 a: {                                     switch (op) {                                         case "=": { a[index] = val; break; }                                         case "+=": { a[index] = (long)a[index] + (long)val; break; }                                         case "-=": { a[index] = (long)a[index] - (long)val; break; }                                         default: throw new InvalidOperationException();                                     }                                     break;                                 }                             case List<object> a: {                                     switch (op) {                                         case "=": { a[index] = val; break; }                                         case "+=": { a[index] = (long)a[index] + (long)val; break; }                                         case "-=": { a[index] = (long)a[index] - (long)val; break; }                                         default: throw new InvalidOperationException();                                     }                                     break;                                 }                             default: throw new InvalidOperationException();                         }                         break;                     }                 case 