These are very useful patterns! I feel that the thing that I haven't found my way around about this style of programming is how to make the types scalable. Onc

These are very useful patterns! I feel that the thing that I haven't found my way around about this style of programming is how to make the types scalable. Once the type `Expr` is set to include literals, addition, substraction, and custom functions, there's no clean way to extend it in a modular fashion with more _typed_ operations (eg say you wanted to add multiplication). When I say modular I mean either in a separate file, or in any other way that doesn't turn every function of `Expr`, over time, into a giant, unreadable pattern-matching statement spanning multiple pages once there are multiple dozens of operators in the type. Any suggestions for that?