Re: Calling getClass() on a Scheme subclassed object

[Sean Luke <sean at cs dot gmu dot edu>]

After some further reading on the list, I've seen (invoke <Foo>  
'getReflectClass), which returns
	class Foo

That looked lots more promising, until I actually tried using it:

(<sim.engine.SimState>:doLoop (invoke <Foo> 'getReflectClass)  
(<java.lang.String[]> (*:toString "-until") (*:toString 5000))

MASON Version 12.  For further options, try adding ' -help' at end.
Job: 0 Seed: 1148961645567
Starting Foo
Invalid parameter, was: Foo
java.lang.ClassCastException: Foo
        at ca.step(ca.scm:11)
        at sim.engine.Repeat.step(Schedule.java:497)
        at sim.engine.Schedule.step(Schedule.java:219)
        at sim.engine.SimState.doLoop(SimState.java:483)
        at sim.engine.SimState.doLoop(SimState.java:294)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at
sun.reflect.NativeMethodAccessorImpl.invoke 
(NativeMethodAccessorImpl.java:39)
        at
sun.reflect.DelegatingMethodAccessorImpl.invoke 
(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at gnu.expr.PrimProcedure.apply(PrimProcedure.java:238)
        at gnu.mapping.CallContext.runUntilDone(CallContext.java:251)
        at gnu.expr.ModuleExp.evalModule(ModuleExp.java:268)
        at kawa.Shell.run(Shell.java:230)
        at kawa.Shell.run(Shell.java:172)
        at kawa.Shell.run(Shell.java:159)
        at kawa.repl.main(repl.java:846)

The doLoop method constructs a Foo using reflection, and ultimately  
passes the instance to ca.step (ca is another Scheme simple-class).   
In the step method we see:

(define-simple-class <ca> (<sim.engine.Steppable>)
    ((step (state :: <sim.engine.SimState>)) :: <void>
	(let ((tut :: <Foo> (as <Foo> state)) ...

So step is being handed an instance of whatever class was provided in  
(invoke <Foo> 'getReflectClass), and it's now trying to cast that  
instance into a <Foo>.  That *ought* to work but it doesn't.

Sean

On May 29, 2006, at 11:52 PM, Sean Luke wrote:

> I maintain a simulation toolkit (MASON) in Java and have been  
> interested in seeing if I can get some simulation apps written in  
> Scheme rather than in raw Java.  So far I've been successful, and  
> after heavily typing the scheme code, it runs at very close (about  
> 1.5) the speed of my Java code.  Not bad!
>
> Unfortunately I'm stuck with a difficulty.  In the system you  
> typically create a subclass of a Java class (sim.engine.SimState),  
> and then populate that class with various data to form your  
> simulation model.  Let's say your simulation is called  
> sim.app.Foo.  The most straightforward way to run your simulation  
> is to then call the following method:
>
> 	doLoop(sim.app.Foo.class, ...)
>
> In Scheme, I create the subclass using define-simple-class:
>
> 	(define-simple-class <Foo> (<sim.engine.SimState>) ... )
>
> But I am utterly stymied as to how to pass the "Class" for the  
> <Foo> scheme class into the doLoop method.  For example, this works  
> using a preexisting Java simulation:
>
> (<sim.engine.SimState>:doLoop  
> <sim.app.tutorial1and2.Tutorial1>:class (<java.lang.String[]>  
> (*:toString "-help")))
>
> But doing something like this:
>
> (<sim.engine.SimState>:doLoop <Foo>:class (<java.lang.String[]>  
> (*:toString "-help")))
>
> ... fails because <Foo> isn't a class but is a  
> gnu.bytecode.ClassType, and the documentation is pretty scarce  
> about how (or if it's even possible) to extract the class proper  
> out of this beast.  Ideas?
>
> Sean