But that is cross-language, which is not ideal but not an internal problem if you work in one code base. (O)Caml also has `let` and is quite a bit older than JS.

C# uses “var” to mean “infer the type”, nothing to do with mutability or not.

“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;” ?