標準ML二叉樹數據類型

Question

我知道這個問題之前已經被問過了，但以前的問題都沒有答案爲我工作，所以我會嘗試一種不同的方法。

我已經做到了這一點：

> datatype which = STRING of string | INT of int; 
datatype which = INT of int | STRING of string 
> datatype whichTree = Empty | Leaf of which | Node of whichTree*whichTree; 
datatype whichTree = Empty | Leaf of which | Node of whichTree * whichTree 

，但是當我嘗試建立一個樹

> val mytree = Node(Leaf(which 2), Leaf(which 6)); 

我得到的錯誤。

Error-Value or constructor (which) has not been declared Found near 
Node(Leaf(which(2)), Leaf(which(6))) 
Error-Value or constructor (which) has not been declared Found near 
Node(Leaf(which(2)), Leaf(which(6))) 
Static errors (pass2) 

Answer 1

which是數據類型的名稱;它不是一個構造函數。相反，你必須創建一棵樹如下：

> val mytree = Node(Leaf(INT 2), Leaf(STRING "6"));