我正在为 SML 中的编程语言类做一个简单的练习,练习是计算树是否平衡。以下代码是我认为有效的解决方案:
datatype IntTree = LEAF of int | NODE of (IntTree * IntTree);
fun balanced (LEAF l) = true
| balanced (NODE (LEAF l, NODE n)) = false
| balanced (NODE (NODE n1, NODE n2)) = balanced(n1) andalso balanced(n2)
| balanced (NODE (NODE n, LEAF l)) = false
| balanced (NODE (LEAF l1, LEAF l2)) = true;
但是,当我尝试在解释器中运行它时,出现以下错误:
stdIn:98.42-98.54 Error: operator and operand don't agree [tycon mismatch]
operator domain: IntTree
operand: IntTree * IntTree
in expression:
balanced n1
stdIn:98.63-98.75 Error: operator and operand don't agree [tycon mismatch]
operator domain: IntTree
operand: IntTree * IntTree
in expression:
balanced n2
但是NODE
应该是IntTree
型,为什么这不起作用?
我现在
没有 SML 编译器,所以我无法测试这个,但请尝试将balanced(n1)
更改为 (balanced (NODE n1))
(与 balanced(n2))
相同。