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 -- Note, only relevant if you use dynamic linking. If you have a program
22 -- that is statically linked with Data.Typeable, and then dynamically link
23 -- a program that also uses Data.Typeable, you'll get two copies of the module.
24 -- That's fine, but behind the scenes, the module uses a mutable variable to
25 -- allocate unique Ids to type constructors. So in the situation described,
26 -- there'll be two separate Id allocators, which aren't comparable to each other.
27 -- This can lead to chaos. (It's a bug that we will fix.) None of
28 -- this matters if you aren't using dynamic linking.
30 -----------------------------------------------------------------------------
35 -- * The Typeable class
36 Typeable( typeOf ), -- :: a -> TypeRep
39 cast, -- :: (Typeable a, Typeable b) => a -> Maybe b
40 gcast, -- a generalisation of cast
42 -- * Type representations
43 TypeRep, -- abstract, instance of: Eq, Show, Typeable
44 TyCon, -- abstract, instance of: Eq, Show, Typeable
46 -- * Construction of type representations
47 mkTyCon, -- :: String -> TyCon
48 mkTyConApp, -- :: TyCon -> [TypeRep] -> TypeRep
49 mkAppTy, -- :: TypeRep -> TypeRep -> TypeRep
50 mkFunTy, -- :: TypeRep -> TypeRep -> TypeRep
52 -- * Observation of type representations
53 splitTyConApp, -- :: TypeRep -> (TyCon, [TypeRep])
54 funResultTy, -- :: TypeRep -> TypeRep -> Maybe TypeRep
55 typeRepTyCon, -- :: TypeRep -> TyCon
56 typeRepArgs, -- :: TypeRep -> [TypeRep]
57 tyConString, -- :: TyCon -> String
59 -- * The other Typeable classes
60 -- | /Note:/ The general instances are provided for GHC only.
61 Typeable1( typeOf1 ), -- :: t a -> TypeRep
62 Typeable2( typeOf2 ), -- :: t a b -> TypeRep
63 Typeable3( typeOf3 ), -- :: t a b c -> TypeRep
64 Typeable4( typeOf4 ), -- :: t a b c d -> TypeRep
65 Typeable5( typeOf5 ), -- :: t a b c d e -> TypeRep
66 Typeable6( typeOf6 ), -- :: t a b c d e f -> TypeRep
67 Typeable7( typeOf7 ), -- :: t a b c d e f g -> TypeRep
68 gcast1, -- :: ... => c (t a) -> Maybe (c (t' a))
69 gcast2, -- :: ... => c (t a b) -> Maybe (c (t' a b))
71 -- * Default instances
72 -- | /Note:/ These are not needed by GHC, for which these instances
73 -- are generated by general instance declarations.
74 typeOfDefault, -- :: (Typeable1 t, Typeable a) => t a -> TypeRep
75 typeOf1Default, -- :: (Typeable2 t, Typeable a) => t a b -> TypeRep
76 typeOf2Default, -- :: (Typeable3 t, Typeable a) => t a b c -> TypeRep
77 typeOf3Default, -- :: (Typeable4 t, Typeable a) => t a b c d -> TypeRep
78 typeOf4Default, -- :: (Typeable5 t, Typeable a) => t a b c d e -> TypeRep
79 typeOf5Default, -- :: (Typeable6 t, Typeable a) => t a b c d e f -> TypeRep
80 typeOf6Default -- :: (Typeable7 t, Typeable a) => t a b c d e f g -> TypeRep
84 import qualified Data.HashTable as HT
89 import Data.List( foldl )
91 #ifdef __GLASGOW_HASKELL__
97 import GHC.Real( rem, Ratio )
99 import GHC.ST -- So we can give Typeable instance for ST
100 import GHC.Ptr -- So we can give Typeable instance for Ptr
101 import GHC.Stable -- So we can give Typeable instance for StablePtr
111 #ifdef __GLASGOW_HASKELL__
112 unsafeCoerce :: a -> b
113 unsafeCoerce = unsafeCoerce#
117 import NonStdUnsafeCoerce (unsafeCoerce)
118 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
121 import NHC.FFI (Ptr,StablePtr)
125 #include "Typeable.h"
129 -------------------------------------------------------------
131 -- Type representations
133 -------------------------------------------------------------
135 -- | A concrete representation of a (monomorphic) type. 'TypeRep'
136 -- supports reasonably efficient equality.
137 data TypeRep = TypeRep !Key TyCon [TypeRep]
139 -- Compare keys for equality
140 instance Eq TypeRep where
141 (TypeRep k1 _ _) == (TypeRep k2 _ _) = k1 == k2
143 -- | An abstract representation of a type constructor. 'TyCon' objects can
144 -- be built using 'mkTyCon'.
145 data TyCon = TyCon !Key String
147 instance Eq TyCon where
148 (TyCon t1 _) == (TyCon t2 _) = t1 == t2
153 -- let fTy = mkTyCon "Foo" in show (mkTyConApp (mkTyCon ",,")
156 -- returns "(Foo,Foo,Foo)"
158 -- The TypeRep Show instance promises to print tuple types
159 -- correctly. Tuple type constructors are specified by a
160 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
161 -- the 5-tuple tycon.
163 ----------------- Construction --------------------
165 -- | Applies a type constructor to a sequence of types
166 mkTyConApp :: TyCon -> [TypeRep] -> TypeRep
167 mkTyConApp tc@(TyCon tc_k _) args
168 = TypeRep (appKeys tc_k arg_ks) tc args
170 arg_ks = [k | TypeRep k _ _ <- args]
172 -- | A special case of 'mkTyConApp', which applies the function
173 -- type constructor to a pair of types.
174 mkFunTy :: TypeRep -> TypeRep -> TypeRep
175 mkFunTy f a = mkTyConApp funTc [f,a]
177 -- | Splits a type constructor application
178 splitTyConApp :: TypeRep -> (TyCon,[TypeRep])
179 splitTyConApp (TypeRep _ tc trs) = (tc,trs)
181 -- | Applies a type to a function type. Returns: @'Just' u@ if the
182 -- first argument represents a function of type @t -> u@ and the
183 -- second argument represents a function of type @t@. Otherwise,
184 -- returns 'Nothing'.
185 funResultTy :: TypeRep -> TypeRep -> Maybe TypeRep
186 funResultTy trFun trArg
187 = case splitTyConApp trFun of
188 (tc, [t1,t2]) | tc == funTc && t1 == trArg -> Just t2
191 -- | Adds a TypeRep argument to a TypeRep.
192 mkAppTy :: TypeRep -> TypeRep -> TypeRep
193 mkAppTy (TypeRep tr_k tc trs) arg_tr
194 = let (TypeRep arg_k _ _) = arg_tr
195 in TypeRep (appKey tr_k arg_k) tc (trs++[arg_tr])
197 -- If we enforce the restriction that there is only one
198 -- @TyCon@ for a type & it is shared among all its uses,
199 -- we can map them onto Ints very simply. The benefit is,
200 -- of course, that @TyCon@s can then be compared efficiently.
202 -- Provided the implementor of other @Typeable@ instances
203 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
206 -- If this constraint does turn out to be a sore thumb, changing
207 -- the Eq instance for TyCons is trivial.
209 -- | Builds a 'TyCon' object representing a type constructor. An
210 -- implementation of "Data.Typeable" should ensure that the following holds:
212 -- > mkTyCon "a" == mkTyCon "a"
215 mkTyCon :: String -- ^ the name of the type constructor (should be unique
216 -- in the program, so it might be wise to use the
217 -- fully qualified name).
218 -> TyCon -- ^ A unique 'TyCon' object
219 mkTyCon str = TyCon (mkTyConKey str) str
221 ----------------- Observation ---------------------
223 -- | Observe the type constructor of a type representation
224 typeRepTyCon :: TypeRep -> TyCon
225 typeRepTyCon (TypeRep _ tc _) = tc
227 -- | Observe the argument types of a type representation
228 typeRepArgs :: TypeRep -> [TypeRep]
229 typeRepArgs (TypeRep _ _ args) = args
231 -- | Observe string encoding of a type representation
232 tyConString :: TyCon -> String
233 tyConString (TyCon _ str) = str
235 ----------------- Showing TypeReps --------------------
237 instance Show TypeRep where
238 showsPrec p (TypeRep _ tycon tys) =
240 [] -> showsPrec p tycon
241 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
242 [a,r] | tycon == funTc -> showParen (p > 8) $
246 xs | isTupleTyCon tycon -> showTuple tycon xs
253 instance Show TyCon where
254 showsPrec _ (TyCon _ s) = showString s
256 isTupleTyCon :: TyCon -> Bool
257 isTupleTyCon (TyCon _ (',':_)) = True
258 isTupleTyCon _ = False
260 -- Some (Show.TypeRep) helpers:
262 showArgs :: Show a => [a] -> ShowS
264 showArgs [a] = showsPrec 10 a
265 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
267 showTuple :: TyCon -> [TypeRep] -> ShowS
268 showTuple (TyCon _ str) args = showChar '(' . go str args
270 go [] [a] = showsPrec 10 a . showChar ')'
271 go _ [] = showChar ')' -- a failure condition, really.
272 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
273 go _ _ = showChar ')'
275 -------------------------------------------------------------
277 -- The Typeable class and friends
279 -------------------------------------------------------------
281 -- | The class 'Typeable' allows a concrete representation of a type to
283 class Typeable a where
284 typeOf :: a -> TypeRep
285 -- ^ Takes a value of type @a@ and returns a concrete representation
286 -- of that type. The /value/ of the argument should be ignored by
287 -- any instance of 'Typeable', so that it is safe to pass 'undefined' as
290 -- | Variant for unary type constructors
291 class Typeable1 t where
292 typeOf1 :: t a -> TypeRep
294 -- | For defining a 'Typeable' instance from any 'Typeable1' instance.
295 typeOfDefault :: (Typeable1 t, Typeable a) => t a -> TypeRep
296 typeOfDefault x = typeOf1 x `mkAppTy` typeOf (argType x)
301 -- | Variant for binary type constructors
302 class Typeable2 t where
303 typeOf2 :: t a b -> TypeRep
305 -- | For defining a 'Typeable1' instance from any 'Typeable2' instance.
306 typeOf1Default :: (Typeable2 t, Typeable a) => t a b -> TypeRep
307 typeOf1Default x = typeOf2 x `mkAppTy` typeOf (argType x)
309 argType :: t a b -> a
312 -- | Variant for 3-ary type constructors
313 class Typeable3 t where
314 typeOf3 :: t a b c -> TypeRep
316 -- | For defining a 'Typeable2' instance from any 'Typeable3' instance.
317 typeOf2Default :: (Typeable3 t, Typeable a) => t a b c -> TypeRep
318 typeOf2Default x = typeOf3 x `mkAppTy` typeOf (argType x)
320 argType :: t a b c -> a
323 -- | Variant for 4-ary type constructors
324 class Typeable4 t where
325 typeOf4 :: t a b c d -> TypeRep
327 -- | For defining a 'Typeable3' instance from any 'Typeable4' instance.
328 typeOf3Default :: (Typeable4 t, Typeable a) => t a b c d -> TypeRep
329 typeOf3Default x = typeOf4 x `mkAppTy` typeOf (argType x)
331 argType :: t a b c d -> a
334 -- | Variant for 5-ary type constructors
335 class Typeable5 t where
336 typeOf5 :: t a b c d e -> TypeRep
338 -- | For defining a 'Typeable4' instance from any 'Typeable5' instance.
339 typeOf4Default :: (Typeable5 t, Typeable a) => t a b c d e -> TypeRep
340 typeOf4Default x = typeOf5 x `mkAppTy` typeOf (argType x)
342 argType :: t a b c d e -> a
345 -- | Variant for 6-ary type constructors
346 class Typeable6 t where
347 typeOf6 :: t a b c d e f -> TypeRep
349 -- | For defining a 'Typeable5' instance from any 'Typeable6' instance.
350 typeOf5Default :: (Typeable6 t, Typeable a) => t a b c d e f -> TypeRep
351 typeOf5Default x = typeOf6 x `mkAppTy` typeOf (argType x)
353 argType :: t a b c d e f -> a
356 -- | Variant for 7-ary type constructors
357 class Typeable7 t where
358 typeOf7 :: t a b c d e f g -> TypeRep
360 -- | For defining a 'Typeable6' instance from any 'Typeable7' instance.
361 typeOf6Default :: (Typeable7 t, Typeable a) => t a b c d e f g -> TypeRep
362 typeOf6Default x = typeOf7 x `mkAppTy` typeOf (argType x)
364 argType :: t a b c d e f g -> a
367 #ifdef __GLASGOW_HASKELL__
368 -- Given a @Typeable@/n/ instance for an /n/-ary type constructor,
369 -- define the instances for partial applications.
370 -- Programmers using non-GHC implementations must do this manually
371 -- for each type constructor.
372 -- (The INSTANCE_TYPEABLE/n/ macros in Typeable.h include this.)
374 -- | One Typeable instance for all Typeable1 instances
375 instance (Typeable1 s, Typeable a)
376 => Typeable (s a) where
377 typeOf = typeOfDefault
379 -- | One Typeable1 instance for all Typeable2 instances
380 instance (Typeable2 s, Typeable a)
381 => Typeable1 (s a) where
382 typeOf1 = typeOf1Default
384 -- | One Typeable2 instance for all Typeable3 instances
385 instance (Typeable3 s, Typeable a)
386 => Typeable2 (s a) where
387 typeOf2 = typeOf2Default
389 -- | One Typeable3 instance for all Typeable4 instances
390 instance (Typeable4 s, Typeable a)
391 => Typeable3 (s a) where
392 typeOf3 = typeOf3Default
394 -- | One Typeable4 instance for all Typeable5 instances
395 instance (Typeable5 s, Typeable a)
396 => Typeable4 (s a) where
397 typeOf4 = typeOf4Default
399 -- | One Typeable5 instance for all Typeable6 instances
400 instance (Typeable6 s, Typeable a)
401 => Typeable5 (s a) where
402 typeOf5 = typeOf5Default
404 -- | One Typeable6 instance for all Typeable7 instances
405 instance (Typeable7 s, Typeable a)
406 => Typeable6 (s a) where
407 typeOf6 = typeOf6Default
409 #endif /* __GLASGOW_HASKELL__ */
411 -------------------------------------------------------------
415 -------------------------------------------------------------
417 -- | The type-safe cast operation
418 cast :: (Typeable a, Typeable b) => a -> Maybe b
421 r = if typeOf x == typeOf (fromJust r)
422 then Just $ unsafeCoerce x
425 -- | A flexible variation parameterised in a type constructor
426 gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
429 r = if typeOf (getArg x) == typeOf (getArg (fromJust r))
430 then Just $ unsafeCoerce x
436 gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
439 r = if typeOf1 (getArg x) == typeOf1 (getArg (fromJust r))
440 then Just $ unsafeCoerce x
445 -- | Cast for * -> * -> *
446 gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
449 r = if typeOf2 (getArg x) == typeOf2 (getArg (fromJust r))
450 then Just $ unsafeCoerce x
455 -------------------------------------------------------------
457 -- Instances of the Typeable classes for Prelude types
459 -------------------------------------------------------------
461 INSTANCE_TYPEABLE1([],listTc,"[]")
462 INSTANCE_TYPEABLE1(Maybe,maybeTc,"Maybe")
463 INSTANCE_TYPEABLE1(Ratio,ratioTc,"Ratio")
464 INSTANCE_TYPEABLE2(Either,eitherTc,"Either")
465 INSTANCE_TYPEABLE2((->),funTc,"->")
466 INSTANCE_TYPEABLE1(IO,ioTc,"IO")
467 #ifdef __GLASGOW_HASKELL__
468 INSTANCE_TYPEABLE2(ST,stTc,"ST")
470 INSTANCE_TYPEABLE0((),unitTc,"()")
472 INSTANCE_TYPEABLE2((,),pairTc,",")
473 INSTANCE_TYPEABLE3((,,),tup3Tc,",,")
476 tup4Tc = mkTyCon ",,,"
478 instance Typeable4 (,,,) where
479 typeOf4 tu = mkTyConApp tup4Tc []
482 tup5Tc = mkTyCon ",,,,"
484 instance Typeable5 (,,,,) where
485 typeOf5 tu = mkTyConApp tup5Tc []
488 tup6Tc = mkTyCon ",,,,,"
490 instance Typeable6 (,,,,,) where
491 typeOf6 tu = mkTyConApp tup6Tc []
494 tup7Tc = mkTyCon ",,,,,,"
496 instance Typeable7 (,,,,,,) where
497 typeOf7 tu = mkTyConApp tup7Tc []
500 INSTANCE_TYPEABLE1(Ptr,ptrTc,"Ptr")
501 INSTANCE_TYPEABLE1(StablePtr,stableptrTc,"StablePtr")
502 INSTANCE_TYPEABLE1(IORef,iorefTc,"IORef")
504 -------------------------------------------------------
506 -- Generate Typeable instances for standard datatypes
508 -------------------------------------------------------
510 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
511 INSTANCE_TYPEABLE0(Char,charTc,"Char")
512 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
513 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
514 INSTANCE_TYPEABLE0(Int,intTc,"Int")
515 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
516 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
517 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
519 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
520 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
521 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
522 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
524 INSTANCE_TYPEABLE0(Word8,word8Tc,"Word8" )
525 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
526 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
527 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
529 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
530 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
532 #ifdef __GLASGOW_HASKELL__
533 INSTANCE_TYPEABLE0(RealWorld,realWorldTc,"RealWorld")
534 INSTANCE_TYPEABLE0(Word,wordTc,"Word" )
535 INSTANCE_TYPEABLE1(MVar,mvarTc,"MVar" )
538 ---------------------------------------------
542 ---------------------------------------------
545 newtype Key = Key Int deriving( Eq )
548 data KeyPr = KeyPr !Key !Key deriving( Eq )
550 hashKP :: KeyPr -> Int32
551 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
553 data Cache = Cache { next_key :: !(IORef Key),
554 tc_tbl :: !(HT.HashTable String Key),
555 ap_tbl :: !(HT.HashTable KeyPr Key) }
557 {-# NOINLINE cache #-}
559 cache = unsafePerformIO $ do
560 empty_tc_tbl <- HT.new (==) HT.hashString
561 empty_ap_tbl <- HT.new (==) hashKP
562 key_loc <- newIORef (Key 1)
563 return (Cache { next_key = key_loc,
564 tc_tbl = empty_tc_tbl,
565 ap_tbl = empty_ap_tbl })
567 newKey :: IORef Key -> IO Key
568 #ifdef __GLASGOW_HASKELL__
569 newKey kloc = do i <- genSym; return (Key i)
571 newKey kloc = do { k@(Key i) <- readIORef kloc ;
572 writeIORef kloc (Key (i+1)) ;
576 #ifdef __GLASGOW_HASKELL__
577 -- In GHC we use the RTS's genSym function to get a new unique,
578 -- because in GHCi we might have two copies of the Data.Typeable
579 -- library running (one in the compiler and one in the running
580 -- program), and we need to make sure they don't share any keys.
582 -- This is really a hack. A better solution would be to centralise the
583 -- whole mutable state used by this module, i.e. both hashtables. But
584 -- the current solution solves the immediate problem, which is that
585 -- dynamics generated in one world with one type were erroneously
586 -- being recognised by the other world as having a different type.
587 foreign import ccall unsafe "genSymZh"
591 mkTyConKey :: String -> Key
593 = unsafePerformIO $ do
594 let Cache {next_key = kloc, tc_tbl = tbl} = cache
595 mb_k <- HT.lookup tbl str
598 Nothing -> do { k <- newKey kloc ;
599 HT.insert tbl str k ;
602 appKey :: Key -> Key -> Key
604 = unsafePerformIO $ do
605 let Cache {next_key = kloc, ap_tbl = tbl} = cache
606 mb_k <- HT.lookup tbl kpr
609 Nothing -> do { k <- newKey kloc ;
610 HT.insert tbl kpr k ;
615 appKeys :: Key -> [Key] -> Key
616 appKeys k ks = foldl appKey k ks