尝试使用图形库 Ocaml 移动圆圈

Question

我是ocaml的新手，并尝试使用Ocaml的图形库移动圆圈。这就是我所做的，但它不起作用。由于"虽然为真"，它应该无限持续很长时间，但它不起作用，我无法给出输入。

#load "graphics.cma";;
#load "unix.cma";;
Graphics.open_graph " 800x250";;
Graphics.remember_mode true;;
Graphics.set_color 100;;
Graphics.foreground;;
let player = [|40;80;10|];;
Graphics.fill_circle player.(0) player.(1) player.(2);;
let rec check button = 
    if button = 'w'
    then
    player.(0) <- player.(0) + 50;
    Graphics.fill_circle player.(0) player.(1) player.(2);
while true do
    let s = Graphics.wait_next_event [Graphics.Button_down; Graphics.Key_pressed]
    and bo=Graphics.key_pressed ()
    in if not bo then check s.Graphics.key;
    done;;

Answer 1

以下是问题的原因：

 Graphics.fill_circle player.(0) player.(1) player.(2);
                                                 ^^^^^^^
                       here should be a double semicolon

如果没有第二个分号，while 表达式被视为作为check功能的一部分，正确的缩进澄清了这一点：

let rec check button = 
  if button = 'w'
  then
    player.(0) <- player.(0) + 50;
  Graphics.fill_circle player.(0) player.(1) player.(2);
  while true do
    let s = Graphics.wait_next_event [Graphics.Button_down; Graphics.Key_pressed]
    and bo=Graphics.key_pressed ()
    in if not bo then check s.Graphics.key;
  done

所以，你只是定义了一个函数检查，从来没有调用过它，这就是为什么什么都没有发生。

此外，OCaml是一种编程语言，因此最好尝试编写OCaml程序，而不是脚本。将以下内容放入graph.ml文件中，

let player = [|40;80;10|]
let init () = 
  Graphics.open_graph " 800x250";
  Graphics.remember_mode true;
  Graphics.set_color 100;
  Graphics.fill_circle player.(0) player.(1) player.(2)
let rec check button = 
  if button = 'w'
  then
    player.(0) <- player.(0) + 50;
  Graphics.fill_circle player.(0) player.(1) player.(2)
let run () = 
  while true do
    let s = Graphics.wait_next_event [
        Graphics.Button_down;
        Graphics.Key_pressed
      ] in
    let bo = Graphics.key_pressed () in
    if not bo then check s.Graphics.key;
  done

let () =
  init ();
  run ()

使用以下命令编译并运行它

 ocamlbuild -pkg graphics graph.native --