We considered it and decided against it for a few reasons.

- We want := to mean "change". The initial binding is not a change. This is precisely the "bindings and assignments" distinction you're talking about.

- A variable may in fact not be mutated.

- A small point is that we want to localize editing when making a change.

So, the way I read

  var y = x * x

is, "y is currently bound to x * x. However, y is a variable, so this binding is not guaranteed to last. Be careful about assuming you know the value of y." If you then see

  y := x * z

it reads as "y's value changes to that of x * z".

So: "=" means "introduced a name with this value"; "var" means "but this binding may change"; ":=" means "and yup, it really _did_ change".