[project @ 2001-06-28 14:15:04 by simonmar]
[packages/old-time.git] / Data / Dynamic.hs
1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
3 --
4 -- Module : Data.Dynamic
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/core/LICENSE)
7 --
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : non-portable
11 --
12 -- $Id: Dynamic.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
13 --
14 -- The Dynamic interface provides basic support for dynamic types.
15 --
16 -- Operations for injecting values of arbitrary type into
17 -- a dynamically typed value, Dynamic, are provided, together
18 -- with operations for converting dynamic values into a concrete
19 -- (monomorphic) type.
20 --
21 -- The Dynamic implementation provided is closely based on code
22 -- contained in Hugs library of the same name.
23 --
24 -----------------------------------------------------------------------------
25
26 module Data.Dynamic
27 (
28 -- dynamic type
29 Dynamic -- abstract, instance of: Show, Typeable
30 , toDyn -- :: Typeable a => a -> Dynamic
31 , fromDyn -- :: Typeable a => Dynamic -> a -> a
32 , fromDynamic -- :: Typeable a => Dynamic -> Maybe a
33
34 -- type representation
35
36 , Typeable(
37 typeOf) -- :: a -> TypeRep
38
39 -- Dynamic defines Typeable instances for the following
40 -- Prelude types: [a], (), (a,b), (a,b,c), (a,b,c,d),
41 -- (a,b,c,d,e), (a->b), (Array a b), Bool, Char,
42 -- (Complex a), Double, (Either a b), Float, Handle,
43 -- Int, Integer, (IO a), (Maybe a), Ordering
44
45 , TypeRep -- abstract, instance of: Eq, Show, Typeable
46 , TyCon -- abstract, instance of: Eq, Show, Typeable
47
48 -- type representation constructors/operators:
49 , mkTyCon -- :: String -> TyCon
50 , mkAppTy -- :: TyCon -> [TypeRep] -> TypeRep
51 , mkFunTy -- :: TypeRep -> TypeRep -> TypeRep
52 , applyTy -- :: TypeRep -> TypeRep -> Maybe TypeRep
53
54 --
55 -- let fTy = mkTyCon "Foo" in show (mkAppTy (mkTyCon ",,")
56 -- [fTy,fTy,fTy])
57 --
58 -- returns "(Foo,Foo,Foo)"
59 --
60 -- The TypeRep Show instance promises to print tuple types
61 -- correctly. Tuple type constructors are specified by a
62 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
63 -- the 5-tuple tycon.
64 ) where
65
66
67 #ifdef __GLASGOW_HASKELL__
68 import GHC.Base
69 import GHC.Maybe
70 import GHC.Show
71 import GHC.Err
72 import GHC.Num
73 import GHC.Float
74 import GHC.IOBase
75 import GHC.Dynamic
76 #endif
77
78 #ifdef __GLASGOW_HASKELL__
79 import GHC.Prim ( unsafeCoerce# )
80
81 unsafeCoerce :: a -> b
82 unsafeCoerce = unsafeCoerce#
83 #endif
84
85 #include "Dynamic.h"
86
87 -- The dynamic type is represented by Dynamic, carrying
88 -- the dynamic value along with its type representation:
89
90 -- the instance just prints the type representation.
91 instance Show Dynamic where
92 showsPrec _ (Dynamic t _) =
93 showString "<<" .
94 showsPrec 0 t .
95 showString ">>"
96
97 -- Operations for going to and from Dynamic:
98
99 toDyn :: Typeable a => a -> Dynamic
100 toDyn v = Dynamic (typeOf v) (unsafeCoerce v)
101
102 fromDyn :: Typeable a => Dynamic -> a -> a
103 fromDyn (Dynamic t v) def
104 | typeOf def == t = unsafeCoerce v
105 | otherwise = def
106
107 fromDynamic :: Typeable a => Dynamic -> Maybe a
108 fromDynamic (Dynamic t v) =
109 case unsafeCoerce v of
110 r | t == typeOf r -> Just r
111 | otherwise -> Nothing
112
113 -- (Abstract) universal datatype:
114
115 instance Show TypeRep where
116 showsPrec p (App tycon tys) =
117 case tys of
118 [] -> showsPrec p tycon
119 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
120 xs
121 | isTupleTyCon tycon -> showTuple tycon xs
122 | otherwise ->
123 showParen (p > 9) $
124 showsPrec p tycon .
125 showChar ' ' .
126 showArgs tys
127
128 showsPrec p (Fun f a) =
129 showParen (p > 8) $
130 showsPrec 9 f . showString " -> " . showsPrec 8 a
131
132 -- To make it possible to convert values with user-defined types
133 -- into type Dynamic, we need a systematic way of getting
134 -- the type representation of an arbitrary type. A type
135 -- class provides just the ticket,
136
137 class Typeable a where
138 typeOf :: a -> TypeRep
139
140 -- NOTE: The argument to the overloaded `typeOf' is only
141 -- used to carry type information, and Typeable instances
142 -- should *never* *ever* look at its value.
143
144 isTupleTyCon :: TyCon -> Bool
145 isTupleTyCon (TyCon _ (',':_)) = True
146 isTupleTyCon _ = False
147
148 instance Show TyCon where
149 showsPrec _ (TyCon _ s) = showString s
150
151 -- If we enforce the restriction that there is only one
152 -- @TyCon@ for a type & it is shared among all its uses,
153 -- we can map them onto Ints very simply. The benefit is,
154 -- of course, that @TyCon@s can then be compared efficiently.
155
156 -- Provided the implementor of other @Typeable@ instances
157 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
158 -- this will work.
159
160 -- If this constraint does turn out to be a sore thumb, changing
161 -- the Eq instance for TyCons is trivial.
162
163 mkTyCon :: String -> TyCon
164 mkTyCon str = unsafePerformIO $ do
165 v <- readIORef uni
166 writeIORef uni (v+1)
167 return (TyCon v str)
168
169 {-# NOINLINE uni #-}
170 uni :: IORef Int
171 uni = unsafePerformIO ( newIORef 0 )
172
173 -- Some (Show.TypeRep) helpers:
174
175 showArgs :: Show a => [a] -> ShowS
176 showArgs [] = id
177 showArgs [a] = showsPrec 10 a
178 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
179
180 showTuple :: TyCon -> [TypeRep] -> ShowS
181 showTuple (TyCon _ str) args = showChar '(' . go str args
182 where
183 go [] [a] = showsPrec 10 a . showChar ')'
184 go _ [] = showChar ')' -- a failure condition, really.
185 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
186 go _ _ = showChar ')'
187
188
189 mkAppTy :: TyCon -> [TypeRep] -> TypeRep
190 mkAppTy tyc args = App tyc args
191
192 mkFunTy :: TypeRep -> TypeRep -> TypeRep
193 mkFunTy f a = Fun f a
194
195 -- Auxillary functions
196
197 -- (f::(a->b)) `dynApply` (x::a) = (f a)::b
198 dynApply :: Dynamic -> Dynamic -> Maybe Dynamic
199 dynApply (Dynamic t1 f) (Dynamic t2 x) =
200 case applyTy t1 t2 of
201 Just t3 -> Just (Dynamic t3 ((unsafeCoerce f) x))
202 Nothing -> Nothing
203
204 dynApp :: Dynamic -> Dynamic -> Dynamic
205 dynApp f x = case dynApply f x of
206 Just r -> r
207 Nothing -> error ("Type error in dynamic application.\n" ++
208 "Can't apply function " ++ show f ++
209 " to argument " ++ show x)
210
211 applyTy :: TypeRep -> TypeRep -> Maybe TypeRep
212 applyTy (Fun t1 t2) t3
213 | t1 == t3 = Just t2
214 applyTy _ _ = Nothing
215
216 -- Prelude types
217
218 listTc :: TyCon
219 listTc = mkTyCon "[]"
220
221 instance Typeable a => Typeable [a] where
222 typeOf ls = mkAppTy listTc [typeOf ((undefined:: [a] -> a) ls)]
223
224 unitTc :: TyCon
225 unitTc = mkTyCon "()"
226
227 instance Typeable () where
228 typeOf _ = mkAppTy unitTc []
229
230 tup2Tc :: TyCon
231 tup2Tc = mkTyCon ","
232
233 instance (Typeable a, Typeable b) => Typeable (a,b) where
234 typeOf tu = mkAppTy tup2Tc [typeOf ((undefined :: (a,b) -> a) tu),
235 typeOf ((undefined :: (a,b) -> b) tu)]
236
237 tup3Tc :: TyCon
238 tup3Tc = mkTyCon ",,"
239
240 instance ( Typeable a , Typeable b , Typeable c) => Typeable (a,b,c) where
241 typeOf tu = mkAppTy tup3Tc [typeOf ((undefined :: (a,b,c) -> a) tu),
242 typeOf ((undefined :: (a,b,c) -> b) tu),
243 typeOf ((undefined :: (a,b,c) -> c) tu)]
244
245 tup4Tc :: TyCon
246 tup4Tc = mkTyCon ",,,"
247
248 instance ( Typeable a
249 , Typeable b
250 , Typeable c
251 , Typeable d) => Typeable (a,b,c,d) where
252 typeOf tu = mkAppTy tup4Tc [typeOf ((undefined :: (a,b,c,d) -> a) tu),
253 typeOf ((undefined :: (a,b,c,d) -> b) tu),
254 typeOf ((undefined :: (a,b,c,d) -> c) tu),
255 typeOf ((undefined :: (a,b,c,d) -> d) tu)]
256
257 tup5Tc :: TyCon
258 tup5Tc = mkTyCon ",,,,"
259
260 instance ( Typeable a
261 , Typeable b
262 , Typeable c
263 , Typeable d
264 , Typeable e) => Typeable (a,b,c,d,e) where
265 typeOf tu = mkAppTy tup5Tc [typeOf ((undefined :: (a,b,c,d,e) -> a) tu),
266 typeOf ((undefined :: (a,b,c,d,e) -> b) tu),
267 typeOf ((undefined :: (a,b,c,d,e) -> c) tu),
268 typeOf ((undefined :: (a,b,c,d,e) -> d) tu),
269 typeOf ((undefined :: (a,b,c,d,e) -> e) tu)]
270
271 instance (Typeable a, Typeable b) => Typeable (a -> b) where
272 typeOf f = mkFunTy (typeOf ((undefined :: (a -> b) -> a) f))
273 (typeOf ((undefined :: (a -> b) -> b) f))
274
275 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
276 INSTANCE_TYPEABLE0(Char,charTc,"Char")
277 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
278 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
279 INSTANCE_TYPEABLE0(Int,intTc,"Int")
280 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
281 INSTANCE_TYPEABLE2(Either,eitherTc,"Either")
282 INSTANCE_TYPEABLE1(IO,ioTc,"IO")
283 INSTANCE_TYPEABLE1(Maybe,maybeTc,"Maybe")
284 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
285
286 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
287 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
288 INSTANCE_TYPEABLE0(Dynamic,dynamicTc,"Dynamic")