Building a Parser from scratch

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Course overview

Parsing or syntactic analysis is one of the first stages in designing and implementing a compiler. A well-designed syntax of your programming language is a big motivation why users would prefer and choose exactly your language.

Note: this is a practical class on building a manual Recursive-descent parser. If you’re interested in parsing theory and automated algorithms you may also consider the [ Parsing Algorithms ] class.


Recursive descent parsers are the group of parsers which are widely used on practice in many production programming languages. In contrast with automated parsing algorithms, the manual implementation allows having full control over the parsing process, and handling complex constructs, which may not be possible in the automatic parsers.

Besides, implementing a full manual parser from scratch allows understanding and seeing this process from inside, demystifying internal structures, and turning building parsers into an interesting engineering task.


In the Building a Parser from scratch class we dive into pure practical implementation, building and learning different aspects of parsers.

In this class you will learn concept of Recursive descent parsing, understand what is Tokenizer and how it cooperates with Parser module, learn what is Abstract Syntax Tree (AST), and how to have different formats of these ASTs, what is “lookahead” and the predictive parsing, and eventually build a parser for a full programming language, similar to Java or JavaScript.

Implementing a parser would also make your practical usage of other programming languages more professional.

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Parsing Algorithms

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Course overview

Parsing or syntactic analysis is one of the first stages in designing and implementing a compiler. A well-designed syntax of your programming language is a big motivation why users would prefer and choose exactly your language.

Note: this is a class on theory of parsers and parsing algorithms. If you’re interested in manual practical parsing class you may also consider the [ Building a Parser from scratch ] where we build a Recursive descent parser.

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The problem with “parsers theory” in classic compiler schools and books is that this theory is often considered as “too advanced”, going right into complicated formal descriptions from the Theory of Computation and formal grammars. As a result students may lose an interest in building a compiler already at parsing stage.

The opposite problem often seen in describing a parser is a superficial approach describing only manual (usually recursive descent) parsing, leaving the students with issues understanding the actual techniques behind the automated parsers.


I believe this deep dive into the parsing theory should be combined together with a hands-on approach, which goes in parallel and allows seeing all the learned theoretical material on practice.

In the Essentials of Parsing (aka Parsing Algorithms) class we dive into different aspects of the parsing theory, describing in detail the LL and LR parsers. However at the same time to make the learning process and understanding easy and fun, we build in parallel an automatic parser for a full programming language, similar to JavaScript or Python, from scratch.

After this class not only you will be able to use a parser generator to build parsers for programming languages, but will also understand how the parser generators work under the hood themselves.

Implementing a parser for a programing language would also make your practical usage of other programming languages more professional.

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Building an Interpreter from scratch

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Building an Interpreter from scratch rating ” This course is amazing! Dmitry goes straight to the point and packs a lot of information in really concise videos. The code is simple and readable, and the production quality is top notch. “Read more →
Course overview

How programming languages work under the hood? What’s the difference between compiler and interpreter? What is a virtual machine, and JIT-compiler? And what about the difference between functional and imperative programming?

There are so many questions when it comes to implementing a programming language!


The problem with “compiler classes” in school is they usually are presented as some “hardcore rocket science” which is only for advanced engineers.

Moreover, classic compiler books start from the least significant topic, such as Lexical analysis, going right away deep down to the theoretical aspects of formal grammars. And by the time of implementing a first Tokenizer module, students simply lose an interest to the topic, not having a chance to actually start implementing a programing language itself. And all this is spread to a whole semester of messing with tokenizers and BNF grammars, without understanding an actual semantics of programming languages.


I believe we should be able to build and understand a full programming language semantics, end-to-end, in 4-6 hours — with a content going straight to the point, showed in live coding sessions as pair-programming, and described in a comprehensible way.

In the Essentials of Interpretations class we focus specifically on runtime semantics, and build an interpreter for a programming language very similar to JavaScript or Python.

Implementing a programing language would also make your practical usage level of other programming languages more professional.

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Automata Theory: building a RegExp machine

Course overview

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State machines — the fundamental concept used today in many practical applications, starting from UI programming in React, automated reply systems, lexical analysis in parsers and formal language theory — i.e. the RegExp machines, — and up to real life use cases, such as simple traffic lights, vending machines, and others.

The state machines are backed by the larger theoretical field of computer science known as Theory of Computation, and also by its direct theoretical model — the Automata Theory.

In this class we study the Automata Theory on the practical example of implementing a Regular Expressions machine.

See also: Essentials of Garbage Collectors class devoted to automatic memory management.

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Garbage Collection Algorithms

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Course overview

Memory leaks and dangling pointers are the main issues of the manual memory management. You delete a parent node in a linked list, forgetting to delete all its children first — and your memory is leaking. You delete an object chain in correct order — but suddenly your program crashes since you forgot about second owner of this resource, which now tries to dereference a null-pointer.

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