Challenge Task 2 of 2 on Swift Closures (On Step 4); Errors?

Challenge Task 2 of 2 on Swift Closures (On Step 4)

Instructions: Using the differenceBetweenNumbers function as an input to mathOperation, compute the difference between any two integers and assign the result to a constant named difference.

Code: func differenceBetweenNumbers(a: Int, b:Int) -> (Int) { return a - b }

// Enter your code below func mathOperation(mathOperationFunc: (Int, Int) -> Int, a: Int, b: Int ) -> (Int) { return mathOperationFunc(a,b) }

let difference = mathOperation(differenceBetweenNumbers, 10, 5)

Error: Make sure you are computing the difference between two integers using the functions created and assigning the result to a constant named difference.

Note: I compiled this code using Xcode 6.4 with success. I’m not sure why I’m receiving an error on the online code checker.

/** 
  For this code challenge, let’s define a math operation as a function that 
  carries out some work on two integers and returns an integer as well. An 
  example is the function below, `differenceBetweenNumbers`, which takes two 
  integers and calculates the difference between the numbers. After calculating, 
  it returns the difference.
*/

func differenceBetweenNumbers(a: Int, b:Int) -> (Int) {
  return a - b
}

// Enter your code below
func mathOperation(mathOperationFunc: (Int,Int) -> Int, a: Int, b: Int ) -> (Int)
{
    return mathOperationFunc(a,b)
}

let difference = mathOperation(differenceBetweenNumbers, 10, 5)