Project Overview

As part of my studies and personal development, I created a lexical analyzer and parser in .NET. This project helped me dive deeper into how compilers process programming languages at the syntactic level. By building a lexer and parser from scratch, I gained a better understanding of how source code gets broken down into tokens and how syntax trees are constructed to validate grammar rules. This post will walk through the project’s key components, and lessons learned.

In this project, I implemented a lexer and parser for a simple programming language. The lexer breaks down the source code into tokens, while the parser checks the syntax and builds a syntax tree. The lexer identifies keywords, identifiers, numbers, operators, and symbols. The parser uses a recursive descent approach to validate the syntax and create a tree structure representing the code. The project is designed to be extensible, allowing for future grammar expansions and additional features.

What is Lexical Analysis?

Lexical analysis is the first phase of a compiler. It reads the source code character by character, groups them into meaningful sequences (called lexemes), and categorizes them into tokens (like keywords, identifiers, symbols, etc.) these are all identified by the person creating the compiler hence why languages may have different keywords, identifiers or even symbols.

In my project, the lexer scans input strings from a file called "test1.txt" (There are 5 text.txt files that were required to be tested with) and generates in a command line when you enter a specific spot in the parser as well as the value when entering it .

For example, the string "int x = 5;" would be tokenized into:

• Keyword: int
• Identifier: x
• Operator: =
• Number: 5
• Symbol: ;

How Parsing Works

Parsing takes the sequence of tokens and organizes them into a syntax tree based on a defined grammar. This step checks if the source code follows the language’s rules and structures.

I implemented a recursive descent parser in C# using .NET. Each function in the parser corresponds to a non-terminal in the grammar, making it intuitive and easy to debug.

The parser also provides clear error messages, indicating the any syntax errors..

Technologies Used

• Language: C#
• Framework: .NET 8.0
• Development Environment: Visual Studio 2022

Key Features

• Lexical analyzer that recognizes identifiers, numbers, operators, and reserved keywords.
• Recursive descent parser that builds and validates syntax trees.
• Clear error reporting.
• Extensible design for future grammar expansions.
• Test files to validate the lexer and parser against various input scenarios.
• Command line interface for easy interaction and testing.

Lessons Learned

Building a lexer and parser from scratch taught me a lot about how programming languages are designed and interpreted. It also strengthened my skills in recursion, data structures (like trees and lists), and algorithmic thinking.

Every programming language has its own syntax and semantics, and understanding these differences is crucial for effective language design. I learned how to identify the core components of a language and how to implement them in code.

Conclusion

This project was a rewarding experience that deepened my understanding of compilers and programming languages. I encourage anyone interested in language design or compiler construction to try building a lexer and parser.