“‘节点’应用于太少的参数”即使有确切的数字

Question

s 和 a 是类型变量。在构造函数中，前两个参数是数据，然后是它的父级，它在图中的级别，然后是它的子级列表。

data Node s a = Root | Node s a (Node s a) Int [Node s a]
createRoot :: (ProblemState s a) => s-> a -> Node s a
createRoot state act= Node (state act Root 0 [])

并且我已经将完全相同数量的 5 个参数传递给 Node 构造函数，但是我遇到了错误。

• Couldn't match expected type ‘Node s a’
              with actual type ‘a1
                                -> Node s1 a1 -> Int -> [Node s1 a1] -> Node s1 a1’
• Probable cause: ‘Node’ is applied to too few arguments
  In the expression: Node (state act Root 0 [])
  In an equation for ‘createRoot’:
      createRoot state act = Node (state act Root 0 [])
• Relevant bindings include
    act :: a (bound at Search.hs:43:24)
    state :: s (bound at Search.hs:43:18)
    createRoot :: s -> a -> Node s a (bound at Search.hs:43:1)

Answer 1

括号用于对表达式进行分组。 (length "hello" + 2) 是单个值，不是 4。

类似地，Node (...) 将 Node 应用于单个参数：(state act Root 0 [])。显然这是错误的（并且需要 state 是一个带四个参数的函数）。

解决方法是去掉括号：

Node state act Root 0 []

现在 Node 应用于五个参数。

“‘节点’应用于太少的参数”即使有确切的数字

"‘Node’ is applied to too few arguments" even though there are exact number

syntax

haskell

function-call