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Antlr Better Error Messages


However, as just noted, we do not have access to the First set at runtime, so how can we get ANTLR to do all the hard work for us? Then consume and return the next token (which was the LA(2) token) as the successful result of the match operation. Fix drywall that lost strength due to hanging curtain rod How to see detailed information about a given PID? If for some reason speed is suffering for you, you can turn off this functionality by simply overriding this method as a blank { }. http://lanprolab.net/error-handling/antlr-4-error-handling.php

In other words, a grammar that uses this vocabulary will also use the paraphrase. share|improve this answer answered Aug 9 '13 at 2:31 Brad Mace 16.2k866104 add a comment| Your Answer draft saved draft discarded Sign up or log in Sign up using Google The default implementation resynchronizes the parser by consuming tokens until we find one in the resynchronization set--loosely the set of tokens that can follow the current rule. protected String escapeWSAndQuote(Strings) protected IntervalSet getErrorRecoverySet(Parserrecognizer) protected website here

Antlr4 Error Handling

It now only remains to sync the input stream to this set within our empty rule. Since recursive-descent recognizers operate by recursively calling the rule-matching methods, this results in a call stack that is populated by the contexts of the recursive-descent methods. The action clearly assumes that there has been an identifier matched previously and that $x points at that token. lastErrorStates protectedIntervalSet lastErrorStates Constructor Detail DefaultErrorStrategy publicDefaultErrorStrategy() Method Detail reset publicvoidreset(Parserrecognizer) Reset the error handler state for the specified recognizer.

The default implementation simply calls endErrorCondition(org.antlr.v4.runtime.Parser). ANTLR Exception Hierarchy ANTLR-generated parsers throw exceptions to signal recognition errors or other stream problems. In order to do this, it must compute a Follow Set for the current parsing point - note that I am trying to avoid technical definitions and jargon here in favor Antlr4 Throw Exception On Error We could of course // use a custom action instead if there were special rules about // recovery for this language - here we just don't want to drop out //

MismatchedTokenException Thrown by Parser.match() when it is looking for a token, but finds a different one on the input stream. Antlr Error Listener Example The First set is used by ANTLR for code generation and analysis and is not available to us when the parser is running. All of the above messages are generated using the getMessage method of the exceptions thrown by ANTLR. navigate to this website more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed

If this method returns non-null, recognizer will not be in error recovery mode since the returned token was a successful match. Antlr Error Strategy How do I align the view to the local axis of an object? Parameters:recognizer - reportMatch publicvoidreportMatch(Parserrecognizer) This method is called by when the parser successfully matches an input symbol. Try to get one again.

Antlr Error Listener Example

I just ended up with NPEs from the actions in the grammar due to the failed matches. antlrv3parsererrorexamplerecovery Overview Content Tools Powered by Atlassian Printed by Atlassian Confluence 1000.328.0 Terms of Use Answers Maintenance Schedule Atlassian {"serverDuration": 156, "requestCorrelationId": "495c4cf18c1bf403"} [antlr-interest] better error messages in tree parsers kferrio Antlr4 Error Handling Such try{} blocks surround the generated code for the grammar element of interest (rule, alternate, token reference, or rule reference). Antlr Baseerrorlistener Specified by: recoverin interfaceANTLRErrorStrategy Parameters:recognizer - the parser instancee - the recognition exception to recover fromSee Also:ANTLRErrorStrategy.reportError(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.RecognitionException) sync publicvoidsync(Parserrecognizer) throws RecognitionException The default implementation of

Note that IO exceptions are passed back as TokenStreamIOException's regardless of this option. my review here current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list. Overview Package Class Use Tree Deprecated Index Help Prev Class Next Class Frames No Frames All Classes Summary: Nested| Field| Constr| Method Detail: Field| Constr| Method Copyright © 1992-2016 ANTLR. recoverysyntaxerrors Overview Content Tools Powered by Atlassian Printed by Atlassian Confluence 1000.328.0 Terms of Use Answers Maintenance Schedule Atlassian {"serverDuration": 145, "requestCorrelationId": "32684721ef446802"} Skip to content Skip to breadcrumbs Skip to Antlr4 Lexer Error Handling

void recover(Parserrecognizer, RecognitionExceptione) This method is called to recover from exception e. Token recoverInline(click site I'd rather receive this as an exception.

In ANTLR, parser exceptions are thrown when (a) there is a syntax error, (b) there is a failed validating semantic predicate, or (c) you throw a parser exception from an action. Antlrerrorlistener It is called by recoverInline(org.antlr.v4.runtime.Parser) if the single-token deletion strategy fails to recover from the mismatched input. I then use the custom ErrorListener in my parsing function: public static String parse(String text) throws ParseCancellationException { MyLexer lexer = new MyLexer(new ANTLRInputStream(text)); lexer.removeErrorListeners(); lexer.addErrorListener(ThrowingErrorListener.INSTANCE); CommonTokenStream tokens = new CommonTokenStream(lexer);

It is generally the case that the destination for errors does not change once lexing and parsing has begun, so a refinement on the above solution is to pass the error

I would love to remove the duplication. Now, this example also serves to highlight the limitations of any recovery method - we are not going to parse the input stream to try and make sense of it, just NoViableAltException The parser finds an unexpected token; that is, it finds a token that does not begin any alternative in the current decision. Antlr Lexer Error Handling This method is not used by lexers.

Otherwise, it calls beginErrorCondition(org.antlr.v4.runtime.Parser) to enter error recovery mode, followed by calling Parser.notifyErrorListeners(java.lang.String). When this method returns, recognizer is in error recovery mode. Because this tutorial is so great, IMHO you could/should: - review it, and extend a little, - generate a PDF (all in one) - publish it on the ANTLR lists, so navigate to this website Is there a way I can get it to report errors via exceptions while retaining the useful info in the message?

This is used to suppress reporting multiple error messages while attempting to recover from a detected syntax error. The documentation for this field reads (for people that don't want to click an extra link): The exception which forced this rule to return. Edit: If you use DefaultErrorStrategy, the parse context exception will not be propagated all the way out to the calling code, so you'll be able to examine the exception field directly. IErrorReporter errorReporter = new StdErrReporter(); myLexer.setErrorReporter(errorReporter); myPaser.setErrorReporter(errorReporter); ...

In error recovery mode, Parser.consume() adds symbols to the parse tree by calling ParserRuleContext.addErrorNode(Token) instead of ParserRuleContext.addChild(Token). What to tell to a following-up rejected candidate? Clearly, when we return from an attempted parse of a classMember, we need to ensure that we resync the input stream to either the start of a new classMember, or the This exception is thrown automatically by failed, validating semantic predicates such as:a : A {false}?

A little madness is the blog of Daniel Ostermeier and Jason Sankey. Thank you, D. protected void endErrorCondition(Parserrecognizer) This method is called to leave error recovery mode after recovering from a recognition exception. If you use BailErrorStrategy, the ParseCancellationException thrown by it will include a RecognitionException if you call getCause().

Each full-context prediction which does not result in a syntax error will call either reportContextSensitivity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, int, org.antlr.v4.runtime.atn.ATNConfigSet) or reportAmbiguity(org.antlr.v4.runtime.Parser, org.antlr.v4.runtime.dfa.DFA, int, int, boolean, java.util.BitSet, org.antlr.v4.runtime.atn.ATNConfigSet). If this method returns true, the caller is responsible for creating and inserting a token with the correct type to produce this behavior. Generated Sat, 01 Oct 2016 00:11:17 GMT by s_bd40 (squid/3.5.20) When exact is true, all of the potentially viable alternatives are truly viable, i.e.

Note that the calling code will not report an error if this method returns successfully. protected void consumeUntil(Parserrecognizer, IntervalSetset) Consume tokens until one matches the given token set. Parser rules throw RecognitionException and TokenStreamException. During loop iteration, it consumes until it sees a token that can start a sub rule or what follows loop.

protected void reportMissingToken(Parserrecognizer) This method is called to report a syntax error which requires the insertion of a missing token into the input stream. If nextToken() sees this, it will convert it to a TokenStreamIOException.