+
+package java_cup.runtime;
+
+import java.util.Stack;
+
+/** This class implements a skeleton table driven LR parser. In general,
+ * LR parsers are a form of bottom up shift-reduce parsers. Shift-reduce
+ * parsers act by shifting input onto a parse stack until the Symbols
+ * matching the right hand side of a production appear on the top of the
+ * stack. Once this occurs, a reduce is performed. This involves removing
+ * the Symbols corresponding to the right hand side of the production
+ * (the so called "handle") and replacing them with the non-terminal from
+ * the left hand side of the production. <p>
+ *
+ * To control the decision of whether to shift or reduce at any given point,
+ * the parser uses a state machine (the "viable prefix recognition machine"
+ * built by the parser generator). The current state of the machine is placed
+ * on top of the parse stack (stored as part of a Symbol object representing
+ * a terminal or non terminal). The parse action table is consulted
+ * (using the current state and the current lookahead Symbol as indexes) to
+ * determine whether to shift or to reduce. When the parser shifts, it
+ * changes to a new state by pushing a new Symbol (containing a new state)
+ * onto the stack. When the parser reduces, it pops the handle (right hand
+ * side of a production) off the stack. This leaves the parser in the state
+ * it was in before any of those Symbols were matched. Next the reduce-goto
+ * table is consulted (using the new state and current lookahead Symbol as
+ * indexes) to determine a new state to go to. The parser then shifts to
+ * this goto state by pushing the left hand side Symbol of the production
+ * (also containing the new state) onto the stack.<p>
+ *
+ * This class actually provides four LR parsers. The methods parse() and
+ * debug_parse() provide two versions of the main parser (the only difference
+ * being that debug_parse() emits debugging trace messages as it parses).
+ * In addition to these main parsers, the error recovery mechanism uses two
+ * more. One of these is used to simulate "parsing ahead" in the input
+ * without carrying out actions (to verify that a potential error recovery
+ * has worked), and the other is used to parse through buffered "parse ahead"
+ * input in order to execute all actions and re-synchronize the actual parser
+ * configuration.<p>
+ *
+ * This is an abstract class which is normally filled out by a subclass
+ * generated by the JavaCup parser generator. In addition to supplying
+ * the actual parse tables, generated code also supplies methods which
+ * invoke various pieces of user supplied code, provide access to certain
+ * special Symbols (e.g., EOF and error), etc. Specifically, the following
+ * abstract methods are normally supplied by generated code:
+ * <dl compact>
+ * <dt> short[][] production_table()
+ * <dd> Provides a reference to the production table (indicating the index of
+ * the left hand side non terminal and the length of the right hand side
+ * for each production in the grammar).
+ * <dt> short[][] action_table()
+ * <dd> Provides a reference to the parse action table.
+ * <dt> short[][] reduce_table()
+ * <dd> Provides a reference to the reduce-goto table.
+ * <dt> int start_state()
+ * <dd> Indicates the index of the start state.
+ * <dt> int start_production()
+ * <dd> Indicates the index of the starting production.
+ * <dt> int EOF_sym()
+ * <dd> Indicates the index of the EOF Symbol.
+ * <dt> int error_sym()
+ * <dd> Indicates the index of the error Symbol.
+ * <dt> Symbol do_action()
+ * <dd> Executes a piece of user supplied action code. This always comes at
+ * the point of a reduce in the parse, so this code also allocates and
+ * fills in the left hand side non terminal Symbol object that is to be
+ * pushed onto the stack for the reduce.
+ * <dt> void init_actions()
+ * <dd> Code to initialize a special object that encapsulates user supplied
+ * actions (this object is used by do_action() to actually carry out the
+ * actions).
+ * </dl>
+ *
+ * In addition to these routines that <i>must</i> be supplied by the
+ * generated subclass there are also a series of routines that <i>may</i>
+ * be supplied. These include:
+ * <dl>
+ * <dt> Symbol scan()
+ * <dd> Used to get the next input Symbol from the scanner.
+ * <dt> Scanner getScanner()
+ * <dd> Used to provide a scanner for the default implementation of
+ * scan().
+ * <dt> int error_sync_size()
+ * <dd> This determines how many Symbols past the point of an error
+ * must be parsed without error in order to consider a recovery to
+ * be valid. This defaults to 3. Values less than 2 are not
+ * recommended.
+ * <dt> void report_error(String message, Object info)
+ * <dd> This method is called to report an error. The default implementation
+ * simply prints a message to System.err and where the error occurred.
+ * This method is often replaced in order to provide a more sophisticated
+ * error reporting mechanism.
+ * <dt> void report_fatal_error(String message, Object info)
+ * <dd> This method is called when a fatal error that cannot be recovered from
+ * is encountered. In the default implementation, it calls
+ * report_error() to emit a message, then throws an exception.
+ * <dt> void syntax_error(Symbol cur_token)
+ * <dd> This method is called as soon as syntax error is detected (but
+ * before recovery is attempted). In the default implementation it
+ * invokes: report_error("Syntax error", null);
+ * <dt> void unrecovered_syntax_error(Symbol cur_token)
+ * <dd> This method is called if syntax error recovery fails. In the default
+ * implementation it invokes:<br>
+ * report_fatal_error("Couldn't repair and continue parse", null);
+ * </dl>
+ *
+ * @see java_cup.runtime.Symbol
+ * @see java_cup.runtime.Symbol
+ * @see java_cup.runtime.virtual_parse_stack
+ * @version last updated: 7/3/96
+ * @author Frank Flannery
+ */
+
+public abstract class lr_parser {
+
+ /*-----------------------------------------------------------*/
+ /*--- Constructor(s) ----------------------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** Simple constructor. */
+ public lr_parser()
+ {
+ /* nothing to do here */
+ }
+
+ /** Constructor that sets the default scanner. [CSA/davidm] */
+ public lr_parser(Scanner s) {
+ this(); /* in case default constructor someday does something */
+ setScanner(s);
+ }
+
+ /*-----------------------------------------------------------*/
+ /*--- (Access to) Static (Class) Variables ------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** The default number of Symbols after an error we much match to consider
+ * it recovered from.
+ */
+ protected final static int _error_sync_size = 3;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The number of Symbols after an error we much match to consider it
+ * recovered from.
+ */
+ protected int error_sync_size() {return _error_sync_size; }
+
+ /*-----------------------------------------------------------*/
+ /*--- (Access to) Instance Variables ------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** Table of production information (supplied by generated subclass).
+ * This table contains one entry per production and is indexed by
+ * the negative-encoded values (reduce actions) in the action_table.
+ * Each entry has two parts, the index of the non-terminal on the
+ * left hand side of the production, and the number of Symbols
+ * on the right hand side.
+ */
+ public abstract short[][] production_table();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The action table (supplied by generated subclass). This table is
+ * indexed by state and terminal number indicating what action is to
+ * be taken when the parser is in the given state (i.e., the given state
+ * is on top of the stack) and the given terminal is next on the input.
+ * States are indexed using the first dimension, however, the entries for
+ * a given state are compacted and stored in adjacent index, value pairs
+ * which are searched for rather than accessed directly (see get_action()).
+ * The actions stored in the table will be either shifts, reduces, or
+ * errors. Shifts are encoded as positive values (one greater than the
+ * state shifted to). Reduces are encoded as negative values (one less
+ * than the production reduced by). Error entries are denoted by zero.
+ *
+ * @see java_cup.runtime.lr_parser#get_action
+ */
+ public abstract short[][] action_table();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The reduce-goto table (supplied by generated subclass). This
+ * table is indexed by state and non-terminal number and contains
+ * state numbers. States are indexed using the first dimension, however,
+ * the entries for a given state are compacted and stored in adjacent
+ * index, value pairs which are searched for rather than accessed
+ * directly (see get_reduce()). When a reduce occurs, the handle
+ * (corresponding to the RHS of the matched production) is popped off
+ * the stack. The new top of stack indicates a state. This table is
+ * then indexed by that state and the LHS of the reducing production to
+ * indicate where to "shift" to.
+ *
+ * @see java_cup.runtime.lr_parser#get_reduce
+ */
+ public abstract short[][] reduce_table();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The index of the start state (supplied by generated subclass). */
+ public abstract int start_state();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The index of the start production (supplied by generated subclass). */
+ public abstract int start_production();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The index of the end of file terminal Symbol (supplied by generated
+ * subclass).
+ */
+ public abstract int EOF_sym();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The index of the special error Symbol (supplied by generated subclass). */
+ public abstract int error_sym();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Internal flag to indicate when parser should quit. */
+ protected boolean _done_parsing = false;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** This method is called to indicate that the parser should quit. This is
+ * normally called by an accept action, but can be used to cancel parsing
+ * early in other circumstances if desired.
+ */
+ public void done_parsing()
+ {
+ _done_parsing = true;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+ /* Global parse state shared by parse(), error recovery, and
+ * debugging routines */
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Indication of the index for top of stack (for use by actions). */
+ protected int tos;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The current lookahead Symbol. */
+ protected Symbol cur_token;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** The parse stack itself. */
+ protected Stack stack = new Stack();
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Direct reference to the production table. */
+ protected short[][] production_tab;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Direct reference to the action table. */
+ protected short[][] action_tab;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Direct reference to the reduce-goto table. */
+ protected short[][] reduce_tab;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** This is the scanner object used by the default implementation
+ * of scan() to get Symbols. To avoid name conflicts with existing
+ * code, this field is private. [CSA/davidm] */
+ private Scanner _scanner;
+
+ /**
+ * Simple accessor method to set the default scanner.
+ */
+ public void setScanner(Scanner s) { _scanner = s; }
+
+ /**
+ * Simple accessor method to get the default scanner.
+ */
+ public Scanner getScanner() { return _scanner; }
+
+ /*-----------------------------------------------------------*/
+ /*--- General Methods ---------------------------------------*/
+ /*-----------------------------------------------------------*/
+
+ /** Perform a bit of user supplied action code (supplied by generated
+ * subclass). Actions are indexed by an internal action number assigned
+ * at parser generation time.
+ *
+ * @param act_num the internal index of the action to be performed.
+ * @param parser the parser object we are acting for.
+ * @param stack the parse stack of that object.
+ * @param top the index of the top element of the parse stack.
+ */
+ public abstract Symbol do_action(
+ int act_num,
+ lr_parser parser,
+ Stack stack,
+ int top)
+ throws java.lang.Exception;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** User code for initialization inside the parser. Typically this
+ * initializes the scanner. This is called before the parser requests
+ * the first Symbol. Here this is just a placeholder for subclasses that
+ * might need this and we perform no action. This method is normally
+ * overridden by the generated code using this contents of the "init with"
+ * clause as its body.
+ */
+ public void user_init() throws java.lang.Exception { }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Initialize the action object. This is called before the parser does
+ * any parse actions. This is filled in by generated code to create
+ * an object that encapsulates all action code.
+ */
+ protected abstract void init_actions() throws java.lang.Exception;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Get the next Symbol from the input (supplied by generated subclass).
+ * Once end of file has been reached, all subsequent calls to scan
+ * should return an EOF Symbol (which is Symbol number 0). By default
+ * this method returns getScanner().next_token(); this implementation
+ * can be overriden by the generated parser using the code declared in
+ * the "scan with" clause. Do not recycle objects; every call to
+ * scan() should return a fresh object.
+ */
+ public Symbol scan() throws java.lang.Exception {
+ Symbol sym = getScanner().next_token();
+ return (sym!=null) ? sym : new Symbol(EOF_sym());
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Report a fatal error. This method takes a message string and an
+ * additional object (to be used by specializations implemented in
+ * subclasses). Here in the base class a very simple implementation
+ * is provided which reports the error then throws an exception.
+ *
+ * @param message an error message.
+ * @param info an extra object reserved for use by specialized subclasses.
+ */
+ public void report_fatal_error(
+ String message,
+ Object info)
+ throws java.lang.Exception
+ {
+ /* stop parsing (not really necessary since we throw an exception, but) */
+ done_parsing();
+
+ /* use the normal error message reporting to put out the message */
+ report_error(message, info);
+
+ /* throw an exception */
+ throw new Exception("Can't recover from previous error(s)");
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Report a non fatal error (or warning). This method takes a message
+ * string and an additional object (to be used by specializations
+ * implemented in subclasses). Here in the base class a very simple
+ * implementation is provided which simply prints the message to
+ * System.err.
+ *
+ * @param message an error message.
+ * @param info an extra object reserved for use by specialized subclasses.
+ */
+ public void report_error(String message, Object info)
+ {
+ System.err.print(message);
+ if (info instanceof Symbol)
+ if (((Symbol)info).left != -1)
+ System.err.println(" at character " + ((Symbol)info).left +
+ " of input");
+ else System.err.println("");
+ else System.err.println("");
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** This method is called when a syntax error has been detected and recovery
+ * is about to be invoked. Here in the base class we just emit a
+ * "Syntax error" error message.
+ *
+ * @param cur_token the current lookahead Symbol.
+ */
+ public void syntax_error(Symbol cur_token)
+ {
+ report_error("Syntax error", cur_token);
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** This method is called if it is determined that syntax error recovery
+ * has been unsuccessful. Here in the base class we report a fatal error.
+ *
+ * @param cur_token the current lookahead Symbol.
+ */
+ public void unrecovered_syntax_error(Symbol cur_token)
+ throws java.lang.Exception
+ {
+ report_fatal_error("Couldn't repair and continue parse", cur_token);
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Fetch an action from the action table. The table is broken up into
+ * rows, one per state (rows are indexed directly by state number).
+ * Within each row, a list of index, value pairs are given (as sequential
+ * entries in the table), and the list is terminated by a default entry
+ * (denoted with a Symbol index of -1). To find the proper entry in a row
+ * we do a linear or binary search (depending on the size of the row).
+ *
+ * @param state the state index of the action being accessed.
+ * @param sym the Symbol index of the action being accessed.
+ */
+ protected final short get_action(int state, int sym)
+ {
+ short tag;
+ int first, last, probe;
+ short[] row = action_tab[state];
+
+ /* linear search if we are < 10 entries */
+ if (row.length < 20)
+ for (probe = 0; probe < row.length; probe++)
+ {
+ /* is this entry labeled with our Symbol or the default? */
+ tag = row[probe++];
+ if (tag == sym || tag == -1)
+ {
+ /* return the next entry */
+ return row[probe];
+ }
+ }
+ /* otherwise binary search */
+ else
+ {
+ first = 0;
+ last = (row.length-1)/2 - 1; /* leave out trailing default entry */
+ while (first <= last)
+ {
+ probe = (first+last)/2;
+ if (sym == row[probe*2])
+ return row[probe*2+1];
+ else if (sym > row[probe*2])
+ first = probe+1;
+ else
+ last = probe-1;
+ }
+
+ /* not found, use the default at the end */
+ return row[row.length-1];
+ }
+
+ /* shouldn't happened, but if we run off the end we return the
+ default (error == 0) */
+ return 0;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Fetch a state from the reduce-goto table. The table is broken up into
+ * rows, one per state (rows are indexed directly by state number).
+ * Within each row, a list of index, value pairs are given (as sequential
+ * entries in the table), and the list is terminated by a default entry
+ * (denoted with a Symbol index of -1). To find the proper entry in a row
+ * we do a linear search.
+ *
+ * @param state the state index of the entry being accessed.
+ * @param sym the Symbol index of the entry being accessed.
+ */
+ protected final short get_reduce(int state, int sym)
+ {
+ short tag;
+ short[] row = reduce_tab[state];
+
+ /* if we have a null row we go with the default */
+ if (row == null)
+ return -1;
+
+ for (int probe = 0; probe < row.length; probe++)
+ {
+ /* is this entry labeled with our Symbol or the default? */
+ tag = row[probe++];
+ if (tag == sym || tag == -1)
+ {
+ /* return the next entry */
+ return row[probe];
+ }
+ }
+ /* if we run off the end we return the default (error == -1) */
+ return -1;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** This method provides the main parsing routine. It returns only when
+ * done_parsing() has been called (typically because the parser has
+ * accepted, or a fatal error has been reported). See the header
+ * documentation for the class regarding how shift/reduce parsers operate
+ * and how the various tables are used.
+ */
+ public Symbol parse() throws java.lang.Exception
+ {
+ /* the current action code */
+ int act;
+
+ /* the Symbol/stack element returned by a reduce */
+ Symbol lhs_sym = null;
+
+ /* information about production being reduced with */
+ short handle_size, lhs_sym_num;
+
+ /* set up direct reference to tables to drive the parser */
+
+ production_tab = production_table();
+ action_tab = action_table();
+ reduce_tab = reduce_table();
+
+ /* initialize the action encapsulation object */
+ init_actions();
+
+ /* do user initialization */
+ user_init();
+
+ /* get the first token */
+ cur_token = scan();
+
+ /* push dummy Symbol with start state to get us underway */
+ stack.removeAllElements();
+ stack.push(new Symbol(0, start_state()));
+ tos = 0;
+
+ /* continue until we are told to stop */
+ for (_done_parsing = false; !_done_parsing; )
+ {
+ /* Check current token for freshness. */
+ if (cur_token.used_by_parser)
+ throw new Error("Symbol recycling detected (fix your scanner).");
+
+ /* current state is always on the top of the stack */
+
+ /* look up action out of the current state with the current input */
+ act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
+
+ /* decode the action -- > 0 encodes shift */
+ if (act > 0)
+ {
+ /* shift to the encoded state by pushing it on the stack */
+ cur_token.parse_state = act-1;
+ cur_token.used_by_parser = true;
+ stack.push(cur_token);
+ tos++;
+
+ /* advance to the next Symbol */
+ cur_token = scan();
+ }
+ /* if its less than zero, then it encodes a reduce action */
+ else if (act < 0)
+ {
+ /* perform the action for the reduce */
+ lhs_sym = do_action((-act)-1, this, stack, tos);
+
+ /* look up information about the production */
+ lhs_sym_num = production_tab[(-act)-1][0];
+ handle_size = production_tab[(-act)-1][1];
+
+ /* pop the handle off the stack */
+ for (int i = 0; i < handle_size; i++)
+ {
+ stack.pop();
+ tos--;
+ }
+
+ /* look up the state to go to from the one popped back to */
+ act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
+
+ /* shift to that state */
+ lhs_sym.parse_state = act;
+ lhs_sym.used_by_parser = true;
+ stack.push(lhs_sym);
+ tos++;
+ }
+ /* finally if the entry is zero, we have an error */
+ else if (act == 0)
+ {
+ /* call user syntax error reporting routine */
+ syntax_error(cur_token);
+
+ /* try to error recover */
+ if (!error_recovery(false))
+ {
+ /* if that fails give up with a fatal syntax error */
+ unrecovered_syntax_error(cur_token);
+
+ /* just in case that wasn't fatal enough, end parse */
+ done_parsing();
+ } else {
+ lhs_sym = (Symbol)stack.peek();
+ }
+ }
+ }
+ return lhs_sym;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Write a debugging message to System.err for the debugging version
+ * of the parser.
+ *
+ * @param mess the text of the debugging message.
+ */
+ public void debug_message(String mess)
+ {
+ System.err.println(mess);
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Dump the parse stack for debugging purposes. */
+ public void dump_stack()
+ {
+ if (stack == null)
+ {
+ debug_message("# Stack dump requested, but stack is null");
+ return;
+ }
+
+ debug_message("============ Parse Stack Dump ============");
+
+ /* dump the stack */
+ for (int i=0; i<stack.size(); i++)
+ {
+ debug_message("Symbol: " + ((Symbol)stack.elementAt(i)).sym +
+ " State: " + ((Symbol)stack.elementAt(i)).parse_state);
+ }
+ debug_message("==========================================");
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Do debug output for a reduce.
+ *
+ * @param prod_num the production we are reducing with.
+ * @param nt_num the index of the LHS non terminal.
+ * @param rhs_size the size of the RHS.
+ */
+ public void debug_reduce(int prod_num, int nt_num, int rhs_size)
+ {
+ debug_message("# Reduce with prod #" + prod_num + " [NT=" + nt_num +
+ ", " + "SZ=" + rhs_size + "]");
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Do debug output for shift.
+ *
+ * @param shift_tkn the Symbol being shifted onto the stack.
+ */
+ public void debug_shift(Symbol shift_tkn)
+ {
+ debug_message("# Shift under term #" + shift_tkn.sym +
+ " to state #" + shift_tkn.parse_state);
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Do debug output for stack state. [CSA]
+ */
+ public void debug_stack() {
+ StringBuffer sb=new StringBuffer("## STACK:");
+ for (int i=0; i<stack.size(); i++) {
+ Symbol s = (Symbol) stack.elementAt(i);
+ sb.append(" <state "+s.parse_state+", sym "+s.sym+">");
+ if ((i%3)==2 || (i==(stack.size()-1))) {
+ debug_message(sb.toString());
+ sb = new StringBuffer(" ");
+ }
+ }
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Perform a parse with debugging output. This does exactly the
+ * same things as parse(), except that it calls debug_shift() and
+ * debug_reduce() when shift and reduce moves are taken by the parser
+ * and produces various other debugging messages.
+ */
+ public Symbol debug_parse()
+ throws java.lang.Exception
+ {
+ /* the current action code */
+ int act;
+
+ /* the Symbol/stack element returned by a reduce */
+ Symbol lhs_sym = null;
+
+ /* information about production being reduced with */
+ short handle_size, lhs_sym_num;
+
+ /* set up direct reference to tables to drive the parser */
+ production_tab = production_table();
+ action_tab = action_table();
+ reduce_tab = reduce_table();
+
+ debug_message("# Initializing parser");
+
+ /* initialize the action encapsulation object */
+ init_actions();
+
+ /* do user initialization */
+ user_init();
+
+ /* the current Symbol */
+ cur_token = scan();
+
+ debug_message("# Current Symbol is #" + cur_token.sym);
+
+ /* push dummy Symbol with start state to get us underway */
+ stack.removeAllElements();
+ stack.push(new Symbol(0, start_state()));
+ tos = 0;
+
+ /* continue until we are told to stop */
+ for (_done_parsing = false; !_done_parsing; )
+ {
+ /* Check current token for freshness. */
+ if (cur_token.used_by_parser)
+ throw new Error("Symbol recycling detected (fix your scanner).");
+
+ /* current state is always on the top of the stack */
+ //debug_stack();
+
+ /* look up action out of the current state with the current input */
+ act = get_action(((Symbol)stack.peek()).parse_state, cur_token.sym);
+
+ /* decode the action -- > 0 encodes shift */
+ if (act > 0)
+ {
+ /* shift to the encoded state by pushing it on the stack */
+ cur_token.parse_state = act-1;
+ cur_token.used_by_parser = true;
+ debug_shift(cur_token);
+ stack.push(cur_token);
+ tos++;
+
+ /* advance to the next Symbol */
+ cur_token = scan();
+ debug_message("# Current token is " + cur_token);
+ }
+ /* if its less than zero, then it encodes a reduce action */
+ else if (act < 0)
+ {
+ /* perform the action for the reduce */
+ lhs_sym = do_action((-act)-1, this, stack, tos);
+
+ /* look up information about the production */
+ lhs_sym_num = production_tab[(-act)-1][0];
+ handle_size = production_tab[(-act)-1][1];
+
+ debug_reduce((-act)-1, lhs_sym_num, handle_size);
+
+ /* pop the handle off the stack */
+ for (int i = 0; i < handle_size; i++)
+ {
+ stack.pop();
+ tos--;
+ }
+
+ /* look up the state to go to from the one popped back to */
+ act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
+ debug_message("# Reduce rule: top state " +
+ ((Symbol)stack.peek()).parse_state +
+ ", lhs sym " + lhs_sym_num + " -> state " + act);
+
+ /* shift to that state */
+ lhs_sym.parse_state = act;
+ lhs_sym.used_by_parser = true;
+ stack.push(lhs_sym);
+ tos++;
+
+ debug_message("# Goto state #" + act);
+ }
+ /* finally if the entry is zero, we have an error */
+ else if (act == 0)
+ {
+ /* call user syntax error reporting routine */
+ syntax_error(cur_token);
+
+ /* try to error recover */
+ if (!error_recovery(true))
+ {
+ /* if that fails give up with a fatal syntax error */
+ unrecovered_syntax_error(cur_token);
+
+ /* just in case that wasn't fatal enough, end parse */
+ done_parsing();
+ } else {
+ lhs_sym = (Symbol)stack.peek();
+ }
+ }
+ }
+ return lhs_sym;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+ /* Error recovery code */
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Attempt to recover from a syntax error. This returns false if recovery
+ * fails, true if it succeeds. Recovery happens in 4 steps. First we
+ * pop the parse stack down to a point at which we have a shift out
+ * of the top-most state on the error Symbol. This represents the
+ * initial error recovery configuration. If no such configuration is
+ * found, then we fail. Next a small number of "lookahead" or "parse
+ * ahead" Symbols are read into a buffer. The size of this buffer is
+ * determined by error_sync_size() and determines how many Symbols beyond
+ * the error must be matched to consider the recovery a success. Next,
+ * we begin to discard Symbols in attempt to get past the point of error
+ * to a point where we can continue parsing. After each Symbol, we attempt
+ * to "parse ahead" though the buffered lookahead Symbols. The "parse ahead"
+ * process simulates that actual parse, but does not modify the real
+ * parser's configuration, nor execute any actions. If we can parse all
+ * the stored Symbols without error, then the recovery is considered a
+ * success. Once a successful recovery point is determined, we do an
+ * actual parse over the stored input -- modifying the real parse
+ * configuration and executing all actions. Finally, we return the the
+ * normal parser to continue with the overall parse.
+ *
+ * @param debug should we produce debugging messages as we parse.
+ */
+ protected boolean error_recovery(boolean debug)
+ throws java.lang.Exception
+ {
+ if (debug) debug_message("# Attempting error recovery");
+
+ /* first pop the stack back into a state that can shift on error and
+ do that shift (if that fails, we fail) */
+ if (!find_recovery_config(debug))
+ {
+ if (debug) debug_message("# Error recovery fails");
+ return false;
+ }
+
+ /* read ahead to create lookahead we can parse multiple times */
+ read_lookahead();
+
+ /* repeatedly try to parse forward until we make it the required dist */
+ for (;;)
+ {
+ /* try to parse forward, if it makes it, bail out of loop */
+ if (debug) debug_message("# Trying to parse ahead");
+ if (try_parse_ahead(debug))
+ {
+ break;
+ }
+
+ /* if we are now at EOF, we have failed */
+ if (lookahead[0].sym == EOF_sym())
+ {
+ if (debug) debug_message("# Error recovery fails at EOF");
+ return false;
+ }
+
+ /* otherwise, we consume another Symbol and try again */
+ // BUG FIX by Bruce Hutton
+ // Computer Science Department, University of Auckland,
+ // Auckland, New Zealand.
+ // It is the first token that is being consumed, not the one
+ // we were up to parsing
+ if (debug)
+ debug_message("# Consuming Symbol #" + lookahead[ 0 ].sym);
+ restart_lookahead();
+ }
+
+ /* we have consumed to a point where we can parse forward */
+ if (debug) debug_message("# Parse-ahead ok, going back to normal parse");
+
+ /* do the real parse (including actions) across the lookahead */
+ parse_lookahead(debug);
+
+ /* we have success */
+ return true;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Determine if we can shift under the special error Symbol out of the
+ * state currently on the top of the (real) parse stack.
+ */
+ protected boolean shift_under_error()
+ {
+ /* is there a shift under error Symbol */
+ return get_action(((Symbol)stack.peek()).parse_state, error_sym()) > 0;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Put the (real) parse stack into error recovery configuration by
+ * popping the stack down to a state that can shift on the special
+ * error Symbol, then doing the shift. If no suitable state exists on
+ * the stack we return false
+ *
+ * @param debug should we produce debugging messages as we parse.
+ */
+ protected boolean find_recovery_config(boolean debug)
+ {
+ Symbol error_token;
+ int act;
+
+ if (debug) debug_message("# Finding recovery state on stack");
+
+ /* Remember the right-position of the top symbol on the stack */
+ int right_pos = ((Symbol)stack.peek()).right;
+ int left_pos = ((Symbol)stack.peek()).left;
+
+ /* pop down until we can shift under error Symbol */
+ while (!shift_under_error())
+ {
+ /* pop the stack */
+ if (debug)
+ debug_message("# Pop stack by one, state was # " +
+ ((Symbol)stack.peek()).parse_state);
+ left_pos = ((Symbol)stack.pop()).left;
+ tos--;
+
+ /* if we have hit bottom, we fail */
+ if (stack.empty())
+ {
+ if (debug) debug_message("# No recovery state found on stack");
+ return false;
+ }
+ }
+
+ /* state on top of the stack can shift under error, find the shift */
+ act = get_action(((Symbol)stack.peek()).parse_state, error_sym());
+ if (debug)
+ {
+ debug_message("# Recover state found (#" +
+ ((Symbol)stack.peek()).parse_state + ")");
+ debug_message("# Shifting on error to state #" + (act-1));
+ }
+
+ /* build and shift a special error Symbol */
+ error_token = new Symbol(error_sym(), left_pos, right_pos);
+ error_token.parse_state = act-1;
+ error_token.used_by_parser = true;
+ stack.push(error_token);
+ tos++;
+
+ return true;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Lookahead Symbols used for attempting error recovery "parse aheads". */
+ protected Symbol lookahead[];
+
+ /** Position in lookahead input buffer used for "parse ahead". */
+ protected int lookahead_pos;
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Read from input to establish our buffer of "parse ahead" lookahead
+ * Symbols.
+ */
+ protected void read_lookahead() throws java.lang.Exception
+ {
+ /* create the lookahead array */
+ lookahead = new Symbol[error_sync_size()];
+
+ /* fill in the array */
+ for (int i = 0; i < error_sync_size(); i++)
+ {
+ lookahead[i] = cur_token;
+ cur_token = scan();
+ }
+
+ /* start at the beginning */
+ lookahead_pos = 0;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Return the current lookahead in our error "parse ahead" buffer. */
+ protected Symbol cur_err_token() { return lookahead[lookahead_pos]; }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Advance to next "parse ahead" input Symbol. Return true if we have
+ * input to advance to, false otherwise.
+ */
+ protected boolean advance_lookahead()
+ {
+ /* advance the input location */
+ lookahead_pos++;
+
+ /* return true if we didn't go off the end */
+ return lookahead_pos < error_sync_size();
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Reset the parse ahead input to one Symbol past where we started error
+ * recovery (this consumes one new Symbol from the real input).
+ */
+ protected void restart_lookahead() throws java.lang.Exception
+ {
+ /* move all the existing input over */
+ for (int i = 1; i < error_sync_size(); i++)
+ lookahead[i-1] = lookahead[i];
+
+ /* read a new Symbol into the last spot */
+ // BUG Fix by Bruce Hutton
+ // Computer Science Department, University of Auckland,
+ // Auckland, New Zealand. [applied 5-sep-1999 by csa]
+ // The following two lines were out of order!!
+ lookahead[error_sync_size()-1] = cur_token;
+ cur_token = scan();
+
+ /* reset our internal position marker */
+ lookahead_pos = 0;
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Do a simulated parse forward (a "parse ahead") from the current
+ * stack configuration using stored lookahead input and a virtual parse
+ * stack. Return true if we make it all the way through the stored
+ * lookahead input without error. This basically simulates the action of
+ * parse() using only our saved "parse ahead" input, and not executing any
+ * actions.
+ *
+ * @param debug should we produce debugging messages as we parse.
+ */
+ protected boolean try_parse_ahead(boolean debug)
+ throws java.lang.Exception
+ {
+ int act;
+ short lhs, rhs_size;
+
+ /* create a virtual stack from the real parse stack */
+ virtual_parse_stack vstack = new virtual_parse_stack(stack);
+
+ /* parse until we fail or get past the lookahead input */
+ for (;;)
+ {
+ /* look up the action from the current state (on top of stack) */
+ act = get_action(vstack.top(), cur_err_token().sym);
+
+ /* if its an error, we fail */
+ if (act == 0) return false;
+
+ /* > 0 encodes a shift */
+ if (act > 0)
+ {
+ /* push the new state on the stack */
+ vstack.push(act-1);
+
+ if (debug) debug_message("# Parse-ahead shifts Symbol #" +
+ cur_err_token().sym + " into state #" + (act-1));
+
+ /* advance simulated input, if we run off the end, we are done */
+ if (!advance_lookahead()) return true;
+ }
+ /* < 0 encodes a reduce */
+ else
+ {
+ /* if this is a reduce with the start production we are done */
+ if ((-act)-1 == start_production())
+ {
+ if (debug) debug_message("# Parse-ahead accepts");
+ return true;
+ }
+
+ /* get the lhs Symbol and the rhs size */
+ lhs = production_tab[(-act)-1][0];
+ rhs_size = production_tab[(-act)-1][1];
+
+ /* pop handle off the stack */
+ for (int i = 0; i < rhs_size; i++)
+ vstack.pop();
+
+ if (debug)
+ debug_message("# Parse-ahead reduces: handle size = " +
+ rhs_size + " lhs = #" + lhs + " from state #" + vstack.top());
+
+ /* look up goto and push it onto the stack */
+ vstack.push(get_reduce(vstack.top(), lhs));
+ if (debug)
+ debug_message("# Goto state #" + vstack.top());
+ }
+ }
+ }
+
+ /*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
+
+ /** Parse forward using stored lookahead Symbols. In this case we have
+ * already verified that parsing will make it through the stored lookahead
+ * Symbols and we are now getting back to the point at which we can hand
+ * control back to the normal parser. Consequently, this version of the
+ * parser performs all actions and modifies the real parse configuration.
+ * This returns once we have consumed all the stored input or we accept.
+ *
+ * @param debug should we produce debugging messages as we parse.
+ */
+ protected void parse_lookahead(boolean debug)
+ throws java.lang.Exception
+ {
+ /* the current action code */
+ int act;
+
+ /* the Symbol/stack element returned by a reduce */
+ Symbol lhs_sym = null;
+
+ /* information about production being reduced with */
+ short handle_size, lhs_sym_num;
+
+ /* restart the saved input at the beginning */
+ lookahead_pos = 0;
+
+ if (debug)
+ {
+ debug_message("# Reparsing saved input with actions");
+ debug_message("# Current Symbol is #" + cur_err_token().sym);
+ debug_message("# Current state is #" +
+ ((Symbol)stack.peek()).parse_state);
+ }
+
+ /* continue until we accept or have read all lookahead input */
+ while(!_done_parsing)
+ {
+ /* current state is always on the top of the stack */
+
+ /* look up action out of the current state with the current input */
+ act =
+ get_action(((Symbol)stack.peek()).parse_state, cur_err_token().sym);
+
+ /* decode the action -- > 0 encodes shift */
+ if (act > 0)
+ {
+ /* shift to the encoded state by pushing it on the stack */
+ cur_err_token().parse_state = act-1;
+ cur_err_token().used_by_parser = true;
+ if (debug) debug_shift(cur_err_token());
+ stack.push(cur_err_token());
+ tos++;
+
+ /* advance to the next Symbol, if there is none, we are done */
+ if (!advance_lookahead())
+ {
+ if (debug) debug_message("# Completed reparse");
+
+ /* scan next Symbol so we can continue parse */
+ // BUGFIX by Chris Harris <ckharris@ucsd.edu>:
+ // correct a one-off error by commenting out
+ // this next line.
+ /*cur_token = scan();*/
+
+ /* go back to normal parser */
+ return;
+ }
+
+ if (debug)
+ debug_message("# Current Symbol is #" + cur_err_token().sym);
+ }
+ /* if its less than zero, then it encodes a reduce action */
+ else if (act < 0)
+ {
+ /* perform the action for the reduce */
+ lhs_sym = do_action((-act)-1, this, stack, tos);
+
+ /* look up information about the production */
+ lhs_sym_num = production_tab[(-act)-1][0];
+ handle_size = production_tab[(-act)-1][1];
+
+ if (debug) debug_reduce((-act)-1, lhs_sym_num, handle_size);
+
+ /* pop the handle off the stack */
+ for (int i = 0; i < handle_size; i++)
+ {
+ stack.pop();
+ tos--;
+ }
+
+ /* look up the state to go to from the one popped back to */
+ act = get_reduce(((Symbol)stack.peek()).parse_state, lhs_sym_num);
+
+ /* shift to that state */
+ lhs_sym.parse_state = act;
+ lhs_sym.used_by_parser = true;
+ stack.push(lhs_sym);
+ tos++;
+
+ if (debug) debug_message("# Goto state #" + act);
+
+ }
+ /* finally if the entry is zero, we have an error
+ (shouldn't happen here, but...)*/
+ else if (act == 0)
+ {
+ report_fatal_error("Syntax error", lhs_sym);
+ return;
+ }
+ }
+
+
+ }
+
+ /*-----------------------------------------------------------*/
+
+ /** Utility function: unpacks parse tables from strings */
+ protected static short[][] unpackFromStrings(String[] sa)
+ {
+ // Concatanate initialization strings.
+ StringBuffer sb = new StringBuffer(sa[0]);
+ for (int i=1; i<sa.length; i++)
+ sb.append(sa[i]);
+ int n=0; // location in initialization string
+ int size1 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
+ short[][] result = new short[size1][];
+ for (int i=0; i<size1; i++) {
+ int size2 = (((int)sb.charAt(n))<<16) | ((int)sb.charAt(n+1)); n+=2;
+ result[i] = new short[size2];
+ for (int j=0; j<size2; j++)
+ result[i][j] = (short) (sb.charAt(n++)-2);
+ }
+ return result;
+ }
+}
+
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