A Simple RPN Calculator in Swift

RPNSolver

struct Stack<T> {
    let values: [T]
    
    init(_ v: [T] = [T]()) {
        self.values = v
    }
    
    func push(elem: T) -> Stack<T> {
        let newValues = [elem] + self.values
        return Stack<T>(newValues)
    }
    
    func pop() -> (T?, Stack<T>) {
        if self.values.isEmpty {
            return (nil, self)
        }
        
        let first = self.values.first
        let cnt = self.values.count
        let newValues = self.values[1..<cnt]
        return (first, Stack<T>(Array(newValues)))
    }
}

typealias BinaryOp = (Double, Double) -> Double

func solveRPN(expr: String) -> Double {
    return expr.characters.split { $0 == " " }.map { String($0) }.reduce(Stack<Double>(), combine: combineFunction).pop().0!
}

func combineFunction(stk: Stack<Double>, str: String) -> Stack<Double> {
    var result: Stack<Double>
    
    switch(str) {
        case "+":
            result = applyBinaryOp(stk, +)
        case "-":
            result = applyBinaryOp(stk, -)
        case "*":
            result = applyBinaryOp(stk, *)
        default:
            result = stk.push(Double(str)!)
    }
    
    return result
}

func applyBinaryOp(s: Stack<Double>, op: BinaryOp) -> Stack<Double> {
    let (v1, s1) = s.pop()
    let (v2, s2) = s1.pop()
    return s2.push(op(v1!, v2!))
}

let expression = "10 3 2 - +";

solveRPN(expression) // output: 11

Hello, mate.
Thank you for the gist.
I've updated it to Swift 3.1
Maybe you want to update yours too.
If that's the case - you are welcome:
https://gist.github.com/8ofproject/0103068289d9f034e62ebaf4e97672cc