Question

我有一个手写的预测解析器。每个非终结符都有一个对应的解析方法，每个解析器方法的类型为tokenlist-> tokenlist * Ast`

在每种方法中，我使用约定“ tokenlist_symbol”在使用特定符号后表示令牌列表。在这一行：let typ tokenlist_typ = parseTyp tokenlist in match tokenlist.head with中，typ是AST，而tokenlist_typ是parseTyp使用完typ前缀之后的其余令牌列表。

但是，我在行This expression has type 'a -> token_list * Ast.typ but an expression was expected of type Ast.typ上遇到(Ast.Declaration(typ, identifier, decls_prime), tokenlist_decls_prime)错误

type token_list = 
  {head : Lexer.token; (** head token. *)
   lexbuf : Lexer.token list}  (** lexer buffer. *)
(** Represents a parser buffer used during parsing of various productions. *)

let default_tokenlist s = {head = Lexer.EOF; lexbuf = Lexer.tokenize s}
(* Create a default [parse_buffer] with the given string [s]. *)

let next tokenlist =
    let {head = _; lexbuf = buf} = tokenlist in
    {head = List.hd buf; lexbuf = List.tl buf}
(** Retrieves a new parser buffer with the next lookahead token. *)

let parseTyp tokenlist = 
    match tokenlist.head with 
    | Lexer.Int -> (next tokenlist, Ast.Int) 
    | Lexer.Bool -> (next tokenlist, Ast.Bool)
    | Lexer.Void -> (next tokenlist, Ast.Void)  
    | Lexer.EOF -> (tokenlist, Ast.Epsilon)
    | _-> let err_msg = "Syntax Error" in
          raise (Syntax_error err_msg)

(*decls = typ “id” decls_prime | epsilon *)
let rec parseDecls tokenlist = 
    let (tokenlist_typ, typ, ) = parseTyp tokenlist in 
        match tokenlist.head with 
        | Lexer.ID identifier -> let (tokenlist_decls_prime, decls_prime) = next tokenlist |> parseDeclsPrime in 
                                (tokenlist_decls_prime, Ast.Declaration(typ, identifier, decls_prime))
        | Lexer.EOF -> (tokenlist, [])
        | _-> let err_msg = Printf.sprintf "Syntax Error" in
              raise (Syntax_error err_msg)

(* decls_prime = vdecl decls | fdecl decls *)
and parseDeclsPrime tokenlist =
    match tokenlist.head with 
    | Lexer.Semicolon -> let tokenlist_vdecl) = next tokenlist in
                let (tokenlist_decls, decls) = parseDecls tokenlist_vdecl in 
                (tokenlist_decls, Ast.DeclsPrime(Lexer.Semicolon, vdecl, decls)) 
    | Lexer.LeftParens -> let (tokenlist_fdecl, fdecl) = next tokenlist |> parseFdecl in 
                let (tokenlist_decls, decls) = parseDecls tokenlist_fdecl in 
                (tokenlist_decls, Ast.DeclsPrime(Lexer.Semicolon, fdecl, decls)) 
    | _-> let err_msg = Printf.sprintf "Syntax Error" in
          raise (Syntax_error err_msg)

Answer 1

你有这个：

let (decls_prime, tokenlist_decls_prime) = 
    next tokenlist |> parseDeclsPrime

从名称来看，看起来parseDeclsPrime返回类型Ast * tokenlist。但是在我看来，解析函数应该返回tokenlist * Ast。

该对中的两个名称很可能颠倒了。

Ocaml类型递归函数的return语句中的错误

1 个答案: