this is nice, especially for the function clauses

Elixir is my daily drive and working in Java made me miserable until I started working around the lack of pattern matching facilities

Error handling is the worst part, I think a simple

  switch (retval) {
    Ok(val):
       ...
       break;
    Error(err):
       ...

would make Java much more pleasant, even without full pattern matching everywhere.

Not so much a nitpick because with checked exceptions your method signature can declare multiple types of exception whereas Result generalizes your specific exceptions to Throwable, which you can't pattern match with the compiler being able to enforce exhaustiveness.

So to achieve the same exhaustiveness as a method like

User createUser() throws IOException, BusinessException

you would need both a Result-like construct and union types

Either<User, IOException | BusinessException> createuser()

which few mainstream languages offer. Otherwise you type is unable to express that only IOException and BusinessException are thrown and you don't need to handle a default Throwable case.

This is only the case for "checked" exceptions though; the important part about the Result type in Rust is that it won't implicitly propagate errors if you try to just use the success value but instead will give a compiler error. I don't code much Java, but my impression is that standard library methods throwing unchecked exceptions is far more common than panicking, the closest equivalent is in Rust.