模块：函子中的类型问题
我对以下代码中的类型有疑问（一些简单的模块功能图实现）。似乎各类型都过着自己的生活。
我有 type t = NotaEdge | int*v*v 的边在 Edge 模块中实现，该类型在模块 Graph 中变为 type edge = Et。对我来说一切似乎都很好，除了事实上我无法对其进行模式匹配，因为构造函数 Edge 在模块 Graph 中仍然未定义。
正是在函数 suc 中，当我尝试与 Edge(l,n,m) 匹配时： #Error: Unbound constructor Edge
希望有人能很好地呈现它，提前谢谢:)
module Vertex : Vertex with type label = int =
struct
type t = NotaNode | Node of int
type label = int
exception No of string
...
module Edge : Edge with type label = int and type v = Vertex.t =
struct
type v = Vertex.t
type t = NotaEdge | Edge of int*v*v
type label = int
exception No of string
...
module Graph (E : Edge) (V : Vertex) : Graph with type vertex = V.t and type edge = E.t =
struct
type vertex = V.t
type edge = E.t
type t = E.t list* V.t list
let empty = ([],[])
let rec suc (x:edge list) (v1:vertex) =
match x with
y::ys -> (match y with
(*Error-->*) Edge(l,n,m) -> if n == v1 then m::(suc ys v1) else suc ys v1
| _ -> [])
|[] -> []
let succ (t1:t) (v1:vertex) =
match t1 with
(x,_) -> suc x v1
...
I have a problem with types in the following code (some easy module functional graph implementation). It seems that types are living their own lives.
I have type t = NotaEdge | Edge of int*v*v implemented in module Edge, this type in module Graph becomes type edge = E.t. Everything seems fine to me, except fact i can't pattern match on it, cause the constructor Edge is still undefined in module Graph.
Exactly in function suc when i try to match with Edge(l,n,m): #Error: Unbound constructor Edge
Hope someone can present it nicely, thx in advance :)
module Vertex : Vertex with type label = int =
struct
type t = NotaNode | Node of int
type label = int
exception No of string
...
module Edge : Edge with type label = int and type v = Vertex.t =
struct
type v = Vertex.t
type t = NotaEdge | Edge of int*v*v
type label = int
exception No of string
...
module Graph (E : Edge) (V : Vertex) : Graph with type vertex = V.t and type edge = E.t =
struct
type vertex = V.t
type edge = E.t
type t = E.t list* V.t list
let empty = ([],[])
let rec suc (x:edge list) (v1:vertex) =
match x with
y::ys -> (match y with
(*Error-->*) Edge(l,n,m) -> if n == v1 then m::(suc ys v1) else suc ys v1
| _ -> [])
|[] -> []
let succ (t1:t) (v1:vertex) =
match t1 with
(x,_) -> suc x v1
...
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这里的情况有点乱；
Error从未定义过，我认为是一些拼写错误。如果您提供已编译的代码，将会更有帮助。把它简化一下，但语法上是正确的。我只能根据有限的信息和常见的陷阱做出推测。了解
Vertex和Edge的签名将非常有帮助，如果在签名
Edge中，类型为t的定义与您提供的Edge实现中的定义相同，然后您可以将变体与E.Edge和E 相匹配。 NotaEdge。如果类型t是抽象的（签名中的唯一信息是type t），那么您将（并且合理地不应该）能够访问实现或模式匹配这样。在这种情况下，实现隐藏在签名后面。在处理函子时，这通常很好（并且是有意的），因为您可以以任何必要且方便的方式实现该模块。Things are a bit messy here;
Erroris never defined, and what I presume to be a few typos. It would be much more helpful if you gave code that compiled. Par it down, but syntactically correct. I can only make conjectures on the limited information and common pitfalls.It would be very helpful to know the signatures to
VertexandEdgeIf in the signature
Edgethe typetis defined the same as in the implementation ofEdgethat you give, then you can match the variant withE.EdgeandE.NotaEdge. If the typetis abstract (the only information in the signature istype t), then you wont (and reasonably should not) be able to access the implementation or pattern match in that way. In this case the implementation is hidden behind the signature. This is usually fine (and intended) when dealing with functors since you can implement the module in any way that is necessary and convenient.