Compilation ocamlyacc上的表达式类型错误

作为学校项目的一部分，我必须识别.dot文件并生成相应的解析树。为了实现这一点，我必须使用ocamlex和ocamlyacc，我遇到了一些困难

这是我的ocaml.mli类型文件：

type id = string 
and node = id
and attr = id * id
and attr_list = attr list list
and attr_stmt =
    Graphs of (attr_list)
    | Nodes of (attr_list)
    | Edge of (attr_list)
and node_stmt = node * attr_list
and node_subgraph = 
    Node of (node)
    | Subgraphs of (graph)  
and edge_stmt = node_subgraph * (node_subgraph list) * attr_list
and stmt = 
    Node_stmt of (node_stmt)
    | Edge_stmt of (edge_stmt)
    | Attr_stmt of (attr_stmt)
    | Attr of (attr)
    | Subgraph of  graph
and graph = 
    Graph_node of (node * stmt list)
    | Graph of (stmt list);;

这是我的lexer文件：

{
    open Parser
}
rule token = parse 
    (* Espacements *)
    | [ ' ' '\t' '\n']+  {token lexbuf}
    (* *)
    | "graph" {GRAPH}
    | "subgraph" {SUBGRAPH}
    | "--" {EDGE}
    (* Délimiteurs *)
    | "{" {LEFT_ACC}
    | "}" {RIGHT_ACC}
    | "(" {LEFT_PAR}
    | ")" {RIGHT_PAR}
    | "[" {LEFT_BRA}
    | "]" {RIGHT_BRA} 
    | "," {COMMA}
    | ";" {SEMICOLON}
    | "=" {EQUAL}
    | ":" {TWOPOINT}
    | ['a'-'z''A'-'Z''0'-'9']*  as id {ID (id)} 
    | eof { raise End_of_file }

这是我尚未完成的yacc文件：

%{
    open Types
%}

%token <string> ID 
%token <string> STR
%token GRAPH SUBGRAPH EDGE
%token LEFT_ACC RIGHT_ACC LEFT_PAR RIGHT_PAR LEFT_BRA RIGHT_BRA
%token COMME SEMICOLON EQUAL TWOPOINT EOF 

%start main
%type <graph> main 

%%

main:
 graph EOF { $1 }


graph:
    GRAPH ID LEFT_ACC content RIGHT_ACC {$4}
    | GRAPH LEFT_ACC content RIGHT_ACC {$3}

subgraph:
    SUBGRAPH ID LEFT_ACC content RIGHT_ACC {$4}
    | SUBGRAPH LEFT_ACC content RIGHT_ACC {$3}

content:
    | ID EDGE ID SEMICOLON {[($1,$3)]}

但是，当我尝试编译解析器接口时，会出现以下错误： 此表达式具有“a列表”类型 但表达式应为Types.graph类型（引用

ID边ID分号{[$1，$3）]}

line）

我不明白，因为{[$1，$3]}有一个（string*string）列表类型。如果我们在寻找types.mli，它可以是一个图形

---

否则，我是否正确理解了ocamlex和ocamlyacc的运行

类型为

graph

的值必须以

graph

或

graph\u节点开始。这与
（string*string）列表完全不同
谢谢！至少现在它可以编译了，但是当我尝试运行程序时，我得到了一个致命的错误：异常End_of_File。我怎样才能解决这个问题？如何查看是否已创建解析树？
graph D {
    A -- B ;
}