Cabal-syntax-3.14.2.0: src/Language/Haskell/Extension.hs
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE OverloadedStrings #-}
-----------------------------------------------------------------------------
-- |
-- Module : Language.Haskell.Extension
-- Copyright : Isaac Jones 2003-2004
-- License : BSD3
--
-- Maintainer : libraries@haskell.org
-- Portability : portable
--
-- Haskell language dialects and extensions
module Language.Haskell.Extension
( Language (..)
, knownLanguages
, classifyLanguage
, Extension (..)
, KnownExtension (..)
, deprecatedExtensions
, classifyExtension
, knownExtensions
) where
import Distribution.Compat.Prelude
import Data.Array (Array, Ix (inRange), accumArray, bounds, (!))
import Distribution.Parsec
import Distribution.Pretty
import qualified Distribution.Compat.CharParsing as P
import qualified Text.PrettyPrint as Disp
-- ------------------------------------------------------------
-- * Language
-- ------------------------------------------------------------
-- | This represents a Haskell language dialect.
--
-- Language 'Extension's are interpreted relative to one of these base
-- languages.
data Language
= -- | The Haskell 98 language as defined by the Haskell 98 report.
-- <http://haskell.org/onlinereport/>
Haskell98
| -- | The Haskell 2010 language as defined by the Haskell 2010 report.
-- <http://www.haskell.org/onlinereport/haskell2010>
Haskell2010
| -- | The GHC2021 collection of language extensions.
-- <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0380-ghc2021.rst>
GHC2021
| -- | The GHC2024 collection of language extensions.
-- <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0613-ghc2024.rst>
GHC2024
| -- | An unknown language, identified by its name.
UnknownLanguage String
deriving (Generic, Show, Read, Eq, Ord, Data)
instance Binary Language
instance Structured Language
instance NFData Language where rnf = genericRnf
-- | List of known (supported) languages for GHC, oldest first.
knownLanguages :: [Language]
knownLanguages = [Haskell98, Haskell2010, GHC2021, GHC2024]
instance Pretty Language where
pretty (UnknownLanguage other) = Disp.text other
pretty other = Disp.text (show other)
instance Parsec Language where
parsec = classifyLanguage <$> P.munch1 isAlphaNum
classifyLanguage :: String -> Language
classifyLanguage = \str -> case lookup str langTable of
Just lang -> lang
Nothing -> UnknownLanguage str
where
langTable =
[ (show lang, lang)
| lang <- knownLanguages
]
-- ------------------------------------------------------------
-- * Extension
-- ------------------------------------------------------------
-- Note: if you add a new 'KnownExtension':
--
-- * also add it to the Distribution.Simple.X.compilerExtensions lists
-- (where X is each compiler: GHC, UHC, HaskellSuite)
--
-- | 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.
data Extension
= -- | Enable a known extension
EnableExtension KnownExtension
| -- | Disable a known extension
DisableExtension KnownExtension
| -- | An unknown extension, identified by the name of its @LANGUAGE@
-- pragma.
UnknownExtension String
deriving (Generic, Show, Read, Eq, Ord, Data)
instance Binary Extension
instance Structured Extension
instance NFData Extension where rnf = genericRnf
-- | Known Haskell language extensions, including deprecated and undocumented
-- ones.
--
-- Check <https://downloads.haskell.org/~ghc/9.2.3/docs/html/users_guide/exts/table.html “Overview of all language extensions” in GHC User’s Guide>
-- for more information.
data KnownExtension
= -- | Allow overlapping class instances, provided there is a unique
-- most specific instance for each use.
OverlappingInstances
| -- | 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.
UndecidableInstances
| -- | 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.
IncoherentInstances
| -- | /(deprecated)/ Deprecated in favour of 'RecursiveDo'.
--
-- Old description: Allow recursive bindings in @do@ blocks, using
-- the @rec@ keyword. See also 'RecursiveDo'.
DoRec
| -- | Allow recursive bindings in @do@ blocks, using the @rec@
-- keyword, or @mdo@, a variant of @do@.
RecursiveDo
| -- | Provide syntax for writing list comprehensions which iterate
-- over several lists together, like the 'zipWith' family of
-- functions.
ParallelListComp
| -- | Allow multiple parameters in a type class.
MultiParamTypeClasses
| -- | Enable the dreaded monomorphism restriction.
MonomorphismRestriction
| -- | Enable deep subsumption, relaxing the simple subsumption rules,
-- implicitly inserting eta-expansions when matching up function types
-- with different quantification structures.
DeepSubsumption
| -- | 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.
FunctionalDependencies
| -- | /(deprecated)/ A synonym for 'RankNTypes'.
--
-- Old description: Like 'RankNTypes' but does not allow a
-- higher-rank type to itself appear on the left of a function
-- arrow.
Rank2Types
| -- | Allow a universally-quantified type to occur on the left of a
-- function arrow.
RankNTypes
| -- | /(deprecated)/ A synonym for 'RankNTypes'.
--
-- Old description: Allow data constructors to have polymorphic
-- arguments. Unlike 'RankNTypes', does not allow this for ordinary
-- functions.
PolymorphicComponents
| -- | Allow existentially-quantified data constructors.
ExistentialQuantification
| -- | Cause a type variable in a signature, which has an explicit
-- @forall@ quantifier, to scope over the definition of the
-- accompanying value declaration.
ScopedTypeVariables
| -- | Deprecated, use 'ScopedTypeVariables' instead.
PatternSignatures
| -- | Enable implicit function parameters with dynamic scope.
ImplicitParams
| -- | Relax some restrictions on the form of the context of a type
-- signature.
FlexibleContexts
| -- | Relax some restrictions on the form of the context of an
-- instance declaration.
FlexibleInstances
| -- | Allow data type declarations with no constructors.
EmptyDataDecls
| -- | Run the C preprocessor on Haskell source code.
CPP
| -- | Allow an explicit kind signature giving the kind of types over
-- which a type variable ranges.
KindSignatures
| -- | Enable a form of pattern which forces evaluation before an
-- attempted match, and a form of strict @let@/@where@ binding.
BangPatterns
| -- | Allow type synonyms in instance heads.
TypeSynonymInstances
| -- | Enable Template Haskell, a system for compile-time
-- metaprogramming.
TemplateHaskell
| -- | Enable the Foreign Function Interface. In GHC, implements the
-- standard Haskell 98 Foreign Function Interface Addendum, plus
-- some GHC-specific extensions.
ForeignFunctionInterface
| -- | Enable arrow notation.
Arrows
| -- | /(deprecated)/ Enable generic type classes, with default instances defined in
-- terms of the algebraic structure of a type.
Generics
| -- | 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.
ImplicitPrelude
| -- | Enable syntax for implicitly binding local names corresponding
-- to the field names of a record. Puns bind specific names, unlike
-- 'RecordWildCards'.
NamedFieldPuns
| -- | Enable a form of guard which matches a pattern and binds
-- variables.
PatternGuards
| -- | Allow a type declared with @newtype@ to use @deriving@ for any
-- class with an instance for the underlying type.
GeneralizedNewtypeDeriving
| -- Synonym for GeneralizedNewtypeDeriving added in GHC 8.6.1.
GeneralisedNewtypeDeriving
| -- | Enable the \"Trex\" extensible records system.
ExtensibleRecords
| -- | Enable type synonyms which are transparent in some definitions
-- and opaque elsewhere, as a way of implementing abstract
-- datatypes.
RestrictedTypeSynonyms
| -- | Enable an alternate syntax for string literals,
-- with string templating.
HereDocuments
| -- | Allow the character @#@ as a postfix modifier on identifiers.
-- Also enables literal syntax for unboxed values.
MagicHash
| -- | Allow data types and type synonyms which are indexed by types,
-- i.e. ad-hoc polymorphism for types.
TypeFamilies
| -- | Allow a standalone declaration which invokes the type class
-- @deriving@ mechanism.
StandaloneDeriving
| -- | Allow certain Unicode characters to stand for certain ASCII
-- character sequences, e.g. keywords and punctuation.
UnicodeSyntax
| -- | Allow the use of unboxed types as foreign types, e.g. in
-- @foreign import@ and @foreign export@.
UnliftedFFITypes
| -- | Enable interruptible FFI.
InterruptibleFFI
| -- | Allow use of CAPI FFI calling convention (@foreign import capi@).
CApiFFI
| -- | Defer validity checking of types until after expanding type
-- synonyms, relaxing the constraints on how synonyms may be used.
LiberalTypeSynonyms
| -- | Allow the name of a type constructor, type class, or type
-- variable to be an infix operator.
TypeOperators
| -- | Enable syntax for implicitly binding local names corresponding
-- to the field names of a record. A wildcard binds all unmentioned
-- names, unlike 'NamedFieldPuns'.
RecordWildCards
| -- | Deprecated, use 'NamedFieldPuns' instead.
RecordPuns
| -- | Allow a record field name to be disambiguated by the type of
-- the record it's in.
DisambiguateRecordFields
| -- | Enable traditional record syntax (as supported by Haskell 98)
TraditionalRecordSyntax
| -- | Enable overloading of string literals using a type class, much
-- like integer literals.
OverloadedStrings
| -- | Enable generalized algebraic data types, in which type
-- variables may be instantiated on a per-constructor basis. Implies
-- 'GADTSyntax'.
GADTs
| -- | Enable GADT syntax for declaring ordinary algebraic datatypes.
GADTSyntax
| -- | /(deprecated)/ Has no effect.
--
-- Old description: Make pattern bindings monomorphic.
MonoPatBinds
| -- | Relax the requirements on mutually-recursive polymorphic
-- functions.
RelaxedPolyRec
| -- | Allow default instantiation of polymorphic types in more
-- situations.
ExtendedDefaultRules
| -- | Allow @default@ declarations to explicitly name the class and
-- be exported.
NamedDefaults
| -- | Enable unboxed tuples.
UnboxedTuples
| -- | Enable @deriving@ for classes 'Data.Typeable.Typeable' and
-- 'Data.Generics.Data'.
DeriveDataTypeable
| -- | Enable @deriving@ for 'GHC.Generics.Generic' and 'GHC.Generics.Generic1'.
DeriveGeneric
| -- | Enable support for default signatures.
DefaultSignatures
| -- | Allow type signatures to be specified in instance declarations.
InstanceSigs
| -- | Allow a class method's type to place additional constraints on
-- a class type variable.
ConstrainedClassMethods
| -- | Allow imports to be qualified by the package name the module is
-- intended to be imported from, e.g.
--
-- > import "network" Network.Socket
PackageImports
| -- | /(deprecated)/ Allow a type variable to be instantiated at a
-- polymorphic type.
ImpredicativeTypes
| -- | /(deprecated)/ Change the syntax for qualified infix operators.
NewQualifiedOperators
| -- | Relax the interpretation of left operator sections to allow
-- unary postfix operators.
PostfixOperators
| -- | Enable quasi-quotation, a mechanism for defining new concrete
-- syntax for expressions and patterns.
QuasiQuotes
| -- | Enable generalized list comprehensions, supporting operations
-- such as sorting and grouping.
TransformListComp
| -- | Enable monad comprehensions, which generalise the list
-- comprehension syntax to work for any monad.
MonadComprehensions
| -- | Enable view patterns, which match a value by applying a
-- function and matching on the result.
ViewPatterns
| -- | 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.
XmlSyntax
| -- | 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.
RegularPatterns
| -- | Enable the use of tuple sections, e.g. @(, True)@ desugars into
-- @\x -> (x, True)@.
TupleSections
| -- | Allow GHC primops, written in C--, to be imported into a Haskell
-- file.
GHCForeignImportPrim
| -- | Support for patterns of the form @n + k@, where @k@ is an
-- integer literal.
NPlusKPatterns
| -- | Improve the layout rule when @if@ expressions are used in a @do@
-- block.
DoAndIfThenElse
| -- | Enable support for multi-way @if@-expressions.
MultiWayIf
| -- | Enable support lambda-@case@ expressions.
LambdaCase
| -- | Makes much of the Haskell sugar be desugared into calls to the
-- function with a particular name that is in scope.
RebindableSyntax
| -- | Make @forall@ a keyword in types, which can be used to give the
-- generalisation explicitly.
ExplicitForAll
| -- | Allow contexts to be put on datatypes, e.g. the @Eq a@ in
-- @data Eq a => Set a = NilSet | ConsSet a (Set a)@.
DatatypeContexts
| -- | Local (@let@ and @where@) bindings are monomorphic.
MonoLocalBinds
| -- | Enable @deriving@ for the 'Data.Functor.Functor' class.
DeriveFunctor
| -- | Enable @deriving@ for the 'Data.Traversable.Traversable' class.
DeriveTraversable
| -- | Enable @deriving@ for the 'Data.Foldable.Foldable' class.
DeriveFoldable
| -- | Enable non-decreasing indentation for @do@ blocks.
NondecreasingIndentation
| -- | 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
SafeImports
| -- | Compile a module in the Safe, Safe Haskell mode -- a restricted
-- form of the Haskell language to ensure type safety.
Safe
| -- | 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.
Trustworthy
| -- | Compile a module in the Unsafe, Safe Haskell mode so that
-- modules compiled using Safe, Safe Haskell mode can't import it.
Unsafe
| -- | Allow type class/implicit parameter/equality 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.
ConstraintKinds
| -- | Enable kind polymorphism.
PolyKinds
| -- | Enable datatype promotion.
DataKinds
| -- | Enable @type data@ declarations, defining constructors at the type level.
TypeData
| -- | Enable parallel arrays syntax (@[:@, @:]@) for /Data Parallel Haskell/.
ParallelArrays
| -- | Enable explicit role annotations, like in (@type role Foo representational representational@).
RoleAnnotations
| -- | Enable overloading of list literals, arithmetic sequences and
-- list patterns using the 'IsList' type class.
OverloadedLists
| -- | Enable case expressions that have no alternatives. Also applies to lambda-case expressions if they are enabled.
EmptyCase
| -- | /(deprecated)/ Deprecated in favour of 'DeriveDataTypeable'.
--
-- Old description: Triggers the generation of derived 'Typeable'
-- instances for every datatype and type class declaration.
AutoDeriveTypeable
| -- | Desugars negative literals directly (without using negate).
NegativeLiterals
| -- | Allow the use of binary integer literal syntax (e.g. @0b11001001@ to denote @201@).
BinaryLiterals
| -- | Allow the use of floating literal syntax for all instances of 'Num', including 'Int' and 'Integer'.
NumDecimals
| -- | Enable support for type classes with no type parameter.
NullaryTypeClasses
| -- | Enable explicit namespaces in module import/export lists.
ExplicitNamespaces
| -- | Allow the user to write ambiguous types, and the type inference engine to infer them.
AllowAmbiguousTypes
| -- | Enable @foreign import javascript@.
JavaScriptFFI
| -- | Allow giving names to and abstracting over patterns.
PatternSynonyms
| -- | Allow anonymous placeholders (underscore) inside type signatures. The
-- type inference engine will generate a message describing the type inferred
-- at the hole's location.
PartialTypeSignatures
| -- | Allow named placeholders written with a leading underscore inside type
-- signatures. Wildcards with the same name unify to the same type.
NamedWildCards
| -- | Enable @deriving@ for any class.
DeriveAnyClass
| -- | Enable @deriving@ for the 'Language.Haskell.TH.Syntax.Lift' class.
DeriveLift
| -- | Enable support for 'static pointers' (and the @static@
-- keyword) to refer to globally stable names, even across
-- different programs.
StaticPointers
| -- | Switches data type declarations to be strict by default (as if
-- they had a bang using @BangPatterns@), and allow opt-in field
-- laziness using @~@.
StrictData
| -- | Switches all pattern bindings to be strict by default (as if
-- they had a bang using @BangPatterns@), ordinary patterns are
-- recovered using @~@. Implies @StrictData@.
Strict
| -- | Allows @do@-notation for types that are @'Applicative'@ as well
-- as @'Monad'@. When enabled, desugaring @do@ notation tries to use
-- @(<*>)@ and @'fmap'@ and @'join'@ as far as possible.
ApplicativeDo
| -- | Allow records to use duplicated field labels for accessors.
DuplicateRecordFields
| -- | Enable explicit type applications with the syntax @id \@Int@.
TypeApplications
| -- | Dissolve the distinction between types and kinds, allowing the compiler
-- to reason about kind equality and therefore enabling GADTs to be promoted
-- to the type-level.
TypeInType
| -- | Allow recursive (and therefore undecidable) super-class relationships.
UndecidableSuperClasses
| -- | A temporary extension to help library authors check if their
-- code will compile with the new planned desugaring of fail.
MonadFailDesugaring
| -- | A subset of @TemplateHaskell@ including only quoting.
TemplateHaskellQuotes
| -- | Allows use of the @#label@ syntax.
OverloadedLabels
| -- | Allow functional dependency annotations on type families to declare them
-- as injective.
TypeFamilyDependencies
| -- | Allow multiple @deriving@ clauses, each optionally qualified with a
-- /strategy/.
DerivingStrategies
| -- | Enable deriving instances via types of the same runtime representation.
-- Implies 'DerivingStrategies'.
DerivingVia
| -- | Enable the use of unboxed sum syntax.
UnboxedSums
| -- | Allow use of hexadecimal literal notation for floating-point values.
HexFloatLiterals
| -- | Allow @do@ blocks etc. in argument position.
BlockArguments
| -- | Allow use of underscores in numeric literals.
NumericUnderscores
| -- | Allow @forall@ in constraints.
QuantifiedConstraints
| -- | Have @*@ refer to @Type@.
StarIsType
| -- | Liberalises deriving to provide instances for empty data types.
EmptyDataDeriving
| -- | Enable detection of complete user-supplied kind signatures.
CUSKs
| -- | Allows the syntax @import M qualified@.
ImportQualifiedPost
| -- | Allow the use of standalone kind signatures.
StandaloneKindSignatures
| -- | Enable unlifted newtypes.
UnliftedNewtypes
| -- | Use whitespace to determine whether the minus sign stands for negation or subtraction.
LexicalNegation
| -- | Enable qualified do-notation desugaring.
QualifiedDo
| -- | Enable linear types.
LinearTypes
| -- | Allow the use of visible forall in types of terms.
RequiredTypeArguments
| -- | Enable the generation of selector functions corresponding to record fields.
FieldSelectors
| -- | Enable the use of record dot-accessor and updater syntax
OverloadedRecordDot
| -- | Provides record @.@ syntax in record updates, e.g. @x {foo.bar = 1}@.
OverloadedRecordUpdate
| -- | Enable data types for which an unlifted or levity-polymorphic result kind is inferred.
UnliftedDatatypes
| -- | Enable syntax for primitive numeric literals, e.g. @3#Int8@
ExtendedLiterals
| -- | Undocumented parsing-related extensions introduced in GHC 7.0.
AlternativeLayoutRule
| -- | Undocumented parsing-related extensions introduced in GHC 7.0.
AlternativeLayoutRuleTransitional
| -- | Undocumented parsing-related extensions introduced in GHC 7.2.
RelaxedLayout
| -- | Allow the use of type abstraction syntax.
TypeAbstractions
| -- | Allow the use of built-in syntax for list, tuple and sum type constructors
-- rather than being exclusive to data constructors.
ListTuplePuns
| -- | Support multiline strings.
MultilineStrings
| -- | Allow use of or-pattern syntax, condensing multiple patterns
-- into a single one.
OrPatterns
deriving (Generic, Show, Read, Eq, Ord, Enum, Bounded, Data)
instance Binary KnownExtension
instance Structured KnownExtension
instance NFData KnownExtension where rnf = genericRnf
-- | Extensions that have been deprecated, possibly paired with another
-- extension that replaces it.
deprecatedExtensions :: [(Extension, Maybe Extension)]
deprecatedExtensions =
[ (EnableExtension RecordPuns, Just (EnableExtension NamedFieldPuns))
, (EnableExtension PatternSignatures, Just (EnableExtension ScopedTypeVariables))
]
-- NOTE: when adding deprecated extensions that have new alternatives
-- we must be careful to make sure that the deprecation messages are
-- valid. We must not recommend aliases that cannot be used with older
-- compilers, perhaps by adding support in Cabal to translate the new
-- name to the old one for older compilers. Otherwise we are in danger
-- of the scenario in ticket #689.
instance Pretty Extension where
pretty (UnknownExtension other) = Disp.text other
pretty (EnableExtension ke) = Disp.text (show ke)
pretty (DisableExtension ke) = Disp.text ("No" ++ show ke)
instance Parsec Extension where
parsec = classifyExtension <$> P.munch1 isAlphaNum
instance Pretty KnownExtension where
pretty ke = Disp.text (show ke)
classifyExtension :: String -> Extension
classifyExtension string =
case classifyKnownExtension string of
Just ext -> EnableExtension ext
Nothing ->
case string of
'N' : 'o' : string' ->
case classifyKnownExtension string' of
Just ext -> DisableExtension ext
Nothing -> UnknownExtension string
_ -> UnknownExtension string
-- | 'read' for 'KnownExtension's is really really slow so for the Text
-- instance
-- what we do is make a simple table indexed off the first letter in the
-- extension name. The extension names actually cover the range @'A'-'Z'@
-- pretty densely and the biggest bucket is 7 so it's not too bad. We just do
-- a linear search within each bucket.
--
-- This gives an order of magnitude improvement in parsing speed, and it'll
-- also allow us to do case insensitive matches in future if we prefer.
classifyKnownExtension :: String -> Maybe KnownExtension
classifyKnownExtension "" = Nothing
classifyKnownExtension string@(c : _)
| inRange (bounds knownExtensionTable) c =
lookup string (knownExtensionTable ! c)
| otherwise = Nothing
knownExtensionTable :: Array Char [(String, KnownExtension)]
knownExtensionTable =
accumArray
(flip (:))
[]
('A', 'Z')
[ (hd, (str, extension)) -- assume KnownExtension's Show returns a non-empty string
| (extension, str@(hd : _)) <- map (\e -> (e, show e)) [toEnum 0 ..]
]
knownExtensions :: [KnownExtension]
knownExtensions = [minBound .. maxBound]