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,
18 pprPred, pprTheta, pprThetaArrow, pprClassPred,
21 liftedTypeKind, unliftedTypeKind, openTypeKind,
22 isLiftedTypeKind, isUnliftedTypeKind, isOpenTypeKind,
23 mkArrowKind, mkArrowKinds,
24 pprKind, pprParendKind
27 #include "HsVersions.h"
29 import {-# SOURCE #-} DataCon( DataCon, dataConName )
33 import Var ( Var, Id, TyVar, tyVarKind )
34 import VarSet ( TyVarSet )
35 import Name ( Name, NamedThing(..), BuiltInSyntax(..), mkWiredInName )
36 import OccName ( mkOccFS, tcName )
37 import BasicTypes ( IPName, tupleParens )
38 import TyCon ( TyCon, mkFunTyCon, tyConArity, tupleTyConBoxity, isTupleTyCon, isRecursiveTyCon )
39 import Class ( Class )
42 import PrelNames ( gHC_PRIM, funTyConKey, listTyConKey, parrTyConKey, hasKey )
46 %************************************************************************
48 \subsection{Type Classifications}
50 %************************************************************************
54 *unboxed* iff its representation is other than a pointer
55 Unboxed types are also unlifted.
57 *lifted* A type is lifted iff it has bottom as an element.
58 Closures always have lifted types: i.e. any
59 let-bound identifier in Core must have a lifted
60 type. Operationally, a lifted object is one that
63 Only lifted types may be unified with a type variable.
65 *algebraic* A type with one or more constructors, whether declared
66 with "data" or "newtype".
67 An algebraic type is one that can be deconstructed
68 with a case expression.
69 *NOT* the same as lifted types, because we also
70 include unboxed tuples in this classification.
72 *data* A type declared with "data". Also boxed tuples.
74 *primitive* iff it is a built-in type that can't be expressed
77 Currently, all primitive types are unlifted, but that's not necessarily
78 the case. (E.g. Int could be primitive.)
80 Some primitive types are unboxed, such as Int#, whereas some are boxed
81 but unlifted (such as ByteArray#). The only primitive types that we
82 classify as algebraic are the unboxed tuples.
84 examples of type classifications:
86 Type primitive boxed lifted algebraic
87 -----------------------------------------------------------------------------
89 ByteArray# Yes Yes No No
90 (# a, b #) Yes No No Yes
91 ( a, b ) No Yes Yes Yes
96 ----------------------
98 ----------------------
103 Then we want N to be represented as an Int, and that's what we arrange.
104 The front end of the compiler [TcType.lhs] treats N as opaque,
105 the back end treats it as transparent [Type.lhs].
107 There's a bit of a problem with recursive newtypes
109 newtype Q = MkQ (Q->Q)
111 Here the 'implicit expansion' we get from treating P and Q as transparent
112 would give rise to infinite types, which in turn makes eqType diverge.
113 Similarly splitForAllTys and splitFunTys can get into a loop.
117 * Newtypes are always represented using NewTcApp, never as TyConApp.
119 * For non-recursive newtypes, P, treat P just like a type synonym after
120 type-checking is done; i.e. it's opaque during type checking (functions
121 from TcType) but transparent afterwards (functions from Type).
122 "Treat P as a type synonym" means "all functions expand NewTcApps
125 Applications of the data constructor P simply vanish:
129 * For recursive newtypes Q, treat the Q and its representation as
130 distinct right through the compiler. Applications of the data consructor
132 Q = \(x::Q->Q). coerce Q x
133 They are rare, so who cares if they are a tiny bit less efficient.
135 The typechecker (TcTyDecls) identifies enough type construtors as 'recursive'
136 to cut all loops. The other members of the loop may be marked 'non-recursive'.
139 %************************************************************************
141 \subsection{The data type}
143 %************************************************************************
151 Type -- Function is *not* a TyConApp or NewTcApp
152 Type -- It must be another AppTy, or TyVarTy
153 -- (or NoteTy of these)
155 | TyConApp -- Application of a TyCon
156 TyCon -- *Invariant* saturated appliations of FunTyCon and
157 -- synonyms have their own constructors, below.
158 [Type] -- Might not be saturated.
160 | NewTcApp -- Application of a NewType TyCon. All newtype applications
161 TyCon -- show up like this until they are fed through newTypeRep,
163 -- * an ordinary TyConApp for non-saturated,
164 -- or recursive newtypes
166 -- * the representation type of the newtype for satuarted,
167 -- non-recursive ones
168 -- [But the result of a call to newTypeRep is always consumed
169 -- immediately; it never lives on in another type. So in any
170 -- type, newtypes are always represented with NewTcApp.]
171 [Type] -- Might not be saturated.
173 | FunTy -- Special case of TyConApp: TyConApp FunTyCon [t1,t2]
177 | ForAllTy -- A polymorphic type
181 | PredTy -- A high level source type
182 PredType -- ...can be expanded to a representation type...
184 | NoteTy -- A type with a note attached
186 Type -- The expanded version
189 = FTVNote TyVarSet -- The free type variables of the noted expression
191 | SynNote Type -- Used for type synonyms
192 -- The Type is always a TyConApp, and is the un-expanded form.
193 -- The type to which the note is attached is the expanded form.
196 -------------------------------------
201 represents a value whose type is the Haskell predicate p,
202 where a predicate is what occurs before the '=>' in a Haskell type.
203 It can be expanded into its representation, but:
205 * The type checker must treat it as opaque
206 * The rest of the compiler treats it as transparent
208 Consider these examples:
209 f :: (Eq a) => a -> Int
210 g :: (?x :: Int -> Int) => a -> Int
211 h :: (r\l) => {r} => {l::Int | r}
213 Here the "Eq a" and "?x :: Int -> Int" and "r\l" are all called *predicates*
214 Predicates are represented inside GHC by PredType:
218 = ClassP Class [Type] -- Class predicate
219 | IParam (IPName Name) Type -- Implicit parameter
221 type ThetaType = [PredType]
224 (We don't support TREX records yet, but the setup is designed
225 to expand to allow them.)
227 A Haskell qualified type, such as that for f,g,h above, is
229 * a FunTy for the double arrow
230 * with a PredTy as the function argument
232 The predicate really does turn into a real extra argument to the
233 function. If the argument has type (PredTy p) then the predicate p is
234 represented by evidence (a dictionary, for example, of type (predRepTy p).
237 %************************************************************************
241 %************************************************************************
243 Despite the fact that DataCon has to be imported via a hi-boot route,
244 this module seems the right place for TyThing, because it's needed for
245 funTyCon and all the types in TysPrim.
248 data TyThing = AnId Id
253 instance Outputable TyThing where
254 ppr (AnId id) = ptext SLIT("AnId") <+> ppr id
255 ppr (ATyCon tc) = ptext SLIT("ATyCon") <+> ppr tc
256 ppr (AClass cl) = ptext SLIT("AClass") <+> ppr cl
257 ppr (ADataCon dc) = ptext SLIT("ADataCon") <+> ppr (dataConName dc)
259 instance NamedThing TyThing where -- Can't put this with the type
260 getName (AnId id) = getName id -- decl, because the DataCon instance
261 getName (ATyCon tc) = getName tc -- isn't visible there
262 getName (AClass cl) = getName cl
263 getName (ADataCon dc) = dataConName dc
267 %************************************************************************
269 \subsection{Wired-in type constructors
271 %************************************************************************
273 We define a few wired-in type constructors here to avoid module knots
276 funTyCon = mkFunTyCon funTyConName (mkArrowKinds [argTypeKind, openTypeKind] liftedTypeKind)
277 -- You might think that (->) should have type (?? -> ? -> *), and you'd be right
278 -- But if we do that we get kind errors when saying
279 -- instance Control.Arrow (->)
280 -- becuase the expected kind is (*->*->*). The trouble is that the
281 -- expected/actual stuff in the unifier does not go contra-variant, whereas
282 -- the kind sub-typing does. Sigh. It really only matters if you use (->) in
283 -- a prefix way, thus: (->) Int# Int#. And this is unusual.
285 funTyConName = mkWiredInName gHC_PRIM
286 (mkOccFS tcName FSLIT("(->)"))
288 Nothing -- No parent object
289 (ATyCon funTyCon) -- Relevant TyCon
294 %************************************************************************
296 \subsection{The external interface}
298 %************************************************************************
300 @pprType@ is the standard @Type@ printer; the overloaded @ppr@ function is
301 defined to use this. @pprParendType@ is the same, except it puts
302 parens around the type, except for the atomic cases. @pprParendType@
303 works just by setting the initial context precedence very high.
306 data Prec = TopPrec -- No parens
307 | FunPrec -- Function args; no parens for tycon apps
308 | TyConPrec -- Tycon args; no parens for atomic
311 maybeParen :: Prec -> Prec -> SDoc -> SDoc
312 maybeParen ctxt_prec inner_prec pretty
313 | ctxt_prec < inner_prec = pretty
314 | otherwise = parens pretty
317 pprType, pprParendType :: Type -> SDoc
318 pprType ty = ppr_type TopPrec ty
319 pprParendType ty = ppr_type TyConPrec ty
322 pprPred :: PredType -> SDoc
323 pprPred (ClassP cls tys) = pprClassPred cls tys
324 pprPred (IParam ip ty) = ppr ip <> dcolon <> pprType ty
326 pprClassPred :: Class -> [Type] -> SDoc
327 pprClassPred clas tys = ppr clas <+> sep (map pprParendType tys)
329 pprTheta :: ThetaType -> SDoc
330 pprTheta theta = parens (sep (punctuate comma (map pprPred theta)))
332 pprThetaArrow :: ThetaType -> SDoc
335 | otherwise = parens (sep (punctuate comma (map pprPred theta))) <+> ptext SLIT("=>")
338 instance Outputable Type where
341 instance Outputable PredType where
344 instance Outputable name => OutputableBndr (IPName name) where
345 pprBndr _ n = ppr n -- Simple for now
348 -- OK, here's the main printer
350 ppr_type :: Prec -> Type -> SDoc
351 ppr_type p (TyVarTy tv) = ppr tv
352 ppr_type p (PredTy pred) = braces (ppr pred)
353 ppr_type p (NoteTy (SynNote ty1) ty2) = ppr_type p ty1
354 ppr_type p (NoteTy other ty2) = ppr_type p ty2
356 ppr_type p (TyConApp tc tys) = ppr_tc_app p tc tys
357 ppr_type p (NewTcApp tc tys) = ifPprDebug (if isRecursiveTyCon tc
358 then ptext SLIT("<recnt>")
359 else ptext SLIT("<nt>")
363 ppr_type p (AppTy t1 t2) = maybeParen p TyConPrec $
364 pprType t1 <+> ppr_type TyConPrec t2
366 ppr_type p (FunTy ty1 ty2)
367 = -- We don't want to lose synonyms, so we mustn't use splitFunTys here.
368 maybeParen p FunPrec $
369 sep (ppr_type FunPrec ty1 : ppr_fun_tail ty2)
371 ppr_fun_tail (FunTy ty1 ty2) = (arrow <+> ppr_type FunPrec ty1) : ppr_fun_tail ty2
372 ppr_fun_tail other_ty = [arrow <+> pprType other_ty]
374 ppr_type p ty@(ForAllTy _ _)
375 = maybeParen p FunPrec $
376 sep [pprForAll tvs, pprThetaArrow ctxt, pprType tau]
378 (tvs, rho) = split1 [] ty
379 (ctxt, tau) = split2 [] rho
381 split1 tvs (ForAllTy tv ty) = split1 (tv:tvs) ty
382 split1 tvs (NoteTy (FTVNote _) ty) = split1 tvs ty
383 split1 tvs ty = (reverse tvs, ty)
385 split2 ps (NoteTy (FTVNote _) arg -- Rather a disgusting case
386 `FunTy` res) = split2 ps (arg `FunTy` res)
387 split2 ps (PredTy p `FunTy` ty) = split2 (p:ps) ty
388 split2 ps (NoteTy (FTVNote _) ty) = split2 ps ty
389 split2 ps ty = (reverse ps, ty)
391 ppr_tc_app :: Prec -> TyCon -> [Type] -> SDoc
395 | tc `hasKey` listTyConKey = brackets (pprType ty)
396 | tc `hasKey` parrTyConKey = ptext SLIT("[:") <> pprType ty <> ptext SLIT(":]")
398 | isTupleTyCon tc && tyConArity tc == length tys
399 = tupleParens (tupleTyConBoxity tc) (sep (punctuate comma (map pprType tys)))
401 = maybeParen p TyConPrec $
402 ppr tc <+> sep (map (ppr_type TyConPrec) tys)
405 pprForAll tvs = ptext SLIT("forall") <+> sep (map pprTvBndr tvs) <> dot
407 pprTvBndr tv | isLiftedTypeKind kind = ppr tv
408 | otherwise = parens (ppr tv <+> dcolon <+> pprKind kind)