Not the OP, but I assume they mean that it's encoded in the type system.
For example Rust gives you a `Result<Thing, ErrorType>`, which might be a `Thing` or might be one of the possible error types given by `ErrorType`. So when you get a function's return value, you have to deal with the fact that it might have failed with this specific error.
For example Rust gives you a `Result<Thing, ErrorType>`, which might be a `Thing` or might be one of the possible error types given by `ErrorType`. So when you get a function's return value, you have to deal with the fact that it might have failed with this specific error.