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ANTLR 3 is the latest version of a language processing toolkit that was originally released as PCCTS in the mid-1990s. As was the case then, this release of the ANTLR toolkit advances the state of the art with its it's new LL
(*) parsing engine. ANTLR (ANother Tool for Language Recognition) provides a framework for the generation of recognizers, compilers, and translators from grammatical descriptions. ANTLR grammatical descriptions can optionally include action code written in what is termed the target language (i.e. the implementation language of the source code artifacts generated by ANTLR).
When it was released, PCCTS supported C as its only target language, but through consulting with NeXT Computer, PCCTS gained C++ support after 1994. PCCTS's immediate successor was ANTLR 2 and it supported Java, C# and Python as target languages in addition to C++. ANTLR 3 already supports Java, C#, Objective C, C, Python and Ruby as target languages. Support for additional target languages including C++, Perl6 and Oberon (yes, Oberon) is either expected or already in progress. This is all due in part to the fact that it is much easier to add support for a target language (or customize the code generated by an existing target) in ANTLR 3.
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Because it can save you time and resources by automating significant portions of the effort involved in building language processing tools. It is well established that generative tools such as compiler compilers have a major, positive impact on developer productivity. In addition, many of ANTLR v3's new features including an improved analysis engine, its it's significantly enhanced parsing strength via LL parsing with arbitrary lookahead, its it's vastly improved tree construction rewrite rules and the availability of the simply fantastic AntlrWorks IDE offers productivity benefits over other comparable generative language processing toolkits.
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- NUMBER defines a token (named "NUMBER") that contains any character between 0 and 9, inclusive, repeated one or more times.
..creates a character range, while {+} means "one or more times". (This suffix should look familiar if you know regular expressions.) - PLUS defines a token with a single character: {+}.
- add defines a parser rule that says "expect a NUMBER token, a PLUS token, and a NUMBER token in that order." Any other tokens, or tokens in a different order, will trigger an error message.
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You hide the token by setting the token's $channel flag to the constant HIDDEN. This requires adding a little code to the lexer, which you do by adding curly brackets:
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WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = HIDDEN; };
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