beaver

Class Parser

java.lang.Object

beaver.Parser

Direct Known Subclasses:

JastAddJavaParser

public abstract class Parser
extends Object

Almost complete implementation of a LALR parser. Two components that it lacks to parse a concrete grammar -- rule actions and parsing tables -- are provided by a generated subclass.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Parser.Events This class "lists" reportable events that might happen during parsing.
static class	Parser.Exception
class	Parser.Simulator Simulator is a stripped (of action code) version of a parser that will try to parse ahead token stream after a syntax error.
class	Parser.TokenStream This class wraps a Scanner and provides a token "accumulator" for a parsing simulation.

Field Summary

Fields

Modifier and Type	Field and Description
protected Symbol[]	_symbols The stack of shifted symbols.
protected short	accept_action_id Cached ID of the ACCEPT action.
protected Parser.Events	report Parsing events notification "gateway"
protected short[]	states The parser's stack.
protected ParsingTables	tables The automaton tables.
protected int	top Index of the stack's top element, i.e.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Parser(ParsingTables tables)

Method Summary

Modifier and Type	Method and Description
protected abstract Symbol	invokeReduceAction(int rule_num, int offset) Invoke actual reduce action routine.
Object	parse(Scanner source) Parses a source and returns a semantic value of the accepted nonterminal
Object	parse(Scanner source, short alt_goal_marker_id) Parses a source and returns a semantic value of the accepted nonterminal.
protected void	recoverFromError(Symbol token, Parser.TokenStream in) Implements parsing error recovery.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

tables

protected final ParsingTables tables

The automaton tables.

accept_action_id

protected final short accept_action_id

Cached ID of the ACCEPT action.

states

protected short[] states

The parser's stack.

top

protected int top

Index of the stack's top element, i.e. it's = -1 when the stack is empty;

_symbols

protected Symbol[] _symbols

The stack of shifted symbols.

report

protected Parser.Events report

Parsing events notification "gateway"

Constructor Detail

Parser

protected Parser(ParsingTables tables)

Method Detail

parse

public Object parse(Scanner source)
             throws IOException,
                    Parser.Exception

Parses a source and returns a semantic value of the accepted nonterminal

Parameters:

source - of tokens - a Scanner

Returns:

semantic value of the accepted nonterminal

Throws:

IOException

Parser.Exception

parse

public Object parse(Scanner source,
                    short alt_goal_marker_id)
             throws IOException,
                    Parser.Exception

Parses a source and returns a semantic value of the accepted nonterminal. Before parsing starts injects alternative goal marker into the source to indicate that an alternative goal should be matched.

Parameters:

source - of tokens - a Scanner

alt_goal_marker_id - ID of a token like symbol that will be used as a marker

Returns:

semantic value of the accepted nonterminal

Throws:

IOException

Parser.Exception

invokeReduceAction

protected abstract Symbol invokeReduceAction(int rule_num,
                                             int offset)

Invoke actual reduce action routine. Method must be implemented by a generated parser

Parameters:

rule_num - ID of a reduce action routine to invoke

offset - to the symbol before first action routine argument

Returns:

reduced nonterminal

recoverFromError

protected void recoverFromError(Symbol token,
                                Parser.TokenStream in)
                         throws IOException,
                                Parser.Exception

Implements parsing error recovery. Tries several simple approaches first, like deleting "bad" token or replacing the latter with one of the expected in his state (if possible). If simple methods did not work tries to do error phrase recovery. It is expected that normally descendant parsers do not need to alter this method. In same cases though they may want to override it if they need a different error recovery strategy.

Parameters:

token - a lookahead terminal symbol that messed parsing

in - token stream

Throws:

IOException - propagated from a scanner if it has issues with the source

Parser.Exception - if Parser cannot recover