I think there are two scenarios which both call for different solution. One scenario is when your goal is to make something new. Something, that would feel dif

I think there are two scenarios which both call for different solution. One scenario is when your goal is to make something new. Something, that would feel different and have different ergonomics. This is like inventing a Python when there are mostly C-style and Pascal-style languages. Other is when you are interested in a particular behaviour of the language. Like type system. Why should you bother whether you write let x = 5; or int x = 5; when all you are interested in is its type. This is likely the case of this paper.