Question

我是Ocaml的新手，我遇到了一个简单的循环问题，这是我的代码：

    open Str;;

let main () =
let quit_loop = ref false in
  while not !quit_loop do
    let str = read_line () in
    if Str.string_match (Str.regexp "create") str 0
      then let train_list = Str.split (Str.regexp "[ \t]+") str in
      print_string "List created\n";
    if Str.string_match (Str.regexp "delete") str 0
      then let train_list = Str.split (Str.regexp "[ \t]+") str in
      print_string "train deleted\n";
    if Str.string_match (Str.regexp "quit") str 0
      then quit_loop := true

done;;

let _ = main ()

代码编译但似乎只有“创建”工作。如果您有任何提示可以帮助我...

谢谢！

Answer 1

如果你正确地缩进它，你就会得到这个：

open Str;;

let main () =
  let quit_loop = ref false in
  while not !quit_loop do
    let str = read_line () in
    if Str.string_match (Str.regexp "create") str 0
    then let train_list = Str.split (Str.regexp "[ \t]+") str in
      print_string "List created\n";
      if Str.string_match (Str.regexp "delete") str 0
      then let train_list = Str.split (Str.regexp "[ \t]+") str in
        print_string "train deleted\n";
        if Str.string_match (Str.regexp "quit") str 0
        then quit_loop := true

  done;;

let _ = main ()

如您所见，其他if嵌套在第一个if块中。这是因为let e = ... in instr1; ...创建了一个包含随后所有内容的块。

你应该写（你可以用begin ... end 替换(...)）：

open Str;;

let main () =
  let quit_loop = ref false in
  while not !quit_loop do
    let str = read_line () in
    if Str.string_match (Str.regexp "create") str 0
    then begin 
      let train_list = Str.split (Str.regexp "[ \t]+") str in
      print_string "List created\n"
    end;
    if Str.string_match (Str.regexp "delete") str 0
    then begin 
      let train_list = Str.split (Str.regexp "[ \t]+") str in
      print_string "train deleted\n"
    end;
    if Str.string_match (Str.regexp "quit") str 0
    then quit_loop := true
  done;;

let _ = main ()

它将按预期工作。

在Ocaml中构建一个循环

1 个答案: