Portability	portable
Stability	transient
Maintainer	Niklas Broberg, niklas.broberg@chalmers.se
Safe Haskell	Safe-Inferred

Language.Haskell.Exts.Extension

Contents

Language definitions
Extensions
Extension groups
Semantics of extensions applied to languages

Description

This module defines the list of recognized modular features of Haskell, most often (sloppily) referred to as extensions.

Closely mimicking the Language.Haskell.Extension module from the Cabal library, this package also includes functionality for computing languages as sets of features. Also, we make no promise not to add extensions not yet recognized by Cabal.

Synopsis

Language definitions

data Language Source

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
HaskellAllDisabled	The minimal language resulting from disabling all recognized extensions - including ones that are part of all known language definitions e.g. MonomorphismRestriction.
UnknownLanguage String	An unknown language, identified by its name.

Instances

Eq Language
Ord Language
Read Language
Show Language

knownLanguages :: [Language]Source

classifyLanguage :: String -> Language Source

prettyLanguage :: Language -> String Source

Extensions

data Extension Source

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

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
Ord Extension
Read Extension
Show Extension

data KnownExtension Source

Constructors

OverlappingInstances	GHC § 7.6.3.4 Allow overlapping class instances, provided there is a unique most specific instance for each use.
UndecidableInstances	GHC § 7.6.3.3 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.
IncoherentInstances	GHC § 7.6.3.4 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.
RecursiveDo	GHC § 7.3.8.2 Deprecated in GHC. Allows recursive bindings using `mdo`, a variant of `do`. `DoRec` provides a different, preferred syntax.
ParallelListComp	GHC § 7.3.9 Provide syntax for writing list comprehensions which iterate over several lists together, like the `zipWith` family of functions.
MultiParamTypeClasses	GHC § 7.6.1.1 Allow multiple parameters in a type class.
MonomorphismRestriction	GHC § 7.17 Enable the dreaded monomorphism restriction.
FunctionalDependencies	GHC § 7.6.2 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.
Rank2Types	GHC § 7.8.5 Like `RankNTypes` but does not allow a higher-rank type to itself appear on the left of a function arrow.
RankNTypes	GHC § 7.8.5 Allow a universally-quantified type to occur on the left of a function arrow.
PolymorphicComponents	GHC § 7.8.5 Allow data constructors to have polymorphic arguments. Unlike `RankNTypes`, does not allow this for ordinary functions.
ExistentialQuantification	GHC § 7.4.4 Allow existentially-quantified data constructors.
ScopedTypeVariables	GHC § 7.8.7 Cause a type variable in a signature, which has an explicit `forall` quantifier, to scope over the definition of the accompanying value declaration.
PatternSignatures	Deprecated, use `ScopedTypeVariables` instead.
ImplicitParams	GHC § 7.8.3 Enable implicit function parameters with dynamic scope.
FlexibleContexts	GHC § 7.8.2 Relax some restrictions on the form of the context of a type signature.
FlexibleInstances	GHC § 7.6.3.2 Relax some restrictions on the form of the context of an instance declaration.
EmptyDataDecls	GHC § 7.4.1 Allow data type declarations with no constructors.
CPP	GHC § 4.10.3 Run the C preprocessor on Haskell source code.
KindSignatures	GHC § 7.8.4 Allow an explicit kind signature giving the kind of types over which a type variable ranges.
BangPatterns	GHC § 7.11 Enable a form of pattern which forces evaluation before an attempted match, and a form of strict `let`/`where` binding.
TypeSynonymInstances	GHC § 7.6.3.1 Allow type synonyms in instance heads.
TemplateHaskell	GHC § 7.9 Enable Template Haskell, a system for compile-time metaprogramming.
ForeignFunctionInterface	GHC § 8 Enable the Foreign Function Interface. In GHC, implements the standard Haskell 98 Foreign Function Interface Addendum, plus some GHC-specific extensions.
Arrows	GHC § 7.10 Enable arrow notation.
Generics	GHC § 7.16 Enable generic type classes, with default instances defined in terms of the algebraic structure of a type.
ImplicitPrelude	GHC § 7.3.11 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.
NamedFieldPuns	GHC § 7.3.15 Enable syntax for implicitly binding local names corresponding to the field names of a record. Puns bind specific names, unlike `RecordWildCards`.
PatternGuards	GHC § 7.3.5 Enable a form of guard which matches a pattern and binds variables.
GeneralizedNewtypeDeriving	GHC § 7.5.4 Allow a type declared with `newtype` to use `deriving` for any class with an instance for the underlying type.
ExtensibleRecords	Hugs § 7.1 Enable the "Trex" extensible records system.
RestrictedTypeSynonyms	Hugs § 7.2 Enable type synonyms which are transparent in some definitions and opaque elsewhere, as a way of implementing abstract datatypes.
HereDocuments	Hugs § 7.3 Enable an alternate syntax for string literals, with string templating.
MagicHash	GHC § 7.3.2 Allow the character `#` as a postfix modifier on identifiers. Also enables literal syntax for unboxed values.
TypeFamilies	GHC § 7.7 Allow data types and type synonyms which are indexed by types, i.e. ad-hoc polymorphism for types.
StandaloneDeriving	GHC § 7.5.2 Allow a standalone declaration which invokes the type class `deriving` mechanism.
UnicodeSyntax	GHC § 7.3.1 Allow certain Unicode characters to stand for certain ASCII character sequences, e.g. keywords and punctuation.
UnliftedFFITypes	GHC § 8.1.1 Allow the use of unboxed types as foreign types, e.g. in `foreign import` and `foreign export`.
LiberalTypeSynonyms	GHC § 7.4.3 Defer validity checking of types until after expanding type synonyms, relaxing the constraints on how synonyms may be used.
TypeOperators	GHC § 7.4.2 Allow the name of a type constructor, type class, or type variable to be an infix operator.
RecordWildCards	GHC § 7.3.16 Enable syntax for implicitly binding local names corresponding to the field names of a record. A wildcard binds all unmentioned names, unlike `NamedFieldPuns`.
RecordPuns	Deprecated, use `NamedFieldPuns` instead.
DisambiguateRecordFields	GHC § 7.3.14 Allow a record field name to be disambiguated by the type of the record it's in.
OverloadedStrings	GHC § 7.6.4 Enable overloading of string literals using a type class, much like integer literals.
GADTs	GHC § 7.4.6 Enable generalized algebraic data types, in which type variables may be instantiated on a per-constructor basis. Implies GADTSyntax.
MonoPatBinds	GHC § 7.17.2 Make pattern bindings monomorphic.
RelaxedPolyRec	GHC § 7.8.8 Relax the requirements on mutually-recursive polymorphic functions.
ExtendedDefaultRules	GHC § 2.4.5 Allow default instantiation of polymorphic types in more situations.
UnboxedTuples	GHC § 7.2.2 Enable unboxed tuples.
DeriveDataTypeable	GHC § 7.5.3 Enable `deriving` for classes `Data.Typeable.Typeable` and `Data.Generics.Data`.
ConstrainedClassMethods	GHC § 7.6.1.3 Allow a class method's type to place additional constraints on a class type variable.
PackageImports	GHC § 7.3.18 Allow imports to be qualified by the package name the module is intended to be imported from, e.g. import "network" Network.Socket
ImpredicativeTypes	GHC § 7.8.6 Deprecated in GHC 6.12 and will be removed in GHC 7. Allow a type variable to be instantiated at a polymorphic type.
NewQualifiedOperators	GHC § 7.3.3 Change the syntax for qualified infix operators.
PostfixOperators	GHC § 7.3.12 Relax the interpretation of left operator sections to allow unary postfix operators.
QuasiQuotes	GHC § 7.9.5 Enable quasi-quotation, a mechanism for defining new concrete syntax for expressions and patterns.
TransformListComp	GHC § 7.3.10 Enable generalized list comprehensions, supporting operations such as sorting and grouping.
ViewPatterns	GHC § 7.3.6 Enable view patterns, which match a value by applying a function and matching on the result.
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	Enables the use of tuple sections, e.g. `(, True)` desugars into `x -> (x, True)`.
GHCForeignImportPrim	Allows 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.
DoAndIfThenElse	Improve the layout rule when `if` expressions are used in a `do` block.
RebindableSyntax	Makes much of the Haskell sugar be desugared into calls to the function with a particular name that is in scope.
ExplicitForAll	Make `forall` a keyword in types, which can be used to give the generalisation explicitly.
DatatypeContexts	Allow contexts to be put on datatypes, e.g. the `Eq a` in `data Eq a => Set a = NilSet \| ConsSet a (Set a)`.
MonoLocalBinds	Local (`let` and `where`) bindings are monomorphic.
DeriveFunctor	Enable `deriving` for the `Data.Functor.Functor` class.
DeriveTraversable	Enable `deriving` for the `Data.Traversable.Traversable` class.
DeriveFoldable	Enable `deriving` for the `Data.Foldable.Foldable` class.
NondecreasingIndentation	Enable non-decreasing indentation for 'do' blocks.
InterruptibleFFI	GHC § 8.1.4 Enable interruptible FFI.
CApiFFI	GHC § 8.1.5 Enable the `capi` calling convention in the foreign function interface.

Instances

Bounded KnownExtension
Enum KnownExtension
Eq KnownExtension
Ord KnownExtension
Read KnownExtension
Show KnownExtension

classifyExtension :: String -> Extension Source

A clever version of read that returns an UnknownExtension if the string is not recognised.

parseExtension :: String -> Extension Source

Parse an enabled or disabled extension; returns UnknownExtension if the parse fails.

prettyExtension :: Extension -> String Source

Pretty print an extension. Disabled extensions are prefixed with 'No'.

Extension groups

ghcDefault :: [Extension]Source

glasgowExts :: [Extension]Source

The list of extensions enabled by GHC's portmanteau -fglasgow-exts flag.

knownExtensions :: [Extension]Source

List of all known extensions, both "yes" and "no" versions.

deprecatedExtensions :: [(Extension, Maybe Extension)]Source

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

Semantics of extensions applied to languages

impliesExts :: [KnownExtension] -> [KnownExtension]Source

Certain extensions imply other extensions, and this function makes the implication explicit. This also handles deprecated extensions, which imply their replacements. The returned value is the transitive closure of implied extensions.

toExtensionList :: Language -> [Extension] -> [KnownExtension]Source