java_cup

Class lr_item_core

java.lang.Object

java_cup.lr_item_core

Direct Known Subclasses:

lalr_item

public class lr_item_core
extends Object

The "core" of an LR item. This includes a production and the position of a marker (the "dot") within the production. Typically item cores are written using a production with an embedded "dot" to indicate their position. For example:

     A ::= B * C d E
  

This represents a point in a parse where the parser is trying to match the given production, and has succeeded in matching everything before the "dot" (and hence is expecting to see the symbols after the dot next). See lalr_item, lalr_item_set, and lalr_start for full details on the meaning and use of items.

Version:

last updated: 11/25/95

Author:

Scott Hudson

See Also:

lalr_item, lalr_item_set, lalr_state

Field Summary

Fields

Modifier and Type	Field and Description
protected int	_core_hash_cache Cache of the hash code.
protected int	_dot_pos The position of the "dot" -- this indicates the part of the production that the marker is before, so 0 indicates a dot at the beginning of the RHS.
protected symbol	_symbol_after_dot Cache of symbol after the dot.
protected production	_the_production The production for the item.

Constructor Summary

Constructors

Constructor and Description
lr_item_core(production prod) Constructor for dot at start of right hand side.
lr_item_core(production prod, int pos) Full constructor.

Method Summary

Methods

Modifier and Type	Method and Description
boolean	core_equals(lr_item_core other) Equality comparison for the core only.
int	core_hashCode() Hash code for the core (separated so we keep non overridden version).
boolean	dot_at_end() Is the dot at the end of the production?
non_terminal	dot_before_nt() Determine if we have a dot before a non terminal, and if so which one (return null or the non terminal).
int	dot_pos() The position of the "dot" -- this indicates the part of the production that the marker is before, so 0 indicates a dot at the beginning of the RHS.
boolean	equals(lr_item_core other) Equality comparison.
boolean	equals(Object other) Generic equality comparison.
int	hashCode() Hash code for the item.
protected int	obj_hash() Return the hash code that object would have provided for us so we have a (nearly) unique id for debugging.
lr_item_core	shift_core() Produce a new lr_item_core that results from shifting the dot one position to the right.
symbol	symbol_after_dot() Return the symbol after the dot.
production	the_production() The production for the item.
String	to_simple_string() Convert to a string (separated out from toString() so we can call it from subclass that overrides toString()).
String	toString() Convert to a string

Methods inherited from class java.lang.Object

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

Field Detail

_the_production

protected production _the_production

The production for the item.

_dot_pos

protected int _dot_pos

The position of the "dot" -- this indicates the part of the production that the marker is before, so 0 indicates a dot at the beginning of the RHS.

_core_hash_cache

protected int _core_hash_cache

Cache of the hash code.

_symbol_after_dot

protected symbol _symbol_after_dot

Cache of symbol after the dot.

Constructor Detail

lr_item_core

public lr_item_core(production prod,
            int pos)
             throws internal_error

Full constructor.

Parameters:

prod - production this item uses.

pos - position of the "dot" within the item.

Throws:

internal_error

lr_item_core

public lr_item_core(production prod)
             throws internal_error

Constructor for dot at start of right hand side.

Parameters:

prod - production this item uses.

Throws:

internal_error

Method Detail

the_production

public production the_production()

The production for the item.

dot_pos

public int dot_pos()

The position of the "dot" -- this indicates the part of the production that the marker is before, so 0 indicates a dot at the beginning of the RHS.

dot_at_end

public boolean dot_at_end()

Is the dot at the end of the production?

symbol_after_dot

public symbol symbol_after_dot()

Return the symbol after the dot. If there is no symbol after the dot we return null.

dot_before_nt

public non_terminal dot_before_nt()

Determine if we have a dot before a non terminal, and if so which one (return null or the non terminal).

shift_core

public lr_item_core shift_core()
                        throws internal_error

Produce a new lr_item_core that results from shifting the dot one position to the right.

Throws:

internal_error

core_equals

public boolean core_equals(lr_item_core other)

Equality comparison for the core only. This is separate out because we need separate access in a super class.

equals

public boolean equals(lr_item_core other)

Equality comparison.

equals

public boolean equals(Object other)

Generic equality comparison.

Overrides:

equals in class Object

core_hashCode

public int core_hashCode()

Hash code for the core (separated so we keep non overridden version).

hashCode

public int hashCode()

Hash code for the item.

Overrides:

hashCode in class Object

obj_hash

protected int obj_hash()

Return the hash code that object would have provided for us so we have a (nearly) unique id for debugging.

to_simple_string

public String to_simple_string()
                        throws internal_error

Convert to a string (separated out from toString() so we can call it from subclass that overrides toString()).

Throws:

internal_error

toString

public String toString()

Convert to a string

Overrides:

toString in class Object