abstract class Exp
abstract class Stmt

case class Plus(e1: Exp, e2: Exp) extends Exp
case class Times(e1: Exp, e2: Exp) extends Exp
case class Equ(e1: Exp, e2: Exp) extends Exp
case class Num(n: Int) extends Exp
case class Var(x: String) extends Exp

case class Label(l: String) extends Stmt
case class Assign(x: String, e: Exp) extends Stmt
case class Goto(l: String) extends Stmt
case class Jmp(e: Exp, l: String) extends Stmt

type Stmts = List[Stmt]
type Env = Map[String, Int]
type Snips = Map[String, Stmts] 

def preproc(sts: Stmts) : Snips = sts match {
  case Nil => Map()
  case Label(l)::rest => preproc(rest) + (l -> rest) 
  case _::rest => preproc(rest)
} 

def Prog(sts: Stmt*) = preproc(Label("")::sts.toList)

def eval_exp(e: Exp, env: Env) : Int = e match {
  case Var(x) => env(x)
  case Num(n) => n
  case Plus(e1, e2) => eval_exp(e1, env) + eval_exp(e2, env)
  case Times(e1, e2) => eval_exp(e1, env) * eval_exp(e2, env)
  case Equ(e1, e2) => 
    if (eval_exp(e1, env) == eval_exp(e2, env)) 1 else 0
}

def eval(sn: Snips) : Env = {
  def eval_stmts(sts: Stmts, env: Env): Env = sts match {
    case Nil => env
    case Label(l)::rest => eval_stmts(rest, env)
    case Assign(x, e)::rest => 
      eval_stmts(rest, env + (x -> eval_exp(e, env)))
    case Goto(l)::rest => eval_stmts(sn(l), env)
    case Jmp(b, l)::rest => 
      if (eval_exp(b, env) == 1) eval_stmts(sn(l), env) 
      else eval_stmts(rest, env)
  }
  eval_stmts(sn(""), Map())
}