You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
1252 lines
45 KiB
1252 lines
45 KiB
/*
|
|
* Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
|
|
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*
|
|
*/
|
|
|
|
|
|
package com.sun.java_cup.internal.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 com.sun.java_cup.internal.runtime.Symbol
|
|
* @see com.sun.java_cup.internal.runtime.Symbol
|
|
* @see com.sun.java_cup.internal.runtime.virtual_parse_stack
|
|
* @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 com.sun.java_cup.internal.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 com.sun.java_cup.internal.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 {
|
|
return getScanner().next_token();
|
|
}
|
|
|
|
/*. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .*/
|
|
|
|
/** 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 */
|
|
if (debug)
|
|
debug_message("# Consuming Symbol #" + cur_err_token().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 */
|
|
cur_token = scan();
|
|
lookahead[error_sync_size()-1] = cur_token;
|
|
|
|
/* 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;
|
|
}
|
|
}
|