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 -- * Representable type classes
38 , Representable0(..), Representable1(..)
41 -- * Representations for base types
42 , Rep0Char, Rep0Int, Rep0Float
43 , Rep0Maybe, Rep1Maybe
48 import {-# SOURCE #-} GHC.Types
50 --------------------------------------------------------------------------------
51 -- Representation types
52 --------------------------------------------------------------------------------
54 -- | Void: used for datatypes without constructors
57 -- | Unit: used for constructors without arguments
60 -- | Used for marking occurrences of the parameter
61 newtype Par1 p = Par1 { unPar1 :: p }
64 -- | Recursive calls of kind * -> *
65 newtype Rec1 f p = Rec1 { unRec1 :: f p }
67 -- | Constants, additional parameters and recursion of kind *
68 newtype K1 i c p = K1 { unK1 :: c }
70 -- | Meta-information (constructor names, etc.)
71 newtype M1 i c f p = M1 { unM1 :: f p }
73 -- | Sums: encode choice between constructors
75 data (:+:) f g p = L1 (f p) | R1 (g p)
77 -- | Products: encode multiple arguments to constructors
79 data (:*:) f g p = f p :*: g p
81 -- | Composition of functors
83 newtype (:.:) f g p = Comp1 { unComp1 :: f (g p) }
85 -- | Tag for K1: recursion (of kind *)
87 -- | Tag for K1: parameters (other than the last)
90 -- | Type synonym for encoding recursion (of kind *)
92 -- | Type synonym for encoding parameters (other than the last)
95 -- | Tag for M1: datatype
97 -- | Tag for M1: constructor
99 -- | Tag for M1: record selector
102 -- | Type synonym for encoding meta-information for datatypes
105 -- | Type synonym for encoding meta-information for constructors
108 -- | Type synonym for encoding meta-information for record selectors
112 -- | Class for datatypes that represent datatypes
113 class Datatype d where
114 -- | The name of the datatype (unqualified)
115 datatypeName :: t d (f :: * -> *) a -> [Char]
116 -- | The fully-qualified name of the module where the type is declared
117 moduleName :: t d (f :: * -> *) a -> [Char]
120 -- | Class for datatypes that represent records
121 class Selector s where
122 -- | The name of the selector
123 selName :: t s (f :: * -> *) a -> [Char]
125 -- | Used for constructor fields without a name
128 instance Selector NoSelector where selName _ = ""
130 -- | Class for datatypes that represent data constructors
131 class Constructor c where
132 -- | The name of the constructor
133 conName :: t c (f :: * -> *) a -> [Char]
135 -- | The fixity of the constructor
136 conFixity :: t c (f :: * -> *) a -> Fixity
139 -- | Marks if this constructor is a record
140 conIsRecord :: t c (f :: * -> *) a -> Bool
141 conIsRecord _ = False
143 -- | Marks if this constructor is a tuple,
144 -- returning arity >=0 if so, <0 if not
145 conIsTuple :: t c (f :: * -> *) a -> Arity
146 conIsTuple _ = NoArity
149 -- | Datatype to represent the arity of a tuple.
150 data Arity = NoArity | Arity Int
151 -- deriving (Eq, Show, Ord, Read)
152 -- TODO: Add these instances to the Prelude
154 -- | Datatype to represent the fixity of a constructor. An infix
155 -- | declaration directly corresponds to an application of 'Infix'.
156 data Fixity = Prefix | Infix Associativity Int
157 -- deriving (Eq, Show, Ord, Read)
158 -- TODO: Add these instances to the Prelude
160 -- | Get the precedence of a fixity value.
161 prec :: Fixity -> Int
165 -- | Datatype to represent the associativy of a constructor
166 data Associativity = LeftAssociative
169 -- deriving (Eq, Show, Ord, Read)
170 -- TODO: Add these instances to the Prelude
173 -- | Representable types of kind *
174 class Representable0 a rep where
175 -- | Convert from the datatype to its representation
177 -- | Convert from the representation to the datatype
180 -- | Representable types of kind * -> *
181 class Representable1 f rep where
182 -- | Convert from the datatype to its representation
183 from1 :: f a -> rep a
184 -- | Convert from the representation to the datatype
187 --------------------------------------------------------------------------------
188 -- Representation for base types
189 --------------------------------------------------------------------------------
191 -- Representation types
194 instance Representable1 Par1 Rep1Par1 where
198 type Rep1Rec1 f = Rec1 f
199 instance Representable1 (Rec1 f) (Rep1Rec1 f) where
206 type Rep0Char = Rec0 Char
207 instance Representable0 Char Rep0Char where
211 type Rep0Int = Rec0 Int
212 instance Representable0 Int Rep0Int where
216 type Rep0Float = Rec0 Float
217 instance Representable0 Float Rep0Float where
229 instance Datatype Maybe_ where
230 datatypeName _ = "Maybe"
231 moduleName _ = "Representation"
233 instance Constructor Nothing_ where
234 conName _ = "Nothing"
236 instance Constructor Just_ where
239 type Rep0Maybe a = D1 Maybe_ (C1 Nothing_ U1 :+: C1 Just_ (Par0 a))
240 instance Representable0 (Maybe a) (Rep0Maybe a) where
241 from0 Nothing = M1 (L1 (M1 U1))
242 from0 (Just x) = M1 (R1 (M1 (K1 x)))
243 to0 (M1 (L1 (M1 U1))) = Nothing
244 to0 (M1 (R1 (M1 (K1 x)))) = Just x
246 type Rep1Maybe = D1 Maybe_ (C1 Nothing_ U1 :+: C1 Just_ Par1)
247 instance Representable1 Maybe Rep1Maybe where
248 from1 Nothing = M1 (L1 (M1 U1))
249 from1 (Just x) = M1 (R1 (M1 (Par1 x)))
250 to1 (M1 (L1 (M1 U1))) = Nothing
251 to1 (M1 (R1 (M1 (Par1 x)))) = Just x
258 instance Datatype [a] where
259 datatypeName _ = "[]"
260 moduleName _ = "Data.List"
262 instance Constructor Nil__ where conName _ = "[]"
263 instance Constructor Cons__ where
265 conFixity _ = Infix RightAssociative 5
267 type Rep0List a = D1 List__ ((C1 Nil__ U1) :+: (C1 Cons__ (Par0 a :*: Rec0 [a])))
268 instance Representable0 [a] (Rep0List a) where
269 from0 [] = M1 (L1 (M1 U1))
270 from0 (h:t) = M1 (R1 (M1 (K1 h :*: K1 t)))
271 to0 (M1 (L1 (M1 U1))) = []
272 to0 (M1 (R1 (M1 (K1 h :*: K1 t)))) = h : t
274 type Rep1List = D1 List__ ((C1 Nil__ U1) :+: (C1 Cons__ (Par1 :*: Rec1 [])))
275 instance Representable1 [] Rep1List where
276 from1 [] = M1 (L1 (M1 U1))
277 from1 (h:t) = M1 (R1 (M1 (Par1 h :*: Rec1 t)))
278 to1 (M1 (L1 (M1 U1))) = []
279 to1 (M1 (R1 (M1 (Par1 h :*: Rec1 t)))) = h : t