This is often referred to as "row typing", and the only language I've ever used that implemented it first-class with polymorphism is Purescript[0]. It's possibl

This is often referred to as "row typing", and the only language I've ever used that implemented it first-class with polymorphism is Purescript[0]. It's possible to model such things in other languages with sufficiently powerful type systems, though they're normally not as nice to use. As an aside, Purescript is one of the most fun languages I've ever used for frontend work, and I lament that Elm seems to have overtaken it in the FP community. [0]: https://hgiasac.github.io/posts/2018-11-18-Record-Row-Type-and-Row-Polymorphism.html https://hgiasac.github.io/posts/2018-11-18-Record-Row-Type-a...