2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1998
5 \section[DataCon]{@DataCon@: Data Constructors}
10 DataCon, DataConIds(..),
13 -- ** Type construction
16 -- ** Type deconstruction
17 dataConRepType, dataConSig, dataConFullSig,
18 dataConName, dataConIdentity, dataConTag, dataConTyCon,
19 dataConOrigTyCon, dataConUserType,
20 dataConUnivTyVars, dataConExTyVars, dataConAllTyVars,
21 dataConEqSpec, eqSpecPreds, dataConTheta,
23 dataConInstArgTys, dataConOrigArgTys, dataConOrigResTy,
24 dataConInstOrigArgTys, dataConRepArgTys,
25 dataConFieldLabels, dataConFieldType,
26 dataConStrictMarks, dataConExStricts,
27 dataConSourceArity, dataConRepArity,
29 dataConWorkId, dataConWrapId, dataConWrapId_maybe, dataConImplicitIds,
32 -- ** Predicates on DataCons
33 isNullarySrcDataCon, isNullaryRepDataCon, isTupleCon, isUnboxedTupleCon,
34 isVanillaDataCon, classDataCon, dataConCannotMatch,
36 -- * Splitting product types
37 splitProductType_maybe, splitProductType, deepSplitProductType,
38 deepSplitProductType_maybe
41 #include "HsVersions.h"
58 import qualified Data.Data as Data
64 Data constructor representation
65 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
66 Consider the following Haskell data type declaration
68 data T = T !Int ![Int]
70 Using the strictness annotations, GHC will represent this as
74 That is, the Int has been unboxed. Furthermore, the Haskell source construction
84 That is, the first argument is unboxed, and the second is evaluated. Finally,
85 pattern matching is translated too:
87 case e of { T a b -> ... }
91 case e of { T a' b -> let a = I# a' in ... }
93 To keep ourselves sane, we name the different versions of the data constructor
94 differently, as follows.
97 Note [Data Constructor Naming]
98 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
99 Each data constructor C has two, and possibly up to four, Names associated with it:
101 OccName Name space Name of Notes
102 ---------------------------------------------------------------------------
103 The "data con itself" C DataName DataCon In dom( GlobalRdrEnv )
104 The "worker data con" C VarName Id The worker
105 The "wrapper data con" $WC VarName Id The wrapper
106 The "newtype coercion" :CoT TcClsName TyCon
108 EVERY data constructor (incl for newtypes) has the former two (the
109 data con itself, and its worker. But only some data constructors have a
110 wrapper (see Note [The need for a wrapper]).
112 Each of these three has a distinct Unique. The "data con itself" name
113 appears in the output of the renamer, and names the Haskell-source
114 data constructor. The type checker translates it into either the wrapper Id
115 (if it exists) or worker Id (otherwise).
117 The data con has one or two Ids associated with it:
119 The "worker Id", is the actual data constructor.
120 * Every data constructor (newtype or data type) has a worker
122 * The worker is very like a primop, in that it has no binding.
124 * For a *data* type, the worker *is* the data constructor;
127 * For a *newtype*, the worker has a compulsory unfolding which
130 The worker for MkT has unfolding
131 \\(x:Int). x `cast` sym CoT
132 Here CoT is the type constructor, witnessing the FC axiom
135 The "wrapper Id", \$WC, goes as follows
137 * Its type is exactly what it looks like in the source program.
139 * It is an ordinary function, and it gets a top-level binding
140 like any other function.
142 * The wrapper Id isn't generated for a data type if there is
143 nothing for the wrapper to do. That is, if its defn would be
146 Note [The need for a wrapper]
147 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
148 Why might the wrapper have anything to do? Two reasons:
150 * Unboxing strict fields (with -funbox-strict-fields)
151 data T = MkT !(Int,Int)
152 \$wMkT :: (Int,Int) -> T
153 \$wMkT (x,y) = MkT x y
154 Notice that the worker has two fields where the wapper has
155 just one. That is, the worker has type
156 MkT :: Int -> Int -> T
158 * Equality constraints for GADTs
159 data T a where { MkT :: a -> T [a] }
161 The worker gets a type with explicit equality
163 MkT :: forall a b. (a=[b]) => b -> T a
165 The wrapper has the programmer-specified type:
167 \$wMkT a x = MkT [a] a [a] x
168 The third argument is a coerion
171 INVARIANT: the dictionary constructor for a class
175 A note about the stupid context
176 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
177 Data types can have a context:
179 data (Eq a, Ord b) => T a b = T1 a b | T2 a
181 and that makes the constructors have a context too
182 (notice that T2's context is "thinned"):
184 T1 :: (Eq a, Ord b) => a -> b -> T a b
185 T2 :: (Eq a) => a -> T a b
187 Furthermore, this context pops up when pattern matching
188 (though GHC hasn't implemented this, but it is in H98, and
189 I've fixed GHC so that it now does):
193 f :: Eq a => T a b -> a
195 I say the context is "stupid" because the dictionaries passed
196 are immediately discarded -- they do nothing and have no benefit.
197 It's a flaw in the language.
199 Up to now [March 2002] I have put this stupid context into the
200 type of the "wrapper" constructors functions, T1 and T2, but
201 that turned out to be jolly inconvenient for generics, and
202 record update, and other functions that build values of type T
203 (because they don't have suitable dictionaries available).
205 So now I've taken the stupid context out. I simply deal with
206 it separately in the type checker on occurrences of a
207 constructor, either in an expression or in a pattern.
209 [May 2003: actually I think this decision could evasily be
210 reversed now, and probably should be. Generics could be
211 disabled for types with a stupid context; record updates now
212 (H98) needs the context too; etc. It's an unforced change, so
213 I'm leaving it for now --- but it does seem odd that the
214 wrapper doesn't include the stupid context.]
216 [July 04] With the advent of generalised data types, it's less obvious
217 what the "stupid context" is. Consider
218 C :: forall a. Ord a => a -> a -> T (Foo a)
219 Does the C constructor in Core contain the Ord dictionary? Yes, it must:
224 C a (d:Ord a) (p:a) (q:a) -> compare d p q
226 Note that (Foo a) might not be an instance of Ord.
228 %************************************************************************
230 \subsection{Data constructors}
232 %************************************************************************
235 -- | A data constructor
238 dcName :: Name, -- This is the name of the *source data con*
239 -- (see "Note [Data Constructor Naming]" above)
240 dcUnique :: Unique, -- Cached from Name
241 dcTag :: ConTag, -- ^ Tag, used for ordering 'DataCon's
245 -- *** As declared by the user
247 -- MkT :: forall x y. (x~y,Ord x) => x -> y -> T (x,y)
249 -- *** As represented internally
251 -- MkT :: forall a. forall x y. (a~(x,y),x~y,Ord x) => x -> y -> T a
253 -- The next six fields express the type of the constructor, in pieces
256 -- dcUnivTyVars = [a]
257 -- dcExTyVars = [x,y]
258 -- dcEqSpec = [a~(x,y)]
259 -- dcOtherTheta = [x~y, Ord x]
260 -- dcOrigArgTys = [a,List b]
263 dcVanilla :: Bool, -- True <=> This is a vanilla Haskell 98 data constructor
264 -- Its type is of form
265 -- forall a1..an . t1 -> ... tm -> T a1..an
266 -- No existentials, no coercions, nothing.
267 -- That is: dcExTyVars = dcEqSpec = dcOtherTheta = []
268 -- NB 1: newtypes always have a vanilla data con
269 -- NB 2: a vanilla constructor can still be declared in GADT-style
270 -- syntax, provided its type looks like the above.
271 -- The declaration format is held in the TyCon (algTcGadtSyntax)
273 dcUnivTyVars :: [TyVar], -- Universally-quantified type vars [a,b,c]
274 -- INVARIANT: length matches arity of the dcRepTyCon
275 --- result type of (rep) data con is exactly (T a b c)
277 dcExTyVars :: [TyVar], -- Existentially-quantified type vars
278 -- In general, the dcUnivTyVars are NOT NECESSARILY THE SAME AS THE TYVARS
279 -- FOR THE PARENT TyCon. With GADTs the data con might not even have
280 -- the same number of type variables.
281 -- [This is a change (Oct05): previously, vanilla datacons guaranteed to
282 -- have the same type variables as their parent TyCon, but that seems ugly.]
284 -- INVARIANT: the UnivTyVars and ExTyVars all have distinct OccNames
285 -- Reason: less confusing, and easier to generate IfaceSyn
287 dcEqSpec :: [(TyVar,Type)], -- Equalities derived from the result type,
288 -- _as written by the programmer_
289 -- This field allows us to move conveniently between the two ways
290 -- of representing a GADT constructor's type:
291 -- MkT :: forall a b. (a ~ [b]) => b -> T a
292 -- MkT :: forall b. b -> T [b]
293 -- Each equality is of the form (a ~ ty), where 'a' is one of
294 -- the universally quantified type variables
296 -- The next two fields give the type context of the data constructor
297 -- (aside from the GADT constraints,
298 -- which are given by the dcExpSpec)
299 -- In GADT form, this is *exactly* what the programmer writes, even if
300 -- the context constrains only universally quantified variables
301 -- MkT :: forall a b. (a ~ b, Ord b) => a -> T a b
302 dcOtherTheta :: ThetaType, -- The other constraints in the data con's type
303 -- other than those in the dcEqSpec
305 dcStupidTheta :: ThetaType, -- The context of the data type declaration
306 -- data Eq a => T a = ...
307 -- or, rather, a "thinned" version thereof
308 -- "Thinned", because the Report says
309 -- to eliminate any constraints that don't mention
310 -- tyvars free in the arg types for this constructor
312 -- INVARIANT: the free tyvars of dcStupidTheta are a subset of dcUnivTyVars
313 -- Reason: dcStupidTeta is gotten by thinning the stupid theta from the tycon
315 -- "Stupid", because the dictionaries aren't used for anything.
316 -- Indeed, [as of March 02] they are no longer in the type of
317 -- the wrapper Id, because that makes it harder to use the wrap-id
318 -- to rebuild values after record selection or in generics.
320 dcOrigArgTys :: [Type], -- Original argument types
321 -- (before unboxing and flattening of strict fields)
322 dcOrigResTy :: Type, -- Original result type, as seen by the user
323 -- NB: for a data instance, the original user result type may
324 -- differ from the DataCon's representation TyCon. Example
325 -- data instance T [a] where MkT :: a -> T [a]
326 -- The OrigResTy is T [a], but the dcRepTyCon might be :T123
328 -- Now the strictness annotations and field labels of the constructor
329 dcStrictMarks :: [HsBang],
330 -- Strictness annotations as decided by the compiler.
331 -- Does *not* include the existential dictionaries
332 -- length = dataConSourceArity dataCon
334 dcFields :: [FieldLabel],
335 -- Field labels for this constructor, in the
336 -- same order as the dcOrigArgTys;
337 -- length = 0 (if not a record) or dataConSourceArity.
339 -- Constructor representation
340 dcRepArgTys :: [Type], -- Final, representation argument types,
341 -- after unboxing and flattening,
342 -- and *including* all existential evidence args
344 dcRepStrictness :: [StrictnessMark],
345 -- One for each *representation* *value* argument
346 -- See also Note [Data-con worker strictness] in MkId.lhs
348 -- Result type of constructor is T t1..tn
349 dcRepTyCon :: TyCon, -- Result tycon, T
351 dcRepType :: Type, -- Type of the constructor
352 -- forall a x y. (a~(x,y), x~y, Ord x) =>
354 -- (this is *not* of the constructor wrapper Id:
355 -- see Note [Data con representation] below)
356 -- Notice that the existential type parameters come *second*.
357 -- Reason: in a case expression we may find:
358 -- case (e :: T t) of
359 -- MkT x y co1 co2 (d:Ord x) (v:r) (w:F s) -> ...
360 -- It's convenient to apply the rep-type of MkT to 't', to get
361 -- forall x y. (t~(x,y), x~y, Ord x) => x -> y -> T t
362 -- and use that to check the pattern. Mind you, this is really only
366 -- The curried worker function that corresponds to the constructor:
367 -- It doesn't have an unfolding; the code generator saturates these Ids
368 -- and allocates a real constructor when it finds one.
370 -- An entirely separate wrapper function is built in TcTyDecls
373 dcInfix :: Bool -- True <=> declared infix
374 -- Used for Template Haskell and 'deriving' only
375 -- The actual fixity is stored elsewhere
378 -- | Contains the Ids of the data constructor functions
380 = DCIds (Maybe Id) Id -- Algebraic data types always have a worker, and
381 -- may or may not have a wrapper, depending on whether
382 -- the wrapper does anything. Newtypes just have a worker
384 -- _Neither_ the worker _nor_ the wrapper take the dcStupidTheta dicts as arguments
386 -- The wrapper takes dcOrigArgTys as its arguments
387 -- The worker takes dcRepArgTys as its arguments
388 -- If the worker is absent, dcRepArgTys is the same as dcOrigArgTys
390 -- The 'Nothing' case of DCIds is important
391 -- Not only is this efficient,
392 -- but it also ensures that the wrapper is replaced
393 -- by the worker (because it *is* the worker)
394 -- even when there are no args. E.g. in
396 -- the (:) *is* the worker.
397 -- This is really important in rule matching,
398 -- (We could match on the wrappers,
399 -- but that makes it less likely that rules will match
400 -- when we bring bits of unfoldings together.)
402 -- | Type of the tags associated with each constructor possibility
406 -- ^ Tags are allocated from here for real constructors
410 Note [Data con representation]
411 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
412 The dcRepType field contains the type of the representation of a contructor
413 This may differ from the type of the contructor *Id* (built
414 by MkId.mkDataConId) for two reasons:
415 a) the constructor Id may be overloaded, but the dictionary isn't stored
416 e.g. data Eq a => T a = MkT a a
418 b) the constructor may store an unboxed version of a strict field.
420 Here's an example illustrating both:
421 data Ord a => T a = MkT Int! a
423 T :: Ord a => Int -> a -> T a
425 Trep :: Int# -> a -> T a
426 Actually, the unboxed part isn't implemented yet!
429 %************************************************************************
431 \subsection{Instances}
433 %************************************************************************
436 instance Eq DataCon where
437 a == b = getUnique a == getUnique b
438 a /= b = getUnique a /= getUnique b
440 instance Ord DataCon where
441 a <= b = getUnique a <= getUnique b
442 a < b = getUnique a < getUnique b
443 a >= b = getUnique a >= getUnique b
444 a > b = getUnique a > getUnique b
445 compare a b = getUnique a `compare` getUnique b
447 instance Uniquable DataCon where
450 instance NamedThing DataCon where
453 instance Outputable DataCon where
454 ppr con = ppr (dataConName con)
456 instance Show DataCon where
457 showsPrec p con = showsPrecSDoc p (ppr con)
459 instance Data.Typeable DataCon where
460 typeOf _ = Data.mkTyConApp (Data.mkTyCon "DataCon") []
462 instance Data.Data DataCon where
464 toConstr _ = abstractConstr "DataCon"
465 gunfold _ _ = error "gunfold"
466 dataTypeOf _ = mkNoRepType "DataCon"
470 %************************************************************************
472 \subsection{Construction}
474 %************************************************************************
477 -- | Build a new data constructor
479 -> Bool -- ^ Is the constructor declared infix?
480 -> [HsBang] -- ^ Strictness annotations written in the source file
481 -> [FieldLabel] -- ^ Field labels for the constructor, if it is a record,
483 -> [TyVar] -- ^ Universally quantified type variables
484 -> [TyVar] -- ^ Existentially quantified type variables
485 -> [(TyVar,Type)] -- ^ GADT equalities
486 -> ThetaType -- ^ Theta-type occuring before the arguments proper
487 -> [Type] -- ^ Original argument types
488 -> Type -- ^ Original result type
489 -> TyCon -- ^ Representation type constructor
490 -> ThetaType -- ^ The "stupid theta", context of the data declaration
491 -- e.g. @data Eq a => T a ...@
492 -> DataConIds -- ^ The Ids of the actual builder functions
494 -- Can get the tag from the TyCon
496 mkDataCon name declared_infix
497 arg_stricts -- Must match orig_arg_tys 1-1
501 orig_arg_tys orig_res_ty rep_tycon
503 -- Warning: mkDataCon is not a good place to check invariants.
504 -- If the programmer writes the wrong result type in the decl, thus:
505 -- data T a where { MkT :: S }
506 -- then it's possible that the univ_tvs may hit an assertion failure
507 -- if you pull on univ_tvs. This case is checked by checkValidDataCon,
508 -- so the error is detected properly... it's just that asaertions here
509 -- are a little dodgy.
511 = -- ASSERT( not (any isEqPred theta) )
512 -- We don't currently allow any equality predicates on
513 -- a data constructor (apart from the GADT ones in eq_spec)
516 is_vanilla = null ex_tvs && null eq_spec && null theta
517 con = MkData {dcName = name, dcUnique = nameUnique name,
518 dcVanilla = is_vanilla, dcInfix = declared_infix,
519 dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs,
521 dcOtherTheta = theta,
522 dcStupidTheta = stupid_theta,
523 dcOrigArgTys = orig_arg_tys, dcOrigResTy = orig_res_ty,
524 dcRepTyCon = rep_tycon,
525 dcRepArgTys = rep_arg_tys,
526 dcStrictMarks = arg_stricts,
527 dcRepStrictness = rep_arg_stricts,
528 dcFields = fields, dcTag = tag, dcRepType = ty,
531 -- Strictness marks for source-args
532 -- *after unboxing choices*,
533 -- but *including existential dictionaries*
535 -- The 'arg_stricts' passed to mkDataCon are simply those for the
536 -- source-language arguments. We add extra ones for the
537 -- dictionary arguments right here.
538 full_theta = eqSpecPreds eq_spec ++ theta
539 real_arg_tys = mkPredTys full_theta ++ orig_arg_tys
540 real_stricts = map mk_dict_strict_mark full_theta ++ arg_stricts
542 -- Representation arguments and demands
543 -- To do: eliminate duplication with MkId
544 (rep_arg_stricts, rep_arg_tys) = computeRep real_stricts real_arg_tys
546 tag = assoc "mkDataCon" (tyConDataCons rep_tycon `zip` [fIRST_TAG..]) con
547 ty = mkForAllTys univ_tvs $ mkForAllTys ex_tvs $
548 mkFunTys rep_arg_tys $
549 mkTyConApp rep_tycon (mkTyVarTys univ_tvs)
551 eqSpecPreds :: [(TyVar,Type)] -> ThetaType
552 eqSpecPreds spec = [ mkEqPred (mkTyVarTy tv, ty) | (tv,ty) <- spec ]
554 mk_dict_strict_mark :: PredType -> HsBang
555 mk_dict_strict_mark pred | isStrictPred pred = HsStrict
556 | otherwise = HsNoBang
560 -- | The 'Name' of the 'DataCon', giving it a unique, rooted identification
561 dataConName :: DataCon -> Name
564 -- | The tag used for ordering 'DataCon's
565 dataConTag :: DataCon -> ConTag
568 -- | The type constructor that we are building via this data constructor
569 dataConTyCon :: DataCon -> TyCon
570 dataConTyCon = dcRepTyCon
572 -- | The original type constructor used in the definition of this data
573 -- constructor. In case of a data family instance, that will be the family
575 dataConOrigTyCon :: DataCon -> TyCon
577 | Just (tc, _) <- tyConFamInst_maybe (dcRepTyCon dc) = tc
578 | otherwise = dcRepTyCon dc
580 -- | The representation type of the data constructor, i.e. the sort
581 -- type that will represent values of this type at runtime
582 dataConRepType :: DataCon -> Type
583 dataConRepType = dcRepType
585 -- | Should the 'DataCon' be presented infix?
586 dataConIsInfix :: DataCon -> Bool
587 dataConIsInfix = dcInfix
589 -- | The universally-quantified type variables of the constructor
590 dataConUnivTyVars :: DataCon -> [TyVar]
591 dataConUnivTyVars = dcUnivTyVars
593 -- | The existentially-quantified type variables of the constructor
594 dataConExTyVars :: DataCon -> [TyVar]
595 dataConExTyVars = dcExTyVars
597 -- | Both the universal and existentiatial type variables of the constructor
598 dataConAllTyVars :: DataCon -> [TyVar]
599 dataConAllTyVars (MkData { dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs })
602 -- | Equalities derived from the result type of the data constructor, as written
603 -- by the programmer in any GADT declaration
604 dataConEqSpec :: DataCon -> [(TyVar,Type)]
605 dataConEqSpec = dcEqSpec
607 -- | The *full* constraints on the constructor type
608 dataConTheta :: DataCon -> ThetaType
609 dataConTheta (MkData { dcEqSpec = eq_spec, dcOtherTheta = theta })
610 = eqSpecPreds eq_spec ++ theta
612 -- | Get the Id of the 'DataCon' worker: a function that is the "actual"
613 -- constructor and has no top level binding in the program. The type may
614 -- be different from the obvious one written in the source program. Panics
615 -- if there is no such 'Id' for this 'DataCon'
616 dataConWorkId :: DataCon -> Id
617 dataConWorkId dc = case dcIds dc of
618 DCIds _ wrk_id -> wrk_id
620 -- | Get the Id of the 'DataCon' wrapper: a function that wraps the "actual"
621 -- constructor so it has the type visible in the source program: c.f. 'dataConWorkId'.
622 -- Returns Nothing if there is no wrapper, which occurs for an algebraic data constructor
623 -- and also for a newtype (whose constructor is inlined compulsorily)
624 dataConWrapId_maybe :: DataCon -> Maybe Id
625 dataConWrapId_maybe dc = case dcIds dc of
626 DCIds mb_wrap _ -> mb_wrap
628 -- | Returns an Id which looks like the Haskell-source constructor by using
629 -- the wrapper if it exists (see 'dataConWrapId_maybe') and failing over to
630 -- the worker (see 'dataConWorkId')
631 dataConWrapId :: DataCon -> Id
632 dataConWrapId dc = case dcIds dc of
633 DCIds (Just wrap) _ -> wrap
634 DCIds Nothing wrk -> wrk -- worker=wrapper
636 -- | Find all the 'Id's implicitly brought into scope by the data constructor. Currently,
637 -- the union of the 'dataConWorkId' and the 'dataConWrapId'
638 dataConImplicitIds :: DataCon -> [Id]
639 dataConImplicitIds dc = case dcIds dc of
640 DCIds (Just wrap) work -> [wrap,work]
641 DCIds Nothing work -> [work]
643 -- | The labels for the fields of this particular 'DataCon'
644 dataConFieldLabels :: DataCon -> [FieldLabel]
645 dataConFieldLabels = dcFields
647 -- | Extract the type for any given labelled field of the 'DataCon'
648 dataConFieldType :: DataCon -> FieldLabel -> Type
649 dataConFieldType con label
650 = case lookup label (dcFields con `zip` dcOrigArgTys con) of
652 Nothing -> pprPanic "dataConFieldType" (ppr con <+> ppr label)
654 -- | The strictness markings decided on by the compiler. Does not include those for
655 -- existential dictionaries. The list is in one-to-one correspondence with the arity of the 'DataCon'
656 dataConStrictMarks :: DataCon -> [HsBang]
657 dataConStrictMarks = dcStrictMarks
659 -- | Strictness of evidence arguments to the wrapper function
660 dataConExStricts :: DataCon -> [HsBang]
661 -- Usually empty, so we don't bother to cache this
662 dataConExStricts dc = map mk_dict_strict_mark $ (dataConTheta dc)
664 -- | Source-level arity of the data constructor
665 dataConSourceArity :: DataCon -> Arity
666 dataConSourceArity dc = length (dcOrigArgTys dc)
668 -- | Gives the number of actual fields in the /representation/ of the
669 -- data constructor. This may be more than appear in the source code;
670 -- the extra ones are the existentially quantified dictionaries
671 dataConRepArity :: DataCon -> Int
672 dataConRepArity (MkData {dcRepArgTys = arg_tys}) = length arg_tys
674 -- | Return whether there are any argument types for this 'DataCon's original source type
675 isNullarySrcDataCon :: DataCon -> Bool
676 isNullarySrcDataCon dc = null (dcOrigArgTys dc)
678 -- | Return whether there are any argument types for this 'DataCon's runtime representation type
679 isNullaryRepDataCon :: DataCon -> Bool
680 isNullaryRepDataCon dc = null (dcRepArgTys dc)
682 dataConRepStrictness :: DataCon -> [StrictnessMark]
683 -- ^ Give the demands on the arguments of a
684 -- Core constructor application (Con dc args)
685 dataConRepStrictness dc = dcRepStrictness dc
687 -- | The \"signature\" of the 'DataCon' returns, in order:
689 -- 1) The result of 'dataConAllTyVars',
691 -- 2) All the 'ThetaType's relating to the 'DataCon' (coercion, dictionary, implicit
692 -- parameter - whatever)
694 -- 3) The type arguments to the constructor
696 -- 4) The /original/ result type of the 'DataCon'
697 dataConSig :: DataCon -> ([TyVar], ThetaType, [Type], Type)
698 dataConSig (MkData {dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs,
699 dcEqSpec = eq_spec, dcOtherTheta = theta,
700 dcOrigArgTys = arg_tys, dcOrigResTy = res_ty})
701 = (univ_tvs ++ ex_tvs, eqSpecPreds eq_spec ++ theta, arg_tys, res_ty)
703 -- | The \"full signature\" of the 'DataCon' returns, in order:
705 -- 1) The result of 'dataConUnivTyVars'
707 -- 2) The result of 'dataConExTyVars'
709 -- 3) The result of 'dataConEqSpec'
711 -- 4) The result of 'dataConDictTheta'
713 -- 5) The original argument types to the 'DataCon' (i.e. before
714 -- any change of the representation of the type)
716 -- 6) The original result type of the 'DataCon'
717 dataConFullSig :: DataCon
718 -> ([TyVar], [TyVar], [(TyVar,Type)], ThetaType, [Type], Type)
719 dataConFullSig (MkData {dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs,
720 dcEqSpec = eq_spec, dcOtherTheta = theta,
721 dcOrigArgTys = arg_tys, dcOrigResTy = res_ty})
722 = (univ_tvs, ex_tvs, eq_spec, theta, arg_tys, res_ty)
724 dataConOrigResTy :: DataCon -> Type
725 dataConOrigResTy dc = dcOrigResTy dc
727 -- | The \"stupid theta\" of the 'DataCon', such as @data Eq a@ in:
729 -- > data Eq a => T a = ...
730 dataConStupidTheta :: DataCon -> ThetaType
731 dataConStupidTheta dc = dcStupidTheta dc
733 dataConUserType :: DataCon -> Type
734 -- ^ The user-declared type of the data constructor
735 -- in the nice-to-read form:
737 -- > T :: forall a b. a -> b -> T [a]
741 -- > T :: forall a c. forall b. (c~[a]) => a -> b -> T c
743 -- NB: If the constructor is part of a data instance, the result type
744 -- mentions the family tycon, not the internal one.
745 dataConUserType (MkData { dcUnivTyVars = univ_tvs,
746 dcExTyVars = ex_tvs, dcEqSpec = eq_spec,
747 dcOtherTheta = theta, dcOrigArgTys = arg_tys,
748 dcOrigResTy = res_ty })
749 = mkForAllTys ((univ_tvs `minusList` map fst eq_spec) ++ ex_tvs) $
750 mkFunTys (mkPredTys theta) $
754 -- | Finds the instantiated types of the arguments required to construct a 'DataCon' representation
755 -- NB: these INCLUDE any dictionary args
756 -- but EXCLUDE the data-declaration context, which is discarded
757 -- It's all post-flattening etc; this is a representation type
758 dataConInstArgTys :: DataCon -- ^ A datacon with no existentials or equality constraints
759 -- However, it can have a dcTheta (notably it can be a
760 -- class dictionary, with superclasses)
761 -> [Type] -- ^ Instantiated at these types
763 dataConInstArgTys dc@(MkData {dcRepArgTys = rep_arg_tys,
764 dcUnivTyVars = univ_tvs, dcEqSpec = eq_spec,
765 dcExTyVars = ex_tvs}) inst_tys
766 = ASSERT2 ( length univ_tvs == length inst_tys
767 , ptext (sLit "dataConInstArgTys") <+> ppr dc $$ ppr univ_tvs $$ ppr inst_tys)
768 ASSERT2 ( null ex_tvs && null eq_spec, ppr dc )
769 map (substTyWith univ_tvs inst_tys) rep_arg_tys
771 -- | Returns just the instantiated /value/ argument types of a 'DataCon',
772 -- (excluding dictionary args)
773 dataConInstOrigArgTys
774 :: DataCon -- Works for any DataCon
775 -> [Type] -- Includes existential tyvar args, but NOT
776 -- equality constraints or dicts
778 -- For vanilla datacons, it's all quite straightforward
779 -- But for the call in MatchCon, we really do want just the value args
780 dataConInstOrigArgTys dc@(MkData {dcOrigArgTys = arg_tys,
781 dcUnivTyVars = univ_tvs,
782 dcExTyVars = ex_tvs}) inst_tys
783 = ASSERT2( length tyvars == length inst_tys
784 , ptext (sLit "dataConInstOrigArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys )
785 map (substTyWith tyvars inst_tys) arg_tys
787 tyvars = univ_tvs ++ ex_tvs
791 -- | Returns the argument types of the wrapper, excluding all dictionary arguments
792 -- and without substituting for any type variables
793 dataConOrigArgTys :: DataCon -> [Type]
794 dataConOrigArgTys dc = dcOrigArgTys dc
796 -- | Returns the arg types of the worker, including all dictionaries, after any
797 -- flattening has been done and without substituting for any type variables
798 dataConRepArgTys :: DataCon -> [Type]
799 dataConRepArgTys dc = dcRepArgTys dc
803 -- | The string @package:module.name@ identifying a constructor, which is attached
804 -- to its info table and used by the GHCi debugger and the heap profiler
805 dataConIdentity :: DataCon -> [Word8]
806 -- We want this string to be UTF-8, so we get the bytes directly from the FastStrings.
807 dataConIdentity dc = bytesFS (packageIdFS (modulePackageId mod)) ++
808 fromIntegral (ord ':') : bytesFS (moduleNameFS (moduleName mod)) ++
809 fromIntegral (ord '.') : bytesFS (occNameFS (nameOccName name))
810 where name = dataConName dc
811 mod = ASSERT( isExternalName name ) nameModule name
815 isTupleCon :: DataCon -> Bool
816 isTupleCon (MkData {dcRepTyCon = tc}) = isTupleTyCon tc
818 isUnboxedTupleCon :: DataCon -> Bool
819 isUnboxedTupleCon (MkData {dcRepTyCon = tc}) = isUnboxedTupleTyCon tc
821 -- | Vanilla 'DataCon's are those that are nice boring Haskell 98 constructors
822 isVanillaDataCon :: DataCon -> Bool
823 isVanillaDataCon dc = dcVanilla dc
827 classDataCon :: Class -> DataCon
828 classDataCon clas = case tyConDataCons (classTyCon clas) of
829 (dict_constr:no_more) -> ASSERT( null no_more ) dict_constr
830 [] -> panic "classDataCon"
834 dataConCannotMatch :: [Type] -> DataCon -> Bool
835 -- Returns True iff the data con *definitely cannot* match a
836 -- scrutinee of type (T tys)
837 -- where T is the type constructor for the data con
838 -- NB: look at *all* equality constraints, not only those
839 -- in dataConEqSpec; see Trac #5168
840 dataConCannotMatch tys con
841 | null theta = False -- Common
842 | all isTyVarTy tys = False -- Also common
844 = typesCantMatch [(Type.substTy subst ty1, Type.substTy subst ty2)
845 | EqPred ty1 ty2 <- theta ]
847 dc_tvs = dataConUnivTyVars con
848 theta = dataConTheta con
849 subst = zipTopTvSubst dc_tvs tys
852 %************************************************************************
854 \subsection{Splitting products}
856 %************************************************************************
859 -- | Extract the type constructor, type argument, data constructor and it's
860 -- /representation/ argument types from a type if it is a product type.
862 -- Precisely, we return @Just@ for any type that is all of:
864 -- * Concrete (i.e. constructors visible)
866 -- * Single-constructor
868 -- * Not existentially quantified
870 -- Whether the type is a @data@ type or a @newtype@
871 splitProductType_maybe
872 :: Type -- ^ A product type, perhaps
873 -> Maybe (TyCon, -- The type constructor
874 [Type], -- Type args of the tycon
875 DataCon, -- The data constructor
876 [Type]) -- Its /representation/ arg types
878 -- Rejecing existentials is conservative. Maybe some things
879 -- could be made to work with them, but I'm not going to sweat
880 -- it through till someone finds it's important.
882 splitProductType_maybe ty
883 = case splitTyConApp_maybe ty of
885 | isProductTyCon tycon -- Includes check for non-existential,
886 -- and for constructors visible
887 -> Just (tycon, ty_args, data_con, dataConInstArgTys data_con ty_args)
889 data_con = ASSERT( not (null (tyConDataCons tycon)) )
890 head (tyConDataCons tycon)
893 -- | As 'splitProductType_maybe', but panics if the 'Type' is not a product type
894 splitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
895 splitProductType str ty
896 = case splitProductType_maybe ty of
898 Nothing -> pprPanic (str ++ ": not a product") (pprType ty)
901 -- | As 'splitProductType_maybe', but in turn instantiates the 'TyCon' returned
902 -- and hence recursively tries to unpack it as far as it able to
903 deepSplitProductType_maybe :: Type -> Maybe (TyCon, [Type], DataCon, [Type])
904 deepSplitProductType_maybe ty
905 = do { (res@(tycon, tycon_args, _, _)) <- splitProductType_maybe ty
907 | Just (ty', _co) <- instNewTyCon_maybe tycon tycon_args
908 , not (isRecursiveTyCon tycon)
909 = deepSplitProductType_maybe ty' -- Ignore the coercion?
910 | isNewTyCon tycon = Nothing -- cannot unbox through recursive
911 -- newtypes nor through families
912 | otherwise = Just res}
916 -- | As 'deepSplitProductType_maybe', but panics if the 'Type' is not a product type
917 deepSplitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
918 deepSplitProductType str ty
919 = case deepSplitProductType_maybe ty of
921 Nothing -> pprPanic (str ++ ": not a product") (pprType ty)
923 -- | Compute the representation type strictness and type suitable for a 'DataCon'
924 computeRep :: [HsBang] -- ^ Original argument strictness
925 -> [Type] -- ^ Original argument types
926 -> ([StrictnessMark], -- Representation arg strictness
929 computeRep stricts tys
930 = unzip $ concat $ zipWithEqual "computeRep" unbox stricts tys
932 unbox HsNoBang ty = [(NotMarkedStrict, ty)]
933 unbox HsStrict ty = [(MarkedStrict, ty)]
934 unbox HsUnpackFailed ty = [(MarkedStrict, ty)]
935 unbox HsUnpack ty = zipEqual "computeRep" (dataConRepStrictness arg_dc) arg_tys
937 (_tycon, _tycon_args, arg_dc, arg_tys)
938 = deepSplitProductType "unbox_strict_arg_ty" ty