Question

我有一个ocaml函数，其中我模式匹配几个案例。我一直遇到类型错误，我无法看到如何处理它。任何帮助，将不胜感激。这是我收到的错误消息：“文件”eval.ml“，第40行，字符18-35：错误：此表达式的类型为Env.symEntry“。第40行是”let l = binding_of env x in“

的行

(* 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;;

以下是我使用的一些功能和类型的代码：

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))
;;

Answer 1

你没有展示足够的定义，看看你提到的线路上发生了什么。

我的猜测是binding_of_env没有返回位置，但value_at需要一个位置。可能您需要从绑定中提取位置。

Answer 2

如果您需要CSE 307项目的帮助，请到办公时间。

你的TA; - ）

为什么会出现此类型错误？

2 个答案: