Gradualizer: A Gradual Type System for Erlang

A type checker for Erlang

The idea

Gradualizer aims to integrate well into existing Erlang code bases in a non intrusive way. It does so by

• having a type system that is based on the principles of Gradual Typing

• using the existing type specs syntax in Erlang.

• allowing for granular opt-in of type checking. Without any type specs, no static typing happens.

  When type specs are added the program is checked against these specs statically. The more type specs, the more static typing.

Usage

To run Gradualizer from the command line

Compile the project as an escript. Then use it to check beam files or erl files. Use the -h option for help.

make escript

bin/gradualizer [ OPTIONS ] [ FILES TO CHECK ]

To run Gradualizer from the Erlang shell

Launch the interactive prompt with all the relevant modules in the path. Then, use the functions in the gradualizer module.

make shell

1> gradualizer:type_check_file("path/to/some_file.erl").

To run Gradualizer from rebar3

There is a rebar3 plugin included. See examples/rebar3/README.md.

To use Gradualizer with Elixir / Mix

Please check out Gradient, the Elixir frontend for Gradualizer. It provides a Mix task to use in your project.

Prerequisites

The Gradualizer requires at least OTP 21 and is built using plain OTP functionality and a self-contained Makefile; alternetively using rebar3. It can also be built using Mix if used as a dependency.

Status

The Gradualizer is close to a beta release. Most of the language constructs and data types are handled, although there are things that don't work yet.

That being said, pull requests are most welcome!

A work-in-progress manual is located on the wiki.

For a non-exhaustive list of known problems, see test/known_problems/. Additionally, these are things which need fixing:

• Support for intersection types
• Support for subtype polymorphism