6.1.2. Overview of all language extensions

GHC supports these language extensions:

Extension Description

AllowAmbiguousTypes

Allow the user to write ambiguous types, and the type inference engine to infer them.

ApplicativeDo

Enable Applicative do-notation desugaring

Arrows

Enable arrow notation extension

BangPatterns

Enable bang patterns.

BinaryLiterals

Enable support for binary literals.

BlockArguments

Allow do blocks and other constructs as function arguments.

CApiFFI

Enable the CAPI calling convention.

ConstrainedClassMethods

Enable constrained class methods.

ConstraintKinds

Enable a kind of constraints.

CPP

Enable the C preprocessor.

CUSKs

Enable detection of complete user-supplied kind signatures.

DataKinds

Enable datatype promotion.

DatatypeContexts

Allow contexts on data types.

DefaultSignatures

Enable default signatures.

DeriveAnyClass

Enable deriving for any class.

DeriveDataTypeable

Enable deriving for the Data class. Implied by (deprecated) AutoDeriveTypeable.

DeriveFoldable

Enable deriving for the Foldable class. Implied by DeriveTraversable.

DeriveFunctor

Enable deriving for the Functor class. Implied by DeriveTraversable.

DeriveGeneric

Enable deriving for the Generic class.

DeriveLift

Enable deriving for the Lift class

DeriveTraversable

Enable deriving for the Traversable class. Implies DeriveFunctor and DeriveFoldable.

DerivingStrategies

Enables deriving strategies.

DerivingVia

Enable deriving instances via types of the same runtime representation. Implies DerivingStrategies.

DisambiguateRecordFields

Enable record field disambiguation. Implied by RecordWildCards.

DuplicateRecordFields

Allow definition of record types with identically-named fields.

EmptyCase

Allow empty case alternatives.

EmptyDataDecls

Allow definition of empty data types.

EmptyDataDeriving

Allow deriving instances of standard type classes for empty data types.

ExistentialQuantification

Enable liberalised type synonyms.

ExplicitForAll

Enable explicit universal quantification. Implied by ScopedTypeVariables, LiberalTypeSynonyms, RankNTypes and ExistentialQuantification.

ExplicitNamespaces

Enable using the keyword type to specify the namespace of entries in imports and exports (Explicit namespaces in import/export). Implied by TypeOperators and TypeFamilies.

ExtendedDefaultRules

Use GHCi's extended default rules in a normal module.

FlexibleContexts

Enable flexible contexts.

FlexibleInstances

Enable flexible instances. Implies TypeSynonymInstances.

ForeignFunctionInterface

Enable foreign function interface.

FunctionalDependencies

Enable functional dependencies. Implies MultiParamTypeClasses.

GADTs

Enable generalised algebraic data types. Implies GADTSyntax and MonoLocalBinds.

GADTSyntax

Enable generalised algebraic data type syntax.

GeneralisedNewtypeDeriving

Enable newtype deriving.

Haskell2010

Use the Haskell 2010 language variant.

Haskell98

Use the Haskell 98 language variant.

HexFloatLiterals

Enable support for hexadecimal floating point literals.

ImplicitParams

Enable Implicit Parameters.

ImplicitPrelude

Don't implicitly import Prelude. Implied by RebindableSyntax.

ImportQualifiedPost

ImportQualifiedPost allows the syntax import M qualified

ImpredicativeTypes

Enable impredicative types. Implies RankNTypes.

IncoherentInstances

Enable incoherent instances. Implies OverlappingInstances.

InstanceSigs

Enable instance signatures.

InterruptibleFFI

Enable interruptible FFI.

KindSignatures

Enable kind signatures. Implied by TypeFamilies and PolyKinds.

LambdaCase

Enable lambda-case expressions.

LexicalNegation

Use whitespace to determine whether the minus sign stands for negation or subtraction.

LiberalTypeSynonyms

Enable liberalised type synonyms.

LinearTypes

Enable linear types.

MagicHash

Allow # as a postfix modifier on identifiers.

MonadComprehensions

Enable monad comprehensions.

MonadFailDesugaring

Enable monadfail desugaring.

MonoLocalBinds

Enable do not generalise local bindings. Implied by TypeFamilies and GADTs.

MonomorphismRestriction

Disable the monomorphism restriction.

MultiParamTypeClasses

Enable multi parameter type classes. Implied by FunctionalDependencies.

MultiWayIf

Enable multi-way if-expressions.

NamedFieldPuns

Enable record puns.

NamedWildCards

Enable named wildcards.

NegativeLiterals

Enable support for negative literals.

NondecreasingIndentation

Allow nested contexts to be at the same indentation level as its enclosing context.

NPlusKPatterns

Enable support for n+k patterns. Implied by Haskell98.

NullaryTypeClasses

Deprecated, does nothing. nullary (no parameter) type classes are now enabled using MultiParamTypeClasses.

NumDecimals

Enable support for 'fractional' integer literals.

NumericUnderscores

Enable support for numeric underscores.

OverlappingInstances

Enable overlapping instances.

OverloadedLabels

Enable overloaded labels.

OverloadedLists

Enable overloaded lists.

OverloadedStrings

Enable overloaded string literals.

PackageImports

Enable package-qualified imports.

ParallelListComp

Enable parallel list comprehensions.

PartialTypeSignatures

Enable partial type signatures.

PatternGuards

Disable pattern guards. Implied by Haskell98.

PatternSynonyms

Enable pattern synonyms.

PolyKinds

Enable kind polymorphism. Implies KindSignatures.

PostfixOperators

Enable postfix operators.

QualifiedDo

Enable qualified do-notation desugaring.

QuantifiedConstraints

Allow forall quantifiers in constraints.

QuasiQuotes

Enable quasiquotation.

Rank2Types

Enable rank-2 types. Synonym for RankNTypes.

RankNTypes

Enable rank-N types. Implied by ImpredicativeTypes.

RebindableSyntax

Employ rebindable syntax. Implies NoImplicitPrelude.

RecordWildCards

Enable record wildcards. Implies DisambiguateRecordFields.

RecursiveDo

Enable recursive do (mdo) notation.

RoleAnnotations

Enable role annotations.

Safe

Enable the Safe Haskell Safe mode.

ScopedTypeVariables

Enable lexically-scoped type variables.

StandaloneDeriving

Enable standalone deriving.

StandaloneKindSignatures

Allow the use of standalone kind signatures.

StarIsType

Treat * as Data.Kind.Type.

StaticPointers

Enable static pointers.

Strict

Make bindings in the current module strict by default.

StrictData

Enable default strict datatype fields.

TemplateHaskell

Enable Template Haskell.

TemplateHaskellQuotes

Enable quotation subset of Template Haskell.

TraditionalRecordSyntax

Disable support for traditional record syntax (as supported by Haskell 98) C {f = x}

TransformListComp

Enable generalised list comprehensions.

Trustworthy

Enable the Safe Haskell Trustworthy mode.

TupleSections

Enable tuple sections.

TypeApplications

Enable type application syntax in terms and types.

TypeFamilies

Enable type families. Implies ExplicitNamespaces, KindSignatures, and MonoLocalBinds.

TypeFamilyDependencies

Enable injective type families. Implies TypeFamilies.

TypeInType

Deprecated. Enable kind polymorphism and datatype promotion.

TypeOperators

Enable type operators. Implies ExplicitNamespaces.

TypeSynonymInstances

Enable type synonyms in instance heads. Implied by FlexibleInstances.

UnboxedSums

Enable unboxed sums.

UnboxedTuples

Enable the use of unboxed tuple syntax.

UndecidableInstances

Enable undecidable instances.

UndecidableSuperClasses

Allow all superclass constraints, including those that may result in non-termination of the typechecker.

UnicodeSyntax

Enable unicode syntax.

UnliftedFFITypes

Enable unlifted FFI types

UnliftedNewtypes

Enable unlifted newtypes.

Unsafe

Enable Safe Haskell Unsafe mode.

ViewPatterns

Enable view patterns.