Minimal examples of Haskell language extensions.

language-extension-examples.hs

a = a :: Eq b => () -- AllowAmbiguousTypes
a = proc b -> id -< b -- Arrows
a = let !b = () in b -- BangPatterns
a = 0b0 -- BinaryLiterals
a = id do 0 -- BlockArguments
foreign import capi "" a :: ()
class A b where c :: Eq b => b -- ConstrainedClassMethods
type A = Eq -- ConstraintKinds
# -- CPP
import Data.Proxy; a = Proxy :: Proxy True -- DataKinds
class C a where m :: [a]; default m :: [a]; m = [] -- DefaultSignatures
data X deriving Num -- DeriveAnyClass
import Data.Data; data X deriving Data -- DeriveDataTypeable
data X a deriving Foldable -- DeriveFoldable
data X a deriving Functor -- DeriveFunctor
import GHC.Generics; data X deriving Generic -- DeriveGeneric
import Language.Haskell.TH.Syntax; data X deriving Lift -- DeriveLift
data X a deriving (Functor, Foldable, Traversable) -- DeriveTraversable
data X deriving stock () -- DerivingStrategies
newtype X = X () deriving Eq via () -- DerivingVia
data A = A { x :: () }; data B = B { x :: () } -- DuplicateRecordFields
x = \ y -> case y of -- EmptyCase
data X deriving Eq -- EmptyDataDeriving
data X = forall a . X a -- ExistentialQuantification
x = Nothing :: forall a . Maybe a -- ExplicitForAll
import Data.Ix ( type Ix ) -- ExplicitNamespaces
default (()) -- ExtendedDefaultRules
a = () :: Eq () => () -- FlexibleContexts
instance Eq (() -> ()) -- FlexibleInstances
class C a | a -> a -- FunctionalDependencies
data X where X :: X -- GADTSyntax
data X a where X :: a -> X () -- GADTs
newtype X = X Int deriving Num -- GeneralizedNewtypeDeriving
a = 0x0.0 -- HexFloatLiterals
a | let ?b = 0 = 0 -- ImplicitParams
import Data.Ix qualified -- ImportQualifiedPost
a = Nothing :: Maybe (forall a . a) -- ImpredicativeTypes
instance Num () where abs :: () -> (); abs = id -- InstanceSigs
foreign import ccall interruptible "" a :: () -- InterruptibleFFI
a = () :: (() :: *) -- KindSignatures
x = \ case _ -> 0 -- LambdaCase
type X a = a; x = undefined :: X (forall a . a) -- LiberalTypeSynonyms
a# = () -- MagicHash
class C a b -- MultiParamTypeClasses
a = if | let -> 0 -- MultiWayIf
a = id -1 -- NegativeLiterals
a (b + 0) = 0 -- NPlusKPatterns
class C -- NullaryTypeClasses
a = 0.0 :: Int -- NumDecimals
a = 0_0 -- NumericUnderscores
import GHC.OverloadedLabels; instance IsLabel "b" () where { fromLabel = () }; a = #b :: IsLabel "b" () => () -- OverloadedLabels
import Data.Set; a = [] :: Set () -- OverloadedLists
import Data.Text; a = "" :: Text -- OverloadedStrings
import "base" Data.Ix -- PackageImports
a = [ 0 | b <- [] | c <- [] ] -- ParallelListComp
a = () :: _ -- PartialTypeSignatures
pattern X = () -- PatternSynonyms
a = let (%) b = b / 100 in (5 %) -- PostfixOperators
a = mdo () -- RecursiveDo
type role X nominal; data X a -- RoleAnnotations
a :: () = () -- ScopedTypeVariables
data X; deriving instance Eq X -- StandaloneDeriving
type T :: *; type T = () -- StandaloneKindSignatures
pure [] -- TemplateHaskell
a = '() -- TemplateHaskellQuotes
a = [ 0 | _ <- [], then id ] -- TransformListComp
a = (0, ) -- TupleSections
a = id @Int 0 -- TypeApplications
type family X -- TypeFamilies
type family X a = b | b -> a -- TypeFamilyDependencies
data a + b = C a b -- TypeOperators
type X = (); instance Num X -- TypeSynonymInstances
a = \ x -> case x of (# a | #) -> () -- UnboxedSums
a = let x = (# #) in 0 -- UnboxedTuples
a = 0 ∷ Int -- UnicodeSyntax
a (id -> b) = b -- ViewPatterns