简单版解释器

package com.moon.tina

/**
  * Created by lin on 2017/5/10.
  */
case class Instruction(name:String,pos:Int)

case class ExecuteInstructions(instructions:List[Instruction],numbers:List[Int])

case class TinaInterpreter() {
  var stack:List[Int]=List[Int]()
  var answer:Int= _
  def loadValue(num:Int): Unit ={
    stack=num +:stack
  }

  def printAnswer(): Unit ={
    answer=stack.head
  }

  def addTwoValues(): Unit ={
    val firstNum=stack.head
    stack=stack.drop(1)
    val secondNum=stack.head
    stack=stack.drop(1)
    val total=firstNum+secondNum
    stack=total+:stack
  }

  def run(einstructions: ExecuteInstructions): Unit ={
    val instructions=einstructions.instructions
    val numbers=einstructions.numbers
    for(eachStep <- instructions){
      if(eachStep.name=="LOAD_VALUE"){
        val number=numbers(eachStep.pos)
        loadValue(number)
      }else if(eachStep.name=="ADD_TWO_VALUES"){
        addTwoValues()
      }else if(eachStep.name=="PRINT_ANSWER"){
        printAnswer()
      }

    }
  }
}

object TinaInterpreter{
  def main(args: Array[String]) {
    val whatToExecute=ExecuteInstructions(List(
      Instruction("LOAD_VALUE",0),
      Instruction("LOAD_VALUE",1),
      Instruction("ADD_TWO_VALUES",-1),
      Instruction("PRINT_ANSWER",-1)
    ),
      List(7,5))

    val interpreter=TinaInterpreter()
    interpreter.run(whatToExecute)
    println(interpreter.stack)
  }
}