The formal notion of *subtype* seems to be getting some solid research attention...

		jkhdigital on Sept 10, 2021 \| parent \| context \| favorite \| on: An Introduction to Type Level Programming in Haske... The formal notion of subtype seems to be getting some solid research attention; see e.g. https://drops.dagstuhl.de/opus/volltexte/2021/13888/pdf/LIPI... Hopefully we see these ideas make their way into functional languages soon.