Home > Error Handling > Antlr Syntax Error Handling

Antlr Syntax Error Handling

Contents

I really am trying to make the API easier to document and support long term by suggesting a more consistent interface for error handling. Technical term to denote opposite of dependency injection? 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 Default Exception Handling in the Lexer Normally you want the lexer to keep trying to get a valid token upon lexical error. http://lanprolab.net/error-handling/antlr-4-error-handling.php

Parser exception handling for grammar rules is a lot like exception handling in a language like C++ or Java. Personal Open source Business Explore Sign up Sign in Pricing Blog Support Search GitHub This repository Watch 188 Star 1,678 Fork 519 antlr/antlr4 Code Issues 216 Pull requests 39 Projects 0 In addition, you may control the generation of default exception handlers with a per-grammar or per-rule option. If the lookahead predicts no alternative of a production in either the parser or lexer, then a NoViableAltException is thrown. this website

Antlr4 Error Handling

We distinguish between three different kinds of errors: The parser could not figure out which path to take in the ATN (none of the available alternatives could possibly match) The current The general form for specifying an exception handler is: exception [label] catch [exceptionType exceptionVariable] { action } catch ... Hijacking Follow Sets as First Sets In order to have ANTLR compute the required recovery set for us, we first note that the set we want is not just the First

This method handles the consumption of any tokens - the caller should not call Parser.consume() after a successful recovery. ANTLR Exception Hierarchy ANTLR-generated parsers throw exceptions to signal recognition errors or other stream problems. Here is an example that uses a bogus semantic exception (which is a subclass of RecognitionException) to demonstrate blasting out of the lexer: class P extends Parser; { public static void Antlr4 Lexer Error Handling Adding a constructor to RecognitionException with the offending token: This is not really relevant to this issue, and would be addressed separately (if at all).

Parser rules throw RecognitionException and TokenStreamException. Antlr Error Listener Example CharStreamIOException The character input stream had an IO exception (e.g., CharBuffer.fill() can throw this). The typical main or parser invoker has try-catch around the invocation: try { ... } catch(TokenStreamException e) { System.err.println("problem with stream: "+e); } catch(RecognitionException re) { System.err.println("bad input: "+re); } Lexer See the examples/java/includeFile directory.This a great way to handle nested include files and so on or to try out multiple grammars to see which appears to fit the data.

The default exception handler will report an error, sync to the follow set of the rule, and return from that rule. Antlr Error Strategy Here is an example that catches an exception for the rule, for an alternate and for a labeled element: rule: a:A B C | D E exception // for alternate catch void recover(Parserrecognizer, RecognitionExceptione) This method is called to recover from exception e. Token recoverInline(Antlr Error Listener Example

You could still rename getCtx() to getContext() for clarity though. While I understand and respect your responses, I do believe that the ANTLRErrorListener.syntaxError method contains redundant / confusing parameters and requires a lot of API knowledge to use properly. Antlr4 Error Handling Such try{} blocks surround the generated code for the grammar element of interest (rule, alternate, token reference, or rule reference). Antlr4 Throw Exception On Error How rich can one single time travelling person actually become?

Matching and control flow continues as if the error had not occurred. my review here If you clone the recognizer, you won't need to store the context in RecognitionException (you can get it from the Parser when it's stored as e.getRecognizer). If you examine a method generated for a parser rule in the Java target, you will see that the rule logic is encapsulated within a try {} catch {} block, which The typical main or parser invoker has try-catch around the invocation: try { ... } catch(TokenStreamException e) { System.err.println("problem with stream: "+e); } catch(RecognitionException re) { System.err.println("bad input: "+re); } Lexer Antlr Baseerrorlistener

The exceptionType is the exception (or class of exceptions) to catch, and the exceptionVariable is the variable name of the caught exception, so that the action can process the exception if This is my goal-3 from above. SUMMARY of my suggestions for a future version of ANTLR: Always populate the "RecognitionException e" parameter of ANTLRErrorListener.syntaxError (including the OffendingToken) so that we can collect these exceptions for batch handling click site Basically an error in the classMember will abandon the parse of the class definition.

In all cases, the recursive-descent functions on the call stack are exited until an exception handler is encountered for that exception type or one of its base classes (in non-object-oriented languages, Antlr Error Handling Example recoverysyntaxerrors Overview Content Tools Powered by Atlassian Printed by Atlassian Confluence 1000.328.0 Terms of Use Answers Maintenance Schedule Atlassian {"serverDuration": 113, "requestCorrelationId": "365685246c486426"} Skip to content Skip to breadcrumbs Skip to Used by TokenStreamSelector.retry() to force nextToken() of stream to re-enter and retry.

What tool can I use?

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 Sometimes your grammar rules cause a loop in a parsing rule to be exited earlier than you would expect or want; sometimes when a certain construct is in error you want Sign up for free to join this conversation on GitHub. Antlr Bailerrorstrategy 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.

It would be great to categorize syntax errors by how well the parser handled it. Root rule is generated as follows (sync method is added at the end of the loop, as per the DefaultErrorStrategy.sync javadoc: public final TestExpressionContext testExpression() throws RecognitionException { TestExpressionContext _localctx = share|improve this answer answered May 3 '12 at 9:21 sm13294 433320 add a comment| Your Answer draft saved draft discarded Sign up or log in Sign up using Google Sign navigate to this website asked 3 years ago viewed 10733 times active 1 year ago Visit Chat Linked 3 Antlr error/exception handling 1 Parse a formula using ANTLR4 1 Handling errors in ANTLR 4 1

Join them; it only takes a minute: Sign up Handling errors in ANTLR4 up vote 24 down vote favorite 10 The default behavior when the parser doesn't know what to do Here is an example that catches an exception for the rule, for an alternate and for a labeled element: rule: a:A B C | D E exception // for alternate catch 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. Used by TokenStreamSelector.retry() to force nextToken() of stream to re-enter and retry.

SemanticException Used to indicate syntactically valid, but nonsensical or otherwise bogus input was found on the input stream. We recommend upgrading to the latest Safari, Google Chrome, or Firefox. Modifying Default Error Messages With Paraphrases The name or definition of a token in your lexer is rarely meaningful to the user of your recognizer or translator. ANTLR will generate default error-handling code, or you may specify your own exception handlers.

where the label is only used for attaching exceptions to labeled elements. You signed in with another tab or window.