Hoge.scala

class Hoge {
  def fib(n: Int, i: Int, a: Int, b: Int) : Int = {
    if (i >= n) b
    else fib(n, i + 1, b, a + b)
  }

  def simple_tailrec(n: Int) : Int = {
    if (n < 0) n else simple_tailrec(n - 1)
  }
}

object Hoge {
  def fib(n: Int, i: Int, a: Int, b: Int) : Int = {
    if (i >= n) b
    else fib(n, i + 1, b, a + b)
  }

  def simple_tailrec(n: Int) : Int = {
    if (n < 0) n else simple_tailrec(n - 1)
  }

  def main(args: Array[String]) = {
    val loop_count = 10000
    println(fib(loop_count, 1, 0, 1))
    println(simple_tailrec(loop_count))

    val hoge = new Hoge
    println(hoge.fib(loop_count, 1, 0, 1))
    println(hoge.simple_tailrec(loop_count))
  }
}


$ komamitsu@carrot ~/lab/scala/tailrec $ scalac Hoge.scala
komamitsu@carrot ~/lab/scala/tailrec $ ls -ltra
total 20
drwxr-xr-x 16 komamitsu komamitsu 4096 2012-05-13 18:25 ..
-rw-rw-r--  1 komamitsu komamitsu  682 2012-05-13 18:28 Hoge.scala
-rw-rw-r--  1 komamitsu komamitsu 1107 2012-05-13 18:29 Hoge$.class
drwxrwxr-x  2 komamitsu komamitsu 4096 2012-05-13 18:29 .
-rw-rw-r--  1 komamitsu komamitsu 1257 2012-05-13 18:29 Hoge.class
komamitsu@carrot ~/lab/scala/tailrec $ scala Hoge
1242044891
-1
java.lang.StackOverflowError
        at Hoge.fib(Hoge.scala:3)
        at Hoge.fib(Hoge.scala:4)
        at Hoge.fib(Hoge.scala:4)
        at Hoge.fib(Hoge.scala:4)
               : 
              snip
               :


komamitsu@carrot ~/lab/scala/tailrec $ javap -c Hoge
Compiled from "Hoge.scala"
public class Hoge extends java.lang.Object implements scala.ScalaObject{
public static final void main(java.lang.String[]);
  Code:
   0:   getstatic       #11; //Field Hoge$.MODULE$:LHoge$;
   3:   aload_0
   4:   invokevirtual   #13; //Method Hoge$.main:([Ljava/lang/String;)V
   7:   return

public int fib(int, int, int, int);
  Code:
   0:   iload_2
   1:   iload_1
   2:   if_icmplt       10
   5:   iload   4
   7:   goto    24
   10:  aload_0
   11:  iload_1
   12:  iload_2
   13:  iconst_1
   14:  iadd
   15:  iload   4
   17:  iload_3
   18:  iload   4
   20:  iadd
   21:  invokevirtual   #20; //Method fib:(IIII)I
   24:  ireturn

public int simple_tailrec(int);
  Code:
   0:   iload_1
   1:   iconst_0
   2:   if_icmpge       9
   5:   iload_1
   6:   goto    16
   9:   aload_0
   10:  iload_1
   11:  iconst_1
   12:  isub
   13:  invokevirtual   #32; //Method simple_tailrec:(I)I
   16:  ireturn

public Hoge();
  Code:
   0:   aload_0
   1:   invokespecial   #38; //Method java/lang/Object."<init>":()V
   4:   return
}

$ komamitsu@carrot ~/lab/scala/tailrec $ javap -c Hoge$
Compiled from "Hoge.scala"
public final class Hoge$ extends java.lang.Object implements scala.ScalaObject{
public static final Hoge$ MODULE$;

public static {};
  Code:
   0:   new     #9; //class Hoge$
   3:   invokespecial   #12; //Method "<init>":()V
   6:   return

public int fib(int, int, int, int);
  Code:
   0:   iload_2
   1:   iload_1
   2:   if_icmplt       8
   5:   iload   4
   7:   ireturn
   8:   iload_2
   9:   iconst_1
   10:  iadd
   11:  iload   4
   13:  iload_3
   14:  iload   4
   16:  iadd
   17:  istore  4
   19:  istore_3
   20:  istore_2
   21:  goto    0

public int simple_tailrec(int);
  Code:
   0:   iload_1
   1:   iconst_0
   2:   if_icmpge       7
   5:   iload_1
   6:   ireturn
   7:   iload_1
   8:   iconst_1
   9:   isub
   10:  istore_1
   11:  goto    0

public void main(java.lang.String[]);  
  Code:
   0:   sipush  10000
   3:   istore_2
   4:   getstatic       #31; //Field scala/Predef$.MODULE$:Lscala/Predef$;
   7:   aload_0
   8:   iload_2
   9:   iconst_1
   10:  iconst_0
   11:  iconst_1
   12:  invokevirtual   #33; //Method fib:(IIII)I
   15:  invokestatic    #39; //Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
   18:  invokevirtual   #43; //Method scala/Predef$.println:(Ljava/lang/Object;)V
   21:  getstatic       #31; //Field scala/Predef$.MODULE$:Lscala/Predef$;
   24:  aload_0
   25:  iload_2
   26:  invokevirtual   #45; //Method simple_tailrec:(I)I
   29:  invokestatic    #39; //Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
   32:  invokevirtual   #43; //Method scala/Predef$.println:(Ljava/lang/Object;)V
   35:  new     #47; //class Hoge
   38:  dup
   39:  invokespecial   #48; //Method Hoge."<init>":()V
   42:  astore_3
   43:  getstatic       #31; //Field scala/Predef$.MODULE$:Lscala/Predef$;
   46:  aload_3
   47:  iload_2
   48:  iconst_1
   49:  iconst_0
   50:  iconst_1
   51:  invokevirtual   #49; //Method Hoge.fib:(IIII)I
   54:  invokestatic    #39; //Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
   57:  invokevirtual   #43; //Method scala/Predef$.println:(Ljava/lang/Object;)V
   60:  getstatic       #31; //Field scala/Predef$.MODULE$:Lscala/Predef$;
   63:  aload_3
   64:  iload_2
   65:  invokevirtual   #50; //Method Hoge.simple_tailrec:(I)I
   68:  invokestatic    #39; //Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
   71:  invokevirtual   #43; //Method scala/Predef$.println:(Ljava/lang/Object;)V
   74:  return