使用For循环遍历字符串

Question

我正在尝试使用for循环遍历字符串的字符但是我得到以下错误

let str = "Hello"
for var=0 to (String.length str -1) do
  let temp = String.get str var
done;;

Error : Syntax error

我在这里尝试了这段代码

let str = "Hello";;
for i = 0 to (String.length str -1) do
    Printf.printf "%s" String.get str i
done;;

这是我得到的错误

Error: This expression has type
         ('a -> 'b -> 'c, out_channel, unit, unit, unit, 'a -> 'b -> 'c)
         CamlinternalFormatBasics.fmt
       but an expression was expected of type
         ('a -> 'b -> 'c, out_channel, unit, unit, unit, unit)
         CamlinternalFormatBasics.fmt
       Type 'a -> 'b -> 'c is not compatible with type unit