haskell - 或采用两个值参数 haskell

Question

我是 haskell 的初学者，我试图为埃拉托色尼筛法定义一个简单的函数，但它说错误:

    • Couldn't match expected type ‘Bool -> Bool’
                  with actual type ‘Bool’
    • The function ‘or’ is applied to two value arguments,
        but its type ‘t Bool -> Bool’ has only one
      In the expression: or (mod n x) (divl l x)
      In an equation for ‘divl’: divl (n : l) x = or (mod n x) (divl l x)
   |
13 | divl (n:l) x = or (mod n x) (divl l x)

erat l [] = l
erat l (x:t) = if divl l x then erat l t else erat (x:t) l

divl (n:l) x = or (mod n x) (divl l x)
divl [] x = True

我试着把它写成带有“`”的运算符，但没有成功

Answer 1

or 不是 bool OR 运算符；那是 (||)。 or 获取 bool 值列表(好吧，Foldable)，如果至少有一个值为 True，则返回 True .

> or []
False
> or [True, False]
True

(请注意，或[]被定义为False以保留身份或xs || or ys == or (xs++ ys) 。作为具体示例，或[] || 或[False] == 或[False]。)