stylish-haskell
Introduction
A simple Haskell code prettifier. The goal is not to format all of the code in
a file, since I find those kind of tools often “get in the way”. However,
manually cleaning up import statements etc. gets tedious very quickly.
This tool tries to help where necessary without getting in the way.
Installation
You can install it using stack install stylish-haskell
or cabal install stylish-haskell
.
You can also install it using your package manager:
- Debian 9 or later:
apt-get install stylish-haskell
- Ubuntu 16.10 or later:
apt-get install stylish-haskell
- Arch Linux:
pacman -S stylish-haskell
Features
- Aligns and sorts
import
statements
- Groups and wraps
{-# LANGUAGE #-}
pragmas, can remove (some) redundant
pragmas
- Removes trailing whitespace
- Aligns branches in
case
and fields in records
- Converts line endings (customizable)
- Replaces tabs by four spaces (turned off by default)
- Replaces some ASCII sequences by their Unicode equivalents (turned off by
default)
- Format data constructors and fields in records.
Feature requests are welcome! Use the issue tracker for that.
Example
Turns:
{-# LANGUAGE ViewPatterns, TemplateHaskell #-}
{-# LANGUAGE GeneralizedNewtypeDeriving,
ViewPatterns,
ScopedTypeVariables #-}
module Bad where
import Control.Applicative ((<$>))
import System.Directory (doesFileExist)
import qualified Data.Map as M
import Data.Map ((!), keys, Map)
data Point = Point { pointX, pointY :: Double , pointName :: String} deriving (Show)
into:
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TemplateHaskell #-}
module Bad where
import Control.Applicative ((<$>))
import System.Directory (doesFileExist)
import Data.Map (Map, keys, (!))
import qualified Data.Map as M
data Point = Point
{ pointX, pointY :: Double
, pointName :: String
} deriving (Show)
Configuration
The tool is customizable to some extent. It tries to find a config file in the
following order:
- A file passed to the tool using the
-c/--config
argument
.stylish-haskell.yaml
in the current directory (useful for per-directory
settings)
.stylish-haskell.yaml
in the nearest ancestor directory (useful for
per-project settings)
stylish-haskell/config.yaml
in the platform’s configuration directory
(on Windows, it is %APPDATA%, elsewhere it defaults to ~/.config
and
can be overridden by the XDG_CONFIG_HOME
environment variable;
useful for user-wide settings)
.stylish-haskell.yaml
in your home directory (useful for user-wide
settings)
- The default settings.
Use stylish-haskell --defaults > .stylish-haskell.yaml
to dump a
well-documented default configuration to a file, this way you can get started
quickly.
Record formatting
Basically, stylish-haskell supports 4 different styles of records, controlled by records
in the config file.
Here’s an example of all four styles:
-- equals: "indent 2", "first_field": "indent 2"
data Foo a
= Foo
{ a :: Int
, a2 :: String
-- ^ some haddock
}
| Bar
{ b :: a
}
deriving (Eq, Show)
deriving (ToJSON) via Bar Foo
-- equals: "same_line", "first_field": "indent 2"
data Foo a = Foo
{ a :: Int
, a2 :: String
-- ^ some haddock
}
| Bar
{ b :: a
}
deriving (Eq, Show)
deriving (ToJSON) via Bar Foo
-- equals: "same_line", "first_field": "same_line"
data Foo a = Foo { a :: Int
, a2 :: String
-- ^ some haddock
}
| Bar { b :: a
}
deriving (Eq, Show)
deriving (ToJSON) via Bar Foo
-- equals: "indent 2", first_field: "same_line"
data Foo a
= Foo { a :: Int
, a2 :: String
-- ^ some haddock
}
| Bar { b :: a
}
deriving (Eq, Show)
deriving (ToJSON) via Bar Foo
Editor integration
Haskell Language Server
Haskell Language Server(HLS) includes a plugin
for stylish-haskell. By changing the formatting provider option
(haskell.formattingProvider
) to stylish-haskell
as described in
HLS options, any editors that support Language Server Protocol
can use stylish-haskell for formatting.
VIM integration
Since it works as a filter it is pretty easy to integrate this with VIM.
You can call
:%!stylish-haskell
and add a keybinding for it.
Or you can define formatprg
:set formatprg=stylish-haskell
and then use gq
.
Alternatively, [vim-autoformat] supports stylish-haskell. To have it
automatically reformat the files on save, add to your vimrc:
autocmd BufWrite *.hs :Autoformat
" Don't automatically indent on save, since vim's autoindent for haskell is buggy
autocmd FileType haskell let b:autoformat_autoindent=0
There are also plugins that run stylish-haskell automatically when you save a
Haskell file:
Emacs integration
haskell-mode for Emacs supports stylish-haskell
. For configuration,
see the “Using external formatters” section of the
haskell-mode manual.
Atom integration
ide-haskell for Atom supports stylish-haskell
.
atom-beautify for Atom supports Haskell using stylish-haskell
.
Visual Studio Code integration
stylish-haskell-vscode for VSCode supports stylish-haskell
.
Using with Continuous Integration
You can quickly grab the latest binary and run stylish-haskell
like so:
curl -sL https://raw.github.com/haskell/stylish-haskell/master/scripts/latest.sh | sh -s .
Where the .
can be replaced with the arguments you pass to stylish-haskell
.
Credits
Written and maintained by Jasper Van der Jeugt.
Contributors:
- Chris Done
- Hiromi Ishii
- Leonid Onokhov
- Michael Snoyman
- Mikhail Glushenkov
- Beatrice Vergani
- Paweł Szulc
- Łukasz Gołębiewski
- Felix Mulder