我想用带有元组(k,v)的键值叶子构建二叉树。
我的代码:
data Tree k v = EmptyTree
| Node (k, v) (Tree k v) (Tree k v)
deriving (Show, Eq, Ord, Read)
emptyTree :: (k,v) -> Tree k v
emptyTree (k,v) = Node (k, v) EmptyTree EmptyTree
treeInsert :: (Ord k) => (k,v) -> Tree k v -> Tree k v
treeInsert (k,v) EmptyTree = emptyTree (k, v)
treeInsert (a, b) (Node (k,v) left right)
| a == k = (Node (a,b) left right)
| a < k = (Node (a, b) (treeInsert (a, b) left) right)
| a > k = (Node (a, b) left (treeInsert (a, b) right))
现在我正在尝试填充这棵树:
fillTree :: Int -> Tree k v -> Tree k v
fillTree x tree = treeInsert (x, x) tree
但是我收到了这个错误:
Couldn't match type `v' with `Int'
`v' is a rigid type variable bound by
the type signature for fillTree :: Int -> Tree k v -> Tree k v
原因是什么以及如何解决?
答案 0 :(得分:6)
您的类型过于笼统或过于具体。它应该是
fillTree :: Int -> Tree Int Int -> Tree Int Int
或
fillTree :: (Ord a) => a -> Tree a a -> Tree a a
您的原始声明是尝试将(Int, Int)
插入Tree k v
中的任何k
,v
。它说无论你有什么样的树,我们都可以插入一对Int
。这显然是无稽之谈,正如您treeInsert
的签名所示,只有(k, v)
类型的对可以插入Tree k v
。
treeInsert :: (Ord k) => (k, v) -> Tree k v -> Tree k v