我在使用此代码时遇到了一些麻烦。 它应该是一个带有Elements BinaryOperations和UnaryOperations的OperationTree。 方法eval进行评估并在地图中查找变量。
这是代码
1 import collection.immutable.HashMap
2 sealed abstract class OpTree[T]{
3
4 def eval(v:HashMap[Char,T]):T = {
5 case Elem(x) => x
6 case UnOp(f,c) => {
7 f(c.eval(v))
8 }
9 case BinOp(f,l,r) => {
10 f(l.eval(v),r.eval(v))
11 }
12 case Var(c) => {
13 v.get(c)
14 }
15 }
16 }
17 //Leaf
18 case class Elem[T](elm:T) extends OpTree[T]
19 //Node with two sons
20 case class UnOp[T](f:T => T, child:OpTree[T]) extends OpTree[T]
21 //Node with one son
22 case class BinOp[T](f:(T,T) => T, left:OpTree[T], right:OpTree[T]) extends OpTree[T]
23 case class Var[T](val c:Char) extends OpTree[T]
编译说:
OpTree.scala:4: error: missing parameter type for expanded function
The argument types of an anonymous function must be fully known. (SLS 8.5)
Expected type was: T
def eval(v:HashMap[Char,T]):T = {
^
one error found
有什么建议吗?
谢谢!
答案 0 :(得分:21)
你忘记了实际匹配的东西......
您的代码:
def eval(v:HashMap[Char,T]):T = {
必要的代码:
def eval(v:HashMap[Char,T]):T = v match {