堆栈机模拟器 Scala

Question

这里我有一个最终函数，它应该在指令列表上执行 foldLeft。我得到

type mismatch;
 found   : (List[Double], scala.collection.immutable.Map[String,Double])
 required: Map[String,Double]
            instructionList.foldLeft(Nil : List[Double], Map.empty[String,Double])((acc:(List[Double], Map[String,Double]), SMI:StackMachineInstruction) => {

我不确定我是否正确初始化了累加器

def emulateStackMachine(instructionList: List[StackMachineInstruction]): Map[String, Double] =
        {
            instructionList.foldLeft((Nil : List[Double], Map.empty[String,Double]))((acc:(List[Double], Map[String,Double]), SMI:StackMachineInstruction) => {
                emulateSingleInstruction(acc._1, acc._2, SMI)
            })
        }

Answer 1

您不是在创建元组，而是像传递两个参数调用一样传递值。使用：

((Nil : List[Double], Map.empty[String,Double])) // double parens

或

(List.empty[Double] -> Map.empty[String,Double]) // -> syntax

创建元组并将其传递到调用中。

另外你必须改变你的输出类型 - 它是

Map[String, Double]

而函数返回的值为：

(List[Double], Map[String,Double])

def emulateStackMachine(instructionList: List[StackMachineInstruction]): (List[Double], Map[String, Double]) = {
  instructionList.foldLeft(List.empty[Double] -> Map.empty[String,Double])((acc, SMI) => {
    emulateSingleInstruction(acc._1, acc._2, SMI)
  })
}
// or
def emulateStackMachine(instructionList: List[StackMachineInstruction]): Map[String, Double] = {
  instructionList.foldLeft(List.empty[Double] -> Map.empty[String,Double])((acc, SMI) => {
    emulateSingleInstruction(acc._1, acc._2, SMI)
  })._2
}

堆栈机模拟器 Scala

Stack Machine Emulator Scala

stack

scala

emulation

pattern-matching