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Or alternatively you use ANTLR, whatever seems simpler to you. So you forbid the internet to use comments in HTML: problem solved. Comments can be used everywhere, and that is not easy to treat with your regular expression. And somebody dares even to use comments like. Therefore you need to eliminate that, too.

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So you now need to parse tr and td, but they are full of tags. Still, you actually cared about the data inside the table. Brilliant! You did it! Except somebody adds attributes toВ their table, such as style or id. You do not believe me?В LetвЂ™s see, you want to find the elements of a table, so you try a regular expression like this one: (.*?). Have you ever tried parsing HTML with a regular expression? It is a terrible idea, for one you risk summoning Cthulhu, but more importantly it does not really work. It is not that easy to use regular expressions But the larger problem is that it is not really scalable: if you are going to put together even just a few regular expressions, you are going to create a fragile mess that would be hard to maintain. Something that quickly became unmaintainable.

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The most obvious is the lack of recursion: you cannot find a (regular) expression inside another one, unless you code it by hand for each level. If you are the typical programmer, you may ask yourself why canвЂ™t I use a regular expression? A regular expression is quite useful, such as when you want to find a number in a string of text, but it also has many limitations. However, it is something to keep in mind while reading other documents. The distinction in moot in our examples shown here, given they are quite simple, so we use the terms interchangeably here. However, you might prefer something more user friendly in the rest of the program. These changes are sometimes necessary because a parse tree might be organized in a way that make parsing easier or better performing. You create the AST by manipulating the parse tree, in order to get something that is easier to use by subsequent parts of your program. The difference is that a parse tree is exactly what comes out of the parser, while the AST is a more refined version of the parse tree. Notice that technically what you get from ANTLR is a parse tree rather than an AST. Usually the вЂњthingвЂќ is a language, but it could also be a data format, a diagram, or any kind of structure that is represented with text. So you need to start by defining a lexer and parser grammarВ for the thing that you are analyzing.

use the generated lexer and parser: you invoke them passing the code to recognize and they return to you a parse tree.

invoke ANTLR: it will generate a lexer and a parser in your target language (e.g., Java, Python, C#, JavaScript).

Graphical representation of an AST for the Euclidean algorithm In other words, we will start from the very beginning and when we reach the end you will have learned all you could possibly need to learn about ANTLR to be productive.

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you will understand errors and you will know how to avoid them by testing your grammar.

you will know how to deal with the common problems you will encounter.

you will be able to create all the rules you need to build a lexer and a parser.

you will be able to write a parser to recognize different formats and languages.

We just expect you to know how to code and how to use a text editor or an IDE. Maybe you have read some tutorial that was too complicated or so incomplete that seemed to assume that you already knew how to use a parser.

present the most advanced and useful features present in ANTLR: you will learn all you need to parse all possible languages.

see how to setup ANTLR to be used from JavaScript, Python, Java and C#.

explain the basics: what a parser is, what it can be used for.

In this complete tutorial we are going to: Parsers are powerful tools and using ANTLR you could write all sort of parsers, usable from many different languages.