错误 - 通过传递列表进行递归函数调用 - OCaml
我正在尝试创建 OCaml 列表中包含的字符串的排列。 到目前为止，我已经处理了以下代码片段，但面临将列表的第一个字符串传递给我的方法的问题。
代码逻辑： 迭代列表的每个元素并将每个元素附加到列表的元素。继续这样做，直到所有元素都已附加到列表中每个可能的位置。
代码：
(* this function appends each string to each word in the list example: "A" with "ABC" *)
let appendtocode n word =
let f x = n ^ x in
f word
;;
(* this function extracts every element of the list and appends it with the string.
Example: "A" with ["AAA","ABC","ACD"] etc.. *)
let appendtolist n list =
let f x =
if (List.length list) > 0 then list
else ((appendtocode n (List.hd list)) ^ (appendtolist n (List.tl list)) )
in
List.map f list
;;
错误：
我收到此错误：
未绑定值appendtolist
在调用时发生：(appendtolist n List.tl list)
我的列表仅由字符串组成。 我仍在编写代码。但由于这个错误而陷入困境。
请帮忙！！！任何输入都会很棒。
I am trying to create permutations of strings contained in a list in OCaml.
I have worked on the following snippet of code till now but am facing a problem passing the first string of the list to my method.
Logic for code:
Iterate to every element of a list and append each element with element of the list. Continue doing till all the elements have been appended to the list in every possible position.
Code:
(* this function appends each string to each word in the list example: "A" with "ABC" *)
let appendtocode n word =
let f x = n ^ x in
f word
;;
(* this function extracts every element of the list and appends it with the string.
Example: "A" with ["AAA","ABC","ACD"] etc.. *)
let appendtolist n list =
let f x =
if (List.length list) > 0 then list
else ((appendtocode n (List.hd list)) ^ (appendtolist n (List.tl list)) )
in
List.map f list
;;
Error:
I get this error:
Unbound value appendtolist
Occurs at call to : (appendtolist n List.tl list)
My list is only consisting of string.
I am still working on the code. But stuck at this because of this error.
Please help!!! Any input would be great.
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评论（3）
要递归地调用该函数，您需要使用
let recappendtolist来定义它，而不仅仅是letappendtolist。然后你会得到一个不同的错误，因为你的代码中还有其他错误......
To call the function recursively, you need to define it with
let rec appendtolistrather than justlet appendtolist.You will then get a different error, because there are other bugs in your code ...
您收到“未绑定值appendtolist”错误，因为您在递归调用
appendtolist时未声明为递归。您需要编写
let recappendtolist n list = ...才能在其定义中递归引用appendtolist。You're getting the "Unbound value appendtolist" error because you're calling
appendtolistrecursively without declaring as recursive.You need to write
let rec appendtolist n list = ...to be able to refer toappendtolistrecursively within its definition.我不太了解 SML，但我认为你需要更多的括号，例如
应该是
I don't know SML well, but I think you need some more parens, e.g.
should be