ANTLR 3 for Ruby¶ ↑

by Kyle Yetter (kcy5b@yahoo.com)¶ ↑

DESCRIPTION:¶ ↑

Fully-featured ANTLR 3 parser generation for Ruby.

ANTLR (ANother Tool for Language Recognition) is a tool that is used to generate code for performing a variety of language recognition tasks: lexing, parsing, abstract syntax tree construction and manipulation, tree structure recognition, and input translation. The tool operates similarly to other parser generators, taking in a grammar specification written in the special ANTLR metalanguage and producing source code that implements the recognition functionality.

While the tool itself is implemented in Java, it has an extensible design that allows for code generation in other programming languages. To implement an ANTLR language target, a developer may supply a set of templates written in the StringTemplate (www.stringtemplate.org) language.

ANTLR is currently distributed with a fairly limited Ruby target implementation. While it does provide implementation for basic lexer and parser classes, the target does not provide any implementation for abstract syntax tree construction, tree parser class generation, input translation, or a number of the other ANTLR features that give the program an edge over traditional code generators.

This gem packages together a complete implementation of the majority of features ANTLR provides for other language targets, such as Java and Python. It contains:

A customized version of the latest ANTLR program, bundling all necessary java code and templates for producing fully featured language recognition in ruby code
a ruby run-time library that collects classes used throughout the code that ANTLR generates
a wrapper script, ‘antlr4ruby’, which executes the ANTLR command line tool after ensuring the ANTLR jar is Java’s class path

FEATURES¶ ↑

generates ruby code capable of:
- lexing text input
- parsing lexical output and responding with arbitrary actions
- constructing Abstract Syntax Trees (ASTs)
- parsing AST structure and responding with arbitrary actions
- translating input source to some desired output format
This package can serve as a powerful assistant when performing tasks such as:
- code compilation
- source code highlighting and formatting
- domain-specific language implementation
- source code extraction and analysis

USAGE¶ ↑

Write an ANTLR grammar specification for a language

grammar SomeLanguage;

options {
  language = Ruby;    // <- this option must be set to Ruby
  output   = AST;
}

top: expr ( ',' expr )*
   ;

and so on...

Run the ANTLR tool with the antlr4ruby command to generate output:

antlr4ruby SomeLanguage.g
# creates:
#   SomeLanguageParser.rb
#   SomeLanguageLexer.rb
#   SomeLanguage.g

Try out the results directly, if you like:

# see how the lexer tokenizes some input
ruby SomeLanguageLexer.rb < path/to/source-code.xyz

# check whether the parser successfully matches some input
ruby SomeLanguageParser.rb --rule=top < path/to/source-code.xyz

Read up on the package documentation for more specific details about loading the recognizers and using their class definitions

ISSUES¶ ↑

Currently, there are a few nuanced ways in which using the ruby output differs from the conventions and examples covered in the ANTLR standard documentation. I am still working on documenting these details.
So far, this has only been tested on Linux with ruby 1.8.7 and ruby 1.9.1. I’m currently working on verifying behavior on other systems and with slightly older versions of ruby.

LICENSE¶ ↑

The “BSD license”

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote products
   derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE AUTHOR “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.