3 {-# OPTIONS_GHC -XNoImplicitPrelude -XTypeOperators #-}
5 module GHC.Generics where
11 data (:+:) a b = Inl a | Inr b
12 data (:*:) a b = a :*: b
17 {-# OPTIONS_GHC -XNoImplicitPrelude #-}
18 {-# OPTIONS_GHC -XEmptyDataDecls #-}
19 {-# OPTIONS_GHC -XMultiParamTypeClasses #-}
20 {-# OPTIONS_GHC -XTypeSynonymInstances #-}
21 {-# OPTIONS_GHC -XTypeOperators #-}
22 {-# OPTIONS_GHC -XKindSignatures #-}
25 -- * Generic representation types
26 V1, U1(..), Par1(..), Rec1(..), K1(..), M1(..)
27 , (:+:)(..), (:*:)(..), (:.:)(..)
29 -- ** Synonyms for convenience
34 , Datatype(..), Constructor(..), Selector(..), NoSelector
35 , Fixity(..), Associativity(..), Arity(..), prec
37 -- * Representation type families
40 -- * Representable type classes
41 , Representable0(..), Representable1(..)
44 -- * Representations for base types
45 , Rep0Char, Rep0Int, Rep0Float
46 , Rep0Maybe, Rep1Maybe
51 import {-# SOURCE #-} GHC.Types -- ([](..), Int, Char, Bool(..))
53 --------------------------------------------------------------------------------
54 -- Representation types
55 --------------------------------------------------------------------------------
57 -- | Void: used for datatypes without constructors
60 -- | Unit: used for constructors without arguments
63 -- | Used for marking occurrences of the parameter
64 newtype Par1 p = Par1 { unPar1 :: p }
67 -- | Recursive calls of kind * -> *
68 newtype Rec1 f p = Rec1 { unRec1 :: f p }
70 -- | Constants, additional parameters and recursion of kind *
71 newtype K1 i c p = K1 { unK1 :: c }
73 -- | Meta-information (constructor names, etc.)
74 newtype M1 i c f p = M1 { unM1 :: f p }
76 -- | Sums: encode choice between constructors
78 data (:+:) f g p = L1 (f p) | R1 (g p)
80 -- | Products: encode multiple arguments to constructors
82 data (:*:) f g p = f p :*: g p
84 -- | Composition of functors
86 newtype (:.:) f g p = Comp1 { unComp1 :: f (g p) }
88 -- | Tag for K1: recursion (of kind *)
90 -- | Tag for K1: parameters (other than the last)
93 -- | Type synonym for encoding recursion (of kind *)
95 -- | Type synonym for encoding parameters (other than the last)
98 -- | Tag for M1: datatype
100 -- | Tag for M1: constructor
102 -- | Tag for M1: record selector
105 -- | Type synonym for encoding meta-information for datatypes
108 -- | Type synonym for encoding meta-information for constructors
111 -- | Type synonym for encoding meta-information for record selectors
115 -- | Class for datatypes that represent datatypes
116 class Datatype d where
117 -- | The name of the datatype (unqualified)
118 datatypeName :: t d (f :: * -> *) a -> [Char]
119 -- | The fully-qualified name of the module where the type is declared
120 moduleName :: t d (f :: * -> *) a -> [Char]
123 -- | Class for datatypes that represent records
124 class Selector s where
125 -- | The name of the selector
126 selName :: t s (f :: * -> *) a -> [Char]
128 -- | Used for constructor fields without a name
131 instance Selector NoSelector where selName _ = ""
133 -- | Class for datatypes that represent data constructors
134 class Constructor c where
135 -- | The name of the constructor
136 conName :: t c (f :: * -> *) a -> [Char]
138 -- | The fixity of the constructor
139 conFixity :: t c (f :: * -> *) a -> Fixity
142 -- | Marks if this constructor is a record
143 conIsRecord :: t c (f :: * -> *) a -> Bool
144 conIsRecord _ = False
146 -- | Marks if this constructor is a tuple,
147 -- returning arity >=0 if so, <0 if not
148 conIsTuple :: t c (f :: * -> *) a -> Arity
149 conIsTuple _ = NoArity
152 -- | Datatype to represent the arity of a tuple.
153 data Arity = NoArity | Arity Int
154 -- deriving (Eq, Show, Ord, Read)
155 -- TODO: Add these instances to the Prelude
157 -- | Datatype to represent the fixity of a constructor. An infix
158 -- | declaration directly corresponds to an application of 'Infix'.
159 data Fixity = Prefix | Infix Associativity Int
160 -- deriving (Eq, Show, Ord, Read)
161 -- TODO: Add these instances to the Prelude
163 -- | Get the precedence of a fixity value.
164 prec :: Fixity -> Int
168 -- | Datatype to represent the associativy of a constructor
169 data Associativity = LeftAssociative
172 -- deriving (Eq, Show, Ord, Read)
173 -- TODO: Add these instances to the Prelude
176 -- | Representable types of kind *
177 class Representable0 a rep where
178 -- | Convert from the datatype to its representation
179 from0 :: a -> Rep0 a x
180 -- | Convert from the representation to the datatype
183 -- | Representable types of kind * -> *
184 class Representable1 f rep where
185 -- | Convert from the datatype to its representation
186 from1 :: f a -> Rep1 f a
187 -- | Convert from the representation to the datatype
188 to1 :: Rep1 f a -> f a
190 --------------------------------------------------------------------------------
191 -- Representation for base types
192 --------------------------------------------------------------------------------
194 -- Representation types
197 instance Representable1 Par1 Rep1Par1 where
201 type Rep1Rec1 f = Rec1 f
202 instance Representable1 (Rec1 f) (Rep1Rec1 f) where
209 type Rep0Char = Rec0 Char
210 instance Representable0 Char Rep0Char where
214 type Rep0Int = Rec0 Int
215 instance Representable0 Int Rep0Int where
219 type Rep0Float = Rec0 Float
220 instance Representable0 Float Rep0Float where
232 instance Datatype Maybe_ where
233 datatypeName _ = "Maybe"
234 moduleName _ = "Representation"
236 instance Constructor Nothing_ where
237 conName _ = "Nothing"
239 instance Constructor Just_ where
242 type Rep0Maybe a = D1 Maybe_ (C1 Nothing_ U1 :+: C1 Just_ (Par0 a))
243 instance Representable0 (Maybe a) (Rep0Maybe a) where
244 from0 Nothing = M1 (L1 (M1 U1))
245 from0 (Just x) = M1 (R1 (M1 (K1 x)))
246 to0 (M1 (L1 (M1 U1))) = Nothing
247 to0 (M1 (R1 (M1 (K1 x)))) = Just x
249 type Rep1Maybe = D1 Maybe_ (C1 Nothing_ U1 :+: C1 Just_ Par1)
250 instance Representable1 Maybe Rep1Maybe where
251 from1 Nothing = M1 (L1 (M1 U1))
252 from1 (Just x) = M1 (R1 (M1 (Par1 x)))
253 to1 (M1 (L1 (M1 U1))) = Nothing
254 to1 (M1 (R1 (M1 (Par1 x)))) = Just x
261 instance Datatype [a] where
262 datatypeName _ = "[]"
263 moduleName _ = "Data.List"
265 instance Constructor Nil__ where conName _ = "[]"
266 instance Constructor Cons__ where
268 conFixity _ = Infix RightAssociative 5
270 type Rep0List a = D1 List__ ((C1 Nil__ U1) :+: (C1 Cons__ (Par0 a :*: Rec0 [a])))
271 instance Representable0 [a] (Rep0List a) where
272 from0 [] = M1 (L1 (M1 U1))
273 from0 (h:t) = M1 (R1 (M1 (K1 h :*: K1 t)))
274 to0 (M1 (L1 (M1 U1))) = []
275 to0 (M1 (R1 (M1 (K1 h :*: K1 t)))) = h : t
277 type Rep1List = D1 List__ ((C1 Nil__ U1) :+: (C1 Cons__ (Par1 :*: Rec1 [])))
278 instance Representable1 [] Rep1List where
279 from1 [] = M1 (L1 (M1 U1))
280 from1 (h:t) = M1 (R1 (M1 (Par1 h :*: Rec1 t)))
281 to1 (M1 (L1 (M1 U1))) = []
282 to1 (M1 (R1 (M1 (Par1 h :*: Rec1 t)))) = h : t