README.md · ormolu · git.iko.soy

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ormolu/README.md

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1# Ormolu

3[![CircleCI](https://circleci.com/gh/tweag/ormolu/tree/master.svg?style=svg&circle-token=cfd37a39265561eb44e608f97cf953cb2a394c03)](https://circleci.com/gh/tweag/ormolu/tree/master)

5Ormolu is a formatter for Haskell source code. The project was created with

6the following features in mind:

8* Using GHC's own parser to avoid parsing problems caused by

9 [`haskell-src-exts`][haskell-src-exts].

10* Let some whitespace be programmable. The layout of the input

11 influence the layout choices in the output. This means that the

12 choices between single-line/multi-line layouts in each particular

13 situation are made by the user, not by an algorithm. This makes the

14 implementation simpler and leaves some control to the user while

15 still guaranteeing that the formatted code is stylistically

16 consistent.

17* Writing code in such a way so it's easy to modify and maintain. Roughly,

18 it means that the project follows the path of [`hindent`][hindent] and is

19 very much about printing AST in a particular way.

20* Implementing one “true” formatting style which admits no configuration.

21* That formatting style aims to result in minimal diffs while still

22 remaining very close to “conventional” Haskell formatting people use.

23* Idempotency: formatting already formatted code doesn't change it.

24* Be well-tested and robust to the point that it can be used in large

25 projects without exposing unfortunate, disappointing bugs here and there.

27## Building

29The easiest way to build the project is with Nix:

31```console

32$ nix-build

33```

35Or with `cabal-install` from the Nix shell:

37```console

38$ nix-shell --run "cabal new-build"

39```

41Alternatively, `stack` could be used with a `stack.yaml` file as follows.

43```console

44$ cat stack.yaml

45resolver: lts-13.19

46packages:

47- '.'

49$ stack build

50```

52## Usage

54The following will print the formatted output to the standard output.

56```console

57$ ormolu Module.hs

58```

60Add `--mode inplace` to replace the contents of the input file with the

61formatted output.

63```console

64$ ormolu --mode inplace Module.hs

65```

67A configuration file can specify the language extensions to use by default.

69```console

70$ cat ormolu.yaml

71ghc-opts:

72 - -XLambdaCase

73unsafe: False

74debug: False

76$ ormolu -c ormolu.yaml Module.hs

77```

79## Contributing

81See [CONTRIBUTING.md](./CONTRIBUTING.md).

83## License

85See [LICENSE.md](./LICENSE.md).

89[haskell-src-exts]: https://hackage.haskell.org/package/haskell-src-exts

90[hindent]: https://hackage.haskell.org/package/hindent