Yes, single-expression functions are a subset of all possible functions... but that's not exactly what I was getting at. I put "proper" in quotes just to signi

Yes, single-expression functions are a subset of all possible functions... but that's not exactly what I was getting at. I put "proper" in quotes just to signify that they have subtle differences that, from a purely type-based abstraction, are different from named functions. For example, you can't serialize (pickle) a lambda function.