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93 lines
2.7 KiB
Markdown
93 lines
2.7 KiB
Markdown
# Ormolu
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[](https://circleci.com/gh/tweag/ormolu/tree/master)
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Ormolu is a formatter for Haskell source code. The project was created with
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the following features in mind:
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* Using GHC's own parser to avoid parsing problems caused by
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[`haskell-src-exts`][haskell-src-exts].
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* Let some whitespace be programmable. The layout of the input
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influence the layout choices in the output. This means that the
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choices between single-line/multi-line layouts in each particular
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situation are made by the user, not by an algorithm. This makes the
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implementation simpler and leaves some control to the user while
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still guaranteeing that the formatted code is stylistically
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consistent.
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* Writing code in such a way so it's easy to modify and maintain. Roughly,
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it means that the project follows the path of [`hindent`][hindent] and is
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very much about printing AST in a particular way.
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* Implementing one “true” formatting style which admits no configuration.
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* That formatting style aims to result in minimal diffs while still
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remaining very close to “conventional” Haskell formatting people use.
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* Idempotency: formatting already formatted code doesn't change it.
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* Be well-tested and robust to the point that it can be used in large
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projects without exposing unfortunate, disappointing bugs here and there.
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## Building
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The easiest way to build the project is with Nix:
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```console
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$ nix-build
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```
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Or with `cabal-install` from the Nix shell:
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```console
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$ nix-shell --run "cabal new-build"
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```
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Alternatively, `stack` could be used with a `stack.yaml` file as follows.
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```console
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$ cat stack.yaml
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resolver: lts-13.19
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packages:
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- '.'
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$ stack build
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```
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## Usage
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The following will print the formatted output to the standard output.
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```console
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$ ormolu Module.hs
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```
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Add `--mode inplace` to replace the contents of the input file with the
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formatted output.
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```console
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$ ormolu --mode inplace Module.hs
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```
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## Running on Hackage
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It's possible to try Ormolu on arbitrary packages from Hackage. For that
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execute:
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```console
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$ nix-build -A hackage.<package>
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```
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Then inspect `result/log.txt` for possible problems. The derivation will
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also contain formatted `.hs` files for inspection and original inputs with
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`.hs-original` extension (those are with CPP dropped, exactly what is fed
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into Ormolu).
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## Contributing
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See [CONTRIBUTING.md](./CONTRIBUTING.md).
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## License
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See [LICENSE.md](./LICENSE.md).
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Copyright © 2018–present Tweag I/O
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[haskell-src-exts]: https://hackage.haskell.org/package/haskell-src-exts
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[hindent]: https://hackage.haskell.org/package/hindent
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