Haven’t had much exposure to other statically typed languages recently, so can’t say off the top of my head. Intuitively it looks like something modern generics

Haven’t had much exposure to other statically typed languages recently, so can’t say off the top of my head. Intuitively it looks like something modern generics should allow easily though, doesn’t it? As to Dhall, for example, I could validate such a constraint (and more) using a function I can be reasonably sure is safe and won’t halt (i.e. without all the drawbacks of TS and other general-purpose languages).