1 abstract class Exp

     2 abstract class Stmt

     3 

     4 case class Plus(e1: Exp, e2: Exp) extends Exp

     5 case class Times(e1: Exp, e2: Exp) extends Exp

     6 case class Equ(e1: Exp, e2: Exp) extends Exp

     7 case class Num(n: Int) extends Exp

     8 case class Var(x: String) extends Exp

     9 

    10 case class Label(l: String) extends Stmt

    11 case class Assign(x: String, e: Exp) extends Stmt

    12 case class Goto(l: String) extends Stmt

    13 case class Jmp(e: Exp, l: String) extends Stmt

    14 

    15 type Stmts = List[Stmt]

    16 type Env = Map[String, Int]

    17 type Snips = Map[String, Stmts] 

    18 

    19 def preproc(sts: Stmts) : Snips = sts match {

    20   case Nil => Map()

    21   case Label(l)::rest => preproc(rest) + (l -> rest) 

    22   case _::rest => preproc(rest)

    23 } 

    24 

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

    26 

    27 def eval_exp(e: Exp, env: Env) : Int = e match {

    28   case Var(x) => env(x)

    29   case Num(n) => n

    30   case Plus(e1, e2) => eval_exp(e1, env) + eval_exp(e2, env)

    31   case Times(e1, e2) => eval_exp(e1, env) * eval_exp(e2, env)

    32   case Equ(e1, e2) => 

    33     if (eval_exp(e1, env) == eval_exp(e2, env)) 1 else 0

    34 }

    35 

    36 def eval(sn: Snips) : Env = {

    37   def eval_stmts(sts: Stmts, env: Env): Env = sts match {

    38     case Nil => env

    39     case Label(l)::rest => eval_stmts(rest, env)

    40     case Assign(x, e)::rest => 

    41       eval_stmts(rest, env + (x -> eval_exp(e, env)))

    42     case Goto(l)::rest => eval_stmts(sn(l), env)

    43     case Jmp(b, l)::rest => 

    44       if (eval_exp(b, env) == 1) eval_stmts(sn(l), env) 

    45       else eval_stmts(rest, env)

    46   }

    47   eval_stmts(sn(""), Map())

    48 }