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 s

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.