Interval. leftClosedRightOpen returning an Either feels janky

[jcoveney]

I don't know if this is a pattern we want to promote...I feel like we should control the way that people come in and out of Intersections such that this sort of thing isn't necessary.

That said, Interval is a hot as hell class. There's some space to continue generalizing but I am loving the direction it has taken #types #types #TYPES

[johnynek]

closed by #279