Type Checker

In practice, if you have a large like L project, for example, we have like half a million lines of elm code at work. And so type unification is different than sub typing and it's got some interesting trade offs. So one of the downsides of unification compared to sub typing is that from a teaching perspective, there are like 95% of the time, sub typing and type unification give you the same answer. But there is a small niche of cases where if you don't realize that your language is using type unification, it might sometimes give you types that are surprising.