堆栈机模拟器Scala [英] Stack Machine Emulator Scala

问题描述

这里我有一个最终函数，该函数应该在指令列表上执行foldLeft。我正在

Here I have a final function which should execute foldLeft on a list of instructions. I'm getting

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

I'm not sure if I'm initializing the accumulator correctly

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)
            })
        }

推荐答案

您不是在创建元组而是在传递值就像是两个参数调用一样。

You aren't creating a tuple but passing values as if it was two parameter call. Use either:

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

或

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

创建一个元组并将其传递给调用。

to create a tuple and pass it into a call.

另外，您必须更改您的输出类型-

Additionally you have to change you output type - it's

Map[String, Double]

而函数返回的值是：

(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
}

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