OCaml-撤消列表 [英] OCaml - Reverse a list

问题描述

我正在尝试实现自己的列表模块，如下所示:

I'm trying to implement my own list module as follows :

type 'a my_list =
    | Item of ('a * 'a my_list)
    | Empty

我已经实现了几个功能，现在正在尝试为我的模块创建一个列表反转功能，如下所示:

I've already implemented several functions and am now trying to create a list reversing function for my module which would look like this :

let rec rev = function
    | Empty             -> (*return reversed list*)
    | Item(i, remnant)  -> (*recursive call to rev*)

此外，我不应该使用诸如'::'，'[]'和'@'之类的列表运算符.

Moreover, I'm not supposed to use list operators such as '::', '[]' and '@'.

编辑，我尝试过的:

let rec rev_append l1 l2 = match l1 with
    | Empty             -> l2
    | Item(i, remnant)  -> rev_append remnant Item(i, l2)

let rev l = rev_append l Empty;;

但是这不起作用，传递给递归调用的第二个参数处有一个错误:"Item(i，l2)"该错误是构造函数Item期望有1个参数，但是这里应用于0个参数"

But this is not working, there is an error at the second argument passed to the recursive call : "Item(i, l2)" The error is "The constructor Item expects 1 argument, but is here applied to 0 arguments".

推荐答案

肢体瘫痪的人！

let rec rev_append l1 l2 = match l1 with
    | Empty             -> l2
    | Item(i, remnant)  -> rev_append remnant (Item (i, l2))

编译器了解到rev_append传递了三个参数，即remnant Item和(i, l2).

The compiler understood that rev_append was passed three argument namely remnant Item and (i, l2).

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