Para Tyflos y para todos!

@interface CalculatorBrain : NSObject
{
if(){}
double operand;
NSString *waitingOperation;
double waitingOperand;
}
- (void)setOperand:(double)aDouble;
- (void)setVariableAsOperand:(NSString *)variableName;
- (double)performOperation:(NSString *)operation;
@property (readonly) id expression;
+ (double)evaluateExpression:(id)anExpression
usingVariableValues:(NSDictionary *)variables;
+ (NSSet *)variablesInExpression:(id)anExpression;
+ (NSString *)descriptionOfExpression:(id)anExpression;
+ (id)propertyListForExpression:(id)anExpression;
+ (id)expressionForPropertyList:(id)propertyList;
@end