Simple translation to ByteCode example

ByteCode.scala

import scala.collection.mutable.ListBuffer

sealed trait ByteCode

object ByteCode {
  case class Push(n: Int) extends ByteCode
  case object Add extends ByteCode
}

sealed trait Instruction

sealed trait Exp extends Instruction 

case class Declare(name: String, value: Primitive) extends Instruction

case class Add(expa: Exp, expb: Exp) extends Exp
case class Read(name: String) extends Exp
case class Primitive(n: Int) extends Exp

case object Program {
  import collection.mutable.Map

  def translate(program: List[Instruction]): List[ByteCode] = {
    val table: Map[String, Int] = Map.empty

    val bytecode: ListBuffer[ByteCode] = new ListBuffer

    def eval(exp: Exp): Unit = exp match {
      case Primitive(n: Int) =>
        bytecode += ByteCode.Push(n)
      case Add(a: Exp, b: Exp) =>
        eval(a)
        eval(b)
        bytecode += ByteCode.Add
      case Read(name) =>
        table.get(name).map { value =>
          bytecode += ByteCode.Push(value)
        }.getOrElse {
          throw new Exception(s"Compilation error: lookup on undeclared variable: $name")
        }
    }

    program.foreach {
      case Declare(name, Primitive(n)) => table(name) = n
      case exp: Exp => eval(exp)
    }

    bytecode.toList
  }
}

object example extends App {
  val program = List(
    Declare("x", Primitive(3)),
    Declare("y", Primitive(4)),
    Add(Primitive(8), Add(Read("x"), Read("y")))
  )

  Program.translate(program) foreach println
}