# extensions ![Logo](https://user-images.githubusercontent.com/8126674/80925339-f09a4e80-8d86-11ea-81f4-fd1a6f50cd6b.png) [![GitHub CI](https://github.com/kowainik/extensions/workflows/CI/badge.svg)](https://github.com/kowainik/extensions/actions) [![Hackage](https://img.shields.io/hackage/v/extensions.svg?logo=haskell)](https://hackage.haskell.org/package/extensions) [![MPL-2.0 license](https://img.shields.io/badge/license-MPL--2.0-blue.svg)](LICENSE) Library and CLI tool to parse Haskell `{-# LANGUAGE #-}` extensions in source files, extract `default-extensions` from `.cabal` files and combine together `default-extensions` and per-module extensions. ## Goals The `extensions` library provides a lighweight way to get Haskell LANGUAGE pragmas for Haskell modules. It has the following goals: 1. Be **lightweight**. Dependency footprint is extremely small, and using `extensions` either as a library or as a tool is straightforward. 2. Support both `default-extensions` in **Cabal** and `{-# LANGUAGE #-}` pragmas in **Haskell** modules. 3. Should work on common and real cases. `extensions` strives to support as many valid syntactic constructions as possible, but it may not work on every possible combination of CPP, comments and pragmas, where GHC would work. We encouragle you to [open issue](https://github.com/kowainik/extensions/issues/new) if you encounter any failures when using `extensions`. ## How to use You can use `extensions` either as a library or as a CLI tool. ### Library #### Usage with Cabal `extensions` is compatible with the latest GHC compiler versions starting from `8.8.3`. In order to start using `extensions` in your project, you will need to set it up with the three easy steps: 1. Add the dependency on `extensions` in your project's `.cabal` file. For this, you should modify the `build-depends` section by adding the name of this library. After the adjustment, this section could look like this: ```haskell build-depends: base ^>= 4.14 , extensions ^>= 0.0 ``` 2. In the module where you wish to extract extensions, you should add the import: ```haskell import Extensions (getPackageExtensions) ``` 3. Now you can use the types and functions from the library: ```haskell main :: IO () main = getPackageExtensions "extensions.cabal" >>= print ``` #### Usage with Stack If `extensions` is not available on your current Stackage resolver yet, fear not! You can still use it from Hackage by adding the following to the `extra-deps` section of your `stack.yaml` file: ```yaml extra-deps: - extensions-0.0.0.0 ``` ### CLI tool To use `extensions` as a CLI tool, you need to install it either with Cabal ``` cabal install extensions ``` or Stack ``` stack install extensions ``` The tool can be used to inspect language extensions in your Haskell project. Some common usages of the tool: 1. Get all extensions in all modules, combined with `default-extensions` from the `.cabal` file. ![All extensions](https://user-images.githubusercontent.com/4276606/80870176-b0f73800-8c9c-11ea-8ffc-dda2d4940d1e.png) 2. Get all extensions for a specific module, combined with Cabal extensions. ![Module extensions](https://user-images.githubusercontent.com/4276606/80870175-b05ea180-8c9c-11ea-9f48-cac7ff854b9c.png) 3. Get extensions defined only in a module. ![Only module](https://user-images.githubusercontent.com/4276606/80870173-afc60b00-8c9c-11ea-9d74-cf92ed0c3940.png) ## Alternatives Alternatively, you can extract Haskell Language extensions using the following ways: 1. Using `ghc` as a library. This approach ties you to a specific GHC version and requires more effort to support multiple GHCs. Also, GHC API is more complicated than `extensions` API (especially if you want to handle `CPP`). And even with `CPP` handling from `ghc` you won't be able to get all extensions defined in a module. However, this approach allows you to fully reproduce GHC behaviour. 2. Using `ghc-lib-parser`. Same as the previous approach, but does not tie you to a specific GHC version. However, `ghc-lib-parser` is rather big dependency. 3. Using the `haskell-src-exts` library. This library parses Haskell source files, but it's not actively maintained anymore and doesn't support `CPP`.