The comma means your code should remove one character from the input string provided to the function as a parameter and add it to a tape-like memory. The dot means it gets copied from memory to a variable later to be returned.

I'm having trouble in the Rust kata understanding what it means to "accept one byte" (with the , instruction).
What exactly does this mean? A byte from where?

Wow, neat! I love the extensibility of this code.

:)

I'm a little confused by the use of let over const, but I really like how straightforward this solution is. Very easy to read.

Sorry for this shameless pass. I'm tired. I'll probably do this solution again later.