java_cup

Class lalr_item_set

java.lang.Object

java_cup.lalr_item_set

public class lalr_item_set
extends Object

This class represents a set of LALR items. For purposes of building these sets, items are considered unique only if they have unique cores (i.e., ignoring differences in their lookahead sets).

This class provides fairly conventional set oriented operations (union, sub/super-set tests, etc.), as well as an LALR "closure" operation (see compute_closure()).

Version:

last updated: 3/6/96

Author:

Scott Hudson

See Also:

lalr_item, lalr_state

Field Summary

Fields

Modifier and Type	Field and Description
protected Hashtable	_all A hash table to implement the set.
protected Integer	hashcode_cache Cached hashcode for this set.

Constructor Summary

Constructors

Constructor and Description
lalr_item_set() Constructor for an empty set.
lalr_item_set(lalr_item_set other) Constructor for cloning from another set.

Method Summary

Methods

Modifier and Type	Method and Description
void	add(lalr_item_set other) Add a complete set, merging lookaheads where items are already in the set
lalr_item	add(lalr_item itm) Add a singleton item, merging lookahead sets if the item is already part of the set.
Enumeration	all() Access to all elements of the set.
void	compute_closure() Compute the closure of the set using the LALR closure rules.
boolean	contains(lalr_item itm) Does the set contain a particular item?
boolean	equals(lalr_item_set other) Equality comparison.
boolean	equals(Object other) Generic equality comparison.
lalr_item	find(lalr_item itm) Return the item in the set matching a particular item (or null if not found)
lalr_item	get_one() Remove and return one item from the set (done in hash order).
int	hashCode() Return hash code.
boolean	is_subset_of(lalr_item_set other) Is this set an (improper) subset of another?
boolean	is_superset_of(lalr_item_set other) Is this set an (improper) superset of another?
protected void	not_null(Object obj) Helper function for null test.
void	remove(lalr_item_set other) Remove (set subtract) a complete set.
void	remove(lalr_item itm) Remove a single item if it is in the set.
int	size() Size of the set
String	toString() Convert to string.

Methods inherited from class java.lang.Object

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

Field Detail

_all

protected Hashtable _all

A hash table to implement the set. We store the items using themselves as keys.

hashcode_cache

protected Integer hashcode_cache

Cached hashcode for this set.

Constructor Detail

lalr_item_set

public lalr_item_set()

Constructor for an empty set.

lalr_item_set

public lalr_item_set(lalr_item_set other)
              throws internal_error

Constructor for cloning from another set.

Parameters:

other - indicates set we should copy from.

Throws:

internal_error

Method Detail

all

public Enumeration all()

Access to all elements of the set.

size

public int size()

Size of the set

contains

public boolean contains(lalr_item itm)

Does the set contain a particular item?

Parameters:

itm - the item in question.

find

public lalr_item find(lalr_item itm)

Return the item in the set matching a particular item (or null if not found)

Parameters:

itm - the item we are looking for.

is_subset_of

public boolean is_subset_of(lalr_item_set other)
                     throws internal_error

Is this set an (improper) subset of another?

Parameters:

other - the other set in question.

Throws:

internal_error

is_superset_of

public boolean is_superset_of(lalr_item_set other)
                       throws internal_error

Is this set an (improper) superset of another?

Parameters:

other - the other set in question.

Throws:

internal_error

add

public lalr_item add(lalr_item itm)
              throws internal_error

Add a singleton item, merging lookahead sets if the item is already part of the set. returns the element of the set that was added or merged into.

Parameters:

itm - the item being added.

Throws:

internal_error

remove

public void remove(lalr_item itm)
            throws internal_error

Remove a single item if it is in the set.

Parameters:

itm - the item to remove.

Throws:

internal_error

add

public void add(lalr_item_set other)
         throws internal_error

Add a complete set, merging lookaheads where items are already in the set

Parameters:

other - the set to be added.

Throws:

internal_error

remove

public void remove(lalr_item_set other)
            throws internal_error

Remove (set subtract) a complete set.

Parameters:

other - the set to remove.

Throws:

internal_error

get_one

public lalr_item get_one()
                  throws internal_error

Remove and return one item from the set (done in hash order).

Throws:

internal_error

not_null

protected void not_null(Object obj)
                 throws internal_error

Helper function for null test. Throws an interal_error exception if its parameter is null.

Parameters:

obj - the object we are testing.

Throws:

internal_error

compute_closure

public void compute_closure()
                     throws internal_error

Compute the closure of the set using the LALR closure rules. Basically for every item of the form:

    [L ::= a *N alpha, l] 
  

(where N is a a non terminal and alpha is a string of symbols) make sure there are also items of the form:

    [N ::= *beta, first(alpha l)] 
  

corresponding to each production of N. Items with identical cores but differing lookahead sets are merged by creating a new item with the same core and the union of the lookahead sets (the LA in LALR stands for "lookahead merged" and this is where the merger is). This routine assumes that nullability and first sets have been computed for all productions before it is called.

Throws:

internal_error

equals

public boolean equals(lalr_item_set other)

Equality comparison.

equals

public boolean equals(Object other)

Generic equality comparison.

Overrides:

equals in class Object

hashCode

public int hashCode()

Return hash code.

Overrides:

hashCode in class Object

toString

public String toString()

Convert to string.

Overrides:

toString in class Object