jpl

Class Variable

java.lang.Object

jpl.Term

jpl.Variable

public class Variable
extends Term

This class provides a Java represenation of a Prolog Variable.

In a sense, the Variable is the only interesting class in the jpl High-Level Interface, though it is also the most difficult to reason about.

Copyright (C) 1998 Fred Dushin

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library Public License for more details.

Version:

$Revision: 1.1.1.1 $

Author:

Fred Dushin

Field Summary

Fields

Modifier and Type	Field and Description
protected term_t	term_ A reference to the term_t (a reference to a term in to Prolog Engine) to which this term is bound.

Constructor Summary

Constructors

Constructor and Description
Variable()

Method Summary

Modifier and Type	Method and Description
protected void	computeSubstitution(Hashtable bindings, Hashtable vars) If this Variable instance is not already in the Hashtable, put the result of converting the term_t to which this variable has been unified to a Term in the Hashtable, keyed on this Variable instance.
String	debugString()
boolean	equals(Object obj) A Variable is equal to another when their corresponding term_ts (internal Prolog represenations) are equal.
protected static Term	from_term_t(Hashtable vars, term_t term) Converts a term_t to a Variable.
protected void	put(Hashtable var_table, term_t term) To put a Variable, we want to be careful that the variable does not already occur in the Term.

Methods inherited from class jpl.Term

computeSubstitutions, debugString, from_term_t, terms_equals, terms_to_term_ts, toString

Methods inherited from class java.lang.Object

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

Field Detail

term_

protected transient term_t term_

A reference to the term_t (a reference to a term in to Prolog Engine) to which this term is bound. This reference is only used in the course of translating a Term to a term_t.

Constructor Detail

Variable

public Variable()

Method Detail

put

protected final void put(Hashtable var_table,
                         term_t term)

To put a Variable, we want to be careful that the variable does not already occur in the Term. If it does, we have already thrown it as a key in the hastable, so we can look it up and use the term_t indexed by the Variable as the term to put; this way, the term_t in the Prolog Engine refers to the same term_t as any other occurrence of the same variable. On the other hand, if the variable does not (already) occur in the Term, put it in the hashtable and put a new variable into the term.

Specified by:

put in class Term

Parameters:

var_table - A Hashtable containing term_t's that are bound to (have packed in) Prolog variables as elements. The Elements are keyed by jpl.Variable instances. Cf. the put() implementation in the Variable class.

term - A (previously created) term_t which is to be packed with a Prolog term-type appropriate to the Term type (e.g., Atom, Variable, Compound, etc.) on which the method is invoked.)

from_term_t

protected static Term from_term_t(Hashtable vars,
                                  term_t term)

Converts a term_t to a Variable. If the term_t is a variable, we just make a new Variable. We are careful to create a List.Nil object if indeed the atom is "[]". Note that nil is an atom in Prolog and jpl.

Parameters:

term - The term_t to convert

Returns:

A new Variable

computeSubstitution

protected final void computeSubstitution(Hashtable bindings,
                                         Hashtable vars)

If this Variable instance is not already in the Hashtable, put the result of converting the term_t to which this variable has been unified to a Term in the Hashtable, keyed on this Variable instance.

Specified by:

computeSubstitution in class Term

Parameters:

table - table holding Term substitutions, keyed on Variables.

equals

public final boolean equals(Object obj)

A Variable is equal to another when their corresponding term_ts (internal Prolog represenations) are equal.

Overrides:

equals in class Object

Parameters:

obj - The Object to compare.

Returns:

true if the Object is the above condition applies.

debugString

public String debugString()

Specified by:

debugString in class Term