CLox

Another implementation of ByteCode Interpreter for Lox in C, with tons of new features.

Introduction

CLox is an implementation of the programming language Lox in C. Currently it uses naive single-pass compiler, and only runtime optimization is performed. In future it is planned to have a multi-pass compiler with AST and compiler optimization. The initial version of CLox has only features already present in the original Lox reference implementation, but subsequent versions will continue to add new features to make it a powerful language. This is an experiment on the design and implementation of language features, before I start to implement the backend of my own programming language Mysidia. Stay tuned.

The original version of Lox programming language can be found at Bob Nystrom's repository: https://github.com/munificent/craftinginterpreters

Features

Original Features

• Stacked based bytecode VM with the basic OPCode support.
• On-demand Scanner, Pratt Parser and Single-Pass Compiler.
• Uniform runtime representation for Lox Value.
• Basic Unary and Binary Expression/Operators.
• Support for global and local variables.
• If..Else and Switch condition Statement.
• While Loop, Break and Continue Statement.
• Functions and Closures with automatic upvalue capture.
• Mark and sweep Garbage Collector.
• Classes, Objects, Methods and this keyword.
• Single Inheritance and super keyword.
• Performance improvement with Faster hash table probing and Nan-Boxing.

New Features

• Framework for creating native functions, methods and classes.
• Array/Dictionary Literals and square bracket notation for array/dictionary access.
• New Operators: Modulo(%), Range(..) and Nil Handling(?., ??, ?:).
• Operator overloading to allow operators to be treated as method calls, thus can be used by user defined classes.
• Variadic Functions, Anonymous Functions(local return) and Lambda Expressions(nonlocal return).
• Object root class for every class in Lox, everything is an object, and every object has a class.
• Object ID and generic object map which enable inheritance for special build-in classes such as String and Array.
• Class methods in class declaration using class keyword, and trait declaration using trait keyword.
• Anonymous classes/traits similar to anonymous functions/lambda.
• Namespace as CLox's module system, allowing importing namespace and aliasing of imported classes, traits and functions.
• CLox Standard Library for packages lang, util, collection, io and net in bullt-in namespace clox.std.
• Raise exception with throw keyword, and exception handling with try/catch/finally statement.
• Interceptor methods which are invoked automatically when getting/setting properties, invoking methods or throwing exceptions.
• Generator functions/methods which can yield control back to the caller and resume at a later point of execution.
• Promise API with event loop provided by libuv library for non-blocking IO operations.
• Introduction of async and await keywords, which allows C#/JS style of concurrency.
• Customized Runtime configuration for CLox using clox.ini.
• Allow loading lox source files in lox script and another lox source file with require keyword.
• Cross-platform build with Cmake and package manager with vcpkg.

Enhanced or Removed Features

• VM is no longer a global variable, allowing CLox VM to be embedded in other host applications.
• Parser is extended with look-ahead capability, with field next storing the next token.
• Print statement removed, use native function print and println instead.
• Initializer method is renamed from init to __init__ as an interceptor method.
• Separated integer values(Int) and floating point(Float) values from Number.
• Improved string concatenation, addition of string interpolation and UTF-8 strings.
• C style For Loop replaced with Python/Kotlin style for-in Loop.
• Global variables are scoped within the file it is declared, effectively becoming module variable.
• Function/Method parameters become immutable by default, but may be mutable with var keyword.
• Built-in and user defined classes/functions become immutable, and cannot be accidentally overwritten.
• Fix reentrancy problem with CLox, calling Lox closures in C API becomes possible.
• Most runtime errors in VM interpreter loop replaced with Exceptions that can be caught at runtime.
• Inline caching for VM optimization, as well as implementation of Shape(Hidden Class) for better instance variable representation.

Roadmap

CLox v1.1.0

• VM is no longer a global variable, allowing CLox VM to be embedded in other host applications.
• Full fledged Framework for writing Native functions, methods and classes.
• Root class Object which serves as superclass of every class.
• Remove print statement and replace it by print and println native functions.

CLox v1.2.0

• Improved object model - Everything is an object, and every object has a class, including nil, true, false, number, string, function, class etc.
• CLox Standard Library for package lang and util, which contains classes such as Boolean, Number, String, Array, Dictionary, DateTime, etc.
• Allow customized runtime configurations for CLox at startup with clox.ini
• Split the Number class into Int and Float classes, which will distinguish between integers and floating numbers.

CLox v1.3.0

• Array/Dictionary Literals and square bracket(subscript) notation for array/dictionary access.
• Variadic Functions, Anonymous Functions(local return) and Lambda Expressions(nonlocal return).
• Replace C style for loop by Kotlin style for-in loop for collection types.
• Clox Standard Library improvement: New package collection and io.

CLox 1.4.0

• Immutable variable declaration with val keyword.
• Function/Method parameters become immutable by default, but may be mutable with var keyword.
• Built-in and user defined classes/functions become be immutable, and cannot be accidentally overwritten.
• New class Range in package collection, as well as range operator(..) for range literals.

CLox 1.5.0

• Refined object model which is similar to Smalltalk's metaclass system.
• Class methods in class declaration, and trait keyword for trait declaration.
• Allow loading lox source files in lox script and another lox source file with require keyword.
• Anonymous classes/traits similar to anonymous functions/lambda.

CLox 1.6.0

• Namespace as CLox's module system, allowing importing namespace and aliasing of imported classes, traits and functions.
• Refactor the existing standard library with namespaces(in clox.std parent package), add new package clox.std.net.
• Fix reentrancy problem with CLox, calling Lox closures from within C API becomes possible.
• Cross-platform build with Cmake, as well as package manager with vcpkg(windows only).

CLox 1.7.0

• Raise exception with throw keyword, and exception handling with try/catch/finally statement.
• Improved CLox standard library with addition of class Exception and various exception subclasses.
• Addition of nil handling operators: Optional chaining operator(?.), Nil coalescing operator(??), and Elvis operator(?:).
• Inline caching for VM optimization, as well as implementation of Shape(Hidden Class) for better instance variable representation.

CLox 1.8.0

• Operator overloading to allow operators to be treated as method calls, thus can be used by user defined classes.
• Improved string concatenation, addition of string interpolation and UTF-8 strings.
• Interceptor methods which are invoked automatically when getting/setting properties, invoking methods or throwing exceptions.
• Object ID and generic object map which enable inheritance for special build-in classes such as String and Array.

CLox 1.9.0(current version)

• Generator functions/methods which can yield control back to the caller and resume at a later point of execution.
• Add class Promise to the standard library(clox.std.util), which uses libuv to handle async tasks that completes in future.
• Introduction of async and await keywords, which allows C#/JS style of concurrency.
• Refactoring package clox.std.io and clox.std.net to use async non-blocking calls.

CLox 2.0.0(next version)

• Multi-pass compiler with abstract syntax tree, semantic analyzer, symbol table, type checker, and generation of bytecode by walking AST.
• Optional static typing support for function/method parameters and return values, types only exist at compile time and are erased at runtime.
• Semicolon inference as well as basic type inference for immutable local/global variables.
• Replace the naive mark and sweep GC with a generational GC which has multiple regions for objects of various 'ages'.

CLox 2.1.0

• Enhanced type system with basic support for generics/parametric polymorphism.
• Capability of saving bytecode into disk as .loxo file, which can be loaded later for faster compilation.
• Allow declaration of object properties outside of class initializer, which also enables optional static typing.
• Trailing closure similar to Kotlin and Swift which allows last lambda argument to be placed outside of parenthesis.

CLox 2.2.0

• Additional type system enhancement for union types, with | operator on types such as String | Number.
• type keyword used as declaration of type alias, useful for complex generic types and union types.
• Object literal syntax similar to Javascript which can be good for configuration objects.
• Redesign of Iterator/Enumerator API for ease of use and implementation of iterable types.

CLox 2.3.0

• Support for structural pattern matching using match keyword, remove switch statement as it has been superceded.
• Refine type system to be non-nullable by default for type declaration, as well as variance for method parameter/return types.
• Allow casting variables to a static type using as keyword, this will pass compile time typecheck and insert runtime typecheck.
• Foreign function interface(FFI) as a way to write CLox libraries in C and load in lox script.

CLox 2.4.0

• Refine if and match as expressions, with the value produced being the last expression/statement of the expression body.
• Add new package clox.std.text which handles text processing for MIME types such as json and xml.
• Implement a profiler which can identify the "Hotspots" of the program and how long they execute.
• Experimental Thread API, initial step towards multi-threading for Lox VM.

Build and Run Clox

Windows(with git, cmake and vcpkg, need to replace [$VCPKG_PATH] with installation path of vcpkg)

git clone -b master https://github.com/HallofFamer/CLox.git
cd CLox
cmake -DCMAKE_TOOLCHAIN_FILE:STRING="[$VCPKG_PATH]/scripts/buildsystems/vcpkg.cmake" -S . -B ./build
cmake --build ./build --config Release
./x64/Release/CLox

Linux(with git, cmake, curl and libuv, need to install one of the libcurl4-dev and libuv1.dev packages)

git clone -b master https://github.com/HallofFamer/CLox.git
cd CLox
mkdir build
cmake -S . -B ./build
cmake --build ./build --config Release
./build/CLox

Docker(linux, need to replace [$LinuxDockerfile] by actual docker file name, ie. UbuntuDockerfile)

git clone -b master https://github.com/HallofFamer/CLox.git
cd CLox
docker build -t clox:linux -f Docker/[$LinuxDockerfile] .
docker run -w /CLox-1.9.0/CLox -i -t clox:linux

Credits & Special Thanks

Below is the attribution list for my CLox's design and implementation, please contact me if anything else is missing. This does not include 3rd-party libraries whose copyrights are already present in the header files.

• Robert Nystrom: For the original Lox language specification and source code that this project is based on.
• Smalltalk-lang: For the inspiration of object and class model.
• Ruby-lang: For the inspiration of generic ID map/table which allows inheritance and properties on any objects.
• Javascript-lang: For the inspiration of object shape/hidden-class.
• Wren-lang: For the inspiration of UTF-8 string implementation as well as dynamic array macros.
• Michael Malone(cometlang): For the inspiration of exception and try/catch/finally statement.
• RevengerWizard(teascript): For the inspiration of reentrancy in Lox language.

FAQ

What is the purpose of this project?

CLox is an implementation of Lox language with bytecode VM instead of treewalk interpreter. It is the last experiment on feature implementations, before I will begin writing my own programming language Mysidia in C.

What will happen to KtLox?

Nothing, KtLox development is on hold until I can figure out a way to generate JVM bytecode instead of running the interpreter by walking down the AST. Treewalk interpreters are way too slow to be practical without JIT.