lexical

Figuring out non-lexical scopes means that my mental model of what the compiler is doing is more difficult than it is right now, which may or may not be the right tradeoff.

Or is all the tech just a glorified lexical parser to fine tune ads to increase their efficiency?

Ruby has real closures with semantics similar to Lisp: lambda expressions that reference variables from their enclosing lexical scope.

Of course Basic English cheats by including all the phrasal verbs, without considering that they are usually separate lexical items.

Non-lexical lifetimes would make certain things easier, but also a bit harder to reason about, because the rules are more complex.

With the introduction of arrow function you won't need to use.bind(this) as arrow functions capture in their lexical scope the variables/keywords: this, arguments, super.

Python doesn't have lexical scope, hence it doesn't have closures.

Even before typing, you'd have to handle the lexical scoping, which may also involve an additional intermediate representation (one distinct IR per each pass is normal).

The macro facility is what differentiates Lisp from other dynamic languages that have, seemingly, all of the same attributes--dynamic/lexical scope, closures, etc.

ES6 gains tail call elimination and lexical block scope.

In a natural language, you would get these along with the borrowings or coinages, to a greater or lesser extent based on the culture's attitude toward lexical borrowing.

Rust's type system design understands very well the ephemeral nature of objects: When a non-`Copy` object is passed around elsewhere, it's truly gone from the current lexical context.

The dynamic version allows dynamic allocation inside lexical pools, keeping static memory management (no GC or "free"), but with possible unbounded memory usage.

(I don't recall whether the borrow checker actually depends on the control flow being reducible, but some of the possible future improvements we've talked about with "non-lexical lifetimes" definitely do.