jtp.fol
Class Variable

java.lang.Object
  |
  +--jtp.fol.Variable

All Implemented Interfaces:

Comparable, Serializable, Unifyable

public class Variable

extends Object

implements Unifyable, Comparable, Serializable

A Variable can be bound to (substituted with) some other Object.

See Also:

Serialized Form

Nested Class Summary

static class

Variable.NameComparator

Constructor Summary

Variable(String s)
Creates a Variable with name s.

Variable(String name, long serialNumber)

Method Summary

int	compareTo(Object o)
boolean	contains(Variable v) Determines whether or not v is contained within this Variable.
String	debugPrintout()
Object	deReferenceVariables() Returns the Object that this Variable is bound to.
String	getName() Name used primarily for printing purposes.
long	getSerialNumber()
Collection	getVariables(Collection c) Retrieves the variables in this Unifyable and places them into a provided target collection.
void	setValue(Object val) Bind this variable to val.
Object	substitute(Map h)
String	toString()
void	unbind() Set the bound value of this Variable to null.
boolean	unify(Object o, List bindings) Attempts to unify this with o.

Methods inherited from class java.lang.Object

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

Constructor Detail

Variable

public Variable(String s)

Creates a Variable with name s.

Parameters:

s - name of the Variable to be created.

Variable

public Variable(String name,
                long serialNumber)

Method Detail

getName

public String getName()

Name used primarily for printing purposes.

Returns:

the name of this Variable

getSerialNumber

public long getSerialNumber()

setValue

public void setValue(Object val)

Bind this variable to val.

Parameters:

val - an Object that this Variable is to be bound to

Throws:

IllegalStateException - If this Variable is already bound to a different value

Error - If binding to val results in a circular dependency, i.e., val is a Variable that is itself bound to this, possibly nested

unbind

public void unbind()

Set the bound value of this Variable to null. This Variable will no longer be bound.

toString

public String toString()

Overrides:

toString in class Object

debugPrintout

public String debugPrintout()

contains

public boolean contains(Variable v)

Determines whether or not v is contained within this Variable.

Specified by:

contains in interface Unifyable

Parameters:

v - a Variable

Returns:

true if v is == to this or if the bound value of this Variable is a Unifyable that contains v

deReferenceVariables

public Object deReferenceVariables()

Returns the Object that this Variable is bound to. If unbound, return this. If the bound value of this is a Unifyable, call deReferenceVariables() on it to get return value. Otherwise, return getValue().

Specified by:

deReferenceVariables in interface Unifyable

Returns:

Object that this is bound to

See Also:

Variable

unify

public boolean unify(Object o,
                     List bindings)

Attempts to unify this with o. Performs occurs check.

Specified by:

unify in interface Unifyable

Parameters:

o - the object to unify with.

bindings - the variable stack

Returns:

true if successful

substitute

public Object substitute(Map h)

getVariables

public Collection getVariables(Collection c)

Description copied from interface: Unifyable

Retrieves the variables in this Unifyable and places them into a provided target collection.

Specified by:

getVariables in interface Unifyable

Parameters:

c - the collection to which the variables are added. If null, and this Unifyable contains variables, a new collection is created.

Returns:

the target collection. If target is null, and there are no variables, null is returned; if a new collection is created, it has to be modifyable.

compareTo

public int compareTo(Object o)

Specified by:

compareTo in interface Comparable