OCaml -警告8:此模式匹配不是详尽的

Question

您好，我有这个程序正常工作，但给我一个警告，我想摆脱

  let rec replace_helper (x::xs) n acc =
    if n = 0 then
      List.rev acc @ symbol :: xs
    else
      replace_helper xs (pred n) (x :: acc)
    in
    replace_helper tape position []
  ;;

这是警告

Warning 8: this pattern-matching is not exhaustive.
Here is an example of a case that is not matched:[]

我能做些什么来摆脱这个？

Answer 1

您的x::xs模式只能匹配非空列表(并且您忘记了处理空列表[]的情况)。请完成以下代码

let rec replace_helper li n acc = match li with
   [] -> (*code something here*) failwith "incomplete"
 | x::xs ->
   if n = 0 then
     List.rev acc @ symbol :: xs
   else
      replace_helper xs (pred n) (x :: acc)
   in
   replace_helper tape position []
 ;;

当然，阅读更多的http://ocaml.org/