1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
4 -- Module : Data.Dynamic
5 -- Copyright : (c) The University of Glasgow 2001
6 -- License : BSD-style (see the file libraries/base/LICENSE)
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : portable
12 -- The Dynamic interface provides basic support for dynamic types.
14 -- Operations for injecting values of arbitrary type into
15 -- a dynamically typed value, Dynamic, are provided, together
16 -- with operations for converting dynamic values into a concrete
17 -- (monomorphic) type.
19 -----------------------------------------------------------------------------
23 -- * The @Dynamic@ type
24 Dynamic, -- abstract, instance of: Show, Typeable
26 -- * Converting to and from @Dynamic@
27 toDyn, -- :: Typeable a => a -> Dynamic
28 fromDyn, -- :: Typeable a => Dynamic -> a -> a
29 fromDynamic, -- :: Typeable a => Dynamic -> Maybe a
31 -- * Applying functions of dynamic type
35 -- * Concrete Type Representations
37 -- | This section is useful if you need to define your own
38 -- instances of 'Typeable'.
40 Typeable( typeOf ), -- :: a -> TypeRep
41 cast, -- :: (Typeable a, Typeable b) => a -> Maybe b
43 -- ** Building concrete type representations
44 TypeRep, -- abstract, instance of: Eq, Show, Typeable
45 TyCon, -- abstract, instance of: Eq, Show, Typeable
47 mkTyCon, -- :: String -> TyCon
48 mkAppTy, -- :: TyCon -> [TypeRep] -> TypeRep
49 mkFunTy, -- :: TypeRep -> TypeRep -> TypeRep
50 applyTy, -- :: TypeRep -> TypeRep -> Maybe TypeRep
53 -- let fTy = mkTyCon "Foo" in show (mkAppTy (mkTyCon ",,")
56 -- returns "(Foo,Foo,Foo)"
58 -- The TypeRep Show instance promises to print tuple types
59 -- correctly. Tuple type constructors are specified by a
60 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
65 import qualified Data.HashTable as HT
70 import Data.List( foldl )
72 #ifdef __GLASGOW_HASKELL__
78 import GHC.Real( rem )
80 import GHC.Ptr -- So we can give Typeable instance for Ptr
81 import GHC.Stable -- So we can give Typeable instance for StablePtr
91 #ifdef __GLASGOW_HASKELL__
92 unsafeCoerce :: a -> b
93 unsafeCoerce = unsafeCoerce#
97 import NonStdUnsafeCoerce (unsafeCoerce)
98 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
103 -------------------------------------------------------------
107 -------------------------------------------------------------
110 A value of type 'Dynamic' is an object encapsulated together with its type.
112 A 'Dynamic' may only represent a monomorphic value; an attempt to
113 create a value of type 'Dynamic' from a polymorphically-typed
114 expression will result in an ambiguity error (see 'toDyn').
116 'Show'ing a value of type 'Dynamic' returns a pretty-printed representation
117 of the object\'s type; useful for debugging.
120 data Dynamic = Dynamic TypeRep Obj
123 instance Show Dynamic where
124 -- the instance just prints the type representation.
125 showsPrec _ (Dynamic t _) =
130 #ifdef __GLASGOW_HASKELL__
131 type Obj = forall a . a
132 -- Dummy type to hold the dynamically typed value.
134 -- In GHC's new eval/apply execution model this type must
135 -- be polymorphic. It can't be a constructor, because then
136 -- GHC will use the constructor convention when evaluating it,
137 -- and this will go wrong if the object is really a function. On
138 -- the other hand, if we use a polymorphic type, GHC will use
139 -- a fallback convention for evaluating it that works for all types.
140 -- (using a function type here would also work).
141 #elif !defined(__HUGS__)
145 -- | Converts an arbitrary value into an object of type 'Dynamic'.
147 -- The type of the object must be an instance of 'Typeable', which
148 -- ensures that only monomorphically-typed objects may be converted to
149 -- 'Dynamic'. To convert a polymorphic object into 'Dynamic', give it
150 -- a monomorphic type signature. For example:
152 -- > toDyn (id :: Int -> Int)
154 toDyn :: Typeable a => a -> Dynamic
155 toDyn v = Dynamic (typeOf v) (unsafeCoerce v)
157 -- | Converts a 'Dynamic' object back into an ordinary Haskell value of
158 -- the correct type. See also 'fromDynamic'.
159 fromDyn :: Typeable a
160 => Dynamic -- ^ the dynamically-typed object
161 -> a -- ^ a default value
162 -> a -- ^ returns: the value of the first argument, if
163 -- it has the correct type, otherwise the value of
164 -- the second argument.
165 fromDyn (Dynamic t v) def
166 | typeOf def == t = unsafeCoerce v
169 -- | Converts a 'Dynamic' object back into an ordinary Haskell value of
170 -- the correct type. See also 'fromDyn'.
173 => Dynamic -- ^ the dynamically-typed object
174 -> Maybe a -- ^ returns: @'Just' a@, if the dyanmically-typed
175 -- object has the correct type (and @a@ is its value),
176 -- or 'Nothing' otherwise.
177 fromDynamic (Dynamic t v) =
178 case unsafeCoerce v of
179 r | t == typeOf r -> Just r
180 | otherwise -> Nothing
182 -- (f::(a->b)) `dynApply` (x::a) = (f a)::b
183 dynApply :: Dynamic -> Dynamic -> Maybe Dynamic
184 dynApply (Dynamic t1 f) (Dynamic t2 x) =
185 case applyTy t1 t2 of
186 Just t3 -> Just (Dynamic t3 ((unsafeCoerce f) x))
189 dynApp :: Dynamic -> Dynamic -> Dynamic
190 dynApp f x = case dynApply f x of
192 Nothing -> error ("Type error in dynamic application.\n" ++
193 "Can't apply function " ++ show f ++
194 " to argument " ++ show x)
197 -------------------------------------------------------------
199 -- Type representations
201 -------------------------------------------------------------
203 -- | A concrete representation of a (monomorphic) type. 'TypeRep'
204 -- supports reasonably efficient equality.
205 data TypeRep = TypeRep !Key TyCon [TypeRep]
207 -- Compare keys for equality
208 instance Eq TypeRep where
209 (TypeRep k1 _ _) == (TypeRep k2 _ _) = k1 == k2
211 -- | An abstract representation of a type constructor. 'TyCon' objects can
212 -- be built using 'mkTyCon'.
213 data TyCon = TyCon !Key String
215 instance Eq TyCon where
216 (TyCon t1 _) == (TyCon t2 _) = t1 == t2
219 ----------------- Type-safe cast ------------------
221 -- | The type-safe cast operation
222 cast :: (Typeable a, Typeable b) => a -> Maybe b
225 r = if typeOf x == typeOf (fromJust r) then
226 Just (unsafeCoerce x)
230 ----------------- Construction --------------------
232 -- | Applies a type constructor to a sequence of types
233 mkAppTy :: TyCon -> [TypeRep] -> TypeRep
234 mkAppTy tc@(TyCon tc_k _) args
235 = TypeRep (appKeys tc_k arg_ks) tc args
237 arg_ks = [k | TypeRep k _ _ <- args]
242 -- | A special case of 'mkAppTy', which applies the function
243 -- type constructor to a pair of types.
244 mkFunTy :: TypeRep -> TypeRep -> TypeRep
245 mkFunTy f a = mkAppTy funTc [f,a]
247 -- | Applies a type to a function type. Returns: @'Just' u@ if the
248 -- first argument represents a function of type @t -> u@ and the
249 -- second argument represents a function of type @t@. Otherwise,
250 -- returns 'Nothing'.
251 applyTy :: TypeRep -> TypeRep -> Maybe TypeRep
252 applyTy (TypeRep _ tc [t1,t2]) t3
253 | tc == funTc && t1 == t3 = Just t2
254 applyTy _ _ = Nothing
256 -- If we enforce the restriction that there is only one
257 -- @TyCon@ for a type & it is shared among all its uses,
258 -- we can map them onto Ints very simply. The benefit is,
259 -- of course, that @TyCon@s can then be compared efficiently.
261 -- Provided the implementor of other @Typeable@ instances
262 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
265 -- If this constraint does turn out to be a sore thumb, changing
266 -- the Eq instance for TyCons is trivial.
268 -- | Builds a 'TyCon' object representing a type constructor. An
269 -- implementation of "Data.Dynamic" should ensure that the following holds:
271 -- > mkTyCon "a" == mkTyCon "a"
273 -- NOTE: GHC\'s implementation is quite hacky, and the above equation
274 -- does not necessarily hold. For defining your own instances of
275 -- 'Typeable', try to ensure that only one call to 'mkTyCon' exists
276 -- for each type constructor (put it at the top level, and annotate the
277 -- corresponding definition with a @NOINLINE@ pragma).
278 mkTyCon :: String -- ^ the name of the type constructor (should be unique
279 -- in the program, so it might be wise to use the
280 -- fully qualified name).
281 -> TyCon -- ^ A unique 'TyCon' object
282 mkTyCon str = TyCon (mkTyConKey str) str
285 ----------------- Showing TypeReps --------------------
287 instance Show TypeRep where
288 showsPrec p (TypeRep _ tycon tys) =
290 [] -> showsPrec p tycon
291 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
292 [a,r] | tycon == funTc -> showParen (p > 8) $
293 showsPrec 9 a . showString " -> " . showsPrec 8 r
294 xs | isTupleTyCon tycon -> showTuple tycon xs
301 instance Show TyCon where
302 showsPrec _ (TyCon _ s) = showString s
304 isTupleTyCon :: TyCon -> Bool
305 isTupleTyCon (TyCon _ (',':_)) = True
306 isTupleTyCon _ = False
308 -- Some (Show.TypeRep) helpers:
310 showArgs :: Show a => [a] -> ShowS
312 showArgs [a] = showsPrec 10 a
313 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
315 showTuple :: TyCon -> [TypeRep] -> ShowS
316 showTuple (TyCon _ str) args = showChar '(' . go str args
318 go [] [a] = showsPrec 10 a . showChar ')'
319 go _ [] = showChar ')' -- a failure condition, really.
320 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
321 go _ _ = showChar ')'
325 -------------------------------------------------------------
327 -- The Typeable class and some instances
329 -------------------------------------------------------------
331 -- | The class 'Typeable' allows a concrete representation of a type to
333 class Typeable a where
334 typeOf :: a -> TypeRep
335 -- ^ Takes a value of type @a@ and returns a concrete representation
336 -- of that type. The /value/ of the argument should be ignored by
337 -- any instance of 'Typeable', so that it is safe to pass 'undefined' as
342 listTc = mkTyCon "[]"
344 instance Typeable a => Typeable [a] where
345 typeOf ls = mkAppTy listTc [typeOf ((undefined :: [a] -> a) ls)]
347 -- typeOf (undefined :: a)
348 -- using scoped type variables, but we use the
349 -- more verbose form here, for compatibility with Hugs
352 unitTc = mkTyCon "()"
354 instance Typeable () where
355 typeOf _ = mkAppTy unitTc []
360 instance (Typeable a, Typeable b) => Typeable (a,b) where
361 typeOf tu = mkAppTy tup2Tc [typeOf ((undefined :: (a,b) -> a) tu),
362 typeOf ((undefined :: (a,b) -> b) tu)]
365 tup3Tc = mkTyCon ",,"
367 instance ( Typeable a , Typeable b , Typeable c) => Typeable (a,b,c) where
368 typeOf tu = mkAppTy tup3Tc [typeOf ((undefined :: (a,b,c) -> a) tu),
369 typeOf ((undefined :: (a,b,c) -> b) tu),
370 typeOf ((undefined :: (a,b,c) -> c) tu)]
373 tup4Tc = mkTyCon ",,,"
375 instance ( Typeable a
378 , Typeable d) => Typeable (a,b,c,d) where
379 typeOf tu = mkAppTy tup4Tc [typeOf ((undefined :: (a,b,c,d) -> a) tu),
380 typeOf ((undefined :: (a,b,c,d) -> b) tu),
381 typeOf ((undefined :: (a,b,c,d) -> c) tu),
382 typeOf ((undefined :: (a,b,c,d) -> d) tu)]
384 tup5Tc = mkTyCon ",,,,"
386 instance ( Typeable a
390 , Typeable e) => Typeable (a,b,c,d,e) where
391 typeOf tu = mkAppTy tup5Tc [typeOf ((undefined :: (a,b,c,d,e) -> a) tu),
392 typeOf ((undefined :: (a,b,c,d,e) -> b) tu),
393 typeOf ((undefined :: (a,b,c,d,e) -> c) tu),
394 typeOf ((undefined :: (a,b,c,d,e) -> d) tu),
395 typeOf ((undefined :: (a,b,c,d,e) -> e) tu)]
397 instance (Typeable a, Typeable b) => Typeable (a -> b) where
398 typeOf f = mkFunTy (typeOf ((undefined :: (a -> b) -> a) f))
399 (typeOf ((undefined :: (a -> b) -> b) f))
402 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
403 INSTANCE_TYPEABLE0(Char,charTc,"Char")
404 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
405 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
406 INSTANCE_TYPEABLE0(Int,intTc,"Int")
407 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
408 INSTANCE_TYPEABLE2(Either,eitherTc,"Either")
409 INSTANCE_TYPEABLE1(IO,ioTc,"IO")
410 INSTANCE_TYPEABLE1(Maybe,maybeTc,"Maybe")
411 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
412 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
413 INSTANCE_TYPEABLE1(Ptr,ptrTc,"Ptr")
414 INSTANCE_TYPEABLE1(StablePtr,stablePtrTc,"StablePtr")
416 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
417 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
418 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
419 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
421 INSTANCE_TYPEABLE0(Word8,word8Tc, "Word8" )
422 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
423 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
424 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
426 INSTANCE_TYPEABLE0(TyCon,tyconTc, "TyCon")
427 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
428 INSTANCE_TYPEABLE0(Dynamic,dynamicTc,"Dynamic")
431 INSTANCE_TYPEABLE1(IORef,ioRefTc,"IORef")
434 ---------------------------------------------
438 ---------------------------------------------
441 newtype Key = Key Int deriving( Eq )
444 data KeyPr = KeyPr !Key !Key deriving( Eq )
446 hashKP :: KeyPr -> Int32
447 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
449 data Cache = Cache { next_key :: !(IORef Key),
450 tc_tbl :: !(HT.HashTable String Key),
451 ap_tbl :: !(HT.HashTable KeyPr Key) }
453 {-# NOINLINE cache #-}
455 cache = unsafePerformIO $ do
456 empty_tc_tbl <- HT.new (==) HT.hashString
457 empty_ap_tbl <- HT.new (==) hashKP
458 key_loc <- newIORef (Key 1)
459 return (Cache { next_key = key_loc,
460 tc_tbl = empty_tc_tbl,
461 ap_tbl = empty_ap_tbl })
463 newKey :: IORef Key -> IO Key
464 newKey kloc = do { k@(Key i) <- readIORef kloc ;
465 writeIORef kloc (Key (i+1)) ;
468 mkTyConKey :: String -> Key
470 = unsafePerformIO $ do
471 let Cache {next_key = kloc, tc_tbl = tbl} = cache
472 mb_k <- HT.lookup tbl str
475 Nothing -> do { k <- newKey kloc ;
476 HT.insert tbl str k ;
479 appKey :: Key -> Key -> Key
481 = unsafePerformIO $ do
482 let Cache {next_key = kloc, ap_tbl = tbl} = cache
483 mb_k <- HT.lookup tbl kpr
486 Nothing -> do { k <- newKey kloc ;
487 HT.insert tbl kpr k ;
492 appKeys :: Key -> [Key] -> Key
493 appKeys k ks = foldl appKey k ks