An explicit goal of Rust is to be "low level", which is an admittedly vague phrase. While you could certainly write a Rust library that clones linked lists left

An explicit goal of Rust is to be "low level", which is an admittedly vague phrase. While you could certainly write a Rust library that clones linked lists left and right, and maybe someone would prefer that, someone else should be able to write a library that does in-place mutation with that delicious imperative goodness (badness?). To GP's point about environment variables, I think that's more of an issue with the fact that Rust tries to be compatible with existing C conventions in the OS. I don't think Rust can do much about it, since it can interface with C libraries that don't care about any Rust constraints on environment variables.