1 // A Small Compiler for a Simple Functional Language

     2 // (includes a lexer and a parser)

     3 

     4 import scala.language.implicitConversions    

     5 import scala.language.reflectiveCalls 

     6 

     7 abstract class Rexp 

     8 case object ZERO extends Rexp

     9 case object ONE extends Rexp

    10 case class CHAR(c: Char) extends Rexp

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

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

    13 case class STAR(r: Rexp) extends Rexp 

    14 case class RECD(x: String, r: Rexp) extends Rexp

    15   

    16 abstract class Val

    17 case object Empty extends Val

    18 case class Chr(c: Char) extends Val

    19 case class Sequ(v1: Val, v2: Val) extends Val

    20 case class Left(v: Val) extends Val

    21 case class Right(v: Val) extends Val

    22 case class Stars(vs: List[Val]) extends Val

    23 case class Rec(x: String, v: Val) extends Val

    24    

    25 // some convenience for typing in regular expressions

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

    27   case Nil => ONE

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

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

    30 }

    31 implicit def string2rexp(s : String) : Rexp = 

    32   charlist2rexp(s.toList)

    33 

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

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

    36   def % = STAR(r)

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

    38 }

    39 

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

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

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

    43   def % = STAR(s)

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

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

    46   def $ (r: Rexp) = RECD(s, r)

    47 }

    48 

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

    50   case ZERO => false

    51   case ONE => true

    52   case CHAR(_) => false

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

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

    55   case STAR(_) => true

    56   case RECD(_, r1) => nullable(r1)

    57 }

    58 

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

    60   case ZERO => ZERO

    61   case ONE => ZERO

    62   case CHAR(d) => if (c == d) ONE else ZERO

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

    64   case SEQ(r1, r2) => 

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

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

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

    68   case RECD(_, r1) => der(c, r1)

    69 }

    70 

    71 

    72 // extracts a string from value

    73 def flatten(v: Val) : String = v match {

    74   case Empty => ""

    75   case Chr(c) => c.toString

    76   case Left(v) => flatten(v)

    77   case Right(v) => flatten(v)

    78   case Sequ(v1, v2) => flatten(v1) + flatten(v2)

    79   case Stars(vs) => vs.map(flatten).mkString

    80   case Rec(_, v) => flatten(v)

    81 }

    82 

    83 // extracts an environment from a value;

    84 // used for tokenise a string

    85 def env(v: Val) : List[(String, String)] = v match {

    86   case Empty => Nil

    87   case Chr(c) => Nil

    88   case Left(v) => env(v)

    89   case Right(v) => env(v)

    90   case Sequ(v1, v2) => env(v1) ::: env(v2)

    91   case Stars(vs) => vs.flatMap(env)

    92   case Rec(x, v) => (x, flatten(v))::env(v)

    93 }

    94 

    95 // The Injection Part of the lexer

    96 

    97 def mkeps(r: Rexp) : Val = r match {

    98   case ONE => Empty

    99   case ALT(r1, r2) => 

   100     if (nullable(r1)) Left(mkeps(r1)) else Right(mkeps(r2))

   101   case SEQ(r1, r2) => Sequ(mkeps(r1), mkeps(r2))

   102   case STAR(r) => Stars(Nil)

   103   case RECD(x, r) => Rec(x, mkeps(r))

   104 }

   105 

   106 def inj(r: Rexp, c: Char, v: Val) : Val = (r, v) match {

   107   case (STAR(r), Sequ(v1, Stars(vs))) => Stars(inj(r, c, v1)::vs)

   108   case (SEQ(r1, r2), Sequ(v1, v2)) => Sequ(inj(r1, c, v1), v2)

   109   case (SEQ(r1, r2), Left(Sequ(v1, v2))) => Sequ(inj(r1, c, v1), v2)

   110   case (SEQ(r1, r2), Right(v2)) => Sequ(mkeps(r1), inj(r2, c, v2))

   111   case (ALT(r1, r2), Left(v1)) => Left(inj(r1, c, v1))

   112   case (ALT(r1, r2), Right(v2)) => Right(inj(r2, c, v2))

   113   case (CHAR(d), Empty) => Chr(c) 

   114   case (RECD(x, r1), _) => Rec(x, inj(r1, c, v))

   115   case _ => { println ("Injection error") ; sys.exit(-1) } 

   116 }

   117 

   118 // some "rectification" functions for simplification

   119 def F_ID(v: Val): Val = v

   120 def F_RIGHT(f: Val => Val) = (v:Val) => Right(f(v))

   121 def F_LEFT(f: Val => Val) = (v:Val) => Left(f(v))

   122 def F_ALT(f1: Val => Val, f2: Val => Val) = (v:Val) => v match {

   123   case Right(v) => Right(f2(v))

   124   case Left(v) => Left(f1(v))

   125 }

   126 def F_SEQ(f1: Val => Val, f2: Val => Val) = (v:Val) => v match {

   127   case Sequ(v1, v2) => Sequ(f1(v1), f2(v2))

   128 }

   129 def F_SEQ_Empty1(f1: Val => Val, f2: Val => Val) = 

   130   (v:Val) => Sequ(f1(Empty), f2(v))

   131 def F_SEQ_Empty2(f1: Val => Val, f2: Val => Val) = 

   132   (v:Val) => Sequ(f1(v), f2(Empty))

   133 def F_RECD(f: Val => Val) = (v:Val) => v match {

   134   case Rec(x, v) => Rec(x, f(v))

   135 }

   136 def F_ERROR(v: Val): Val = throw new Exception("error")

   137 

   138 def simp(r: Rexp): (Rexp, Val => Val) = r match {

   139   case ALT(r1, r2) => {

   140     val (r1s, f1s) = simp(r1)

   141     val (r2s, f2s) = simp(r2)

   142     (r1s, r2s) match {

   143       case (ZERO, _) => (r2s, F_RIGHT(f2s))

   144       case (_, ZERO) => (r1s, F_LEFT(f1s))

   145       case _ => if (r1s == r2s) (r1s, F_LEFT(f1s))

   146                 else (ALT (r1s, r2s), F_ALT(f1s, f2s)) 

   147     }

   148   }

   149   case SEQ(r1, r2) => {

   150     val (r1s, f1s) = simp(r1)

   151     val (r2s, f2s) = simp(r2)

   152     (r1s, r2s) match {

   153       case (ZERO, _) => (ZERO, F_ERROR)

   154       case (_, ZERO) => (ZERO, F_ERROR)

   155       case (ONE, _) => (r2s, F_SEQ_Empty1(f1s, f2s))

   156       case (_, ONE) => (r1s, F_SEQ_Empty2(f1s, f2s))

   157       case _ => (SEQ(r1s,r2s), F_SEQ(f1s, f2s))

   158     }

   159   }

   160   case RECD(x, r1) => {

   161     val (r1s, f1s) = simp(r1)

   162     (RECD(x, r1s), F_RECD(f1s))

   163   }

   164   case r => (r, F_ID)

   165 }

   166 

   167 // lexing functions including simplification

   168 def lex_simp(r: Rexp, s: List[Char]) : Val = s match {

   169   case Nil => if (nullable(r)) mkeps(r) else { println ("Lexing Error") ; sys.exit(-1) } 

   170   case c::cs => {

   171     val (r_simp, f_simp) = simp(der(c, r))

   172     inj(r, c, f_simp(lex_simp(r_simp, cs)))

   173   }

   174 }

   175 

   176 def lexing_simp(r: Rexp, s: String) = env(lex_simp(r, s.toList))

   177 

   178 

   179 // The Lexing Rules for the Fun Language

   180 

   181 def PLUS(r: Rexp) = r ~ r.%

   182 

   183 val SYM = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | 

   184           "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | 

   185           "w" | "x" | "y" | "z" | "T" | "_"

   186 val DIGIT = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

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

   188 val NUM = PLUS(DIGIT)

   189 val KEYWORD : Rexp = "if" | "then" | "else" | "write" | "def"

   190 val SEMI: Rexp = ";"

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

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

   193 val RPAREN: Rexp = ")"

   194 val LPAREN: Rexp = "("

   195 val COMMA: Rexp = ","

   196 val ALL = SYM | DIGIT | OP | " " | ":" | ";" | "\"" | "=" | "," | "(" | ")"

   197 val ALL2 = ALL | "\n"

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

   199 

   200 

   201 val WHILE_REGS = (("k" $ KEYWORD) | 

   202                   ("i" $ ID) | 

   203                   ("o" $ OP) | 

   204                   ("n" $ NUM) | 

   205                   ("s" $ SEMI) | 

   206                   ("c" $ COMMA) |

   207                   ("pl" $ LPAREN) |

   208                   ("pr" $ RPAREN) |

   209                   ("w" $ (WHITESPACE | COMMENT))).%

   210 

   211 

   212 

   213 // The tokens for the Fun language

   214 

   215 abstract class Token

   216 case object T_SEMI extends Token

   217 case object T_COMMA extends Token

   218 case object T_LPAREN extends Token

   219 case object T_RPAREN extends Token

   220 case class T_ID(s: String) extends Token

   221 case class T_OP(s: String) extends Token

   222 case class T_NUM(n: Int) extends Token

   223 case class T_KWD(s: String) extends Token

   224 

   225 val token : PartialFunction[(String, String), Token] = {

   226   case ("k", s) => T_KWD(s)

   227   case ("i", s) => T_ID(s)

   228   case ("o", s) => T_OP(s)

   229   case ("n", s) => T_NUM(s.toInt)

   230   case ("s", _) => T_SEMI

   231   case ("c", _) => T_COMMA

   232   case ("pl", _) => T_LPAREN

   233   case ("pr", _) => T_RPAREN

   234 }

   235 

   236 

   237 def tokenise(s: String) : List[Token] = 

   238   lexing_simp(WHILE_REGS, s).collect(token)

   239 

   240 

   241 

   242 // Parser combinators

   243 abstract class Parser[I, T](implicit ev: I => Seq[_]) {

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

   245 

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

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

   248 

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

   250     case List(t) => t

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

   252   }

   253 }

   254 

   255 // convenience for matching later on

   256 case class ~[+A, +B](_1: A, _2: B)

   257 

   258 

   259 class SeqParser[I, T, S](p: => Parser[I, T], 

   260                          q: => Parser[I, S])(implicit ev: I => Seq[_]) extends Parser[I, ~[T, S]] {

   261   def parse(sb: I) = 

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

   263          (head2, tail2) <- q.parse(tail1)) yield (new ~(head1, head2), tail2)

   264 }

   265 

   266 class AltParser[I, T](p: => Parser[I, T], 

   267                       q: => Parser[I, T])(implicit ev: I => Seq[_]) extends Parser[I, T] {

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

   269 }

   270 

   271 class FunParser[I, T, S](p: => Parser[I, T], 

   272                          f: T => S)(implicit ev: I => Seq[_]) extends Parser[I, S] {

   273   def parse(sb: I) = 

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

   275 }

   276 

   277 implicit def ParserOps[I, T](p: Parser[I, T])(implicit ev: I => Seq[_]) = new {

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

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

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

   281 }

   282 

   283 def ListParser[I, T, S](p: => Parser[I, T], 

   284                         q: => Parser[I, S])(implicit ev: I => Seq[_]): Parser[I, List[T]] = {

   285   (p ~ q ~ ListParser(p, q)) ==> { case x ~ _ ~ z => x :: z : List[T] } ||

   286   (p ==> ((s) => List(s)))

   287 }

   288 

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

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

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

   292     case _ => Set ()

   293   }

   294 }

   295 

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

   297 

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

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

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

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

   302 }

   303 

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

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

   306     case T_NUM(n)::ts => Set((n, ts)) 

   307     case _ => Set ()

   308   }

   309 }

   310 

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

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

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

   314     case _ => Set ()

   315   }

   316 }

   317 

   318 

   319 

   320 // Abstract syntax trees for Fun

   321 abstract class Exp

   322 abstract class BExp 

   323 abstract class Decl

   324 

   325 case class Def(name: String, args: List[String], body: Exp) extends Decl

   326 case class Main(e: Exp) extends Decl

   327 

   328 case class Call(name: String, args: List[Exp]) extends Exp

   329 case class If(a: BExp, e1: Exp, e2: Exp) extends Exp

   330 case class Write(e: Exp) extends Exp

   331 case class Var(s: String) extends Exp

   332 case class Num(i: Int) extends Exp

   333 case class Aop(o: String, a1: Exp, a2: Exp) extends Exp

   334 case class Sequence(e1: Exp, e2: Exp) extends Exp

   335 case class Bop(o: String, a1: Exp, a2: Exp) extends BExp

   336 

   337 

   338 

   339 // Grammar Rules for Fun

   340 

   341 // arithmetic expressions

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

   343   (T_KWD("if") ~ BExp ~ T_KWD("then") ~ Exp ~ T_KWD("else") ~ Exp) ==>

   344     { case _ ~ y ~ _ ~ u ~ _ ~ w => If(y, u, w): Exp } ||

   345   (M ~ T_SEMI ~ Exp) ==> { case x ~ _ ~ z => Sequence(x, z): Exp } || M

   346 lazy val M: Parser[List[Token], Exp] =

   347   (T_KWD("write") ~ L) ==> { case _ ~ y => Write(y): Exp } || L

   348 lazy val L: Parser[List[Token], Exp] = 

   349   (T ~ T_OP("+") ~ Exp) ==> { case x ~ _ ~ z => Aop("+", x, z): Exp } ||

   350   (T ~ T_OP("-") ~ Exp) ==> { case x ~ _ ~ z => Aop("-", x, z): Exp } || T  

   351 lazy val T: Parser[List[Token], Exp] = 

   352   (F ~ T_OP("*") ~ T) ==> { case x ~ _ ~ z => Aop("*", x, z): Exp } || 

   353   (F ~ T_OP("/") ~ T) ==> { case x ~ _ ~ z => Aop("/", x, z): Exp } || 

   354   (F ~ T_OP("%") ~ T) ==> { case x ~ _ ~ z => Aop("%", x, z): Exp } || F

   355 lazy val F: Parser[List[Token], Exp] = 

   356   (IdParser ~ T_LPAREN ~ ListParser(Exp, T_COMMA) ~ T_RPAREN) ==> 

   357     { case x ~ _ ~ z ~ _ => Call(x, z): Exp } ||

   358   (T_LPAREN ~ Exp ~ T_RPAREN) ==> { case _ ~ y ~ _ => y: Exp } || 

   359   IdParser ==> { case x => Var(x): Exp } || 

   360   NumParser ==> { case x => Num(x): Exp }

   361 

   362 // boolean expressions

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

   364   (Exp ~ T_OP("==") ~ Exp) ==> { case x ~ _ ~ z => Bop("==", x, z): BExp } || 

   365   (Exp ~ T_OP("!=") ~ Exp) ==> { case x ~ _ ~ z => Bop("!=", x, z): BExp } || 

   366   (Exp ~ T_OP("<") ~ Exp) ==> { case x ~ _ ~ z => Bop("<", x, z): BExp } || 

   367   (Exp ~ T_OP(">") ~ Exp) ==> { case x ~ _ ~ z => Bop("<", z, x): BExp } || 

   368   (Exp ~ T_OP("<=") ~ Exp) ==> { case x ~ _ ~ z => Bop("<=", x, z): BExp } || 

   369   (Exp ~ T_OP("=>") ~ Exp) ==> { case x ~ _ ~ z => Bop("<=", z, x): BExp }  

   370 

   371 lazy val Defn: Parser[List[Token], Decl] =

   372    (T_KWD("def") ~ IdParser ~ T_LPAREN ~ ListParser(IdParser, T_COMMA) ~ T_RPAREN ~ T_OP("=") ~ Exp) ==>

   373      { case x ~ y ~ z ~ w ~ u ~ v ~ r => Def(y, w, r): Decl }

   374 

   375 lazy val Prog: Parser[List[Token], List[Decl]] =

   376   (Defn ~ T_SEMI ~ Prog) ==> { case x ~ _ ~ z => x :: z : List[Decl] } ||

   377   (Exp ==> ((s) => List(Main(s)) : List[Decl]))

   378 

   379 

   380 // compiler - built-in functions 

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

   382 //

   383 

   384 val library = """

   385 .class public XXX.XXX

   386 .super java/lang/Object

   387 

   388 .method public static write(I)V 

   389         .limit locals 1 

   390         .limit stack 2 

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

   392         iload 0

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

   394         return 

   395 .end method

   396 

   397 """

   398 

   399 // calculating the maximal needed stack size

   400 def max_stack_exp(e: Exp): Int = e match {

   401   case Call(_, args) => args.map(max_stack_exp).sum

   402   case If(a, e1, e2) => max_stack_bexp(a) + (List(max_stack_exp(e1), max_stack_exp(e2)).max)

   403   case Write(e) => max_stack_exp(e) + 1

   404   case Var(_) => 1

   405   case Num(_) => 1

   406   case Aop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)

   407   case Sequence(e1, e2) => List(max_stack_exp(e1), max_stack_exp(e2)).max

   408 }

   409 def max_stack_bexp(e: BExp): Int = e match {

   410   case Bop(_, a1, a2) => max_stack_exp(a1) + max_stack_exp(a2)

   411 }

   412 

   413 

   414 // for generating new labels

   415 var counter = -1

   416 

   417 def Fresh(x: String) = {

   418   counter += 1

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

   420 }

   421 

   422 // convenient string interpolations 

   423 // for instructions, labels and methods

   424 import scala.language.implicitConversions

   425 import scala.language.reflectiveCalls

   426 

   427 implicit def sring_inters(sc: StringContext) = new {

   428     def i(args: Any*): String = "   " ++ sc.s(args:_*) ++ "\n"

   429     def l(args: Any*): String = sc.s(args:_*) ++ ":\n"

   430     def m(args: Any*): String = sc.s(args:_*) ++ "\n"

   431 }

   432 

   433 

   434 type Env = Map[String, Int]

   435 

   436 

   437 def compile_expT(a: Exp, env : Env, name: String) : String = a match {

   438   case Num(i) => i"ldc $i"

   439   case Var(s) => i"iload ${env(s)}"

   440   case Aop("+", a1, a2) => compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"iadd"

   441   case Aop("-", a1, a2) => compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"isub"

   442   case Aop("*", a1, a2) => compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"imul"

   443   case Aop("/", a1, a2) => compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"idiv"

   444   case Aop("%", a1, a2) => compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"irem"

   445   case If(b, a1, a2) => {

   446     val if_else = Fresh("If_else")

   447     val if_end = Fresh("If_end")

   448     compile_bexpT(b, env, if_else) ++

   449     compile_expT(a1, env, name) ++

   450     i"goto $if_end" ++

   451     l"$if_else" ++

   452     compile_expT(a2, env, name) ++

   453     l"$if_end"

   454   }

   455   case Call(n, args) => if (name == n) { 

   456     val stores = args.zipWithIndex.map { case (x, y) => i"istore $y" } 

   457     args.map(a => compile_expT(a, env, "")).mkString ++

   458     stores.reverse.mkString ++ 

   459     i"goto ${n}_Start" 

   460   } else {

   461     val is = "I" * args.length

   462     args.map(a => compile_expT(a, env, "")).mkString ++

   463     i"invokestatic XXX/XXX/${n}(${is})I"

   464   }

   465   case Sequence(a1, a2) => {

   466     compile_expT(a1, env, "") ++ i"pop" ++ compile_expT(a2, env, name)

   467   }

   468   case Write(a1) => {

   469     compile_expT(a1, env, "") ++

   470     i"dup" ++

   471     i"invokestatic XXX/XXX/write(I)V"

   472   }

   473 }

   474 

   475 def compile_bexpT(b: BExp, env : Env, jmp: String) : String = b match {

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

   477     compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"if_icmpne $jmp"

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

   479     compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"if_icmpeq $jmp"

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

   481     compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"if_icmpge $jmp"

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

   483     compile_expT(a1, env, "") ++ compile_expT(a2, env, "") ++ i"if_icmpgt $jmp"

   484 }

   485 

   486 

   487 def compile_decl(d: Decl) : String = d match {

   488   case Def(name, args, a) => { 

   489     val env = args.zipWithIndex.toMap

   490     val is = "I" * args.length

   491     m".method public static $name($is)I" ++

   492     m".limit locals ${args.length}" ++

   493     m".limit stack ${1 + max_stack_exp(a)}" ++

   494     l"${name}_Start" ++   

   495     compile_expT(a, env, name) ++

   496     i"ireturn" ++ 

   497     m".end method\n"

   498   }

   499   case Main(a) => {

   500     m".method public static main([Ljava/lang/String;)V" ++

   501     m".limit locals 200" ++

   502     m".limit stack 200" ++

   503     compile_expT(a, Map(), "") ++

   504     i"invokestatic XXX/XXX/write(I)V" ++

   505     i"return\n" ++

   506     m".end method\n"

   507   }

   508 }

   509 

   510 // main compiler functions

   511 

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

   513   val start = System.nanoTime()

   514   for (j <- 1 to i) code

   515   val end = System.nanoTime()

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

   517 }

   518 

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

   520   val tks = tokenise(input)

   521   val ast = Prog.parse_single(tks)

   522   val instructions = ast.map(compile_decl).mkString

   523   (library + instructions).replaceAllLiterally("XXX", class_name)

   524 }

   525 

   526 def compile_file(class_name: String) = {

   527   val input = io.Source.fromFile(s"${class_name}.fun").mkString

   528   val output = compile(class_name, input)

   529   scala.tools.nsc.io.File(s"${class_name}.j").writeAll(output)

   530 }

   531 

   532 import scala.sys.process._

   533 

   534 def compile_run(class_name: String) : Unit = {

   535   compile_file(class_name)

   536   (s"java -jar jvm/jasmin-2.4/jasmin.jar ${class_name}.j").!!

   537   println("Time: " + time_needed(2, (s"java ${class_name}/${class_name}").!))

   538 }

   539 

   540 

   541 //examples

   542 compile_run("defs")

   543 compile_run("fact")