Mag

Mag is an optionally typed, expression-oriented programming language with multimethods and pattern matching.

Quick start

cargo run          # start the REPL
cargo run -- run <file.mag>   # run a source file
cargo run -- --debug          # REPL with instruction/register output

Language overview

Arithmetic and comparisons

>>> 1 + 2
3
>>> 10 / 4
2.5
>>> 3 > 2
true

Multimethods

Define the same method name multiple times with different signatures. The runtime picks the right one based on the argument:

>>> def fib(0) 0
>>> def fib(1) 1
>>> def fib(n Int) fib(n - 1) + fib(n - 2)
>>> fib(10)
55

Type-based dispatch

Type annotations on parameters create distinct dispatch entries:

>>> def double(n Int) n * 2
>>> def double(n String) n + n
>>> double(5)
10
>>> double("hi")
hihi

Conditionals

>>> if 3 > 2 then print("yes") else print("no") end
yes

Variables

>>> var x = 42
>>> x
42

Inside a method body, var binds a local variable:

>>> def greet(name String)
...   var msg = "hello " + name
...   msg
... end
>>> greet("world")
hello world

Early return

>>> def abs(n Int)
...   if n < 0 then return 0 - n end
...   n
... end
>>> abs(-5)
5

Credits

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

License

Licensed under the MIT license.