And a lot more bug prone. I'm just explaining the OP because people didn't get it. I'm not saying dynamic languages are bad. I'm saying they have different trade-offs.
I have a feeling you are misunderstanding what is meant by "theorems for free" here. For example, one theorem that is proven by all safe Rust programs is that they don't have data races. That should always be a requirement for functional software. This is a more pragmatic type of automatic theorem proving that doesn't require a direct proof from the code author. The compiler does the proof for you. Otherwise the theorem would not be "free" as stated in OP.
Industry will choose not to verify that your function does not produce NullPointerException wasting hours of the client's work, because in order to do that they would have to have actual requirements for software developers, and in order to do that they would have to
1 - have the managers be actually technically literate, and
2 - pay the developers properly
That's it. That's the theorems. The "formal verification" we're talking about here are those of the likes of "this value is a damn integer", or as you could interpret it "your code is not stupidly broken".
To be clear, I'm not writing this big comment for you, I know you're trolling or whatever you're into, I'm writing this to inform other readers. ✌🏻
Yes, that's why we use typing, to get better working code more easily. That's why I use type annotation and enforced checkers in Python. It makes it so much easier and quicker to create good systems of any significance.
I may just be an old country lawyer PHP developer... but don't most dynamic languages also support static type checking and general analysis at this point?
Yes but no. Modern PHP lets you put types in function signatures and it will then attempt to convert your inputs to those types at runtime.
JS/TS and Python don't do this. They have optional type annotations that's treated as syntactic sugar. You can use static checkers against this but if you get an error like "expected string got int" you can still run the code. It won't behave any differently because you have annotations.
Yes if you use type annotations. Languages like Python and Typescript end up resorting to "Any" types a lot of the time, which breaks any kind of theorem proving you might have otherwise benefited from.
Java developers aren't allowed to not know better by this point. If they think skipping types is somehow ideologically purer, keep hitting with that stick until you hit deckplate.
Though even statically-typed languages can need to check types sometimes; parsing runtime data for instance. I can see how you'd do that with pure statics, but it'd just be shifting the work (e.g. if token == QUOTE: proc.call(read_str(bytes, len))). It'd be cool to see a counter example that isn't unreadable gibberish, however.