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()).

Version:

last updated: 7/3/96

Author:

Frank Flannery

See Also:

production_part, symbol_part, action_part

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.
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.
symbol_part	lhs() The left hand side non-terminal.
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()
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.
void	set_precedence_num(int prec_num) Setting the precedence of a rule
void	set_precedence_side(int prec_side)
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

getClass, notify, notifyAll, wait, wait, wait

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.

Throws:

internal_error

production

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

Constructor with no action string.

Throws:

internal_error

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

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

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.

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

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.

Overrides:

equals in class java.lang.Object

hashCode

public int hashCode()

Produce a hash code.

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.String toString()

Convert to a string.

Overrides:

toString in class java.lang.Object

to_simple_string

public java.lang.String to_simple_string()
                                  throws internal_error

Convert to a simpler string.

Throws:

internal_error