Code works in Xcode but not here

/** 
  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(someFunc: ((Int , Int) -> (Int)) , c: Int , d: Int) -> (Int) {
   return someFunc(c , d)

}

let difference = mathOperation(differenceBetweenNumbers, 2, 1 )