Description of Program (CS193P Assignment 2)

descriptionOfProgram.m

+ (NSString *) descriptionOfProgram:(id)program
{
  NSMutableArray *stack;
  if ([program isKindOfClass:[NSArray class]]) stack = [program mutableCopy];
  NSString *programDescription = @"";
  while (stack.count) {
    programDescription = [programDescription stringByAppendingString:[self descriptionOfTopOfStack:stack]];
    if (stack.count) {
      programDescription = [programDescription stringByAppendingString:@", "];
    }
  }
  return programDescription;
}

+ (NSString *) descriptionOfTopOfStack:(NSMutableArray *)stack
{
  NSString *description = @"";
  id topOfStack = [stack lastObject];
  if (topOfStack) [stack removeLastObject];
  if ([topOfStack isKindOfClass:[NSNumber class]]){
    description = [NSString stringWithFormat:@"%g", [topOfStack doubleValue]];
  } else if ([topOfStack isKindOfClass:[NSString class]]) {
    if ([self isOperation:topOfStack] && [self isSingleOperandOperation:topOfStack]) {
      description = [NSString stringWithFormat:@"%@(%@)", topOfStack, [self descriptionOfTopOfStack:stack]];
    } else if ([self isOperation:topOfStack] && ![self isSingleOperandOperation:topOfStack] && ![self isNoOperand:topOfStack]) {
      NSString *first = [self descriptionOfTopOfStack:stack];
      NSString *second = [self descriptionOfTopOfStack:stack];
      if ([topOfStack isEqualToString:@"+"] || [topOfStack isEqualToString:@"-"]){
        description = [NSString stringWithFormat:@"(%@%@%@)",second,topOfStack,first];
      } else description = [NSString stringWithFormat:@"%@%@%@",second,topOfStack,first];
    } else description = topOfStack;
  } 
  return description;
}

+ (BOOL) isOperation:(NSString *) stringInQuestion
{
  NSSet *operationsSet = [NSSet setWithObjects: @"+", @"-", @"*", @"/", @"sin", @"cos", @"sqrt", @"π", @"+/-", @"e", @"log", nil];
  return [operationsSet containsObject:stringInQuestion];
}
                                          
+ (BOOL) isSingleOperandOperation:(NSString *) operationInQuestion
{
  NSSet *operationSet = [NSSet setWithObjects:@"sin", @"cos", @"sqrt", @"log", nil];
  return [operationSet containsObject:operationInQuestion];
}

+ (BOOL)isNoOperand:(NSString *)operation 
{ 
  return [[NSSet setWithObjects:@"π",@"x",@"y",@"foo", nil] containsObject:operation]; 
}

Thanks for posting these. Had trouble getting the ball rolling on this one, but these helped with understanding it all very much.