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.
DeepSubsumption	Enable deep subsumption
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.
FieldSelectors	Control visibility of field selector functions.
FlexibleContexts	Remove some restrictions on class 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.
GHC2021	Use GHC’s set of default language extensions from 2021
GHCForeignImportPrim	Enable prim calling convention. Intended for internal use only.
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.
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.
OverloadedRecordDot	Record '.' syntax
OverloadedRecordUpdate	Record '.' syntax record updates
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, patterns 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.
UnliftedDatatypes	Enable unlifted data types.
UnliftedFFITypes	Enable unlifted FFI types
UnliftedNewtypes	Enable unlifted newtypes.
Unsafe	Enable Safe Haskell Unsafe mode.
ViewPatterns	Enable view patterns.