在 OCaml 中对列表进行排序

Question

这是对任何给定列表进行排序的代码：

let rec sort lst =
   match lst with
     [] -> []
   | head :: tail -> insert head (sort tail)
 and insert elt lst =
   match lst with
     [] -> [elt]
   | head :: tail -> if elt <= head then elt :: lst else head :: insert elt tail;;

[来源：代码

但是，我收到未绑定错误：

Unbound value tail
# let rec sort lst =
   match lst with
     [] -> []
   | head :: tail -> insert head (sort tail)
 and insert elt lst =
   match lst with
     [] -> [elt]
   | head :: tail -> if elt <= head then elt :: lst else head :: insert elt tail;;
Characters 28-29:
     | head :: tail -> if elt <= head then elt :: lst else head :: insert elt tail;;
     ^
Error: Syntax error

任何人都可以帮我理解这里的问题吗？我没有在任何地方或代码中找到head或tail预定义

Answer 1

您的代码似乎是正确的，并且可以为我编译：

    Objective Caml version 3.11.1

# let rec sort lst = ...

val sort : 'a list -> 'a list = <fun>
val insert : 'a -> 'a list -> 'a list = <fun>

# sort [ 1 ; 3 ; 9 ; 2 ; 5 ; 4; 4; 8 ; 4 ] ;;
- : int list = [1; 2; 3; 4; 4; 4; 5; 8; 9]