Intro to HM Damas-Hindley-Milner (HM) is a type system for Standard ML and the ML-family languages. River and I wrote about it earlier this month. Check out that post if you would like an introduction or refresher. In this post, we’ll add row polymorphism to it. We’ll do it in the context of Algorithm J, but the core ideas should be algorithm-independent. Records A record is an unordered collection of name to value mappings, like { x = 1, y = "hello" }. Scrapscript has a very dynamic notion of r...