Linear base

Linear base is a standard library for developing applications with linear types. It is named linear-base to be an analog to the original base package that ships with GHC.

The purpose of linear-base is to provide the minimal facilities you need to write practical Linear Haskell code, i.e., Haskell code that uses the -XLinearTypes language extension.

Motivation

Why do you need linear-base to write linear projects?

1. Data types, functions and classes in base are not linear types aware. For instance, if n is a linearly-bound Int, the RHS of a definition cannot write n + 1 — this will not type check. We need linear variants of Num, Functors, Monads, ($), etc.

2. This library exports new abstractions that leverage linear types for resource safety or performance. For example, there are new APIs for file and socket I/O as well as for safe in-place mutation of arrays.

Getting started

-XLinearTypes is released with GHC 9, and linear-base is released on Hackage.

All source files with linear types need a language extension pragma at the top:

{-# LANGUAGE LinearTypes #-}

User Guide

If you already know what -XLinearTypes does and what the linear arrow a %1-> b means, then read the User Guide and explore the examples/ folder to know how to use linear-base.

Learning about -XLinearTypes

If you’re a Haskeller who hasn’t written any Linear Haskell code, don’t fear! There are plenty of excellent resources and examples to help you.

Tutorials and examples

• See the examples/ folder.
• Linear examples on watertight 3D models

Reading material

• There is a wiki page.
• Key Blog posts
  • Predictable performance (the first blog post from Tweag on this)
  • IO State Transitions
  • Streaming
  • See here for all of Tweag’s blog posts on linear types.
• Here is the paper behind -XLinearTypes.

Talks

• Practical Linearity in a higher-order polymorphic language – POPL 2018
• Practical Linearity in a higher-order polymorphic language – Curry on 2018
• Practical Linearity in a higher-order polymorphic language – Haskell Exchange 2018
• Implementing Linear Haskell
• In-place array update with linear types – ZuriHac 2020

Contributing

Linear base is maintained by Tweag.

To contribute please see the Design Document for instructions and advice on making pull requests.

Licence

See the Licence file.

Copyright © Tweag Holding and its affiliates.