Types 在F中实现队列类型#

我试图在F#中实现一个队列，到目前为止，这就是我所拥有的，但我认为它更像一个堆栈：

type 'a queue = NL| Que of 'a * 'a queue;;

let enque m = function
    |NL -> Que(m, NL)
    |Que(x, xs) -> Que(m, Que(x, xs));;

let rec peek  = function
    |NL -> failwith "queue is empty"
    |Que(x, xs) -> x;;

let rec deque  = function
    |NL -> failwith "queue is empty"
    |Que(x, xs) -> xs;;

let rec build = function
    | [] -> NL
    | x::xs -> enque x (build xs);;

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除了enque，其他操作都很正常，我想让它在队列后面添加一个新元素，而不是在队列前面。

目前您将它放在队列前面；如果您想在队列末尾排队，您必须一直前进到队列末尾，然后输入您的值：

let rec enque m = function
  NL          -> Que (m, NL)
| Que (x, xs) -> Que (x, enque m xs) // Note : not tail-rec

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函数队列的规范方法是有两个列表，这导致摊销O（1）访问：

类型队列
type queue<'a> =
    | Queue of 'a list * 'a list

let empty = Queue([], [])

let enqueue q e = 
    match q with
    | Queue(fs, bs) -> Queue(e :: fs, bs)

let dequeue q = 
    match q with
    | Queue([], []) -> failwith "Empty queue!"
    | Queue(fs, b :: bs) -> b, Queue(fs, bs)
    | Queue(fs, []) -> 
        let bs = List.rev fs
        bs.Head, Queue([], bs.Tail)