ghc-plugin-non-empty: GHC Plugin for non-empty lists

[ compiler-plugin, ghc, library, mpl ] [ Propose Tags ]

GHC Plugin for compile-time transformation of list literals to NonEmpty lists.

{-# OPTIONS_GHC -fplugin=GhcPluginNonEmpty #-}

import Data.List.NonEmpty (NonEmpty)

portsToListen :: NonEmpty Int
portsToListen = [8000, 8080, 8081]

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Dependencies base (>=4.16 && <4.17), ghc (>=9.2 && <9.3), syb (>=0.7 && <0.8) [details]
License MPL-2.0
Copyright 2022 Dmitrii Kovanikov
Author Dmitrii Kovanikov
Maintainer Dmitrii Kovanikov <>
Category GHC, Compiler Plugin
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Source repo head: git clone
Uploaded by shersh at 2022-07-17T15:23:36Z
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Readme for ghc-plugin-non-empty-

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GitHub CI Hackage MPL-2.0 license

GHC Compiler Plugin for automatically converting list literals to the NonEmpty type from the Data.List.NonEmpty module in base.

This plugin checks statically defined list literals and transforms them into NonEmpty lists during compile time. In other words, it provides compile-time guarantees for non-emptiness checks and allows the following expression to type-check:

portsToListen :: NonEmpty Int
portsToListen = [8000, 8080, 8081]

Compare to usage without the plugin:

portsToListen :: NonEmpty Int
portsToListen = 8000 :| [8080, 8081]

ℹ️ DISCLAIMER: ghc-plugin-non-empty is developed and maintained in free time by volunteers. The development may continue for decades or may stop tomorrow. You can use GitHub Sponsorship to support the development of this project.

How to use?

ghc-plugin-non-empty is compatible with the following GHC versions — supported versions

In order to start using ghc-plugin-non-empty in your project, you'll need to set it up with these steps:

  1. Add the dependency on ghc-plugin-non-empty in your project's .cabal file. For this, you should modify the build-depends section according to the below section:

      , base                 ^>= LATEST_SUPPORTED_BASE
      , ghc-plugin-non-empty ^>= LATEST_VERSION
  2. To use this package, refer to the below example.

    {-# OPTIONS_GHC -fplugin=GhcPluginNonEmpty #-}
    module Main (main) where
    import Data.List.NonEmpty (NonEmpty)
    exampleList :: NonEmpty Int
    exampleList = [100, 5, 74]
    main :: IO ()
    main = print exampleList

For contributors

Check for contributing guidelines.

To build the project and run the tests, use cabal:

cabal build all
cabal test --enable-tests --test-show-details=direct