我应该如何实施“添加"功能?斯卡拉译员吗? [英] How should I implement "add" interpreter in scala?
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问题描述
我正在实现Scala解释器,但遇到了一些问题
I am implementing scala interpreter and I have some problem
我具有Value.scala
中的值类:
case class IntV(value: Int) extends Value
我也遵循文件Expr.scala
中的类:
case class IntE(value: Int) extends Expr
case class Add(left: Expr, right: Expr) extends Expr
当我按如下方式实现Int解释器时:
When I implemented Int interpreter as followed:
case IntE(value)=>IntV(value)
效果很好,但是当我实现添加解释器时(它执行3 + 4 = 7之类的加法运算),如下所示:
It worked well but when I implemented add interpreter(which does addition like 3+4=7)as followed:
case Add(left, right)=>IntV(left)+IntV(right)
返回错误,该错误表示变量为left和right,需要Int
,但找到了expr
.
我做错什么了?我该怎么做才能获得正确的回报?
It returns error which says for variable left and right, it requires Int
but it found expr
.
What did I do wrong? What should I do to get correct return?
推荐答案
您应递归调用解释器.
例如
sealed trait Value
case class IntV(value: Int) extends Value
sealed trait Expr
case class IntE(value: Int) extends Expr
case class Add(left: Expr, right: Expr) extends Expr
def interpret(expr: Expr): Value = expr match {
case IntE(value) => IntV(value)
case Add(left, right) => (interpret(left), interpret(right)) match {
case (IntV(v1), IntV(v2)) => IntV(v1 + v2)
}
}
interpret(IntE(1)) // IntV(1)
interpret(Add(IntE(3), IntE(4))) // IntV(7)
或使用针对IntV
的已定义方法+
Or with a defined method +
for IntV
sealed trait Value
case class IntV(value: Int) extends Value {
def +(other: IntV): IntV = IntV(value + other.value)
}
sealed trait Expr
case class IntE(value: Int) extends Expr
case class Add(left: Expr, right: Expr) extends Expr
def interpret(expr: Expr): Value = expr match {
case IntE(value) => IntV(value)
case Add(left, right) => (interpret(left), interpret(right)) match {
case (v1: IntV, v2: IntV) => v1 + v2
}
}
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