Home > Error Handling > Antlr Syntax Error

Antlr Syntax Error

Contents

TokenStreamException Indicates that something went wrong while generating a stream of tokens. andexpression RPAREN!; Any function is composed of its name and arguments in parenthesis. If you want behavior that is different to this, then you can override the match() method, or more likely, the recoverFromMismatchedToken() method. 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. http://lanprolab.net/error-handling/antlr-syntax-error-handling.php

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 The examples shown use the Java language, but the same techniques should apply to all ANTLR targets. Lexer rule matching any integer: NUMBER: ('0'..'9')+; Of course, you can combine expressions. LISTMEMBER)*; New abstract syntax tree has much better structure than previous one:lownumbers -- 2 -- 3 -- 4 How Parser WorksParser starts knowing which rule should correspond to the input and

Antlr Parser Get Error

Next two rules are equivalent to previous two rules: binaryAnd: a+=expression AND a+=expression AND a+=expression -> ^(AND $a+); binaryAnd: a+=expression AND a+=expression AND a+=expression -> ^(AND $a*); The input bwahaha && MismatchedTokenException Thrown by Parser.match() when it is looking for a token, but finds a different one on the input stream. This method is not used by lexers. If they would be after it, lexer would never recognize them: error(208): S007BooleanWithFunctions.g:59:1: The following token definitions can never be matched because prior tokens match the same input: ALL,ATLEASTONE,NEITHER,NOTALL The atom

However, it reports warning to the console: warning(200): Decision can match input such as "TOKEN TOKEN" using multiple alternatives: 1, 2 As a result, alternative(s) 2 were disabled for that input The author specifies a parser-grammar option to load the lexer tokens. We want finer * grained control of the recovery and error mechanisms. */ protected void syncToSet() { // Compute the followset that is in context wherever we are in the // Antlr4 Error Handling Example You signed in with another tab or window.

ANTLRErrorStrategy specifies how to recover from syntax errors and how to compute error messages. So, before attempting this, let us pause and examine what ANTLR can provide us automatically. Unfortunately, LONGTOKEN does not match the input:line 1:5 mismatched character 'Q' expecting 'c' If no token matches the input, an error is reported:line 1:0 no viable alternative at character 'Q' FragmentsOnce http://stackoverflow.com/questions/10386499/handling-antlr-syntax-errors-or-how-to-give-a-better-message-on-unexpected-token The greedy algorithm matches all abc blocks available, including the last one.

We'll get back to that later. Antlr Error Handling It is possible to repeat any structure surrounding repeated list label. For example, we may rewrite previous:NUMBER_NO_LEADING_ZEROS: ('0'..'9') | (('1'..'9')('0'..'9')+); to cleaner:fragment DIGIT: ('0'..'9'); fragment DIGIT_NOT_ZERO: ('1'..'9'); NUMBER_NO_LEADING_ZEROS: DIGIT | (DIGIT_NOT_ZERO DIGIT+); Important: you can reference only fragment rules. As a result, the alternative unknowperson will not be used.

Antlr Recover From Mismatched Token

Method Summary Methods Modifier and Type Method and Description void reportAmbiguity(Parserrecognizer, DFAdfa, intstartIndex, intstopIndex, booleanexact, BitSetambigAlts, https://theantlrguy.atlassian.net/wiki/display/ANTLR3/Custom+Syntax+Error+Recovery Sometimes you want exceptions to pop out of the lexer--usually when you want to abort the entire parsing process upon syntax error. Antlr Parser Get Error If no exception handlers (default or otherwise) are specified, then the exception will propagate all the way out of the parser to the calling program. Antlr Error Listener Example The token SALUTATION is mapped to the SALUTATION part of the rule and the token ENDSYMBOL is mapped to the ENDSYMBOL part of the rule.

You signed in with another tab or window. my review here Lexer rule always starts with a token name. Those are great, but very limited. At runtime, before any rule is invoked from any other rule, the pre-calculated follow set is made available on a stack, and we can use the top set (or indeed any Antlr4 Error Handling

In other words, backtrack=true option automatically adds condition (syntactic predicate) wherever needed. To decide which rule should be used, it investigates (look ahead) incoming token stream and decides accordingly. I will continue looking into Antlr error handling but I thought I would post this here to look for some insights. http://lanprolab.net/error-handling/antlr-4-error-handling.php ANTLR's default exception handling is good to get something working, but you will have more control over error-reporting and resynchronization if you write your own exception handlers.

Is there any way to make the cut command read the last field only? Antlr4 Throw Exception On Error Use them to help parser decide which alternative it should take:rule: (condition_rule1) => alternative1 | (condition_rule2) => alternative2 | ... ; The parser uses conditions to decide between rule alternatives. You can directly subclass this if you want to define your own exceptions unless they live more properly under one of the specific exceptions below.

Jul 23, 2012, 7:54:00 PM Anonymous said...

You signed out in another tab or window. following is wrong://non-fragment rule SALUTATION: 'Hello'; //Incorrect rule - ANTLR fails. In other words, a grammar that uses this vocabulary will also use the paraphrase. Antlrerrorstrategy Thank you for posting this, specifically the conditional re-write rules, it was exactly what I was searching for.

We wont go into details, this chapter contains only necessary minimum needed to understand and use ANTLR. Reload to refresh your session. We recommend upgrading to the latest Safari, Google Chrome, or Firefox. navigate to this website When exact is true, all of the potentially viable alternatives are truly viable, i.e.

sharwell closed this Jan 7, 2014 jonathandandries commented Jan 7, 2014 Thanks for the quick reply and consideration. If the incoming token stream matches condition_rule1, the parser will use alternative1.If the first condition does not match, the parser tries second one. Is this safe to display MySQL query error in webpage if something went wrong? All of the above messages are generated using the getMessage method of the exceptions thrown by ANTLR.

Personal Open source Business Explore Sign up Sign in Pricing Blog Support Search GitHub This repository Watch 18 Star 118 Fork 30 antlr/intellij-plugin-v4 Code Issues 24 Pull requests 1 Projects 0 CharStreamIOException The character input stream had an IO exception (e.g., CharBuffer.fill() can throw this). Root node is dummy node - it does not correspond to any token. 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

SemanticException Used to indicate syntactically valid, but nonsensical or otherwise bogus input was found on the input stream. While your at it, make sure the e.getMessage() is set to return the value currently in the msg parameter. An attempt to parse the expression "Tree !" with a previous grammar would lead to following error: line 1:0 no viable alternative at input 'Tree ' This algorithm has several consequences void syntaxError(Recognizerrecognizer, ObjectoffendingSymbol, intline, intcharPositionInLine, Stringmsg, RecognitionExceptione) Upon syntax error,

Or, as you will see from the default implementation, ANTLR will first see if it can fix things by ignoring a token, then go on to see if it can fix Aug 30, 2012, 7:24:00 AM Anonymous said... I figured that ANTLR must have a way to retrieve the information, and a little digging uncovered it. Obviously creating your own within a custom implementation of syntaxError is perfectly acceptable.

The lexer has no knowledge of parser rules. 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, condition. In this case, parser reads first two tokens and depending on the second one decides which alternative to use.

Specifying Parser Exception-Handlers You may attach exception handlers to a rule, an alternative, or a labeled element. Share it! LISTMEMBER)*; Put '^' symbol after the node you wish to be a parent://remove ',' comma from the output; LISTNAME is the root list: LISTNAME^ LISTMEMBER (','! For instance, if RecognitionException is non-null, should we rely on the msg parameter or e.getMessage()?