Haskell +计算子字符串

Question

我非常接近这个，但我仍然陷入困境：/

txt :: String
txt = "[1] and [2] both feature characters who will do whatever it takes to " ++
  "get to their goal, and in the end the thing they want the most ends " ++
  "up destroying them.  In case of [3] this is a whale..."
references :: String -> Int

split :: String -> [String]
split str = words str

find :: [String] -> [String]
find xs = [ x | x <- xs, x == "["++"1"++"]" ]                           
references x = length (find (split x ))

我需要找到时间段[n]出现在n为数字0的字符串中。

在上面的例子中n = 3。

我似乎无法编写谓词来捕获括号"[1]"或"[3]"括起来的所有数字。 （我在这里的代码中硬编码1）