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
*/
@SuppressWarnings (
{ "all", "deprecation", "unchecked" } )
public abstract class lr_parser
{
/*-----------------------------------------------------------*/
/*--- Constructor(s) ----------------------------------------*/
/*-----------------------------------------------------------*/
/**
* Simple constructor.
*/
public lr_parser ()
{
}
/**
* Constructor that sets the default scanner. [CSA/davidm]
*/
public lr_parser ( Scanner s )
{
this ( s, new DefaultSymbolFactory () ); // TUM 20060327 old cup v10
// Symbols as default
}
/**
* Constructor that sets the default scanner and a SymbolFactory
*/
public lr_parser ( Scanner s, SymbolFactory symfac )
{
this (); // in case default constructor someday does something
symbolFactory = symfac;
setScanner ( s );
}
public SymbolFactory symbolFactory;// = new DefaultSymbolFactory();
/**
* Whenever creation of a new Symbol is necessary, one should use this
* factory.
*/
public SymbolFactory getSymbolFactory ()
{
return symbolFactory;
}
/*-----------------------------------------------------------*/
/*--- (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 : getSymbolFactory ().newSymbol (
"END_OF_FILE", 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 );
System.err.flush ();
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 ( getSymbolFactory ().startSymbol ( "START", 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 ( getSymbolFactory ().startSymbol ( "START", 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 */
Symbol right = ( ( Symbol ) stack.peek () );// TUM 20060327 removed .right
Symbol left = right;// TUM 20060327 removed .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 = ( ( Symbol ) stack.pop () ); // TUM 20060327 removed .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 = getSymbolFactory ().newSymbol ( "ERROR", error_sym (), left,
right );
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;
}
}