org.antlr.runtime.debug

Interface DebugEventListener

All Known Implementing Classes:

BlankDebugEventListener, DebugEventHub, DebugEventRepeater, DebugEventSocketProxy, ParseTreeBuilder, Profiler, TraceDebugEventListener, Tracer

public interface DebugEventListener

All debugging events that a recognizer can trigger. I did not create a separate AST debugging interface as it would create lots of extra classes and DebugParser has a dbg var defined, which makes it hard to change to ASTDebugEventListener. I looked hard at this issue and it is easier to understand as one monolithic event interface for all possible events. Hopefully, adding ST debugging stuff won't be bad. Leave for future. 4/26/2006.

Field Summary

Fields

Modifier and Type	Field and Description
static int	FALSE
static String	PROTOCOL_VERSION Moved to version 2 for v3.1: added grammar name to enter/exit Rule
static int	TRUE serialized version of true

Method Summary

Methods

Modifier and Type	Method and Description
void	addChild(Object root, Object child) Make childID a child of rootID.
void	becomeRoot(Object newRoot, Object oldRoot) Make a node the new root of an existing root.
void	beginBacktrack(int level)
void	beginResync() Indicates the recognizer is about to consume tokens to resynchronize the parser.
void	commence() Announce that parsing has begun.
void	consumeHiddenToken(Token t) An off-channel input token was consumed.
void	consumeNode(Object t) Input for a tree parser is an AST, but we know nothing for sure about a node except its type and text (obtained from the adaptor).
void	consumeToken(Token t) An input token was consumed; matched by any kind of element.
void	createNode(Object t) Announce a new node built from token elements such as type etc...
void	createNode(Object node, Token token) Announce a new node built from an existing token.
void	endBacktrack(int level, boolean successful)
void	endResync() Indicates that the recognizer has finished consuming tokens in order to resychronize.
void	enterAlt(int alt) Because rules can have lots of alternatives, it is very useful to know which alt you are entering.
void	enterDecision(int decisionNumber, boolean couldBacktrack) Every decision, fixed k or arbitrary, has an enter/exit event so that a GUI can easily track what LT/consume events are associated with prediction.
void	enterRule(String grammarFileName, String ruleName) The parser has just entered a rule.
void	enterSubRule(int decisionNumber) Track entry into any (...) subrule other EBNF construct
void	errorNode(Object t) Upon syntax error, recognizers bracket the error with an error node if they are building ASTs.
void	exitDecision(int decisionNumber)
void	exitRule(String grammarFileName, String ruleName) This is the last thing executed before leaving a rule.
void	exitSubRule(int decisionNumber)
void	location(int line, int pos) To watch a parser move through the grammar, the parser needs to inform the debugger what line/charPos it is passing in the grammar.
void	LT(int i, Object t) The tree parser lookedahead.
void	LT(int i, Token t) Somebody (anybody) looked ahead.
void	mark(int marker) The parser is going to look arbitrarily ahead; mark this location, the token stream's marker is sent in case you need it.
void	nilNode(Object t) A nil was created (even nil nodes have a unique ID...
void	recognitionException(RecognitionException e) A recognition exception occurred such as NoViableAltException.
void	rewind() Rewind to the input position of the last marker.
void	rewind(int marker) After an arbitrairly long lookahead as with a cyclic DFA (or with any backtrack), this informs the debugger that stream should be rewound to the position associated with marker.
void	semanticPredicate(boolean result, String predicate) A semantic predicate was evaluate with this result and action text
void	setTokenBoundaries(Object t, int tokenStartIndex, int tokenStopIndex) Set the token start/stop token index for a subtree root or node.
void	terminate() Parsing is over; successfully or not.

Field Detail

PROTOCOL_VERSION

static final String PROTOCOL_VERSION

Moved to version 2 for v3.1: added grammar name to enter/exit Rule

See Also:

Constant Field Values

TRUE

static final int TRUE

serialized version of true

See Also:

Constant Field Values

FALSE

static final int FALSE

See Also:

Constant Field Values

Method Detail

enterRule

void enterRule(String grammarFileName,
             String ruleName)

The parser has just entered a rule. No decision has been made about which alt is predicted. This is fired AFTER init actions have been executed. Attributes are defined and available etc... The grammarFileName allows composite grammars to jump around among multiple grammar files.

enterAlt

void enterAlt(int alt)

Because rules can have lots of alternatives, it is very useful to know which alt you are entering. This is 1..n for n alts.

exitRule

void exitRule(String grammarFileName,
            String ruleName)

This is the last thing executed before leaving a rule. It is executed even if an exception is thrown. This is triggered after error reporting and recovery have occurred (unless the exception is not caught in this rule). This implies an "exitAlt" event. The grammarFileName allows composite grammars to jump around among multiple grammar files.

enterSubRule

void enterSubRule(int decisionNumber)

Track entry into any (...) subrule other EBNF construct

exitSubRule

void exitSubRule(int decisionNumber)

enterDecision

void enterDecision(int decisionNumber,
                 boolean couldBacktrack)

Every decision, fixed k or arbitrary, has an enter/exit event so that a GUI can easily track what LT/consume events are associated with prediction. You will see a single enter/exit subrule but multiple enter/exit decision events, one for each loop iteration.

exitDecision

void exitDecision(int decisionNumber)

consumeToken

void consumeToken(Token t)

An input token was consumed; matched by any kind of element. Trigger after the token was matched by things like match(), matchAny().

consumeHiddenToken

void consumeHiddenToken(Token t)

An off-channel input token was consumed. Trigger after the token was matched by things like match(), matchAny(). (unless of course the hidden token is first stuff in the input stream).

LT

void LT(int i,
      Token t)

Somebody (anybody) looked ahead. Note that this actually gets triggered by both LA and LT calls. The debugger will want to know which Token object was examined. Like consumeToken, this indicates what token was seen at that depth. A remote debugger cannot look ahead into a file it doesn't have so LT events must pass the token even if the info is redundant.

mark

void mark(int marker)

The parser is going to look arbitrarily ahead; mark this location, the token stream's marker is sent in case you need it.

rewind

void rewind(int marker)

After an arbitrairly long lookahead as with a cyclic DFA (or with any backtrack), this informs the debugger that stream should be rewound to the position associated with marker.

rewind

void rewind()

Rewind to the input position of the last marker. Used currently only after a cyclic DFA and just before starting a sem/syn predicate to get the input position back to the start of the decision. Do not "pop" the marker off the state. mark(i) and rewind(i) should balance still.

beginBacktrack

void beginBacktrack(int level)

endBacktrack

void endBacktrack(int level,
                boolean successful)

location

void location(int line,
            int pos)

To watch a parser move through the grammar, the parser needs to inform the debugger what line/charPos it is passing in the grammar. For now, this does not know how to switch from one grammar to the other and back for island grammars etc... This should also allow breakpoints because the debugger can stop the parser whenever it hits this line/pos.

recognitionException

void recognitionException(RecognitionException e)

A recognition exception occurred such as NoViableAltException. I made this a generic event so that I can alter the exception hierachy later without having to alter all the debug objects. Upon error, the stack of enter rule/subrule must be properly unwound. If no viable alt occurs it is within an enter/exit decision, which also must be rewound. Even the rewind for each mark must be unwount. In the Java target this is pretty easy using try/finally, if a bit ugly in the generated code. The rewind is generated in DFA.predict() actually so no code needs to be generated for that. For languages w/o this "finally" feature (C++?), the target implementor will have to build an event stack or something. Across a socket for remote debugging, only the RecognitionException data fields are transmitted. The token object or whatever that caused the problem was the last object referenced by LT. The immediately preceding LT event should hold the unexpected Token or char. Here is a sample event trace for grammar: b : C ({;}A|B) // {;} is there to prevent A|B becoming a set | D ; The sequence for this rule (with no viable alt in the subrule) for input 'c c' (there are 3 tokens) is: commence LT(1) enterRule b location 7 1 enter decision 3 LT(1) exit decision 3 enterAlt1 location 7 5 LT(1) consumeToken [c/<4>,1:0] location 7 7 enterSubRule 2 enter decision 2 LT(1) LT(1) recognitionException NoViableAltException 2 1 2 exit decision 2 exitSubRule 2 beginResync LT(1) consumeToken [c/<4>,1:1] LT(1) endResync LT(-1) exitRule b terminate

beginResync

void beginResync()

Indicates the recognizer is about to consume tokens to resynchronize the parser. Any consume events from here until the recovered event are not part of the parse--they are dead tokens.

endResync

void endResync()

Indicates that the recognizer has finished consuming tokens in order to resychronize. There may be multiple beginResync/endResync pairs before the recognizer comes out of errorRecovery mode (in which multiple errors are suppressed). This will be useful in a gui where you want to probably grey out tokens that are consumed but not matched to anything in grammar. Anything between a beginResync/endResync pair was tossed out by the parser.

semanticPredicate

void semanticPredicate(boolean result,
                     String predicate)

A semantic predicate was evaluate with this result and action text

commence

void commence()

Announce that parsing has begun. Not technically useful except for sending events over a socket. A GUI for example will launch a thread to connect and communicate with a remote parser. The thread will want to notify the GUI when a connection is made. ANTLR parsers trigger this upon entry to the first rule (the ruleLevel is used to figure this out).

terminate

void terminate()

Parsing is over; successfully or not. Mostly useful for telling remote debugging listeners that it's time to quit. When the rule invocation level goes to zero at the end of a rule, we are done parsing.

consumeNode

void consumeNode(Object t)

Input for a tree parser is an AST, but we know nothing for sure about a node except its type and text (obtained from the adaptor). This is the analog of the consumeToken method. Again, the ID is the hashCode usually of the node so it only works if hashCode is not implemented. If the type is UP or DOWN, then the ID is not really meaningful as it's fixed--there is just one UP node and one DOWN navigation node.

Parameters:

t -

LT

void LT(int i,
      Object t)

The tree parser lookedahead. If the type is UP or DOWN, then the ID is not really meaningful as it's fixed--there is just one UP node and one DOWN navigation node.

nilNode

void nilNode(Object t)

A nil was created (even nil nodes have a unique ID... they are not "null" per se). As of 4/28/2006, this seems to be uniquely triggered when starting a new subtree such as when entering a subrule in automatic mode and when building a tree in rewrite mode. If you are receiving this event over a socket via RemoteDebugEventSocketListener then only t.ID is set.

errorNode

void errorNode(Object t)

Upon syntax error, recognizers bracket the error with an error node if they are building ASTs.

Parameters:

t -

createNode

void createNode(Object t)

Announce a new node built from token elements such as type etc... If you are receiving this event over a socket via RemoteDebugEventSocketListener then only t.ID, type, text are set.

createNode

void createNode(Object node,
              Token token)

Announce a new node built from an existing token. If you are receiving this event over a socket via RemoteDebugEventSocketListener then only node.ID and token.tokenIndex are set.

becomeRoot

void becomeRoot(Object newRoot,
              Object oldRoot)

Make a node the new root of an existing root. See Note: the newRootID parameter is possibly different than the TreeAdaptor.becomeRoot() newRoot parameter. In our case, it will always be the result of calling TreeAdaptor.becomeRoot() and not root_n or whatever. The listener should assume that this event occurs only when the current subrule (or rule) subtree is being reset to newRootID. If you are receiving this event over a socket via RemoteDebugEventSocketListener then only IDs are set.

See Also:

TreeAdaptor.becomeRoot(java.lang.Object, java.lang.Object)

addChild

void addChild(Object root,
            Object child)

Make childID a child of rootID. If you are receiving this event over a socket via RemoteDebugEventSocketListener then only IDs are set.

See Also:

TreeAdaptor.addChild(java.lang.Object, java.lang.Object)

setTokenBoundaries

void setTokenBoundaries(Object t,
                      int tokenStartIndex,
                      int tokenStopIndex)

Set the token start/stop token index for a subtree root or node. If you are receiving this event over a socket via RemoteDebugEventSocketListener then only t.ID is set.