plate

Plate isn't really in the same space as SQL. SQL is such a shockingly good engineering choice that if you can use it I would. So even if Plate was done I would use Postgres instead of a Plate-based datastore inside my apps. Plate serves a different purpose: schema'ing human-readable formats like iCalendar (https://en.wikipedia.org/wiki/ICalendar)[1] or JSON APIs. So even if you're using SQL within your app Plate may come in useful at the boundaries. [1] Even if iCalendar was in JSON you couldn't write a Plate schema for it for the reasons listed here (https://github.com/seagreen/plate/blob/master/docs/prioritie...), but it serves as an example of a common human-readable data format.

It's only like Haskell's type system compared to other schema languages (most of which don't even have product and sum types). Plate has parametric polymorphism, phantom types, and algebraic data types. It doesn't have typeclasses however (I don't see a way to implement them, thoughts here: https://github.com/seagreen/plate/issues/1#issuecomment-3028...) and so advanced Haskell features like type families are out.