Question

首先是代码：

module type ENV_CORE =
sig 
type variable 
type 'a environment
exception Unbound_variable
val empty : unit -> variable
val bind : 'a -> 'a environment -> 'a environment
val unbind : variable -> 'a -> 'a environment -> 'a environment
val is_bound : variable -> 'a environment -> bool
val lookup : variable -> 'a environment -> bool
val fold : (variable -> 'a -> 'b -> 'b) -> 'a environment -> 'b -> 'b
end;;


module EnvCoreList : ENV_CORE =

struct
    type variable = string list
    type 'a environment = variable * variable -> 'a
    exception Unbound_variable
    let empty () = []
    let bind elt l = elt::l
    let rec unbind elt l =
        match l with
        |[] -> raise Unbound_variable
        |a::r -> if (elt = a)
            then r
            else a::(unbind elt r)
    let rec is_bound elt l =
        match l with
        |[] -> raise Unbound_variable
        |a::r -> if (elt = a)
            then true
            else is_bound elt r
    let rec lookup elt l =
        match l with
        |[] -> false
        |a::r -> if (elt = a)
            then true
            else lookup elt r
    let rec fold f rho gamma =
        match rho with
        |[] -> gamma
        |a::r -> f a (fold f r gamma)
end;;

当我编译它时，我收到以下错误：

Error: Signature mismatch:
   Modules do not match:
     sig
       type variable = string list
       type 'a environment = variable * variable -> 'a
       exception Unbound_variable
       val empty : unit -> 'a list
       val bind : 'a -> 'a list -> 'a list
       val unbind : 'a -> 'a list -> 'a list
       val is_bound : 'a -> 'a list -> bool
       val lookup : 'a -> 'a list -> bool
       val fold : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
     end
   is not included in
     ENV_CORE
   Values do not match:
     val bind : 'a -> 'a list -> 'a list
   is not included in
     val bind : 'a -> 'a environment -> 'a environment

我不明白更具体的类型如何不包含在更一般的类型中？我找不到任何类似的问题，也无法解决这个问题。感谢名单

Answer 1

类型'a list和'a environment之间没有明显的关系。我不明白为什么你会考虑比另一个更一般。

在我看来，您应该在实现中更改environment的定义，或者应该重写bind，以便它适用于您为environment指定的类型。

签名不匹配ocaml

1 个答案: