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, dataConUserType,
19 dataConUnivTyVars, dataConExTyVars, dataConAllTyVars,
20 dataConEqSpec, eqSpecPreds, dataConEqTheta, dataConDictTheta, dataConStupidTheta,
21 dataConInstArgTys, dataConOrigArgTys, dataConOrigResTy,
22 dataConInstOrigArgTys, dataConInstOrigDictsAndArgTys,
24 dataConFieldLabels, dataConFieldType,
25 dataConStrictMarks, dataConExStricts,
26 dataConSourceArity, dataConRepArity,
28 dataConWorkId, dataConWrapId, dataConWrapId_maybe, dataConImplicitIds,
31 -- ** Predicates on DataCons
32 isNullarySrcDataCon, isNullaryRepDataCon, isTupleCon, isUnboxedTupleCon,
33 isVanillaDataCon, classDataCon,
35 -- * Splitting product types
36 splitProductType_maybe, splitProductType, deepSplitProductType,
37 deepSplitProductType_maybe
40 #include "HsVersions.h"
59 import Data.List ( partition )
63 Data constructor representation
64 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
65 Consider the following Haskell data type declaration
67 data T = T !Int ![Int]
69 Using the strictness annotations, GHC will represent this as
73 That is, the Int has been unboxed. Furthermore, the Haskell source construction
83 That is, the first argument is unboxed, and the second is evaluated. Finally,
84 pattern matching is translated too:
86 case e of { T a b -> ... }
90 case e of { T a' b -> let a = I# a' in ... }
92 To keep ourselves sane, we name the different versions of the data constructor
93 differently, as follows.
96 Note [Data Constructor Naming]
97 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
98 Each data constructor C has two, and possibly up to four, Names associated with it:
100 OccName Name space Name of
101 ---------------------------------------------------------------------------
102 * The "data con itself" C DataName DataCon
103 * The "worker data con" C VarName Id (the worker)
104 * The "wrapper data con" \$WC VarName Id (the wrapper)
105 * The "newtype coercion" :CoT TcClsName TyCon
107 EVERY data constructor (incl for newtypes) has the former two (the
108 data con itself, and its worker. But only some data constructors have a
109 wrapper (see Note [The need for a wrapper]).
111 Each of these three has a distinct Unique. The "data con itself" name
112 appears in the output of the renamer, and names the Haskell-source
113 data constructor. The type checker translates it into either the wrapper Id
114 (if it exists) or worker Id (otherwise).
116 The data con has one or two Ids associated with it:
118 The "worker Id", is the actual data constructor.
119 * Every data constructor (newtype or data type) has a worker
121 * The worker is very like a primop, in that it has no binding.
123 * For a *data* type, the worker *is* the data constructor;
126 * For a *newtype*, the worker has a compulsory unfolding which
129 The worker for MkT has unfolding
130 \\(x:Int). x `cast` sym CoT
131 Here CoT is the type constructor, witnessing the FC axiom
134 The "wrapper Id", \$WC, goes as follows
136 * Its type is exactly what it looks like in the source program.
138 * It is an ordinary function, and it gets a top-level binding
139 like any other function.
141 * The wrapper Id isn't generated for a data type if there is
142 nothing for the wrapper to do. That is, if its defn would be
145 Note [The need for a wrapper]
146 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
147 Why might the wrapper have anything to do? Two reasons:
149 * Unboxing strict fields (with -funbox-strict-fields)
150 data T = MkT !(Int,Int)
151 \$wMkT :: (Int,Int) -> T
152 \$wMkT (x,y) = MkT x y
153 Notice that the worker has two fields where the wapper has
154 just one. That is, the worker has type
155 MkT :: Int -> Int -> T
157 * Equality constraints for GADTs
158 data T a where { MkT :: a -> T [a] }
160 The worker gets a type with explicit equality
162 MkT :: forall a b. (a=[b]) => b -> T a
164 The wrapper has the programmer-specified type:
166 \$wMkT a x = MkT [a] a [a] x
167 The third argument is a coerion
170 INVARIANT: the dictionary constructor for a class
174 A note about the stupid context
175 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
176 Data types can have a context:
178 data (Eq a, Ord b) => T a b = T1 a b | T2 a
180 and that makes the constructors have a context too
181 (notice that T2's context is "thinned"):
183 T1 :: (Eq a, Ord b) => a -> b -> T a b
184 T2 :: (Eq a) => a -> T a b
186 Furthermore, this context pops up when pattern matching
187 (though GHC hasn't implemented this, but it is in H98, and
188 I've fixed GHC so that it now does):
192 f :: Eq a => T a b -> a
194 I say the context is "stupid" because the dictionaries passed
195 are immediately discarded -- they do nothing and have no benefit.
196 It's a flaw in the language.
198 Up to now [March 2002] I have put this stupid context into the
199 type of the "wrapper" constructors functions, T1 and T2, but
200 that turned out to be jolly inconvenient for generics, and
201 record update, and other functions that build values of type T
202 (because they don't have suitable dictionaries available).
204 So now I've taken the stupid context out. I simply deal with
205 it separately in the type checker on occurrences of a
206 constructor, either in an expression or in a pattern.
208 [May 2003: actually I think this decision could evasily be
209 reversed now, and probably should be. Generics could be
210 disabled for types with a stupid context; record updates now
211 (H98) needs the context too; etc. It's an unforced change, so
212 I'm leaving it for now --- but it does seem odd that the
213 wrapper doesn't include the stupid context.]
215 [July 04] With the advent of generalised data types, it's less obvious
216 what the "stupid context" is. Consider
217 C :: forall a. Ord a => a -> a -> T (Foo a)
218 Does the C constructor in Core contain the Ord dictionary? Yes, it must:
223 C a (d:Ord a) (p:a) (q:a) -> compare d p q
225 Note that (Foo a) might not be an instance of Ord.
227 %************************************************************************
229 \subsection{Data constructors}
231 %************************************************************************
234 -- | A data constructor
237 dcName :: Name, -- This is the name of the *source data con*
238 -- (see "Note [Data Constructor Naming]" above)
239 dcUnique :: Unique, -- Cached from Name
240 dcTag :: ConTag, -- ^ Tag, used for ordering 'DataCon's
244 -- *** As declared by the user
246 -- MkT :: forall x y. (x~y,Ord x) => x -> y -> T (x,y)
248 -- *** As represented internally
250 -- MkT :: forall a. forall x y. (a:=:(x,y),x~y,Ord x) => x -> y -> T a
252 -- The next six fields express the type of the constructor, in pieces
255 -- dcUnivTyVars = [a]
256 -- dcExTyVars = [x,y]
257 -- dcEqSpec = [a:=:(x,y)]
259 -- dcDictTheta = [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 = dcEqTheta = dcDictTheta = []
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
274 -- INVARIANT: length matches arity of the dcRepTyCon
276 dcExTyVars :: [TyVar], -- Existentially-quantified type vars
277 -- In general, the dcUnivTyVars are NOT NECESSARILY THE SAME AS THE TYVARS
278 -- FOR THE PARENT TyCon. With GADTs the data con might not even have
279 -- the same number of type variables.
280 -- [This is a change (Oct05): previously, vanilla datacons guaranteed to
281 -- have the same type variables as their parent TyCon, but that seems ugly.]
283 -- INVARIANT: the UnivTyVars and ExTyVars all have distinct OccNames
284 -- Reason: less confusing, and easier to generate IfaceSyn
286 dcEqSpec :: [(TyVar,Type)], -- Equalities derived from the result type,
287 -- _as written by the programmer_
288 -- This field allows us to move conveniently between the two ways
289 -- of representing a GADT constructor's type:
290 -- MkT :: forall a b. (a :=: [b]) => b -> T a
291 -- MkT :: forall b. b -> T [b]
292 -- Each equality is of the form (a :=: ty), where 'a' is one of
293 -- the universally quantified type variables
295 -- The next two fields give the type context of the data constructor
296 -- (aside from the GADT constraints,
297 -- which are given by the dcExpSpec)
298 -- In GADT form, this is *exactly* what the programmer writes, even if
299 -- the context constrains only universally quantified variables
300 -- MkT :: forall a b. (a ~ b, Ord b) => a -> T a b
301 dcEqTheta :: ThetaType, -- The *equational* constraints
302 dcDictTheta :: ThetaType, -- The *type-class and implicit-param* constraints
304 dcStupidTheta :: ThetaType, -- The context of the data type declaration
305 -- data Eq a => T a = ...
306 -- or, rather, a "thinned" version thereof
307 -- "Thinned", because the Report says
308 -- to eliminate any constraints that don't mention
309 -- tyvars free in the arg types for this constructor
311 -- INVARIANT: the free tyvars of dcStupidTheta are a subset of dcUnivTyVars
312 -- Reason: dcStupidTeta is gotten by thinning the stupid theta from the tycon
314 -- "Stupid", because the dictionaries aren't used for anything.
315 -- Indeed, [as of March 02] they are no longer in the type of
316 -- the wrapper Id, because that makes it harder to use the wrap-id
317 -- to rebuild values after record selection or in generics.
319 dcOrigArgTys :: [Type], -- Original argument types
320 -- (before unboxing and flattening of strict fields)
321 dcOrigResTy :: Type, -- Original result type
322 -- NB: for a data instance, the original user result type may
323 -- differ from the DataCon's representation TyCon. Example
324 -- data instance T [a] where MkT :: a -> T [a]
325 -- The OrigResTy is T [a], but the dcRepTyCon might be :T123
327 -- Now the strictness annotations and field labels of the constructor
328 dcStrictMarks :: [StrictnessMark],
329 -- Strictness annotations as decided by the compiler.
330 -- Does *not* include the existential dictionaries
331 -- length = dataConSourceArity dataCon
333 dcFields :: [FieldLabel],
334 -- Field labels for this constructor, in the
335 -- same order as the dcOrigArgTys;
336 -- length = 0 (if not a record) or dataConSourceArity.
338 -- Constructor representation
339 dcRepArgTys :: [Type], -- Final, representation argument types,
340 -- after unboxing and flattening,
341 -- and *including* existential dictionaries
343 dcRepStrictness :: [StrictnessMark], -- One for each *representation* argument
344 -- See also Note [Data-con worker strictness] in MkId.lhs
346 -- Result type of constructor is T t1..tn
347 dcRepTyCon :: TyCon, -- Result tycon, T
349 dcRepType :: Type, -- Type of the constructor
350 -- forall a x y. (a:=:(x,y), x~y, Ord x) =>
352 -- (this is *not* of the constructor wrapper Id:
353 -- see Note [Data con representation] below)
354 -- Notice that the existential type parameters come *second*.
355 -- Reason: in a case expression we may find:
356 -- case (e :: T t) of
357 -- MkT x y co1 co2 (d:Ord x) (v:r) (w:F s) -> ...
358 -- It's convenient to apply the rep-type of MkT to 't', to get
359 -- forall x y. (t:=:(x,y), x~y, Ord x) => x -> y -> T t
360 -- and use that to check the pattern. Mind you, this is really only
364 -- The curried worker function that corresponds to the constructor:
365 -- It doesn't have an unfolding; the code generator saturates these Ids
366 -- and allocates a real constructor when it finds one.
368 -- An entirely separate wrapper function is built in TcTyDecls
371 dcInfix :: Bool -- True <=> declared infix
372 -- Used for Template Haskell and 'deriving' only
373 -- The actual fixity is stored elsewhere
376 -- | Contains the Ids of the data constructor functions
378 = DCIds (Maybe Id) Id -- Algebraic data types always have a worker, and
379 -- may or may not have a wrapper, depending on whether
380 -- the wrapper does anything. Newtypes just have a worker
382 -- _Neither_ the worker _nor_ the wrapper take the dcStupidTheta dicts as arguments
384 -- The wrapper takes dcOrigArgTys as its arguments
385 -- The worker takes dcRepArgTys as its arguments
386 -- If the worker is absent, dcRepArgTys is the same as dcOrigArgTys
388 -- The 'Nothing' case of DCIds is important
389 -- Not only is this efficient,
390 -- but it also ensures that the wrapper is replaced
391 -- by the worker (because it *is* the worker)
392 -- even when there are no args. E.g. in
394 -- the (:) *is* the worker.
395 -- This is really important in rule matching,
396 -- (We could match on the wrappers,
397 -- but that makes it less likely that rules will match
398 -- when we bring bits of unfoldings together.)
400 -- | Type of the tags associated with each constructor possibility
404 -- ^ Tags are allocated from here for real constructors
408 Note [Data con representation]
409 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
410 The dcRepType field contains the type of the representation of a contructor
411 This may differ from the type of the contructor *Id* (built
412 by MkId.mkDataConId) for two reasons:
413 a) the constructor Id may be overloaded, but the dictionary isn't stored
414 e.g. data Eq a => T a = MkT a a
416 b) the constructor may store an unboxed version of a strict field.
418 Here's an example illustrating both:
419 data Ord a => T a = MkT Int! a
421 T :: Ord a => Int -> a -> T a
423 Trep :: Int# -> a -> T a
424 Actually, the unboxed part isn't implemented yet!
427 %************************************************************************
429 \subsection{Instances}
431 %************************************************************************
434 instance Eq DataCon where
435 a == b = getUnique a == getUnique b
436 a /= b = getUnique a /= getUnique b
438 instance Ord DataCon where
439 a <= b = getUnique a <= getUnique b
440 a < b = getUnique a < getUnique b
441 a >= b = getUnique a >= getUnique b
442 a > b = getUnique a > getUnique b
443 compare a b = getUnique a `compare` getUnique b
445 instance Uniquable DataCon where
448 instance NamedThing DataCon where
451 instance Outputable DataCon where
452 ppr con = ppr (dataConName con)
454 instance Show DataCon where
455 showsPrec p con = showsPrecSDoc p (ppr con)
459 %************************************************************************
461 \subsection{Construction}
463 %************************************************************************
466 -- | Build a new data constructor
468 -> Bool -- ^ Is the constructor declared infix?
469 -> [StrictnessMark] -- ^ Strictness annotations written in the source file
470 -> [FieldLabel] -- ^ Field labels for the constructor, if it is a record, otherwise empty
471 -> [TyVar] -- ^ Universally quantified type variables
472 -> [TyVar] -- ^ Existentially quantified type variables
473 -> [(TyVar,Type)] -- ^ GADT equalities
474 -> ThetaType -- ^ Theta-type occuring before the arguments proper
475 -> [Type] -- ^ Argument types
476 -> TyCon -- ^ Type constructor we are for
477 -> ThetaType -- ^ The "stupid theta", context of the data declaration e.g. @data Eq a => T a ...@
478 -> DataConIds -- ^ The Ids of the actual builder functions
480 -- Can get the tag from the TyCon
482 mkDataCon name declared_infix
483 arg_stricts -- Must match orig_arg_tys 1-1
489 -- Warning: mkDataCon is not a good place to check invariants.
490 -- If the programmer writes the wrong result type in the decl, thus:
491 -- data T a where { MkT :: S }
492 -- then it's possible that the univ_tvs may hit an assertion failure
493 -- if you pull on univ_tvs. This case is checked by checkValidDataCon,
494 -- so the error is detected properly... it's just that asaertions here
495 -- are a little dodgy.
497 = -- ASSERT( not (any isEqPred theta) )
498 -- We don't currently allow any equality predicates on
499 -- a data constructor (apart from the GADT ones in eq_spec)
502 is_vanilla = null ex_tvs && null eq_spec && null theta
503 con = MkData {dcName = name, dcUnique = nameUnique name,
504 dcVanilla = is_vanilla, dcInfix = declared_infix,
505 dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs,
507 dcStupidTheta = stupid_theta,
508 dcEqTheta = eq_theta, dcDictTheta = dict_theta,
509 dcOrigArgTys = orig_arg_tys, dcOrigResTy = orig_res_ty,
511 dcRepArgTys = rep_arg_tys,
512 dcStrictMarks = arg_stricts,
513 dcRepStrictness = rep_arg_stricts,
514 dcFields = fields, dcTag = tag, dcRepType = ty,
517 -- Strictness marks for source-args
518 -- *after unboxing choices*,
519 -- but *including existential dictionaries*
521 -- The 'arg_stricts' passed to mkDataCon are simply those for the
522 -- source-language arguments. We add extra ones for the
523 -- dictionary arguments right here.
524 (eq_theta,dict_theta) = partition isEqPred theta
525 dict_tys = mkPredTys dict_theta
526 real_arg_tys = dict_tys ++ orig_arg_tys
527 real_stricts = map mk_dict_strict_mark dict_theta ++ arg_stricts
530 -- data instance T (b,c) where
531 -- TI :: forall e. e -> T (e,e)
533 -- The representation tycon looks like this:
534 -- data :R7T b c where
535 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
536 -- In this case orig_res_ty = T (e,e)
537 orig_res_ty = mkFamilyTyConApp tycon (substTyVars (mkTopTvSubst eq_spec) univ_tvs)
539 -- Representation arguments and demands
540 -- To do: eliminate duplication with MkId
541 (rep_arg_stricts, rep_arg_tys) = computeRep real_stricts real_arg_tys
543 tag = assoc "mkDataCon" (tyConDataCons tycon `zip` [fIRST_TAG..]) con
544 ty = mkForAllTys univ_tvs $ mkForAllTys ex_tvs $
545 mkFunTys (mkPredTys (eqSpecPreds eq_spec)) $
546 mkFunTys (mkPredTys eq_theta) $
547 -- NB: the dict args are already in rep_arg_tys
548 -- because they might be flattened..
549 -- but the equality predicates are not
550 mkFunTys rep_arg_tys $
551 mkTyConApp tycon (mkTyVarTys univ_tvs)
553 eqSpecPreds :: [(TyVar,Type)] -> ThetaType
554 eqSpecPreds spec = [ mkEqPred (mkTyVarTy tv, ty) | (tv,ty) <- spec ]
556 mk_dict_strict_mark :: PredType -> StrictnessMark
557 mk_dict_strict_mark pred | isStrictPred pred = MarkedStrict
558 | otherwise = NotMarkedStrict
562 -- | The 'Name' of the 'DataCon', giving it a unique, rooted identification
563 dataConName :: DataCon -> Name
566 -- | The tag used for ordering 'DataCon's
567 dataConTag :: DataCon -> ConTag
570 -- | The type constructor that we are building via this data constructor
571 dataConTyCon :: DataCon -> TyCon
572 dataConTyCon = dcRepTyCon
574 -- | The representation type of the data constructor, i.e. the sort
575 -- type that will represent values of this type at runtime
576 dataConRepType :: DataCon -> Type
577 dataConRepType = dcRepType
579 -- | Should the 'DataCon' be presented infix?
580 dataConIsInfix :: DataCon -> Bool
581 dataConIsInfix = dcInfix
583 -- | The universally-quantified type variables of the constructor
584 dataConUnivTyVars :: DataCon -> [TyVar]
585 dataConUnivTyVars = dcUnivTyVars
587 -- | The existentially-quantified type variables of the constructor
588 dataConExTyVars :: DataCon -> [TyVar]
589 dataConExTyVars = dcExTyVars
591 -- | Both the universal and existentiatial type variables of the constructor
592 dataConAllTyVars :: DataCon -> [TyVar]
593 dataConAllTyVars (MkData { dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs })
596 -- | Equalities derived from the result type of the data constructor, as written
597 -- by the programmer in any GADT declaration
598 dataConEqSpec :: DataCon -> [(TyVar,Type)]
599 dataConEqSpec = dcEqSpec
601 -- | The equational constraints on the data constructor type
602 dataConEqTheta :: DataCon -> ThetaType
603 dataConEqTheta = dcEqTheta
605 -- | The type class and implicit parameter contsraints on the data constructor type
606 dataConDictTheta :: DataCon -> ThetaType
607 dataConDictTheta = dcDictTheta
609 -- | Get the Id of the 'DataCon' worker: a function that is the "actual"
610 -- constructor and has no top level binding in the program. The type may
611 -- be different from the obvious one written in the source program. Panics
612 -- if there is no such 'Id' for this 'DataCon'
613 dataConWorkId :: DataCon -> Id
614 dataConWorkId dc = case dcIds dc of
615 DCIds _ wrk_id -> wrk_id
617 -- | Get the Id of the 'DataCon' wrapper: a function that wraps the "actual"
618 -- constructor so it has the type visible in the source program: c.f. 'dataConWorkId'.
619 -- Returns Nothing if there is no wrapper, which occurs for an algebraic data constructor
620 -- and also for a newtype (whose constructor is inlined compulsorily)
621 dataConWrapId_maybe :: DataCon -> Maybe Id
622 dataConWrapId_maybe dc = case dcIds dc of
623 DCIds mb_wrap _ -> mb_wrap
625 -- | Returns an Id which looks like the Haskell-source constructor by using
626 -- the wrapper if it exists (see 'dataConWrapId_maybe') and failing over to
627 -- the worker (see 'dataConWorkId')
628 dataConWrapId :: DataCon -> Id
629 dataConWrapId dc = case dcIds dc of
630 DCIds (Just wrap) _ -> wrap
631 DCIds Nothing wrk -> wrk -- worker=wrapper
633 -- | Find all the 'Id's implicitly brought into scope by the data constructor. Currently,
634 -- the union of the 'dataConWorkId' and the 'dataConWrapId'
635 dataConImplicitIds :: DataCon -> [Id]
636 dataConImplicitIds dc = case dcIds dc of
637 DCIds (Just wrap) work -> [wrap,work]
638 DCIds Nothing work -> [work]
640 -- | The labels for the fields of this particular 'DataCon'
641 dataConFieldLabels :: DataCon -> [FieldLabel]
642 dataConFieldLabels = dcFields
644 -- | Extract the type for any given labelled field of the 'DataCon'
645 dataConFieldType :: DataCon -> FieldLabel -> Type
646 dataConFieldType con label = expectJust "unexpected label" $
647 lookup label (dcFields con `zip` dcOrigArgTys con)
649 -- | The strictness markings decided on by the compiler. Does not include those for
650 -- existential dictionaries. The list is in one-to-one correspondence with the arity of the 'DataCon'
651 dataConStrictMarks :: DataCon -> [StrictnessMark]
652 dataConStrictMarks = dcStrictMarks
654 -- | Strictness of /existential/ arguments only
655 dataConExStricts :: DataCon -> [StrictnessMark]
656 -- Usually empty, so we don't bother to cache this
657 dataConExStricts dc = map mk_dict_strict_mark $ dcDictTheta dc
659 -- | Source-level arity of the data constructor
660 dataConSourceArity :: DataCon -> Arity
661 dataConSourceArity dc = length (dcOrigArgTys dc)
663 -- | Gives the number of actual fields in the /representation/ of the
664 -- data constructor. This may be more than appear in the source code;
665 -- the extra ones are the existentially quantified dictionaries
666 dataConRepArity :: DataCon -> Int
667 dataConRepArity (MkData {dcRepArgTys = arg_tys}) = length arg_tys
669 -- | Return whether there are any argument types for this 'DataCon's original source type
670 isNullarySrcDataCon :: DataCon -> Bool
671 isNullarySrcDataCon dc = null (dcOrigArgTys dc)
673 -- | Return whether there are any argument types for this 'DataCon's runtime representation type
674 isNullaryRepDataCon :: DataCon -> Bool
675 isNullaryRepDataCon dc = null (dcRepArgTys dc)
677 dataConRepStrictness :: DataCon -> [StrictnessMark]
678 -- ^ Give the demands on the arguments of a
679 -- Core constructor application (Con dc args)
680 dataConRepStrictness dc = dcRepStrictness dc
682 -- | The \"signature\" of the 'DataCon' returns, in order:
684 -- 1) The result of 'dataConAllTyVars',
686 -- 2) All the 'ThetaType's relating to the 'DataCon' (coercion, dictionary, implicit
687 -- parameter - whatever)
689 -- 3) The type arguments to the constructor
691 -- 4) The /original/ result type of the 'DataCon'
692 dataConSig :: DataCon -> ([TyVar], ThetaType, [Type], Type)
693 dataConSig (MkData {dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs, dcEqSpec = eq_spec,
694 dcEqTheta = eq_theta, dcDictTheta = dict_theta, dcOrigArgTys = arg_tys, dcOrigResTy = res_ty})
695 = (univ_tvs ++ ex_tvs, eqSpecPreds eq_spec ++ eq_theta ++ dict_theta, arg_tys, res_ty)
697 -- | The \"full signature\" of the 'DataCon' returns, in order:
699 -- 1) The result of 'dataConUnivTyVars'
701 -- 2) The result of 'dataConExTyVars'
703 -- 3) The result of 'dataConEqSpec'
705 -- 4) The result of 'dataConDictTheta'
707 -- 5) The original argument types to the 'DataCon' (i.e. before any change of the representation of the type)
709 -- 6) The original result type of the 'DataCon'
710 dataConFullSig :: DataCon
711 -> ([TyVar], [TyVar], [(TyVar,Type)], ThetaType, ThetaType, [Type], Type)
712 dataConFullSig (MkData {dcUnivTyVars = univ_tvs, dcExTyVars = ex_tvs, dcEqSpec = eq_spec,
713 dcEqTheta = eq_theta, dcDictTheta = dict_theta, dcOrigArgTys = arg_tys, dcOrigResTy = res_ty})
714 = (univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, res_ty)
716 dataConOrigResTy :: DataCon -> Type
717 dataConOrigResTy dc = dcOrigResTy dc
719 -- | The \"stupid theta\" of the 'DataCon', such as @data Eq a@ in:
721 -- > data Eq a => T a = ...
722 dataConStupidTheta :: DataCon -> ThetaType
723 dataConStupidTheta dc = dcStupidTheta dc
725 dataConUserType :: DataCon -> Type
726 -- ^ The user-declared type of the data constructor
727 -- in the nice-to-read form:
729 -- > T :: forall a b. a -> b -> T [a]
733 -- > T :: forall a c. forall b. (c=[a]) => a -> b -> T c
735 -- NB: If the constructor is part of a data instance, the result type
736 -- mentions the family tycon, not the internal one.
737 dataConUserType (MkData { dcUnivTyVars = univ_tvs,
738 dcExTyVars = ex_tvs, dcEqSpec = eq_spec,
739 dcEqTheta = eq_theta, dcDictTheta = dict_theta, dcOrigArgTys = arg_tys,
740 dcOrigResTy = res_ty })
741 = mkForAllTys ((univ_tvs `minusList` map fst eq_spec) ++ ex_tvs) $
742 mkFunTys (mkPredTys eq_theta) $
743 mkFunTys (mkPredTys dict_theta) $
747 -- | Finds the instantiated types of the arguments required to construct a 'DataCon' representation
748 -- NB: these INCLUDE any dictionary args
749 -- but EXCLUDE the data-declaration context, which is discarded
750 -- It's all post-flattening etc; this is a representation type
751 dataConInstArgTys :: DataCon -- ^ A datacon with no existentials or equality constraints
752 -- However, it can have a dcTheta (notably it can be a
753 -- class dictionary, with superclasses)
754 -> [Type] -- ^ Instantiated at these types
756 dataConInstArgTys dc@(MkData {dcRepArgTys = rep_arg_tys,
757 dcUnivTyVars = univ_tvs, dcEqSpec = eq_spec,
758 dcExTyVars = ex_tvs}) inst_tys
759 = ASSERT2 ( length univ_tvs == length inst_tys
760 , ptext (sLit "dataConInstArgTys") <+> ppr dc $$ ppr univ_tvs $$ ppr inst_tys)
761 ASSERT2 ( null ex_tvs && null eq_spec, ppr dc )
762 map (substTyWith univ_tvs inst_tys) rep_arg_tys
764 -- | Returns just the instantiated /value/ arguments of a 'DataCon',
765 -- as opposed to including the dictionary args as in 'dataConInstOrigDictsAndArgTys'
766 dataConInstOrigArgTys
767 :: DataCon -- Works for any DataCon
768 -> [Type] -- Includes existential tyvar args, but NOT
769 -- equality constraints or dicts
771 -- For vanilla datacons, it's all quite straightforward
772 -- But for the call in MatchCon, we really do want just the value args
773 dataConInstOrigArgTys dc@(MkData {dcOrigArgTys = arg_tys,
774 dcUnivTyVars = univ_tvs,
775 dcExTyVars = ex_tvs}) inst_tys
776 = ASSERT2( length tyvars == length inst_tys
777 , ptext (sLit "dataConInstOrigArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys )
778 map (substTyWith tyvars inst_tys) arg_tys
780 tyvars = univ_tvs ++ ex_tvs
782 -- | Returns just the instantiated dicts and /value/ arguments for a 'DataCon',
783 -- as opposed to excluding the dictionary args as in 'dataConInstOrigArgTys'
784 dataConInstOrigDictsAndArgTys
785 :: DataCon -- Works for any DataCon
786 -> [Type] -- Includes existential tyvar args, but NOT
787 -- equality constraints or dicts
789 dataConInstOrigDictsAndArgTys dc@(MkData {dcOrigArgTys = arg_tys,
791 dcUnivTyVars = univ_tvs,
792 dcExTyVars = ex_tvs}) inst_tys
793 = ASSERT2( length tyvars == length inst_tys
794 , ptext (sLit "dataConInstOrigDictsAndArgTys") <+> ppr dc $$ ppr tyvars $$ ppr inst_tys )
795 map (substTyWith tyvars inst_tys) (mkPredTys dicts ++ arg_tys)
797 tyvars = univ_tvs ++ ex_tvs
801 -- | Returns the argument types of the wrapper, excluding all dictionary arguments
802 -- and without substituting for any type variables
803 dataConOrigArgTys :: DataCon -> [Type]
804 dataConOrigArgTys dc = dcOrigArgTys dc
806 -- | Returns the arg types of the worker, including all dictionaries, after any
807 -- flattening has been done and without substituting for any type variables
808 dataConRepArgTys :: DataCon -> [Type]
809 dataConRepArgTys dc = dcRepArgTys dc
813 -- | The string @package:module.name@ identifying a constructor, which is attached
814 -- to its info table and used by the GHCi debugger and the heap profiler
815 dataConIdentity :: DataCon -> [Word8]
816 -- We want this string to be UTF-8, so we get the bytes directly from the FastStrings.
817 dataConIdentity dc = bytesFS (packageIdFS (modulePackageId mod)) ++
818 fromIntegral (ord ':') : bytesFS (moduleNameFS (moduleName mod)) ++
819 fromIntegral (ord '.') : bytesFS (occNameFS (nameOccName name))
820 where name = dataConName dc
821 mod = nameModule name
825 isTupleCon :: DataCon -> Bool
826 isTupleCon (MkData {dcRepTyCon = tc}) = isTupleTyCon tc
828 isUnboxedTupleCon :: DataCon -> Bool
829 isUnboxedTupleCon (MkData {dcRepTyCon = tc}) = isUnboxedTupleTyCon tc
831 -- | Vanilla 'DataCon's are those that are nice boring Haskell 98 constructors
832 isVanillaDataCon :: DataCon -> Bool
833 isVanillaDataCon dc = dcVanilla dc
837 classDataCon :: Class -> DataCon
838 classDataCon clas = case tyConDataCons (classTyCon clas) of
839 (dict_constr:no_more) -> ASSERT( null no_more ) dict_constr
840 [] -> panic "classDataCon"
843 %************************************************************************
845 \subsection{Splitting products}
847 %************************************************************************
850 -- | Extract the type constructor, type argument, data constructor and it's
851 -- /representation/ argument types from a type if it is a product type.
853 -- Precisely, we return @Just@ for any type that is all of:
855 -- * Concrete (i.e. constructors visible)
857 -- * Single-constructor
859 -- * Not existentially quantified
861 -- Whether the type is a @data@ type or a @newtype@
862 splitProductType_maybe
863 :: Type -- ^ A product type, perhaps
864 -> Maybe (TyCon, -- The type constructor
865 [Type], -- Type args of the tycon
866 DataCon, -- The data constructor
867 [Type]) -- Its /representation/ arg types
869 -- Rejecing existentials is conservative. Maybe some things
870 -- could be made to work with them, but I'm not going to sweat
871 -- it through till someone finds it's important.
873 splitProductType_maybe ty
874 = case splitTyConApp_maybe ty of
876 | isProductTyCon tycon -- Includes check for non-existential,
877 -- and for constructors visible
878 -> Just (tycon, ty_args, data_con, dataConInstArgTys data_con ty_args)
880 data_con = ASSERT( not (null (tyConDataCons tycon)) )
881 head (tyConDataCons tycon)
884 -- | As 'splitProductType_maybe', but panics if the 'Type' is not a product type
885 splitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
886 splitProductType str ty
887 = case splitProductType_maybe ty of
889 Nothing -> pprPanic (str ++ ": not a product") (pprType ty)
892 -- | As 'splitProductType_maybe', but in turn instantiates the 'TyCon' returned
893 -- and hence recursively tries to unpack it as far as it able to
894 deepSplitProductType_maybe :: Type -> Maybe (TyCon, [Type], DataCon, [Type])
895 deepSplitProductType_maybe ty
896 = do { (res@(tycon, tycon_args, _, _)) <- splitProductType_maybe ty
898 | Just (ty', _co) <- instNewTyCon_maybe tycon tycon_args
899 , not (isRecursiveTyCon tycon)
900 = deepSplitProductType_maybe ty' -- Ignore the coercion?
901 | isNewTyCon tycon = Nothing -- cannot unbox through recursive
902 -- newtypes nor through families
903 | otherwise = Just res}
907 -- | As 'deepSplitProductType_maybe', but panics if the 'Type' is not a product type
908 deepSplitProductType :: String -> Type -> (TyCon, [Type], DataCon, [Type])
909 deepSplitProductType str ty
910 = case deepSplitProductType_maybe ty of
912 Nothing -> pprPanic (str ++ ": not a product") (pprType ty)
914 -- | Compute the representation type strictness and type suitable for a 'DataCon'
915 computeRep :: [StrictnessMark] -- ^ Original argument strictness
916 -> [Type] -- ^ Original argument types
917 -> ([StrictnessMark], -- Representation arg strictness
920 computeRep stricts tys
921 = unzip $ concat $ zipWithEqual "computeRep" unbox stricts tys
923 unbox NotMarkedStrict ty = [(NotMarkedStrict, ty)]
924 unbox MarkedStrict ty = [(MarkedStrict, ty)]
925 unbox MarkedUnboxed ty = zipEqual "computeRep" (dataConRepStrictness arg_dc) arg_tys
927 (_tycon, _tycon_args, arg_dc, arg_tys)
928 = deepSplitProductType "unbox_strict_arg_ty" ty