Composite Steppers

[Eric Dean Tribble <tribble>]

Composite Steppers might be an elegant way of using several Steppers
in a loop.  Your insistence that a composite Stepper have a sensible
value works fine (some kind of Tuple).  I imagine the typical use will
just get values directly from the sub-Steppers rather than pulling
apart a composite value from the Composite Stepper.  Thus:

tableSt = someTable ->stepper();
setSt = someSet ->stepper();
countSt = CountStepper(someTable ->lowerBound());

while (tableSt ->hasValue() && setSt ->hasValue()) {
    resultVector ->store(countSt ->value(), 
                      munge(setSt ->value(), tableSt ->value));
    tableSt ->step();
    setSt ->step();
    countSt ->step();
}

I realize that I've ignored some necessary casts, but ignore that.
With CompositeSteppers:

tableSt = someTable ->stepper();
setSt = someSet ->stepper();
countSt = CountStepper(someTable ->lowerBound());
stepper = MultiStepper(tableSt, setSt, countSt);

while (stepper ->hasValue()) {
    resultVector ->store(countSt ->value(), 
                      munge(setSt ->value(), tableSt ->value));
    stepper ->step();
}

It's certainly more readable.  Not enough more useful in this example
to bother building it yet.  We can build it if we run into harder
problems.

comments?
dean