Thanks for the reference. Espresso doesn't support recursive records. Does system in your paper allow for those? Is there anything particularly tricky about supporting them?

Hi, author here, yes your paper was a huge inspiration and I really should add a references section in the readme. The row types in Expresso use very simple lacks constraints, similar to the old Hugs TREX system, and don't permit duplicate/scoped labels. I felt this was also a pretty good sweet spot.

Thanks :-) TREX (by Mark Jones and Benedict Gaster) is great. The beauty is that a lacks constraints can get translated to fields offsets at runtime making it super efficient!

E.g. a type like:

foo :: r/x => { x :: int | r } -> int

foo r = r.x

Gets translated at runtime to a function where the lacks constraint r/x becomes an actual offset parameter.