> Which is often the case with claims of solving long-lasting problems This is what I really like about programming language theory: problems which are literal

> Which is often the case with claims of solving long-lasting problems This is what I really like about programming language theory: problems which are literally undecidable in existing languages, can be made almost trivial by designing a language with that problem in mind. The trick is to have the language keep track of the information needed for the solution, so we're not dealing with "black boxes". A classic example is annotating every variable with a type, and propagating that information through compound expressions; lets us spot problems like trying to use a number as a string, without worrying about the halting problem (we do this by forbidding some technically-valid programs, like `1 + (true? 10 : "hello")`). Of course, this leaves the much harder problems of (a) keeping the burden imposed by this extra information down to a reasonable level, and (b) trying to make the language compelling enough for people to actually use. Rust is one of the few examples of going all-in on a new ecosystem, and it actually being embraced. Often it's easier to "embed" a new language inside an existing language, to piggy-back on the existing tooling (e.g. the variety of auto-differentiating languages built in Python)