Durations form a vector space

[treeowl]

If we admit negative durations (e.g., X happened -1 seconds after Y = X happened 1 second before y), then durations form a vector space. I don't know enough about vector space classes available on Hackage, but we could instantiate them ... if we admitted negative Time. I don't understand why it's not allowed.

[dcastro]

I'm not familiar with vector spaces, but I too have previously wondered why negative durations are not allowed, and the initial rationale has not been documented anywhere (AFAIK).

To give a concrete use case, this would be useful to calculate the period between two events t0 and t1 where you don't know which event will happen first (i.e. t1 - t0 could be positive or negative).

Also, another related issue: #118

However, doing this at this stage would be a significant breaking change. @gromakovsky what do you think about this?