TESTS.md

HIndent test codes

This file is a test suite. Each section maps to an HSpec test, and each line that is followed by a Haskell code fence is tested to make sure re-formatting that code snippet produces the same result.

You can browse through this document to see what HIndent's style is like, or contribute additional sections to it, or regression tests.

Shebangs

No newlines after a shebang

#!/usr/bin/env stack

-- stack runghc
main =
 pure ()
-- https://github.com/mihaimaruseac/hindent/issues/208

#!/usr/bin/env stack
-- stack runghc
main = pure ()
-- https://github.com/mihaimaruseac/hindent/issues/208

Double shebangs

#!/usr/bin/env stack
#!/usr/bin/env stack
main = pure ()

Modules

Empty module

Module headers

Without an export list

module X where

x = 1

With an export list

module X
  ( x
  , y
  , Z
  , P(x, z)
  , Q(..)
  , module Foo
  ) where

With an export list; indentation 4

module X
    ( x
    , y
    , Z
    , P(x, z)
    ) where

Module-level pragmas

A pragma's name is converted to the SHOUT_CASE.

{-# lAnGuAgE CPP #-}

{-# LANGUAGE CPP #-}

Pragmas, GHC options, and haddock options.

{-# LANGUAGE CPP #-}
{-# LANGUAGE NoRebindableSyntax #-}
{-# OPTIONS_GHC -fno-warn-missing-import-lists #-}
{-# OPTIONS_GHC -w #-}
{-# OPTIONS_HADDOCK show-extensions #-}

module Foo where

Accept pragmas via OPTIONS -XFOO

{-# OPTIONS -XPatternSynonyms #-}

import Foo (pattern Bar)

Accept pragmas via OPTIONS_GHC -XFOO

{-# OPTIONS_GHC -XPatternSynonyms #-}

import Foo (pattern Bar)

A pragma's length is adjusted automatically

{-#         LANGUAGE OverloadedStrings          #-}

{-# LANGUAGE OverloadedStrings #-}

Collect multiple extensions correctly

{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE PatternSynonyms #-}

import Language.C.Types (pattern TypeName)

Collect multiple extensions separated by commas correctly

{-# LANGUAGE TypeApplications,
    PatternSynonyms #-}

import Foo (pattern Bar)

foo = bar @Int 3

{-# LANGUAGE TypeApplications, PatternSynonyms #-}

import Foo (pattern Bar)

foo = bar @Int 3

Do not collect pragma-like comments

-- {-# LANGUAGE StaticPointers #-}
{-

{-# LANGUAGE StaticPointers #-}

-}
-- @static@ is no longer a valid identifier
-- once `StaticPointers` is enabled.
static = 3

WARNING

Without messages and an export list.

module Foo {-# WARNING [] #-} where

With a string without an export list.

module Foo {-# WARNING "Debug purpose only." #-} where

With a list of reasons without an export list.

module Foo {-# WARNING ["Debug purpose only.", "Okay?"] #-} where

DEPRECATED

Without messages and an export list.

module Foo {-# DEPRECATED [] #-} where

With a string without an export list.

module Foo {-# DEPRECATED "Use Bar." #-} where

With a list of reasons and an export list.

module Foo {-# DEPRECATED ["Use Bar.", "Or use Baz."] #-}
  ( x
  , y
  , z
  ) where

Imports, foreign imports, and foreign exports

Import lists

import Control.Lens (_2, _Just)
import Data.Text
import Data.Text
import qualified Data.Text as T
import qualified Data.Text (a, b, c)
import Data.Text (a, b, c)
import Data.Text hiding (a, b, c)

Shorter identifiers come first

import Foo ((!), (!!))

Import with ExplicitNamespaces.

{-# LANGUAGE ExplicitNamespaces #-}

import Prlude (type FilePath)

Import a pattern

{-# LANGUAGE PatternSynonyms #-}

import Foo (pattern Bar)

Sorted

import B
import A

import A
import B

Explicit imports - capitals first (typeclasses/types), then operators, then identifiers

import qualified MegaModule as M ((>>>), MonadBaseControl, void, MaybeT(..), join, Maybe(Nothing, Just), liftIO, Either, (<<<), Monad(return, (>>=), (>>)))

import qualified MegaModule as M
  ( Either
  , Maybe(Just, Nothing)
  , MaybeT(..)
  , Monad((>>), (>>=), return)
  , MonadBaseControl
  , (<<<)
  , (>>>)
  , join
  , liftIO
  , void
  )

Pretty import specification

{-# LANGUAGE ForeignFunctionInterface #-}

import A hiding
  ( foobarbazqux
  , foobarbazqux
  , foobarbazqux
  , foobarbazqux
  , foobarbazqux
  , foobarbazqux
  , foobarbazqux
  )

import Name hiding ()

import {-# SOURCE #-} safe qualified Module as M hiding (a, b, c, d, e, f)

An import declaration importing lots of data constructors

import Language
  ( Language(Ada, Ada, Assembly, C, CPlusPlus, CSharp, Clojure, Cobol, Dart, Elixir,
             Elm, Erlang, Fortran, Go, Groovy, Haskell, Java, JavaScript, Julia,
             Kotlin, Lisp, Lua, ObjectiveC, PHP, Pascal, Perl, Prolog, Python, Ruby,
             Rust, Scala)
  , allLanguages
  )

Preserve newlines between import groups

-- https://github.com/mihaimaruseac/hindent/issues/200
import GHC.Monad

import CommentAfter -- Comment here shouldn't affect newlines
import HelloWorld

import CommentAfter -- Comment here shouldn't affect newlines

-- Comment here shouldn't affect newlines
import CommentAfter

PackageImports

-- https://github.com/mihaimaruseac/hindent/issues/480
{-# LANGUAGE PackageImports #-}

import qualified "base" Prelude as P

ImportQualifiedPost

{-# LANGUAGE ImportQualifiedPost #-}

import Data.Text qualified as T

Importing a #

-- https://github.com/mihaimaruseac/hindent/issues/547
import Diagrams.Prelude ((#))

Foreign imports and exports

A ccall foreign export

{-# LANGUAGE ForeignFunctionInterface #-}

foreign export ccall "test" test :: IO ()

A ccall unsafe foreign import

{-# LANGUAGE ForeignFunctionInterface #-}

foreign import ccall unsafe "test" test :: IO ()

A capi foreign import

{-# LANGUAGE CApiFFI #-}
{-# LANGUAGE ForeignFunctionInterface #-}

foreign import capi safe "foo" test :: IO Int

A stdcall foreign import

{-# LANGUAGE ForeignFunctionInterface #-}

foreign import stdcall safe "test" bar :: IO ()

A prim foreign import

{-# LANGUAGE ForeignFunctionInterface #-}

foreign import prim safe "test" test :: IO ()

A javascript foreign import

{-# LANGUAGE ForeignFunctionInterface #-}

foreign import javascript safe "test" test :: IO ()

Declarations

Data family

data family Foo a

StandaloneKindSignatures

{-# LANGUAGE StandaloneKindSignatures #-}

type Foo :: Type -> Type -> Type
data Foo a b =
  Foo a b

Default declaration

default (Integer, Double)

ANN pragmas

Value annotation.

{-# ANN foo "annotation" #-}

Type annotation.

{-# ANN type Foo "annotation" #-}

Module annotation.

{-# ANN module "annotation" #-}

Class declarations

Default signatures

-- https://github.com/chrisdone/hindent/issues/283
class Foo a where
  bar :: a -> a -> a
  default bar :: Monoid a => a -> a -> a
  bar = mappend

TypeOperators and MultiParamTypeClasses

-- https://github.com/chrisdone/hindent/issues/277
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE MultiParamTypeClasses #-}

class (a :< b) c

Class constraints

Empty

class () =>
      Foo a

Long

class ( Foo a
      , Bar a
      , Baz a
      , Hoge a
      , Fuga a
      , Piyo a
      , Hogera a
      , Hogehoge a
      , Spam a
      , Ham a
      ) =>
      Quux a

Class methods

With class constraints

class Foo f where
  myEq :: (Eq a) => f a -> f a -> Bool

Long signatures

class Foo a where
  fooBarBazQuuxHogeFuga ::
       a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a

Associated type synonyms

Associated type synonyms

class Foo a where
  type Bar b

Associated type synonyms annotated with injectivity information

-- https://github.com/commercialhaskell/hindent/issues/528
class C a where
  type F a = b | b -> a

Class instance declarations

Without methods

instance C a

With methods

instance C a where
  foobar = do
    x y
    k p

With type operators

-- https://github.com/mihaimaruseac/hindent/issues/342
instance Foo (->)

instance Foo (^>)

instance Foo (T.<^)

With a type alias

instance Foo a where
  type Bar a = Int

A where clause between instance functions

instance Pretty HsModule where
  pretty' = undefined
    where
      a = b
  commentsBefore = Nothing

With a SPECIALISE pragma

instance (Show a) => Show (Foo a) where
  {-# SPECIALISE instance Show (Foo String) #-}
  show = undefined

With associated data types

-- https://github.com/mihaimaruseac/hindent/issues/493
instance GM 'Practice where
  data MatchConfig 'Practice = MatchConfig'Practice
    { teamSize :: Int
    , ladder :: Ladder
    }

With associated newtypes

-- https://github.com/mihaimaruseac/hindent/issues/837
instance Foo a where
  newtype Bar a =
    FooBar a

With overlapping pragmas

OVERLAPPING

-- https://github.com/mihaimaruseac/hindent/issues/386
instance {-# OVERLAPPING #-} Arbitrary (Set Int) where
  arbitrary = undefined

OVERLAPPABLE

instance {-# OVERLAPPABLE #-} Arbitrary Int where
  arbitrary = undefined

OVERLAPS

instance {-# OVERLAPS #-} Arbitrary String where
  arbitrary = undefined

INCOHERENT

instance {-# INCOHERENT #-} Arbitrary String where
  arbitrary = undefined

With class constraints

Short name

-- https://github.com/mihaimaruseac/hindent/issues/244
instance Num a => C a

Long name

-- https://github.com/mihaimaruseac/hindent/issues/244
instance Nuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuum a =>
         C a where
  f = undefined

Explicit foralls

Without class constraints

-- https://github.com/mihaimaruseac/hindent/issues/218
instance forall x. C

With class constraints

-- https://github.com/mihaimaruseac/hindent/issues/218
instance forall x. Show x => C x

Symbol class constructor

Infix

instance Bool :?: Bool

Prefix

instance (:?:) Int Bool

Data declarations

Data declaration with underscore

data Stanza = MkStanza
  { _stanzaBuildInfo :: BuildInfo
  , stanzaIsSourceFilePath :: FilePath -> Bool
  }

A data declaration with typeclass constraints

data Ord a =>
     Foo =
  Foo a

Multiple constructors at once

data Foo = Foo
  { foo, bar, baz, qux, quux :: Int
  }

No fields

data Foo

Single field

data Foo =
  Foo

Multiple unnamed fields

data HttpException
  = InvalidStatusCode Int
  | MissingContentHeader

A lot of unnamed fields in a constructor

data Foo =
  Foo
    String
    String
    String
    String
    String
    String
    String
    String
    String
    String
    String

A banged field

data Foo =
  Foo !Int

A record constructor with a field

data Foo = Foo
  { foo :: Int
  }

Multiple constructors with fields

data Expression a
  = VariableExpression
      { id :: Id Expression
      , label :: a
      }
  | FunctionExpression
      { var :: Id Expression
      , body :: Expression a
      , label :: a
      }
  | ApplyExpression
      { func :: Expression a
      , arg :: Expression a
      , label :: a
      }
  | ConstructorExpression
      { id :: Id Constructor
      , label :: a
      }

A mixture of constructors with unnamed fields and record constructors

-- https://github.com/mihaimaruseac/hindent/issues/393
data X
  = X
      { x :: Int
      , x' :: Int
      }
  | X'

An infix data constructor

data Foo =
  Int :--> Int

An UNPACKed field.

data Foo = Foo
  { x :: {-# UNPACK #-} Int
  }

An NOUNPACKed field.

data Foo = Foo
  { x :: {-# NOUNPACK #-} !Int
  }

A lazy field.

data Foo = Foo
  { x :: ~Int
  }

Fields with forall constraints

Single

data D =
  forall a. D a

Multiple

-- https://github.com/mihaimaruseac/hindent/issues/443
{-# LANGUAGE ExistentialQuantification #-}

data D =
  forall a b c. D a b c

With an infix constructor

data D =
  forall a. a :== a

Fields with contexts

Without a forall

data Foo =
  Eq a => Foo a

With a forall

-- https://github.com/mihaimaruseac/hindent/issues/278
data Link c1 c2 a c =
  forall b. (c1 a b, c2 b c) =>
            Link (Proxy b)

With an infix constructor without a forall

data Foo =
  Eq a => a :== a

With an infix constructor with a forall

data Foo =
  forall a. Eq a =>
            a :== a

Derivings

With a single constructor

data Simple =
  Simple
  deriving (Show)

With multiple constructors

data Stuffs
  = Things
  | This
  | That
  deriving (Show)

With a record constructor

-- From https://github.com/mihaimaruseac/hindent/issues/167
data Person = Person
  { firstName :: !String -- ^ First name
  , lastName :: !String -- ^ Last name
  , age :: !Int -- ^ Age
  } deriving (Eq, Show)

Multiple derivings

-- https://github.com/mihaimaruseac/hindent/issues/289
newtype Foo =
  Foo Proxy
  deriving ( Functor
           , Applicative
           , Monad
           , Semigroup
           , Monoid
           , Alternative
           , MonadPlus
           , Foldable
           , Traversable
           )

Various deriving strategies

-- https://github.com/mihaimaruseac/hindent/issues/503
{-# LANGUAGE DerivingStrategies #-}
{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DeriveVia #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}

module Foo where

import Data.Typeable
import GHC.Generics

newtype Number a =
  Number a
  deriving (Generic)
  deriving stock (Ord)
  deriving newtype (Eq)
  deriving anyclass (Typeable)
  deriving (Show) via a

StandaloneDeriving

{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE StandaloneDeriving #-}

data Foo =
  Foo

deriving instance Eq Foo

deriving stock instance Ord Foo

deriving via (Foo a) instance Show (Bar a)

GADT declarations

With a kind signature

data Ty :: (* -> *) where
  TCon
    :: { field1 :: Int
       , field2 :: Bool}
    -> Ty Bool
  TCon' :: (a :: *) -> a -> Ty a

Without a kind signature

data Foo where
  Foo
    :: forall v. Ord v
    => v
    -> v
    -> Foo

With a forall but no contexts

data Foo where
  Foo :: forall v. v -> v -> Foo

With a context but no foralls

data Foo where
  Foo :: (Ord v) => v -> v -> Foo

With methods with record signatures

-- https://github.com/mihaimaruseac/hindent/issues/581
data Test where
  Test :: Eq a => { test :: a } -> Test

Data instance declarations

Without type applications

data instance Foo Int =
  FInt

With type applications

data instance Foo @k a =
  FString

Function declarations

Case inside do and lambda

foo =
  \x -> do
    case x of
      Just _ -> 1
      Nothing -> 2

A case inside a let.

f = do
  let (x, xs) =
        case gs of
          [] -> undefined
          (x':xs') -> (x', xs')
  undefined

A do inside a lambda.

printCommentsAfter =
  case commentsAfter p of
    xs -> do
      forM_ xs $ \(L loc c) -> do
        eolCommentsArePrinted

Case with natural pattern (See NPat of https://hackage.haskell.org/package/ghc-lib-parser-9.2.3.20220527/docs/Language-Haskell-Syntax-Pat.html#t:Pat)

foo =
  case x of
    0 -> pure ()
    _ -> undefined

s8_stripPrefix bs1@(S.PS _ _ l1) bs2
  | bs1 `S.isPrefixOf` bs2 = Just (S.unsafeDrop l1 bs2)
  | otherwise = Nothing

A do inside a guard arm

f
  | x == 1 = do
    a
    b

if having a long condition

foo =
  if fooooooo
       || baaaaaaaaaaaaaaaaaaaaa
       || apsdgiuhasdpfgiuahdfpgiuah
       || bazzzzzzzzzzzzz
    then a
    else b

A long signature inside a where clause

cppSplitBlocks :: ByteString -> [CodeBlock]
cppSplitBlocks inp = undefined
  where
    spanCPPLines ::
         [(Int, ByteString)] -> ([(Int, ByteString)], [(Int, ByteString)])
    spanCPPLines = undefined

A forall type inside a where clause

replaceAllNotUsedAnns :: HsModule -> HsModule
replaceAllNotUsedAnns = everywhere app
  where
    app ::
         forall a. Data a
      => (a -> a)
    app = undefined

f :: a
f = undefined
  where
    ggg ::
         forall a. Typeable a
      => a
      -> a
    ggg = undefined

Prefix notation for operators

(+) a b = a

Guards and pattern guards

f x
  | x <- Just x
  , x <- Just x =
    case x of
      Just x -> e
  | otherwise = do
    e
  where
    x = y

Where clause

sayHello = do
  name <- getLine
  putStrLn $ greeting name
  where
    greeting name = "Hello, " ++ name ++ "!"

An empty line is inserted after an empty where

f = evalState
    -- A comment
  where

f = evalState
    -- A comment
  where

Multiple function declarations with an empty where

f = undefined
  where


g = undefined

Let inside a where

g x =
  let x = 1
   in x
  where
    foo =
      let y = 2
          z = 3
       in y

The indent after a top-level where has always 2 spaces.

f = undefined
  where
    g = undefined

The indent after a where inside a case depends on the indent space setting

f =
    case x of
        x -> undefined
            where y = undefined

Pattern matchings

View pattern

foo (f -> Just x) = print x
foo _ = Nothing

Match against a list

head [] = undefined
head [x] = x
head xs = head $ init xs

foo [Coord _ _, Coord _ _] = undefined

Multiple matchings

head' [] = Nothing
head' (x:_) = Just x

n+k patterns

{-# LANGUAGE NPlusKPatterns #-}

f (n+5) = 0

Binary symbol data constructor in pattern

f (x :| _) = x

f' ((:|) x _) = x

f'' ((Data.List.NonEmpty.:|) x _) = x

g (x:xs) = x

g' ((:) x _) = x

Infix constructor pattern

-- https://github.com/mihaimaruseac/hindent/issues/424
a = from $ \(author `InnerJoin` post) -> pure ()

Unboxed sum pattern matching.

{-# LANGUAGE UnboxedSums #-}

f (# (# n, _ #) | #) = (# n | #)
f (# | b #) = (# | b #)

Pattern matching against a infix constructor with a module name prefix

foo (a FOO.:@: b) = undefined

Pattern matchings against record

Short

fun Rec {alpha = beta, gamma = delta, epsilon = zeta, eta = theta, iota = kappa} = do
  beta + delta + zeta + theta + kappa

Long

fun Rec { alpha = beta
        , gamma = delta
        , epsilon = zeta
        , eta = theta
        , iota = kappa
        , lambda = mu
        } =
  beta + delta + zeta + theta + kappa + mu + beta + delta + zeta + theta + kappa

Another long one

resetModuleStartLine m@HsModule { hsmodAnn = epa@EpAnn {..}
                                , hsmodName = Just (L (SrcSpanAnn _ (RealSrcSpan sp _)) _)
                                } = undefined

Symbol constructor, short

fun ((:..?) {}) = undefined

Symbol constructor, long

fun (:..?) { alpha = beta
           , gamma = delta
           , epsilon = zeta
           , eta = theta
           , iota = kappa
           , lambda = mu
           } =
  beta + delta + zeta + theta + kappa + mu + beta + delta + zeta + theta + kappa

Symbol field

f (X {(..?) = x}) = x

Punned symbol field

f' (X {(..?)}) = (..?)

RecordWileCards

-- https://github.com/mihaimaruseac/hindent/issues/274
foo (bar@Bar {..}) = Bar {..}

resetModuleNameColumn m@HsModule {hsmodName = Just (L (SrcSpanAnn epa@EpAnn {..} sp) name)} =
  m

bar Bar {baz = before, ..} = Bar {baz = after, ..}

As pattern

f all@(x:xs) = all

Infix declarations

infixl

infixl 1 ^-^

infixr

infixr 1 ^-^

infix

infix 1 ^-^

Pattern synonym declarations

Unidirectional with a pattern type signature

{-# LANGUAGE PatternSynonyms #-}

pattern Foo :: Int -> Int -> [Int]
pattern Foo x y <- [x, y]

Bidirectional record pattern

{-# LANGUAGE PatternSynonyms #-}

pattern Pair {x, y} = (x, y)

Explicit bidirectional

With a prefix constructor

{-# LANGUAGE PatternSynonyms #-}

pattern Fst x <- (x, x)
  where Fst x = (x, 0)

With an infix constructor

{-# LANGUAGE PatternSynonyms #-}

pattern x :| xs <- x : xs
  where a :| b = a : b

Pragma declarations

INLINE

-- https://github.com/mihaimaruseac/hindent/issues/255
{-# INLINE f #-}
f :: Int -> Int
f n = n

NOINLINE with an operator enclosed by parentheses

-- https://github.com/mihaimaruseac/hindent/issues/415
{-# NOINLINE (<>) #-}

INLINABLE

{-# INLINABLE f #-}
f :: a
f = undefined

OPAQUE

{-# OPAQUE f #-}
f :: a
f = undefined

INLINE with levels

{-# INLINE [0] f #-}
{-# INLINE [~1] g #-}

A DEPRECATED.

{-# DEPRECATED
giveUp "Never give up."
 #-}

giveUp = undefined

A WARNING.

{-# WARNING
debugCode "The use of 'debugCode'"
 #-}

A COMPLETE

{-# COMPLETE Single, Anylist #-}

Top-level SPECIALISE

{-# SPECIALISE lookup :: [(Int, Int)] -> Int -> Maybe Int #-}

Multiple signatures in a SPECIALISE

-- https://github.com/mihaimaruseac/hindent/pull/784
{-# SPECIALISE foo :: Int -> Int, Double -> Double #-}

A SCC

{-# SCC bar #-}

Rule declarations

Without foralls

{-# RULES
"foo/bar" foo = bar
 #-}

With forall but no type signatures

{-# RULES
"piyo/pochi" forall a. piyo a = pochi a a
 #-}

With forall and type signatures

{-# RULES
"hoge/fuga" forall (a :: Int). hoge a = fuga a a
 #-}

Role annotation declarations

normal

{-# LANGUAGE RoleAnnotations #-}

type role Foo nominal

representational

{-# LANGUAGE RoleAnnotations #-}

type role Bar representational

phantom

{-# LANGUAGE RoleAnnotations #-}

type role Baz phantom

Type family declarations

Without annotations

type family Id a

With annotations

type family Id a :: *

With injectivity annotations

type family Id a = r | r -> a

Closed type families

type family Closed (a :: k) :: Bool where
  Closed (x @Int) = 'Int
  Closed x = 'True

Type family instance declarations

Without holes

type instance Id Int = Int

With a hole

type instance Id _ = String

Type signature declarations

Multiple function signatures at once

a, b, c :: Int

Type using a numeric value

f :: Foo 0

Type using a character value

f :: Foo 'a'

Type using a unicode string value

f :: Foo "あ"

A dot not enclosed by spaces is printed correctly if OverloadedRecordDot is not enabled.

f :: forall a.(Data a, Typeable a) => a

f :: forall a. (Data a, Typeable a)
  => a

Short

-- https://github.com/mihaimaruseac/hindent/issues/390
fun :: Short
fun = undefined

Always break after :: on overlong signatures

-- https://github.com/mihaimaruseac/hindent/issues/390
someFunctionSignature ::
     Wiiiiiiiiiiiiiiiiith
  -> Enough
  -> (Arguments -> To ())
  -> Overflow (The Line Limit)

A long type is broken into lines

-- https://github.com/mihaimaruseac/hindent/issues/359
thing ::
     ( ResB.BomEx
     , Maybe
         [( Entity BomSnapshot
          , ( [ResBS.OrderSubstituteAggr]
            , ( Maybe (Entity BomSnapshotHistory)
              , Maybe (Entity BomSnapshotHistory))))])
  -> [(ResB.BomEx, Maybe ResBS.BomSnapshotAggr)]

Long parameter list with a forall

fooooooooo ::
     forall a.
     Fooooooooooooooo a
  -> Fooooooooooooooo a
  -> Fooooooooooooooo a
  -> Fooooooooooooooo a

Implicit parameters

{-# LANGUAGE ImplicitParams #-}

f :: (?x :: Int) => Int

Quasiquotes in types

{-# LANGUAGE QuasiQuotes #-}

fun :: [a|bc|]

Tuples

fun :: (a, b, c) -> (a, b)

Infix operator

-- https://github.com/mihaimaruseac/hindent/issues/301
(+) :: ()

With a record

url :: r {url :: String} => r -> Integer

forall type

f :: (forall a. Data a => a -> a) -> (forall a b. Data a => a -> b)
g :: forall a b. a -> b

An infix operator containing #

(#!) :: Int -> Int -> Int

Multiple line function signature inside a where

foo = undefined
  where
    go :: Fooooooooooooooooooooooo
       -> Fooooooooooooooooooooooo
       -> Fooooooooooooooooooooooo
       -> Fooooooooooooooooooooooo
    go = undefined

Types with many type applications

foo ::
     Foo
       LongLongType
       LongLongType
       LongLongType
       LongLongType
       LongLongType
       LongLongType
  -> Int

Promoted types

Class constraints should leave :: on same line

-- see https://github.com/chrisdone/hindent/pull/266#issuecomment-244182805
fun ::
     (Class a, Class b)
  => fooooooooooo bar mu zot
  -> fooooooooooo bar mu zot
  -> c

An infix operator containing #

(#!) :: Int -> Int -> Int

Prefix promoted symbol type constructor

a :: '(T.:->) 'True 'False
b :: (T.:->) 'True 'False
c :: '(:->) 'True 'False
d :: (:->) 'True 'False

Promoted lists

Short

fun1 :: Def ('[ Ref s (Stored Uint32), IBool] T.:-> IBool)
fun1 = undefined

fun2 :: Def ('[ Ref s (Stored Uint32), IBool] :-> IBool)
fun2 = undefined

Long

-- https://github.com/mihaimaruseac/hindent/issues/522
type OurContext
  = '[ AuthHandler W.Request (ExtendedPayloadWrapper UserSession)
     , BasicAuthCheck GameInstanceId
     , BasicAuthCheck (RegionId, RegionName)
     , BasicAuthCheck Alert.SourceId
     , M.MultipartOptions M.Tmp
     ]

Nested

-- https://github.com/mihaimaruseac/hindent/issues/348
a :: A '[ 'True]
-- nested promoted list with multiple elements.
b :: A '[ '[ 'True, 'False], '[ 'False, 'True]]

Symbol type constructors

Infix

f :: a :?: b

Prefix

f' :: (:?:) a b

Type signature with class constraints

Single

-- https://github.com/mihaimaruseac/hindent/issues/244
x :: Num a => a
x = undefined

Multiple

fun :: (Class a, Class b) => a -> b -> c

Multiple without parentheses

-- https://github.com/mihaimaruseac/hindent/issues/554
g :: Semigroup a => Monoid a => Maybe a -> a

Long constraints

-- https://github.com/mihaimaruseac/hindent/issues/222
foo ::
     ( Foooooooooooooooooooooooooooooooooooooooooo
     , Foooooooooooooooooooooooooooooooooooooooooo
     )
  => A

Class constraints should leave :: on same line

-- see https://github.com/mihaimaruseac/hindent/pull/266#issuecomment-244182805
fun ::
     (Class a, Class b)
  => fooooooooooo bar mu zot
  -> fooooooooooo bar mu zot
  -> c

Symbol class constructor in class constraint

f :: (a :?: b) => (a, b)
f' :: ((:?:) a b) => (a, b)

Unboxed types

Short unboxed sums

{-# LANGUAGE UnboxedSums #-}

f :: (# (# Int, String #) | String #) -> (# Int | String #)

Long unboxed sums

{-# LANGUAGE UnboxedSums #-}

f' ::
     (# (# Int, String #)
      | Either Bool Int
      | Either Bool Int
      | Either Bool Int
      | Either Bool Int
      | Either Bool Int
      | String #)
  -> (# Int | String #)

Large unboxed tuples

{-# LANGUAGE UnboxedTuples #-}

f :: (# Looooooooooooooooooooooooooooooooooooooooooooong
      , Looooooooooooooooooooooooooooooooooooooooooooong
      , Looooooooooooooooooooooooooooooooooooooooooooong #)

Type synonym declarations

Short

type EventSource a = (AddHandler a, a -> IO ())

Long

-- https://github.com/mihaimaruseac/hindent/issues/290
type MyContext m
  = ( MonadState Int m
    , MonadReader Int m
    , MonadError Text m
    , MonadMask m
    , Monoid m
    , Functor m)

Very higher-kinded type

-- https://github.com/mihaimaruseac/hindent/issues/534
type SomeTypeSynonym
  = RecordWithManyFields
      FieldNumber1
      FieldNumber2
      FieldNumber3
      FieldNumber4
      FieldNumber5
      FieldNumber6
      FieldNumber7
      FieldNumber8
      FieldNumber9
      FieldNumber10
      FieldNumber11
      FieldNumber12
      FieldNumber13
      FieldNumber14
      FieldNumber15

Infix type constructor

-- https://github.com/mihaimaruseac/hindent/issues/417
type API = api1 :<|> api2

Type with a string

-- https://github.com/mihaimaruseac/hindent/issues/451
type Y = X "abc\n\n\ndef"

TypeOperators

-- https://github.com/mihaimaruseac/hindent/issues/277
{-# LANGUAGE TypeOperators #-}

type m ~> n = ()

Functional dependencies

Single

-- https://github.com/commercialhaskell/hindent/issues/323
class Foo a b | a -> b where
  f :: a -> b

Multiple dependencies in a line

class Foo a b | a -> b, b -> a

Long

-- https://github.com/commercialhaskell/hindent/issues/323
class Foo a b c d e f
  | a b c d e -> f
  , a b c d f -> e
  , a b c e f -> d
  , a b d e f -> c
  , a c d e f -> b
  , b c d e f -> a
  where
  foo :: a -> b -> c -> d -> e -> f

With class constraints

Single

-- https://github.com/commercialhaskell/hindent/issues/459
class Class1 a =>
      Class2 a
  where
  f :: a -> Int

Multiple

-- https://github.com/commercialhaskell/hindent/issues/459
class (Eq a, Show a) =>
      Num a
  where
  (+), (-), (*) :: a -> a -> a
  negate :: a -> a
  abs, signum :: a -> a
  fromInteger :: Integer -> a

MINIMAL pragmas

Monad example

class A where
  {-# MINIMAL return, ((>>=) | (join, fmap)) #-}

Very long names #310

class A where
  {-# MINIMAL averylongnamewithnoparticularmeaning
            | ananotherverylongnamewithnomoremeaning #-}

Expressions

A minus sign

f = -(3 + 5)

Lists

exceptions = [InvalidStatusCode, MissingContentHeader, InternalServerError]

exceptions =
  [ InvalidStatusCode
  , MissingContentHeader
  , InternalServerError
  , InvalidStatusCode
  , MissingContentHeader
  , InternalServerError
  ]

Multi-way if

x =
  if | x <- Just x
     , x <- Just x ->
       case x of
         Just x -> e
         Nothing -> p
     | otherwise -> e

Type application

{-# LANGUAGE TypeApplications #-}

a = fun @Int 12

An expression with a SCC pragma

foo = {-# SCC foo #-} undefined

A hole

foo = 3 + _

Implicit value

{-# LANGUAGE ImplicitParams #-}

foo = ?undefined

UnboxedSums

{-# LANGUAGE UnboxedSums #-}

f = (# | Bool #)

StaticPointers

{-# LANGUAGE StaticPointers #-}

f = static 1

OverloadedLabels

{-# LANGUAGE OverloadedLabels #-}

f = #foo

Arrows

-<

{-# LANGUAGE Arrows #-}

f =
  proc foo -> do
    bar -< baz
    aaa >- bbb

-<<

{-# LANGUAGE Arrows #-}

f =
  proc foo -> do
    g bar -<< baz
    aaaaa >>- h bbb

(| ... |)

{-# LANGUAGE Arrows #-}

f = proc g -> (|foo (bar -< g) (baz -< g)|) zz

Lambda equation.

{-# LANGUAGE Arrows #-}

f = proc g -> \x -> x -< g

Case expression.

{-# LANGUAGE Arrows #-}

f =
  proc g ->
    case h of
      [] -> i -< ()
      (_:_) -> j -< ()

Lambda case

{-# LANGUAGE Arrows #-}
{-# LANGUAGE LambdaCase #-}

f =
  proc g ->
    \case
      _ -> h -< ()

if ... then ... else

{-# LANGUAGE Arrows #-}

f =
  proc g ->
    if x
      then h -< g
      else t -< g

let ... in

{-# LANGUAGE Arrows #-}

f =
  proc g ->
    let x = undefined
        y = undefined
     in returnA -< g

Case expressions

Normal case

strToMonth :: String -> Int
strToMonth month =
  case month of
    "Jan" -> 1
    "Feb" -> 2
    _ -> error $ "Unknown month " ++ month

Inside a where and do

g x =
  case x of
    a -> x
  where
    foo =
      case x of
        _ -> do
          launchMissiles
      where
        y = 2

Empty case

-- https://github.com/mihaimaruseac/hindent/issues/414
{-# LANGUAGE EmptyCase #-}

f1 = case () of {}

Empty lambda case

-- https://github.com/mihaimaruseac/hindent/issues/414
{-# LANGUAGE EmptyCase #-}
{-# LANGUAGE LambdaCase #-}

f2 = \case {}

A guard in a case

f =
  case g of
    []
      | even h -> Nothing
    _ -> undefined

cases

{-# LANGUAGE Arrows #-}
{-# LANGUAGE LambdaCase #-}

foo =
  \cases
    1 1 -> 1
    _ _ -> 2

do expressions

Long function applications

test = do
  alphaBetaGamma deltaEpsilonZeta etaThetaIota kappaLambdaMu nuXiOmicron piRh79
  alphaBetaGamma deltaEpsilonZeta etaThetaIota kappaLambdaMu nuXiOmicron piRho80
  alphaBetaGamma
    deltaEpsilonZeta
    etaThetaIota
    kappaLambdaMu
    nuXiOmicron
    piRhoS81

Do as a left-hand side of an infix operation

-- https://github.com/mihaimaruseac/hindent/issues/238
-- https://github.com/mihaimaruseac/hindent/issues/296
block = do
  ds <- inBraces $ inWhiteSpace declarations
  return $ Block ds
  <?> "block"

Bindings

Short

foo = do
  mcp <- findCabalFiles (takeDirectory abssrcpath) (takeFileName abssrcpath)
  print mcp

Large

-- https://github.com/mihaimaruseac/hindent/issues/221
x = do
  config <- execParser options
  comments <-
    case config of
      Diff False args -> commentsFromDiff args
      Diff True args -> commentsFromDiff ("--cached" : args)
      Files args -> commentsFromFiles args
  mapM_ (putStrLn . Fixme.formatTodo) (concatMap Fixme.getTodos comments)

let bindings

With type signatures but no class constraints

f = do
  let g :: Int
      g = 3
  print g

With both type signatures and class constraints

f = do
  let try :: Typeable b => b
      try = undefined
  undefined

RecursiveDo

rec

{-# LANGUAGE RecursiveDo #-}

f = do
  a <- foo
  rec b <- a c
      c <- a b
  return $ b + c

mdo

{-# LANGUAGE RecursiveDo #-}

g = mdo
  foo
  bar

QualifiedDo

Qualified do

{-# LANGUAGE QualifiedDo #-}

f = Module.Path.do
  a <- foo
  return a

Qualified do with mdo

{-# LANGUAGE RecursiveDo #-}
{-# LANGUAGE QualifiedDo #-}

f = Module.Path.mdo
  a <- foo
  return a

Function applications

Long line, tuple

a =
  test
    (alphaBetaGamma, deltaEpsilonZeta, etaThetaIota, kappaLambdaMu, nuXiOmic79)
    (alphaBetaGamma, deltaEpsilonZeta, etaThetaIota, kappaLambdaMu, nuXiOmicr80)
    ( alphaBetaGamma
    , deltaEpsilonZeta
    , etaThetaIota
    , kappaLambdaMu
    , nuXiOmicro81)

Long line, tuple section

a =
  test
    (, alphaBetaGamma, , deltaEpsilonZeta, , etaThetaIota, kappaLambdaMu, nu79)
    (, alphaBetaGamma, , deltaEpsilonZeta, , etaThetaIota, kappaLambdaMu, nuX80)
    (
    , alphaBetaGamma
    ,
    , deltaEpsilonZeta
    ,
    , etaThetaIota
    , kappaLambdaMu
    , nuXi81
    ,)

Linebreaks after very short names if the total line length goes over the limit

-- https://github.com/mihaimaruseac/hindent/issues/405
t =
  f "this is a very loooooooooooooooooooooooooooong string that goes over the line length"
    argx
    argy
    argz

t =
  function
    "this is a very loooooooooooooooooooooooooooong string that goes over the line length"
    argx
    argy
    argz

Lambda expressions

Lazy patterns

f = \ ~a -> undefined
-- \~a yields parse error on input ‘\~’

Bang patterns

f = \ !a -> undefined
-- \!a yields parse error on input ‘\!’

An infix operator with a lambda expression

a =
  for xs $ \x -> do
    left x
    right x

Nested lambdas

foo :: IO ()
foo =
  alloca 10 $ \a ->
    alloca 20 $ \b ->
      cFunction fooo barrr muuu (fooo barrr muuu) (fooo barrr muuu)

In a case

f x =
  case filter (\y -> isHappy y x) of
    [] -> Nothing
    (z:_) -> Just (\a b -> makeSmile z a b)

Let ... in expressions

With bang parameters

f =
  let !x = 3
   in x

With implicit parameters

{-# LANGUAGE ImplicitParams #-}

f =
  let ?x = 42
   in f

inside a do

-- https://github.com/mihaimaruseac/hindent/issues/467
main :: IO ()
main = do
  let x = 5
   in when (x > 0) (return ())

List comprehensions

Short

map f xs = [f x | x <- xs]

Long

defaultExtensions =
  [ e
  | EnableExtension {extensionField1 = extensionField1} <-
      knownExtensions knownExtensions
  , let a = b
    -- comment
  , let c = d
    -- comment
  ]

Another long one

-- https://github.com/mihaimaruseac/hindent/issues/357
foo =
  [ (x, y)
  | x <- [1 .. 10]
  , y <- [11 .. 20]
  , even x
  , even x
  , even x
  , even x
  , even x
  , odd y
  ]

With operators

defaultExtensions =
  [e | e@EnableExtension {} <- knownExtensions]
    \\ map EnableExtension badExtensions

Transform list comprehensions

list =
  [ (x, y, map the v)
  | x <- [1 .. 10]
  , y <- [1 .. 10]
  , let v = x + y
  , then group by v using groupWith
  , then take 10
  , then group using permutations
  , t <- concat v
  , then takeWhile by t < 3
  ]

Parallel list comprehensions

Short

zip xs ys = [(x, y) | x <- xs | y <- ys]

Long

fun xs ys =
  [ (alphaBetaGamma, deltaEpsilonZeta)
  | x <- xs
  , z <- zs
  | y <- ys
  , cond
  , let t = t
  ]

Operators

With do

a =
  for xs $ do
    left x
    right x

With lambda-case

a =
  for xs $ \case
    Left x -> x

Qualified operator as an argument

-- https://github.com/mihaimaruseac/hindent/issues/273
foo = foldr1 (V.++) [V.empty, V.empty]

Apply an infix operator in prefix style

-- https://github.com/mihaimaruseac/hindent/issues/273
ys = (++) [] []

Qualified operator

-- https://github.com/mihaimaruseac/hindent/issues/273
xs = V.empty V.++ V.empty

In parentheses

cat = (++)

Qualified operator in parentheses

-- https://github.com/mihaimaruseac/hindent/issues/273
cons = (V.++)

A list constructor enclosed by parentheses

cons = (:)

A data constructor enclosed by parentheses

-- https://github.com/mihaimaruseac/hindent/issues/422
data T a =
  a :@ a

test = (:@)

Force indent and print RHS in a top-level expression

-- https://github.com/mihaimaruseac/hindent/issues/473
a =
  template
    $ haskell
        [ SomeVeryLongName
        , AnotherLongNameEvenLongToBreakTheLine
        , LastLongNameInList
        ]

Operator chains

Applicative style

x =
  Value
    <$> thing
    <*> secondThing
    <*> thirdThing
    <*> fourthThing
    <*> Just thisissolong
    <*> Just stilllonger
    <*> evenlonger

$ chain

f =
  Right
    $ S.lazyByteStrings
    $ addPrefix prefix
    $ S.toLazyByteString
    $ prettyPrint m

Arithmetic operations

f =
  aaaaaaaaaa * bbbbbbbbbbbbbb / cccccccccccccccccccccc
    + dddddddddddddd * eeeeeeeeeeeeeeee
    - ffffffffffffffff / -ggggggggggggg

Lens operators

updateUsr usr =
  usr
    & userFirstName .~ "newfirst"
    & userLastName .~ "newlast"
    & userEmail .~ "newemail"
    & userPassword .~ "newpass"

Primitive type values

Char

a = 'a'

\n as a Char

a = '\n'

String with a \n

a = "bcd\nefgh"

Multiple line string

foo =
  "hoge \
 \ fuga"
  where
    bar =
      "foo \
     \ bar"

Hex integers

a = 0xa5

Unboxed integers

{-# LANGUAGE MagicHash #-}

a = 0#

Unboxed floating point numbers

{-# LANGUAGE MagicHash #-}

a = 3.3#

Unboxed Char

{-# LANGUAGE MagicHash #-}

a = 'c'#

Unboxed String

{-# LANGUAGE MagicHash #-}

a = "Foo"#

UnboxedTuple

{-# LANGUAGE UnboxedTuples #-}

f :: (# Int, Int #) -> (# Int, Int #)
f t =
  case t of
    (# x, y #) -> (# x, y #)

NumericUnderscores

-- https://github.com/mihaimaruseac/hindent/issues/542
{-# LANGUAGE NumericUnderscores #-}

foo = 10_000

Quasi-quotes

Body has multiple lines.

{-# LANGUAGE QuasiQuotes #-}

f =
  [s|First line
Second line|]

Body has a top-level declaration.

{-# LANGUAGE QuasiQuotes #-}

f =
  [d| f :: Int -> Int
      f = undefined |]

Typed quote.

f = [||a||]

Preserve the trailing newline.

{-# LANGUAGE QuasiQuotes #-}

f =
  [s|foo
|]

Ranges

from

a = [1 ..]

from to

a = [1 .. 9]

from then

b = [1,3 ..]

from then to

c = [1,3 .. 9]

Records

No fields

-- https://github.com/mihaimaruseac/hindent/issues/366
foo = Nothing {}

Short

getGitProvider :: EventProvider GitRecord ()
getGitProvider =
  EventProvider {getModuleName = "Git", getEvents = getRepoCommits}

Medium

commitToEvent :: FolderPath -> TimeZone -> Commit -> Event.Event
commitToEvent gitFolderPath timezone commit =
  Event.Event
    {pluginName = getModuleName getGitProvider, eventIcon = "glyphicon-cog"}

Long

commitToEvent :: FolderPath -> TimeZone -> Commit -> Event.Event
commitToEvent gitFolderPath timezone commit =
  Event.Event
    { pluginName = getModuleName getGitProvider
    , eventIcon = "glyphicon-cog"
    , eventDate = localTimeToUTC timezone (commitDate commit)
    }

Another long one

-- https://github.com/mihaimaruseac/hindent/issues/358
foo =
  assert
    sanityCheck
    BomSnapshotAggr
      { snapshot = Just bs
      , previousId = M.bomSnapshotHistoryPreviousId . entityVal <$> bsp
      , nextId = M.bomSnapshotHistoryNextId . entityVal <$> bsn
      , bomEx = bx''
      , orderSubstitutes =
          S.fromList . map OrderSubstituteAggrByCreatedAtAsc $ subs
      , snapshotSubstitute = msub
      }

Record body may be in one line even if a new line is inserted after the variable name.

addCommentsToNode mkNodeComment newComments nodeInfo@(NodeInfo (SrcSpanInfo _ _) existingComments) =
  nodeInfo
    {nodeInfoComments = existingComments <> map mkBeforeNodeComment newComments}

Symbol constructor

f = (:..?) {}

Symbol field

f x = x {(..?) = wat}

g x = Rec {(..?)}

A field updater in a do inside a let ... in.

f = undefined
  where
    g h =
      let x = undefined
       in do
            foo
            pure
              h
                { grhssLocalBinds =
                    HsValBinds x (ValBinds (newSigs newSigMethods))
                }

OverloadedRecordDot

{-# LANGUAGE OverloadedRecordDot #-}

data Rectangle = Rectangle
  { width :: Int
  , height :: Int
  }

area :: Rectangle -> Int
area r = r.width * r.height

foo = (.x.y)

OverloadedRecordUpdate

{-# LANGUAGE OverloadedRecordDot #-}
{-# LANGUAGE OverloadedRecordUpdate #-}

foo = bar {baz.qux = 1}

Sections

With a LHS

double = (2 *)

With a RHS

halve = (/ 2)

With a large RHS

foo =
  (`elem` concat
            [ [20, 68, 92, 112, 28, 124, 116, 80]
            , [21, 84, 87, 221, 127, 255, 241, 17]
            ])

Template Haskell

Expression brackets

add1 x = [|x + 1|]

Pattern brackets

{-# LANGUAGE TemplateHaskell #-}

mkPat = [p|(x, y)|]

Type brackets

{-# LANGUAGE TemplateHaskell #-}

foo :: $([t|Bool|]) -> a

A quoted TH name from a type name

-- https://github.com/mihaimaruseac/hindent/issues/412
{-# LANGUAGE TemplateHaskell #-}

data (-)

q = ''(-)

Quoted list constructors

{-# LANGUAGE TemplateHaskell #-}

cons = '(:)

Pattern splices

{-# LANGUAGE TemplateHaskell #-}

f $pat = ()

g =
  case x of
    $(mkPat y z) -> True
    _ -> False

Typed splice

{-# LANGUAGE TemplateHaskell #-}

foo = $$bar

Comments

Only comments

-- foo

Double comments in a line

f = undefined {- Comment 1 -} {- Comment 2 -} -- Comment 3

Comments within a declaration

bob -- after bob
 =
  foo -- next to foo
  -- line after foo
    (bar
       foo -- next to bar foo
       bar -- next to bar
     ) -- next to the end paren of (bar)
    -- line after (bar)
    mu -- next to mu
    -- line after mu
    -- another line after mu
    zot -- next to zot
    -- line after zot
    (case casey -- after casey
           of
       Just -- after Just
        -> do
         justice -- after justice
           * foo
               (blah * blah
                  + z
                  + 2 / 4
                  + a
                  - -- before a line break
                   2
                     * -- inside this mess
                      z
                     / 2
                     / 2
                     / aooooo
                     / aaaaa -- bob comment
                )
           + (sdfsdfsd fsdfsdf) -- blah comment
         putStrLn "")
    [1, 2, 3]
    [ 1 -- foo
    , ( 2 -- bar
      , 2.5 -- mu
       )
    , 3
    ]
    -- in the end of the function
  where
    alpha = alpha
    -- between alpha and beta
    beta = beta
    -- after beta

foo = 1 -- after foo

gamma = do
  delta
  epsilon
  -- in the end of a do-block 1

gamma = do
  delta
  epsilon
  -- the very last block is detected differently

Comments in a do expression

gamma = do
  -- in the beginning of a do-block
  delta

Comments in a class instance

instance Pretty MatchForCase
  -- TODO: Do not forget to handle comments!
                                             where
  pretty' = undefined

Comments in a case expression

-- https://github.com/mihaimaruseac/hindent/issues/553
f x =
  case x of
    -- Bla bla
    Nothing -> 0
    Just y -> y

Haddock comments

-- | Module comment.
module X where

-- | Main doc.
main :: IO ()
main = return ()

data X
  = X -- ^ X is for xylophone.
  | Y -- ^ Y is for why did I eat that pizza.

data X = X
  { field1 :: Int -- ^ Field1 is the first field.
  , field11 :: Char
    -- ^ This field comment is on its own line.
  , field2 :: Int -- ^ Field2 is the second field.
  , field3 :: Char -- ^ This is a long comment which starts next to
    -- the field but continues onto the next line, it aligns exactly
    -- with the field name.
  , field4 :: Char
    -- ^ This is a long comment which starts on the following line
    -- from from the field, lines continue at the sme column.
  }

foo ::
     String -- ^ Reason for eating pizza.
  -> Int -- ^ How many did you eat pizza?
  -> String -- ^ The report.
foo = undefined

Haddock for a class method

-- https://github.com/mihaimaruseac/hindent/issues/607
class Foo a where
  -- | Doc
  foo :: a

Module header with haddock comments

-- | A module
module HIndent -- Foo
  ( -- * Formatting functions.
    reformat
  , -- * Testing
    test
  ) where

Comments around regular declarations

-- This is some random comment.
-- | Main entry point.
main = putStrLn "Hello, World!"
-- This is another random comment.

Multi-line comments

bob {- after bob -}
 =
  foo {- next to foo -}
  {- line after foo -}
    (bar
       foo {- next to bar foo -}
       bar {- next to bar -}
     ) {- next to the end paren of (bar) -}
    {- line after (bar) -}
    mu {- next to mu -}
    {- line after mu -}
    {- another line after mu -}
    zot {- next to zot -}
    {- line after zot -}
    (case casey {- after casey -}
           of
       Just {- after Just -}
        -> do
         justice {- after justice -}
           * foo
               (blah * blah
                  + z
                  + 2 / 4
                  + a
                  - {- before a line break -}
                   2
                     * {- inside this mess -}
                      z
                     / 2
                     / 2
                     / aooooo
                     / aaaaa {- bob comment -}
                )
           + (sdfsdfsd fsdfsdf) {- blah comment -}
         putStrLn "")
    [1, 2, 3]
    [ 1 {- foo -}
    , ( 2 {- bar -}
      , 2.5 {- mu -}
       )
    , 3
    ]

foo = 1 {- after foo -}

Multi-line comments with multi-line contents

{- | This is some random comment.
Here is more docs and such.
Etc.
-}
main = putStrLn "Hello, World!"
{- This is another random comment. -}

Comments on functions in where clause

-- https://github.com/mihaimaruseac/hindent/issues/540
topLevelFunc1 = f
  where
    -- comment on func in where clause
    -- stays in the where clause
    f = undefined

topLevelFunc2 = f . g
    -- Another comment
  where
    {- multi
       line
       comment -}
    f = undefined -- single line comment
    -- single line comment
        -- Different size of indent
    g :: a
    g = undefined

Comments in a 'where' clause

foo = undefined
  where
    bar
      -- A comment
     = undefined
      where
        a = b
    baz = undefined

Haddocks around data constructors

data Foo
    -- | A haddock comment for 'Bar'.
  = Bar
    -- | A haddock comment for 'Baz'.
  | Baz
    -- | A haddock comment for 'Quuz'.
  | Quuz

Identifiers

Unicode

α = γ * "ω"
-- υ

rec and mdo are valid identifiers unless RecursiveDo is enabled

-- https://github.com/mihaimaruseac/hindent/issues/328
rec = undefined

mdo = undefined

The first character of an infix operator can be @ unless TypeApplications is enabled.

-- https://github.com/mihaimaruseac/hindent/issues/421
a @: b = a + b

main = print (2 @: 2)

Complex input

A complex, slow-to-print decl

{-# LANGUAGE TemplateHaskell #-}

quasiQuotes =
  [ ( ''[]
    , \(typeVariable:_) _automaticPrinter ->
        (let presentVar = varE (presentVarName typeVariable)
          in lamE
               [varP (presentVarName typeVariable)]
               [|(let typeString = "[" ++ fst $(presentVar) ++ "]"
                   in ( typeString
                      , \xs ->
                          case fst $(presentVar) of
                            "GHC.Types.Char" ->
                              ChoicePresentation
                                "String"
                                [ ( "String"
                                  , StringPresentation
                                      "String"
                                      (concatMap
                                         getCh
                                         (map (snd $(presentVar)) xs)))
                                , ( "List of characters"
                                  , ListPresentation
                                      typeString
                                      (map (snd $(presentVar)) xs))
                                ]
                              where getCh (CharPresentation "GHC.Types.Char" ch) =
                                      ch
                                    getCh (ChoicePresentation _ ((_, CharPresentation _ ch):_)) =
                                      ch
                                    getCh _ = ""
                            _ ->
                              ListPresentation
                                typeString
                                (map (snd $(presentVar)) xs)))|]))
  ]

Random snippet from hindent itself

exp' (App _ op a) = do
  (fits, st) <- fitsOnOneLine (spaced (map pretty (f : args)))
  if fits
    then put st
    else do
      pretty f
      newline
      spaces <- getIndentSpaces
      indented spaces (lined (map pretty args))
  where
    (f, args) = flatten op [a]
    flatten :: Exp NodeInfo -> [Exp NodeInfo] -> (Exp NodeInfo, [Exp NodeInfo])
    flatten (App _ f' a') b = flatten f' (a' : b)
    flatten f' as = (f', as)

Quasi quotes

{-# LANGUAGE QuasiQuotes #-}

exp = [name|exp|]

f [qq|pattern|] = ()

C preprocessor

Conditionals (#if)

isDebug :: Bool
#if DEBUG
isDebug = True
#else
isDebug = False
#endif

Conditionals inside a where with empty lines and CPP

-- https://github.com/mihaimaruseac/hindent/issues/779
foo = bar + baz
  where

#if 0
    bar = 1
    
    baz = 1
#else
    bar = 2
    
    baz = 2
#endif

Macro definitions (#define)

#define STRINGIFY(x) #x
f = STRINGIFY (y)

Escaped newlines

#define LONG_MACRO_DEFINITION \
  data Pair a b = Pair \
    { first :: a \
    , second :: b \
    }
#define SHORT_MACRO_DEFINITION \
  x

Language extensions are effective across CPP boundaries.

{-# LANGUAGE PatternSynonyms #-}
#if 1
pattern Foo :: Int -> Bar
#else
pattern Foo :: Int -> Bar
#endif

Literate Haskell

Code with >s

> -- https://github.com/mihaimaruseac/hindent/issues/103
> foo :: a
> foo = undefined