| 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.
|
| DoRec | - GHC § 7.3.8
- Allows recursive bindings in do blocks,
using the rec keyword.
|
| 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.
|
| GADTSyntax | Enable GADT syntax for declaring ordinary algebraic datatypes.
|
| 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.
|
| SafeImports | - GHC § 7.20.3
- 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
|
| Safe | - GHC § 7.20
- Compile a module in the Safe, Safe Haskell
mode -- a restricted form of the Haskell language to ensure
type safety.
|
| Trustworthy | - GHC § 7.20
- 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.
|
| ConstraintKinds | - GHC § 7.40
- Allow type classimplicit parameterequality
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.
|
