java_cup
Class production

java.lang.Object
  java_cup.production

Direct Known Subclasses:

action_production

public class production

extends java.lang.Object

This class represents a production in the grammar. It contains a LHS non terminal, and an array of RHS symbols. As various transformations are done on the RHS of the production, it may shrink. As a result a separate length is always maintained to indicate how much of the RHS array is still valid.

I addition to construction and manipulation operations, productions provide methods for factoring out actions (see remove_embedded_actions()), for computing the nullability of the production (i.e., can it derive the empty string, see check_nullable()), and operations for computing its first set (i.e., the set of terminals that could appear at the beginning of some string derived from the production, see check_first_set()).

See Also:

production_part, symbol_part, action_part

Field Summary

protected action_part	_action An action_part containing code for the action to be performed when we reduce with this production.
protected static java.util.Hashtable	_all Table of all productions.
protected terminal_set	_first_set First set of the production.
protected int	_index Index number of the production.
protected symbol_part	_lhs The left hand side non-terminal.
protected boolean	_nullable Nullability of the production (can it derive the empty string).
protected boolean	_nullable_known Is the nullability of the production known or unknown?
protected int	_num_reductions Count of number of reductions using this production.
protected production_part[]	_rhs A collection of parts for the right hand side.
protected int	_rhs_assoc
protected int	_rhs_length How much of the right hand side array we are presently using.
protected int	_rhs_prec The precedence of the rule
protected static int	next_index Static counter for assigning unique index numbers.

Constructor Summary

production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l)
Constructor with no action string.

production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, int prec_num, int prec_side)

production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, java.lang.String action_str)
Full constructor.

production(non_terminal lhs_sym, production_part[] rhs_parts, int rhs_l, java.lang.String action_str, int prec_num, int prec_side)

Method Summary

action_part	action() An action_part containing code for the action to be performed when we reduce with this production.
static java.util.Enumeration	all() Access to all productions.
terminal_set	check_first_set() Update (and return) the first set based on current NT firsts.
boolean	check_nullable() Check to see if the production (now) appears to be nullable.
protected java.lang.String	declare_labels(production_part[] rhs, int rhs_len, java.lang.String final_action) Declare label names as valid variables within the action string
boolean	equals(java.lang.Object other) Generic equality comparison.
boolean	equals(production other) Equality comparison.
static production	find(int indx) Lookup a production by index.
terminal_set	first_set() First set of the production.
int	hashCode() Produce a hash code.
int	index() Index number of the production.
protected static boolean	is_id_char(char c) Determine if a character can be in a label id.
protected static boolean	is_id_start(char c) Determine if a given character can be a label id starter.
symbol_part	lhs() The left hand side non-terminal.
protected java.lang.String	make_declaration(java.lang.String labelname, java.lang.String stack_type, int offset) Return label declaration code
protected int	merge_adjacent_actions(production_part[] rhs_parts, int len) Helper routine to merge adjacent actions in a set of RHS parts
void	note_reduction_use() Increment the count of reductions with this non-terminal
boolean	nullable_known() Is the nullability of the production known or unknown?
boolean	nullable() Nullability of the production (can it derive the empty string).
int	num_reductions() Count of number of reductions using this production.
static int	number() Total number of productions.
int	precedence_num() Access to the precedence of the rule
int	precedence_side()
protected void	remove_embedded_actions() Remove all embedded actions from a production by factoring them out into individual action production using new non terminals.
int	rhs_length() How much of the right hand side array we are presently using.
production_part	rhs(int indx) Access to the collection of parts for the right hand side.
(package private) boolean	set_nullable(boolean v) set (and return) nullability
void	set_precedence_num(int prec_num) Setting the precedence of a rule
void	set_precedence_side(int prec_side)
protected action_part	strip_trailing_action(production_part[] rhs_parts, int len) Helper routine to strip a trailing action off rhs and return it
java.lang.String	to_simple_string() Convert to a simpler string.
java.lang.String	toString() Convert to a string.

Methods inherited from class java.lang.Object

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

Field Detail

_all

protected static java.util.Hashtable _all

Table of all productions. Elements are stored using their index as the key.

next_index

protected static int next_index

Static counter for assigning unique index numbers.

_lhs

protected symbol_part _lhs

The left hand side non-terminal.

_rhs_prec

protected int _rhs_prec

The precedence of the rule

_rhs_assoc

protected int _rhs_assoc

_rhs

protected production_part[] _rhs

A collection of parts for the right hand side.

_rhs_length

protected int _rhs_length

How much of the right hand side array we are presently using.

_action

protected action_part _action

An action_part containing code for the action to be performed when we reduce with this production.

_index

protected int _index

Index number of the production.

_num_reductions

protected int _num_reductions

Count of number of reductions using this production.

_nullable_known

protected boolean _nullable_known

Is the nullability of the production known or unknown?

_nullable

protected boolean _nullable

Nullability of the production (can it derive the empty string).

_first_set

protected terminal_set _first_set

First set of the production. This is the set of terminals that could appear at the front of some string derived from this production.

Constructor Detail

production

public production(non_terminal lhs_sym,
                  production_part[] rhs_parts,
                  int rhs_l,
                  java.lang.String action_str)
           throws internal_error

Full constructor. This constructor accepts a LHS non terminal, an array of RHS parts (including terminals, non terminals, and actions), and a string for a final reduce action. It does several manipulations in the process of creating a production object. After some validity checking it translates labels that appear in actions into code for accessing objects on the runtime parse stack. It them merges adjacent actions if they appear and moves any trailing action into the final reduce actions string. Next it removes any embedded actions by factoring them out with new action productions. Finally it assigns a unique index to the production.

Factoring out of actions is accomplished by creating new "hidden" non terminals. For example if the production was originally:

    A ::= B {action} C D
  

then it is factored into two productions:

    A ::= B X C D
    X ::= {action}
  

(where X is a unique new non terminal). This has the effect of placing all actions at the end where they can be handled as part of a reduce by the parser.

production

public production(non_terminal lhs_sym,
                  production_part[] rhs_parts,
                  int rhs_l)
           throws internal_error

Constructor with no action string.

production

public production(non_terminal lhs_sym,
                  production_part[] rhs_parts,
                  int rhs_l,
                  java.lang.String action_str,
                  int prec_num,
                  int prec_side)
           throws internal_error

production

public production(non_terminal lhs_sym,
                  production_part[] rhs_parts,
                  int rhs_l,
                  int prec_num,
                  int prec_side)
           throws internal_error

Method Detail

all

public static java.util.Enumeration all()

Access to all productions.

find

public static production find(int indx)

Lookup a production by index.

number

public static int number()

Total number of productions.

lhs

public symbol_part lhs()

The left hand side non-terminal.

precedence_num

public int precedence_num()

Access to the precedence of the rule

precedence_side

public int precedence_side()

set_precedence_num

public void set_precedence_num(int prec_num)

Setting the precedence of a rule

set_precedence_side

public void set_precedence_side(int prec_side)

rhs

public production_part rhs(int indx)
                    throws internal_error

Access to the collection of parts for the right hand side.

Throws:

internal_error

rhs_length

public int rhs_length()

How much of the right hand side array we are presently using.

action

public action_part action()

An action_part containing code for the action to be performed when we reduce with this production.

index

public int index()

Index number of the production.

num_reductions

public int num_reductions()

Count of number of reductions using this production.

note_reduction_use

public void note_reduction_use()

Increment the count of reductions with this non-terminal

nullable_known

public boolean nullable_known()

Is the nullability of the production known or unknown?

nullable

public boolean nullable()

Nullability of the production (can it derive the empty string).

first_set

public terminal_set first_set()

First set of the production. This is the set of terminals that could appear at the front of some string derived from this production.

is_id_start

protected static boolean is_id_start(char c)

Determine if a given character can be a label id starter.

Parameters:

c - the character in question.

is_id_char

protected static boolean is_id_char(char c)

Determine if a character can be in a label id.

Parameters:

c - the character in question.

make_declaration

protected java.lang.String make_declaration(java.lang.String labelname,
                                            java.lang.String stack_type,
                                            int offset)

Return label declaration code

Parameters:

labelname - the label name

stack_type - the stack type of label?

declare_labels

protected java.lang.String declare_labels(production_part[] rhs,
                                          int rhs_len,
                                          java.lang.String final_action)

Declare label names as valid variables within the action string

Parameters:

rhs - array of RHS parts.

rhs_len - how much of rhs to consider valid.

final_action - the final action string of the production.

merge_adjacent_actions

protected int merge_adjacent_actions(production_part[] rhs_parts,
                                     int len)

Helper routine to merge adjacent actions in a set of RHS parts

Parameters:

rhs_parts - array of RHS parts.

len - amount of that array that is valid.

Returns:

remaining valid length.

strip_trailing_action

protected action_part strip_trailing_action(production_part[] rhs_parts,
                                            int len)

Helper routine to strip a trailing action off rhs and return it

Parameters:

rhs_parts - array of RHS parts.

len - how many of those are valid.

Returns:

the removed action part.

remove_embedded_actions

protected void remove_embedded_actions()
                                throws internal_error

Remove all embedded actions from a production by factoring them out into individual action production using new non terminals. if the original production was:

    A ::= B {action1} C {action2} D 
  

then it will be factored into:

    A ::= B NT$1 C NT$2 D
    NT$1 ::= {action1}
    NT$2 ::= {action2}
  

where NT$1 and NT$2 are new system created non terminals.

Throws:

internal_error

check_nullable

public boolean check_nullable()
                       throws internal_error

Check to see if the production (now) appears to be nullable. A production is nullable if its RHS could derive the empty string. This results when the RHS is empty or contains only non terminals which themselves are nullable.

Throws:

internal_error

set_nullable

boolean set_nullable(boolean v)

set (and return) nullability

check_first_set

public terminal_set check_first_set()
                             throws internal_error

Update (and return) the first set based on current NT firsts. This assumes that nullability has already been computed for all non terminals and productions.

Throws:

internal_error

equals

public boolean equals(production other)

Equality comparison.

equals

public boolean equals(java.lang.Object other)

Generic equality comparison.

hashCode

public int hashCode()

Produce a hash code.

toString

public java.lang.String toString()

Convert to a string.

to_simple_string

public java.lang.String to_simple_string()
                                  throws internal_error

Convert to a simpler string.

Throws:

internal_error