1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
4 -- Module : Data.Typeable
5 -- Copyright : (c) The University of Glasgow, CWI 2001--2004
6 -- License : BSD-style (see the file libraries/base/LICENSE)
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : portable
12 -- The Typeable class reifies types to some extent by associating type
13 -- representations to types. These type representations can be compared,
14 -- and one can in turn define a type-safe cast operation. To this end,
15 -- an unsafe cast is guarded by a test for type (representation)
16 -- equivalence. The module Data.Dynamic uses Typeable for an
17 -- implementation of dynamics. The module Data.Generics uses Typeable
18 -- and type-safe cast (but not dynamics) to support the \"Scrap your
19 -- boilerplate\" style of generic programming.
21 -----------------------------------------------------------------------------
26 -- * The Typeable class
27 Typeable( typeOf ), -- :: a -> TypeRep
30 cast, -- :: (Typeable a, Typeable b) => a -> Maybe b
31 gcast, -- a generalisation of cast
33 -- * Type representations
34 TypeRep, -- abstract, instance of: Eq, Show, Typeable
35 TyCon, -- abstract, instance of: Eq, Show, Typeable
37 -- * Construction of type representations
38 mkTyCon, -- :: String -> TyCon
39 mkAppTy, -- :: TyCon -> [TypeRep] -> TypeRep
40 mkFunTy, -- :: TypeRep -> TypeRep -> TypeRep
41 applyTy, -- :: TypeRep -> TypeRep -> Maybe TypeRep
42 popStarTy, -- :: TypeRep -> TypeRep -> TypeRep
44 -- * Observation of type representations
45 typerepTyCon, -- :: TypeRep -> TyCon
46 typerepArgs, -- :: TypeRep -> [TypeRep]
47 tyconString, -- :: TyCon -> String
49 -- * The other Typeable classes
50 Typeable1( typeOf1 ), -- :: t a -> TypeRep
51 Typeable2( typeOf2 ), -- :: t a b -> TypeRep
52 Typeable3( typeOf3 ), -- :: t a b c -> TypeRep
53 Typeable4( typeOf4 ), -- :: t a b c d -> TypeRep
54 Typeable5( typeOf5 ), -- :: t a b c d e -> TypeRep
55 Typeable6( typeOf6 ), -- :: t a b c d e f -> TypeRep
56 Typeable7( typeOf7 ), -- :: t a b c d e f g -> TypeRep
57 gcast1, -- :: ... => c (t a) -> Maybe (c (t' a))
58 gcast2 -- :: ... => c (t a b) -> Maybe (c (t' a b))
63 import qualified Data.HashTable as HT
68 import Data.List( foldl )
70 #ifdef __GLASGOW_HASKELL__
76 import GHC.Real( rem, Ratio )
78 import GHC.Ptr -- So we can give Typeable instance for Ptr
79 import GHC.Stable -- So we can give Typeable instance for StablePtr
89 #ifdef __GLASGOW_HASKELL__
90 unsafeCoerce :: a -> b
91 unsafeCoerce = unsafeCoerce#
95 import NonStdUnsafeCoerce (unsafeCoerce)
96 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
104 -------------------------------------------------------------
106 -- Type representations
108 -------------------------------------------------------------
111 -- | A concrete representation of a (monomorphic) type. 'TypeRep'
112 -- supports reasonably efficient equality.
113 data TypeRep = TypeRep !Key TyCon [TypeRep]
115 -- Compare keys for equality
116 instance Eq TypeRep where
117 (TypeRep k1 _ _) == (TypeRep k2 _ _) = k1 == k2
119 -- | An abstract representation of a type constructor. 'TyCon' objects can
120 -- be built using 'mkTyCon'.
121 data TyCon = TyCon !Key String
123 instance Eq TyCon where
124 (TyCon t1 _) == (TyCon t2 _) = t1 == t2
129 -- let fTy = mkTyCon "Foo" in show (mkAppTy (mkTyCon ",,")
132 -- returns "(Foo,Foo,Foo)"
134 -- The TypeRep Show instance promises to print tuple types
135 -- correctly. Tuple type constructors are specified by a
136 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
137 -- the 5-tuple tycon.
140 ----------------- Construction --------------------
142 -- | Applies a type constructor to a sequence of types
143 mkAppTy :: TyCon -> [TypeRep] -> TypeRep
144 mkAppTy tc@(TyCon tc_k _) args
145 = TypeRep (appKeys tc_k arg_ks) tc args
147 arg_ks = [k | TypeRep k _ _ <- args]
150 -- The function type constructor
155 -- | A special case of 'mkAppTy', which applies the function
156 -- type constructor to a pair of types.
157 mkFunTy :: TypeRep -> TypeRep -> TypeRep
158 mkFunTy f a = mkAppTy funTc [f,a]
161 -- | Applies a type to a function type. Returns: @'Just' u@ if the
162 -- first argument represents a function of type @t -> u@ and the
163 -- second argument represents a function of type @t@. Otherwise,
164 -- returns 'Nothing'.
165 applyTy :: TypeRep -> TypeRep -> Maybe TypeRep
166 applyTy (TypeRep _ tc [t1,t2]) t3
167 | tc == funTc && t1 == t3 = Just t2
168 applyTy _ _ = Nothing
171 -- | Adds a TypeRep argument to a TypeRep.
172 popStarTy :: TypeRep -> TypeRep -> TypeRep
173 popStarTy (TypeRep tr_k tc trs) arg_tr
174 = let (TypeRep arg_k _ _) = arg_tr
175 in TypeRep (appKey tr_k arg_k) tc (trs++[arg_tr])
178 -- If we enforce the restriction that there is only one
179 -- @TyCon@ for a type & it is shared among all its uses,
180 -- we can map them onto Ints very simply. The benefit is,
181 -- of course, that @TyCon@s can then be compared efficiently.
183 -- Provided the implementor of other @Typeable@ instances
184 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
187 -- If this constraint does turn out to be a sore thumb, changing
188 -- the Eq instance for TyCons is trivial.
190 -- | Builds a 'TyCon' object representing a type constructor. An
191 -- implementation of "Data.Typeable" should ensure that the following holds:
193 -- > mkTyCon "a" == mkTyCon "a"
196 mkTyCon :: String -- ^ the name of the type constructor (should be unique
197 -- in the program, so it might be wise to use the
198 -- fully qualified name).
199 -> TyCon -- ^ A unique 'TyCon' object
200 mkTyCon str = TyCon (mkTyConKey str) str
204 ----------------- Observation ---------------------
207 -- | Observe the type constructor of a type representation
208 typerepTyCon :: TypeRep -> TyCon
209 typerepTyCon (TypeRep _ tc _) = tc
212 -- | Observe the argument types of a type representation
213 typerepArgs :: TypeRep -> [TypeRep]
214 typerepArgs (TypeRep _ _ args) = args
217 -- | Observe string encoding of a type representation
218 tyconString :: TyCon -> String
219 tyconString (TyCon _ str) = str
222 ----------------- Showing TypeReps --------------------
224 instance Show TypeRep where
225 showsPrec p (TypeRep _ tycon tys) =
227 [] -> showsPrec p tycon
228 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
229 [a,r] | tycon == funTc -> showParen (p > 8) $
233 xs | isTupleTyCon tycon -> showTuple tycon xs
240 instance Show TyCon where
241 showsPrec _ (TyCon _ s) = showString s
243 isTupleTyCon :: TyCon -> Bool
244 isTupleTyCon (TyCon _ (',':_)) = True
245 isTupleTyCon _ = False
248 -- Some (Show.TypeRep) helpers:
250 showArgs :: Show a => [a] -> ShowS
252 showArgs [a] = showsPrec 10 a
253 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
255 showTuple :: TyCon -> [TypeRep] -> ShowS
256 showTuple (TyCon _ str) args = showChar '(' . go str args
258 go [] [a] = showsPrec 10 a . showChar ')'
259 go _ [] = showChar ')' -- a failure condition, really.
260 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
261 go _ _ = showChar ')'
264 -------------------------------------------------------------
266 -- The Typeable class and friends
268 -------------------------------------------------------------
271 -- | The class 'Typeable' allows a concrete representation of a type to
273 class Typeable a where
274 typeOf :: a -> TypeRep
275 -- ^ Takes a value of type @a@ and returns a concrete representation
276 -- of that type. The /value/ of the argument should be ignored by
277 -- any instance of 'Typeable', so that it is safe to pass 'undefined' as
282 #define INSTANCE_TYPEABLE1x(tycon,tcname,str) \
283 instance Typeable a => Typeable (tycon a) where { \
284 typeOf x = mkAppTy tcname [typeOf ((undefined :: tycon a -> a) x) ] }
285 #define INSTANCE_TYPEABLE2x(tycon,tcname,str) \
286 instance (Typeable a, Typeable b) => Typeable (tycon a b) where { \
287 typeOf x = mkAppTy tcname [typeOf ((undefined :: tycon a b -> a) x), \
288 typeOf ((undefined :: tycon a b -> b) x)] }
290 INSTANCE_TYPEABLE1x(Ratio,ratioTc,"Ratio")
291 INSTANCE_TYPEABLE2x(Either,eitherTc,"Either")
292 INSTANCE_TYPEABLE1(IO,ioTc,"IO")
293 INSTANCE_TYPEABLE1x(Maybe,maybeTc,"Maybe")
294 INSTANCE_TYPEABLE1(Ptr,ptrTc,"Ptr")
295 INSTANCE_TYPEABLE1(StablePtr,stablePtrTc,"StablePtr")
296 INSTANCE_TYPEABLE1(IORef,ioRefTc,"IORef")
299 -- | Variant for unary type constructors
300 class Typeable1 t where
301 typeOf1 :: t a -> TypeRep
305 -- | One Typeable instance for all Typeable1 instances
306 instance (Typeable1 s, Typeable a)
307 => Typeable (s a) where
308 typeOf x = typeOf1 x `popStarTy` typeOf (argType x)
315 -- | Variant for binary type constructors
316 class Typeable2 t where
317 typeOf2 :: t a b -> TypeRep
321 -- | One Typeable1 instance for all Typeable2 instances
322 instance (Typeable2 s, Typeable a)
323 => Typeable1 (s a) where
324 typeOf1 x = typeOf2 x `popStarTy` typeOf (argType x)
326 argType :: t x y -> x
331 -- | Variant for 3-ary type constructors
332 class Typeable3 t where
333 typeOf3 :: t a b c -> TypeRep
337 -- | One Typeable2 instance for all Typeable3 instances
338 instance (Typeable3 s, Typeable a)
339 => Typeable2 (s a) where
340 typeOf2 x = typeOf3 x `popStarTy` typeOf (argType x)
342 argType :: t x y z -> x
347 -- | Variant for 4-ary type constructors
348 class Typeable4 t where
349 typeOf4 :: t a b c d -> TypeRep
353 -- | One Typeable3 instance for all Typeable4 instances
354 instance (Typeable4 s, Typeable a)
355 => Typeable3 (s a) where
356 typeOf3 x = typeOf4 x `popStarTy` typeOf (argType x)
358 argType :: t x y z z' -> x
363 -- | Variant for 5-ary type constructors
364 class Typeable5 t where
365 typeOf5 :: t a b c d e -> TypeRep
369 -- | One Typeable4 instance for all Typeable5 instances
370 instance (Typeable5 s, Typeable a)
371 => Typeable4 (s a) where
372 typeOf4 x = typeOf5 x `popStarTy` typeOf (argType x)
374 argType :: t x y z z' z'' -> x
379 -- | Variant for 6-ary type constructors
380 class Typeable6 t where
381 typeOf6 :: t a b c d e f -> TypeRep
385 -- | One Typeable5 instance for all Typeable6 instances
386 instance (Typeable6 s, Typeable a)
387 => Typeable5 (s a) where
388 typeOf5 x = typeOf6 x `popStarTy` typeOf (argType x)
390 argType :: t x y z z' z'' z''' -> x
395 -- | Variant for 7-ary type constructors
396 class Typeable7 t where
397 typeOf7 :: t a b c d e f g -> TypeRep
401 -- | One Typeable6 instance for all Typeable7 instances
402 instance (Typeable7 s, Typeable a)
403 => Typeable6 (s a) where
404 typeOf6 x = typeOf7 x `popStarTy` typeOf (argType x)
406 argType :: t x y z z' z'' z''' z'''' -> x
412 -------------------------------------------------------------
416 -------------------------------------------------------------
418 -- | The type-safe cast operation
419 cast :: (Typeable a, Typeable b) => a -> Maybe b
422 r = if typeOf x == typeOf (fromJust r)
423 then Just $ unsafeCoerce x
427 -- | A flexible variation parameterised in a type constructor
428 gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
431 r = if typeOf (getArg x) == typeOf (getArg (fromJust r))
432 then Just $ unsafeCoerce x
440 gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
443 r = if typeOf1 (getArg x) == typeOf1 (getArg (fromJust r))
444 then Just $ unsafeCoerce x
450 -- | Cast for * -> * -> *
451 gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
454 r = if typeOf2 (getArg x) == typeOf2 (getArg (fromJust r))
455 then Just $ unsafeCoerce x
462 -------------------------------------------------------------
464 -- Instances of the Typeable classes for Prelude types
466 -------------------------------------------------------------
469 unitTc = mkTyCon "()"
471 instance Typeable () where
472 typeOf _ = mkAppTy unitTc []
476 tup3Tc = mkTyCon ",,"
478 instance Typeable3 (,,) where
479 typeOf3 tu = mkAppTy tup3Tc []
483 tup4Tc = mkTyCon ",,,"
485 instance Typeable4 (,,,) where
486 typeOf4 tu = mkAppTy tup4Tc []
490 tup5Tc = mkTyCon ",,,,"
492 instance Typeable5 (,,,,) where
493 typeOf5 tu = mkAppTy tup5Tc []
497 tup6Tc = mkTyCon ",,,,,"
499 instance Typeable6 (,,,,,) where
500 typeOf6 tu = mkAppTy tup6Tc []
504 tup7Tc = mkTyCon ",,,,,"
506 instance Typeable7 (,,,,,,) where
507 typeOf7 tu = mkAppTy tup7Tc []
511 listTc = mkTyCon "[]"
513 -- | Instance for lists
514 instance Typeable1 [] where
515 typeOf1 _ = mkAppTy listTc []
519 maybeTc = mkTyCon "Maybe"
521 -- | Instance for maybes
522 instance Typeable1 Maybe where
523 typeOf1 _ = mkAppTy maybeTc []
527 ratioTc = mkTyCon "Ratio"
529 -- | Instance for ratios
530 instance Typeable1 Ratio where
531 typeOf1 _ = mkAppTy ratioTc []
535 pairTc = mkTyCon "(,)"
537 -- | Instance for products
538 instance Typeable2 (,) where
539 typeOf2 _ = mkAppTy pairTc []
543 eitherTc = mkTyCon "Either"
545 -- | Instance for sums
546 instance Typeable2 Either where
547 typeOf2 _ = mkAppTy eitherTc []
550 -- | Instance for functions
551 instance Typeable2 (->) where
552 typeOf2 _ = mkAppTy funTc []
555 #ifdef __GLASGOW_HASKELL__
558 ioTc = mkTyCon "GHC.IOBase.IO"
560 instance Typeable1 IO where
561 typeOf1 _ = mkAppTy ioTc []
565 ptrTc = mkTyCon "GHC.Ptr.Ptr"
567 instance Typeable1 Ptr where
568 typeOf1 _ = mkAppTy ptrTc []
572 stableptrTc = mkTyCon "GHC.Stable.StablePtr"
574 instance Typeable1 StablePtr where
575 typeOf1 _ = mkAppTy stableptrTc []
579 iorefTc = mkTyCon "GHC.IOBase.IORef"
581 instance Typeable1 IORef where
582 typeOf1 _ = mkAppTy iorefTc []
588 -------------------------------------------------------
590 -- Generate Typeable instances for standard datatypes
592 -------------------------------------------------------
595 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
596 INSTANCE_TYPEABLE0(Char,charTc,"Char")
597 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
598 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
599 INSTANCE_TYPEABLE0(Int,intTc,"Int")
600 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
601 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
602 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
604 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
605 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
606 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
607 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
609 INSTANCE_TYPEABLE0(Word8,word8Tc,"Word8" )
610 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
611 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
612 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
614 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
615 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
618 #ifdef __GLASGOW_HASKELL__
619 INSTANCE_TYPEABLE0(Word,wordTc,"Word" )
624 ---------------------------------------------
628 ---------------------------------------------
631 newtype Key = Key Int deriving( Eq )
634 data KeyPr = KeyPr !Key !Key deriving( Eq )
636 hashKP :: KeyPr -> Int32
637 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
639 data Cache = Cache { next_key :: !(IORef Key),
640 tc_tbl :: !(HT.HashTable String Key),
641 ap_tbl :: !(HT.HashTable KeyPr Key) }
643 {-# NOINLINE cache #-}
645 cache = unsafePerformIO $ do
646 empty_tc_tbl <- HT.new (==) HT.hashString
647 empty_ap_tbl <- HT.new (==) hashKP
648 key_loc <- newIORef (Key 1)
649 return (Cache { next_key = key_loc,
650 tc_tbl = empty_tc_tbl,
651 ap_tbl = empty_ap_tbl })
653 newKey :: IORef Key -> IO Key
654 #ifdef __GLASGOW_HASKELL__
655 newKey kloc = do i <- genSym; return (Key i)
657 newKey kloc = do { k@(Key i) <- readIORef kloc ;
658 writeIORef kloc (Key (i+1)) ;
662 #ifdef __GLASGOW_HASKELL__
663 -- In GHC we use the RTS's genSym function to get a new unique,
664 -- because in GHCi we might have two copies of the Data.Typeable
665 -- library running (one in the compiler and one in the running
666 -- program), and we need to make sure they don't share any keys.
668 -- This is really a hack. A better solution would be to centralise the
669 -- whole mutable state used by this module, i.e. both hashtables. But
670 -- the current solution solves the immediate problem, which is that
671 -- dynamics generated in one world with one type were erroneously
672 -- being recognised by the other world as having a different type.
673 foreign import ccall unsafe "genSymZh"
677 mkTyConKey :: String -> Key
679 = unsafePerformIO $ do
680 let Cache {next_key = kloc, tc_tbl = tbl} = cache
681 mb_k <- HT.lookup tbl str
684 Nothing -> do { k <- newKey kloc ;
685 HT.insert tbl str k ;
688 appKey :: Key -> Key -> Key
690 = unsafePerformIO $ do
691 let Cache {next_key = kloc, ap_tbl = tbl} = cache
692 mb_k <- HT.lookup tbl kpr
695 Nothing -> do { k <- newKey kloc ;
696 HT.insert tbl kpr k ;
701 appKeys :: Key -> [Key] -> Key
702 appKeys k ks = foldl appKey k ks