Difference between revisions of "Language extensions"
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Language extensions are used to enable language features in Haskell that may seem useful in certain cases. They can be used to loosen restrictions in the type system or add completely new language constructs to Haskell. |
Language extensions are used to enable language features in Haskell that may seem useful in certain cases. They can be used to loosen restrictions in the type system or add completely new language constructs to Haskell. |
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− | They can be enabled using the [http://www.haskell.org/ghc/docs/7.0.4/html/users_guide/pragmas.html#language-pragma LANGUAGE pragma] |
+ | They can be enabled using the [http://www.haskell.org/ghc/docs/7.0.4/html/users_guide/pragmas.html#language-pragma LANGUAGE pragma] |
+ | |||
+ | <hask> |
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+ | {-# LANGUAGE <Extension>, <Extension> #-} |
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+ | </hask> |
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+ | |||
+ | or (in GHC) using [https://downloads.haskell.org/~ghc/master/users-guide/lang.html flags] <code>-X<Extension></code>. |
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Before just using the language extension that fits your need, [[Use of language extensions|think about |
Before just using the language extension that fits your need, [[Use of language extensions|think about |
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* [[Datatype contexts|DatatypeContexts]] : Add type constraints to your datatype. |
* [[Datatype contexts|DatatypeContexts]] : Add type constraints to your datatype. |
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* [[Default signatures|DefaultSignatures]] |
* [[Default signatures|DefaultSignatures]] |
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+ | * Derive: |
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− | * [[Generics|DeriveGeneric]] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable DeriveDataTypeable] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable DeriveGeneric] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable DeriveFunctor] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable DeriveFoldable] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#deriving-typeable DeriveTraversable] |
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+ | ** [http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html#id616911 GeneralizedNewtypeDeriving] |
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+ | * [https://downloads.haskell.org/~ghc/master/users-guide/glasgow_exts.html#duplicate-record-fields DuplicateRecordFields] (GHC 8.0.1+) : Allow definition of record types with identically-named fields. |
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* [[Existential type|ExistentialQuantification]] |
* [[Existential type|ExistentialQuantification]] |
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* [[Flexible contexts|FlexibleContexts]] |
* [[Flexible contexts|FlexibleContexts]] |
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* [[KindSignatures]] |
* [[KindSignatures]] |
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* [[Multi-parameter type class|MultiParamTypeClasses]] : Enable multiple type parameters in type classes. |
* [[Multi-parameter type class|MultiParamTypeClasses]] : Enable multiple type parameters in type classes. |
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+ | * [[Monomorphism restriction|NoMonomorphismRestriction]] |
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* [[Overlapping instance|OverlappingInstances]] |
* [[Overlapping instance|OverlappingInstances]] |
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* [[Rank-N types|Rank2Types]] |
* [[Rank-N types|Rank2Types]] |
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* [[Scoped type variables|ScopedTypeVariables]] |
* [[Scoped type variables|ScopedTypeVariables]] |
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* [[Template Haskell|TemplateHaskell]] |
* [[Template Haskell|TemplateHaskell]] |
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+ | * [http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#tuple-sections TupleSections] : Allow tuples to be partially applied. |
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* [[GHC/Type families|TypeFamilies]] |
* [[GHC/Type families|TypeFamilies]] |
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* [[Undecidable instance|UndecidableInstances]] |
* [[Undecidable instance|UndecidableInstances]] |
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+ | * [http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#view-patterns ViewPatterns] |
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+ | |||
+ | = See also = |
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+ | |||
+ | * [[Use of language extensions]] |
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Revision as of 09:17, 14 February 2017
Language extensions are used to enable language features in Haskell that may seem useful in certain cases. They can be used to loosen restrictions in the type system or add completely new language constructs to Haskell.
They can be enabled using the LANGUAGE pragma
{-# LANGUAGE <Extension>, <Extension> #-}
or (in GHC) using flags -X<Extension>
.
Before just using the language extension that fits your need, think about when it is useful and what risk it may bring to your program.
List of language extensions by name
This list is far from complete and needs extension.
- DatatypeContexts : Add type constraints to your datatype.
- DefaultSignatures
- Derive:
- DuplicateRecordFields (GHC 8.0.1+) : Allow definition of record types with identically-named fields.
- ExistentialQuantification
- FlexibleContexts
- FlexibleInstances : Allow a type parameter to occure twice within a type class instance.
- FunctionalDependencies : Are used to constrain the parameters of type classes.
- GADTs : Generalised algebraic datatypes - A more general approach to algebraic datatypes.
- ImplicitParams
- KindSignatures
- MultiParamTypeClasses : Enable multiple type parameters in type classes.
- NoMonomorphismRestriction
- OverlappingInstances
- Rank2Types
- RankNTypes
- ScopedTypeVariables
- TemplateHaskell
- TupleSections : Allow tuples to be partially applied.
- TypeFamilies
- UndecidableInstances
- ViewPatterns