Basic Understanding of ANTLR

ANTLR

ANTLR stands for “ANother Tool for Language Recognition”

There are multiple language recognition tools available they are also parser generator.

So either we can write our parser with lexer with visitors and listeners functions for transformation and then create a AST (abstract syntax tree)

OR

We can use ANTLR like PARSER generation tools by just providing on grammar files, rest things will be taken care by tools.

To describe it again — In ANTLR, we just need to write a grammar files(.g4), rest parser generation programs (like components, different kind of files, classes, functions) will be generated by ANTLR.

Required for ANTLR based PARSER

ANTLR is a JAVA tool, we just need to include ANTLR JAR in our code. Once we have grammar files (.g4) then run a simple commands java commands to generate parser code.

Let’s talk about terminologies —

Parser generators — Here ANTLR is parser generator which creates parser program for us by just providing grammar files.

Grammar files (.g4) — there two files ANTLR expects us to provide as input, one is for lexers or tokeniser for lexical analysis, and second one is for Parser to analyse syntactical rules, specifying how tokens combine to form valid sentences or expressions. Both files are called grammar files and their extension is “.g4”

Lexer rules in an ANTLR grammar must start with an uppercase letter (e.g., INT : ‘0’..’9'+ ;). And Lexer rules try to match the longest possible sequence of characters from the input. If multiple rules match the same length, the rule defined first in the grammar takes precedence.

Parser rules must start with a lowercase letter (e.g., declaration : INT ID EQUALS NUMBER SEMI ;). And Parser rules are composed of other parser rules and/or lexer tokens.

Parsing tree — this is also called abstract syntax tree (ast). this created when parser analyse the source code using Visitors and Listeners.

Visitors — is controlled traversal in AST to process the parse tree.

Listeners — similar to visitors but kind of interceptors based on event driven. Suitable for logging, transformation.

Now Let’s talk about flow — how ANTLR generates parser, and how parser generates AST. We can understand using following diagrams.

Detailed flow of parser generation and source code interpretation

1. ANTLR build PARSER — which is available for lexical analysis and syntactical analysis of input source code
2. After this parser build an abstract syntax tree
3. while traversal on AST, visitors and listeners are used to process and transform
4. which helps to interpret source input.

This blog is just an introduction to start with ANTLR or any parser generation tool. For detailed understanding of ANTLR, you can checkout following references.

References —

[embed]ANTLR ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or…www.antlr.org

[embed]

[embed]GitHub - antlr/antlr4: ANTLR (ANother Tool for Language Recognition) is a powerful parser generator… ANTLR (ANother Tool for Language Recognition) is a powerful parser generator for reading, processing, executing, or…github.com

[embed]The Definitive ANTLR 4 Reference We improve the lives of professional developers. We create timely, practical books on classic and cutting-edge topics…pragprog.com

[embed]

[embed]