[still_grokking]

I don't think Rust can enforce referential transparency, nor does it have any focus on doing this manually. But I would say referential transparency is one the most important properties in functional programming, if not even the most distinguishing property.

Referential transparency is the one feature that makes reasoning about a program easy. You can think about referential transparent programs purely in the substitution model. You can move referential transparent expressions freely around as you please.

You can't think of a Rust program this way. It's inherently procedural.

Rust gets a lot of things quite right! But it's not a FP language. It's a better C. It's about shoveling bits and bytes around, as safely and efficient as possible.