C Recursive Descent Parser

Static Analysis

A project assigned to illustrate the complexity of writing an efficient compiler and intermediate representation code generator.

Thumbnail for the recursive descent parser project.

The Journey

Writing a recursive descent parser in C can be a remarkably educational experience, especially for someone transitioning from a C++ background. Unlike C++, C requires more meticulous memory management and a different approach to data structures, like strings and hash tables. Here is an exploration of that learning journey, touching on the key concepts you mentioned.

The Shift from C++ to C

C++ offers a high level of abstraction, especially with its Standard Template Library (STL). Moving from C++ to C, one must adapt to a lower-level programming paradigm. Strings, which are first-class citizens in C++, are replaced with char* in C, requiring manual management. This means allocating memory for strings with malloc, handling their own deallocation with free, and being careful with buffer overflows and memory leaks. The lack of built-in string operations in C means that tasks like concatenation, comparison, and searching require custom functions. This can be challenging but also enlightening, as it necessitates a deeper understanding of how data is represented and manipulated at a fundamental level.

Grammars and Recursive Descent Parsers

Grammars are the foundation of language processing. They define the syntax of a language in a set of rules, which the parser uses to recognize whether a sequence of tokens conforms to the language. Recursive descent parsers, which are a type of top-down parser, implement these grammar rules as a set of recursive functions. Writing a recursive descent parser in C is a hands-on way to understand the mechanics of parsing and the structure of languages.

Static Analysis and Intermediate Representations

Static analysis involves examining code without executing it. Part of this process is to convert code into an intermediate representation (IR) that abstracts away some of the details of the source language but retains its computational properties. Implementing IR can teach you a lot about the computational semantics of programming languages and the design of compilers and interpreters.

Symbol Tables and Hash Tables

In compiler design, symbol tables are crucial for keeping track of identifiers and their attributes. Implementing a symbol table from scratch in C often leads to choosing a hash table for its efficiency in look-up operations. Designing a hash table involves understanding hashing functions, collision resolution strategies, and dynamic resizing, which are fundamental concepts in computer science.

Register Allocation Simulation

Simulating register allocation as part of the IR process involves assigning variables to a limited number of registers. This is a complex problem in compiler design, often involving graph coloring algorithms to handle live variable analysis and spill code generation. Implementing this in C requires careful data structure management and algorithmic design.

Project Description

The parser project described presents a real-world application of these concepts. It requires a lexer to tokenize the input, a parser to analyze the syntax, and a symbol table to track identifiers, with a suggestion to implement the symbol table as a hash table for efficiency. The project’s constraints, such as handling comments, multi-line statements, and reporting errors, add layers of complexity that simulate the challenges faced in professional compiler construction.


This journey of implementing a parser and an IR with register allocation simulation in C, especially coming from a C++ background, is a deep dive into the fundamentals of programming languages and compilers. It’s a challenging but rewarding experience that hones problem-solving skills and deepens one’s understanding of both high-level and low-level programming concepts.

To learn more about this project, check out the GitHub Repo