* * 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: 11/25/95 * @author Scott Hudson */ 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;
/* 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");
/* translate labels appearing in action strings */
action_str = translate_labels(
rhs_parts, rhs_l, action_str, lhs_sym.stack_type());
/* 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--;
/* allocate and copy over the right-hand-side */
_rhs = new production_part[_rhs_length];
for (i=0; i<_rhs_length; i++)
_rhs[i] = rhs_parts[i];
/* count use of each rhs symbol */
for (i=0; i<_rhs_length; i++)
if (!_rhs[i].is_action())
((symbol_part)_rhs[i]).the_symbol().note_use();
/* merge any trailing action with action string parameter */
if (action_str == null) action_str = "";
if (tail_action != null && tail_action.code_string() != null)
action_str = tail_action.code_string() + action_str;
/* 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);
}
/*-----------------------------------------------------------*/
/*--- (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();};
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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;}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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 ---------------------------------------*/
/*-----------------------------------------------------------*/
/** Determine the translation for one label id found within a code_string.
* Symbols appearing in the RHS correspond to objects found on the parse
* stack at runtime. The code to access them, becomes code to access an
* object at the appropriate offset from the top of the stack, and then
* cast that to the proper type.
*
* @param id_str the name of the id to be translated.
* @param act_pos the original position of the action it appears in.
* @param label_map a hash table mapping labels to positions in the RHS.
* @param type_map a hash table mapping labels to declared symbol types.
*/
protected String label_translate(
String id_str, /* the id string we are (possibly) translating */
int act_pos, /* position of the action */
Hashtable label_map, /* map from labels to positions in the RHS */
Hashtable label_types)/* map from labels to stack types */
{
Integer label_pos;
String label_type;
int offset;
/* look up the id */
label_pos = (Integer)label_map.get(id_str);
/* if we don't find it, just return the id */
if (label_pos == null) return id_str;
/* extract the type of the labeled symbol */
label_type = (String)label_types.get(id_str);
/* is this for the LHS? */
if (label_pos.intValue() == -1)
{
/* return the result object cast properly */
return "((" + label_type + ")" + emit.pre("result") + ")";
}
/* its a RHS label */
/* if the label appears after the action, we have an error */
if (label_pos.intValue() > act_pos)
{
/* emit an error message */
System.err.println("*** Label \"" + id_str +
"\" appears in action before it appears in production");
lexer.error_count++;
// later need to print the production this is in
/* just return the id unchanged */
return id_str;
}
/* calculate the stack offset as the difference in position from
label to action minus one */
offset = (act_pos - label_pos.intValue())-1;
/* translation is properly cast element at that offset from TOS */
return "(/*"+id_str+"*/("+label_type+")" +
emit.pre("stack") + ".elementAt(" + emit.pre("top") +"-"+ offset + "))";
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Translate all the label names within an action string to appropriate code.
* @param act_string the string to be translated
* @param act_pos the position that the action originally held in the
* production.
* @param label_map a hash table mapping labels to positions in the RHS.
* @param type_map a hash table mapping labels to declared symbol types.
*/
protected String action_translate(
String act_string, /* the action string */
int act_pos, /* the position of the action on the RHS */
Hashtable label_map, /* map from labels to RHS positions */
Hashtable label_types) /* map from labels to symbol stack types */
{
int id_start;
int pos;
int len;
String id_str;
boolean in_id;
StringBuffer result;
char buffer[];
/* if we have no string we are done */
if (act_string == null || act_string.length()== 0) return act_string;
len = act_string.length();
/* set up a place to put the result */
result = new StringBuffer(len + 50);
/* extract string into array */
buffer = new char[len + 1];
act_string.getChars(0, len, buffer, 0);
/* put terminator in buffer so we can look one past the end */
buffer[len] = '\0';
/* walk down the input buffer looking for identifiers */
in_id = false;
for (pos = id_start = 0; pos <= len; pos++)
{
/* are we currently working on an id? */
if (in_id)
{
/* does this end the id? */
if (!is_id_char(buffer[pos]))
{
/* extract the id string and translate it */
id_str = new String(buffer, id_start, pos - id_start);
result.append(
label_translate(id_str, act_pos, label_map,label_types));
/* copy over the ending character */
if (buffer[pos] != '\0')
result.append(buffer, pos, 1);
/* and we are done with this id */
in_id = false;
}
else
{
/* we are still in the id, so just keep going */
}
}
else /* we are not inside an id */
{
/* start a new id? */
if (is_id_start(buffer[pos]))
{
/* start keeping these chars as an id */
in_id = true;
id_start = pos;
}
else
{
/* just copy over the char */
if (buffer[pos] != '\0')
result.append(buffer, pos, 1);
}
}
}
/* return the accumulated result */
return result.toString();
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** Translate label names to appropriate code within all action strings.
* @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 translate_labels(
production_part rhs[],
int rhs_len,
String final_action,
String lhs_type)
{
Hashtable label_map = new Hashtable(11);
Hashtable label_types = new Hashtable(11);
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 enter it in the tables */
if (part.label() != null)
{
label_map.put(part.label(), new Integer(pos));
label_types.put(part.label(), part.the_symbol().stack_type());
}
}
}
/* add a label for the LHS */
label_map.put("RESULT", new Integer(-1));
label_types.put("RESULT", lhs_type);
/* now walk across and do each action string */
for (pos = 0; pos < rhs_len; pos++)
{
if (rhs[pos].is_action())
{
act_part = (action_part)rhs[pos];
act_part.set_code_string(
action_translate(
act_part.code_string(), pos, label_map, label_types));
}
}
/* now do the final action string at the position after the last */
return action_translate(final_action, rhs_len, label_map, label_types);
}
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
/** 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 NT$1 C NT$2 D
* NT$1 ::= {action1}
* NT$2 ::= {action2}
*
* where NT$1 and NT$2 are new system created non terminals.
*/
protected void remove_embedded_actions() throws internal_error
{
non_terminal new_nt;
production new_prod;
/* 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())
{
/* create a new non terminal for the action production */
new_nt = non_terminal.create_new();
/* create a new production with just the action */
new_prod = new action_production(this, new_nt, null, 0,
((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