Question

我正在尝试用ocaml编写一个玩具编译器。目前，我正在尝试为我的词法分析器实现offside rule。但是，我在使用ocaml语法时遇到了一些麻烦（编译器错误非常缺乏信息）。下面的代码（33行）导致第34行出错，超出了源代码的末尾。我不确定是什么导致了这个错误。

open Printf

let s = (Stack.create():int Stack.t);

let rec check x =
    (
        if Stack.is_empty s then
            Stack.push x s
        else if Stack.top s < x then
            (
                Stack.push x s;
                printf "INDENT\n";
            )
        else if Stack.top s > x then
            (
                printf "DEDENT\n";
                Stack.pop s;
                check x;
            )
        else
            printf "MATCHED\n";
     );

let main () =
    (
        check 0;
        check 4;
        check 6;
        check 8;
        check 5;
    );

let _ = Printexc.print main ()

Ocaml输出：

File "lexer.ml", line 34, characters 0-0:
Error: Syntax error

有人可以帮我弄清楚错误是由什么引起的，并帮助我修复它吗？

Answer 1

main ， check 和 s 的定义之后的尾随; 是错误的。

将这三个出现用 ;; 替换如下：

let s = (Stack.create():int Stack.t);;

let rec check x =
  (
      (* ...sequence of imperative statements... *)
  );;

let main () =
  (
      (* ...sequence of imperative statements... *)
  );;

; 用于以下情况：

对命令性陈述进行排序
作为列表元素之间的分隔符
作为数组元素之间的分隔符
作为记录字段之间的分隔符

一些例子：

let hello_world1 () =
  print_endline "Hello";
  print_endline "World !"
;;

let hello_world2 () =
  begin
    print_endline "Hello";
    print_endline "World !"
  end
;;

let hello_world3 () =
  (
    print_endline "Hello";
    print_endline "World !";
  )
;;

let some_list =
  [1; 2; 3]
;;

let some_array =
  [| 'a'; 'b'; 'c' |]
;;

type my_process =
  {
    pid: int;
    executable_path: string;
  }
;;

let p1 = { pid = 142; executable_path = "./my_exec" };;

Answer 2

只需移除;即可：

open Printf

let (s:int Stack.t) = Stack.create() 

let rec check x =
    (
        if Stack.is_empty s then
            Stack.push x s
        else if Stack.top s < x then
            (
                Stack.push x s;
                printf "INDENT\n";
            )
        else if Stack.top s > x then
            (
                printf "DEDENT\n";
                Stack.pop s;
                check x;
            )
        else
            printf "MATCHED\n";
     )  

let main () =
    (
        check 0;
        check 4;
        check 6;
        check 8;
        check 5;
    ) 

let _ = 
  Printexc.print main ()

运行它：

gaius@debian:~/Projects/TestCase$ ./lexer 
INDENT
INDENT
INDENT
DEDENT
DEDENT
INDENT

超出程序结束的语法错误

2 个答案: