在 F# 中实现队列类型 [英] Implement a queue type in F#

问题描述

到目前为止，我正在尝试在 F# 中实现一个队列，这是我所拥有的，但我认为它更像是一个堆栈:

I'm trying to implement a queue in F# so far this is what I have but I think it's acting more like a stack:

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);;

除了 enque 之外，其他操作都很好，我想让它在队列的后面而不是前面添加一个新元素.

The operations are working fine except for enque, I want to make it so it adds a new element to the back of the queue instead of the front.

推荐答案

目前你把它放在最前面；如果你想在队列的末尾排队，你必须一直前进到最后，然后输入你的值:

Currently you are putting it at the front ; if you want to enqueue at the end of the queue you have to progress all the way to that end and then put your value :

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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