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
281 -- | Variant for unary type constructors
282 class Typeable1 t where
283 typeOf1 :: t a -> TypeRep
286 -- | One Typeable instance for all Typeable1 instances
287 instance (Typeable1 s, Typeable a)
288 => Typeable (s a) where
289 typeOf x = typeOf1 x `popStarTy` typeOf (argType x)
295 -- | Variant for binary type constructors
296 class Typeable2 t where
297 typeOf2 :: t a b -> TypeRep
300 -- | One Typeable1 instance for all Typeable2 instances
301 instance (Typeable2 s, Typeable a)
302 => Typeable1 (s a) where
303 typeOf1 x = typeOf2 x `popStarTy` typeOf (argType x)
305 argType :: t x y -> x
309 -- | Variant for 3-ary type constructors
310 class Typeable3 t where
311 typeOf3 :: t a b c -> TypeRep
314 -- | One Typeable2 instance for all Typeable3 instances
315 instance (Typeable3 s, Typeable a)
316 => Typeable2 (s a) where
317 typeOf2 x = typeOf3 x `popStarTy` typeOf (argType x)
319 argType :: t x y z -> x
323 -- | Variant for 4-ary type constructors
324 class Typeable4 t where
325 typeOf4 :: t a b c d -> TypeRep
328 -- | One Typeable3 instance for all Typeable4 instances
329 instance (Typeable4 s, Typeable a)
330 => Typeable3 (s a) where
331 typeOf3 x = typeOf4 x `popStarTy` typeOf (argType x)
333 argType :: t x y z z' -> x
337 -- | Variant for 5-ary type constructors
338 class Typeable5 t where
339 typeOf5 :: t a b c d e -> TypeRep
342 -- | One Typeable4 instance for all Typeable5 instances
343 instance (Typeable5 s, Typeable a)
344 => Typeable4 (s a) where
345 typeOf4 x = typeOf5 x `popStarTy` typeOf (argType x)
347 argType :: t x y z z' z'' -> x
351 -- | Variant for 6-ary type constructors
352 class Typeable6 t where
353 typeOf6 :: t a b c d e f -> TypeRep
356 -- | One Typeable5 instance for all Typeable6 instances
357 instance (Typeable6 s, Typeable a)
358 => Typeable5 (s a) where
359 typeOf5 x = typeOf6 x `popStarTy` typeOf (argType x)
361 argType :: t x y z z' z'' z''' -> x
365 -- | Variant for 7-ary type constructors
366 class Typeable7 t where
367 typeOf7 :: t a b c d e f g -> TypeRep
370 -- | One Typeable6 instance for all Typeable7 instances
371 instance (Typeable7 s, Typeable a)
372 => Typeable6 (s a) where
373 typeOf6 x = typeOf7 x `popStarTy` typeOf (argType x)
375 argType :: t x y z z' z'' z''' z'''' -> x
380 -------------------------------------------------------------
384 -------------------------------------------------------------
386 -- | The type-safe cast operation
387 cast :: (Typeable a, Typeable b) => a -> Maybe b
390 r = if typeOf x == typeOf (fromJust r)
391 then Just $ unsafeCoerce x
395 -- | A flexible variation parameterised in a type constructor
396 gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
399 r = if typeOf (getArg x) == typeOf (getArg (fromJust r))
400 then Just $ unsafeCoerce x
408 gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
411 r = if typeOf1 (getArg x) == typeOf1 (getArg (fromJust r))
412 then Just $ unsafeCoerce x
418 -- | Cast for * -> * -> *
419 gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
422 r = if typeOf2 (getArg x) == typeOf2 (getArg (fromJust r))
423 then Just $ unsafeCoerce x
430 -------------------------------------------------------------
432 -- Instances of the Typeable classes for Prelude types
434 -------------------------------------------------------------
437 unitTc = mkTyCon "()"
439 instance Typeable () where
440 typeOf _ = mkAppTy unitTc []
444 tup3Tc = mkTyCon ",,"
446 instance Typeable3 (,,) where
447 typeOf3 tu = mkAppTy tup3Tc []
451 tup4Tc = mkTyCon ",,,"
453 instance Typeable4 (,,,) where
454 typeOf4 tu = mkAppTy tup4Tc []
458 tup5Tc = mkTyCon ",,,,"
460 instance Typeable5 (,,,,) where
461 typeOf5 tu = mkAppTy tup5Tc []
465 tup6Tc = mkTyCon ",,,,,"
467 instance Typeable6 (,,,,,) where
468 typeOf6 tu = mkAppTy tup6Tc []
472 tup7Tc = mkTyCon ",,,,,"
474 instance Typeable7 (,,,,,,) where
475 typeOf7 tu = mkAppTy tup7Tc []
479 listTc = mkTyCon "[]"
481 -- | Instance for lists
482 instance Typeable1 [] where
483 typeOf1 _ = mkAppTy listTc []
487 maybeTc = mkTyCon "Maybe"
489 -- | Instance for maybes
490 instance Typeable1 Maybe where
491 typeOf1 _ = mkAppTy maybeTc []
495 ratioTc = mkTyCon "Ratio"
497 -- | Instance for ratios
498 instance Typeable1 Ratio where
499 typeOf1 _ = mkAppTy ratioTc []
503 pairTc = mkTyCon "(,)"
505 -- | Instance for products
506 instance Typeable2 (,) where
507 typeOf2 _ = mkAppTy pairTc []
511 eitherTc = mkTyCon "Either"
513 -- | Instance for sums
514 instance Typeable2 Either where
515 typeOf2 _ = mkAppTy eitherTc []
518 -- | Instance for functions
519 instance Typeable2 (->) where
520 typeOf2 _ = mkAppTy funTc []
523 #ifdef __GLASGOW_HASKELL__
526 ioTc = mkTyCon "GHC.IOBase.IO"
528 instance Typeable1 IO where
529 typeOf1 _ = mkAppTy ioTc []
533 ptrTc = mkTyCon "GHC.Ptr.Ptr"
535 instance Typeable1 Ptr where
536 typeOf1 _ = mkAppTy ptrTc []
540 stableptrTc = mkTyCon "GHC.Stable.StablePtr"
542 instance Typeable1 StablePtr where
543 typeOf1 _ = mkAppTy stableptrTc []
547 iorefTc = mkTyCon "GHC.IOBase.IORef"
549 instance Typeable1 IORef where
550 typeOf1 _ = mkAppTy iorefTc []
556 -------------------------------------------------------
558 -- Generate Typeable instances for standard datatypes
560 -------------------------------------------------------
563 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
564 INSTANCE_TYPEABLE0(Char,charTc,"Char")
565 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
566 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
567 INSTANCE_TYPEABLE0(Int,intTc,"Int")
568 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
569 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
570 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
572 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
573 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
574 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
575 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
577 INSTANCE_TYPEABLE0(Word8,word8Tc,"Word8" )
578 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
579 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
580 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
582 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
583 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
586 #ifdef __GLASGOW_HASKELL__
587 INSTANCE_TYPEABLE0(Word,wordTc,"Word" )
592 ---------------------------------------------
596 ---------------------------------------------
599 newtype Key = Key Int deriving( Eq )
602 data KeyPr = KeyPr !Key !Key deriving( Eq )
604 hashKP :: KeyPr -> Int32
605 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
607 data Cache = Cache { next_key :: !(IORef Key),
608 tc_tbl :: !(HT.HashTable String Key),
609 ap_tbl :: !(HT.HashTable KeyPr Key) }
611 {-# NOINLINE cache #-}
613 cache = unsafePerformIO $ do
614 empty_tc_tbl <- HT.new (==) HT.hashString
615 empty_ap_tbl <- HT.new (==) hashKP
616 key_loc <- newIORef (Key 1)
617 return (Cache { next_key = key_loc,
618 tc_tbl = empty_tc_tbl,
619 ap_tbl = empty_ap_tbl })
621 newKey :: IORef Key -> IO Key
622 #ifdef __GLASGOW_HASKELL__
623 newKey kloc = do i <- genSym; return (Key i)
625 newKey kloc = do { k@(Key i) <- readIORef kloc ;
626 writeIORef kloc (Key (i+1)) ;
630 #ifdef __GLASGOW_HASKELL__
631 -- In GHC we use the RTS's genSym function to get a new unique,
632 -- because in GHCi we might have two copies of the Data.Typeable
633 -- library running (one in the compiler and one in the running
634 -- program), and we need to make sure they don't share any keys.
636 -- This is really a hack. A better solution would be to centralise the
637 -- whole mutable state used by this module, i.e. both hashtables. But
638 -- the current solution solves the immediate problem, which is that
639 -- dynamics generated in one world with one type were erroneously
640 -- being recognised by the other world as having a different type.
641 foreign import ccall unsafe "genSymZh"
645 mkTyConKey :: String -> Key
647 = unsafePerformIO $ do
648 let Cache {next_key = kloc, tc_tbl = tbl} = cache
649 mb_k <- HT.lookup tbl str
652 Nothing -> do { k <- newKey kloc ;
653 HT.insert tbl str k ;
656 appKey :: Key -> Key -> Key
658 = unsafePerformIO $ do
659 let Cache {next_key = kloc, ap_tbl = tbl} = cache
660 mb_k <- HT.lookup tbl kpr
663 Nothing -> do { k <- newKey kloc ;
664 HT.insert tbl kpr k ;
669 appKeys :: Key -> [Key] -> Key
670 appKeys k ks = foldl appKey k ks