[masklinn]

> Is there a simple real-world example that would explain when dynamic scoping would be better than some kind of access protocol to a shared value?

Safely intercepting global IO.

The average language is never going to thread IO explicitly, so if your callee has not added explicit hook points then all you can do is try to swap out the relevant subsystem, but your average standard IO is usually not even thread-local, and when it is that doesn't help when the language has sub-tread stack swapping (e.g. Python's generator will just suspend the stack relevant section of the stack entirely so if you've updated a threadlocal in a coroutine it is not rolled back on suspension). Plus you still need to remember to properly clean up your threadlocals as they won't self-revert.

With dynamic variables you can just rebind the variable. Only stack frames following yours will see the update, other stacks will be unmolested and none the wiser regardless of your shenanigans.