partiallyappliedstack.swift

typealias Stack<T> = (push:(T) -> (), pop:() -> (T?))
func createStack<T>() -> Stack<T> {
    var array:[T] = []
    return ( push: { array.append($0)                                          },
             pop:  { array.count > 0 ? array.remove(at: array.count - 1) : nil } )
}

let s:Stack<Int> = createStack()

s.push(1)
s.push(2)
s.push(3)

print(String(describing: s.pop() )) // -> 3
print(String(describing: s.pop() )) // -> 2
print(String(describing: s.pop() )) // -> 1
print(String(describing: s.pop() )) // -> nil