Evaluate postfix operation

EvaluatePostfix.swift

var Operations: [String: (Double, Double) -> Double] = [
    "*": { $0 * $1 },
    "+": { $0 + $1 },
    "-": { $1 - $0 },
    "/": { $1 / $0 }
]

let Operators = ["+", "-", "*", "/"]

func postfix(_ expression: String) -> Double {
    
    guard !expression.isEmpty else { return 0.0 }
    let exp = expression.components(separatedBy: " ")
    var stack = [Double]()
    
    for char in exp {
        
        switch (Double(char), Operations[char]) {
        case (.some(let number), _): stack.append(number)
        case (_, .some(let op)):
            let lastNumber = stack.removeLast()
            stack.append(op(stack.last!, lastNumber))
            
        default:
            print("Not an operand or operations")
        }
    }
    
    return stack.last!
}

postfix("1 2 * 3 *")