Copyright | (c) The University of Glasgow CWI 2001--2004 |
---|---|
License | BSD-style (see the file libraries/base/LICENSE) |
Maintainer | libraries@haskell.org |
Stability | experimental |
Portability | non-portable (local universal quantification) |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
"Scrap your boilerplate" --- Generic programming in Haskell. See
http://www.haskell.org/haskellwiki/Research_papers/Generics#Scrap_your_boilerplate.21.
This module provides the Data
class with its primitives for
generic programming, along with instances for many datatypes. It
corresponds to a merge between the previous Data.Generics.Basics
and almost all of Data.Generics.Instances. The instances that are
not present in this module were moved to the
Data.Generics.Instances
module in the syb
package.
For more information, please visit the new SYB wiki: http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/SYB.
- module Data.Typeable
- class Typeable a => Data a where
- data DataType
- mkDataType :: String -> [Constr] -> DataType
- mkIntType :: String -> DataType
- mkFloatType :: String -> DataType
- mkCharType :: String -> DataType
- mkNoRepType :: String -> DataType
- dataTypeName :: DataType -> String
- data DataRep
- dataTypeRep :: DataType -> DataRep
- repConstr :: DataType -> ConstrRep -> Constr
- isAlgType :: DataType -> Bool
- dataTypeConstrs :: DataType -> [Constr]
- indexConstr :: DataType -> ConIndex -> Constr
- maxConstrIndex :: DataType -> ConIndex
- isNorepType :: DataType -> Bool
- data Constr
- type ConIndex = Int
- data Fixity
- mkConstr :: DataType -> String -> [String] -> Fixity -> Constr
- mkIntegralConstr :: (Integral a, Show a) => DataType -> a -> Constr
- mkRealConstr :: (Real a, Show a) => DataType -> a -> Constr
- mkCharConstr :: DataType -> Char -> Constr
- constrType :: Constr -> DataType
- data ConstrRep
- constrRep :: Constr -> ConstrRep
- constrFields :: Constr -> [String]
- constrFixity :: Constr -> Fixity
- constrIndex :: Constr -> ConIndex
- showConstr :: Constr -> String
- readConstr :: DataType -> String -> Maybe Constr
- tyconUQname :: String -> String
- tyconModule :: String -> String
- fromConstr :: Data a => Constr -> a
- fromConstrB :: Data a => (forall d. Data d => d) -> Constr -> a
- fromConstrM :: forall m a. (Monad m, Data a) => (forall d. Data d => m d) -> Constr -> m a
Module Data.Typeable re-exported for convenience
module Data.Typeable
The Data class for processing constructor applications
class Typeable a => Data a where Source #
The Data
class comprehends a fundamental primitive gfoldl
for
folding over constructor applications, say terms. This primitive can
be instantiated in several ways to map over the immediate subterms
of a term; see the gmap
combinators later in this class. Indeed, a
generic programmer does not necessarily need to use the ingenious gfoldl
primitive but rather the intuitive gmap
combinators. The gfoldl
primitive is completed by means to query top-level constructors, to
turn constructor representations into proper terms, and to list all
possible datatype constructors. This completion allows us to serve
generic programming scenarios like read, show, equality, term generation.
The combinators gmapT
, gmapQ
, gmapM
, etc are all provided with
default definitions in terms of gfoldl
, leaving open the opportunity
to provide datatype-specific definitions.
(The inclusion of the gmap
combinators as members of class Data
allows the programmer or the compiler to derive specialised, and maybe
more efficient code per datatype. Note: gfoldl
is more higher-order
than the gmap
combinators. This is subject to ongoing benchmarking
experiments. It might turn out that the gmap
combinators will be
moved out of the class Data
.)
Conceptually, the definition of the gmap
combinators in terms of the
primitive gfoldl
requires the identification of the gfoldl
function
arguments. Technically, we also need to identify the type constructor
c
for the construction of the result type from the folded term type.
In the definition of gmapQ
x combinators, we use phantom type
constructors for the c
in the type of gfoldl
because the result type
of a query does not involve the (polymorphic) type of the term argument.
In the definition of gmapQl
we simply use the plain constant type
constructor because gfoldl
is left-associative anyway and so it is
readily suited to fold a left-associative binary operation over the
immediate subterms. In the definition of gmapQr, extra effort is
needed. We use a higher-order accumulation trick to mediate between
left-associative constructor application vs. right-associative binary
operation (e.g., (:)
). When the query is meant to compute a value
of type r
, then the result type withing generic folding is r -> r
.
So the result of folding is a function to which we finally pass the
right unit.
With the -XDeriveDataTypeable
option, GHC can generate instances of the
Data
class automatically. For example, given the declaration
data T a b = C1 a b | C2 deriving (Typeable, Data)
GHC will generate an instance that is equivalent to
instance (Data a, Data b) => Data (T a b) where gfoldl k z (C1 a b) = z C1 `k` a `k` b gfoldl k z C2 = z C2 gunfold k z c = case constrIndex c of 1 -> k (k (z C1)) 2 -> z C2 toConstr (C1 _ _) = con_C1 toConstr C2 = con_C2 dataTypeOf _ = ty_T con_C1 = mkConstr ty_T "C1" [] Prefix con_C2 = mkConstr ty_T "C2" [] Prefix ty_T = mkDataType "Module.T" [con_C1, con_C2]
This is suitable for datatypes that are exported transparently.
:: (forall d b. Data d => c (d -> b) -> d -> c b) | defines how nonempty constructor applications are folded. It takes the folded tail of the constructor application and its head, i.e., an immediate subterm, and combines them in some way. |
-> (forall g. g -> c g) | defines how the empty constructor application is folded, like the neutral / start element for list folding. |
-> a | structure to be folded. |
-> c a | result, with a type defined in terms of |
Left-associative fold operation for constructor applications.
The type of gfoldl
is a headache, but operationally it is a simple
generalisation of a list fold.
The default definition for gfoldl
is
, which is
suitable for abstract datatypes with no substructures.const
id
gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c a Source #
Unfolding constructor applications
toConstr :: a -> Constr Source #
Obtaining the constructor from a given datum. For proper terms, this is meant to be the top-level constructor. Primitive datatypes are here viewed as potentially infinite sets of values (i.e., constructors).
dataTypeOf :: a -> DataType Source #
The outer type constructor of the type
dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c a) Source #
Mediate types and unary type constructors.
In Data
instances of the form T a
, dataCast1
should be defined
as gcast1
.
The default definition is
, which is appropriate
for non-unary type constructors.const
Nothing
dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c a) Source #
Mediate types and binary type constructors.
In Data
instances of the form T a b
, dataCast2
should be
defined as gcast2
.
The default definition is
, which is appropriate
for non-binary type constructors.const
Nothing
gmapT :: (forall b. Data b => b -> b) -> a -> a Source #
A generic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c
in the
type of gfoldl
to an identity datatype constructor, using the
isomorphism pair as injection and projection.
gmapQl :: forall r r'. (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> a -> r Source #
A generic query with a left-associative binary operator
gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> a -> r Source #
A generic query with a right-associative binary operator
gmapQ :: (forall d. Data d => d -> u) -> a -> [u] Source #
A generic query that processes the immediate subterms and returns a list of results. The list is given in the same order as originally specified in the declaration of the data constructors.
gmapQi :: forall u. Int -> (forall d. Data d => d -> u) -> a -> u Source #
A generic query that processes one child by index (zero-based)
gmapM :: forall m. Monad m => (forall d. Data d => d -> m d) -> a -> m a Source #
A generic monadic transformation that maps over the immediate subterms
The default definition instantiates the type constructor c
in
the type of gfoldl
to the monad datatype constructor, defining
injection and projection using return
and >>=
.
gmapMp :: forall m. MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a Source #
Transformation of at least one immediate subterm does not fail
gmapMo :: forall m. MonadPlus m => (forall d. Data d => d -> m d) -> a -> m a Source #
Transformation of one immediate subterm with success
Data Bool # | Since: 4.0.0.0 |
Data Char # | Since: 4.0.0.0 |
Data Double # | Since: 4.0.0.0 |
Data Float # | Since: 4.0.0.0 |
Data Int # | Since: 4.0.0.0 |
Data Int8 # | Since: 4.0.0.0 |
Data Int16 # | Since: 4.0.0.0 |
Data Int32 # | Since: 4.0.0.0 |
Data Int64 # | Since: 4.0.0.0 |
Data Integer # | Since: 4.0.0.0 |
Data Natural # | Since: 4.8.0.0 |
Data Ordering # | Since: 4.0.0.0 |
Data Word # | Since: 4.0.0.0 |
Data Word8 # | Since: 4.0.0.0 |
Data Word16 # | Since: 4.0.0.0 |
Data Word32 # | Since: 4.0.0.0 |
Data Word64 # | Since: 4.0.0.0 |
Data () # | Since: 4.0.0.0 |
Data DecidedStrictness # | Since: 4.9.0.0 |
Data SourceStrictness # | Since: 4.9.0.0 |
Data SourceUnpackedness # | Since: 4.9.0.0 |
Data Associativity # | Since: 4.9.0.0 |
Data Fixity # | Since: 4.9.0.0 |
Data Any # | Since: 4.8.0.0 |
Data All # | Since: 4.8.0.0 |
Data Version # | Since: 4.7.0.0 |
Data SpecConstrAnnotation # | |
Data Void # | |
Data a => Data [a] # | Since: 4.0.0.0 |
Data a => Data (Maybe a) # | Since: 4.0.0.0 |
(Data a, Integral a) => Data (Ratio a) # | Since: 4.0.0.0 |
Data a => Data (Ptr a) # | Since: 4.8.0.0 |
Data p => Data (Par1 p) # | Since: 4.9.0.0 |
Data a => Data (Last a) # | Since: 4.8.0.0 |
Data a => Data (First a) # | Since: 4.8.0.0 |
Data a => Data (Product a) # | Since: 4.8.0.0 |
Data a => Data (Sum a) # | Since: 4.8.0.0 |
Data a => Data (Dual a) # | Since: 4.8.0.0 |
Data a => Data (ForeignPtr a) # | Since: 4.8.0.0 |
Data a => Data (Identity a) # | Since: 4.9.0.0 |
Data a => Data (NonEmpty a) # | |
Data a => Data (Option a) # | |
Data m => Data (WrappedMonoid m) # | |
Data a => Data (Last a) # | |
Data a => Data (First a) # | |
Data a => Data (Max a) # | |
Data a => Data (Min a) # | |
Typeable * a => Data (Fixed a) # | Since: 4.1.0.0 |
Data a => Data (Complex a) # | |
(Data a, Data b) => Data (Either a b) # | Since: 4.0.0.0 |
Data p => Data (V1 * p) # | Since: 4.9.0.0 |
Data p => Data (U1 * p) # | Since: 4.9.0.0 |
(Data a, Data b) => Data (a, b) # | Since: 4.0.0.0 |
Data t => Data (Proxy * t) # | Since: 4.7.0.0 |
(Data b, Data a) => Data (Arg a b) # | |
(Data (f p), Typeable (* -> *) f, Data p) => Data (Rec1 * f p) # | Since: 4.9.0.0 |
(Data a, Data b, Data c) => Data (a, b, c) # | Since: 4.0.0.0 |
((~) * a b, Data a) => Data ((:~:) * a b) # | Since: 4.7.0.0 |
(Coercible * a b, Data a, Data b) => Data (Coercion * a b) # | Since: 4.7.0.0 |
(Data (f a), Data a, Typeable (* -> *) f) => Data (Alt * f a) # | Since: 4.8.0.0 |
(Typeable * k3, Data a, Typeable k3 b) => Data (Const k3 a b) # | Since: 4.10.0.0 |
(Typeable * i, Data p, Data c) => Data (K1 * i c p) # | Since: 4.9.0.0 |
(Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f p), Data (g p)) => Data ((:+:) * f g p) # | Since: 4.9.0.0 |
(Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f p), Data (g p)) => Data ((:*:) * f g p) # | Since: 4.9.0.0 |
(Data a, Data b, Data c, Data d) => Data (a, b, c, d) # | Since: 4.0.0.0 |
(Typeable * i2, Typeable * j2, Typeable i2 a, Typeable j2 b, (~~) i2 j2 a b) => Data ((:~~:) i2 j2 a b) # | Since: 4.10.0.0 |
(Data (g a), Data (f a), Typeable * k, Typeable (k -> *) g, Typeable (k -> *) f, Typeable k a) => Data (Sum k f g a) # | |
(Data (g a), Data (f a), Typeable * k, Typeable (k -> *) g, Typeable (k -> *) f, Typeable k a) => Data (Product k f g a) # | |
(Data p, Data (f p), Typeable Meta c, Typeable * i, Typeable (* -> *) f) => Data (M1 * i c f p) # | Since: 4.9.0.0 |
(Typeable (* -> *) f, Typeable (* -> *) g, Data p, Data (f (g p))) => Data ((:.:) * * f g p) # | Since: 4.9.0.0 |
(Data a, Data b, Data c, Data d, Data e) => Data (a, b, c, d, e) # | Since: 4.0.0.0 |
(Data (f (g a)), Typeable * k2, Typeable * k1, Typeable (k2 -> k1) g, Typeable (k1 -> *) f, Typeable k2 a) => Data (Compose k1 k2 f g a) # | |
(Data a, Data b, Data c, Data d, Data e, Data f) => Data (a, b, c, d, e, f) # | Since: 4.0.0.0 |
(Data a, Data b, Data c, Data d, Data e, Data f, Data g) => Data (a, b, c, d, e, f, g) # | Since: 4.0.0.0 |
Datatype representations
Representation of datatypes. A package of constructor representations with names of type and module.
Constructors
mkNoRepType :: String -> DataType Source #
Constructs a non-representation for a non-representable type
Observers
dataTypeName :: DataType -> String Source #
Gets the type constructor including the module
Public representation of datatypes
dataTypeRep :: DataType -> DataRep Source #
Gets the public presentation of a datatype
Convenience functions
dataTypeConstrs :: DataType -> [Constr] Source #
Gets the constructors of an algebraic datatype
indexConstr :: DataType -> ConIndex -> Constr Source #
Gets the constructor for an index (algebraic datatypes only)
maxConstrIndex :: DataType -> ConIndex Source #
Gets the maximum constructor index of an algebraic datatype
isNorepType :: DataType -> Bool Source #
Test for a non-representable type
Data constructor representations
Unique index for datatype constructors, counting from 1 in the order they are given in the program text.
Constructors
Observers
constrType :: Constr -> DataType Source #
Gets the datatype of a constructor
Public representation of constructors
constrFields :: Constr -> [String] Source #
Gets the field labels of a constructor. The list of labels is returned in the same order as they were given in the original constructor declaration.
constrFixity :: Constr -> Fixity Source #
Gets the fixity of a constructor
Convenience function: algebraic data types
constrIndex :: Constr -> ConIndex Source #
Gets the index of a constructor (algebraic datatypes only)
From strings to constructors and vice versa: all data types
showConstr :: Constr -> String Source #
Gets the string for a constructor
Convenience functions: take type constructors apart
tyconUQname :: String -> String Source #
Gets the unqualified type constructor: drop *.*.*... before name
tyconModule :: String -> String Source #
Gets the module of a type constructor: take *.*.*... before name
Generic operations defined in terms of gunfold
fromConstr :: Data a => Constr -> a Source #
Build a term skeleton
fromConstrB :: Data a => (forall d. Data d => d) -> Constr -> a Source #
Build a term and use a generic function for subterms
fromConstrM :: forall m a. (Monad m, Data a) => (forall d. Data d => m d) -> Constr -> m a Source #
Monadic variation on fromConstrB