Error - Recursive function calls by passing lists - OCaml

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 ever开发者_运维问答y 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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To call the function recursively, you need to define it with let rec appendtolist rather than just let appendtolist.

You will then get a different error, because there are other bugs in your code ...

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You're getting the "Unbound value appendtolist" error because you're calling appendtolist recursively without declaring as recursive.

You need to write let rec appendtolist n list = ... to be able to refer to appendtolist recursively within its definition.

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I don't know SML well, but I think you need some more parens, e.g.

else ((append-to-code n List.hd list) ^ (append-to-list n List.tl list) ) 

should be

else ((append-to-code n (List.hd list)) ^ (append-to-list n (List.tl list)) )