sablevm-developer Mailing List for SableVM (Page 64)

SourceForge Headquarters 225 Broadway Suite 1600 San Diego, CA 92101 +1 (858) 422-6466

> In fact, can you write for me a simple example that requires
> continuation?
> 
Here goes:  

I took this example from 
http://www.nightmare.com/schintro-v14/schintro_127.html
which I need to read through -- it seems to have lots of useful
information.
-------------------------------------------
(define some-flag #t)

(define (my-abortable-proc escape-proc)
(display "in my-abortable-proc")
(if some-flag
      (escape-proc "ABORTED"))
(display "still in my-abortable-proc")
  "NOT ABORTED")

(define (my-resumable-proc)
  (do-something)
  (display (call-with-current-continuation my-abortable-proc))
  (do-some-more))

(define (do-something)
  (display "Doing something."))

(define (do-some-more)
  (display "Doing some more."))

(my-resumable-proc)
-------------------------------------------------

The result of this is:

Doing something.
in my-abortable-proc
still in my-abortable-proc
ABORTED
Doing some more.

The "ABORTED" shows that the call-with-current-continuation
was used to jump back to its calling point.

A neat Scheme-on-java implementation (SILK)
http://www.cs.brandeis.edu/silk/silkweb/doc/resources/HOWTO.html#class
allows you to compile Scheme to Java.  Running this test.scm
through that yields this:

------------------------------------------------------------------
// no package name;
  /**
    * this file is automatically generated by the silk->javac compiler
Compiler.scm. 
    * Modify at your own risk!
    */
  import silk.*;
  import java.lang.reflect.*;
  import java.util.*;

  public class test extends silk.Procedure implements silk.Function,
Runnable {  
      public int whichcode=0;  // corresponds to a numbering of the toplevel
procedures of the program
      public int whichtype=0;  // 0 = user defined procedure, 1 = java
literal
      public static final int USER_DEF=0, JAVA_LIT=1;
      public Pair frame;
      public test() { super();}
      public test(int t, int n, Pair f) {
          whichtype = t;
          whichcode = n;
          frame = f;
      }

      private Boolean addImport(String s) {
         silk.Import.addImport(s);
         return Boolean.TRUE;
      }

      public void run() {
        this.invoke(null);
      } 

      public Object apply(Object[] args) {
        return invoke((Pair)args[0]);
      }

      public Object apply(Pair args) {
        return invoke(args);
      }

      public Object invoke(Pair args)
      {
        return LCO.eval(invoke1(args));
      }

    static Object tmp;

    public static void load() { 
       new test().init();
    }

    public static void load(String shellArgs[]) {
       silk.Symbol.intern("shellArgs").setGlobalValue(shellArgs);
       load();
    }

    public static void main(String shellArgs[]) {
       Symbol main = silk.Symbol.intern("main");
       load(shellArgs);
       if (main.isDefined())
          ((silk.Procedure) main.getGlobalValue()).apply(new
Pair(shellArgs,Pair.EMPTY));
     }

      public Object invoke1(Pair args) {
      if (whichtype == USER_DEF) {
       switch (whichcode) {
          case 0: return(_L0(args)); 
          case 1: return(_L1(args)); 
          case 2: return(_L2(args)); 
          case 3: return(_L3(args)); 

         default: System.exit(0); break;
       }}
      else {
       switch (whichcode) {

         default: System.exit(0); break;
       }}

      return null;
      }

   public void init() {
     Pair Args = null;
     Symbol.intern("this").setGlobalValue(this);
     Class _p = Primitive.class; // this loads the primitives
Symbol.intern("some-flag").setGlobalValue(_C0);

Symbol.intern("my-abortable-proc").setGlobalValue(new test(USER_DEF, 0, new
Pair( Args, this.frame)));

Symbol.intern("my-resumable-proc").setGlobalValue(new test(USER_DEF, 1, new
Pair( Args, this.frame)));

Symbol.intern("do-something").setGlobalValue(new test(USER_DEF, 2, new Pair(
Args, this.frame)));

Symbol.intern("do-some-more").setGlobalValue(new test(USER_DEF, 3, new Pair(
Args, this.frame)));

((silk.Procedure)
((Symbol)my_45_resumable_45_proc).getGlobalValue()).apply(Pair.EMPTY);

   }

 // definitions of global variables 
public static Object some_45_flag = Symbol.intern("some-flag");

public static Object my_45_abortable_45_proc =
Symbol.intern("my-abortable-proc");

public static Object my_45_resumable_45_proc =
Symbol.intern("my-resumable-proc");

 // definitions of Scheme variables defined externally
   static Object display= Symbol.intern("display");

   static Object do_45_something= Symbol.intern("do-something");

   static Object call_45_with_45_current_45_continuation=
Symbol.intern("call-with-current-continuation");

   static Object do_45_some_45_more= Symbol.intern("do-some-more");

 // definitions of quoted terms 
   static Object _C0=Boolean.FALSE;

   static Object _C1="in my-abortable-proc";

   static Object _C2="ABORTED";

   static Object _C3=Boolean.TRUE;

   static Object _C4="still in my-abortable-proc";

   static Object _C5="NOT ABORTED";

   static Object _C6="Doing something.";

   static Object _C7="Doing some more.";

 // definitions of embedded lambdas 
 Object _L0(Pair Args){
   Object tmp; 
 tmp = ((silk.Procedure) ((Symbol)display).getGlobalValue()).apply(new
Pair(_C1,
    Pair.EMPTY));

tmp = 
  (Boolean.FALSE.equals(((Symbol)some_45_flag).getGlobalValue())
  ?
  _C3
  :
  ((silk.Procedure) (( Pair) Args).getEltNover2(1)).apply(new Pair(_C2,
    Pair.EMPTY))
  );

tmp = ((silk.Procedure) ((Symbol)display).getGlobalValue()).apply(new
Pair(_C4,
    Pair.EMPTY));

tmp = _C5;

   return tmp; 
}

 Object _L1(Pair Args){
   Object tmp; 
 tmp = ((silk.Procedure)
((Symbol)do_45_something).getGlobalValue()).apply(Pair.EMPTY);

tmp = ((silk.Procedure) ((Symbol)display).getGlobalValue()).apply(new
Pair(((silk.Procedure)
((Symbol)call_45_with_45_current_45_continuation).getGlobalValue()).apply(ne
w Pair(((Symbol)my_45_abortable_45_proc).getGlobalValue(),
    Pair.EMPTY)),
    Pair.EMPTY));

tmp = new LCO(((Symbol)do_45_some_45_more).getGlobalValue(),Pair.EMPTY);

   return tmp; 
}

 Object _L2(Pair Args){
   Object tmp; 
 tmp = new LCO(((Symbol)display).getGlobalValue(),new Pair(_C6,
    Pair.EMPTY));

   return tmp; 
}

 Object _L3(Pair Args){
   Object tmp; 
 tmp = new LCO(((Symbol)display).getGlobalValue(),new Pair(_C7,
    Pair.EMPTY));

   return tmp; 
}

-------------------------------

This class obviously relies on the Silk interpreter code.  I
tried creating a stand-alone version (in a *.class file) under
Kawa, but couldn't get it to work right under Windows (damn
pathnames!).

Thanks,

-Brent 

2000	Jan	Feb	Mar	Apr	May	Jun	Jul (27)	Aug (22)	Sep (1)	Oct	Nov (1)	Dec (30)
2001	Jan (2)	Feb	Mar	Apr	May	Jun	Jul	Aug (2)	Sep (32)	Oct	Nov	Dec
2002	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug (69)	Sep (10)	Oct (31)	Nov (15)	Dec (58)
2003	Jan (33)	Feb (81)	Mar (85)	Apr (24)	May (15)	Jun (14)	Jul (6)	Aug (9)	Sep (101)	Oct (59)	Nov (142)	Dec (34)
2004	Jan (107)	Feb (164)	Mar (181)	Apr (96)	May (81)	Jun (71)	Jul (1)	Aug	Sep	Oct	Nov	Dec

sablevm-developer Mailing List for SableVM (Page 64)

sablevm-developer — SableVM developer mailing list