Introduction

Mag is an optionally typed, object-oriented programming language with patterns, classes and multimethods.

A simple example showing some code for a (very inefficent) recursive Fibonacci function can be defined like this using multimethods:

def fib(0) 0
def fib(1) 1
def fib(n Int) fib(n - 2) + fib(n - 1)

This defines the same fib method multiple times, which is okay since the method signatures differ between the implementations, replacing the need for a separate conditional check inside the function.

More documentation will follow in the future, and make sure to check out Robert Nystrom's blog posts about Magpie for further information. His posts serve as the foundational inspiration for this project.

Features

Extensibility

The parser and compiler structures use a modular, trait-based architecture with structs which handle the actual translation, which means that the actual interpretation of semantics is dynamic and may be extended by Mag code at runtime using a special parselet, a concept which could even be extended to compilation and execution to provide a very flexible programming environment.

Pattern Matching

Patterns are not just used in Rust-like match expresions, they are actually dispersed throughout the whole language fabric of mag and magc, where it is used for method arguments, variable destructuring, error reporting and many other useful things.

Getting Started

Enough fuzzy talk, let's start a REPL from the command line to get this project up and running.

Run the following command from the project root to start the REPL:

cargo run

Try to enter simple arithmetic expressions like 1 + 2 or 3 * 7 to see the execution pipeline in action. Expect a lot of bugs for now!

Credits

Mag is based on the Magpie language by Robert Nystrom, who is a language engineer at Google with a blog and a lot of amazing ideas. His various blog posts are what started and inspired this project, and I plan on continuing his legacy even if the original codebase ceases further development.

However, since there are a few syntactical differences to the original Magpie language, the two languages are source-incompatible and thus have different names. In particular, Bob's implementation substitutes the dot commonly used for calling methods on objects with a space (usually a meaningless character), which I find rather unintuitive, especially for new programmers.