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520
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1 |
abstract class Exp
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abstract class Stmt
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case class Plus(e1: Exp, e2: Exp) extends Exp
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case class Times(e1: Exp, e2: Exp) extends Exp
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case class Equ(e1: Exp, e2: Exp) extends Exp
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case class Num(n: Int) extends Exp
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case class Var(x: String) extends Exp
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case class Label(l: String) extends Stmt
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case class Assign(x: String, e: Exp) extends Stmt
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case class Goto(l: String) extends Stmt
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case class Jmp(e: Exp, l: String) extends Stmt
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type Stmts = List[Stmt]
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type Env = Map[String, Int]
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type Snips = Map[String, Stmts]
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def preproc(sts: Stmts) : Snips = sts match {
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case Nil => Map()
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case Label(l)::rest => preproc(rest) + (l -> rest)
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case _::rest => preproc(rest)
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}
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def Prog(sts: Stmt*) = preproc(Label("")::sts.toList)
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def eval_exp(e: Exp, env: Env) : Int = e match {
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case Var(x) => env(x)
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case Num(n) => n
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case Plus(e1, e2) => eval_exp(e1, env) + eval_exp(e2, env)
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case Times(e1, e2) => eval_exp(e1, env) * eval_exp(e2, env)
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case Equ(e1, e2) =>
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if (eval_exp(e1, env) == eval_exp(e2, env)) 1 else 0
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}
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def eval(sn: Snips) : Env = {
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def eval_stmts(sts: Stmts, env: Env): Env = sts match {
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case Nil => env
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case Label(l)::rest => eval_stmts(rest, env)
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case Assign(x, e)::rest =>
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eval_stmts(rest, env + (x -> eval_exp(e, env)))
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case Goto(l)::rest => eval_stmts(sn(l), env)
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case Jmp(b, l)::rest =>
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if (eval_exp(b, env) == 1) eval_stmts(sn(l), env)
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else eval_stmts(rest, env)
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}
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47 |
eval_stmts(sn(""), Map())
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}
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