How is it not clear that var is variable?
if mutable is expensive, and should be difficult then "let mut" makes more sense.
var looks like a default to me, not a special case that needs care.
“Let” feels like some in-joke, coming from a math via lisp heritage of “let k be any number...” to distinguish it in English from the surrounding writing. I have to guess that in early lisp (= k 5) would be an error as k isn’t defined and (k 5) errors because k isn’t a function and (let (k 5)) comes out of need for a binding function and why not “let”.
In c-like languages “k=5” is an established binding that both programmers and compilers can deal with. What does “let k=5;” add to Rust over “k=5;” ?
val => value => is immutable
Of course people are different, but this seems clear as day, assmuning very basic familiarity with functional programming?