm realizing the correct thing to do is use (^/) from Data.VectorSpace.

One reason I prefer thyme over time is that it's built using many more of these abstractions.

[liyang]

Ah, so you're scaling a time difference. Yes, use (^/) or even (*^) or (^*). :)

[jasonzoladz]

Please add this to the docs. Just lost 1.5 hours of my life. :)

[liyang]

@jasonzoladz At the top of Data.Thyme.Clock, it says:

Num, Real, Fractional and RealFrac instances for DiffTime and NominalDiffTime are only available by importing Data.Thyme.Time. In their stead are instances of AdditiveGroup, HasBasis and VectorSpace, with Scalar DiffTime ≡ Scalar NominalDiffTime ≡ Rational.

I'll try to make it more obvious.