Moggi

A statically typed, purely functional, strictly evaluated programming language that compiles to PHP, JVM and .NET. One .mog source — algebraic data types, GADT's, pattern matching, type classes, explicit-effect IO — becomes a .phar, a .jar or a .dll or native executable.

data Shape = Circle Double | Rect Double Double
  deriving (Show, Eq)

area :: Shape -> Double
area s = case s of
  Circle r -> 3.141592653589793 * r * r
  Rect w h -> w * h

main :: IO ()
main = do
  putStrLn (show (area (Circle 1.0)))
  putStrLn (show (map area [Rect 2.0 3.0, Circle 1.0]))

3.141592653589793
[6.0,3.141592653589793]

Quick start

Download the distribution for your platform from the releases page and unpack it — it is a complete installation, and running it needs nothing else:

tar -xzf moggi-0.1.0-linux-x86_64.tar.gz   # or the .zip on Windows
cd moggi
./bin/moggi version

Write a program:

-- hello.mog
main = putStrLn "Hello, world!"

./bin/moggi run hello.mog                    # compile and run it
./bin/moggi run examples/factorial           # or run one of the shipped examples
./bin/moggi repl                             # try expressions interactively

Build an artifact you can deploy on its own:

./bin/moggi compile hello.mog                # -> hello.phar
php hello.phar

./bin/moggi compile hello.mog --backend jvm  # -> hello.jar
java -jar hello.jar

./bin/moggi compile hello.mog --backend dotnet   # -> hello.dll
dotnet hello.dll

Which distributions bundle which runtime, and how to use a checkout instead:

Without -o the artifact is named after the entry source file; pass a full file name to choose your own (-o app.phar, -o app.jar, -o app.dll).

Useful flags: --unpacked keeps the generated tree instead of packaging it, --native builds a native executable (GraalVM native-image, .NET PublishAot), and --tokens/--ast/--typed-ast/--ir/--opt-ir dump the compiler's intermediate stages. --help lists everything.

Documentation

Read them in order, or pick the question you have.

Full index: docs/README.md, which also lists the compiler's own documentation.

Moggi is alpha: the language and standard library are still being completed, and the three backends are kept byte-for-byte identical by a differential test.

Development

Working on the compiler itself. Moggi the language needs none of this.

Environment

The flake pins every toolchain the compiler and test suite use — PHP 8.5, a JDK 21 (GraalVM, so native-image is there too), the .NET 8 SDK — and puts moggi and runtest on your PATH:

nix develop

Nix is for development, on Linux and macOS. On Windows, or without Nix, the same two commands work directly and use whatever toolchains you have installed:

php moggi.php version       # the compiler (what the `moggi` wrapper runs)
php test.php                # the test suite (what the `runtest` wrapper runs)

php moggi.php --help documents the compiler's commands; php test.php --help documents the suite's selection and reporting flags.

Repository layout

The editor extension is a separate project with its own release: moggi-lang/moggi-vscode-plugin.

Tests

runtest                            # the default backend (php)
runtest --backend jvm              # another backend
runtest --backend all --native     # every backend, plus native builds
runtest --group semantics          # one group; a path below a group narrows further
runtest --list                     # what would run

The suite runs the compiler end to end: it compiles cases and compares generated code, IR, diagnostics and program output against goldens, on each backend they declare. docs/development/testing.md describes the layout, what a case looks like, and how goldens are updated.

More

AI disclaimer

Parts of this project — code, tests and documentation — were generated by large language models and reviewed by a human.