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Antlr Custom Error Handling


Single token insertion and deletion As of v3.1, you can turn on and off single token insertion/deletion error recovery. So far, this is the BEST ANTLR tutorial I've ever red, and even if ANTLR is pretty heavy, most users(I know) who read your tutorial understood it much better based on SemanticException Used to indicate syntactically valid, but nonsensical or otherwise bogus input was found on the input stream. That leaves us with case 4, which is still a little on the cryptic side: $ java NotifyConditionParserTest "failure or (changed and success" Caught error: expecting RIGHT_PAREN, found 'null' It would More about the author

asked 3 years ago viewed 10733 times active 1 year ago Linked 3 Antlr error/exception handling 1 Parse a formula using ANTLR4 1 Handling errors in ANTLR 4 1 antlr4 - Please try the request again. Error reporting is covered elsewhere in the Wiki but essentially, if the parser is not already in error recovery mode, then reportError() increments the count of errors it has seen and MismatchedCharException Thrown by CharScanner.match() when it is looking for a character, but finds a different one on the input stream. http://stackoverflow.com/questions/13624624/antlr-handling-exceptions

Antlr Lexer Error Handling

Don't be afraid to do this - generic mechanisms, by their very nature cannot cover all your specialized cases and all the language targets allow you to override the default behaviors. I often use the following listener as a starting point, as it includes the name of the source file with the messages. Can drained water from potted plants be used again to water another house plant? Parameters:recognizer - the parser instance Throws: RecognitionException - if an error is detected by the error strategy but cannot be automatically recovered at the current state in

Does mean=mode imply a symmetric distribution? 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. First and Follow sets I have tried to keep this article as free from jargon as possible, but here we must use a little of it. Antlr Error Listener Example Usage of "it" to start a sentence Convince people not to share their password with trusted others Does the existence of Prawn weapons suggest other hostile races in the District 9

The information you want is available in the exception that already gets thrown. –Sam Harwell Aug 9 '13 at 11:25 Gentle Reader, if you are like me, you're wondering Antlr Exception Handling Add the following to your grammar to override the default insert/delete behavior: @members { protected Object recoverFromMismatchedToken(IntStream input, int ttype, BitSet follow) throws RecognitionException { throw new MismatchedTokenException(ttype, input); } } The First set is used by ANTLR for code generation and analysis and is not available to us when the parser is running. From there we can check if we have errors in our custom code.

This is done by setting the defaultErrorHandler option to false: class NotifyConditionParser extends Parser; options { buildAST=true; defaultErrorHandler=false; } With that done, the ANTLR-generated code will throw exceptions on errors. Antlr4 Throw Exception On Error Note that I removed the call to getMessage because not all exceptions derived off of RecognitionException fill it in. When this process is complete, ANTLR can then compute the First and Follow sets for rules. Note that the '@' exception specification of PCCTS 1.33 does not apply to ANTLR.

Antlr Exception Handling

I updated the answer to show that not all errors can be recovered from and that you'll have to account for them separately. –user1201210 Nov 30 '12 at 17:18 add a https://theantlrguy.atlassian.net/wiki/display/ANTLR3/Error+reporting+and+recovery Because our rule is generic, we can use it anywhere in our grammar that it is required, and ANTLR will supply us with correct set of tokens for the location it Antlr Lexer Error Handling Please see sample grammar: grammar i; options { output=AST; } @header { package com.data; } @rulecatch { catch(RecognitionException e) { throw e; } } // by having these below it makes Antlr4 Error Handling Inspecting the default implementation (in the Java runtime) we find that the match method will call the method recoverFromMismatchedToken() and this in turn will try to use the current Follow set

NoViableAltForCharException The lexer finds an unexpected character; that is, it finds a character that does not begin any alternative in the current decision. http://lanprolab.net/error-handling/antlr-syntax-error-handling.php recoverysyntaxerrors Overview Content Tools Powered by Atlassian Printed by Atlassian Confluence 1000.328.0 Terms of Use Answers Maintenance Schedule Atlassian {"serverDuration": 134, "requestCorrelationId": "263c2efa866e8b8c"} JavaScript is disabled on your browser. void sync(Parserrecognizer) This method provides the error handler with an opportunity to handle syntactic or semantic errors in the input stream before they result in a Conclusion The built-in recovery mechanisms of ANTLR are suitable for almost all general parsing problems; however we can clearly see that there are cases where you must take things in to Antlr Error Listener

void reportError(title="class in org.antlr.v4.runtime">Parserrecognizer, RecognitionExceptione) Report any kind of RecognitionException. In that case, you'll have to catch the exceptions in parseMQL or somewhere around there. (You could try writing your own recovery code, but I wouldn't recommend that you do.) Here The Follow set is used for standard error recovery and as its name also implies, is the set of tokens that should follow on when a rule has finished parsing. click site Either case results (where supported by the language) in the creation of a try/catch block.

a little madness A man needs a little madness, or else he never dares cut the rope and be free -Nikos Kazantzakis Home « ANTLR By Example: Part 4: Tree Parsing Antlr Baseerrorlistener This in fact is the Follow Set for the rule classMember in this production, and hence we can hijack that set and use it as our resync set. Am I supposed to use something like ((InputMismatchException) pce.getCause()).getCtx().exception to get at the useful error message? –Brad Mace Aug 9 '13 at 2:36 @BradMace I added a bunch more

Is this safe to display MySQL query error in webpage if something went wrong?

You can have something listen on a socket for multiple input types without knowing which type will show up when. How to book a flight if my passport doesn't state my gender? Which is faster? Antlr Error Strategy All of the above messages are generated using the getMessage method of the exceptions thrown by ANTLR.

final PhantomSQLLexer lex = new PhantomSQLLexer(input); final CommonTokenStream tokens = new CommonTokenStream(lex); final PhantomSQLParser g = new PhantomSQLParser(tokens); g.setTreeAdaptor(new PhantomTreeAdaptor()); final start_rule_return r = g.start_rule(); if (g.getNumberOfSyntaxErrors() == 0) { if Thanks Kunnummal December 31st, 2006 at 2:49 am Demetrios Kyriakis says: Thank you very much for this great tutorial. Wrap Up Well, that just about does it. http://lanprolab.net/error-handling/antlr-4-error-handling.php To fix the former problem, we can add paraphrase options to our lexer tokens.

The only slight risk here is that the // block becomes MORE inclusive than it should but as the script is // in error, this is a better course than throwing We can now issue errors that will say "While trying to parse class XYZ" rather than "While parsing a script", and within classMember we can apply similar techniques, so that we Is there a way I can get it to report errors via exceptions while retaining the useful info in the message? In error recovery mode, Parser.consume() adds symbols to the parse tree by calling ParserRuleContext.addErrorNode(Token) instead of ParserRuleContext.addChild(Token).

IErrorReporter errorReporter = new StdErrReporter(); myLexer.setErrorReporter(errorReporter); myPaser.setErrorReporter(errorReporter); ... 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 org.antlr.v4.runtime Interface ANTLRErrorStrategy All Known Were slings used for throwing hand grenades? In the definition for ID, use the paraphrase option: ID options { paraphrase = "an identifier"; } : ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'_'|'0'..'9')* ; Note that this paraphrase goes into the token types text

This happens because TreeParser overrides recoverFromMismatchedToken() to do nothing but throw an exception. Default Exception Handling in the Lexer Normally you want the lexer to keep trying to get a valid token upon lexical error. share|improve this answer answered Nov 29 '12 at 12:29 Greg 1,1191818 I also have setup a custom TreeAdaptor, and can get data back from the Tree. Other Recovery Mechanisms Within ANTLR Runtimes There is one other aspect of recovery which you may need to customize, and that is what happens when a mismatch() occurs.

I think this is the easiest of the 3 proposed solutions. –Kami Dec 29 '14 at 9:19 This is the right way to go. This exception was produced by the code above. share|improve this answer edited Aug 9 '13 at 2:56 answered Aug 8 '13 at 22:31 Sam Harwell 68.5k9136209 Ok...how do I make use of that though? Error Reporting As pulse allows users to enter their own boolean expressions (to configure when they receive build notifications), decent error reporting is paramount.

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