enum ExpressionParser {
func parse(from input: String) -> Formula {
let operandQueue: [Double] = []
let operatorQueue: [Operator] = []

operandQueue = componentsByOperators(from: input).map { Double($0) }
operatorQueue
for ele in input {
if !ele.isNumber {
operatorQueue.append(<#T##newElement: Operator##Operator#>)
}
}
return Formula(operands: oper, operators: <#T##CalculatorItemQueue<Operator>#>)
}

func componentsByOperators(from input: String) -> [String] {

var realNums: [String] = []
var nums: [String] = []
for element in input {
if element.isNumber {
nums.append(String(element))
} else {
realNums.append(nums.joined())
nums = []
}
}

// var numbers: [String] = []
// for a in Operator.allCases {
// switch a {
// case .add:
// numbers = input.split(with: "+")
// case .subtract:
// separateNumbers(sep: "-", numbers: &numbers)
// case .divide:
// separateNumbers(sep: "/", numbers: &numbers)
// case .mulitiply:
// separateNumbers(sep: "*", numbers: &numbers)
// }
// }
}

func separateNumbers(sep: Character, numbers: inout [String]) {
for (idx, num) in numbers.enumerated() {
if let _ = Int(num) {
continue
}
numbers.remove(at: idx)
for x in num.split(with: sep).reversed() {
numbers.insert(x, at: idx)
}
}
}
}