2 % (c) The GRASP/AQUA Project, Glasgow University, 1998
4 \section[TypeRep]{Type - friends' interface}
9 Type(..), TyNote(..), -- Representation visible
10 PredType(..), -- to friends
12 Kind, ThetaType, -- Synonyms
17 pprType, pprParendType, pprTyThingCategory,
18 pprPred, pprTheta, pprThetaArrow, pprClassPred,
21 liftedTypeKind, unliftedTypeKind, openTypeKind,
22 argTypeKind, ubxTupleKind,
23 isLiftedTypeKindCon, isLiftedTypeKind,
24 mkArrowKind, mkArrowKinds,
26 -- Kind constructors...
27 liftedTypeKindTyCon, openTypeKindTyCon, unliftedTypeKindTyCon,
28 argTypeKindTyCon, ubxTupleKindTyCon,
31 unliftedTypeKindTyConName, openTypeKindTyConName,
32 ubxTupleKindTyConName, argTypeKindTyConName,
33 liftedTypeKindTyConName,
36 tySuperKind, coSuperKind,
37 isTySuperKind, isCoSuperKind,
38 tySuperKindTyCon, coSuperKindTyCon,
42 pprKind, pprParendKind
45 #include "HsVersions.h"
47 import {-# SOURCE #-} DataCon( DataCon, dataConName )
48 import Monad ( guard )
51 import Var ( Var, Id, TyVar, tyVarKind )
52 import VarSet ( TyVarSet )
53 import Name ( Name, NamedThing(..), BuiltInSyntax(..), mkWiredInName )
54 import OccName ( mkOccNameFS, tcName, parenSymOcc )
55 import BasicTypes ( IPName, tupleParens )
56 import TyCon ( TyCon, mkFunTyCon, tyConArity, tupleTyConBoxity, isTupleTyCon, isRecursiveTyCon, isNewTyCon, mkVoidPrimTyCon, mkSuperKindTyCon, isSuperKindTyCon, mkCoercionTyCon )
57 import Class ( Class )
60 import PrelNames ( gHC_PRIM, funTyConKey, tySuperKindTyConKey,
61 coSuperKindTyConKey, liftedTypeKindTyConKey,
62 openTypeKindTyConKey, unliftedTypeKindTyConKey,
63 ubxTupleKindTyConKey, argTypeKindTyConKey, listTyConKey,
64 parrTyConKey, hasKey, eqCoercionKindTyConKey )
68 %************************************************************************
70 \subsection{Type Classifications}
72 %************************************************************************
76 *unboxed* iff its representation is other than a pointer
77 Unboxed types are also unlifted.
79 *lifted* A type is lifted iff it has bottom as an element.
80 Closures always have lifted types: i.e. any
81 let-bound identifier in Core must have a lifted
82 type. Operationally, a lifted object is one that
85 Only lifted types may be unified with a type variable.
87 *algebraic* A type with one or more constructors, whether declared
88 with "data" or "newtype".
89 An algebraic type is one that can be deconstructed
90 with a case expression.
91 *NOT* the same as lifted types, because we also
92 include unboxed tuples in this classification.
94 *data* A type declared with "data". Also boxed tuples.
96 *primitive* iff it is a built-in type that can't be expressed
99 Currently, all primitive types are unlifted, but that's not necessarily
100 the case. (E.g. Int could be primitive.)
102 Some primitive types are unboxed, such as Int#, whereas some are boxed
103 but unlifted (such as ByteArray#). The only primitive types that we
104 classify as algebraic are the unboxed tuples.
106 examples of type classifications:
108 Type primitive boxed lifted algebraic
109 -----------------------------------------------------------------------------
111 ByteArray# Yes Yes No No
112 (# a, b #) Yes No No Yes
113 ( a, b ) No Yes Yes Yes
118 ----------------------
119 A note about newtypes
120 ----------------------
125 Then we want N to be represented as an Int, and that's what we arrange.
126 The front end of the compiler [TcType.lhs] treats N as opaque,
127 the back end treats it as transparent [Type.lhs].
129 There's a bit of a problem with recursive newtypes
131 newtype Q = MkQ (Q->Q)
133 Here the 'implicit expansion' we get from treating P and Q as transparent
134 would give rise to infinite types, which in turn makes eqType diverge.
135 Similarly splitForAllTys and splitFunTys can get into a loop.
139 * Newtypes are always represented using TyConApp.
141 * For non-recursive newtypes, P, treat P just like a type synonym after
142 type-checking is done; i.e. it's opaque during type checking (functions
143 from TcType) but transparent afterwards (functions from Type).
144 "Treat P as a type synonym" means "all functions expand NewTcApps
147 Applications of the data constructor P simply vanish:
151 * For recursive newtypes Q, treat the Q and its representation as
152 distinct right through the compiler. Applications of the data consructor
154 Q = \(x::Q->Q). coerce Q x
155 They are rare, so who cares if they are a tiny bit less efficient.
157 The typechecker (TcTyDecls) identifies enough type construtors as 'recursive'
158 to cut all loops. The other members of the loop may be marked 'non-recursive'.
161 %************************************************************************
163 \subsection{The data type}
165 %************************************************************************
173 Type -- Function is *not* a TyConApp
174 Type -- It must be another AppTy, or TyVarTy
175 -- (or NoteTy of these)
177 | TyConApp -- Application of a TyCon, including newtypes *and* synonyms
178 TyCon -- *Invariant* saturated appliations of FunTyCon and
179 -- synonyms have their own constructors, below.
180 -- However, *unsaturated* FunTyCons do appear as TyConApps.
182 [Type] -- Might not be saturated.
183 -- Even type synonyms are not necessarily saturated;
184 -- for example unsaturated type synonyms can appear as the
185 -- RHS of a type synonym.
187 | FunTy -- Special case of TyConApp: TyConApp FunTyCon [t1,t2]
191 | ForAllTy -- A polymorphic type
195 | PredTy -- The type of evidence for a type predictate
196 PredType -- Can be expanded to a representation type.
197 -- NB: A PredTy (EqPred _ _) can appear only as the kind
198 -- of a coercion variable; never as the argument or result
199 -- of a FunTy (unlike ClassP, IParam)
201 | NoteTy -- A type with a note attached
203 Type -- The expanded version
205 type Kind = Type -- Invariant: a kind is always
207 -- or TyConApp PrimTyCon [...]
208 -- or TyVar kv (during inference only)
209 -- or ForAll ... (for top-level coercions)
211 type SuperKind = Type -- Invariant: a super kind is always
212 -- TyConApp SuperKindTyCon ...
216 type CoercionKind = Kind
218 data TyNote = FTVNote TyVarSet -- The free type variables of the noted expression
221 -------------------------------------
226 represents a value whose type is the Haskell predicate p,
227 where a predicate is what occurs before the '=>' in a Haskell type.
228 It can be expanded into its representation, but:
230 * The type checker must treat it as opaque
231 * The rest of the compiler treats it as transparent
233 Consider these examples:
234 f :: (Eq a) => a -> Int
235 g :: (?x :: Int -> Int) => a -> Int
236 h :: (r\l) => {r} => {l::Int | r}
238 Here the "Eq a" and "?x :: Int -> Int" and "r\l" are all called *predicates*
239 Predicates are represented inside GHC by PredType:
243 = ClassP Class [Type] -- Class predicate
244 | IParam (IPName Name) Type -- Implicit parameter
245 | EqPred Type Type -- Equality predicate (ty1 :=: ty2)
247 type ThetaType = [PredType]
250 (We don't support TREX records yet, but the setup is designed
251 to expand to allow them.)
253 A Haskell qualified type, such as that for f,g,h above, is
255 * a FunTy for the double arrow
256 * with a PredTy as the function argument
258 The predicate really does turn into a real extra argument to the
259 function. If the argument has type (PredTy p) then the predicate p is
260 represented by evidence (a dictionary, for example, of type (predRepTy p).
263 %************************************************************************
267 %************************************************************************
269 Despite the fact that DataCon has to be imported via a hi-boot route,
270 this module seems the right place for TyThing, because it's needed for
271 funTyCon and all the types in TysPrim.
274 data TyThing = AnId Id
279 instance Outputable TyThing where
280 ppr thing = pprTyThingCategory thing <+> quotes (ppr (getName thing))
282 pprTyThingCategory :: TyThing -> SDoc
283 pprTyThingCategory (ATyCon _) = ptext SLIT("Type constructor")
284 pprTyThingCategory (AClass _) = ptext SLIT("Class")
285 pprTyThingCategory (AnId _) = ptext SLIT("Identifier")
286 pprTyThingCategory (ADataCon _) = ptext SLIT("Data constructor")
288 instance NamedThing TyThing where -- Can't put this with the type
289 getName (AnId id) = getName id -- decl, because the DataCon instance
290 getName (ATyCon tc) = getName tc -- isn't visible there
291 getName (AClass cl) = getName cl
292 getName (ADataCon dc) = dataConName dc
296 %************************************************************************
298 Wired-in type constructors
300 %************************************************************************
302 We define a few wired-in type constructors here to avoid module knots
305 --------------------------
306 -- First the TyCons...
308 funTyCon = mkFunTyCon funTyConName (mkArrowKinds [argTypeKind, openTypeKind] liftedTypeKind)
309 -- You might think that (->) should have type (?? -> ? -> *), and you'd be right
310 -- But if we do that we get kind errors when saying
311 -- instance Control.Arrow (->)
312 -- becuase the expected kind is (*->*->*). The trouble is that the
313 -- expected/actual stuff in the unifier does not go contra-variant, whereas
314 -- the kind sub-typing does. Sigh. It really only matters if you use (->) in
315 -- a prefix way, thus: (->) Int# Int#. And this is unusual.
318 tySuperKindTyCon = mkSuperKindTyCon tySuperKindTyConName
319 coSuperKindTyCon = mkSuperKindTyCon coSuperKindTyConName
321 liftedTypeKindTyCon = mkKindTyCon liftedTypeKindTyConName
322 openTypeKindTyCon = mkKindTyCon openTypeKindTyConName
323 unliftedTypeKindTyCon = mkKindTyCon unliftedTypeKindTyConName
324 ubxTupleKindTyCon = mkKindTyCon ubxTupleKindTyConName
325 argTypeKindTyCon = mkKindTyCon argTypeKindTyConName
326 eqCoercionKindTyCon =
327 mkCoercionTyCon eqCoercionKindTyConName 2 (\ _ -> coSuperKind)
329 mkKindTyCon :: Name -> TyCon
330 mkKindTyCon name = mkVoidPrimTyCon name tySuperKind 0
332 --------------------------
333 -- ... and now their names
335 tySuperKindTyConName = mkPrimTyConName FSLIT("BOX") tySuperKindTyConKey tySuperKindTyCon
336 coSuperKindTyConName = mkPrimTyConName FSLIT("COERCION") coSuperKindTyConKey coSuperKindTyCon
337 liftedTypeKindTyConName = mkPrimTyConName FSLIT("*") liftedTypeKindTyConKey liftedTypeKindTyCon
338 openTypeKindTyConName = mkPrimTyConName FSLIT("?") openTypeKindTyConKey openTypeKindTyCon
339 unliftedTypeKindTyConName = mkPrimTyConName FSLIT("#") unliftedTypeKindTyConKey unliftedTypeKindTyCon
340 ubxTupleKindTyConName = mkPrimTyConName FSLIT("(##)") ubxTupleKindTyConKey ubxTupleKindTyCon
341 argTypeKindTyConName = mkPrimTyConName FSLIT("??") argTypeKindTyConKey argTypeKindTyCon
342 funTyConName = mkPrimTyConName FSLIT("(->)") funTyConKey funTyCon
344 eqCoercionKindTyConName = mkWiredInName gHC_PRIM (mkOccNameFS tcName (FSLIT(":=:")))
345 eqCoercionKindTyConKey Nothing (ATyCon eqCoercionKindTyCon)
348 mkPrimTyConName occ key tycon = mkWiredInName gHC_PRIM (mkOccNameFS tcName occ)
350 Nothing -- No parent object
353 -- All of the super kinds and kinds are defined in Prim and use BuiltInSyntax,
354 -- because they are never in scope in the source
357 -- We also need Kinds and SuperKinds, locally and in TyCon
359 kindTyConType :: TyCon -> Type
360 kindTyConType kind = TyConApp kind []
362 liftedTypeKind = kindTyConType liftedTypeKindTyCon
363 unliftedTypeKind = kindTyConType unliftedTypeKindTyCon
364 openTypeKind = kindTyConType openTypeKindTyCon
365 argTypeKind = kindTyConType argTypeKindTyCon
366 ubxTupleKind = kindTyConType ubxTupleKindTyCon
368 mkArrowKind :: Kind -> Kind -> Kind
369 mkArrowKind k1 k2 = FunTy k1 k2
371 mkArrowKinds :: [Kind] -> Kind -> Kind
372 mkArrowKinds arg_kinds result_kind = foldr mkArrowKind result_kind arg_kinds
374 tySuperKind, coSuperKind :: SuperKind
375 tySuperKind = kindTyConType tySuperKindTyCon
376 coSuperKind = kindTyConType coSuperKindTyCon
378 isTySuperKind (NoteTy _ ty) = isTySuperKind ty
379 isTySuperKind (TyConApp kc []) = kc `hasKey` tySuperKindTyConKey
380 isTySuperKind other = False
382 isCoSuperKind (NoteTy _ ty) = isCoSuperKind ty
383 isCoSuperKind (TyConApp kc []) = kc `hasKey` coSuperKindTyConKey
384 isCoSuperKind other = False
386 isCoercionKindTyCon kc = kc `hasKey` eqCoercionKindTyConKey
390 -- lastly we need a few functions on Kinds
392 isLiftedTypeKindCon tc = tc `hasKey` liftedTypeKindTyConKey
394 isLiftedTypeKind (TyConApp tc []) = isLiftedTypeKindCon tc
395 isLiftedTypeKind other = False
402 %************************************************************************
404 \subsection{The external interface}
406 %************************************************************************
408 @pprType@ is the standard @Type@ printer; the overloaded @ppr@ function is
409 defined to use this. @pprParendType@ is the same, except it puts
410 parens around the type, except for the atomic cases. @pprParendType@
411 works just by setting the initial context precedence very high.
414 data Prec = TopPrec -- No parens
415 | FunPrec -- Function args; no parens for tycon apps
416 | TyConPrec -- Tycon args; no parens for atomic
419 maybeParen :: Prec -> Prec -> SDoc -> SDoc
420 maybeParen ctxt_prec inner_prec pretty
421 | ctxt_prec < inner_prec = pretty
422 | otherwise = parens pretty
425 pprType, pprParendType :: Type -> SDoc
426 pprType ty = ppr_type TopPrec ty
427 pprParendType ty = ppr_type TyConPrec ty
430 pprPred :: PredType -> SDoc
431 pprPred (ClassP cls tys) = pprClassPred cls tys
432 pprPred (IParam ip ty) = ppr ip <> dcolon <> pprType ty
433 pprPred (EqPred ty1 ty2) = sep [ppr ty1, nest 2 (ptext SLIT(":=:")), ppr ty2]
435 pprClassPred :: Class -> [Type] -> SDoc
436 pprClassPred clas tys = parenSymOcc (getOccName clas) (ppr clas)
437 <+> sep (map pprParendType tys)
439 pprTheta :: ThetaType -> SDoc
440 pprTheta theta = parens (sep (punctuate comma (map pprPred theta)))
442 pprThetaArrow :: ThetaType -> SDoc
445 | otherwise = parens (sep (punctuate comma (map pprPred theta))) <+> ptext SLIT("=>")
448 instance Outputable Type where
451 instance Outputable PredType where
454 instance Outputable name => OutputableBndr (IPName name) where
455 pprBndr _ n = ppr n -- Simple for now
458 -- OK, here's the main printer
461 pprParendKind = pprParendType
463 ppr_type :: Prec -> Type -> SDoc
464 ppr_type p (TyVarTy tv) = ppr tv
465 ppr_type p (PredTy pred) = braces (ppr pred)
466 ppr_type p (NoteTy other ty2) = ppr_type p ty2
467 ppr_type p (TyConApp tc tys) = ppr_tc_app p tc tys
469 ppr_type p (AppTy t1 t2) = maybeParen p TyConPrec $
470 pprType t1 <+> ppr_type TyConPrec t2
472 ppr_type p ty@(ForAllTy _ _) = ppr_forall_type p ty
473 ppr_type p ty@(FunTy (PredTy _) _) = ppr_forall_type p ty
475 ppr_type p (FunTy ty1 ty2)
476 = -- We don't want to lose synonyms, so we mustn't use splitFunTys here.
477 maybeParen p FunPrec $
478 sep (ppr_type FunPrec ty1 : ppr_fun_tail ty2)
480 ppr_fun_tail (FunTy ty1 ty2) = (arrow <+> ppr_type FunPrec ty1) : ppr_fun_tail ty2
481 ppr_fun_tail other_ty = [arrow <+> pprType other_ty]
483 ppr_forall_type :: Prec -> Type -> SDoc
485 = maybeParen p FunPrec $
486 sep [pprForAll tvs, pprThetaArrow ctxt, pprType tau]
488 (tvs, rho) = split1 [] ty
489 (ctxt, tau) = split2 [] rho
491 split1 tvs (ForAllTy tv ty) = split1 (tv:tvs) ty
492 split1 tvs (NoteTy _ ty) = split1 tvs ty
493 split1 tvs ty = (reverse tvs, ty)
495 split2 ps (NoteTy _ arg -- Rather a disgusting case
496 `FunTy` res) = split2 ps (arg `FunTy` res)
497 split2 ps (PredTy p `FunTy` ty) = split2 (p:ps) ty
498 split2 ps (NoteTy _ ty) = split2 ps ty
499 split2 ps ty = (reverse ps, ty)
501 ppr_tc_app :: Prec -> TyCon -> [Type] -> SDoc
505 | tc `hasKey` listTyConKey = brackets (pprType ty)
506 | tc `hasKey` parrTyConKey = ptext SLIT("[:") <> pprType ty <> ptext SLIT(":]")
507 | tc `hasKey` liftedTypeKindTyConKey = ptext SLIT("*")
508 | tc `hasKey` unliftedTypeKindTyConKey = ptext SLIT("#")
509 | tc `hasKey` openTypeKindTyConKey = ptext SLIT("(?)")
510 | tc `hasKey` ubxTupleKindTyConKey = ptext SLIT("(#)")
511 | tc `hasKey` argTypeKindTyConKey = ptext SLIT("??")
514 | isTupleTyCon tc && tyConArity tc == length tys
515 = tupleParens (tupleTyConBoxity tc) (sep (punctuate comma (map pprType tys)))
517 = maybeParen p TyConPrec $
518 ppr_tc tc <+> sep (map (ppr_type TyConPrec) tys)
520 ppr_tc :: TyCon -> SDoc
521 ppr_tc tc = parenSymOcc (getOccName tc) (pp_nt_debug <> ppr tc)
523 pp_nt_debug | isNewTyCon tc = ifPprDebug (if isRecursiveTyCon tc
524 then ptext SLIT("<recnt>")
525 else ptext SLIT("<nt>"))
530 pprForAll tvs = ptext SLIT("forall") <+> sep (map pprTvBndr tvs) <> dot
532 pprTvBndr tv | isLiftedTypeKind kind = ppr tv
533 | otherwise = parens (ppr tv <+> dcolon <+> pprKind kind)