func compute(_ addition: Bool) -> (Int, Int) -> Int {    
  func add(_ a: Int, _ b: Int) -> Int { 
         return a + b  
  }    
  func subtract(_ a: Int, _ b: Int) -> Int {
        return a – b
  }
  if addition {
        return add     
  } else {
        return subtract
  }
}
let computeFunction = compute(true)
let result = computeFunction(1, 2)
print(result)