我有以下Haskell数据定义:
data Tree = Leaf Int | Node Int Tree Tree deriving Show
我编写了以下程序来遍历树木预订,订单和后序:
preorder(Leaf n) = n
preorder(Node n t0 t1) = [n] ++ preorder t0 ++ preorder t1
inorder(Leaf n) = n
inorder(Node n t0 t1) = inorder t0 ++ [n] ++ inorder t1
postorder(Leaf n) = n
postorder(Node n t0 t1) = postorder t0 ++ postorder t1 ++ [n]
我得到的错误是:
- Type error in application
*** Expression : preorder t0 ++ preorder t1
*** Term : preorder …