Immutable variable isn't a oxymoron. It can still vary between instantiations. If you have (a)=>{const b = a}, b can have different values even though it can't be reassigned.
In the case of the code that you have cited, these are all different elaborations of the binding at the invocation of the lambda, due to the interplay between activation records and scope rules.
It's not really an "immutable variable" - it's a local binding getting bound to different values on each scope entry.
EDIT: By the way, the `b` binding in your code can be modified. Did you mean `const b = a;` ?
> it's a local binding getting bound to different values
on each scope entry.
It is, I just wanted to point out that the term "immutable variable" is sensible. I think a good way to put it is that b is a variable, and when the statement runs a value is bound to b. So the value bound to b varies yet b can be immutable, in contrast to a constant which is a binding to always the same value.
