> And, get this, writing one FORCES YOU to fully understand every possible state and edge case of the problem you're solving.

lol? ;P Here is just one example of a bug I know of that should exist, today, in Chrome, because, in fact, state machines are extremely hard to reason about. (I have filed previous ones that were fixed, and tons of bugs in Chrome in general are in this category. This one is top of mind as they haven't even acknowledged it yet.)

https://issues.webrtc.org/issues/339131894

Now, you are going to tell me "they are doing state machines wrong as they don't have a way to discriminate on what the state even is in the first place"... and yet, that's the problem: the term "state machine" does not, in fact, mean a very narrow piece of inherent algorithmic limitations any more than "regular expressions" implies the language is regular, as this is an engineering term, not a computer science one.

In the field, state machines just kind of happen by accident when a ton of engineers all try to add their own little corner of logic, and the state is then implied by the cross-product of the state of every variable manipulated by the edges of the machine. This results in a complete mess where, in fact, it is essentially impossible to prove that you've provided edges for every possible state. Nothing in the type system saves you from this, as the state isn't reified.

This contrasts with approaches to these problems that involve more structured concurrency, wherein the compiler is able to not only deduce but even some concept of what kinds of edges are possible and where the state lies. (This, FWIW, is a reason why async/await is so much preferable to the kind of callback hell that people would find themselves in, maintaining a massive implicit state machine and hoping they covered all the cases.)