Veil

Veil is planned to be a gradually typed, and multi-paradigm programming language supports both object-oriented & functional programming.

This project serves as an exercise on C++ and a way to learn how a programming language with a runtime could work under the hood. My current goal of this project is to complete the runtime, then implement a simple compiler in whatever language I feel comfortable in (Python or Java), and re-implement the compiler in Veil language as a proof of principle.

Ofcoz there is a much harder quest to implement a just-in-time compiler targeting branches (or I should say it is a trace JIT), which based on a exposed compiler interface in the runtime, so that we can support any type of compiler backend. The JIT will most likely be built with a language with memory-safety, maybe in Rust or even in Veil itself...

The Fabric runtime

The Fabric runtime is for running the Fabric bytecode generated by a compiler from the Veil code, and is implemented by C++, is designed from the ground up to support multi-threaded environment. And to be fully embeddable into other C++ projects, there will be no globally defined states.

To keep the code structure as clear as possible, I planned to use the fully power of OOP provided by C++, and leave all rooms of performance enhancements & optimizations to the JIT compiler.

Future prospects includes adding a JIT compiler, rewrite part of the VM service code base using Veil... etc.

Structure Diagram

Naming conventions

• Namespaces: lowercase single word.
• Class: CamelCase
• Methods: snake_case, with single words for public action methods; multi-word for private methods or methods that are not supposed to be used or exposed outside of class scope.
• Variables: snake_case and better to be verbose with at least one _ to avoid collision with comments.
• Attributes: snake_case and better to be verbose with at least one _ to avoid collision with comments.
• Constants: ALL_CAPS and use keyword const but not macros.
• Structs: CamelCase as a multi-part wrapper; snake_case_t as a primitive capsule.
• Macros: CamelCase
• Labels: CamelCase

Code structure

• Integer like types in the code should use the typedef defined types in fabric/src/typedefs.hpp.
• All error code of the VM runtime should be type uint32 and reside in a namespace specific for their usage, and defined only in fabric/src/errors.hpp.
• Except for special header files, all code under a subdirectory of fabric/src should be defined in a specific namespace.
• All native or OS related platform specific code of a subdirectory of fabric/src should all be placed within os.hpp & os.cpp, and reside in the namespace of veil::os.
• Platform specific methods under the namespace of veil::os should all contain an error return parameter: some_native_method(..., uint32 &error).
• All class that will be part of the VM structure should either be a subtype of HeapObject , Arenaobject or ValueObject.

Implementation roadmap

1. Implement utility structures.

   • ArrayList

2. Implement the memory management.

   • Implement the core modules.
     • Management
     • Pointer
     • Allocator
     • Interface of Algorithm
   • Implement the standard management algorithm.

3. Implement all encapsulations of OS specific threading primitives.

   • Thread
     • Implement the basic encapsulations.
     • Able to execute a VMService.
     • Priority settings for all OS threads.
   • Mutex
   • ConditionVariable
   • Atomics
   • Add handling for spurious wakeup of ConditionVariable.

4. Implement VM specific threading primitives.

   • A low object memory footprint queue-based thread synchronization primitive OrderedQueue.

5. Exchange all existing usage of <atomic> and <condition_variable> to the encapsulations.

   • OrderedQueue

6. Implement the thread management.

   • All management's functionality should be protected by a mutex.
     • This is a legacy requirement, since the management (aka. scheduler) is running a single threaded loop to process all thread controls.
   • Service spawning & termination using the underlying thread.
   • Thread sleep & wake.
   • Thread interrupt.
   • Thread pause & resume.
   • VMService joining with another VMService.
   • Scheduler termination.

7. Implement the Veil execution environment.

   • Design the Veil VM bytecode specifications.
   • Implement the Veil bytecode interpreter.
   • Implement VeilThread.