Difference between revisions of "Language extensions"
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− | or (in GHC) using [https:// |
+ | or (in GHC) using [https://downloads.haskell.org/ghc/latest/docs/html/users_guide/lang.html flags] <code>-X<Extension></code>. |
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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* [[Default signatures|DefaultSignatures]] |
* [[Default signatures|DefaultSignatures]] |
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* Derive: |
* Derive: |
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− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#deriving-typeable-instances DeriveDataTypeable] |
− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-DeriveGeneric DeriveGeneric] |
− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-DeriveFunctor DeriveFunctor] |
− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-DeriveFoldable DeriveFoldable] |
− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-DeriveTraversable DeriveTraversable] |
− | ** [ |
+ | ** [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-GeneralizedNewtypeDeriving GeneralizedNewtypeDeriving] |
− | * [https:// |
+ | * [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-DuplicateRecordFields DuplicateRecordFields] (GHC 8.0.1+) : Allow definition of record types with identically-named fields. |
* [[Existential type|ExistentialQuantification]] |
* [[Existential type|ExistentialQuantification]] |
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* [[Flexible contexts|FlexibleContexts]] |
* [[Flexible contexts|FlexibleContexts]] |
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* [[Rank-N types|RankNTypes]] |
* [[Rank-N types|RankNTypes]] |
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* [[Scoped type variables|ScopedTypeVariables]] |
* [[Scoped type variables|ScopedTypeVariables]] |
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+ | * [[GHC/Stand-alone_deriving_declarations|StandaloneDeriving]] |
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* [[Template Haskell|TemplateHaskell]] |
* [[Template Haskell|TemplateHaskell]] |
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− | * |
+ | * {{GHCUsersGuide|exts/tuple_sections||section on TupleSections}} It allows tuples to be partially applied. |
* [[GHC/Type families|TypeFamilies]] |
* [[GHC/Type families|TypeFamilies]] |
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* [[Undecidable instance|UndecidableInstances]] |
* [[Undecidable instance|UndecidableInstances]] |
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− | * [ |
+ | * [https://downloads.haskell.org/~ghc/8.10.3/docs/html/users_guide/glasgow_exts.html#extension-ViewPatterns ViewPatterns] |
+ | * [[QualifiedDo]] |
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= See also = |
= See also = |
Latest revision as of 05:36, 9 September 2021
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
- StandaloneDeriving
- TemplateHaskell
- The GHC Users Guide has section on TupleSections. It allows tuples to be partially applied.
- TypeFamilies
- UndecidableInstances
- ViewPatterns
- QualifiedDo