爲什麼這種類型的錯誤一直在發生？

我有一個ocaml函數，其中我模式匹配幾個案例。我不斷收到一個類型錯誤，我看不出如何處理它。任何幫助，將不勝感激。這是我收到的錯誤消息：「文件」eval.ml「，第40行，字符18-35：錯誤：此表達式具有類型Env.symEntry」。第40行是「讓L = binding_of ENV X在」爲什麼這種類型的錯誤一直在發生？

(* eval_expr: expr -> proc_state -> env -> store -> value *) 
(* eval_expr: expr -> proc_state -> env -> store -> int *) 
let rec eval_expr (expr:expr) (ps:proc_state) (env:environment) (store:store) : int = match expr with 
     Add (e1, e2) -> 
     let r1 = eval_expr e1 ps env store in 
     let r2 = eval_expr e2 ps env store in 
     r1 + r2 
    | Sub (e1, e2) -> 
     let r1 = eval_expr e1 ps env store in 
     let r2 = eval_expr e2 ps env store in 
     r1 - r2 
    | Mul (e1, e2) -> 
     let r1 = eval_expr e1 ps env store in 
     let r2 = eval_expr e2 ps env store in 
     r1 * r2 
    | Div (e1, e2) -> 
     let r1 = eval_expr e1 ps env store in 
     let r2 = eval_expr e2 ps env store in 
     r1/r2 
    | Neg (e1) -> 
     let r1 = eval_expr e1 ps env store in 
     r1 * -1 
    | IntConst i -> i 

    (* - variable reads: handle the Id constructor from expr. 
    use binding_of and 
     value_at *) 

    | Id(x) -> 
    let l = binding_of env x in 
    let i = value_at store l in i;;

下面是一些功能和類型我使用的代碼行：

module IntMap = Map.Make(struct type t = int let compare = compare end);; 
type store = int IntMap.t;; 
let value_at store loc = IntMap.find loc store;; 
let insert_value store loc v = IntMap.add loc v store;; 


let enter_scope env scope = scope::env;; 
let exit_scope env = List.tl env;; 
let current_scope env = List.hd env;; 

type expr = (* Expressions in C-flat *) 

    (* int operations *) 
    Add of expr * expr 
| Sub of expr * expr 
| Mul of expr * expr 
| Div of expr * expr 
| Neg of expr 

    (* constants/variables *) 
| Id of string 
| IntConst of int 

    (* array/pointer operations *) 
| At of expr * expr 
| Deref of expr 
| AddressOf of expr 

    (* function *) 
| Call of string * expr list 

    (* pre- & post-increment *) 
| Pre of expr 
| Post of expr 
;; 



let binding_of env name = 
    let lookup name symTab = List.assoc name symTab in 
    try 
    lookup name (List.hd env) 
    with Not_found -> 
    lookup name (List.hd (List.tl env)) 
;;

來源

2015-05-05 user4789552