sclass Operation {
  S function;
  int[] registers;
  int outRegister = -1;
  
  *(S *function, int... regs) {
    registers = subArray(regs, 0, l(regs)-1);
    outRegister = last(regs);
  }
}

sclass Machine {
  O[] registers = new O[10];
  new TreeMap<S, O> functions;
  
  void function(S name, O implementation) {
    functions.put(name, implementation);
  }
  
  void set(int register, O value) {
    if (register >= l(registers))
      registers = resizeArray(registers, register+1);
    registers[register] = value;
  }
  
  O get(int register) {
    ret _get(registers, register);
  }
  
  void run(Operation op) {
    O f = functions.get(op.function);
    if (f == null) fail("Unknown operation: " + op.function);
    int n = l(op.registers);
    O[] arguments = new O[n];
    for i to n: arguments[i] = get(op.registers[i]);
    O result = callF(f, arguments);
    if (op.outRegister >= 0)
      set(op.outRegister, result);
  }
}