jpl

Class List

java.lang.Object

jpl.Term

jpl.Compound

jpl.List

public class List
extends Compound

A List is a Compound, but with just two args, a head and a tail. Use this class to create representations of Prolog lists:

 List el = 
     new List(
         new Atom( "a" ),
         new List(
             new Atom( "b" ),
             new List(
                 new Atom( "c" ),
                 List.NIL ) ) );
 

This constructor (somewhat longwindedly) creates a List that corresponds to the Prolog list [a,b,c], or more accurately, [a|[b|[c|[]]]].

Note the following:

The special Term (static instance) List.NIL is of type List.Nil, which extends Atom, not List. So the terminus of a List is an Atom, not a List. This is consistent with the Prolog representation.

The List class provides 11 (convenience) list() methods for creating Listing without the long-windedness of the above constructor

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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	List.Nil The Nil class is used to terminate a List.

Field Summary

Fields

Modifier and Type	Field and Description
static Atom	NIL

Fields inherited from class jpl.Compound

args_, atom_

Constructor Summary

Constructors

Constructor and Description
List(Term head, Term tail) This constructor is used to create a List.

Method Summary

Modifier and Type	Method and Description
String	debugString()
Enumeration	elements() This method return an enumeration of a nil-terminated List.
Term	head()
int	length() This method returns the length of a List.
static Atom	list()
static List	list(Term t0)
static List	list(Term t0, Term t1)
static List	list(Term t0, Term t1, Term t2)
static List	list(Term t0, Term t1, Term t2, Term t3)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4, Term t5)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4, Term t5, Term t6)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4, Term t5, Term t6, Term t7)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4, Term t5, Term t6, Term t7, Term t8)
static List	list(Term t0, Term t1, Term t2, Term t3, Term t4, Term t5, Term t6, Term t7, Term t8, Term t9)
protected boolean	nil_terminated()
Term	tail()
boolean	tailIsNil()
String	toString() Converts a Compound to its String form, atom( arg_1, ..., arg_n )
Term[]	toTermArray() This method returns an array containg the Terms in the List.

Methods inherited from class jpl.Compound

args, atom, computeSubstitution, equals, from_term_t, ith, put

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, wait, wait, wait

Field Detail

NIL

public static final Atom NIL

Constructor Detail

List

public List(Term head,
            Term tail)

This constructor is used to create a List. Typically, the "last" item in a List is the List.NIL instance, or at least an instance of the List.Nil type, though as in Prolog, this need not necessarily be the case. Lists are therefore usually built "inside-out", or from the tail to the head, though you can also use any of the 11 factory list() methods for creating Lists if the elements of the List are known beforehand.

Parameters:

head - the List's head

tail - the List's tail

Method Detail

head

public final Term head()

Returns:

the head of the List

tail

public final Term tail()

Returns:

the tail of the List

tailIsNil

public final boolean tailIsNil()

Returns:

true if tail of this List is an instance of Nil; false o/w

toString

public String toString()

Description copied from class: Compound

Converts a Compound to its String form, atom( arg_1, ..., arg_n )

Overrides:

toString in class Compound

Returns:

the String representation of this List. In this case, we use the simplest Prolog represenation [H|T]. For example, the list [a,b,c] is represented [a|[b|[c|[]]]].

debugString

public String debugString()

Overrides:

debugString in class Compound

list

public static Atom list()

Returns:

a jpl.List representing [] (i.e., the Atom List.NIL.

list

public static List list(Term t0)

Returns:

a jpl.List representing [t0]

list

public static List list(Term t0,
                        Term t1)

Returns:

a jpl.List representing [t0,t1]

list

public static List list(Term t0,
                        Term t1,
                        Term t2)

Returns:

a jpl.List representing [t0,t1,t2,t3]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3)

Returns:

a jpl.List representing [t0,t1,t2,t3]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4,
                        Term t5)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4,t5]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4,
                        Term t5,
                        Term t6)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4,t5,t6]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4,
                        Term t5,
                        Term t6,
                        Term t7)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4,t5,t6,t7]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4,
                        Term t5,
                        Term t6,
                        Term t7,
                        Term t8)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4,t5,t6,t7,t8]

list

public static List list(Term t0,
                        Term t1,
                        Term t2,
                        Term t3,
                        Term t4,
                        Term t5,
                        Term t6,
                        Term t7,
                        Term t8,
                        Term t9)

Returns:

a jpl.List representing [t0,t1,t2,t3,t4,t5,t6,t7,t8,t9]

length

public int length()

This method returns the length of a List. It assumes that the List is List.Nil terminated.

Returns:

the length of the List

toTermArray

public Term[] toTermArray()

This method returns an array containg the Terms in the List. It assumes that the List is List.Nil terminated.

Returns:

a Term array containing the Terms in the List

nil_terminated

protected boolean nil_terminated()

Returns:

elements

public Enumeration elements()

This method return an enumeration of a nil-terminated List. Calling this method on a List whose last cdr is not an instance of List.Nil will cause a JPLException to be thrown.

Returns:

A java.util.Enumeration of all the elements of the List