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`	Allow do-notation statements to be desugared via `Applicative`.
`Arrows`	Allow arrow notation (e.g. `proc`)
`BangPatterns`	Allow bang pattern syntax.
`BinaryLiterals`	Allow binary literal syntax.
`BlockArguments`	Allow `do` blocks and other constructs as function arguments.
`CApiFFI`	Allow `foreign import`s to be declared with the `capi` calling convention.
`ConstrainedClassMethods`	Allow class methods to have non-empty contexts.
`ConstraintKinds`	Allow constraints to be used as types of kind `Constraint`.
`CPP`	Resolve C preprocessor directives.
`CUSKs`	Detect complete user-supplied kind signatures.
`DataKinds`	Allow use of data constructors in types.
`DatatypeContexts`	Allow contexts on `data` types.
`DeepSubsumption`	Use GHC's deep subsumption checking.
`DefaultSignatures`	Allow default signatures for typeclass methods.
`DeriveAnyClass`	Allow `deriving` syntax to be used for any class.
`DeriveDataTypeable`	Allow deriving for the `Data` class.
`DeriveFoldable`	Allow deriving for the `Foldable` class.
`DeriveFunctor`	Allow deriving for the `Functor` class.
`DeriveGeneric`	Allow deriving of `Generic` instances.
`DeriveLift`	Allow deriving for the `Lift` class
`DeriveTraversable`	Allow deriving for the `Traversable` class.
`DerivingStrategies`	Allow use of instance deriving strategies.
`DerivingVia`	Allow deriving instances `via` types of the same runtime representation.
`DisambiguateRecordFields`	Automatically disambiguate some record field references.
`DuplicateRecordFields`	Allow definition of record types with identically-named fields.
`EmptyCase`	Allow `case` expressions with no alternatives.
`EmptyDataDecls`	Allow definition of empty `data` types.
`EmptyDataDeriving`	Allow deriving instances of standard type classes for empty data types.
`ExistentialQuantification`	Allow existentially quantified type variables in types.
`ExplicitForAll`	Allow explicit universal quantification.
`ExplicitNamespaces`	Allow use of the keyword `type` to specify the namespace of entries in imports and exports.
`ExtendedDefaultRules`	Use GHCi's extended default rules in a normal module.
`ExtendedLiterals`	Allow numeric literal postfix syntax for unboxed integers.
`FieldSelectors`	Make record field selector functions visible in expressions.
`FlexibleContexts`	Remove some restrictions on class contexts
`FlexibleInstances`	Allow instance heads to mention arbitrary nested types.
`ForeignFunctionInterface`	Allow foreign function interface syntax.
`FunctionalDependencies`	Allow functional dependencies to be given on typeclass declarations.
`GADTs`	Allow definition of generalised algebraic data types.
`GADTSyntax`	Allow generalised algebraic data type syntax.
`GeneralisedNewtypeDeriving`	Allow instances to be derived via `newtype` deriving.
`GHC2021`	Use GHC’s set of default language extensions from 2021
`GHC2024`	Use GHC’s set of default language extensions from 2024
`GHCForeignImportPrim`	Allow `prim` calling convention. Intended for internal use only.
`Haskell2010`	Use the Haskell 2010 language edition.
`Haskell98`	Use the Haskell 98 language edition.
`HexFloatLiterals`	Allow hexadecimal floating-point literal syntax.
`ImplicitParams`	Allow implicit parameter constraints.
`ImplicitPrelude`	Implicitly import `Prelude`.
`ImportQualifiedPost`	Allows the syntax `import M qualified`
`ImpredicativeTypes`	Allow impredicative types.
`IncoherentInstances`	Allow definitions of instances that may result in incoherence.
`InstanceSigs`	Allow type signatures to be written for instance methods.
`InterruptibleFFI`	Allow `interruptible` FFI imports.
`KindSignatures`	Allow kind signatures to be given for types.
`LambdaCase`	Allow `\case` expressions.
`LexicalNegation`	Use whitespace to determine whether the minus sign stands for negation or subtraction.
`LiberalTypeSynonyms`	Relax many of Haskell 98's rules on type synonym definitions.
`LinearTypes`	Allow writing of linear arrow types. Implies `MonoLocalBinds`.
`ListTuplePuns`	Enable punning for list, tuple and sum types.
`MagicHash`	Allow `#` as a postfix modifier on identifiers.
`MonadComprehensions`	Allow list comprehension syntax to be used at monads other than `List`.
`MonoLocalBinds`	Do not generalise types of local bindings.
`MonomorphismRestriction`	Apply the Haskell 2010 monomorphism restriction.
`MultiParamTypeClasses`	Enable multi-parameter type classes.
`MultiWayIf`	Allow multi-way `if`-expressions.
`NamedFieldPuns`	Allow record field punning syntax.
`NamedWildCards`	Allow named wildcards in types.
`NegativeLiterals`	Allow negative numeric literal syntax.
`NondecreasingIndentation`	Allow nested contexts to be at the same indentation level as its enclosing context.
`NPlusKPatterns`	Allow use of `n+k` patterns.
`NullaryTypeClasses`	Deprecated, does nothing. nullary type classes are now enabled using `MultiParamTypeClasses`.
`NumDecimals`	Allow use of scientific notation syntax for integer literals.
`NumericUnderscores`	Allow underscores in numeric literals.
`OverlappingInstances`	Allow definition of overlapping instances.
`OverloadedLabels`	Allow overloaded label syntax.
`OverloadedLists`	Desugar list syntax via the `IsList` class.
`OverloadedRecordDot`	Allow `.` to be used for record field access.
`OverloadedRecordUpdate`	Allow `.` syntax in record updates
`OverloadedStrings`	Desugar string literals via `IsString` class.
`PackageImports`	Allow package-qualified `import` syntax.
`ParallelListComp`	Allow parallel list comprehension syntax.
`PartialTypeSignatures`	Allow type signatures to contain wildcards.
`PatternGuards`	Allow pattern guards syntax.
`PatternSynonyms`	Allow definition of pattern synonyms.
`PolyKinds`	Allow kind polymorphism.
`PostfixOperators`	Allow the use of postfix operators.
`QualifiedDo`	Allow qualified `do`-notation desugaring.
`QuantifiedConstraints`	Allow `forall` quantifiers in constraints.
`QuasiQuotes`	Allow quasiquotation syntax.
`Rank2Types`	Enable rank-2 types.
`RankNTypes`	Allow types of rank greater than one.
`RebindableSyntax`	Allow rebinding of builtin syntax.
`RecordWildCards`	Allow use of record wildcard syntax.
`RecursiveDo`	Allow recursive do (e.g. `mdo`) notation.
`RequiredTypeArguments`	Allow use of required type argument syntax in terms.
`RoleAnnotations`	Allow role annotation syntax.
`Safe`	Enable the Safe Haskell Safe mode.
`ScopedTypeVariables`	Lexically scope explicitly-introduced type variables.
`StandaloneDeriving`	Allow standalone instance deriving declarations.
`StandaloneKindSignatures`	Allow standalone kind signature declarations.
`StarIsType`	Treat `*` as `Data.Kind.Type`.
`StaticPointers`	Allow `static` syntax.
`Strict`	Make bindings in the current module strict by default.
`StrictData`	Treat datatype fields as strict by default.
`TemplateHaskell`	Allow Template Haskell's splice and quotation syntax.
`TemplateHaskellQuotes`	Allow Template Haskell's quotation syntax.
`TraditionalRecordSyntax`	Allow traditional record syntax (e.g. `C {f = x}`).
`TransformListComp`	Allow generalised list comprehension syntax.
`Trustworthy`	Enable the Safe Haskell Trustworthy mode.
`TupleSections`	Allow use of tuple section synxtax.
`TypeAbstractions`	Allow type abstraction syntax in patterns and type variable binders.
`TypeApplications`	Allow type application syntax in terms and types.
`TypeData`	Allow `type data` declarations.
`TypeFamilies`	Allow definition of type families.
`TypeFamilyDependencies`	Allow injectivity annotations on type families.
`TypeInType`	Deprecated. Enable kind polymorphism and datatype promotion.
`TypeOperators`	Allow type constructors to be given operator names.
`TypeSynonymInstances`	Allow type synonyms to be mentioned in instance heads.
`UnboxedSums`	Allow the use of unboxed sum syntax.
`UnboxedTuples`	Allow the use of unboxed tuple syntax.
`UndecidableInstances`	Allow definition of instances which may make solving undecidable.
`UndecidableSuperClasses`	Allow all superclass constraints, including those that may result in non-termination of the typechecker.
`UnicodeSyntax`	Enable unicode syntax.
`UnliftedDatatypes`	Allow the definition of unlifted data types.
`UnliftedFFITypes`	Allow the types of foreign imports to contain certain unlifted types.
`UnliftedNewtypes`	Allow definition of unlifted newtypes.
`Unsafe`	Enable Safe Haskell Unsafe mode.
`ViewPatterns`	Allow view pattern syntax.