package com.sun.java_cup.internal;
/** 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: <pre>
* A ::= B * C d E
* </pre>
* 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.
*
* @see com.sun.java_cup.internal.lalr_item
* @see com.sun.java_cup.internal.lalr_item_set
* @see com.sun.java_cup.internal.lalr_state
* @version last updated: 11/25/95
* @author Scott Hudson
*/
public class lr_item_core {
/*-----------------------------------------------------------*/
/*--- Constructor(s) ----------------------------------------*/
/*-----------------------------------------------------------*/
/** Full constructor.
* @param prod production this item uses.
* @param pos position of the "dot" within the item.
*/
public lr_item_core(production prod, int pos) throws internal_error
{
symbol after_dot = null;
production_part part;
if (prod == null)
throw new internal_error(
"Attempt to create an lr_item_core with a null production");
_the_production = prod;
if (pos < 0 || pos > _the_production.rhs_length())
throw new internal_error(
"Attempt to create an lr_item_core with a bad dot position");
_dot_pos = pos;
/* compute and cache hash code now */
_core_hash_cache = 13*_the_production.hashCode() + pos;
/* cache the symbol after the dot */
if (_dot_pos < _the_production.rhs_length())
{
part = _the_production.rhs(_dot_pos);
if (!part.is_action())
_symbol_after_dot = ((symbol_part)part).the_symbol();
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Constructor for dot at start of right hand side.
* @param prod production this item uses.
*/
public lr_item_core(production prod) throws internal_error
{
this(prod,0);
}
/*-----------------------------------------------------------*/
/*--- (Access to) Instance Variables ------------------------*/
/*-----------------------------------------------------------*/
/** The production for the item. */
protected production _the_production;
/** The production for the item. */
public production the_production() {return _the_production;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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 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.
*/
public int dot_pos() {return _dot_pos;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Cache of the hash code. */
protected int _core_hash_cache;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Cache of symbol after the dot. */
protected symbol _symbol_after_dot = null;
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Is the dot at the end of the production? */
public boolean dot_at_end()
{
return _dot_pos >= _the_production.rhs_length();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Return the symbol after the dot. If there is no symbol after the dot
* we return null. */
public symbol symbol_after_dot()
{
/* use the cached symbol */
return _symbol_after_dot;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if we have a dot before a non terminal, and if so which one
* (return null or the non terminal).
*/
public non_terminal dot_before_nt()
{
symbol sym;
/* get the symbol after the dot */
sym = symbol_after_dot();
/* if it exists and is a non terminal, return it */
if (sym != null && sym.is_non_term())
return (non_terminal)sym;
else
return null;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Produce a new lr_item_core that results from shifting the dot one
* position to the right.
*/
public lr_item_core shift_core() throws internal_error
{
if (dot_at_end())
throw new internal_error(
"Attempt to shift past end of an lr_item_core");
return new lr_item_core(_the_production, _dot_pos+1);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Equality comparison for the core only. This is separate out because we
* need separate access in a super class.
*/
public boolean core_equals(lr_item_core other)
{
return other != null &&
_the_production.equals(other._the_production) &&
_dot_pos == other._dot_pos;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Equality comparison. */
public boolean equals(lr_item_core other) {return core_equals(other);}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Generic equality comparison. */
public boolean equals(Object other)
{
if (!(other instanceof lr_item_core))
return false;
else
return equals((lr_item_core)other);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Hash code for the core (separated so we keep non overridden version). */
public int core_hashCode()
{
return _core_hash_cache;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Hash code for the item. */
public int hashCode()
{
return _core_hash_cache;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Return the hash code that object would have provided for us so we have
* a (nearly) unique id for debugging.
*/
protected int obj_hash()
{
return super.hashCode();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Convert to a string (separated out from toString() so we can call it
* from subclass that overrides toString()).
*/
public String to_simple_string() throws internal_error
{
String result;
production_part part;
if (_the_production.lhs() != null &&
_the_production.lhs().the_symbol() != null &&
_the_production.lhs().the_symbol().name() != null)
result = _the_production.lhs().the_symbol().name();
else
result = "$$NULL$$";
result += " ::= ";
for (int i = 0; i<_the_production.rhs_length(); i++)
{
/* do we need the dot before this one? */
if (i == _dot_pos)
result += "(*) ";
/* print the name of the part */
if (_the_production.rhs(i) == null)
{
result += "$$NULL$$ ";
}
else
{
part = _the_production.rhs(i);
if (part == null)
result += "$$NULL$$ ";
else if (part.is_action())
result += "{ACTION} ";
else if (((symbol_part)part).the_symbol() != null &&
((symbol_part)part).the_symbol().name() != null)
result += ((symbol_part)part).the_symbol().name() + " ";
else
result += "$$NULL$$ ";
}
}
/* put the dot after if needed */
if (_dot_pos == _the_production.rhs_length())
result += "(*) ";
return result;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Convert to a string */
public String toString()
{
/* can't throw here since super class doesn't, so we crash instead */
try {
return to_simple_string();
} catch(internal_error e) {
e.crash();
return null;
}
}
/*-----------------------------------------------------------*/
}
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