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))
60 -- * Default instances
61 typeOfDefault, -- :: (Typeable1 t, Typeable a) => t a -> TypeRep
62 typeOf1Default, -- :: (Typeable2 t, Typeable a) => t a b -> TypeRep
63 typeOf2Default, -- :: (Typeable2 t, Typeable a) => t a b c -> TypeRep
64 typeOf3Default, -- :: (Typeable2 t, Typeable a) => t a b c d -> TypeRep
65 typeOf4Default, -- :: (Typeable2 t, Typeable a) => t a b c d e -> TypeRep
66 typeOf5Default, -- :: (Typeable2 t, Typeable a) => t a b c d e f -> TypeRep
67 typeOf6Default -- :: (Typeable2 t, Typeable a) => t a b c d e f g -> TypeRep
72 import qualified Data.HashTable as HT
77 import Data.List( foldl )
79 #ifdef __GLASGOW_HASKELL__
85 import GHC.Real( rem, Ratio )
87 import GHC.Ptr -- So we can give Typeable instance for Ptr
88 import GHC.Stable -- So we can give Typeable instance for StablePtr
98 #ifdef __GLASGOW_HASKELL__
99 unsafeCoerce :: a -> b
100 unsafeCoerce = unsafeCoerce#
104 import NonStdUnsafeCoerce (unsafeCoerce)
105 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
107 #include "Typeable.h"
113 -------------------------------------------------------------
115 -- Type representations
117 -------------------------------------------------------------
120 -- | A concrete representation of a (monomorphic) type. 'TypeRep'
121 -- supports reasonably efficient equality.
122 data TypeRep = TypeRep !Key TyCon [TypeRep]
124 -- Compare keys for equality
125 instance Eq TypeRep where
126 (TypeRep k1 _ _) == (TypeRep k2 _ _) = k1 == k2
128 -- | An abstract representation of a type constructor. 'TyCon' objects can
129 -- be built using 'mkTyCon'.
130 data TyCon = TyCon !Key String
132 instance Eq TyCon where
133 (TyCon t1 _) == (TyCon t2 _) = t1 == t2
138 -- let fTy = mkTyCon "Foo" in show (mkAppTy (mkTyCon ",,")
141 -- returns "(Foo,Foo,Foo)"
143 -- The TypeRep Show instance promises to print tuple types
144 -- correctly. Tuple type constructors are specified by a
145 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
146 -- the 5-tuple tycon.
149 ----------------- Construction --------------------
151 -- | Applies a type constructor to a sequence of types
152 mkAppTy :: TyCon -> [TypeRep] -> TypeRep
153 mkAppTy tc@(TyCon tc_k _) args
154 = TypeRep (appKeys tc_k arg_ks) tc args
156 arg_ks = [k | TypeRep k _ _ <- args]
159 -- | A special case of 'mkAppTy', which applies the function
160 -- type constructor to a pair of types.
161 mkFunTy :: TypeRep -> TypeRep -> TypeRep
162 mkFunTy f a = mkAppTy funTc [f,a]
165 -- | Applies a type to a function type. Returns: @'Just' u@ if the
166 -- first argument represents a function of type @t -> u@ and the
167 -- second argument represents a function of type @t@. Otherwise,
168 -- returns 'Nothing'.
169 applyTy :: TypeRep -> TypeRep -> Maybe TypeRep
170 applyTy (TypeRep _ tc [t1,t2]) t3
171 | tc == funTc && t1 == t3 = Just t2
172 applyTy _ _ = Nothing
175 -- | Adds a TypeRep argument to a TypeRep.
176 popStarTy :: TypeRep -> TypeRep -> TypeRep
177 popStarTy (TypeRep tr_k tc trs) arg_tr
178 = let (TypeRep arg_k _ _) = arg_tr
179 in TypeRep (appKey tr_k arg_k) tc (trs++[arg_tr])
182 -- If we enforce the restriction that there is only one
183 -- @TyCon@ for a type & it is shared among all its uses,
184 -- we can map them onto Ints very simply. The benefit is,
185 -- of course, that @TyCon@s can then be compared efficiently.
187 -- Provided the implementor of other @Typeable@ instances
188 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
191 -- If this constraint does turn out to be a sore thumb, changing
192 -- the Eq instance for TyCons is trivial.
194 -- | Builds a 'TyCon' object representing a type constructor. An
195 -- implementation of "Data.Typeable" should ensure that the following holds:
197 -- > mkTyCon "a" == mkTyCon "a"
200 mkTyCon :: String -- ^ the name of the type constructor (should be unique
201 -- in the program, so it might be wise to use the
202 -- fully qualified name).
203 -> TyCon -- ^ A unique 'TyCon' object
204 mkTyCon str = TyCon (mkTyConKey str) str
208 ----------------- Observation ---------------------
211 -- | Observe the type constructor of a type representation
212 typerepTyCon :: TypeRep -> TyCon
213 typerepTyCon (TypeRep _ tc _) = tc
216 -- | Observe the argument types of a type representation
217 typerepArgs :: TypeRep -> [TypeRep]
218 typerepArgs (TypeRep _ _ args) = args
221 -- | Observe string encoding of a type representation
222 tyconString :: TyCon -> String
223 tyconString (TyCon _ str) = str
226 ----------------- Showing TypeReps --------------------
228 instance Show TypeRep where
229 showsPrec p (TypeRep _ tycon tys) =
231 [] -> showsPrec p tycon
232 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
233 [a,r] | tycon == funTc -> showParen (p > 8) $
237 xs | isTupleTyCon tycon -> showTuple tycon xs
244 instance Show TyCon where
245 showsPrec _ (TyCon _ s) = showString s
247 isTupleTyCon :: TyCon -> Bool
248 isTupleTyCon (TyCon _ (',':_)) = True
249 isTupleTyCon _ = False
252 -- Some (Show.TypeRep) helpers:
254 showArgs :: Show a => [a] -> ShowS
256 showArgs [a] = showsPrec 10 a
257 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
259 showTuple :: TyCon -> [TypeRep] -> ShowS
260 showTuple (TyCon _ str) args = showChar '(' . go str args
262 go [] [a] = showsPrec 10 a . showChar ')'
263 go _ [] = showChar ')' -- a failure condition, really.
264 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
265 go _ _ = showChar ')'
268 -------------------------------------------------------------
270 -- The Typeable class and friends
272 -------------------------------------------------------------
275 -- | The class 'Typeable' allows a concrete representation of a type to
277 class Typeable a where
278 typeOf :: a -> TypeRep
279 -- ^ Takes a value of type @a@ and returns a concrete representation
280 -- of that type. The /value/ of the argument should be ignored by
281 -- any instance of 'Typeable', so that it is safe to pass 'undefined' as
284 -- | Variant for unary type constructors
285 class Typeable1 t where
286 typeOf1 :: t a -> TypeRep
288 -- | For defining a 'Typeable' instance from any 'Typeable1' instance.
289 typeOfDefault :: (Typeable1 t, Typeable a) => t a -> TypeRep
290 typeOfDefault x = typeOf1 x `popStarTy` typeOf (argType x)
295 #ifdef __GLASGOW_HASKELL__
296 -- | One Typeable instance for all Typeable1 instances
297 instance (Typeable1 s, Typeable a)
298 => Typeable (s a) where
299 typeOf = typeOfDefault
303 -- | Variant for binary type constructors
304 class Typeable2 t where
305 typeOf2 :: t a b -> TypeRep
307 -- | For defining a 'Typeable1' instance from any 'Typeable2' instance.
308 typeOf1Default :: (Typeable2 t, Typeable a) => t a b -> TypeRep
309 typeOf1Default x = typeOf2 x `popStarTy` typeOf (argType x)
311 argType :: t a b -> a
315 #ifdef __GLASGOW_HASKELL__
316 -- | One Typeable1 instance for all Typeable2 instances
317 instance (Typeable2 s, Typeable a)
318 => Typeable1 (s a) where
319 typeOf1 = typeOf1Default
323 -- | Variant for 3-ary type constructors
324 class Typeable3 t where
325 typeOf3 :: t a b c -> TypeRep
327 -- | For defining a 'Typeable2' instance from any 'Typeable3' instance.
328 typeOf2Default :: (Typeable3 t, Typeable a) => t a b c -> TypeRep
329 typeOf2Default x = typeOf3 x `popStarTy` typeOf (argType x)
331 argType :: t a b c -> a
335 #ifdef __GLASGOW_HASKELL__
336 -- | One Typeable2 instance for all Typeable3 instances
337 instance (Typeable3 s, Typeable a)
338 => Typeable2 (s a) where
339 typeOf2 = typeOf2Default
343 -- | Variant for 4-ary type constructors
344 class Typeable4 t where
345 typeOf4 :: t a b c d -> TypeRep
347 -- | For defining a 'Typeable3' instance from any 'Typeable4' instance.
348 typeOf3Default :: (Typeable4 t, Typeable a) => t a b c d -> TypeRep
349 typeOf3Default x = typeOf4 x `popStarTy` typeOf (argType x)
351 argType :: t a b c d -> a
355 #ifdef __GLASGOW_HASKELL__
356 -- | One Typeable3 instance for all Typeable4 instances
357 instance (Typeable4 s, Typeable a)
358 => Typeable3 (s a) where
359 typeOf3 = typeOf3Default
363 -- | Variant for 5-ary type constructors
364 class Typeable5 t where
365 typeOf5 :: t a b c d e -> TypeRep
367 -- | For defining a 'Typeable4' instance from any 'Typeable5' instance.
368 typeOf4Default :: (Typeable5 t, Typeable a) => t a b c d e -> TypeRep
369 typeOf4Default x = typeOf5 x `popStarTy` typeOf (argType x)
371 argType :: t a b c d e -> a
375 #ifdef __GLASGOW_HASKELL__
376 -- | One Typeable4 instance for all Typeable5 instances
377 instance (Typeable5 s, Typeable a)
378 => Typeable4 (s a) where
379 typeOf4 = typeOf4Default
383 -- | Variant for 6-ary type constructors
384 class Typeable6 t where
385 typeOf6 :: t a b c d e f -> TypeRep
387 -- | For defining a 'Typeable5' instance from any 'Typeable6' instance.
388 typeOf5Default :: (Typeable6 t, Typeable a) => t a b c d e f -> TypeRep
389 typeOf5Default x = typeOf6 x `popStarTy` typeOf (argType x)
391 argType :: t a b c d e f -> a
395 #ifdef __GLASGOW_HASKELL__
396 -- | One Typeable5 instance for all Typeable6 instances
397 instance (Typeable6 s, Typeable a)
398 => Typeable5 (s a) where
399 typeOf5 = typeOf5Default
403 -- | Variant for 7-ary type constructors
404 class Typeable7 t where
405 typeOf7 :: t a b c d e f g -> TypeRep
407 -- | For defining a 'Typeable6' instance from any 'Typeable7' instance.
408 typeOf6Default :: (Typeable7 t, Typeable a) => t a b c d e f g -> TypeRep
409 typeOf6Default x = typeOf7 x `popStarTy` typeOf (argType x)
411 argType :: t a b c d e f g -> a
415 #ifdef __GLASGOW_HASKELL__
416 -- | One Typeable6 instance for all Typeable7 instances
417 instance (Typeable7 s, Typeable a)
418 => Typeable6 (s a) where
419 typeOf6 = typeOf6Default
424 -------------------------------------------------------------
428 -------------------------------------------------------------
430 -- | The type-safe cast operation
431 cast :: (Typeable a, Typeable b) => a -> Maybe b
434 r = if typeOf x == typeOf (fromJust r)
435 then Just $ unsafeCoerce x
439 -- | A flexible variation parameterised in a type constructor
440 gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
443 r = if typeOf (getArg x) == typeOf (getArg (fromJust r))
444 then Just $ unsafeCoerce x
452 gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
455 r = if typeOf1 (getArg x) == typeOf1 (getArg (fromJust r))
456 then Just $ unsafeCoerce x
462 -- | Cast for * -> * -> *
463 gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
466 r = if typeOf2 (getArg x) == typeOf2 (getArg (fromJust r))
467 then Just $ unsafeCoerce x
474 -------------------------------------------------------------
476 -- Instances of the Typeable classes for Prelude types
478 -------------------------------------------------------------
481 INSTANCE_TYPEABLE1([],listTc,"[]")
482 INSTANCE_TYPEABLE1(Maybe,maybeTc,"Maybe")
483 INSTANCE_TYPEABLE1(Ratio,ratioTc,"Ratio")
484 INSTANCE_TYPEABLE2(Either,eitherTc,"Either")
485 INSTANCE_TYPEABLE2((->),funTc,"->")
486 INSTANCE_TYPEABLE0((),unitTc,"()")
487 INSTANCE_TYPEABLE2((,),pairTc,"(,)")
488 INSTANCE_TYPEABLE3((,,),tup3Tc,",,")
491 tup4Tc = mkTyCon ",,,"
493 instance Typeable4 (,,,) where
494 typeOf4 tu = mkAppTy tup4Tc []
498 tup5Tc = mkTyCon ",,,,"
500 instance Typeable5 (,,,,) where
501 typeOf5 tu = mkAppTy tup5Tc []
505 tup6Tc = mkTyCon ",,,,,"
507 instance Typeable6 (,,,,,) where
508 typeOf6 tu = mkAppTy tup6Tc []
512 tup7Tc = mkTyCon ",,,,,"
514 instance Typeable7 (,,,,,,) where
515 typeOf7 tu = mkAppTy tup7Tc []
517 INSTANCE_TYPEABLE1(IO,ioTc,"System.IO.IO")
518 INSTANCE_TYPEABLE1(Ptr,ptrTc,"Foreign.Ptr.Ptr")
519 INSTANCE_TYPEABLE1(StablePtr,stableptrTc,"Foreign.StablePtr.StablePtr")
520 INSTANCE_TYPEABLE1(IORef,iorefTc,"Data.IORef.IORef")
521 #endif /* ! __NHC__ */
523 -------------------------------------------------------
525 -- Generate Typeable instances for standard datatypes
527 -------------------------------------------------------
530 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
531 INSTANCE_TYPEABLE0(Char,charTc,"Char")
532 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
533 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
534 INSTANCE_TYPEABLE0(Int,intTc,"Int")
535 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
536 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
537 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
539 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
540 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
541 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
542 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
544 INSTANCE_TYPEABLE0(Word8,word8Tc,"Word8" )
545 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
546 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
547 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
549 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
550 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
551 #endif /* !__NHC__ */
553 #ifdef __GLASGOW_HASKELL__
554 INSTANCE_TYPEABLE0(Word,wordTc,"Word" )
557 ---------------------------------------------
561 ---------------------------------------------
564 newtype Key = Key Int deriving( Eq )
567 data KeyPr = KeyPr !Key !Key deriving( Eq )
569 hashKP :: KeyPr -> Int32
570 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
572 data Cache = Cache { next_key :: !(IORef Key),
573 tc_tbl :: !(HT.HashTable String Key),
574 ap_tbl :: !(HT.HashTable KeyPr Key) }
576 {-# NOINLINE cache #-}
578 cache = unsafePerformIO $ do
579 empty_tc_tbl <- HT.new (==) HT.hashString
580 empty_ap_tbl <- HT.new (==) hashKP
581 key_loc <- newIORef (Key 1)
582 return (Cache { next_key = key_loc,
583 tc_tbl = empty_tc_tbl,
584 ap_tbl = empty_ap_tbl })
586 newKey :: IORef Key -> IO Key
587 #ifdef __GLASGOW_HASKELL__
588 newKey kloc = do i <- genSym; return (Key i)
590 newKey kloc = do { k@(Key i) <- readIORef kloc ;
591 writeIORef kloc (Key (i+1)) ;
595 #ifdef __GLASGOW_HASKELL__
596 -- In GHC we use the RTS's genSym function to get a new unique,
597 -- because in GHCi we might have two copies of the Data.Typeable
598 -- library running (one in the compiler and one in the running
599 -- program), and we need to make sure they don't share any keys.
601 -- This is really a hack. A better solution would be to centralise the
602 -- whole mutable state used by this module, i.e. both hashtables. But
603 -- the current solution solves the immediate problem, which is that
604 -- dynamics generated in one world with one type were erroneously
605 -- being recognised by the other world as having a different type.
606 foreign import ccall unsafe "genSymZh"
610 mkTyConKey :: String -> Key
612 = unsafePerformIO $ do
613 let Cache {next_key = kloc, tc_tbl = tbl} = cache
614 mb_k <- HT.lookup tbl str
617 Nothing -> do { k <- newKey kloc ;
618 HT.insert tbl str k ;
621 appKey :: Key -> Key -> Key
623 = unsafePerformIO $ do
624 let Cache {next_key = kloc, ap_tbl = tbl} = cache
625 mb_k <- HT.lookup tbl kpr
628 Nothing -> do { k <- newKey kloc ;
629 HT.insert tbl kpr k ;
634 appKeys :: Key -> [Key] -> Key
635 appKeys k ks = foldl appKey k ks