Antlr Syntax Error
Contents |
no alternative of a production in either the parser or lexer, then a NoViableAltException is thrown. The methods in the lexer base class used to
Antlr Parser Get Error
match characters (match et al) throw analogous exceptions. ANTLR will generate default antlr recover from mismatched token error-handling code, or you may specify your own exception handlers. Either case results (where supported by the language) in antlr error listener example the creation of a try/catch block. Such try{} blocks surround the generated code for the grammar element of interest (rule, alternate, token reference, or rule reference). If no exception handlers
Antlr4 Error Handling
(default or otherwise) are specified, then the exception will propagate all the way out of the parser to the calling program. 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. Note that the '@' exception specification of PCCTS 1.33 does not apply to ANTLR.
Antlr4 Error Handling Example
ANTLR Exception Hierarchy ANTLR-generated parsers throw exceptions to signal recognition errors or other stream problems. All exceptions derive from ANTLRException. The following diagram shows the hierarchy: Exception Description ANTLRException Root of the exception hiearchy. 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. CharStreamException Something bad that happens on the character input stream. Most of the time it will be an IO problem, but you could define an exception for input coming from a dialog box or whatever. CharStreamIOException The character input stream had an IO exception (e.g., CharBuffer.fill() can throw this). If nextToken() sees this, it will convert it to a TokenStreamIOException. RecognitionException A generic recognition problem with the input. Use this as your "catch all" exception in your main() or other method that invokes a parser, lexer, or treeparser. All parser rules throw this exception. MismatchedCharException Thrown by CharScanner.match() when it is looking for a character, but finds a different one on the input stream. MismatchedTokenException Thrown by Parser.match() when it is looking
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring antlr error handling developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question
Antlr4 Throw Exception On Error
x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; antlrerrorstrategy it only takes a minute: Sign up Handling Antlr Syntax Errors or how to give a better message on unexpected token up vote 4 down vote favorite 1 We have the following sub-part of an Antlr grammar: signed_int : http://www.antlr2.org/doc/err.html SIGN? INT ; INT : '0'..'9'+ ; When someone enters a numeric value everything is fine, but if they mistakenly type something like 1O (one and capital o) we get a cryptic error message like: error 1 : Missing token at offset 14 near [Index: 0 (Start: 0-Stop: 0) ='
Gadgets About Confluence Log in ANTLR 3PagesBlogChild pagesArticlesCustom Syntax Error RecoveryBrowse pagesConfigureSpace tools Attachments (0) Page History Page Information Resolved comments Link to this Pageā¦ https://theantlrguy.atlassian.net/wiki/display/ANTLR3/Custom+Syntax+Error+Recovery View in Hierarchy View Source Export to PDF Export to Word Pages ANTLR 3 Wiki Home Articles Skip to end of banner JIRA links Go to start of banner http://meri-stuff.blogspot.com/2011/09/antlr-tutorial-expression-language.html Custom Syntax Error Recovery Skip to end of metadata Created by Unknown User (jimi@idle.ws), last modified on Oct 05, 2010 Go to start of metadata Custom Syntax Error Recovery An error handling important part of a robust and useful parser is the behavior it exhibits when the next token in its incoming token stream is not one that the grammar specifies should be there. This is generally known as a syntax error. Here we look at how ANTLR recovers from the various mismatch cases and what techniques you can use to antlr4 error handling override or influence that recovery. The examples shown use the Java language, but the same techniques should apply to all ANTLR targets. ANTLR implements good error recovery mechanisms by default within the runtimes of all target languages but in some cases the way a grammar is structured impairs the ability of the algorithms to recover to exactly where you might expect or wish. 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 to skip everything up to the end of that construct instead of resuming at wherever ANTLR sees a token that looks like it is a valid recovery point. There are many reasons you may wish to influence or override the standard recovery behavior. However, before we can examine how to implement your own recovery, we need to know something about how ANTLR recovers from mismatch problems. Recognition Exception Once a mismatch is detected, the generated code causes the target language
called grammar file as an input and generates two classes: lexer and parser. This post explains what is lexer, what is parser and how to write grammar files to generate them. In the end of the post, you will be able to create a compiler into abstract syntax tree for any simple programming language. Our example project, a boolean expression language, is written in Java and available on Github. Besides that, everything explained in this post is language independent. Grammar files are the same in all languages. This is our second post on the topic. First post showed how to use ANTLR in a maven project, how to add error handling to it and how to create a 'Hello World' language parser in Java. Posts are independent - you do not have to read the first one to understand the second one. Table of ContentsFirst part shows how to:add ANLR into a maven project, create simple "Hello Word!" grammar, add error handling into it, add custom catch clause to parser rules, add new methods and fields to generated classes, override generated methods. Second part contains:lexer basics, parser basics, boolean expression language, rewrite rules - how to specify abstract syntax tree structure, better boolean expression language. OverviewThe overview is taken from the previous article. Skip it if you wish so. ANTLR generates two classes from grammar file: lexer and parser. Lexer runs first and splits input into pieces called tokens. Each token represents more or less meaningful piece of input. The stream of tokes is passed to parser which does all necessary work. It is the parser who builds abstract syntax tree, interprets the code or translate it into some other form. Grammar file contains everything ANTLR needs to generate correct lexer and parser. Whether it should generate java or python classes, whether parser generates abstract syntax tree, assembler code, directly interprets code and so on. As this tutorial shows how to build abstract syntax tree, we will ignore other options in following explanations. Most importantly, grammar file describes how to split input into tokens and how to build tree from tokens. In other words, grammar file contains lexer rules and parser rules. Lexer - BasicsLexer takes characters stream as an input and splits it into stream of tokens. Lexer rules define tokens, each rule represents one token. Lexer rule always starts with a token name. Token name must start with an uppercase letter and is followed by regular expression that describes it:TokenName: regular expression; R