Have you ever needed to know if two intervals overlap? I wrote Rampart, a small Haskell library to help with that.

The other day at work we were working on a system that needed to select accounts that were active during a certain timeframe. This seemingly simple problem prompted a bunch of discussion. We spent some time puzzling through inequalities before we landed on something that everyone agreed would do what we wanted. I figured we could save ourselves and others time in the future by making a library to handle the tricky interval logic.

You may be thinking that this is a trivial problem. Did you know that there are 13 different ways that two intervals can relate to each other? Here they are:

Rampart is a tiny Haskell module that can take two intervals and tell you how they relate. For example, how does the interval from 2 to 4 relate to the interval from 3 to 5?

>>> import Rampart >>> relate (toInterval (2, 4)) (toInterval (3, 5)) Overlaps

It’s easy to show off with numbers, but it works with anything that’s orderable: dates, times, money, and so on. So if you find yourself asking questions about intervals, consider using Rampart to answer them.

You can find the documentation here: https://hackage.haskell.org/package/rampart-1.0.0.1/docs/Rampart.html.