string - 如何将另一个字符串列表的元素追加到 Ocaml 中新创建的字符串列表中，并分别用 "1"和 "0"扩展？

Question

我有一个这样的列表:["0","1"] - 我想创建一个如下所示的新列表:["00", "01"，“10”，“11”] - 也就是说我想创建原始字符串的扩展，添加“0”或“1”。

我尝试了以下代码，但它不起作用:

let extendedPartialSolutions partialSolutions = let rec aux extendedSolutions originalList =
                                                        match originalList with
                                                        [] -> extendedSolutions
                                                        | x::tail -> 
                                                            aux x^"1"::x^"0"::extendedSolutions tail
                                                    in aux [] partialSolutions

编译器发出以下错误:

# let extendedPartialSolutions partialSolutions = let rec aux extendedSolutions originalList =
#                                                       match originalList with
#                                                       [] -> extendedSolutions
#                                                       | x::tail -> 
#                                                           aux x^"1"::x^"0"::extendedSolutions tail
#                                                   in aux [] partialSolutions;;
File "", line 5, characters 15-20:
Error: This expression has type 'a list -> 'a
       but an expression was expected of type string

如何修复它？

Answer 1

我找到了解决办法!它是:

let extendSolutions originalList =
List.flatten (List.map (fun x -> [x^"0";x^"1"]) originalList);;