felipemolinari / lang-parser

Using ANTLR tool to generate a parser usable from a Python code

lang-parser

ANTLR is a parser generator, in other words, a tool that helps you to create parser. A parser takes a piece of text and transform it in an organized structure. A parse tree or a Abstract Syntax Tree (AST) is a tree that describe the logical representation of a language.

How it's works:

1. First of all, you need to define a lexer and a parser grammar.
2. Invoke ANTLR: It will generate a lexer and a parser in your target language. (In this project we are using Python, but could also be Java, C# and Javascript).
3. Use The Generated lexer and parser: You invoke them passing the code to recognize and they return to you a parse tree.

Lexers and Parsers

Before looking into parsers, we need to first look into lexers. A lexer takes the individual characters and transform them in tokens.

437 + 734

The lexer scans the text and find '4', '3', '7' and then the space ' '. So it undestand that the first caracter is actually a number following by a '+' symbol and then finally it finds another number.

Creating a Gammar