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package java_cup;
import java.util.Hashtable;
import java.util.Enumeration;
/** 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 java_cup.production_part
* @see java_cup.symbol_part
* @see java_cup.action_part
* @version last updated: 7/3/96
* @author Frank Flannery
*/
public class production {
/*-----------------------------------------------------------*/
/*--- Constructor(s) ----------------------------------------*/
/*-----------------------------------------------------------*/
/** 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.
*/
public production(
non_terminal lhs_sym,
production_part rhs_parts[],
int rhs_l,
String action_str)
throws internal_error
{
int i;
action_part tail_action;
String declare_str;
int rightlen = rhs_l;
/* remember the length */
if (rhs_l >= 0)
_rhs_length = rhs_l;
else if (rhs_parts != null)
_rhs_length = rhs_parts.length;
else
_rhs_length = 0;
/* make sure we have a valid left-hand-side */
if (lhs_sym == null)
throw new internal_error(
"Attempt to construct a production with a null LHS");
/* I'm not translating labels anymore, I'm adding code to declare
labels as valid variables. This way, the users code string is
untouched
6/96 frankf */
/* check if the last part of the right hand side is an action. If
it is, it won't be on the stack, so we don't want to count it
in the rightlen. Then when we search down the stack for a
Symbol, we don't try to search past action */
if (rhs_l > 0) {
if (rhs_parts[rhs_l - 1].is_action()) {
rightlen = rhs_l - 1;
} else {
rightlen = rhs_l;
}
}
/* get the generated declaration code for the necessary labels. */
declare_str = declare_labels(
rhs_parts, rightlen, action_str);
if (action_str == null)
action_str = declare_str;
else
action_str = declare_str + action_str;
/* count use of lhs */
lhs_sym.note_use();
/* create the part for left-hand-side */
_lhs = new symbol_part(lhs_sym);
/* merge adjacent actions (if any) */
_rhs_length = merge_adjacent_actions(rhs_parts, _rhs_length);
/* strip off any trailing action */
tail_action = strip_trailing_action(rhs_parts, _rhs_length);
if (tail_action != null) _rhs_length--;
/* Why does this run through the right hand side happen
over and over? here a quick combination of two
prior runs plus one I wanted of my own
frankf 6/25/96 */
/* allocate and copy over the right-hand-side */
/* count use of each rhs symbol */
_rhs = new production_part[_rhs_length];
for (i=0; i<_rhs_length; i++) {
_rhs[i] = rhs_parts[i];
if (!_rhs[i].is_action()) {
((symbol_part)_rhs[i]).the_symbol().note_use();
if (((symbol_part)_rhs[i]).the_symbol() instanceof terminal) {
_rhs_prec =
((terminal)((symbol_part)_rhs[i]).the_symbol()).precedence_num();
_rhs_assoc =
((terminal)((symbol_part)_rhs[i]).the_symbol()).precedence_side();
}
}
}
/*now action string is really declaration string, so put it in front!
6/14/96 frankf */
if (action_str == null) action_str = "";
if (tail_action != null && tail_action.code_string() != null)
action_str = action_str + "\t\t" + tail_action.code_string();
/* stash the action */
_action = new action_part(action_str);
/* rewrite production to remove any embedded actions */
remove_embedded_actions();
/* assign an index */
_index = next_index++;
/* put us in the global collection of productions */
_all.put(new Integer(_index),this);
/* put us in the production list of the lhs non terminal */
lhs_sym.add_production(this);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Constructor with no action string. */
public production(
non_terminal lhs_sym,
production_part rhs_parts[],
int rhs_l)
throws internal_error
{
this(lhs_sym,rhs_parts,rhs_l,null);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/* Constructor with precedence and associativity of production
contextually define */
public production(
non_terminal lhs_sym,
production_part rhs_parts[],
int rhs_l,
String action_str,
int prec_num,
int prec_side)
throws internal_error
{
this(lhs_sym,rhs_parts,rhs_l,action_str);
/* set the precedence */
set_precedence_num(prec_num);
set_precedence_side(prec_side);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/* Constructor w/ no action string and contextual precedence
defined */
public production(
non_terminal lhs_sym,
production_part rhs_parts[],
int rhs_l,
int prec_num,
int prec_side)
throws internal_error
{
this(lhs_sym,rhs_parts,rhs_l,null);
/* set the precedence */
set_precedence_num(prec_num);
set_precedence_side(prec_side);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/*-----------------------------------------------------------*/
/*--- (Access to) Static (Class) Variables ------------------*/
/*-----------------------------------------------------------*/
/** Table of all productions. Elements are stored using their index as
* the key.
*/
protected static Hashtable _all = new Hashtable();
/** Access to all productions. */
public static Enumeration all() {return _all.elements();}
/** Lookup a production by index. */
public static production find(int indx) {
return (production) _all.get(new Integer(indx));
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Total number of productions. */
public static int number() {return _all.size();}
/** Static counter for assigning unique index numbers. */
protected static int next_index;
/*-----------------------------------------------------------*/
/*--- (Access to) Instance Variables ------------------------*/
/*-----------------------------------------------------------*/
/** The left hand side non-terminal. */
protected symbol_part _lhs;
/** The left hand side non-terminal. */
public symbol_part lhs() {return _lhs;}
/** The precedence of the rule */
protected int _rhs_prec = -1;
protected int _rhs_assoc = -1;
/** Access to the precedence of the rule */
public int precedence_num() { return _rhs_prec; }
public int precedence_side() { return _rhs_assoc; }
/** Setting the precedence of a rule */
public void set_precedence_num(int prec_num) {
_rhs_prec = prec_num;
}
public void set_precedence_side(int prec_side) {
_rhs_assoc = prec_side;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** A collection of parts for the right hand side. */
protected production_part _rhs[];
/** Access to the collection of parts for the right hand side. */
public production_part rhs(int indx) throws internal_error
{
if (indx >= 0 && indx < _rhs_length)
return _rhs[indx];
else
throw new internal_error(
"Index out of range for right hand side of production");
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** How much of the right hand side array we are presently using. */
protected int _rhs_length;
/** How much of the right hand side array we are presently using. */
public int rhs_length() {return _rhs_length;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** An action_part containing code for the action to be performed when we
* reduce with this production.
*/
protected action_part _action;
/** An action_part containing code for the action to be performed when we
* reduce with this production.
*/
public action_part action() {return _action;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Index number of the production. */
protected int _index;
/** Index number of the production. */
public int index() {return _index;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Count of number of reductions using this production. */
protected int _num_reductions = 0;
/** Count of number of reductions using this production. */
public int num_reductions() {return _num_reductions;}
/** Increment the count of reductions with this non-terminal */
public void note_reduction_use() {_num_reductions++;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Is the nullability of the production known or unknown? */
protected boolean _nullable_known = false;
/** Is the nullability of the production known or unknown? */
public boolean nullable_known() {return _nullable_known;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Nullability of the production (can it derive the empty string). */
protected boolean _nullable = false;
/** Nullability of the production (can it derive the empty string). */
public boolean nullable() {return _nullable;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** First set of the production. This is the set of terminals that
* could appear at the front of some string derived from this production.
*/
protected terminal_set _first_set = new terminal_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.
*/
public terminal_set first_set() {return _first_set;}
/*-----------------------------------------------------------*/
/*--- Static Methods ----------------------------------------*/
/*-----------------------------------------------------------*/
/** Determine if a given character can be a label id starter.
* @param c the character in question.
*/
protected static boolean is_id_start(char c)
{
return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c == '_');
//later need to handle non-8-bit chars here
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Determine if a character can be in a label id.
* @param c the character in question.
*/
protected static boolean is_id_char(char c)
{
return is_id_start(c) || (c >= '0' && c <= '9');
}
/*-----------------------------------------------------------*/
/*--- General Methods ---------------------------------------*/
/*-----------------------------------------------------------*/
/** Return label declaration code
* @param labelname the label name
* @param stack_type the stack type of label?
* @author frankf
*/
protected String make_declaration(
String labelname,
String stack_type,
int offset)
{
String ret;
/* Put in the left/right value labels */
if (emit.lr_values())
ret = "\t\tint " + labelname + "left = ((java_cup.runtime.Symbol)" +
emit.pre("stack") + ".elementAt(" + emit.pre("top") +
"-" + offset + ")).left;\n" +
"\t\tint " + labelname + "right = ((java_cup.runtime.Symbol)" +
emit.pre("stack") + ".elementAt(" + emit.pre("top") +
"-" + offset + ")).right;\n";
else ret = "";
/* otherwise, just declare label. */
return ret + "\t\t" + stack_type + " " + labelname + " = (" + stack_type +
")((" + "java_cup.runtime.Symbol) " + emit.pre("stack") + ".elementAt(" + emit.pre("top")
+ "-" + offset + ")).value;\n";
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Declare label names as valid variables within the action string
* @param rhs array of RHS parts.
* @param rhs_len how much of rhs to consider valid.
* @param final_action the final action string of the production.
* @param lhs_type the object type associated with the LHS symbol.
*/
protected String declare_labels(
production_part rhs[],
int rhs_len,
String final_action)
{
String declaration = "";
symbol_part part;
action_part act_part;
int pos;
/* walk down the parts and extract the labels */
for (pos = 0; pos < rhs_len; pos++)
{
if (!rhs[pos].is_action())
{
part = (symbol_part)rhs[pos];
/* if it has a label, make declaration! */
if (part.label() != null)
{
declaration = declaration +
make_declaration(part.label(), part.the_symbol().stack_type(),
rhs_len-pos-1);
}
}
}
return declaration;
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Helper routine to merge adjacent actions in a set of RHS parts
* @param rhs_parts array of RHS parts.
* @param len amount of that array that is valid.
* @return remaining valid length.
*/
protected int merge_adjacent_actions(production_part rhs_parts[], int len)
{
int from_loc, to_loc, merge_cnt;
/* bail out early if we have no work to do */
if (rhs_parts == null || len == 0) return 0;
merge_cnt = 0;
to_loc = -1;
for (from_loc=0; from_loc
* A ::= B {action1} C {action2} D
*
* 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.
*/
/* the declarations added to the parent production are also passed along,
as they should be perfectly valid in this code string, since it
was originally a code string in the parent, not on its own.
frank 6/20/96 */
protected void remove_embedded_actions(
) throws internal_error
{
non_terminal new_nt;
production new_prod;
String declare_str;
/* walk over the production and process each action */
for (int act_loc = 0; act_loc < rhs_length(); act_loc++)
if (rhs(act_loc).is_action())
{
declare_str = declare_labels(
_rhs, act_loc, "");
/* create a new non terminal for the action production */
new_nt = non_terminal.create_new();
new_nt.is_embedded_action = true; /* 24-Mar-1998, CSA */
/* create a new production with just the action */
new_prod = new action_production(this, new_nt, null, 0,
declare_str + ((action_part)rhs(act_loc)).code_string());
/* replace the action with the generated non terminal */
_rhs[act_loc] = new symbol_part(new_nt);
}
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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.
*/
public boolean check_nullable() throws internal_error
{
production_part part;
symbol sym;
int pos;
/* if we already know bail out early */
if (nullable_known()) return nullable();
/* if we have a zero size RHS we are directly nullable */
if (rhs_length() == 0)
{
/* stash and return the result */
return set_nullable(true);
}
/* otherwise we need to test all of our parts */
for (pos=0; pos