package java_cup;
import java.util.Enumeration;
import java.util.Hashtable;
/**
* This class represents a non-terminal symbol in the grammar. Each non terminal
* has a textual name, an index, and a string which indicates the type of object
* it will be implemented with at runtime (i.e. the class of object that will be
* pushed on the parse stack to represent it).
*
* @version last updated: 11/25/95
* @author Scott Hudson
*/
@SuppressWarnings (
{ "all", "unchecked" } )
public class non_terminal extends symbol
{
/*-----------------------------------------------------------*/
/*--- Constructor(s) ----------------------------------------*/
/*-----------------------------------------------------------*/
/**
* Full constructor.
*
* @param nm the name of the non terminal.
* @param tp the type string for the non terminal.
*/
public non_terminal ( String nm, String tp )
{
/* super class does most of the work */
super ( nm, tp );
/* add to set of all non terminals and check for duplicates */
Object conflict = _all.put ( nm, this );
if ( conflict != null )
// can't throw an exception here because these are used in static
// initializers, so we crash instead
// was:
// throw new internal_error("Duplicate non-terminal ("+nm+") created");
( new internal_error ( "Duplicate non-terminal (" + nm + ") created" ) )
.crash ();
/* assign a unique index */
_index = next_index++ ;
/* add to by_index set */
_all_by_index.put ( new Integer ( _index ), this );
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/**
* Constructor with default type.
*
* @param nm the name of the non terminal.
*/
public non_terminal ( String nm )
{
this ( nm, null );
}
/*-----------------------------------------------------------*/
/*--- (Access to) Static (Class) Variables ------------------*/
/*-----------------------------------------------------------*/
/**
* Table of all non-terminals -- elements are stored using name strings as the
* key
*/
protected static Hashtable _all = new Hashtable ();
// Hm Added clear to clear all static fields
public static void clear ()
{
_all.clear ();
_all_by_index.clear ();
next_index = 0;
next_nt = 0;
}
/** Access to all non-terminals. */
public static Enumeration all ()
{
return _all.elements ();
}
/** lookup a non terminal by name string */
public static non_terminal find ( String with_name )
{
if ( with_name == null )
return null;
else
return ( non_terminal ) _all.get ( with_name );
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Table of all non terminals indexed by their index number. */
protected static Hashtable _all_by_index = new Hashtable ();
/** Lookup a non terminal by index. */
public static non_terminal find ( int indx )
{
Integer the_indx = new Integer ( indx );
return ( non_terminal ) _all_by_index.get ( the_indx );
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Total number of non-terminals. */
public static int number ()
{
return _all.size ();
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Static counter to assign unique indexes. */
protected static int next_index = 0;
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Static counter for creating unique non-terminal names */
static protected int next_nt = 0;
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** special non-terminal for start symbol */
public static final non_terminal START_nt = new non_terminal ( "$START" );
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** flag non-terminals created to embed action productions */
public boolean is_embedded_action = false; /* added 24-Mar-1998, CSA */
/*-----------------------------------------------------------*/
/*--- Static Methods ----------------------------------------*/
/*-----------------------------------------------------------*/
/**
* Method for creating a new uniquely named hidden non-terminal using the
* given string as a base for the name (or "NT$" if null is passed).
*
* @param prefix base name to construct unique name from.
*/
static non_terminal create_new ( String prefix ) throws internal_error
{
return create_new ( prefix, null ); // TUM 20060608 embedded actions patch
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** static routine for creating a new uniquely named hidden non-terminal */
static non_terminal create_new () throws internal_error
{
return create_new ( null );
}
/**
* TUM 20060608 bugfix for embedded action codes
*/
static non_terminal create_new ( String prefix, String type )
throws internal_error
{
if ( prefix == null )
prefix = "NT$";
return new non_terminal ( prefix + next_nt++ , type );
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Compute nullability of all non-terminals. */
public static void compute_nullability () throws internal_error
{
boolean change = true;
non_terminal nt;
Enumeration e;
production prod;
/* repeat this process until there is no change */
while ( change )
{
/* look for a new change */
change = false;
/* consider each non-terminal */
for ( e = all () ; e.hasMoreElements () ; )
{
nt = ( non_terminal ) e.nextElement ();
/* only look at things that aren't already marked nullable */
if ( !nt.nullable () )
{
if ( nt.looks_nullable () )
{
nt._nullable = true;
change = true;
}
}
}
}
/* do one last pass over the productions to finalize all of them */
for ( e = production.all () ; e.hasMoreElements () ; )
{
prod = ( production ) e.nextElement ();
prod.set_nullable ( prod.check_nullable () );
}
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/**
* Compute first sets for all non-terminals. This assumes nullability has
* already computed.
*/
public static void compute_first_sets () throws internal_error
{
boolean change = true;
Enumeration n;
Enumeration p;
non_terminal nt;
production prod;
terminal_set prod_first;
/* repeat this process until we have no change */
while ( change )
{
/* look for a new change */
change = false;
/* consider each non-terminal */
for ( n = all () ; n.hasMoreElements () ; )
{
nt = ( non_terminal ) n.nextElement ();
/* consider every production of that non terminal */
for ( p = nt.productions () ; p.hasMoreElements () ; )
{
prod = ( production ) p.nextElement ();
/* get the updated first of that production */
prod_first = prod.check_first_set ();
/* if this going to add anything, add it */
if ( !prod_first.is_subset_of ( nt._first_set ) )
{
change = true;
nt._first_set.add ( prod_first );
}
}
}
}
}
/*-----------------------------------------------------------*/
/*--- (Access to) Instance Variables ------------------------*/
/*-----------------------------------------------------------*/
/** Table of all productions with this non terminal on the LHS. */
protected Hashtable _productions = new Hashtable ( 11 );
/** Access to productions with this non terminal on the LHS. */
public Enumeration productions ()
{
return _productions.elements ();
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Total number of productions with this non terminal on the LHS. */
public int num_productions ()
{
return _productions.size ();
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Add a production to our set of productions. */
public void add_production ( production prod ) throws internal_error
{
/* catch improper productions */
if ( prod == null || prod.lhs () == null
|| prod.lhs ().the_symbol () != this )
throw new internal_error (
"Attempt to add invalid production to non terminal production table" );
/* add it to the table, keyed with itself */
_productions.put ( prod, prod );
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Nullability of this non terminal. */
protected boolean _nullable;
/** Nullability of this non terminal. */
public boolean nullable ()
{
return _nullable;
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** First set for this non-terminal. */
protected terminal_set _first_set = new terminal_set ();
/** First set for this non-terminal. */
public terminal_set first_set ()
{
return _first_set;
}
/*-----------------------------------------------------------*/
/*--- General Methods ---------------------------------------*/
/*-----------------------------------------------------------*/
/** Indicate that this symbol is a non-terminal. */
public boolean is_non_term ()
{
return true;
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** Test to see if this non terminal currently looks nullable. */
protected boolean looks_nullable () throws internal_error
{
/* look and see if any of the productions now look nullable */
for ( Enumeration e = productions () ; e.hasMoreElements () ; )
/* if the production can go to empty, we are nullable */
if ( ( ( production ) e.nextElement () ).check_nullable () )
return true;
/* none of the productions can go to empty, so we are not nullable */
return false;
}
/* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . */
/** convert to string */
public String toString ()
{
return super.toString () + "[" + index () + "]" + ( nullable () ? "*" : "" );
}
/*-----------------------------------------------------------*/
}