Okay, so it's union types plus pattern matching that are missing (among other things I'm sure). Thanks, that's helpful. > You cannot safely "match" on the comm

Okay, so it's union types plus pattern matching that are missing (among other things I'm sure). Thanks, that's helpful. > You cannot safely "match" on the command in the same way you can in other languages, because the compiler doesn't know that there are only exactly 3 types of commands. Perhaps the visitor pattern? Command processing receives an object and calls its command method, which knows what permissions it has. I guess the fact that I have to keep saying "patterns" is a hint that some flexibility is missing. Still, I'd rather have Java/C++ static types than nothing at all.