Language.Haskell.Extension

Cabal-1.22.5.0: A framework for packaging Haskell software

Copyright | Isaac Jones 2003-2004
License | BSD3
Maintainer | libraries@haskell.org
Portability | portable
Safe Haskell | Safe
Language | Haskell98

Language.Haskell.Extension

Description

Haskell language dialects and extensions

Synopsis

- data Language
  - = Haskell98
  - | Haskell2010
  - | UnknownLanguage String
- knownLanguages :: [Language]
- data Extension
  - = EnableExtension KnownExtension
  - | DisableExtension KnownExtension
  - | UnknownExtension String
- data KnownExtension
  - = OverlappingInstances
  - | UndecidableInstances
  - | IncoherentInstances
  - | DoRec
  - | RecursiveDo
  - | ParallelListComp
  - | MultiParamTypeClasses
  - | MonomorphismRestriction
  - | FunctionalDependencies
  - | Rank2Types
  - | RankNTypes
  - | PolymorphicComponents
  - | ExistentialQuantification
  - | ScopedTypeVariables
  - | PatternSignatures
  - | ImplicitParams
  - | FlexibleContexts
  - | FlexibleInstances
  - | EmptyDataDecls
  - | CPP
  - | KindSignatures
  - | BangPatterns
  - | TypeSynonymInstances
  - | TemplateHaskell
  - | ForeignFunctionInterface
  - | Arrows
  - | Generics
  - | ImplicitPrelude
  - | NamedFieldPuns
  - | PatternGuards
  - | GeneralizedNewtypeDeriving
  - | ExtensibleRecords
  - | RestrictedTypeSynonyms
  - | HereDocuments
  - | MagicHash
  - | TypeFamilies
  - | StandaloneDeriving
  - | UnicodeSyntax
  - | UnliftedFFITypes
  - | InterruptibleFFI
  - | CApiFFI
  - | LiberalTypeSynonyms
  - | TypeOperators
  - | RecordWildCards
  - | RecordPuns
  - | DisambiguateRecordFields
  - | TraditionalRecordSyntax
  - | OverloadedStrings
  - | GADTs
  - | GADTSyntax
  - | MonoPatBinds
  - | RelaxedPolyRec
  - | ExtendedDefaultRules
  - | UnboxedTuples
  - | DeriveDataTypeable
  - | DeriveGeneric
  - | DefaultSignatures
  - | InstanceSigs
  - | ConstrainedClassMethods
  - | PackageImports
  - | ImpredicativeTypes
  - | NewQualifiedOperators
  - | PostfixOperators
  - | QuasiQuotes
  - | TransformListComp
  - | MonadComprehensions
  - | ViewPatterns
  - | XmlSyntax
  - | RegularPatterns
  - | TupleSections
  - | GHCForeignImportPrim
  - | NPlusKPatterns
  - | DoAndIfThenElse
  - | MultiWayIf
  - | LambdaCase
  - | RebindableSyntax
  - | ExplicitForAll
  - | DatatypeContexts
  - | MonoLocalBinds
  - | DeriveFunctor
  - | DeriveTraversable
  - | DeriveFoldable
  - | NondecreasingIndentation
  - | SafeImports
  - | Safe
  - | Trustworthy
  - | Unsafe
  - | ConstraintKinds
  - | PolyKinds
  - | DataKinds
  - | ParallelArrays
  - | RoleAnnotations
  - | OverloadedLists
  - | EmptyCase
  - | AutoDeriveTypeable
  - | NegativeLiterals
  - | BinaryLiterals
  - | NumDecimals
  - | NullaryTypeClasses
  - | ExplicitNamespaces
  - | AllowAmbiguousTypes
  - | JavaScriptFFI
  - | PatternSynonyms
  - | PartialTypeSignatures
  - | NamedWildCards
  - | DeriveAnyClass
- knownExtensions :: [KnownExtension]
- deprecatedExtensions :: [(Extension, Maybe Extension)]

# Documentation

data Language

This represents a Haskell language dialect.

Language `Extension`s are interpreted relative to one of these base languages.

Constructors

Haskell98 | The Haskell 98 language as defined by the Haskell 98 report. http://haskell.org/onlinereport/
Haskell2010 | The Haskell 2010 language as defined by the Haskell 2010 report. http://www.haskell.org/onlinereport/haskell2010
UnknownLanguage String | An unknown language, identified by its name.

Instances

Eq Language |
Data Language |
Read Language |
Show Language |
Generic Language |
Binary Language |
Text Language |
type Rep Language |

knownLanguages :: [Language]

data Extension

This represents language extensions beyond a base `Language` definition (such as `Haskell98`) that are supported by some implementations, usually in some special mode.

Where applicable, references are given to an implementation's official documentation.

Constructors

EnableExtension KnownExtension | Enable a known extension
DisableExtension KnownExtension | Disable a known extension
UnknownExtension String | An unknown extension, identified by the name of its `LANGUAGE` pragma.

Instances

Eq Extension |
Data Extension |
Ord Extension |
Read Extension |
Show Extension |
Generic Extension |
Binary Extension |
Text Extension |
type Rep Extension |

data KnownExtension

Constructors

OverlappingInstances | Allow overlapping class instances, provided there is a unique most specific instance for each use. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-overlap
UndecidableInstances | Ignore structural rules guaranteeing the termination of class instance resolution. Termination is guaranteed by a fixed-depth recursion stack, and compilation may fail if this depth is exceeded. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#undecidable-instances
IncoherentInstances | Implies `OverlappingInstances`. Allow the implementation to choose an instance even when it is possible that further instantiation of types will lead to a more specific instance being applicable. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-overlap
DoRec | (deprecated) Allow recursive bindings in `do` blocks, using the `rec` keyword. See also `RecursiveDo`.
RecursiveDo | Allow recursive bindings using `mdo`, a variant of `do`. `DoRec` provides a different, preferred syntax. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#recursive-do-notation
ParallelListComp | Provide syntax for writing list comprehensions which iterate over several lists together, like the `zipWith` family of functions. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#parallel-list-comprehensions
MultiParamTypeClasses | Allow multiple parameters in a type class. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#multi-param-type-classes
MonomorphismRestriction | Enable the dreaded monomorphism restriction. http://www.haskell.org/ghc/docs/latest/html/users_guide/monomorphism.html
FunctionalDependencies | Allow a specification attached to a multi-parameter type class which indicates that some parameters are entirely determined by others. The implementation will check that this property holds for the declared instances, and will use this property to reduce ambiguity in instance resolution. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#functional-dependencies
Rank2Types | Like `RankNTypes` but does not allow a higher-rank type to itself appear on the left of a function arrow. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#universal-quantification
RankNTypes | Allow a universally-quantified type to occur on the left of a function arrow. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#universal-quantification
PolymorphicComponents | Allow data constructors to have polymorphic arguments. Unlike `RankNTypes`, does not allow this for ordinary functions. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#universal-quantification
ExistentialQuantification | Allow existentially-quantified data constructors. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#existential-quantification
ScopedTypeVariables | Cause a type variable in a signature, which has an explicit `forall` quantifier, to scope over the definition of the accompanying value declaration. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#scoped-type-variables
PatternSignatures | Deprecated, use `ScopedTypeVariables` instead.
ImplicitParams | Enable implicit function parameters with dynamic scope. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#implicit-parameters
FlexibleContexts | Relax some restrictions on the form of the context of a type signature. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#flexible-contexts
FlexibleInstances | Relax some restrictions on the form of the context of an instance declaration. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-rules
EmptyDataDecls | Allow data type declarations with no constructors. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#nullary-types
CPP | Run the C preprocessor on Haskell source code. http://www.haskell.org/ghc/docs/latest/html/users_guide/options-phases.html#c-pre-processor
KindSignatures | Allow an explicit kind signature giving the kind of types over which a type variable ranges. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#kinding
BangPatterns | Enable a form of pattern which forces evaluation before an attempted match, and a form of strict `let`/`where` binding. http://www.haskell.org/ghc/docs/latest/html/users_guide/bang-patterns.html
TypeSynonymInstances | Allow type synonyms in instance heads. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#flexible-instance-head
TemplateHaskell | Enable Template Haskell, a system for compile-time metaprogramming. http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.html
ForeignFunctionInterface | Enable the Foreign Function Interface. In GHC, implements the standard Haskell 98 Foreign Function Interface Addendum, plus some GHC-specific extensions. http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi.html
Arrows | Enable arrow notation. http://www.haskell.org/ghc/docs/latest/html/users_guide/arrow-notation.html
Generics | (deprecated) Enable generic type classes, with default instances defined in terms of the algebraic structure of a type. http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-classes.html
ImplicitPrelude | Enable the implicit importing of the module Prelude. When disabled, when desugaring certain built-in syntax into ordinary identifiers, use whatever is in scope rather than the Prelude -- version. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#rebindable-syntax
NamedFieldPuns | Enable syntax for implicitly binding local names corresponding to the field names of a record. Puns bind specific names, unlike `RecordWildCards`. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#record-puns
PatternGuards | Enable a form of guard which matches a pattern and binds variables. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#pattern-guards
GeneralizedNewtypeDeriving | Allow a type declared with `newtype` to use `deriving` for any class with an instance for the underlying type. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#newtype-deriving
ExtensibleRecords | Enable the "Trex" extensible records system. http://cvs.haskell.org/Hugs/pages/users_guide/hugs-only.html#TREX
RestrictedTypeSynonyms | Enable type synonyms which are transparent in some definitions and opaque elsewhere, as a way of implementing abstract datatypes. http://cvs.haskell.org/Hugs/pages/users_guide/restricted-synonyms.html
HereDocuments | Enable an alternate syntax for string literals, with string templating. http://cvs.haskell.org/Hugs/pages/users_guide/here-documents.html
MagicHash | Allow the character `#` as a postfix modifier on identifiers. Also enables literal syntax for unboxed values. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#magic-hash
TypeFamilies | Allow data types and type synonyms which are indexed by types, i.e. ad-hoc polymorphism for types. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-families.html
StandaloneDeriving | Allow a standalone declaration which invokes the type class `deriving` mechanism. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#stand-alone-deriving
UnicodeSyntax | Allow certain Unicode characters to stand for certain ASCII character sequences, e.g. keywords and punctuation. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#unicode-syntax
UnliftedFFITypes | Allow the use of unboxed types as foreign types, e.g. in `foreign import` and `foreign export`. http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi.html#id681687
InterruptibleFFI | Enable interruptible FFI. http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi.html#ffi-interruptible
CApiFFI | Allow use of CAPI FFI calling convention (`foreign import capi`). http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi.html#ffi-capi
LiberalTypeSynonyms | Defer validity checking of types until after expanding type synonyms, relaxing the constraints on how synonyms may be used. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#type-synonyms
TypeOperators | Allow the name of a type constructor, type class, or type variable to be an infix operator.
RecordWildCards | Enable syntax for implicitly binding local names corresponding to the field names of a record. A wildcard binds all unmentioned names, unlike `NamedFieldPuns`. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#record-wildcards
RecordPuns | Deprecated, use `NamedFieldPuns` instead.
DisambiguateRecordFields | Allow a record field name to be disambiguated by the type of the record it's in. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#disambiguate-fields
TraditionalRecordSyntax | Enable traditional record syntax (as supported by Haskell 98) http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#traditional-record-syntax
OverloadedStrings | Enable overloading of string literals using a type class, much like integer literals. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#overloaded-strings
GADTs | Enable generalized algebraic data types, in which type variables may be instantiated on a per-constructor basis. Implies `GADTSyntax`. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#gadt
GADTSyntax | Enable GADT syntax for declaring ordinary algebraic datatypes. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#gadt-style
MonoPatBinds | Make pattern bindings monomorphic. http://www.haskell.org/ghc/docs/latest/html/users_guide/monomorphism.html#id630981
RelaxedPolyRec | Relax the requirements on mutually-recursive polymorphic functions. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#typing-binds
ExtendedDefaultRules | Allow default instantiation of polymorphic types in more situations. http://www.haskell.org/ghc/docs/latest/html/users_guide/interactive-evaluation.html#extended-default-rules
UnboxedTuples | Enable unboxed tuples. http://www.haskell.org/ghc/docs/latest/html/users_guide/primitives.html#unboxed-tuples
DeriveDataTypeable | Enable `deriving` for classes `Typeable` and `Data`. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable
DeriveGeneric | Enable `deriving` for `Generic` and `Generic1`. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable
DefaultSignatures | Enable support for default signatures. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#class-default-signatures
InstanceSigs | Allow type signatures to be specified in instance declarations. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#instance-sigs
ConstrainedClassMethods | Allow a class method's type to place additional constraints on a class type variable. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#class-method-types
PackageImports | Allow imports to be qualified by the package name the module is intended to be imported from, e.g.
    import "network" Network.Socket
http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#package-imports
ImpredicativeTypes | (deprecated) Allow a type variable to be instantiated at a polymorphic type. http://www.haskell.org/ghc/docs/6.12.3/html/users_guide/other-type-extensions.html#impredicative-polymorphism
NewQualifiedOperators | (deprecated) Change the syntax for qualified infix operators. http://www.haskell.org/ghc/docs/6.12.3/html/users_guide/syntax-extns.html#new-qualified-operators
PostfixOperators | Relax the interpretation of left operator sections to allow unary postfix operators. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#postfix-operators
QuasiQuotes | Enable quasi-quotation, a mechanism for defining new concrete syntax for expressions and patterns. http://www.haskell.org/ghc/docs/latest/html/users_guide/template-haskell.html#th-quasiquotation
TransformListComp | Enable generalized list comprehensions, supporting operations such as sorting and grouping. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#generalised-list-comprehensions
MonadComprehensions | Enable monad comprehensions, which generalise the list comprehension syntax to work for any monad. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#monad-comprehensions
ViewPatterns | Enable view patterns, which match a value by applying a function and matching on the result. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#view-patterns
XmlSyntax | Allow concrete XML syntax to be used in expressions and patterns, as per the Haskell Server Pages extension language: http://www.haskell.org/haskellwiki/HSP. The ideas behind it are discussed in the paper "Haskell Server Pages through Dynamic Loading" by Niklas Broberg, from Haskell Workshop '05.
RegularPatterns | Allow regular pattern matching over lists, as discussed in the paper "Regular Expression Patterns" by Niklas Broberg, Andreas Farre and Josef Svenningsson, from ICFP '04.
TupleSections | Enable the use of tuple sections, e.g. `(, True)` desugars into `x -> (x, True)`. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#tuple-sections
GHCForeignImportPrim | Allow GHC primops, written in C--, to be imported into a Haskell file.
NPlusKPatterns | Support for patterns of the form `n + k`, where `k` is an integer literal. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#n-k-patterns
DoAndIfThenElse | Improve the layout rule when `if` expressions are used in a `do` block.
MultiWayIf | Enable support for multi-way `if`-expressions. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#multi-way-if
LambdaCase | Enable support lambda-`case` expressions. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#lambda-case
RebindableSyntax | Makes much of the Haskell sugar be desugared into calls to the function with a particular name that is in scope. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#rebindable-syntax
ExplicitForAll | Make `forall` a keyword in types, which can be used to give the generalisation explicitly. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#explicit-foralls
DatatypeContexts | Allow contexts to be put on datatypes, e.g. the `Eq a` in `data Eq a => Set a = NilSet | ConsSet a (Set a)`. http://www.haskell.org/ghc/docs/latest/html/users_guide/data-type-extensions.html#datatype-contexts
MonoLocalBinds | Local (`let` and `where`) bindings are monomorphic. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#mono-local-binds
DeriveFunctor | Enable `deriving` for the `Functor` class. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable
DeriveTraversable | Enable `deriving` for the `Traversable` class. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable
DeriveFoldable | Enable `deriving` for the `Foldable` class. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable
NondecreasingIndentation | Enable non-decreasing indentation for `do` blocks. http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs-and-infelicities.html#infelicities-syntax
SafeImports | Allow imports to be qualified with a safe keyword that requires the imported module be trusted as according to the Safe Haskell definition of trust.
    import safe Network.Socket
http://www.haskell.org/ghc/docs/latest/html/users_guide/safe-haskell.html#safe-imports
Safe | Compile a module in the Safe, Safe Haskell mode -- a restricted form of the Haskell language to ensure type safety. http://www.haskell.org/ghc/docs/latest/html/users_guide/safe-haskell.html#safe-trust
Trustworthy | Compile a module in the Trustworthy, Safe Haskell mode -- no restrictions apply but the module is marked as trusted as long as the package the module resides in is trusted. http://www.haskell.org/ghc/docs/latest/html/users_guide/safe-haskell.html#safe-trust
Unsafe | Compile a module in the Unsafe, Safe Haskell mode so that modules compiled using Safe, Safe Haskell mode can't import it. http://www.haskell.org/ghc/docs/latest/html/users_guide/safe-haskell.html#safe-trust
ConstraintKinds | Allow type classimplicit parameterequality constraints to be used as types with the special kind constraint. Also generalise the `(ctxt => ty)` syntax so that any type of kind constraint can occur before the arrow. http://www.haskell.org/ghc/docs/latest/html/users_guide/constraint-kind.html
PolyKinds | Enable kind polymorphism. http://www.haskell.org/ghc/docs/latest/html/users_guide/kind-polymorphism.html
DataKinds | Enable datatype promotion. http://www.haskell.org/ghc/docs/latest/html/users_guide/promotion.html
ParallelArrays | Enable parallel arrays syntax (`[:`, `:]`) for Data Parallel Haskell. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell
RoleAnnotations | Enable explicit role annotations, like in (`type role Foo representational representational`). http://www.haskell.org/ghc/docs/latest/html/users_guide/roles.html
OverloadedLists | Enable overloading of list literals, arithmetic sequences and list patterns using the `IsList` type class. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#overloaded-lists
EmptyCase | Enable case expressions that have no alternatives. Also applies to lambda-case expressions if they are enabled. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#empty-case
AutoDeriveTypeable | Triggers the generation of derived `Typeable` instances for every datatype and type class declaration. http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#auto-derive-typeable
NegativeLiterals | Desugars negative literals directly (without using negate). http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#negative-literals
BinaryLiterals | Allow the use of binary integer literal syntax (e.g. `0b11001001` to denote `201`). http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#binary-literals
NumDecimals | Allow the use of floating literal syntax for all instances of `Num`, including `Int` and `Integer`. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#num-decimals
NullaryTypeClasses | Enable support for type classes with no type parameter. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-class-extensions.html#nullary-type-classes
ExplicitNamespaces | Enable explicit namespaces in module import/export lists. http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#explicit-namespaces
AllowAmbiguousTypes | Allow the user to write ambiguous types, and the type inference engine to infer them. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#ambiguity
JavaScriptFFI | Enable `foreign import javascript`.
PatternSynonyms | Allow giving names to and abstracting over patterns. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#pattern-synonyms
PartialTypeSignatures | Allow anonymous placeholders (underscore) inside type signatures. The type inference engine will generate a message describing the type inferred at the hole's location. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#partial-type-signatures
NamedWildCards | Allow named placeholders written with a leading underscore inside type signatures. Wildcards with the same name unify to the same type. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#named-wildcards
DeriveAnyClass | Enable `deriving` for any class. http://www.haskell.org/ghc/docs/latest/html/users_guide/other-type-extensions.html#derive-any-class

Instances

Bounded KnownExtension |
Enum KnownExtension |
Eq KnownExtension |
Data KnownExtension |
Ord KnownExtension |
Read KnownExtension |
Show KnownExtension |
Generic KnownExtension |
Binary KnownExtension |
Text KnownExtension |
type Rep KnownExtension |

knownExtensions :: [KnownExtension]

Deprecated: KnownExtension is an instance of Enum and Bounded, use those instead.

deprecatedExtensions :: [(Extension, Maybe Extension)]

Extensions that have been deprecated, possibly paired with another extension that replaces it.