[project @ 2004-08-10 11:35:24 by simonpj]
[ghc.git] / libraries / base / Data / Typeable.hs
1 {-# OPTIONS -fno-implicit-prelude #-}
2 -----------------------------------------------------------------------------
3 -- |
4 -- Module : Data.Typeable
5 -- Copyright : (c) The University of Glasgow, CWI 2001--2004
6 -- License : BSD-style (see the file libraries/base/LICENSE)
7 --
8 -- Maintainer : libraries@haskell.org
9 -- Stability : experimental
10 -- Portability : portable
11 --
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.
20 --
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.
29 --
30 -----------------------------------------------------------------------------
31
32 module Data.Typeable
33 (
34
35 -- * The Typeable class
36 Typeable( typeOf ), -- :: a -> TypeRep
37
38 -- * Type-safe cast
39 cast, -- :: (Typeable a, Typeable b) => a -> Maybe b
40 gcast, -- a generalisation of cast
41
42 -- * Type representations
43 TypeRep, -- abstract, instance of: Eq, Show, Typeable
44 TyCon, -- abstract, instance of: Eq, Show, Typeable
45
46 -- * Construction of type representations
47 mkTyCon, -- :: String -> TyCon
48 mkTyConApp, -- :: TyCon -> [TypeRep] -> TypeRep
49 mkAppTy, -- :: TypeRep -> TypeRep -> TypeRep
50 mkFunTy, -- :: TypeRep -> TypeRep -> TypeRep
51
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
58
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))
70
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
81
82 ) where
83
84 import qualified Data.HashTable as HT
85 import Data.Maybe
86 import Data.Either
87 import Data.Int
88 import Data.Word
89 import Data.List( foldl )
90
91 #ifdef __GLASGOW_HASKELL__
92 import GHC.Base
93 import GHC.Show
94 import GHC.Err
95 import GHC.Num
96 import GHC.Float
97 import GHC.Real( rem, Ratio )
98 import GHC.IOBase
99 import GHC.Ptr -- So we can give Typeable instance for Ptr
100 import GHC.Stable -- So we can give Typeable instance for StablePtr
101 #endif
102
103 #ifdef __HUGS__
104 import Hugs.Prelude
105 import Hugs.IO
106 import Hugs.IORef
107 import Hugs.IOExts
108 #endif
109
110 #ifdef __GLASGOW_HASKELL__
111 unsafeCoerce :: a -> b
112 unsafeCoerce = unsafeCoerce#
113 #endif
114
115 #ifdef __NHC__
116 import NonStdUnsafeCoerce (unsafeCoerce)
117 import NHC.IOExtras (IORef,newIORef,readIORef,writeIORef,unsafePerformIO)
118 import IO (Handle)
119 import Ratio (Ratio)
120 import NHC.FFI (Ptr,StablePtr)
121 #else
122 #endif
123
124 #include "Typeable.h"
125
126 #ifndef __HUGS__
127
128 -------------------------------------------------------------
129 --
130 -- Type representations
131 --
132 -------------------------------------------------------------
133
134 -- | A concrete representation of a (monomorphic) type. 'TypeRep'
135 -- supports reasonably efficient equality.
136 data TypeRep = TypeRep !Key TyCon [TypeRep]
137
138 -- Compare keys for equality
139 instance Eq TypeRep where
140 (TypeRep k1 _ _) == (TypeRep k2 _ _) = k1 == k2
141
142 -- | An abstract representation of a type constructor. 'TyCon' objects can
143 -- be built using 'mkTyCon'.
144 data TyCon = TyCon !Key String
145
146 instance Eq TyCon where
147 (TyCon t1 _) == (TyCon t2 _) = t1 == t2
148
149 #endif
150
151 --
152 -- let fTy = mkTyCon "Foo" in show (mkTyConApp (mkTyCon ",,")
153 -- [fTy,fTy,fTy])
154 --
155 -- returns "(Foo,Foo,Foo)"
156 --
157 -- The TypeRep Show instance promises to print tuple types
158 -- correctly. Tuple type constructors are specified by a
159 -- sequence of commas, e.g., (mkTyCon ",,,,") returns
160 -- the 5-tuple tycon.
161
162 ----------------- Construction --------------------
163
164 -- | Applies a type constructor to a sequence of types
165 mkTyConApp :: TyCon -> [TypeRep] -> TypeRep
166 mkTyConApp tc@(TyCon tc_k _) args
167 = TypeRep (appKeys tc_k arg_ks) tc args
168 where
169 arg_ks = [k | TypeRep k _ _ <- args]
170
171 -- | A special case of 'mkTyConApp', which applies the function
172 -- type constructor to a pair of types.
173 mkFunTy :: TypeRep -> TypeRep -> TypeRep
174 mkFunTy f a = mkTyConApp funTc [f,a]
175
176 -- | Splits a type constructor application
177 splitTyConApp :: TypeRep -> (TyCon,[TypeRep])
178 splitTyConApp (TypeRep _ tc trs) = (tc,trs)
179
180 -- | Applies a type to a function type. Returns: @'Just' u@ if the
181 -- first argument represents a function of type @t -> u@ and the
182 -- second argument represents a function of type @t@. Otherwise,
183 -- returns 'Nothing'.
184 funResultTy :: TypeRep -> TypeRep -> Maybe TypeRep
185 funResultTy trFun trArg
186 = case splitTyConApp trFun of
187 (tc, [t1,t2]) | tc == funTc && t1 == trArg -> Just t2
188 _ -> Nothing
189
190 -- | Adds a TypeRep argument to a TypeRep.
191 mkAppTy :: TypeRep -> TypeRep -> TypeRep
192 mkAppTy (TypeRep tr_k tc trs) arg_tr
193 = let (TypeRep arg_k _ _) = arg_tr
194 in TypeRep (appKey tr_k arg_k) tc (trs++[arg_tr])
195
196 -- If we enforce the restriction that there is only one
197 -- @TyCon@ for a type & it is shared among all its uses,
198 -- we can map them onto Ints very simply. The benefit is,
199 -- of course, that @TyCon@s can then be compared efficiently.
200
201 -- Provided the implementor of other @Typeable@ instances
202 -- takes care of making all the @TyCon@s CAFs (toplevel constants),
203 -- this will work.
204
205 -- If this constraint does turn out to be a sore thumb, changing
206 -- the Eq instance for TyCons is trivial.
207
208 -- | Builds a 'TyCon' object representing a type constructor. An
209 -- implementation of "Data.Typeable" should ensure that the following holds:
210 --
211 -- > mkTyCon "a" == mkTyCon "a"
212 --
213
214 mkTyCon :: String -- ^ the name of the type constructor (should be unique
215 -- in the program, so it might be wise to use the
216 -- fully qualified name).
217 -> TyCon -- ^ A unique 'TyCon' object
218 mkTyCon str = TyCon (mkTyConKey str) str
219
220 ----------------- Observation ---------------------
221
222 -- | Observe the type constructor of a type representation
223 typeRepTyCon :: TypeRep -> TyCon
224 typeRepTyCon (TypeRep _ tc _) = tc
225
226 -- | Observe the argument types of a type representation
227 typeRepArgs :: TypeRep -> [TypeRep]
228 typeRepArgs (TypeRep _ _ args) = args
229
230 -- | Observe string encoding of a type representation
231 tyConString :: TyCon -> String
232 tyConString (TyCon _ str) = str
233
234 ----------------- Showing TypeReps --------------------
235
236 instance Show TypeRep where
237 showsPrec p (TypeRep _ tycon tys) =
238 case tys of
239 [] -> showsPrec p tycon
240 [x] | tycon == listTc -> showChar '[' . shows x . showChar ']'
241 [a,r] | tycon == funTc -> showParen (p > 8) $
242 showsPrec 9 a .
243 showString " -> " .
244 showsPrec 8 r
245 xs | isTupleTyCon tycon -> showTuple tycon xs
246 | otherwise ->
247 showParen (p > 9) $
248 showsPrec p tycon .
249 showChar ' ' .
250 showArgs tys
251
252 instance Show TyCon where
253 showsPrec _ (TyCon _ s) = showString s
254
255 isTupleTyCon :: TyCon -> Bool
256 isTupleTyCon (TyCon _ (',':_)) = True
257 isTupleTyCon _ = False
258
259 -- Some (Show.TypeRep) helpers:
260
261 showArgs :: Show a => [a] -> ShowS
262 showArgs [] = id
263 showArgs [a] = showsPrec 10 a
264 showArgs (a:as) = showsPrec 10 a . showString " " . showArgs as
265
266 showTuple :: TyCon -> [TypeRep] -> ShowS
267 showTuple (TyCon _ str) args = showChar '(' . go str args
268 where
269 go [] [a] = showsPrec 10 a . showChar ')'
270 go _ [] = showChar ')' -- a failure condition, really.
271 go (',':xs) (a:as) = showsPrec 10 a . showChar ',' . go xs as
272 go _ _ = showChar ')'
273
274 -------------------------------------------------------------
275 --
276 -- The Typeable class and friends
277 --
278 -------------------------------------------------------------
279
280 -- | The class 'Typeable' allows a concrete representation of a type to
281 -- be calculated.
282 class Typeable a where
283 typeOf :: a -> TypeRep
284 -- ^ Takes a value of type @a@ and returns a concrete representation
285 -- of that type. The /value/ of the argument should be ignored by
286 -- any instance of 'Typeable', so that it is safe to pass 'undefined' as
287 -- the argument.
288
289 -- | Variant for unary type constructors
290 class Typeable1 t where
291 typeOf1 :: t a -> TypeRep
292
293 -- | For defining a 'Typeable' instance from any 'Typeable1' instance.
294 typeOfDefault :: (Typeable1 t, Typeable a) => t a -> TypeRep
295 typeOfDefault x = typeOf1 x `mkAppTy` typeOf (argType x)
296 where
297 argType :: t a -> a
298 argType = undefined
299
300 -- | Variant for binary type constructors
301 class Typeable2 t where
302 typeOf2 :: t a b -> TypeRep
303
304 -- | For defining a 'Typeable1' instance from any 'Typeable2' instance.
305 typeOf1Default :: (Typeable2 t, Typeable a) => t a b -> TypeRep
306 typeOf1Default x = typeOf2 x `mkAppTy` typeOf (argType x)
307 where
308 argType :: t a b -> a
309 argType = undefined
310
311 -- | Variant for 3-ary type constructors
312 class Typeable3 t where
313 typeOf3 :: t a b c -> TypeRep
314
315 -- | For defining a 'Typeable2' instance from any 'Typeable3' instance.
316 typeOf2Default :: (Typeable3 t, Typeable a) => t a b c -> TypeRep
317 typeOf2Default x = typeOf3 x `mkAppTy` typeOf (argType x)
318 where
319 argType :: t a b c -> a
320 argType = undefined
321
322 -- | Variant for 4-ary type constructors
323 class Typeable4 t where
324 typeOf4 :: t a b c d -> TypeRep
325
326 -- | For defining a 'Typeable3' instance from any 'Typeable4' instance.
327 typeOf3Default :: (Typeable4 t, Typeable a) => t a b c d -> TypeRep
328 typeOf3Default x = typeOf4 x `mkAppTy` typeOf (argType x)
329 where
330 argType :: t a b c d -> a
331 argType = undefined
332
333 -- | Variant for 5-ary type constructors
334 class Typeable5 t where
335 typeOf5 :: t a b c d e -> TypeRep
336
337 -- | For defining a 'Typeable4' instance from any 'Typeable5' instance.
338 typeOf4Default :: (Typeable5 t, Typeable a) => t a b c d e -> TypeRep
339 typeOf4Default x = typeOf5 x `mkAppTy` typeOf (argType x)
340 where
341 argType :: t a b c d e -> a
342 argType = undefined
343
344 -- | Variant for 6-ary type constructors
345 class Typeable6 t where
346 typeOf6 :: t a b c d e f -> TypeRep
347
348 -- | For defining a 'Typeable5' instance from any 'Typeable6' instance.
349 typeOf5Default :: (Typeable6 t, Typeable a) => t a b c d e f -> TypeRep
350 typeOf5Default x = typeOf6 x `mkAppTy` typeOf (argType x)
351 where
352 argType :: t a b c d e f -> a
353 argType = undefined
354
355 -- | Variant for 7-ary type constructors
356 class Typeable7 t where
357 typeOf7 :: t a b c d e f g -> TypeRep
358
359 -- | For defining a 'Typeable6' instance from any 'Typeable7' instance.
360 typeOf6Default :: (Typeable7 t, Typeable a) => t a b c d e f g -> TypeRep
361 typeOf6Default x = typeOf7 x `mkAppTy` typeOf (argType x)
362 where
363 argType :: t a b c d e f g -> a
364 argType = undefined
365
366 #ifdef __GLASGOW_HASKELL__
367 -- Given a @Typeable@/n/ instance for an /n/-ary type constructor,
368 -- define the instances for partial applications.
369 -- Programmers using non-GHC implementations must do this manually
370 -- for each type constructor.
371 -- (The INSTANCE_TYPEABLE/n/ macros in Typeable.h include this.)
372
373 -- | One Typeable instance for all Typeable1 instances
374 instance (Typeable1 s, Typeable a)
375 => Typeable (s a) where
376 typeOf = typeOfDefault
377
378 -- | One Typeable1 instance for all Typeable2 instances
379 instance (Typeable2 s, Typeable a)
380 => Typeable1 (s a) where
381 typeOf1 = typeOf1Default
382
383 -- | One Typeable2 instance for all Typeable3 instances
384 instance (Typeable3 s, Typeable a)
385 => Typeable2 (s a) where
386 typeOf2 = typeOf2Default
387
388 -- | One Typeable3 instance for all Typeable4 instances
389 instance (Typeable4 s, Typeable a)
390 => Typeable3 (s a) where
391 typeOf3 = typeOf3Default
392
393 -- | One Typeable4 instance for all Typeable5 instances
394 instance (Typeable5 s, Typeable a)
395 => Typeable4 (s a) where
396 typeOf4 = typeOf4Default
397
398 -- | One Typeable5 instance for all Typeable6 instances
399 instance (Typeable6 s, Typeable a)
400 => Typeable5 (s a) where
401 typeOf5 = typeOf5Default
402
403 -- | One Typeable6 instance for all Typeable7 instances
404 instance (Typeable7 s, Typeable a)
405 => Typeable6 (s a) where
406 typeOf6 = typeOf6Default
407
408 #endif /* __GLASGOW_HASKELL__ */
409
410 -------------------------------------------------------------
411 --
412 -- Type-safe cast
413 --
414 -------------------------------------------------------------
415
416 -- | The type-safe cast operation
417 cast :: (Typeable a, Typeable b) => a -> Maybe b
418 cast x = r
419 where
420 r = if typeOf x == typeOf (fromJust r)
421 then Just $ unsafeCoerce x
422 else Nothing
423
424 -- | A flexible variation parameterised in a type constructor
425 gcast :: (Typeable a, Typeable b) => c a -> Maybe (c b)
426 gcast x = r
427 where
428 r = if typeOf (getArg x) == typeOf (getArg (fromJust r))
429 then Just $ unsafeCoerce x
430 else Nothing
431 getArg :: c x -> x
432 getArg = undefined
433
434 -- | Cast for * -> *
435 gcast1 :: (Typeable1 t, Typeable1 t') => c (t a) -> Maybe (c (t' a))
436 gcast1 x = r
437 where
438 r = if typeOf1 (getArg x) == typeOf1 (getArg (fromJust r))
439 then Just $ unsafeCoerce x
440 else Nothing
441 getArg :: c x -> x
442 getArg = undefined
443
444 -- | Cast for * -> * -> *
445 gcast2 :: (Typeable2 t, Typeable2 t') => c (t a b) -> Maybe (c (t' a b))
446 gcast2 x = r
447 where
448 r = if typeOf2 (getArg x) == typeOf2 (getArg (fromJust r))
449 then Just $ unsafeCoerce x
450 else Nothing
451 getArg :: c x -> x
452 getArg = undefined
453
454 -------------------------------------------------------------
455 --
456 -- Instances of the Typeable classes for Prelude types
457 --
458 -------------------------------------------------------------
459
460 INSTANCE_TYPEABLE1([],listTc,"[]")
461 INSTANCE_TYPEABLE1(Maybe,maybeTc,"Maybe")
462 INSTANCE_TYPEABLE1(Ratio,ratioTc,"Ratio")
463 INSTANCE_TYPEABLE2(Either,eitherTc,"Either")
464 INSTANCE_TYPEABLE2((->),funTc,"->")
465 INSTANCE_TYPEABLE1(IO,ioTc,"IO")
466 INSTANCE_TYPEABLE0((),unitTc,"()")
467 #ifndef __NHC__
468 INSTANCE_TYPEABLE2((,),pairTc,",")
469 INSTANCE_TYPEABLE3((,,),tup3Tc,",,")
470
471 tup4Tc :: TyCon
472 tup4Tc = mkTyCon ",,,"
473
474 instance Typeable4 (,,,) where
475 typeOf4 tu = mkTyConApp tup4Tc []
476
477 tup5Tc :: TyCon
478 tup5Tc = mkTyCon ",,,,"
479
480 instance Typeable5 (,,,,) where
481 typeOf5 tu = mkTyConApp tup5Tc []
482
483 tup6Tc :: TyCon
484 tup6Tc = mkTyCon ",,,,,"
485
486 instance Typeable6 (,,,,,) where
487 typeOf6 tu = mkTyConApp tup6Tc []
488
489 tup7Tc :: TyCon
490 tup7Tc = mkTyCon ",,,,,"
491
492 instance Typeable7 (,,,,,,) where
493 typeOf7 tu = mkTyConApp tup7Tc []
494
495 #endif /* __NHC__ */
496 INSTANCE_TYPEABLE1(Ptr,ptrTc,"Ptr")
497 INSTANCE_TYPEABLE1(StablePtr,stableptrTc,"StablePtr")
498 INSTANCE_TYPEABLE1(IORef,iorefTc,"IORef")
499
500 -------------------------------------------------------
501 --
502 -- Generate Typeable instances for standard datatypes
503 --
504 -------------------------------------------------------
505
506 INSTANCE_TYPEABLE0(Bool,boolTc,"Bool")
507 INSTANCE_TYPEABLE0(Char,charTc,"Char")
508 INSTANCE_TYPEABLE0(Float,floatTc,"Float")
509 INSTANCE_TYPEABLE0(Double,doubleTc,"Double")
510 INSTANCE_TYPEABLE0(Int,intTc,"Int")
511 INSTANCE_TYPEABLE0(Integer,integerTc,"Integer")
512 INSTANCE_TYPEABLE0(Ordering,orderingTc,"Ordering")
513 INSTANCE_TYPEABLE0(Handle,handleTc,"Handle")
514
515 INSTANCE_TYPEABLE0(Int8,int8Tc,"Int8")
516 INSTANCE_TYPEABLE0(Int16,int16Tc,"Int16")
517 INSTANCE_TYPEABLE0(Int32,int32Tc,"Int32")
518 INSTANCE_TYPEABLE0(Int64,int64Tc,"Int64")
519
520 INSTANCE_TYPEABLE0(Word8,word8Tc,"Word8" )
521 INSTANCE_TYPEABLE0(Word16,word16Tc,"Word16")
522 INSTANCE_TYPEABLE0(Word32,word32Tc,"Word32")
523 INSTANCE_TYPEABLE0(Word64,word64Tc,"Word64")
524
525 INSTANCE_TYPEABLE0(TyCon,tyconTc,"TyCon")
526 INSTANCE_TYPEABLE0(TypeRep,typeRepTc,"TypeRep")
527
528 #ifdef __GLASGOW_HASKELL__
529 INSTANCE_TYPEABLE0(Word,wordTc,"Word" )
530 #endif
531
532 ---------------------------------------------
533 --
534 -- Internals
535 --
536 ---------------------------------------------
537
538 #ifndef __HUGS__
539 newtype Key = Key Int deriving( Eq )
540 #endif
541
542 data KeyPr = KeyPr !Key !Key deriving( Eq )
543
544 hashKP :: KeyPr -> Int32
545 hashKP (KeyPr (Key k1) (Key k2)) = (HT.hashInt k1 + HT.hashInt k2) `rem` HT.prime
546
547 data Cache = Cache { next_key :: !(IORef Key),
548 tc_tbl :: !(HT.HashTable String Key),
549 ap_tbl :: !(HT.HashTable KeyPr Key) }
550
551 {-# NOINLINE cache #-}
552 cache :: Cache
553 cache = unsafePerformIO $ do
554 empty_tc_tbl <- HT.new (==) HT.hashString
555 empty_ap_tbl <- HT.new (==) hashKP
556 key_loc <- newIORef (Key 1)
557 return (Cache { next_key = key_loc,
558 tc_tbl = empty_tc_tbl,
559 ap_tbl = empty_ap_tbl })
560
561 newKey :: IORef Key -> IO Key
562 #ifdef __GLASGOW_HASKELL__
563 newKey kloc = do i <- genSym; return (Key i)
564 #else
565 newKey kloc = do { k@(Key i) <- readIORef kloc ;
566 writeIORef kloc (Key (i+1)) ;
567 return k }
568 #endif
569
570 #ifdef __GLASGOW_HASKELL__
571 -- In GHC we use the RTS's genSym function to get a new unique,
572 -- because in GHCi we might have two copies of the Data.Typeable
573 -- library running (one in the compiler and one in the running
574 -- program), and we need to make sure they don't share any keys.
575 --
576 -- This is really a hack. A better solution would be to centralise the
577 -- whole mutable state used by this module, i.e. both hashtables. But
578 -- the current solution solves the immediate problem, which is that
579 -- dynamics generated in one world with one type were erroneously
580 -- being recognised by the other world as having a different type.
581 foreign import ccall unsafe "genSymZh"
582 genSym :: IO Int
583 #endif
584
585 mkTyConKey :: String -> Key
586 mkTyConKey str
587 = unsafePerformIO $ do
588 let Cache {next_key = kloc, tc_tbl = tbl} = cache
589 mb_k <- HT.lookup tbl str
590 case mb_k of
591 Just k -> return k
592 Nothing -> do { k <- newKey kloc ;
593 HT.insert tbl str k ;
594 return k }
595
596 appKey :: Key -> Key -> Key
597 appKey k1 k2
598 = unsafePerformIO $ do
599 let Cache {next_key = kloc, ap_tbl = tbl} = cache
600 mb_k <- HT.lookup tbl kpr
601 case mb_k of
602 Just k -> return k
603 Nothing -> do { k <- newKey kloc ;
604 HT.insert tbl kpr k ;
605 return k }
606 where
607 kpr = KeyPr k1 k2
608
609 appKeys :: Key -> [Key] -> Key
610 appKeys k ks = foldl appKey k ks