That's not the assumption. The assumption is that the system does not receive new node-types at runtime. Think of the JVM: you can load new bytecode (e.g. clas

That's not the assumption. The assumption is that the system does not receive new node-types at runtime. Think of the JVM: you can load new bytecode (e.g. classes) at runtime, but you can't load bytecode that contains features of newer jvm versions that isn't compatible with the existing one. I don't think this is a "functional programming-like assumption".