Pole.swift

//: Playground - noun: a place where people can play

import UIKit

class Pole{
    let left:Int
    let right: Int
    init(_ left:Int, _ right:Int){
        self.left = left
        self.right = right
    }
    
    func landLeft(birds:Int) -> Pole?{
        if(abs(birds + left - right) < 4){
            return Pole((left + birds), right)
        }
        return nil
    }

    func landRight(birds:Int) -> Pole?{
        if(abs(left - (right + birds)) < 4){
            return Pole(left, right + birds)
        }
        return nil
    }

    func banana() -> Pole?{
        return nil
    }
}

let p1 = Pole(0, 0).landLeft(3)?.landLeft(1)
let p2 = Pole(0, 0).landLeft(3)?.landRight(2)

func return_<T> (p:T) -> T?{
    return Optional.Some(p)
}


func do_() -> Pole?{
    if let
        start = return_(Pole(0, 0)),
        first = start.landLeft(2),
        second = first.landLeft(1),
        last = second.landRight(2)
    {
        return return_(last)
    }
    return Optional.None
}

let p = do_()