import scala.language.implicitConversions    
import scala.language.reflectiveCalls 
import scala.util._
import scala.annotation.tailrec
import scala.sys.process._

abstract class Rexp 
case object NULL extends Rexp
case object EMPTY extends Rexp
case class CHAR(c: Char) extends Rexp
case class ALT(r1: Rexp, r2: Rexp) extends Rexp 
case class RANGE(cs: List[Char]) extends Rexp 
case class SEQ(r1: Rexp, r2: Rexp) extends Rexp 
case class PLUS(r: Rexp) extends Rexp 
case class STAR(r: Rexp) extends Rexp 
case class NTIMES(r: Rexp, n: Int) extends Rexp 
case class NUPTOM(r: Rexp, n: Int, m: Int) extends Rexp

object RANGE {
  def apply(s: String) : RANGE = RANGE(s.toList)
}
def NMTIMES(r: Rexp, n: Int, m: Int) = {
  if(m < n) throw new IllegalArgumentException("the number m cannot be smaller than n.")
  else NUPTOM(r, n, m - n)
}

case class NOT(r: Rexp) extends Rexp 
case class OPT(r: Rexp) extends Rexp 

// some convenience for typing in regular expressions
def charlist2rexp(s : List[Char]) : Rexp = s match {
  case Nil => EMPTY
  case c::Nil => CHAR(c)
  case c::s => SEQ(CHAR(c), charlist2rexp(s))
}
implicit def string2rexp(s : String) : Rexp = charlist2rexp(s.toList)

implicit def RexpOps (r: Rexp) = new {
  def | (s: Rexp) = ALT(r, s)
  def % = STAR(r)
  def ~ (s: Rexp) = SEQ(r, s)
}

implicit def stringOps (s: String) = new {
  def | (r: Rexp) = ALT(s, r)
  def | (r: String) = ALT(s, r)
  def % = STAR(s)
  def ~ (r: Rexp) = SEQ(s, r)
  def ~ (r: String) = SEQ(s, r)
}


// nullable function: tests whether the regular 
// expression can recognise the empty string
def nullable (r: Rexp) : Boolean = r match {
  case NULL => false
  case EMPTY => true
  case CHAR(_) => false
  case ALT(r1, r2) => nullable(r1) || nullable(r2)
  case SEQ(r1, r2) => nullable(r1) && nullable(r2)
  case STAR(_) => true
  case PLUS(r) => nullable(r)
  case NTIMES(r, i) => if (i == 0) true else nullable(r)
  case NUPTOM(r, i, j) => if (i == 0) true else nullable(r)
  case RANGE(_) => false
  case NOT(r) => !(nullable(r))
  case OPT(_) => true
}

// derivative of a regular expression w.r.t. a character
def der (c: Char, r: Rexp) : Rexp = r match {
  case NULL => NULL
  case EMPTY => NULL
  case CHAR(d) => if (c == d) EMPTY else NULL
  case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))
  case SEQ(r1, r2) => 
    if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))
    else SEQ(der(c, r1), r2)
  case STAR(r) => SEQ(der(c, r), STAR(r))
  case PLUS(r) => SEQ(der(c, r), STAR(r))
  case NTIMES(r, i) => 
    if (i == 0) NULL else der(c, SEQ(r, NTIMES(r, i - 1)))
  case NUPTOM(r, i, j) =>
    if (i == 0 && j == 0) NULL else 
    if (i == 0) ALT(der(c, NTIMES(r, j)), der(c, NUPTOM(r, 0, j - 1)))
    else der(c, SEQ(r, NUPTOM(r, i - 1, j)))
  case RANGE(cs) => if (cs contains c) EMPTY else NULL
  case NOT(r) => NOT(der (c, r))
  case OPT(r) => der(c, r)
}

def zeroable (r: Rexp) : Boolean = r match {
  case NULL => true
  case EMPTY => false
  case CHAR(_) => false
  case ALT(r1, r2) => zeroable(r1) && zeroable(r2)
  case SEQ(r1, r2) => zeroable(r1) || zeroable(r2)
  case STAR(_) => false
  case PLUS(r) => zeroable(r)
  case NTIMES(r, i) => if (i == 0) false else zeroable(r)
  case NUPTOM(r, i, j) => if (i == 0) false else zeroable(r)
  case RANGE(_) => false
  case NOT(r) => !(zeroable(r))     // bug: incorrect definition for NOT
  case OPT(_) => false
}

// derivative w.r.t. a string (iterates der)
def ders (s: List[Char], r: Rexp) : Rexp = s match {
  case Nil => r
  case c::s => ders(s, der(c, r))
}


// regular expressions for the While language
val SYM = RANGE("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_".toList)
val DIGIT = RANGE("0123456789".toList)
val ID = SYM ~ (SYM | DIGIT).% 
val NUM = PLUS(DIGIT)
val KEYWORD : Rexp = "skip" | "while" | "do" | "if" | "then" | "else" | "read" | "write" | "true" | "false"
val SEMI: Rexp = ";"
val OP: Rexp = ":=" | "==" | "-" | "+" | "*" | "!=" | "<" | ">" | "%" | "/"
val WHITESPACE = PLUS(" " | "\n" | "\t")
val RPAREN: Rexp = ")"
val LPAREN: Rexp = "("
val BEGIN: Rexp = "{"
val END: Rexp = "}"
val ALL = SYM | DIGIT | OP | " " | ":" | ";" | "\"" | "(" | ")" | "{" | "}" 
val ALL2 = ALL | "\n"
val COMMENT2 = ("/*" ~ NOT(ALL.% ~ "*/" ~ ALL.%) ~ "*/")
val COMMENT = ("/*" ~ ALL2.% ~ "*/") | ("//" ~ ALL.% ~ "\n")
val STRING = "\"" ~ ALL.% ~ "\""


// token for While language
abstract class Token
case object T_WHITESPACE extends Token
case object T_SEMI extends Token
case object T_LPAREN extends Token
case object T_RPAREN extends Token
case object T_BEGIN extends Token
case object T_END extends Token
case object T_COMMENT extends Token
case class T_ID(s: String) extends Token
case class T_OP(s: String) extends Token
case class T_NUM(s: String) extends Token
case class T_KWD(s: String) extends Token
case class T_STRING(s: String) extends Token
case class T_ERR(s: String) extends Token // special error token


type TokenFun = String => Token
type LexRules = List[(Rexp, TokenFun)]
val While_lexing_rules: LexRules = 
  List((KEYWORD, (s) => T_KWD(s)),
       (ID, (s) => T_ID(s)),
       (COMMENT, (s) => T_COMMENT),
       (OP, (s) => T_OP(s)),
       (NUM, (s) => T_NUM(s)),
       (SEMI, (s) => T_SEMI),
       (LPAREN, (s) => T_LPAREN),
       (RPAREN, (s) => T_RPAREN),
       (BEGIN, (s) => T_BEGIN),
       (END, (s) => T_END),
       (STRING, (s) => T_STRING(s.drop(1).dropRight(1))),
       (WHITESPACE, (s) => T_WHITESPACE))


// calculates derivatives until all of them are zeroable
@tailrec
def munch(s: List[Char], 
          pos: Int, 
          rs: LexRules, 
          last: Option[(Int, TokenFun)]): Option[(Int, TokenFun)] = {
  rs match {
  case Nil => last
  case rs if (s.length <= pos) => last
  case rs => {
    val ders = rs.map({case (r, tf) => (der(s(pos), r), tf)})
    val rs_nzero = ders.filterNot({case (r, _) => zeroable(r)})
    val rs_nulls = ders.filter({case (r, _) => nullable(r)})
    val new_last = if (rs_nulls != Nil) Some((pos, rs_nulls.head._2)) else last
    munch(s, 1 + pos, rs_nzero, new_last)
  }
}}

// iterates the munching function and returns a Token list
def tokenize(s: String, rs: LexRules) : List[Token] = munch(s.toList, 0, rs, None) match {
  case None if (s == "") => Nil
  case None => List(T_ERR(s"Lexing error: $s"))
  case Some((n, tf)) => {
    val (head, tail) = s.splitAt(n + 1)
    tf(head)::tokenize(tail, rs)
  }
}

def tokenizer(s:String) : List[Token] = 
  tokenize(s, While_lexing_rules).filter {
    case T_ERR(s) => { println(s); sys.exit(-1) }
    case T_WHITESPACE => false
    case T_COMMENT => false
    case _ => true
  } 

def fromFile(name: String) : String = 
  io.Source.fromFile(name).mkString

// tokenizer tests
//println(tokenizer(fromFile("loops.while")).mkString("\n"))
//println(tokenizer(fromFile("fib.while")).mkString("\n"))
//println(tokenizer(fromFile("collatz.while")).mkString("\n"))





// Parser - Abstract syntax trees
abstract class Stmt
abstract class AExp
abstract class BExp 
type Block = List[Stmt]
case object Skip extends Stmt
case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt
case class While(b: BExp, bl: Block) extends Stmt
case class Assign(s: String, a: AExp) extends Stmt
case class Read(s: String) extends Stmt
case class Write(s: String) extends Stmt
case class WriteS(s: String) extends Stmt

case class Var(s: String) extends AExp
case class Num(i: Int) extends AExp
case class Aop(o: String, a1: AExp, a2: AExp) extends AExp

case object True extends BExp
case object False extends BExp
case class Bop(o: String, a1: AExp, a2: AExp) extends BExp

// Parser combinators
abstract class Parser[I <% Seq[_], T] {
  def parse(ts: I): Set[(T, I)]

  def parse_all(ts: I) : Set[T] =
    for ((head, tail) <- parse(ts); if (tail.isEmpty)) yield head

  def parse_single(ts: I) : T = parse_all(ts).toList match {
    case List(t) => t
    case _ => { println ("Parse Error") ; sys.exit(-1) }
  }
}

class SeqParser[I <% Seq[_], T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, (T, S)] {
  def parse(sb: I) = 
    for ((head1, tail1) <- p.parse(sb); 
         (head2, tail2) <- q.parse(tail1)) yield ((head1, head2), tail2)
}

class AltParser[I <% Seq[_], T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] {
  def parse(sb: I) = p.parse(sb) ++ q.parse(sb)   
}

class FunParser[I <% Seq[_], T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] {
  def parse(sb: I) = 
    for ((head, tail) <- p.parse(sb)) yield (f(head), tail)
}


case class TokParser(tok: Token) extends Parser[List[Token], Token] {
  def parse(ts: List[Token]) = ts match {
    case t::ts if (t == tok) => Set((t, ts)) 
    case _ => Set ()
  }
}
implicit def token2tparser(t: Token) = TokParser(t)

case object NumParser extends Parser[List[Token], Int] {
  def parse(ts: List[Token]) = ts match {
    case T_NUM(s)::ts => Set((s.toInt, ts)) 
    case _ => Set ()
  }
}

case object IdParser extends Parser[List[Token], String] {
  def parse(ts: List[Token]) = ts match {
    case T_ID(s)::ts => Set((s, ts)) 
    case _ => Set ()
  }
}

case object StringParser extends Parser[List[Token], String] {
  def parse(ts: List[Token]) = ts match {
    case T_STRING(s)::ts => Set((s, ts)) 
    case _ => Set ()
  }
}

implicit def ParserOps[I<% Seq[_], T](p: Parser[I, T]) = new {
  def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)
  def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)
  def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)
}
implicit def TokOps(t: Token) = new {
  def || (q : => Parser[List[Token], Token]) = new AltParser[List[Token], Token](t, q)
  def ==>[S] (f: => Token => S) = new FunParser[List[Token], Token, S](t, f)
  def ~[S](q : => Parser[List[Token], S]) = new SeqParser[List[Token], Token, S](t, q)
}

// arithmetic expressions
lazy val AExp: Parser[List[Token], AExp] = 
  (T ~ T_OP("+") ~ AExp) ==> { case ((x, y), z) => Aop("+", x, z): AExp } ||
  (T ~ T_OP("-") ~ AExp) ==> { case ((x, y), z) => Aop("-", x, z): AExp } || T  
lazy val T: Parser[List[Token], AExp] = 
  (F ~ T_OP("*") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || 
  (F ~ T_OP("/") ~ T) ==> { case ((x, y), z) => Aop("/", x, z): AExp } || 
  (F ~ T_OP("%") ~ T) ==> { case ((x, y), z) => Aop("%", x, z): AExp } || F
lazy val F: Parser[List[Token], AExp] = 
  (T_LPAREN ~ AExp ~ T_RPAREN) ==> { case ((x, y), z) => y: AExp }|| 
  IdParser ==> { case x => Var(x): AExp } || 
  NumParser ==> { case x => Num(x): AExp }

// boolean expressions
lazy val BExp: Parser[List[Token], BExp] = 
  (AExp ~ T_OP("==") ~ AExp) ==> { case ((x, y), z) => Bop("==", x, z): BExp } || 
  (AExp ~ T_OP("!=") ~ AExp) ==> { case ((x, y), z) => Bop("!=", x, z): BExp } || 
  (AExp ~ T_OP("<") ~ AExp) ==> { case ((x, y), z) => Bop("<", x, z): BExp } || 
  (AExp ~ T_OP(">") ~ AExp) ==> { case ((x, y), z) => Bop("<", z, x): BExp } || 
  (T_KWD("true") ==> ((_) => True)) || 
  (T_KWD("false") ==> ((_) => False: BExp))

lazy val Stmt: Parser[List[Token], Stmt] =
  (T_KWD("skip") ==> ((_) => Skip: Stmt)) ||
  (IdParser ~ T_OP(":=") ~ AExp) ==> { case ((x, y), z) => Assign(x, z): Stmt } ||
  (T_KWD("if") ~ BExp ~ T_KWD("then") ~ Block ~ T_KWD("else") ~ Block) ==>
    { case (((((x,y),z),u),v),w) => If(y, u, w): Stmt } ||
  (T_KWD("while") ~ BExp ~ T_KWD("do") ~ Block) ==> { case (((x, y), z), w) => While(y, w) } ||
  (T_KWD("read") ~ IdParser) ==> { case (x, y) => Read(y) } ||
  (T_KWD("write") ~ IdParser) ==> { case (x, y) => Write(y) } ||
  (T_KWD("write") ~ StringParser) ==> { case (x, y) => WriteS(y) }

lazy val Stmts: Parser[List[Token], Block] =
  (Stmt ~ T_SEMI ~ Stmts) ==> { case ((x, y), z) => x :: z : Block } ||
  (Stmt ==> ((s) => List(s) : Block))

lazy val Block: Parser[List[Token], Block] =
  (T_BEGIN ~ Stmts ~ T_END) ==> { case ((x, y), z) => y : Block } || 
  (Stmt ==> ((s) => List(s)))



// parser examples
val p1 = "x := 5"
val p1_toks = tokenizer(p1) 
val p1_ast = Block.parse_all(p1_toks)
//println(p1_toks)
//println(p1_ast)

val p2 = "{ x := 5; y := 8}"
val p2_toks = tokenizer(p2) 
val p2_ast = Block.parse_all(p2_toks)
//println(p2_ast)

val p3 = "5 == 6"
val p3_toks = tokenizer(p3) 
val p3_ast = BExp.parse_all(p3_toks)
//println(p3_ast)

val p4 = "true"
val p4_toks = tokenizer(p4) 
val p4_ast = BExp.parse_all(p4_toks)
//println(p4_ast)

val p5 = "if true then skip else skip"
val p5_toks = tokenizer(p5) 
val p5_ast = Stmt.parse_all(p5_toks)
//println(p5_ast)

val p6 = "if true then x := 5 else x := 10"
val p6_toks = tokenizer(p6) 
val p6_ast = Stmt.parse_all(p6_toks)
//println(p6_ast)

val p7 = "if false then x := 5 else x := 10"
val p7_toks = tokenizer(p7) 
val p7_ast = Stmt.parse_all(p7_toks)
//println(p7_ast)

val p8 = "write x; write \"foo\"; read x "
val p8_toks = tokenizer(p8) 
val p8_ast = Stmts.parse_all(p8_toks)
//println(p8_ast)

// multiplication
val p9 = """  x := 5;
              y := 4;
              r := 0;
              while y > 0 do {
                 r := r + x;
                 y := y - 1
              } 
         """
val p9_toks = tokenizer(p9) 
val p9_ast = Stmts.parse_all(p9_toks)
//println(p9_ast)

// fibonacci numbers
val p10 = """
 write "Fib: ";
 read n;
 minus1 := 0;
 minus2 := 1;
 temp := 0;
 while n > 0 do  {
   temp := minus2;
   minus2 := minus1 + minus2;
   minus1 := temp;
   n := n - 1
 };
 write "Result:";
 write minus2
"""
val p10_toks = tokenizer(p10) 
val p10_ast = Stmts.parse_all(p10_toks)
//println(p10_ast)


// an interpreter for the WHILE language
type Env = Map[String, Int]

def eval_aexp(a: AExp, env : Env) : Int = a match {
  case Num(i) => i
  case Var(s) => env(s)
  case Aop("+", a1, a2) => eval_aexp(a1, env) + eval_aexp(a2, env)
  case Aop("-", a1, a2) => eval_aexp(a1, env) - eval_aexp(a2, env)
  case Aop("*", a1, a2) => eval_aexp(a1, env) * eval_aexp(a2, env)
}

def eval_bexp(b: BExp, env: Env) : Boolean = b match {
  case True => true
  case False => false
  case Bop("==", a1, a2) => eval_aexp(a1, env) == eval_aexp(a2, env)
  case Bop("!=", a1, a2) => !(eval_aexp(a1, env) == eval_aexp(a2, env))
  case Bop("<", a1, a2) => eval_aexp(a1, env) < eval_aexp(a2, env)
}

def eval_stmt(s: Stmt, env: Env) : Env = s match {
  case Skip => env
  case Assign(x, a) => env + (x -> eval_aexp(a, env))
  case If(b, bl1, bl2) => if (eval_bexp(b, env)) eval_bl(bl1, env) else eval_bl(bl2, env) 
  case While(b, bl) => 
    if (eval_bexp(b, env)) eval_stmt(While(b, bl), eval_bl(bl, env))
    else env
  case WriteS(s: String) => { println(s); env }
  case Write(s: String) => { println(env(s)); env }
  case Read(s: String) => tokenizer(Console.readLine) match {
    case List(T_NUM(n)) => env + (s -> n.toInt)
    case _ => { println("not a number"); eval_stmt(Read(s: String), env) }
  }
}

def eval_bl(bl: Block, env: Env) : Env = bl match {
  case Nil => env
  case s::bl => eval_bl(bl, eval_stmt(s, env))
}

def eval(bl: Block) : Env = eval_bl(bl, Map())

def interpret(s: String): Unit =
  eval(Stmts.parse_all(tokenizer(s)).head)

// interpreter example
//interpret(p10)



// compiler - built-in functions 
// copied from http://www.ceng.metu.edu.tr/courses/ceng444/link/jvm-cpm.html
//

val beginning = """
.class public XXX.XXX
.super java/lang/Object

.method public <init>()V
        aload_0
        invokenonvirtual java/lang/Object/<init>()V
        return
.end method

.method public static write(I)V 
        .limit locals 5 
        .limit stack 5 
        iload 0 
        getstatic java/lang/System/out Ljava/io/PrintStream; 
        swap 
        invokevirtual java/io/PrintStream/println(I)V 
        return 
.end method

.method public static writes(Ljava/lang/String;)V
       .limit stack 2
       .limit locals 2
       getstatic java/lang/System/out Ljava/io/PrintStream;
       aload 0
       invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V
       return
.end method

.method public static read()I 
      .limit locals 10 
      .limit stack 10

      ldc 0 
      istore 1  ; this will hold our final integer 
Label1: 
      getstatic java/lang/System/in Ljava/io/InputStream; 
      invokevirtual java/io/InputStream/read()I 
      istore 2 
      iload 2 
      ldc 10   ; the newline delimiter 
      isub 
      ifeq Label2 
      iload 2 
      ldc 32   ; the space delimiter 
      isub 
      ifeq Label2

      iload 2 
      ldc 48   ; we have our digit in ASCII, have to subtract it from 48 
      isub 
      ldc 10 
      iload 1 
      imul 
      iadd 
      istore 1 
      goto Label1 
Label2: 
      ;when we come here we have our integer computed in Local Variable 1 
      iload 1 
      ireturn 
.end method

.method public static main([Ljava/lang/String;)V
      .limit locals 200
      .limit stack 200

"""

val ending = """

      return

.end method
"""

// for generating new labels
var counter = -1

def Fresh(x: String) = {
  counter += 1
  x ++ "_" ++ counter.toString()
}

type Mem = Map[String, String]
type Instrs = List[String]

def compile_aexp(a: AExp, env : Mem) : Instrs = a match {
  case Num(i) => List("ldc " + i.toString + "\n")
  case Var(s) => List("iload " + env(s) + "\n")
  case Aop("+", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("iadd\n")
  case Aop("-", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("isub\n")
  case Aop("*", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("imul\n")
  case Aop("/", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("idiv\n")
  case Aop("%", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("irem\n") 
}

def compile_bexp(b: BExp, env : Mem, jmp: String) : Instrs = b match {
  case True => Nil
  case False => List("goto " + jmp + "\n")
  case Bop("==", a1, a2) => 
    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpne " + jmp + "\n")
  case Bop("!=", a1, a2) => 
    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpeq " + jmp + "\n")
  case Bop("<", a1, a2) => 
    compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpge " + jmp + "\n")
}


def compile_stmt(s: Stmt, env: Mem) : (Instrs, Mem) = s match {
  case Skip => (Nil, env)
  case Assign(x, a) => {
    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size.toString
    (compile_aexp(a, env) ++ 
     List("istore " + index + "\n"), env + (x -> index))
  } 
  case If(b, bl1, bl2) => {
    val if_else = Fresh("If_else")
    val if_end = Fresh("If_end")
    val (instrs1, env1) = compile_bl(bl1, env)
    val (instrs2, env2) = compile_bl(bl2, env1)
    (compile_bexp(b, env, if_else) ++
     instrs1 ++
     List("goto " + if_end + "\n") ++
     List("\n" + if_else + ":\n\n") ++
     instrs2 ++
     List("\n" + if_end + ":\n\n"), env2)
  }
  case While(b, bl) => {
    val loop_begin = Fresh("Loop_begin")
    val loop_end = Fresh("Loop_end")
    val (instrs1, env1) = compile_bl(bl, env)
    (List("\n" + loop_begin + ":\n\n") ++
     compile_bexp(b, env, loop_end) ++
     instrs1 ++
     List("goto " + loop_begin + "\n") ++
     List("\n" + loop_end + ":\n\n"), env1)
  }
  case Write(x) => 
    (List("iload " + env(x) + "\n" + 
          "invokestatic XXX/XXX/write(I)V\n"), env)
  case WriteS(x) => 
    (List("ldc \"" + x + "\"\n" + 
          "invokestatic XXX/XXX/writes(Ljava/lang/String;)V\n"), env)
  case Read(x) => {
    val index = if (env.isDefinedAt(x)) env(x) else env.keys.size.toString
    (List("invokestatic XXX/XXX/read()I\n" + 
          "istore " + index + "\n"), env + (x -> index))
  } 
}


def compile_bl(bl: Block, env: Mem) : (Instrs, Mem) = bl match {
  case Nil => (Nil, env)
  case s::bl => {
    val (instrs1, env1) = compile_stmt(s, env)
    val (instrs2, env2) = compile_bl(bl, env1)
    (instrs1 ++ instrs2, env2)
  }
}

def compile(class_name: String, input: String) : String = {
  val tks = tokenizer(input)
  println("Output\n" + Stmts.parse(tks))
  val ast = Stmts.parse_single(tks)
  val instructions = compile_bl(ast, Map.empty)._1
  (beginning ++ instructions.mkString ++ ending).replaceAllLiterally("XXX", class_name)
}


def compile_file(file_name: String) = {
  val class_name = file_name.split('.')(0)
  val output = compile(class_name, fromFile(file_name))
  val fw = new java.io.FileWriter(class_name + ".j") 
  fw.write(output) 
  fw.close()
}

def time_needed[T](i: Int, code: => T) = {
  val start = System.nanoTime()
  for (j <- 1 to i) code
  val end = System.nanoTime()
  (end - start)/(i * 1.0e9)
}


def compile_run(file_name: String) : Unit = {
  val class_name = file_name.split('.')(0)
  compile_file(file_name)
  val test = ("java -jar jvm/jasmin-2.4/jasmin.jar " + class_name + ".j").!!
  ("java " + class_name + "/" + class_name).!
}


//examples
//println(compile("test", p9))
//compile_run("loops.while")
compile_run("p.while")
//compile_run("test.while")