PyLox

A Python implementation of the Lox programming language.

About Lox

Lox is a dynamically-typed, high-level scripting language designed by Robert Nystrom for his book Crafting Interpreters. It features C-style syntax with first-class functions, closures, and object-oriented programming support.

Features

This implementation includes:

• Lexical Analysis: Tokenization of Lox source code
• Parsing: Recursive descent parser with precedence handling
• AST Generation: Abstract Syntax Tree representation
• Semantic Analysis: Variable resolution and scope checking
• Interpretation: Tree-walk interpreter with runtime evaluation
• Data Types: Numbers, strings, booleans, nil
• Variables: Declaration and assignment
• Functions: First-class functions with closures
• Classes: Object-oriented programming with inheritance
• Control Flow: if/else, while, for loops, break, return
• Native Functions: Built-in functions like clock()

Example Usage

// src.lox
fun fibonacci(n) {
  if (n <= 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

for (var i = 0; i < 10; i = i + 1) {
  print fibonacci(i);
}

Run with:

python3 -m app.main run src.lox

Project Structure

The interpreter follows a traditional compiler pipeline architecture:

Frontend (Lexing & Parsing)

• scanner.py - Tokenizes source code into tokens
• token.py - Token data structure and types
• parser.py - Recursive descent parser producing AST
• expr.py - Expression AST node definitions
• stmt.py - Statement AST node definitions

Semantic Analysis

• resolver.py - Static variable resolution, scope checking etc.

Runtime (Interpreter)

• interpreter.py - Tree-walk interpreter executing AST
• environment.py - Scope and variable binding management
• lox_callable.py - Interface for callable objects
• lox_function.py - User-defined function implementation
• lox_class.py - Class and inheritance support
• lox_instance.py - Object instance representation
• native_fns.py - Built-in standard library functions

Utilities

• main.py - Entry point and command-line interface
• AstPrinter.py - Debug AST visualization
• errors.py - Error handling and reporting
• runtime_error.py - Runtime exception types
• return_error.py - Function return control flow
• break_error.py - Loop break control flow
• utils.py - Helper functions