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Diffstat (limited to 'docs/users_guide/glasgow_exts.rst')
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1 files changed, 557 insertions, 21 deletions
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst index ac64153dfa..3083d43666 100644 --- a/docs/users_guide/glasgow_exts.rst +++ b/docs/users_guide/glasgow_exts.rst @@ -49,10 +49,15 @@ Although not recommended, the deprecated :ghc-flag:`-fglasgow-exts` flag enables a large swath of the extensions supported by GHC at once. .. ghc-flag:: -fglasgow-exts + :shortdesc: Deprecated. Enable most language extensions; + see :ref:`options-language` for exactly which ones. + :type: dynamic + :reverse: -fno-glasgow-exts + :category: The flag ``-fglasgow-exts`` is equivalent to enabling the following extensions: - .. include:: what_glasgow_exts_does.gen.rst + .. include:: what_glasgow_exts_does.rst Enabling these options is the *only* effect of ``-fglasgow-exts``. We are trying to move away from this portmanteau flag, and towards enabling features @@ -201,6 +206,12 @@ Unboxed tuples -------------- .. ghc-flag:: -XUnboxedTuples + :shortdesc: Enable :ref:`unboxed tuples <unboxed-tuples>`. + :type: dynamic + :reverse: -XNoUnboxedTuples + :category: + + :since: 6.8.1 Enable the use of unboxed tuple syntax. @@ -262,6 +273,12 @@ Unboxed sums ------------ .. ghc-flag:: -XUnboxedSums + :shortdesc: Enable :ref: `unboxed sums <unboxed-sums>`. + :type: dynamic + :reverse: -XNoUnboxedSums + :category: + + :since: 8.2.1 Enable the use of unboxed sum syntax. @@ -344,6 +361,12 @@ Unicode syntax -------------- .. ghc-flag:: -XUnicodeSyntax + :shortdesc: Enable :ref:`unicode syntax <unicode-syntax>`. + :type: dynamic + :reverse: -XNoUnicodeSyntax + :category: + + :since: 6.8.1 Enable the use of Unicode characters in place of their equivalent ASCII sequences. @@ -391,6 +414,12 @@ The magic hash -------------- .. ghc-flag:: -XMagicHash + :shortdesc: Allow ``#`` as a :ref:`postfix modifier on identifiers <magic-hash>`. + :type: dynamic + :reverse: -XNoMagicHash + :category: + + :since: 6.8.1 Enable the use of the hash character (``#``) as an identifier suffix. @@ -433,6 +462,10 @@ Negative literals ----------------- .. ghc-flag:: -XNegativeLiterals + :shortdesc: Enable support for :ref:`negative literals <negative-literals>`. + :type: dynamic + :reverse: -XNoNegativeLiterals + :category: :since: 7.8.1 @@ -454,6 +487,10 @@ Fractional looking integer literals ----------------------------------- .. ghc-flag:: -XNumDecimals + :shortdesc: Enable support for 'fractional' integer literals. + :type: dynamic + :reverse: -XNoNumDecimals + :category: :since: 7.8.1 @@ -472,6 +509,10 @@ Binary integer literals ----------------------- .. ghc-flag:: -XBinaryLiterals + :shortdesc: Enable support for :ref:`binary literals <binary-literals>`. + :type: dynamic + :reverse: -XNoBinaryLiterals + :category: :since: 7.10.1 @@ -492,6 +533,11 @@ Pattern guards -------------- .. ghc-flag:: -XNoPatternGuards + :shortdesc: Disable :ref:`pattern guards <pattern-guards>`. + Implied by :ghc-flag:`-XHaskell98`. + :type: dynamic + :reverse: -XPatternGuards + :category: :implied by: :ghc-flag:`-XHaskell98` :since: 6.8.1 @@ -505,6 +551,12 @@ View patterns ------------- .. ghc-flag:: -XViewPatterns + :shortdesc: Enable :ref:`view patterns <view-patterns>`. + :type: dynamic + :reverse: -XNoViewPatterns + :category: + + :since: 6.10.1 Allow use of view pattern syntax. @@ -643,9 +695,14 @@ n+k patterns ------------ .. ghc-flag:: -XNPlusKPatterns + :shortdesc: Enable support for ``n+k`` patterns. + Implied by :ghc-flag:`-XHaskell98`. + :type: dynamic + :reverse: -XNoNPlusKPatterns + :category: :implied by: :ghc-flag:`-XHaskell98` - :since: 6.12 + :since: 6.12.1 Enable use of ``n+k`` patterns. @@ -655,6 +712,12 @@ The recursive do-notation ------------------------- .. ghc-flag:: -XRecursiveDo + :shortdesc: Enable :ref:`recursive do (mdo) notation <recursive-do-notation>`. + :type: dynamic + :reverse: -XNoRecursiveDo + :category: + + :since: 6.8.1 Allow the use of recursive ``do`` notation. @@ -867,6 +930,10 @@ Applicative do-notation single: do-notation; Applicative .. ghc-flag:: -XApplicativeDo + :shortdesc: Enable :ref:`Applicative do-notation desugaring <applicative-do>` + :type: dynamic + :reverse: -XNoApplicativeDo + :category: :since: 8.0.1 @@ -957,6 +1024,10 @@ cases it might miss an opportunity. There is an algorithm that finds the optimal solution, provided as an option: .. ghc-flag:: -foptimal-applicative-do + :shortdesc: Use a slower but better algorithm for ApplicativeDo + :type: dynamic + :reverse: -fno-optimal-applicative-do + :category: optimization :since: 8.0.1 @@ -1093,6 +1164,14 @@ Parallel List Comprehensions single: parallel list comprehensions .. ghc-flag:: -XParallelListComp + :shortdesc: Enable :ref:`parallel list comprehensions + <parallel-list-comprehensions>`. + Implied by :ghc-flag:`-XParallelArrays`. + :type: dynamic + :reverse: -XNoParallelListComp + :category: + + :since: 6.8.1 Allow parallel list comprehension syntax. @@ -1142,6 +1221,13 @@ Generalised (SQL-like) List Comprehensions single: SQL .. ghc-flag:: -XTransformListComp + :shortdesc: Enable :ref:`generalised list comprehensions + <generalised-list-comprehensions>`. + :type: dynamic + :reverse: -XNoTransformListComp + :category: + + :since: 6.10.1 Allow use of generalised list (SQL-like) comprehension syntax. This introduces the ``group``, ``by``, and ``using`` keywords. @@ -1280,8 +1366,12 @@ Monad comprehensions single: monad comprehensions .. ghc-flag:: -XMonadComprehensions + :shortdesc: Enable :ref:`monad comprehensions <monad-comprehensions>`. + :type: dynamic + :reverse: -XNoMonadComprehensions + :category: - :since: 7.2 + :since: 7.2.1 Enable list comprehension syntax for arbitrary monads. @@ -1442,6 +1532,10 @@ New monadic failure desugaring mechanism ---------------------------------------- .. ghc-flag:: -XMonadFailDesugaring + :shortdesc: Enable :ref:`monadfail desugaring <monadfail-desugaring>`. + :type: dynamic + :reverse: -XNoMonadFailDesugaring + :category: :since: 8.0.1 @@ -1464,6 +1558,13 @@ Rebindable syntax and the implicit Prelude import ------------------------------------------------- .. ghc-flag:: -XNoImplicitPrelude + :shortdesc: Don't implicitly ``import Prelude``. + Implied by :ghc-flag:`-XRebindableSyntax`. + :type: dynamic + :reverse: -XImplicitPrelude + :category: + + :since: 6.8.1 Don't import ``Prelude`` by default. @@ -1474,6 +1575,11 @@ don't call it ``Prelude``; the Haskell module namespace is flat, and you must not conflict with any Prelude module.) .. ghc-flag:: -XRebindableSyntax + :shortdesc: Employ :ref:`rebindable syntax <rebindable-syntax>`. + Implies :ghc-flag:`-XNoImplicitPrelude`. + :type: dynamic + :reverse: -XNoRebindableSyntax + :category: :implies: :ghc-flag:`-XNoImplicitPrelude` :since: 7.0.1 @@ -1574,6 +1680,12 @@ Postfix operators ----------------- .. ghc-flag:: -XPostfixOperators + :shortdesc: Enable :ref:`postfix operators <postfix-operators>`. + :type: dynamic + :reverse: -XNoPostfixOperators + :category: + + :since: 7.10.1 Allow the use of post-fix operators @@ -1606,6 +1718,10 @@ Tuple sections -------------- .. ghc-flag:: -XTupleSections + :shortdesc: Enable :ref:`tuple sections <tuple-sections>`. + :type: dynamic + :reverse: -XNoTupleSections + :category: :since: 6.12 @@ -1647,6 +1763,10 @@ Lambda-case ----------- .. ghc-flag:: -XLambdaCase + :shortdesc: Enable :ref:`lambda-case expressions <lambda-case>`. + :type: dynamic + :reverse: -XNoLambdaCase + :category: :since: 7.6.1 @@ -1673,6 +1793,10 @@ Empty case alternatives ----------------------- .. ghc-flag:: -XEmptyCase + :shortdesc: Allow :ref:`empty case alternatives <empty-case>`. + :type: dynamic + :reverse: -XNoEmptyCase + :category: :since: 7.8.1 @@ -1720,6 +1844,10 @@ Multi-way if-expressions ------------------------ .. ghc-flag:: -XMultiWayIf + :shortdesc: Enable :ref:`multi-way if-expressions <multi-way-if>`. + :type: dynamic + :reverse: -XNoMultiWayIf + :category: :since: 7.6.1 @@ -1836,6 +1964,12 @@ Package-qualified imports ~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XPackageImports + :shortdesc: Enable :ref:`package-qualified imports <package-imports>`. + :type: dynamic + :reverse: -XNoPackageImports + :category: + + :since: 6.10.1 Allow the use of package-qualified ``import`` syntax. @@ -1867,11 +2001,32 @@ Safe imports ~~~~~~~~~~~~ .. ghc-flag:: -XSafe - -XTrustworthy - -XUnsafe + :shortdesc: Enable the :ref:`Safe Haskell <safe-haskell>` Safe mode. + :type: dynamic + :category: + :noindex: + + :since: 7.2.1 + + Declare the Safe Haskell state of the current module. + +.. ghc-flag:: -XTrustworthy + :shortdesc: Enable the :ref:`Safe Haskell <safe-haskell>` Trustworthy mode. + :type: dynamic + :category: + :noindex: + + :since: 7.2.1 + + Declare the Safe Haskell state of the current module. + +.. ghc-flag:: -XUnsafe + :shortdesc: Enable :ref:`Safe Haskell <safe-haskell>` Unsafe mode. + :type: dynamic + :category: :noindex: - :since: 7.2 + :since: 7.4.1 Declare the Safe Haskell state of the current module. @@ -1892,6 +2047,12 @@ Explicit namespaces in import/export ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XExplicitNamespaces + :shortdesc: Enable using the keyword ``type`` to specify the namespace of + entries in imports and exports (:ref:`explicit-namespaces`). + Implied by :ghc-flag:`-XTypeOperators` and :ghc-flag:`-XTypeFamilies`. + :type: dynamic + :reverse: -XNoExplicitNamespaces + :category: :since: 7.6.1 @@ -2027,6 +2188,12 @@ Data types with no constructors ------------------------------- .. ghc-flag:: -XEmptyDataDecls + :shortdesc: Allow definition of empty ``data`` types. + :type: dynamic + :reverse: -XNoEmptyDataDecls + :category: + + :since: 6.8.1 Allow definition of empty ``data`` types. @@ -2049,6 +2216,10 @@ Data type contexts ------------------ .. ghc-flag:: -XDatatypeContexts + :shortdesc: Allow contexts on ``data`` types. + :type: dynamic + :reverse: -XNoEmptyDataDecls + :category: :since: 7.0.1 @@ -2121,8 +2292,14 @@ Type operators -------------- .. ghc-flag:: -XTypeOperators + :shortdesc: Enable :ref:`type operators <type-operators>`. + Implies :ghc-flag:`-XExplicitNamespaces`. + :type: dynamic + :reverse: -XNoTypeOperators + :category: :implies: :ghc-flag:`-XExplicitNamespaces` + :since: 6.8.1 Allow the use and definition of types with operator names. @@ -2172,8 +2349,13 @@ Liberalised type synonyms ------------------------- .. ghc-flag:: -XLiberalTypeSynonyms + :shortdesc: Enable :ref:`liberalised type synonyms <type-synonyms>`. + :type: dynamic + :reverse: -XNoLiberalTypeSynonyms + :category: :implies: :ghc-flag:`-XExplicitForAll` + :since: 6.8.1 Relax many of the Haskell 98 rules on type synonym definitions. @@ -2250,8 +2432,13 @@ Existentially quantified data constructors ------------------------------------------ .. ghc-flag:: -XExistentialQuantification + :shortdesc: Enable :ref:`liberalised type synonyms <type-synonyms>`. + :type: dynamic + :reverse: -XNoLiberalTypeSynonyms + :category: :implies: :ghc-flag:`-XExplicitForAll` + :since: 6.8.1 Allow existentially quantified type variables in types. @@ -2506,8 +2693,12 @@ Declaring data types with explicit constructor signatures --------------------------------------------------------- .. ghc-flag:: -XGADTSyntax + :shortdesc: Enable :ref:`generalised algebraic data type syntax <gadt-style>`. + :type: dynamic + :reverse: -XNoGADTSyntax + :category: - :since: 7.2 + :since: 7.2.1 Allow the use of GADT syntax in data type definitions (but not GADTs themselves; for this see :ghc-flag:`-XGADTs`) @@ -2758,8 +2949,14 @@ Generalised Algebraic Data Types (GADTs) ---------------------------------------- .. ghc-flag:: -XGADTs + :shortdesc: Enable :ref:`generalised algebraic data types <gadt>`. + Implies :ghc-flag:`-XGADTSyntax` and :ghc-flag:`-XMonoLocalBinds`. + :type: dynamic + :reverse: -XNoGADTs + :category: :implies: :ghc-flag:`-XMonoLocalBinds`, :ghc-flag:`-XGADTSyntax` + :since: 6.8.1 Allow use of Generalised Algebraic Data Types (GADTs). @@ -2897,6 +3094,11 @@ Traditional record syntax ------------------------- .. ghc-flag:: -XNoTraditionalRecordSyntax + :shortdesc: Disable support for traditional record syntax + (as supported by Haskell 98) ``C {f = x}`` + :type: dynamic + :reverse: -XTraditionalRecordSyntax + :category: :since: 7.4.1 @@ -2911,6 +3113,13 @@ Record field disambiguation --------------------------- .. ghc-flag:: -XDisambiguateRecordFields + :shortdesc: Enable :ref:`record field disambiguation <disambiguate-fields>`. + Implied by :ghc-flag:`-XRecordWildCards`. + :type: dynamic + :reverse: -XNoDisambiguateRecordFields + :category: + + :since: 6.8.1 :since: 6.8.1 @@ -2984,6 +3193,10 @@ Duplicate record fields ----------------------- .. ghc-flag:: -XDuplicateRecordFields + :shortdesc: Allow definition of record types with identically-named fields. + :type: dynamic + :reverse: -XNoDuplicateRecordFields + :category: :implies: :ghc-flag:`-XDisambiguateRecordFields` :since: 8.0.1 @@ -3118,6 +3331,12 @@ Record puns ----------- .. ghc-flag:: -XNamedFieldPuns + :shortdesc: Enable :ref:`record puns <record-puns>`. + :type: dynamic + :reverse: -XNoNamedFieldPuns + :category: + + :since: 6.10.1 Allow use of record puns. @@ -3179,8 +3398,14 @@ Record wildcards ---------------- .. ghc-flag:: -XRecordWildCards + :shortdesc: Enable :ref:`record wildcards <record-wildcards>`. + Implies :ghc-flag:`-XDisambiguateRecordFields`. + :type: dynamic + :reverse: -XNoRecordWildCards + :category: :implies: :ghc-flag:`-XDisambiguateRecordFields`. + :since: 6.8.1 Allow the use of wildcards in record construction and pattern matching. @@ -3487,6 +3712,12 @@ Stand-alone deriving declarations --------------------------------- .. ghc-flag:: -XStandaloneDeriving + :shortdesc: Enable :ref:`standalone deriving <stand-alone-deriving>`. + :type: dynamic + :reverse: -XNoStandaloneDeriving + :category: + + :since: 6.8.1 Allow the use of stand-alone ``deriving`` declarations. @@ -3588,28 +3819,46 @@ Deriving instances of extra classes (``Data``, etc.) ---------------------------------------------------- .. ghc-flag:: -XDeriveGeneric + :shortdesc: Enable :ref:`deriving for the Generic class <deriving-typeable>`. + :type: dynamic + :reverse: -XNoDeriveGeneric + :category: - :since: 7.2 + :since: 7.2.1 Allow automatic deriving of instances for the ``Generic`` typeclass. .. ghc-flag:: -XDeriveFunctor + :shortdesc: Enable :ref:`deriving for the Functor class <deriving-extra>`. + Implied by :ghc-flag:`-XDeriveTraversable`. + :type: dynamic + :reverse: -XNoDeriveFunctor + :category: - :since: 6.12 + :since: 7.10.1 Allow automatic deriving of instances for the ``Functor`` typeclass. .. ghc-flag:: -XDeriveFoldable + :shortdesc: Enable :ref:`deriving for the Foldable class <deriving-extra>`. + Implied by :ghc-flag:`-XDeriveTraversable`. + :type: dynamic + :reverse: -XNoDeriveFoldable + :category: - :since: 6.12 + :since: 7.10.1 Allow automatic deriving of instances for the ``Foldable`` typeclass. .. ghc-flag:: -XDeriveTraversable - - :since: 6.12 + :shortdesc: Enable :ref:`deriving for the Traversable class <deriving-extra>`. + Implies :ghc-flag:`-XDeriveFunctor` and :ghc-flag:`-XDeriveFoldable`. + :type: dynamic + :reverse: -XNoDeriveTraversable + :category: :implies: :ghc-flag:`-XDeriveFoldable`, :ghc-flag:`-XDeriveFunctor` + :since: 7.10.1 Allow automatic deriving of instances for the ``Traversable`` typeclass. @@ -4048,6 +4297,13 @@ Deriving ``Data`` instances ------------------------------- .. ghc-flag:: -XDeriveDataTypeable + :shortdesc: Enable ``deriving`` for the :ref:`Data class + <deriving-typeable>`. Implied by :ghc-flag:`-XAutoDeriveTypeable`. + :type: dynamic + :reverse: -XNoDeriveDataTypeable + :category: + + :since: 6.8.1 Enable automatic deriving of instances for the ``Data`` typeclass @@ -4100,8 +4356,12 @@ Deriving ``Lift`` instances --------------------------- .. ghc-flag:: -XDeriveLift + :shortdesc: Enable :ref:`deriving for the Lift class <deriving-lift>` + :type: dynamic + :reverse: -XNoDeriveLift + :category: - :since: 8.0.1 + :since: 7.2.1 Enable automatic deriving of instances for the ``Lift`` typeclass for Template Haskell. @@ -4181,6 +4441,12 @@ Generalised derived instances for newtypes .. ghc-flag:: -XGeneralisedNewtypeDeriving -XGeneralizedNewtypeDeriving + :shortdesc: Enable :ref:`newtype deriving <newtype-deriving>`. + :type: dynamic + :reverse: -XNoGeneralizedNewtypeDeriving + :category: + + :since: 6.8.1 Enable GHC's cunning generalised deriving mechanism for ``newtype``\s @@ -4499,6 +4765,10 @@ Deriving any other class ------------------------ .. ghc-flag:: -XDeriveAnyClass + :shortdesc: Enable :ref:`deriving for any class <derive-any-class>`. + :type: dynamic + :reverse: -XNoDeriveAnyClass + :category: :since: 7.10.1 @@ -4645,6 +4915,12 @@ Deriving strategies ------------------- .. ghc-flag:: -XDerivingStrategies + :shortdesc: Enables :ref:`deriving strategies <deriving-strategies>`. + :type: dynamic + :reverse: -XNoDerivingStrategies + :category: + + :since: 8.2.1 Allow multiple ``deriving``, each optionally qualified with a *strategy*. @@ -4707,6 +4983,10 @@ Pattern synonyms ================ .. ghc-flag:: -XPatternSynonyms + :shortdesc: Enable :ref:`pattern synonyms <pattern-synonyms>`. + :type: dynamic + :reverse: -XNoPatternSynonyms + :category: :since: 7.8.1 @@ -5157,8 +5437,15 @@ Multi-parameter type classes ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XMultiParamTypeClasses + :shortdesc: Enable :ref:`multi parameter type classes + <multi-param-type-classes>`. Implied by + :ghc-flag:`-XFunctionalDependencies`. + :type: dynamic + :reverse: -XNoMultiParamTypeClasses + :category: :implies: :ghc-flag:`-XConstrainedClassMethods` + :since: 6.8.1 Allow the definition of typeclasses with more than one parameter. @@ -5175,6 +5462,13 @@ The superclasses of a class declaration ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XFlexibleContexts + :shortdesc: Enable :ref:`flexible contexts <flexible-contexts>`. Implied by + :ghc-flag:`-XImplicitParams`. + :type: dynamic + :reverse: -XNoFlexibleContexts + :category: + + :since: 6.8.1 Allow the use of complex constraints in class declaration contexts. @@ -5225,6 +5519,12 @@ Constrained class method types ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XConstrainedClassMethods + :shortdesc: Enable :ref:`constrained class methods <class-method-types>`. + :type: dynamic + :reverse: -XNoConstrainedClassMethods + :category: + + :since: 6.8.1 Allows the definition of further constraints on individual class methods. @@ -5265,8 +5565,12 @@ Default method signatures ~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XDefaultSignatures + :shortdesc: Enable :ref:`default signatures <class-default-signatures>`. + :type: dynamic + :reverse: -XNoDefaultSignatures + :category: - :since: 7.2 + :since: 7.2.1 Allows the definition of default method signatures in class definitions. @@ -5358,6 +5662,12 @@ Nullary type classes ~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XNullaryTypeClasses + :shortdesc: Deprecated, does nothing. :ref:`nullary (no parameter) type + classes <nullary-type-classes>` are now enabled using + :ghc-flag:`-XMultiParamTypeClasses`. + :type: dynamic + :reverse: -XNoNullaryTypeClasses + :category: :since: 7.8.1 @@ -5394,8 +5704,14 @@ Functional dependencies ----------------------- .. ghc-flag:: -XFunctionalDependencies + :shortdesc: Enable :ref:`functional dependencies <functional-dependencies>`. + Implies :ghc-flag:`-XMultiParamTypeClasses`. + :type: dynamic + :reverse: -XNoFunctionalDependencies + :category: :implies: :ghc-flag:`-XMultiParamTypeClasses` + :since: 6.8.1 Allow use of functional dependencies in class declarations. @@ -5732,12 +6048,26 @@ Relaxed rules for the instance head ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XTypeSynonymInstances + :shortdesc: Enable :ref:`type synonyms in instance heads + <flexible-instance-head>`. Implied by :ghc-flag:`-XFlexibleInstances`. + :type: dynamic + :reverse: -XNoTypeSynonymInstances + :category: + + :since: 6.8.1 Allow definition of type class instances for type synonyms. .. ghc-flag:: -XFlexibleInstances + :shortdesc: Enable :ref:`flexible instances <instance-rules>`. + Implies :ghc-flag:`-XTypeSynonymInstances`. + Implied by :ghc-flag:`-XImplicitParams`. + :type: dynamic + :reverse: -XNoFlexibleInstances + :category: :implies: :ghc-flag:`-XTypeSynonymInstances` + :since: 6.8.1 Allow definition of type class instances with arbitrary nested types in the instance head. @@ -5809,6 +6139,12 @@ Instance termination rules ~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XUndecidableInstances + :shortdesc: Enable :ref:`undecidable instances <undecidable-instances>`. + :type: dynamic + :reverse: -XNoUndecidableInstances + :category: + + :since: 6.8.1 Permit definition of instances which may lead to type-checker non-termination. @@ -6002,9 +6338,24 @@ Overlapping instances ~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XOverlappingInstances - -XIncoherentInstances + :shortdesc: Enable :ref:`overlapping instances <instance-overlap>`. + :type: dynamic + :reverse: -XNoOverlappingInstances + :category: + + Deprecated flag to weaken checks intended to ensure instance resolution + termination. + +.. ghc-flag:: -XIncoherentInstances + :shortdesc: Enable :ref:`incoherent instances <instance-overlap>`. + Implies :ghc-flag:`-XOverlappingInstances`. + :type: dynamic + :reverse: -XNoIncoherentInstances + :category: - Deprecated flags to weaken checks intended to ensure instance resolution + :since: 6.8.1 + + Deprecated flag to weaken checks intended to ensure instance resolution termination. In general, as discussed in :ref:`instance-resolution`, *GHC requires @@ -6219,6 +6570,10 @@ Instance signatures: type signatures in instance declarations ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .. ghc-flag:: -XInstanceSigs + :shortdesc: Enable :ref:`instance signatures <instance-sigs>`. + :type: dynamic + :reverse: -XNoInstanceSigs + :category: :since: 7.6.1 @@ -6276,6 +6631,12 @@ Overloaded string literals -------------------------- .. ghc-flag:: -XOverloadedStrings + :shortdesc: Enable :ref:`overloaded string literals <overloaded-strings>`. + :type: dynamic + :reverse: -XNoOverloadedStrings + :category: + + :since: 6.8.1 Enable overloaded string literals (e.g. string literals desugared via the ``IsString`` class). @@ -6356,6 +6717,10 @@ Overloaded labels ----------------- .. ghc-flag:: -XOverloadedLabels + :shortdesc: Enable :ref:`overloaded labels <overloaded-labels>`. + :type: dynamic + :reverse: -XNoOverloadedLabels + :category: :since: 8.0.1 @@ -6448,6 +6813,10 @@ Overloaded lists ---------------- .. ghc-flag:: -XOverloadedLists + :shortdesc: Enable :ref:`overloaded lists <overloaded-lists>`. + :type: dynamic + :reverse: -XNoOverloadedLists + :category: :since: 7.8.1 @@ -6615,6 +6984,11 @@ Undecidable (or recursive) superclasses --------------------------------------- .. ghc-flag:: -XUndecidableSuperClasses + :shortdesc: Allow all superclass constraints, including those that may + result in non-termination of the typechecker. + :type: dynamic + :reverse: -XNoUndecidableSuperClasses + :category: :since: 8.0.1 @@ -6673,9 +7047,16 @@ Type families ============= .. ghc-flag:: -XTypeFamilies + :shortdesc: Enable :ref:`type families <type-families>`. + Implies :ghc-flag:`-XExplicitNamespaces`, :ghc-flag:`-XKindSignatures`, + and :ghc-flag:`-XMonoLocalBinds`. + :type: dynamic + :reverse: -XNoTypeFamilies + :category: :implies: :ghc-flag:`-XMonoLocalBinds`, :ghc-flag:`-XKindSignatures`, :ghc-flag:`-XExplicitNamespaces` + :since: 6.8.1 Allow use and definition of indexed type and data families. @@ -7569,6 +7950,11 @@ Injective type families ----------------------- .. ghc-flag:: -XTypeFamilyDependencies + :shortdesc: Enable :ref:`injective type families <injective-ty-fams>`. + Implies :ghc-flag:`-XTypeFamilies`. + :type: dynamic + :reverse: -XNoTypeFamilyDependencies + :category: :implies: :ghc-flag:`-XTypeFamilies` :since: 8.0.1 @@ -7697,6 +8083,10 @@ Datatype promotion ================== .. ghc-flag:: -XDataKinds + :shortdesc: Enable :ref:`datatype promotion <promotion>`. + :type: dynamic + :reverse: -XNoDataKinds + :category: :since: 7.4.1 @@ -7915,6 +8305,14 @@ Kind polymorphism and Type-in-Type ================================== .. ghc-flag:: -XTypeInType + :shortdesc: Allow :ref:`kinds to be used as types <type-in-type>`, + including explicit kind variable quantification, higher-rank + kinds, kind synonyms, and kind families. + Implies :ghc-flag:`-XDataKinds`, :ghc-flag:`-XKindSignatures`, + and :ghc-flag:`-XPolyKinds`. + :type: dynamic + :reverse: -XNoTypeInType + :category: :implies: :ghc-flag:`-XPolyKinds`, :ghc-flag:`-XDataKinds`, :ghc-flag:`-XKindSignatures` :since: 8.0.1 @@ -7924,6 +8322,11 @@ Kind polymorphism and Type-in-Type families in kinds, among other features. .. ghc-flag:: -XPolyKinds + :shortdesc: Enable :ref:`kind polymorphism <kind-polymorphism>`. + Implies :ghc-flag:`-XKindSignatures`. + :type: dynamic + :reverse: -XNoPolyKinds + :category: :implies: :ghc-flag:`-XKindSignatures` :since: 7.4.1 @@ -8590,9 +8993,14 @@ Printing levity-polymorphic types --------------------------------- .. ghc-flag:: -Wprint-explicit-runtime-rep + :shortdesc: Print ``RuntimeRep`` variables in types which are + runtime-representation polymorphic. + :type: dynamic + :reverse: -fno-print-explicit-runtime-reps + :category: - Print ``RuntimeRep`` parameters as they appear; otherwise, they are - defaulted to ``'LiftedRep``. + Print ``RuntimeRep`` parameters as they appear; otherwise, they are + defaulted to ``'LiftedRep``. Most GHC users will not need to worry about levity polymorphism or unboxed types. For these users, seeing the levity polymorphism @@ -8810,6 +9218,10 @@ The ``Constraint`` kind ----------------------- .. ghc-flag:: -XConstraintKinds + :shortdesc: Enable a :ref:`kind of constraints <constraint-kind>`. + :type: dynamic + :reverse: -XNoConstraintKinds + :category: :since: 7.4.1 @@ -8894,8 +9306,14 @@ Explicit universal quantification (forall) ------------------------------------------ .. ghc-flag:: -XExplicitForAll + :shortdesc: Enable :ref:`explicit universal quantification <explicit-foralls>`. + Implied by :ghc-flag:`-XScopedTypeVariables`, :ghc-flag:`-XLiberalTypeSynonyms`, + :ghc-flag:`-XRankNTypes` and :ghc-flag:`-XExistentialQuantification`. + :type: dynamic + :reverse: -XNoExplicitForAll + :category: - :since: 6.12 + :since: 6.12.1 Allow use of the ``forall`` keyword in places where universal quantification is implicit. @@ -8955,6 +9373,11 @@ Ambiguous types and the ambiguity check --------------------------------------- .. ghc-flag:: -XAllowAmbiguousTypes + :shortdesc: Allow the user to write :ref:`ambiguous types <ambiguity>`, and + the type inference engine to infer them. + :type: dynamic + :reverse: -XNoAllowAmbiguousTypes + :category: :since: 7.8.1 @@ -9080,6 +9503,13 @@ Explicitly-kinded quantification -------------------------------- .. ghc-flag:: -XKindSignatures + :shortdesc: Enable :ref:`kind signatures <kinding>`. + Implied by :ghc-flag:`-XTypeFamilies` and :ghc-flag:`-XPolyKinds`. + :type: dynamic + :reverse: -XNoKindSignatures + :category: + + :since: 6.8.1 Allow explicit kind signatures on type variables. @@ -9144,8 +9574,14 @@ Lexically scoped type variables =============================== .. ghc-flag:: -XScopedTypeVariables + :shortdesc: Enable :ref:`lexically-scoped type variables + <scoped-type-variables>`. + :type: dynamic + :reverse: -XNoScopedTypeVariables + :category: :implies: :ghc-flag:`-XExplicitForAll` + :since: 6.8.1 Enable lexical scoping of type variables explicitly introduced with ``forall``. @@ -9367,8 +9803,13 @@ Switching off the dreaded Monomorphism Restriction -------------------------------------------------- .. ghc-flag:: -XNoMonomorphismRestriction + :shortdesc: Disable the :ref:`monomorphism restriction <monomorphism>`. + :type: dynamic + :reverse: -XMonomorphismRestriction + :category: :default: on + :since: 6.8.1 Prevents the compiler from applying the monomorphism restriction to bindings lacking explicit type signatures. @@ -9386,8 +9827,13 @@ Let-generalisation ------------------ .. ghc-flag:: -XMonoLocalBinds + :shortdesc: Enable :ref:`do not generalise local bindings <mono-local-binds>`. + Implied by :ghc-flag:`-XTypeFamilies` and :ghc-flag:`-XGADTs`. + :type: dynamic + :reverse: -XNoMonoLocalBinds + :category: - :since: 6.12 + :since: 6.12.1 Infer less polymorphic types for local bindings by default. @@ -9493,6 +9939,10 @@ Visible type application ======================== .. ghc-flag:: -XTypeApplications + :shortdesc: Enable :ref:`type application syntax <visible-type-application>`. + :type: dynamic + :reverse: -XNoTypeApplications + :category: :since: 8.0.1 @@ -9622,6 +10072,13 @@ Implicit parameters =================== .. ghc-flag:: -XImplicitParams + :shortdesc: Enable :ref:`Implicit Parameters <implicit-parameters>`. + Implies :ghc-flag:`-XFlexibleContexts` and :ghc-flag:`-XFlexibleInstances`. + :type: dynamic + :reverse: -XNoImplicitParams + :category: + + :since: 6.8.1 Allow definition of functions expecting implicit parameters. @@ -9819,12 +10276,25 @@ Arbitrary-rank polymorphism =========================== .. ghc-flag:: -XRankNTypes + :shortdesc: Enable :ref:`rank-N types <universal-quantification>`. + Implied by :ghc-flag:`-XImpredicativeTypes`. + :type: dynamic + :reverse: -XNoRankNTypes + :category: :implies: :ghc-flag:`-XExplicitForAll` + :since: 6.8.1 Allow types of arbitrary rank. .. ghc-flag:: -XRank2Types + :shortdesc: Enable :ref:`rank-2 types <universal-quantification>`. + Synonym for :ghc-flag:`-XRankNTypes`. + :type: dynamic + :reverse: -XNoRank2Types + :category: + + :since: 6.8.1 A deprecated alias of :ghc-flag:`-XRankNTypes`. @@ -10085,8 +10555,14 @@ Impredicative polymorphism ========================== .. ghc-flag:: -XImpredicativeTypes + :shortdesc: Enable :ref:`impredicative types <impredicative-polymorphism>`. + Implies :ghc-flag:`-XRankNTypes`. + :type: dynamic + :reverse: -XNoImpredicativeTypes + :category: :implies: :ghc-flag:`-XRankNTypes` + :since: 6.10.1 Allow impredicative polymorphic types. @@ -10275,6 +10751,9 @@ There's a flag for controlling the amount of context information shown for typed holes: .. ghc-flag:: -fshow-hole-constraints + :shortdesc: Show constraints when reporting typed holes + :type: dynamic + :category: verbosity When reporting typed holes, also print constraints that are in scope. Example: :: @@ -10305,6 +10784,10 @@ Partial Type Signatures ======================= .. ghc-flag:: -XPartialTypeSignatures + :shortdesc: Enable :ref:`partial type signatures <partial-type-signatures>`. + :type: dynamic + :reverse: -XNoPartialTypeSignatures + :category: :since: 7.10.1 @@ -10418,6 +10901,10 @@ Named Wildcards ~~~~~~~~~~~~~~~ .. ghc-flag:: -XNamedWildCards + :shortdesc: Enable :ref:`named wildcards <named-wildcards>`. + :type: dynamic + :reverse: -XNoNamedWildCards + :category: :since: 7.10.1 @@ -10819,13 +11306,22 @@ Syntax ------ .. ghc-flag:: -XTemplateHaskell + :shortdesc: Enable :ref:`Template Haskell <template-haskell>`. + :type: dynamic + :reverse: -XNoTemplateHaskell + :category: - :since: 6.0. Typed splices introduced in GHC 7.8.1. :implies: :ghc-flag:`-XTemplateHaskellQuotes` + :since: 6.0. Typed splices introduced in GHC 7.8.1. Enable Template Haskell's splice and quotation syntax. .. ghc-flag:: -XTemplateHaskellQuotes + :shortdesc: Enable quotation subset of + :ref:`Template Haskell <template-haskell>`. + :type: dynamic + :reverse: -XNoTemplateHaskellQuotes + :category: :since: 8.0.1 @@ -11333,6 +11829,12 @@ Template Haskell Quasi-quotation -------------------------------- .. ghc-flag:: -XQuasiQuotes + :shortdesc: Enable :ref:`quasiquotation <th-quasiquotation>`. + :type: dynamic + :reverse: -XNoQuasiQuotes + :category: + + :since: 6.10.1 Enable Template Haskell Quasi-quotation syntax. @@ -11510,6 +12012,12 @@ Arrow notation ============== .. ghc-flag:: -XArrows + :shortdesc: Enable :ref:`arrow notation <arrow-notation>` extension + :type: dynamic + :reverse: -XNoArrows + :category: + + :since: 6.8.1 Enable arrow notation. @@ -11951,6 +12459,12 @@ Bang patterns ------------- .. ghc-flag:: -XBangPatterns + :shortdesc: Enable :ref:`bang patterns <bang-patterns>`. + :type: dynamic + :reverse: -XNoBangPatterns + :category: + + :since: 6.8.1 Allow use of bang pattern syntax. @@ -12047,6 +12561,10 @@ Strict-by-default data types ---------------------------- .. ghc-flag:: -XStrictData + :shortdesc: Enable :ref:`default strict datatype fields <strict-data>`. + :type: dynamic + :reverse: -XNoStrictData + :category: :since: 8.0.1 @@ -12075,6 +12593,10 @@ Strict-by-default pattern bindings ---------------------------------- .. ghc-flag:: -XStrict + :shortdesc: Make bindings in the current module strict by default. + :type: dynamic + :reverse: -XNoStrict + :category: :implies: :ghc-flag:`-XStrictData` :since: 8.0.1 @@ -12450,6 +12972,10 @@ Static pointers single: Static pointers .. ghc-flag:: -XStaticPointers + :shortdesc: Enable :ref:`static pointers <static-pointers>`. + :type: dynamic + :reverse: -XNoStaticPointers + :category: :since: 7.10.1 @@ -13493,6 +14019,12 @@ individual rule firing and :ghc-flag:`-ddump-rule-rewrites` also shows what the code looks like before and after the rewrite. .. ghc-flag:: -fenable-rewrite-rules + :shortdesc: Switch on all rewrite rules (including rules generated by + automatic specialisation of overloaded functions). Implied by + :ghc-flag:`-O`. + :type: dynamic + :reverse: -fno-enable-rewrite-rules + :category: optimization Allow the compiler to apply rewrite rules to the source program. @@ -14321,6 +14853,10 @@ Role annotations ---------------- .. ghc-flag:: -XRoleAnnotations + :shortdesc: Enable :ref:`role annotations <role-annotations>`. + :type: dynamic + :reverse: -XNoRoleAnnotations + :category: :since: 7.8.1 |