[adamch]

Wow, higher-kinded data. I've never heard of that, but it would absolutely be useful. E.g. for converting JSON inputs, where any field might be missing, into a version of the data which definitely has values for all the fields. Or a version of the struct where the values are actually read from a cache/database.

[twic]

I proposed using it to model lifecycles of entities:

https://github.com/tim-group/higher-kinded-lifecycle/blob/ma...

(in this code, "idea" is a domain concept from the firm i worked for at the time - basically a recommendation to buy a stock, which is 'opened' on a certain date, and 'closed' when it no longer seems like a good recommendation)

My collegues didn't like it, and stuck to using separate types for objects in different stages of the lifecycle!

[IggleSniggle]

TypeScript (as you might expect from a lang built for dealing with JS Objects), has really great tooling for this kind of type narrowing these days (including on string template matching now) and I miss it so much now that I’m writing Go.

[glittershark]

yes! once you use it you start wanting it everywhere, which is a big part of why I wish I could do it in Rust