Introduction

magc is a compiler library that translates Mag source code into Strontium bytecode. It combines a lexer, a Pratt parser, and a modular code generation stage into a single pipeline.

What works today

• Arithmetic and comparison: +, -, *, /, ^, %, ==, !=, <, <=, >, >=
• Multimethods: define multiple implementations of the same method with different signatures; the runtime dispatches based on argument value or type
• Type-based dispatch: def foo(n Int) and def foo(n String) coexist correctly — type annotations on parameters generate type-matching dispatch patterns
• Conditionals: if <cond> then <expr> else <expr> end
• Variables: var x = <expr> at the top level (stored in named registers) or inside method bodies (stored in stack-frame locals)
• Return: return <expr> exits a method early
• Literals: integers, floats, strings, booleans

Architecture

The compiler uses a compilelet pattern: a HashMap<String, &dyn Compilelet> routes each expression type to the piece of code that generates bytecode for it. Adding support for a new expression kind means adding a new Compilelet implementation and registering it — no large match arms to touch.

Method bodies are compiled separately from the main program, then linked together in link_bytecode. Conditional branches use compile-time pseudo-instructions (LabelTarget, JumpToLabel, JumpCToLabel) that are resolved to absolute byte addresses during linking.

Credits

Mag is based on the Magpie language by Robert Nystrom. His blog posts are the foundational inspiration for this project.