Another source code that demonstrates how things that are easy to write, read and understand in FP languages are a nightmare in Rust. Maybe making functional code indecipherable is not the best example of what Rust may actually be good for.
I'm actually finding the opposite. This is mapping very nicely to Rust. But of course not as nicely as it would if I could encode things as lambda terms in the language itself. I'm currently working on an impl of Fn for the Expression. Maybe it'll work out.
This code isn't really meant to be an easily digestible read. I don't make much effort to explain the church numerals for example, I just show that it works with a few tests.
I personally find a lot of good FP principles come into play in Rust quite frequently.
