1 import scala.language.implicitConversions    

     2 import scala.language.reflectiveCalls 

     3 import scala.util._

     4 import scala.annotation.tailrec

     5 import scala.sys.process._

     6 

     7 abstract class Rexp 

     8 case object NULL extends Rexp

     9 case object EMPTY extends Rexp

    10 case class CHAR(c: Char) extends Rexp

    11 case class ALT(r1: Rexp, r2: Rexp) extends Rexp 

    12 case class RANGE(cs: List[Char]) extends Rexp 

    13 case class SEQ(r1: Rexp, r2: Rexp) extends Rexp 

    14 case class PLUS(r: Rexp) extends Rexp 

    15 case class STAR(r: Rexp) extends Rexp 

    16 case class NTIMES(r: Rexp, n: Int) extends Rexp 

    17 case class NUPTOM(r: Rexp, n: Int, m: Int) extends Rexp

    18 

    19 object RANGE {

    20   def apply(s: String) : RANGE = RANGE(s.toList)

    21 }

    22 def NMTIMES(r: Rexp, n: Int, m: Int) = {

    23   if(m < n) throw new IllegalArgumentException("the number m cannot be smaller than n.")

    24   else NUPTOM(r, n, m - n)

    25 }

    26 

    27 case class NOT(r: Rexp) extends Rexp 

    28 case class OPT(r: Rexp) extends Rexp 

    29 

    30 // some convenience for typing in regular expressions

    31 def charlist2rexp(s : List[Char]) : Rexp = s match {

    32   case Nil => EMPTY

    33   case c::Nil => CHAR(c)

    34   case c::s => SEQ(CHAR(c), charlist2rexp(s))

    35 }

    36 implicit def string2rexp(s : String) : Rexp = charlist2rexp(s.toList)

    37 

    38 implicit def RexpOps (r: Rexp) = new {

    39   def | (s: Rexp) = ALT(r, s)

    40   def % = STAR(r)

    41   def ~ (s: Rexp) = SEQ(r, s)

    42 }

    43 

    44 implicit def stringOps (s: String) = new {

    45   def | (r: Rexp) = ALT(s, r)

    46   def | (r: String) = ALT(s, r)

    47   def % = STAR(s)

    48   def ~ (r: Rexp) = SEQ(s, r)

    49   def ~ (r: String) = SEQ(s, r)

    50 }

    51 

    52 

    53 // nullable function: tests whether the regular 

    54 // expression can recognise the empty string

    55 def nullable (r: Rexp) : Boolean = r match {

    56   case NULL => false

    57   case EMPTY => true

    58   case CHAR(_) => false

    59   case ALT(r1, r2) => nullable(r1) || nullable(r2)

    60   case SEQ(r1, r2) => nullable(r1) && nullable(r2)

    61   case STAR(_) => true

    62   case PLUS(r) => nullable(r)

    63   case NTIMES(r, i) => if (i == 0) true else nullable(r)

    64   case NUPTOM(r, i, j) => if (i == 0) true else nullable(r)

    65   case RANGE(_) => false

    66   case NOT(r) => !(nullable(r))

    67   case OPT(_) => true

    68 }

    69 

    70 // derivative of a regular expression w.r.t. a character

    71 def der (c: Char, r: Rexp) : Rexp = r match {

    72   case NULL => NULL

    73   case EMPTY => NULL

    74   case CHAR(d) => if (c == d) EMPTY else NULL

    75   case ALT(r1, r2) => ALT(der(c, r1), der(c, r2))

    76   case SEQ(r1, r2) => 

    77     if (nullable(r1)) ALT(SEQ(der(c, r1), r2), der(c, r2))

    78     else SEQ(der(c, r1), r2)

    79   case STAR(r) => SEQ(der(c, r), STAR(r))

    80   case PLUS(r) => SEQ(der(c, r), STAR(r))

    81   case NTIMES(r, i) => 

    82     if (i == 0) NULL else der(c, SEQ(r, NTIMES(r, i - 1)))

    83   case NUPTOM(r, i, j) =>

    84     if (i == 0 && j == 0) NULL else 

    85     if (i == 0) ALT(der(c, NTIMES(r, j)), der(c, NUPTOM(r, 0, j - 1)))

    86     else der(c, SEQ(r, NUPTOM(r, i - 1, j)))

    87   case RANGE(cs) => if (cs contains c) EMPTY else NULL

    88   case NOT(r) => NOT(der (c, r))

    89   case OPT(r) => der(c, r)

    90 }

    91 

    92 def zeroable (r: Rexp) : Boolean = r match {

    93   case NULL => true

    94   case EMPTY => false

    95   case CHAR(_) => false

    96   case ALT(r1, r2) => zeroable(r1) && zeroable(r2)

    97   case SEQ(r1, r2) => zeroable(r1) || zeroable(r2)

    98   case STAR(_) => false

    99   case PLUS(r) => zeroable(r)

   100   case NTIMES(r, i) => if (i == 0) false else zeroable(r)

   101   case NUPTOM(r, i, j) => if (i == 0) false else zeroable(r)

   102   case RANGE(_) => false

   103   case NOT(r) => !(zeroable(r))     // bug: incorrect definition for NOT

   104   case OPT(_) => false

   105 }

   106 

   107 // derivative w.r.t. a string (iterates der)

   108 def ders (s: List[Char], r: Rexp) : Rexp = s match {

   109   case Nil => r

   110   case c::s => ders(s, der(c, r))

   111 }

   112 

   113 

   114 // regular expressions for the While language

   115 val SYM = RANGE("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz_")

   116 val DIGIT = RANGE("0123456789")

   117 val ID = SYM ~ (SYM | DIGIT).% 

   118 val NUM = PLUS(DIGIT)

   119 val KEYWORD : Rexp = "skip" | "while" | "do" | "if" | "then" | "else" | "read" | "write" | "true" | "false"

   120 val SEMI: Rexp = ";"

   121 val OP: Rexp = ":=" | "==" | "-" | "+" | "*" | "!=" | "<" | ">" | "%" | "/"

   122 val WHITESPACE = PLUS(" " | "\n" | "\t")

   123 val RPAREN: Rexp = ")"

   124 val LPAREN: Rexp = "("

   125 val BEGIN: Rexp = "{"

   126 val END: Rexp = "}"

   127 val ALL = SYM | DIGIT | " " | ":" | ";" | "\"" | "="

   128 val ALL2 = ALL | "\n"

   129 val COMMENT2 = ("/*" ~ NOT(ALL.% ~ "*/" ~ ALL.%) ~ "*/")

   130 val COMMENT = ("/*" ~ ALL2.% ~ "*/") | ("//" ~ ALL.% ~ "\n")

   131 val STRING = "\"" ~ ALL.% ~ "\""

   132 

   133 

   134 // token for While languag

   135 abstract class Token

   136 case object T_WHITESPACE extends Token

   137 case object T_SEMI extends Token

   138 case object T_LPAREN extends Token

   139 case object T_RPAREN extends Token

   140 case object T_BEGIN extends Token

   141 case object T_END extends Token

   142 case object T_COMMENT extends Token

   143 case class T_ID(s: String) extends Token

   144 case class T_OP(s: String) extends Token

   145 case class T_NUM(s: String) extends Token

   146 case class T_KWD(s: String) extends Token

   147 case class T_STRING(s: String) extends Token

   148 case class T_ERR(s: String) extends Token // special error token

   149 

   150 

   151 type TokenFun = String => Token

   152 type LexRules = List[(Rexp, TokenFun)]

   153 val While_lexing_rules: LexRules = 

   154   List((KEYWORD, (s) => T_KWD(s)),

   155        (ID, (s) => T_ID(s)),

   156        (COMMENT, (s) => T_COMMENT),

   157        (OP, (s) => T_OP(s)),

   158        (NUM, (s) => T_NUM(s)),

   159        (SEMI, (s) => T_SEMI),

   160        (LPAREN, (s) => T_LPAREN),

   161        (RPAREN, (s) => T_RPAREN),

   162        (BEGIN, (s) => T_BEGIN),

   163        (END, (s) => T_END),

   164        (STRING, (s) => T_STRING(s.drop(1).dropRight(1))),

   165        (WHITESPACE, (s) => T_WHITESPACE))

   166 

   167 

   168 // calculates derivatives until all of them are zeroable

   169 @tailrec

   170 def munch(s: List[Char], 

   171           pos: Int, 

   172           rs: LexRules, 

   173           last: Option[(Int, TokenFun)]): Option[(Int, TokenFun)] = {

   174   rs match {

   175   case Nil => last

   176   case rs if (s.length <= pos) => last

   177   case rs => {

   178     val ders = rs.map({case (r, tf) => (der(s(pos), r), tf)})

   179     val rs_nzero = ders.filterNot({case (r, _) => zeroable(r)})

   180     val rs_nulls = ders.filter({case (r, _) => nullable(r)})

   181     val new_last = if (rs_nulls != Nil) Some((pos, rs_nulls.head._2)) else last

   182     munch(s, 1 + pos, rs_nzero, new_last)

   183   }

   184 }}

   185 

   186 // iterates the munching function and returns a Token list

   187 def tokenize(s: String, rs: LexRules) : List[Token] = munch(s.toList, 0, rs, None) match {

   188   case None if (s == "") => Nil

   189   case None => List(T_ERR(s"Lexing error: $s"))

   190   case Some((n, tf)) => {

   191     val (head, tail) = s.splitAt(n + 1)

   192     tf(head)::tokenize(tail, rs)

   193   }

   194 }

   195 

   196 def tokenizer(s:String) : List[Token] = 

   197   tokenize(s, While_lexing_rules).filter {

   198     case T_ERR(s) => { println(s); sys.exit(-1) }

   199     case T_WHITESPACE => false

   200     case T_COMMENT => false

   201     case _ => true

   202   } 

   203 

   204 def fromFile(name: String) : String = 

   205   io.Source.fromFile(name).mkString

   206 

   207 // tokenizer tests

   208 //println(tokenizer(fromFile("loops.while")).mkString("\n"))

   209 //println(tokenizer(fromFile("fib.while")).mkString("\n"))

   210 //println(tokenizer(fromFile("collatz.while")).mkString("\n"))

   211 

   212 

   213 

   214 

   215 

   216 // Parser - Abstract syntax trees

   217 abstract class Stmt

   218 abstract class AExp

   219 abstract class BExp 

   220 type Block = List[Stmt]

   221 case object Skip extends Stmt

   222 case class If(a: BExp, bl1: Block, bl2: Block) extends Stmt

   223 case class While(b: BExp, bl: Block) extends Stmt

   224 case class Assign(s: String, a: AExp) extends Stmt

   225 case class Read(s: String) extends Stmt

   226 case class Write(s: String) extends Stmt

   227 case class WriteS(s: String) extends Stmt

   228 

   229 case class Var(s: String) extends AExp

   230 case class Num(i: Int) extends AExp

   231 case class Aop(o: String, a1: AExp, a2: AExp) extends AExp

   232 

   233 case object True extends BExp

   234 case object False extends BExp

   235 case class Bop(o: String, a1: AExp, a2: AExp) extends BExp

   236 

   237 // Parser combinators

   238 abstract class Parser[I <% Seq[_], T] {

   239   def parse(ts: I): Set[(T, I)]

   240 

   241   def parse_all(ts: I) : Set[T] =

   242     for ((head, tail) <- parse(ts); if (tail.isEmpty)) yield head

   243 

   244   def parse_single(ts: I) : T = parse_all(ts).toList match {

   245     case List(t) => t

   246     case _ => { println ("Parse Error") ; sys.exit(-1) }

   247   }

   248 }

   249 

   250 class SeqParser[I <% Seq[_], T, S](p: => Parser[I, T], q: => Parser[I, S]) extends Parser[I, (T, S)] {

   251   def parse(sb: I) = 

   252     for ((head1, tail1) <- p.parse(sb); 

   253          (head2, tail2) <- q.parse(tail1)) yield ((head1, head2), tail2)

   254 }

   255 

   256 class AltParser[I <% Seq[_], T](p: => Parser[I, T], q: => Parser[I, T]) extends Parser[I, T] {

   257   def parse(sb: I) = p.parse(sb) ++ q.parse(sb)   

   258 }

   259 

   260 class FunParser[I <% Seq[_], T, S](p: => Parser[I, T], f: T => S) extends Parser[I, S] {

   261   def parse(sb: I) = 

   262     for ((head, tail) <- p.parse(sb)) yield (f(head), tail)

   263 }

   264 

   265 

   266 case class TokParser(tok: Token) extends Parser[List[Token], Token] {

   267   def parse(ts: List[Token]) = ts match {

   268     case t::ts if (t == tok) => Set((t, ts)) 

   269     case _ => Set ()

   270   }

   271 }

   272 implicit def token2tparser(t: Token) = TokParser(t)

   273 

   274 case object NumParser extends Parser[List[Token], Int] {

   275   def parse(ts: List[Token]) = ts match {

   276     case T_NUM(s)::ts => Set((s.toInt, ts)) 

   277     case _ => Set ()

   278   }

   279 }

   280 

   281 case object IdParser extends Parser[List[Token], String] {

   282   def parse(ts: List[Token]) = ts match {

   283     case T_ID(s)::ts => Set((s, ts)) 

   284     case _ => Set ()

   285   }

   286 }

   287 

   288 case object StringParser extends Parser[List[Token], String] {

   289   def parse(ts: List[Token]) = ts match {

   290     case T_STRING(s)::ts => Set((s, ts)) 

   291     case _ => Set ()

   292   }

   293 }

   294 

   295 implicit def ParserOps[I<% Seq[_], T](p: Parser[I, T]) = new {

   296   def || (q : => Parser[I, T]) = new AltParser[I, T](p, q)

   297   def ==>[S] (f: => T => S) = new FunParser[I, T, S](p, f)

   298   def ~[S] (q : => Parser[I, S]) = new SeqParser[I, T, S](p, q)

   299 }

   300 implicit def TokOps(t: Token) = new {

   301   def || (q : => Parser[List[Token], Token]) = new AltParser[List[Token], Token](t, q)

   302   def ==>[S] (f: => Token => S) = new FunParser[List[Token], Token, S](t, f)

   303   def ~[S](q : => Parser[List[Token], S]) = new SeqParser[List[Token], Token, S](t, q)

   304 }

   305 

   306 // arithmetic expressions

   307 lazy val AExp: Parser[List[Token], AExp] = 

   308   (T ~ T_OP("+") ~ AExp) ==> { case ((x, y), z) => Aop("+", x, z): AExp } ||

   309   (T ~ T_OP("-") ~ AExp) ==> { case ((x, y), z) => Aop("-", x, z): AExp } || T  

   310 lazy val T: Parser[List[Token], AExp] = 

   311   (F ~ T_OP("*") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || 

   312   (F ~ T_OP("/") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || 

   313   (F ~ T_OP("%") ~ T) ==> { case ((x, y), z) => Aop("*", x, z): AExp } || F

   314 lazy val F: Parser[List[Token], AExp] = 

   315   (T_LPAREN ~ AExp ~ T_RPAREN) ==> { case ((x, y), z) => y: AExp }|| 

   316   IdParser ==> { case x => Var(x): AExp } || 

   317   NumParser ==> { case x => Num(x): AExp }

   318 

   319 // boolean expressions

   320 lazy val BExp: Parser[List[Token], BExp] = 

   321   (AExp ~ T_OP("==") ~ AExp) ==> { case ((x, y), z) => Bop("==", x, z): BExp } || 

   322   (AExp ~ T_OP("!=") ~ AExp) ==> { case ((x, y), z) => Bop("!=", x, z): BExp } || 

   323   (AExp ~ T_OP("<") ~ AExp) ==> { case ((x, y), z) => Bop("<", x, z): BExp } || 

   324   (AExp ~ T_OP(">") ~ AExp) ==> { case ((x, y), z) => Bop("<", z, x): BExp } || 

   325   (T_KWD("true") ==> ((_) => True)) || 

   326   (T_KWD("false") ==> ((_) => False: BExp))

   327 

   328 lazy val Stmt: Parser[List[Token], Stmt] =

   329   (T_KWD("skip") ==> ((_) => Skip: Stmt)) ||

   330   (IdParser ~ T_OP(":=") ~ AExp) ==> { case ((x, y), z) => Assign(x, z): Stmt } ||

   331   (T_KWD("if") ~ BExp ~ T_KWD("then") ~ Block ~ T_KWD("else") ~ Block) ==>

   332     { case (((((x,y),z),u),v),w) => If(y, u, w): Stmt } ||

   333   (T_KWD("while") ~ BExp ~ T_KWD("do") ~ Block) ==> { case (((x, y), z), w) => While(y, w) } ||

   334   (T_KWD("read") ~ IdParser) ==> { case (x, y) => Read(y) } ||

   335   (T_KWD("write") ~ IdParser) ==> { case (x, y) => Write(y) } ||

   336   (T_KWD("write") ~ StringParser) ==> { case (x, y) => WriteS(y) }

   337 

   338 lazy val Stmts: Parser[List[Token], Block] =

   339   (Stmt ~ T_SEMI ~ Stmts) ==> { case ((x, y), z) => x :: z : Block } ||

   340   (Stmt ==> ((s) => List(s) : Block))

   341 

   342 lazy val Block: Parser[List[Token], Block] =

   343   (T_BEGIN ~ Stmts ~ T_END) ==> { case ((x, y), z) => y : Block } || 

   344   (Stmt ==> ((s) => List(s)))

   345 

   346 

   347 

   348 // parser examples

   349 val p1 = "x := 5"

   350 val p1_toks = tokenizer(p1) 

   351 val p1_ast = Block.parse_all(p1_toks)

   352 //println(p1_toks)

   353 //println(p1_ast)

   354 

   355 val p2 = "{ x := 5; y := 8}"

   356 val p2_toks = tokenizer(p2) 

   357 val p2_ast = Block.parse_all(p2_toks)

   358 //println(p2_ast)

   359 

   360 val p3 = "5 == 6"

   361 val p3_toks = tokenizer(p3) 

   362 val p3_ast = BExp.parse_all(p3_toks)

   363 //println(p3_ast)

   364 

   365 val p4 = "true"

   366 val p4_toks = tokenizer(p4) 

   367 val p4_ast = BExp.parse_all(p4_toks)

   368 //println(p4_ast)

   369 

   370 val p5 = "if true then skip else skip"

   371 val p5_toks = tokenizer(p5) 

   372 val p5_ast = Stmt.parse_all(p5_toks)

   373 //println(p5_ast)

   374 

   375 val p6 = "if true then x := 5 else x := 10"

   376 val p6_toks = tokenizer(p6) 

   377 val p6_ast = Stmt.parse_all(p6_toks)

   378 //println(p6_ast)

   379 

   380 val p7 = "if false then x := 5 else x := 10"

   381 val p7_toks = tokenizer(p7) 

   382 val p7_ast = Stmt.parse_all(p7_toks)

   383 //println(p7_ast)

   384 

   385 val p8 = "write x; write \"foo\"; read x "

   386 val p8_toks = tokenizer(p8) 

   387 val p8_ast = Stmts.parse_all(p8_toks)

   388 //println(p8_ast)

   389 

   390 // multiplication

   391 val p9 = """  x := 5;

   392               y := 4;

   393               r := 0;

   394               while y > 0 do {

   395                  r := r + x;

   396                  y := y - 1

   397               } 

   398          """

   399 val p9_toks = tokenizer(p9) 

   400 val p9_ast = Stmts.parse_all(p9_toks)

   401 //println(p9_ast)

   402 

   403 // fibonacci numbers

   404 val p10 = """

   405  write "Fib: ";

   406  read n;

   407  minus1 := 0;

   408  minus2 := 1;

   409  temp := 0;

   410  while n > 0 do  {

   411    temp := minus2;

   412    minus2 := minus1 + minus2;

   413    minus1 := temp;

   414    n := n - 1

   415  };

   416  write "Result:";

   417  write minus2

   418 """

   419 val p10_toks = tokenizer(p10) 

   420 val p10_ast = Stmts.parse_all(p10_toks)

   421 //println(p10_ast)

   422 

   423 

   424 // an interpreter for the WHILE language

   425 type Env = Map[String, Int]

   426 

   427 def eval_aexp(a: AExp, env : Env) : Int = a match {

   428   case Num(i) => i

   429   case Var(s) => env(s)

   430   case Aop("+", a1, a2) => eval_aexp(a1, env) + eval_aexp(a2, env)

   431   case Aop("-", a1, a2) => eval_aexp(a1, env) - eval_aexp(a2, env)

   432   case Aop("*", a1, a2) => eval_aexp(a1, env) * eval_aexp(a2, env)

   433 }

   434 

   435 def eval_bexp(b: BExp, env: Env) : Boolean = b match {

   436   case True => true

   437   case False => false

   438   case Bop("==", a1, a2) => eval_aexp(a1, env) == eval_aexp(a2, env)

   439   case Bop("!=", a1, a2) => !(eval_aexp(a1, env) == eval_aexp(a2, env))

   440   case Bop("<", a1, a2) => eval_aexp(a1, env) < eval_aexp(a2, env)

   441 }

   442 

   443 def eval_stmt(s: Stmt, env: Env) : Env = s match {

   444   case Skip => env

   445   case Assign(x, a) => env + (x -> eval_aexp(a, env))

   446   case If(b, bl1, bl2) => if (eval_bexp(b, env)) eval_bl(bl1, env) else eval_bl(bl2, env) 

   447   case While(b, bl) => 

   448     if (eval_bexp(b, env)) eval_stmt(While(b, bl), eval_bl(bl, env))

   449     else env

   450   case WriteS(s: String) => { println(s); env }

   451   case Write(s: String) => { println(env(s)); env }

   452   case Read(s: String) => tokenizer(Console.readLine) match {

   453     case List(T_NUM(n)) => env + (s -> n.toInt)

   454     case _ => { println("not a number"); eval_stmt(Read(s: String), env) }

   455   }

   456 }

   457 

   458 def eval_bl(bl: Block, env: Env) : Env = bl match {

   459   case Nil => env

   460   case s::bl => eval_bl(bl, eval_stmt(s, env))

   461 }

   462 

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

   464 

   465 def interpret(s: String): Unit =

   466   eval(Stmts.parse_all(tokenizer(s)).head)

   467 

   468 // interpreter example

   469 //interpret(p10)

   470 

   471 

   472 

   473 // compiler - built-in functions 

   474 // copied from http://www.ceng.metu.edu.tr/courses/ceng444/link/jvm-cpm.html

   475 //

   476 

   477 val beginning = """

   478 .class public XXX.XXX

   479 .super java/lang/Object

   480 

   481 .method public <init>()V

   482         aload_0

   483         invokenonvirtual java/lang/Object/<init>()V

   484         return

   485 .end method

   486 

   487 .method public static write(I)V 

   488         .limit locals 5 

   489         .limit stack 5 

   490         iload 0 

   491         getstatic java/lang/System/out Ljava/io/PrintStream; 

   492         swap 

   493         invokevirtual java/io/PrintStream/println(I)V 

   494         return 

   495 .end method

   496 

   497 .method public static writes(Ljava/lang/String;)V

   498        .limit stack 2

   499        .limit locals 2

   500        getstatic java/lang/System/out Ljava/io/PrintStream;

   501        aload 0

   502        invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

   503        return

   504 .end method

   505 

   506 .method public static read()I 

   507       .limit locals 10 

   508       .limit stack 10

   509 

   510       ldc 0 

   511       istore 1  ; this will hold our final integer 

   512 Label1: 

   513       getstatic java/lang/System/in Ljava/io/InputStream; 

   514       invokevirtual java/io/InputStream/read()I 

   515       istore 2 

   516       iload 2 

   517       ldc 10   ; the newline delimiter 

   518       isub 

   519       ifeq Label2 

   520       iload 2 

   521       ldc 32   ; the space delimiter 

   522       isub 

   523       ifeq Label2

   524 

   525       iload 2 

   526       ldc 48   ; we have our digit in ASCII, have to subtract it from 48 

   527       isub 

   528       ldc 10 

   529       iload 1 

   530       imul 

   531       iadd 

   532       istore 1 

   533       goto Label1 

   534 Label2: 

   535       ;when we come here we have our integer computed in Local Variable 1 

   536       iload 1 

   537       ireturn 

   538 .end method

   539 

   540 .method public static main([Ljava/lang/String;)V

   541       .limit locals 200

   542       .limit stack 200

   543 

   544 """

   545 

   546 val ending = """

   547 

   548       return

   549 

   550 .end method

   551 """

   552 

   553 // for generating new labels

   554 var counter = -1

   555 

   556 def Fresh(x: String) = {

   557   counter += 1

   558   x ++ "_" ++ counter.toString()

   559 }

   560 

   561 type Mem = Map[String, String]

   562 type Instrs = List[String]

   563 

   564 def compile_aexp(a: AExp, env : Mem) : Instrs = a match {

   565   case Num(i) => List("ldc " + i.toString + "\n")

   566   case Var(s) => List("iload " + env(s) + "\n")

   567   case Aop("+", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("iadd\n")

   568   case Aop("-", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("isub\n")

   569   case Aop("*", a1, a2) => compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("imul\n")

   570 }

   571 

   572 def compile_bexp(b: BExp, env : Mem, jmp: String) : Instrs = b match {

   573   case True => Nil

   574   case False => List("goto " + jmp + "\n")

   575   case Bop("=", a1, a2) => 

   576     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpne " + jmp + "\n")

   577   case Bop("!=", a1, a2) => 

   578     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpeq " + jmp + "\n")

   579   case Bop("<", a1, a2) => 

   580     compile_aexp(a1, env) ++ compile_aexp(a2, env) ++ List("if_icmpge " + jmp + "\n")

   581 }

   582 

   583 

   584 def compile_stmt(s: Stmt, env: Mem) : (Instrs, Mem) = s match {

   585   case Skip => (Nil, env)

   586   case Assign(x, a) => {

   587     val index = if (env.isDefinedAt(x)) env(x) else env.keys.size.toString

   588     (compile_aexp(a, env) ++ 

   589      List("istore " + index + "\n"), env + (x -> index))

   590   } 

   591   case If(b, bl1, bl2) => {

   592     val if_else = Fresh("If_else")

   593     val if_end = Fresh("If_end")

   594     val (instrs1, env1) = compile_bl(bl1, env)

   595     val (instrs2, env2) = compile_bl(bl2, env1)

   596     (compile_bexp(b, env, if_else) ++

   597      instrs1 ++

   598      List("goto " + if_end + "\n") ++

   599      List("\n" + if_else + ":\n\n") ++

   600      instrs2 ++

   601      List("\n" + if_end + ":\n\n"), env2)

   602   }

   603   case While(b, bl) => {

   604     val loop_begin = Fresh("Loop_begin")

   605     val loop_end = Fresh("Loop_end")

   606     val (instrs1, env1) = compile_bl(bl, env)

   607     (List("\n" + loop_begin + ":\n\n") ++

   608      compile_bexp(b, env, loop_end) ++

   609      instrs1 ++

   610      List("goto " + loop_begin + "\n") ++

   611      List("\n" + loop_end + ":\n\n"), env1)

   612   }

   613   case Write(x) => 

   614     (List("iload " + env(x) + "\n" + 

   615           "invokestatic XXX/XXX/write(I)V\n"), env)

   616   case WriteS(x) => 

   617     (List("ldc \"" + x + "\"\n" + 

   618           "invokestatic XXX/XXX/writes(Ljava/lang/String;)V\n"), env)

   619   case Read(x) => {

   620     val index = if (env.isDefinedAt(x)) env(x) else env.keys.size.toString

   621     (List("invokestatic XXX/XXX/read()I\n" + 

   622           "istore " + index + "\n"), env + (x -> index))

   623   } 

   624 }

   625 

   626 

   627 def compile_bl(bl: Block, env: Mem) : (Instrs, Mem) = bl match {

   628   case Nil => (Nil, env)

   629   case s::bl => {

   630     val (instrs1, env1) = compile_stmt(s, env)

   631     val (instrs2, env2) = compile_bl(bl, env1)

   632     (instrs1 ++ instrs2, env2)

   633   }

   634 }

   635 

   636 def compile(class_name: String, input: String) : String = {

   637   val tks = tokenizer(input)

   638   val ast = Stmts.parse_single(tks)

   639   val instructions = compile_bl(ast, Map.empty)._1

   640   (beginning ++ instructions.mkString ++ ending).replaceAllLiterally("XXX", class_name)

   641 }

   642 

   643 

   644 def compile_file(file_name: String) = {

   645   val class_name = file_name.split('.')(0)

   646   val output = compile(class_name, fromFile(file_name))

   647   val fw = new java.io.FileWriter(class_name + ".j") 

   648   fw.write(output) 

   649   fw.close()

   650 }

   651 

   652 def time_needed[T](i: Int, code: => T) = {

   653   val start = System.nanoTime()

   654   for (j <- 1 to i) code

   655   val end = System.nanoTime()

   656   (end - start)/(i * 1.0e9)

   657 }

   658 

   659 

   660 def compile_run(file_name: String) : Unit = {

   661   val class_name = file_name.split('.')(0)

   662   compile_file(file_name)

   663   val test = ("java -jar jvm/jasmin-2.4/jasmin.jar " + class_name + ".j").!!

   664   //("java " + class_name + "/" + class_name).!

   665 }

   666 

   667 

   668 //examples

   669 //println(compile("test", p9))

   670 //compile_run("loops.while")

   671 compile_run("fib.while")

   672 //compile_run("test.while")