org.abora.white.spaces.cross
Class MergeStepper

java.lang.Object
  |
  +--org.abora.white.xpp.basic.Heaper
        |
        +--org.abora.white.collection.steppers.Stepper
              |
              +--org.abora.white.spaces.cross.MergeStepper

public class MergeStepper

extends Stepper

A Stepper for doing a merge-sort like ordered interleaving of two other steppers. It is assumed that the other two steppers are constructed so that their values are also produced in order according to the same OrderSpec. A tree of these operates much like a heap as found in heapsort.

Field Summary

protected Stepper	myA
protected Stepper	myB
protected OrderSpec	myOrder
protected Position	myValue

Fields inherited from class org.abora.white.collection.steppers.Stepper

TheEmptyStepper

Constructor Summary

MergeStepper(Rcvr receiver)

MergeStepper(Stepper a, Stepper b, OrderSpec order, Position value)

Method Summary

Stepper	copy() Return a new stepper which steps independently of me, but whose current value is the same as mine, and which must produce a future history of values which satisfies the same obligation that my contract obligates me to produce now.
Heaper	fetch() If I am exhausted (i.e., if (!! this->hasValue())), then return NULL.
boolean	hasValue() Iff I have a current value (i.e.
static MergeStepper	make(Stepper a, Stepper b, OrderSpec order)
void	sendSelfTo(Xmtr xmtr)
void	step() Essential.

Methods inherited from class org.abora.white.collection.steppers.Stepper

actualHashForEqual, atEnd, emptyStepper, get, info, isEqual, itemStepper, stepMany, stepMany, theOne

Methods inherited from class org.abora.white.xpp.basic.Heaper

destroy, destruct, equals, hashForEqual, printContentsOn, printOn, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

myA

protected Stepper myA

myB

protected Stepper myB

myOrder

protected OrderSpec myOrder

myValue

protected Position myValue

Constructor Detail

MergeStepper

public MergeStepper(Stepper a,
                    Stepper b,
                    OrderSpec order,
                    Position value)

MergeStepper

public MergeStepper(Rcvr receiver)

Method Detail

copy

public Stepper copy()

Description copied from class: Stepper

Return a new stepper which steps independently of me, but whose current value is the same as mine, and which must produce a future history of values which satisfies the same obligation that my contract obligates me to produce now. Typically, this will mean that he must produce the same future history that I'm going to produce. However, let's say that I am enumerating the elements of a partial order in some full order which is consistent with the partial order. If a copy of me is made after I'm part way through, then me and my copy may produce any future history compatable both with the partial order and the elements I've already produced by the time of the copy. Of course, a subclass or a Stepper creating message (like IntegerRegion::stepper()) may specify the more stringent requirement (that a copy must produce the same sequence). To prevent aliasing, Steppers should typically be passed by copy. See class comment.

Specified by:

copy in class Stepper

fetch

public Heaper fetch()

Description copied from class: Stepper

If I am exhausted (i.e., if (!! this->hasValue())), then return NULL. Else return current element. I return wimpily since most items returned are held by collections. If I create a new object, I should cache it.

Specified by:

fetch in class Stepper

hasValue

public boolean hasValue()

Description copied from class: Stepper

Iff I have a current value (i.e. this message returns true), then I am not exhasted. 'fetch' and 'get' will both return this value, and I can be 'step'ped to my next state. As I am stepped, eventually I may become exhausted (the reverse of all the above), which is a permanent condition. Note that not all steppers have to be exhaustable. A Stepper which enumerates all primes is perfectly reasonable. Assuming otherwise will create infinite loops. See class comment.

Specified by:

hasValue in class Stepper

step

public void step()

Description copied from class: Stepper

Essential. If I am currently exhausted (see Stepper::hasValue()), then it is an error to step me. The result of doing so isn't currently specified (we probably should specify it to BLAST, but I know that the implementation doesn't currently live up to that spec). If I am not exhausted, then this advances me to my next state. If my current value (see Stepper::get()) was my final value, then I am now exhausted, otherwise my new current value is the next value.

Specified by:

step in class Stepper

sendSelfTo

public void sendSelfTo(Xmtr xmtr)

Overrides:

sendSelfTo in class Heaper

make

public static MergeStepper make(Stepper a,
                                Stepper b,
                                OrderSpec order)