I'm sorry, dear stranger. I've done this to show you a truth.

TerribleThings.swift

var theCounter:Int = 0
var theString:String = ""

func doIt() -> String {
    if theCounter++ % 2 == 0 {
        return "wakka"
    } else {
        return " "
    }
}

func notSoPure<T>(tuple:(T, T)) -> T {
    theString.extend(doIt())
    print(theString)
    if theString.characters.count % 2 == 0 {
        return tuple.0
    } else {
        return tuple.1
    }
}

let theInput = (3, 4)

notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)
notSoPure(theInput)