Edited: In the optimized version the author use bytes and generators and avoid using strings. I don't know if Rust generators are optimized for speed or memory, ideally you could define the length of the buffer according to the memory cache available.
Edited: I find strange using input = read_input_file()? and then using eval(&input), what happens when there is an error reading the file? Rust is supposed to be a high security language. In CL there are keyword like if-does-not-exists to decide what to do and also read accepts additional parameters for end-of-file and for expressing that this read is inside a recursive procedure inside another read.
I should stop comparing Rust to CL, better learn Rust first. I consider this kind of articles a very good way of learning Rust for those interested in parsing and optimizations. Rust seems to be a very nice language when you can afford the time to develop your program.