Stream: show and tell

Topic: Announcing roc-time v0.1.0

Luke Boswell (Sep 07 2026 at 12:51):

I met Kip Cole at the Melbourne Elixir meetup where he shared about his work on Tempo and I thought the design and idea there were really appealing and would be a good fit for Roc -- I decided to try it out... and now I would like to share my latest package with the community.

roc-time is for working with time the ways humans actually think about it, as a bounded span on a timeline and not as a scalar instant.

import time.ExactInterval
import time.Coverage

opening = "2026-06-15T09:00:00Z/2026-06-15T17:00:00Z"
booking = "2026-06-15T12:00:00+02:00/2026-06-15T14:00:00+02:00"
busy = Coverage.from_spans([ExactInterval.span(booking)])
free_windows = Coverage.complement_within(busy, ExactInterval.span(opening))

I would say the package is already quite useful for many use cases; though there is still a lot more on the roadmap.

I've been getting distracted with fuzz testing, setting up oracles, and generally messing around with benchmarks or profiling Roc for a bit of fun. There isn't really an accepted benchmark for time projects that I could find, so I combined ideas from various places and made my own simple one for comparison.

Here are some results from a recent run on my machine;

roc-time is roughly slower than Rust's chrono and jiff, about the same as Go's time, and faster than Python's datetime.

Jonathan (Sep 08 2026 at 15:52):

Thanks for releasing it! Does roc-time plan to encompass all your time-based needs? Just reading the docs for Tempo, it advises to reach for the stdlib instead when you don't need all the span related gizmos and can live within a bubble of local time etc. (and to use an agent if I do want to use Tempo :thinking:). I just need something for formatting / parsing 8601 or 3339 style date strings, so I guess thats in OffsetTimestamp?

Edit: I suppose this is better restated as: roc-time/Tempo expose the gory details of working with time, but for simple use cases where time-based footguns apply less, the api is quite involved, but the name suggests it is general purpose.

Luke Boswell (Sep 08 2026 at 20:00):

My understanding is that it should cover most of your needs, similar to Rust's chrono

But its new to me too, so I'm still learning a lot about it all. If you run into any friction or gaps I'm keen to know about those.

Last updated: Sep 24 2026 at 15:59 UTC