Lox

This repo contains two implementations of the Lox language from Crafting Interpreters.

The first implementation, Pylox, is a Python port of the tree-walk interpreter, Jlox, from part two of the book.

The second, Clox, is the C implementation of the bytecode VM from part three.

This repo also contains a shared test runner for testing the two Lox implementations.

Pylox

Pylox is a port of Jlox to Python. The source code is in the python directory.

The functionality of Pylox mostly lines up with Jlox, but there are a couple of key differences in the implementation (apart from being written in Python):

1. I've used Lark for parsing in place of implementing the lexer and parser described in the book. I chose this approach out of interest in learning more about parser generators.
2. I've skipped using code to generate the AST classes. This is because the AST implemenation using Python's Data Classes isn't much more verbose than the code to generate them would have been.

Running and Developing

To start the REPL, run:

$ ./pylox

You can also specify a Lox file to run instead:

$ ./pylox my_file.lox

To run all tests for Pylox:

$ make test_pylox

To check types with Mypy:

$ make typecheck_pylox

Clox

⚠️ WIP - this implementation of Clox is not complete yet and doesn't have all of the features of Lox.

Clox is lifted directly from the code in the book (apart from some minor differences in formatting). The source code is in the c directory.

Running and Developing

To build the Clox interpreter, run:

$ make clox

After building, you can start the REPL:

$ ./clox

You can also specify a Lox file to run instead:

$ ./clox my_file.lox

To run all tests for Clox:

$ make test_clox

Test Runner

The Crafting Interpreters text omits tests, but the Github repo for the book includes a full test suite and custom test runner.

I've included a test runner in this repo (based on the implementation in the book's Github repo) and copied over the test files. The source code is in the tooling directory.

Usage

The Makefile contains convenience targets for running all tests for either Pylox or Clox, but you can also call the test runner directly via Poetry:

$ poetry run test interpreter_path test_pattern

Usage:

test [-h] interpreter_path test_pattern [test_pattern ...]

positional arguments:
  interpreter_path  path to the interpreter executable
  test_pattern      pattern for test(s) to run (supports glob syntax)

optional arguments:
  -h, --help        show this help message and exit

Developing

To run all tests that test the test runner itself:

$ make test_tooling

To check types with Mypy:

$ make typecheck_tooling