2 % (c) The AQUA Project, Glasgow University, 1996-1998
4 \section[TcTyClsDecls]{Typecheck type and class declarations}
11 #include "HsVersions.h"
13 import HsSyn ( TyClDecl(..), HsConDetails(..), HsTyVarBndr(..),
14 ConDecl(..), Sig(..), NewOrData(..), ResType(..),
15 tyClDeclTyVars, isSynDecl, isClassDecl, hsConArgs,
16 LTyClDecl, tcdName, hsTyVarName, LHsTyVarBndr
18 import HsTypes ( HsBang(..), getBangStrictness )
19 import BasicTypes ( RecFlag(..), StrictnessMark(..) )
20 import HscTypes ( implicitTyThings, ModDetails )
21 import BuildTyCl ( buildClass, buildAlgTyCon, buildSynTyCon, buildDataCon,
22 mkDataTyConRhs, mkNewTyConRhs )
24 import TcEnv ( TyThing(..),
25 tcLookupLocated, tcLookupLocatedGlobal,
26 tcExtendGlobalEnv, tcExtendKindEnv, tcExtendKindEnvTvs,
27 tcExtendRecEnv, tcLookupTyVar, InstInfo )
28 import TcTyDecls ( calcRecFlags, calcClassCycles, calcSynCycles )
29 import TcClassDcl ( tcClassSigs, tcAddDeclCtxt )
30 import TcHsType ( kcHsTyVars, kcHsLiftedSigType, kcHsType,
31 kcHsContext, tcTyVarBndrs, tcHsKindedType, tcHsKindedContext,
32 kcHsSigType, tcHsBangType, tcLHsConResTy, tcDataKindSig )
33 import TcMType ( newKindVar, checkValidTheta, checkValidType,
35 UserTypeCtxt(..), SourceTyCtxt(..) )
36 import TcType ( TcKind, TcType, Type, tyVarsOfType, mkPhiTy,
37 mkArrowKind, liftedTypeKind, mkTyVarTys,
38 tcSplitSigmaTy, tcEqTypes, tcGetTyVar_maybe )
39 import Type ( PredType(..), splitTyConApp_maybe, mkTyVarTy
40 -- pprParendType, pprThetaArrow
42 import Generics ( validGenericMethodType, canDoGenerics )
43 import Class ( Class, className, classTyCon, DefMeth(..), classBigSig, classTyVars )
44 import TyCon ( TyCon, AlgTyConRhs( AbstractTyCon ),
45 tyConDataCons, mkForeignTyCon, isProductTyCon, isRecursiveTyCon,
46 tyConStupidTheta, synTyConRhs, isSynTyCon, tyConName,
48 import DataCon ( DataCon, dataConUserType, dataConName,
49 dataConFieldLabels, dataConTyCon, dataConAllTyVars,
50 dataConFieldType, dataConResTys )
51 import Var ( TyVar, idType, idName )
52 import VarSet ( elemVarSet, mkVarSet )
53 import Name ( Name, getSrcLoc )
55 import Maybe ( isJust )
56 import Maybes ( expectJust )
57 import Unify ( tcMatchTys, tcMatchTyX )
58 import Util ( zipLazy, isSingleton, notNull, sortLe )
59 import List ( partition )
60 import SrcLoc ( Located(..), unLoc, getLoc, srcLocSpan )
61 import ListSetOps ( equivClasses, minusList )
62 import List ( delete )
63 import Digraph ( SCC(..) )
64 import DynFlags ( DynFlag( Opt_GlasgowExts, Opt_Generics,
65 Opt_UnboxStrictFields ) )
69 %************************************************************************
71 \subsection{Type checking for type and class declarations}
73 %************************************************************************
77 Consider a mutually-recursive group, binding
78 a type constructor T and a class C.
80 Step 1: getInitialKind
81 Construct a KindEnv by binding T and C to a kind variable
84 In that environment, do a kind check
86 Step 3: Zonk the kinds
88 Step 4: buildTyConOrClass
89 Construct an environment binding T to a TyCon and C to a Class.
90 a) Their kinds comes from zonking the relevant kind variable
91 b) Their arity (for synonyms) comes direct from the decl
92 c) The funcional dependencies come from the decl
93 d) The rest comes a knot-tied binding of T and C, returned from Step 4
94 e) The variances of the tycons in the group is calculated from
98 In this environment, walk over the decls, constructing the TyCons and Classes.
99 This uses in a strict way items (a)-(c) above, which is why they must
100 be constructed in Step 4. Feed the results back to Step 4.
101 For this step, pass the is-recursive flag as the wimp-out flag
105 Step 6: Extend environment
106 We extend the type environment with bindings not only for the TyCons and Classes,
107 but also for their "implicit Ids" like data constructors and class selectors
109 Step 7: checkValidTyCl
110 For a recursive group only, check all the decls again, just
111 to check all the side conditions on validity. We could not
112 do this before because we were in a mutually recursive knot.
114 Identification of recursive TyCons
115 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
116 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
119 Identifying a TyCon as recursive serves two purposes
121 1. Avoid infinite types. Non-recursive newtypes are treated as
122 "transparent", like type synonyms, after the type checker. If we did
123 this for all newtypes, we'd get infinite types. So we figure out for
124 each newtype whether it is "recursive", and add a coercion if so. In
125 effect, we are trying to "cut the loops" by identifying a loop-breaker.
127 2. Avoid infinite unboxing. This is nothing to do with newtypes.
131 Well, this function diverges, but we don't want the strictness analyser
132 to diverge. But the strictness analyser will diverge because it looks
133 deeper and deeper into the structure of T. (I believe there are
134 examples where the function does something sane, and the strictness
135 analyser still diverges, but I can't see one now.)
137 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
138 newtypes. I did this as an experiment, to try to expose cases in which
139 the coercions got in the way of optimisations. If it turns out that we
140 can indeed always use a coercion, then we don't risk recursive types,
141 and don't need to figure out what the loop breakers are.
143 For newtype *families* though, we will always have a coercion, so they
144 are always loop breakers! So you can easily adjust the current
145 algorithm by simply treating all newtype families as loop breakers (and
146 indeed type families). I think.
149 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
150 -> TcM TcGblEnv -- Input env extended by types and classes
151 -- and their implicit Ids,DataCons
152 tcTyAndClassDecls boot_details decls
153 = do { -- First check for cyclic type synonysm or classes
154 -- See notes with checkCycleErrs
157 ; traceTc (text "tcTyAndCl" <+> ppr mod)
158 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(rec_syn_tycons, rec_alg_tyclss) ->
159 do { let { -- Calculate variances and rec-flag
160 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
162 -- Extend the global env with the knot-tied results
163 -- for data types and classes
165 -- We must populate the environment with the loop-tied T's right
166 -- away, because the kind checker may "fault in" some type
167 -- constructors that recursively mention T
168 ; let { gbl_things = mkGlobalThings alg_decls rec_alg_tyclss }
169 ; tcExtendRecEnv gbl_things $ do
171 -- Kind-check the declarations
172 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
174 ; let { calc_rec = calcRecFlags boot_details rec_alg_tyclss
175 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
176 -- Type-check the type synonyms, and extend the envt
177 ; syn_tycons <- tcSynDecls kc_syn_decls
178 ; tcExtendGlobalEnv syn_tycons $ do
180 -- Type-check the data types and classes
181 { alg_tyclss <- mappM tc_decl kc_alg_decls
182 ; return (syn_tycons, alg_tyclss)
184 -- Finished with knot-tying now
185 -- Extend the environment with the finished things
186 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
188 -- Perform the validity check
189 { traceTc (text "ready for validity check")
190 ; mappM_ (addLocM checkValidTyCl) decls
191 ; traceTc (text "done")
193 -- Add the implicit things;
194 -- we want them in the environment because
195 -- they may be mentioned in interface files
196 ; let { implicit_things = concatMap implicitTyThings alg_tyclss }
197 ; traceTc ((text "Adding" <+> ppr alg_tyclss) $$ (text "and" <+> ppr implicit_things))
198 ; tcExtendGlobalEnv implicit_things getGblEnv
201 mkGlobalThings :: [LTyClDecl Name] -- The decls
202 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
204 -- Driven by the Decls, and treating the TyThings lazily
205 -- make a TypeEnv for the new things
206 mkGlobalThings decls things
207 = map mk_thing (decls `zipLazy` things)
209 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
211 mk_thing (L _ decl, ~(ATyCon tc))
212 = (tcdName decl, ATyCon tc)
216 %************************************************************************
220 %************************************************************************
222 We need to kind check all types in the mutually recursive group
223 before we know the kind of the type variables. For example:
226 op :: D b => a -> b -> b
229 bop :: (Monad c) => ...
231 Here, the kind of the locally-polymorphic type variable "b"
232 depends on *all the uses of class D*. For example, the use of
233 Monad c in bop's type signature means that D must have kind Type->Type.
235 However type synonyms work differently. They can have kinds which don't
236 just involve (->) and *:
237 type R = Int# -- Kind #
238 type S a = Array# a -- Kind * -> #
239 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
240 So we must infer their kinds from their right-hand sides *first* and then
241 use them, whereas for the mutually recursive data types D we bring into
242 scope kind bindings D -> k, where k is a kind variable, and do inference.
245 kcTyClDecls syn_decls alg_decls
246 = do { -- First extend the kind env with each data
247 -- type and class, mapping them to a type variable
248 alg_kinds <- mappM getInitialKind alg_decls
249 ; tcExtendKindEnv alg_kinds $ do
251 -- Now kind-check the type synonyms, in dependency order
252 -- We do these differently to data type and classes,
253 -- because a type synonym can be an unboxed type
255 -- and a kind variable can't unify with UnboxedTypeKind
256 -- So we infer their kinds in dependency order
257 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
258 ; tcExtendKindEnv syn_kinds $ do
260 -- Now kind-check the data type and class declarations,
261 -- returning kind-annotated decls
262 { kc_alg_decls <- mappM (wrapLocM kcTyClDecl) alg_decls
264 ; return (kc_syn_decls, kc_alg_decls) }}}
266 ------------------------------------------------------------------------
267 getInitialKind :: LTyClDecl Name -> TcM (Name, TcKind)
268 -- Only for data type and class declarations
269 -- Get as much info as possible from the data or class decl,
270 -- so as to maximise usefulness of error messages
271 getInitialKind (L _ decl)
272 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
273 ; res_kind <- mk_res_kind decl
274 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
276 mk_arg_kind (UserTyVar _) = newKindVar
277 mk_arg_kind (KindedTyVar _ kind) = return kind
279 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
280 -- On GADT-style declarations we allow a kind signature
281 -- data T :: *->* where { ... }
282 mk_res_kind other = return liftedTypeKind
286 kcSynDecls :: [SCC (LTyClDecl Name)]
287 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
288 [(Name,TcKind)]) -- Kind bindings
291 kcSynDecls (group : groups)
292 = do { (decl, nk) <- kcSynDecl group
293 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
294 ; return (decl:decls, nk:nks) }
297 kcSynDecl :: SCC (LTyClDecl Name)
298 -> TcM (LTyClDecl Name, -- Kind-annotated decls
299 (Name,TcKind)) -- Kind bindings
300 kcSynDecl (AcyclicSCC ldecl@(L loc decl))
301 = tcAddDeclCtxt decl $
302 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
303 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
304 <+> brackets (ppr k_tvs))
305 ; (k_rhs, rhs_kind) <- kcHsType (tcdSynRhs decl)
306 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
307 ; let tc_kind = foldr (mkArrowKind . kindedTyVarKind) rhs_kind k_tvs
308 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
309 (unLoc (tcdLName decl), tc_kind)) })
311 kcSynDecl (CyclicSCC decls)
312 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
313 -- of out-of-scope tycons
315 kindedTyVarKind (L _ (KindedTyVar _ k)) = k
317 ------------------------------------------------------------------------
318 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
319 -- Not used for type synonyms (see kcSynDecl)
321 kcTyClDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
322 = kcTyClDeclBody decl $ \ tvs' ->
323 do { ctxt' <- kcHsContext ctxt
324 ; cons' <- mappM (wrapLocM kc_con_decl) cons
325 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdCons = cons'}) }
327 kc_con_decl (ConDecl name expl ex_tvs ex_ctxt details res) = do
328 kcHsTyVars ex_tvs $ \ex_tvs' -> do
329 ex_ctxt' <- kcHsContext ex_ctxt
330 details' <- kc_con_details details
332 ResTyH98 -> return ResTyH98
333 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
334 return (ConDecl name expl ex_tvs' ex_ctxt' details' res')
336 kc_con_details (PrefixCon btys)
337 = do { btys' <- mappM kc_larg_ty btys ; return (PrefixCon btys') }
338 kc_con_details (InfixCon bty1 bty2)
339 = do { bty1' <- kc_larg_ty bty1; bty2' <- kc_larg_ty bty2; return (InfixCon bty1' bty2') }
340 kc_con_details (RecCon fields)
341 = do { fields' <- mappM kc_field fields; return (RecCon fields') }
343 kc_field (fld, bty) = do { bty' <- kc_larg_ty bty ; return (fld, bty') }
345 kc_larg_ty bty = case new_or_data of
346 DataType -> kcHsSigType bty
347 NewType -> kcHsLiftedSigType bty
348 -- Can't allow an unlifted type for newtypes, because we're effectively
349 -- going to remove the constructor while coercing it to a lifted type.
350 -- And newtypes can't be bang'd
353 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs})
354 = kcTyClDeclBody decl $ \ tvs' ->
355 do { is_boot <- tcIsHsBoot
356 ; ctxt' <- kcHsContext ctxt
357 ; sigs' <- mappM (wrapLocM kc_sig) sigs
358 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs'}) }
360 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
361 ; return (TypeSig nm op_ty') }
362 kc_sig other_sig = return other_sig
364 kcTyClDecl decl@(ForeignType {})
367 kcTyClDeclBody :: TyClDecl Name
368 -> ([LHsTyVarBndr Name] -> TcM a)
370 -- getInitialKind has made a suitably-shaped kind for the type or class
371 -- Unpack it, and attribute those kinds to the type variables
372 -- Extend the env with bindings for the tyvars, taken from
373 -- the kind of the tycon/class. Give it to the thing inside, and
374 -- check the result kind matches
375 kcTyClDeclBody decl thing_inside
376 = tcAddDeclCtxt decl $
377 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
378 ; let tc_kind = case tc_ty_thing of { AThing k -> k }
379 (kinds, _) = splitKindFunTys tc_kind
380 hs_tvs = tcdTyVars decl
381 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
382 [ L loc (KindedTyVar (hsTyVarName tv) k)
383 | (L loc tv, k) <- zip hs_tvs kinds]
384 ; tcExtendKindEnvTvs kinded_tvs (thing_inside kinded_tvs) }
388 %************************************************************************
390 \subsection{Type checking}
392 %************************************************************************
395 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
396 tcSynDecls [] = return []
397 tcSynDecls (decl : decls)
398 = do { syn_tc <- addLocM tcSynDecl decl
399 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
400 ; return (syn_tc : syn_tcs) }
403 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
404 = tcTyVarBndrs tvs $ \ tvs' -> do
405 { traceTc (text "tcd1" <+> ppr tc_name)
406 ; rhs_ty' <- tcHsKindedType rhs_ty
407 ; return (ATyCon (buildSynTyCon tc_name tvs' rhs_ty')) }
410 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM TyThing
412 tcTyClDecl calc_isrec decl
413 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
415 tcTyClDecl1 calc_isrec
416 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
417 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
418 = tcTyVarBndrs tvs $ \ tvs' -> do
419 { extra_tvs <- tcDataKindSig mb_ksig
420 ; let final_tvs = tvs' ++ extra_tvs
421 ; stupid_theta <- tcHsKindedContext ctxt
422 ; want_generic <- doptM Opt_Generics
423 ; unbox_strict <- doptM Opt_UnboxStrictFields
424 ; gla_exts <- doptM Opt_GlasgowExts
425 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
427 -- Check that we don't use GADT syntax in H98 world
428 ; checkTc (gla_exts || h98_syntax) (badGadtDecl tc_name)
430 -- Check that the stupid theta is empty for a GADT-style declaration
431 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
433 -- Check that there's at least one condecl,
434 -- or else we're reading an hs-boot file, or -fglasgow-exts
435 ; checkTc (not (null cons) || gla_exts || is_boot)
436 (emptyConDeclsErr tc_name)
438 -- Check that a newtype has exactly one constructor
439 ; checkTc (new_or_data == DataType || isSingleton cons)
440 (newtypeConError tc_name (length cons))
442 ; tycon <- fixM (\ tycon -> do
443 { data_cons <- mappM (addLocM (tcConDecl unbox_strict new_or_data
447 if null cons && is_boot -- In a hs-boot file, empty cons means
448 then return AbstractTyCon -- "don't know"; hence Abstract
449 else case new_or_data of
450 DataType -> return (mkDataTyConRhs data_cons)
452 ASSERT( isSingleton data_cons )
453 mkNewTyConRhs tc_name tycon (head data_cons)
454 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
455 (want_generic && canDoGenerics data_cons) h98_syntax
457 ; return (ATyCon tycon)
460 is_rec = calc_isrec tc_name
461 h98_syntax = case cons of -- All constructors have same shape
462 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
465 tcTyClDecl1 calc_isrec
466 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
467 tcdCtxt = ctxt, tcdMeths = meths,
468 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
469 = tcTyVarBndrs tvs $ \ tvs' -> do
470 { ctxt' <- tcHsKindedContext ctxt
471 ; fds' <- mappM (addLocM tc_fundep) fundeps
472 -- !!!TODO: process `ats`; what do we want to store in the `Class'? -=chak
473 ; sig_stuff <- tcClassSigs class_name sigs meths
474 ; clas <- fixM (\ clas ->
475 let -- This little knot is just so we can get
476 -- hold of the name of the class TyCon, which we
477 -- need to look up its recursiveness and variance
478 tycon_name = tyConName (classTyCon clas)
479 tc_isrec = calc_isrec tycon_name
481 buildClass class_name tvs' ctxt' fds'
483 ; return (AClass clas) }
485 tc_fundep (tvs1, tvs2) = do { tvs1' <- mappM tcLookupTyVar tvs1 ;
486 ; tvs2' <- mappM tcLookupTyVar tvs2 ;
487 ; return (tvs1', tvs2') }
490 tcTyClDecl1 calc_isrec
491 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
492 = returnM (ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0))
494 -----------------------------------
495 tcConDecl :: Bool -- True <=> -funbox-strict_fields
496 -> NewOrData -> TyCon -> [TyVar]
497 -> ConDecl Name -> TcM DataCon
499 tcConDecl unbox_strict NewType tycon tc_tvs -- Newtypes
500 (ConDecl name _ ex_tvs ex_ctxt details ResTyH98)
501 = do { let tc_datacon field_lbls arg_ty
502 = do { arg_ty' <- tcHsKindedType arg_ty -- No bang on newtype
503 ; buildDataCon (unLoc name) False {- Prefix -}
505 (map unLoc field_lbls)
506 tc_tvs [] -- No existentials
507 [] [] -- No equalities, predicates
511 -- Check that a newtype has no existential stuff
512 ; checkTc (null ex_tvs && null (unLoc ex_ctxt)) (newtypeExError name)
515 PrefixCon [arg_ty] -> tc_datacon [] arg_ty
516 RecCon [(field_lbl, arg_ty)] -> tc_datacon [field_lbl] arg_ty
517 other -> failWithTc (newtypeFieldErr name (length (hsConArgs details)))
518 -- Check that the constructor has exactly one field
521 tcConDecl unbox_strict DataType tycon tc_tvs -- Data types
522 (ConDecl name _ tvs ctxt details res_ty)
523 = tcTyVarBndrs tvs $ \ tvs' -> do
524 { ctxt' <- tcHsKindedContext ctxt
525 ; (univ_tvs, ex_tvs, eq_preds, data_tc) <- tcResultType tycon tc_tvs tvs' res_ty
527 tc_datacon is_infix field_lbls btys
528 = do { let bangs = map getBangStrictness btys
529 ; arg_tys <- mappM tcHsBangType btys
530 ; buildDataCon (unLoc name) is_infix
531 (argStrictness unbox_strict tycon bangs arg_tys)
532 (map unLoc field_lbls)
533 univ_tvs ex_tvs eq_preds ctxt' arg_tys
535 -- NB: we put data_tc, the type constructor gotten from the constructor
536 -- type signature into the data constructor; that way
537 -- checkValidDataCon can complain if it's wrong.
540 PrefixCon btys -> tc_datacon False [] btys
541 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
542 RecCon fields -> tc_datacon False field_names btys
544 (field_names, btys) = unzip fields
548 tcResultType :: TyCon
549 -> [TyVar] -- data T a b c = ...
550 -> [TyVar] -- where MkT :: forall a b c. ...
552 -> TcM ([TyVar], -- Universal
553 [TyVar], -- Existential
554 [(TyVar,Type)], -- Equality predicates
555 TyCon) -- TyCon given in the ResTy
556 -- We don't check that the TyCon given in the ResTy is
557 -- the same as the parent tycon, becuase we are in the middle
558 -- of a recursive knot; so it's postponed until checkValidDataCon
560 tcResultType decl_tycon tc_tvs dc_tvs ResTyH98
561 = return (tc_tvs, dc_tvs, [], decl_tycon)
562 -- In H98 syntax the dc_tvs are the existential ones
563 -- data T a b c = forall d e. MkT ...
564 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
566 tcResultType _ tc_tvs dc_tvs (ResTyGADT res_ty)
567 -- E.g. data T a b c where
568 -- MkT :: forall x y z. T (x,y) z z
570 -- ([a,z,c], [x,y], [a:=:(x,y), c:=:z], T)
572 = do { (dc_tycon, res_tys) <- tcLHsConResTy res_ty
573 -- NB: tc_tvs and dc_tvs are distinct
574 ; let univ_tvs = choose_univs [] tc_tvs res_tys
575 -- Each univ_tv is either a dc_tv or a tc_tv
576 ex_tvs = dc_tvs `minusList` univ_tvs
577 eq_spec = [ (tv, ty) | (tv,ty) <- univ_tvs `zip` res_tys,
579 ; return (univ_tvs, ex_tvs, eq_spec, dc_tycon) }
581 -- choose_univs uses the res_ty itself if it's a type variable
582 -- and hasn't already been used; otherwise it uses one of the tc_tvs
583 choose_univs used tc_tvs []
584 = ASSERT( null tc_tvs ) []
585 choose_univs used (tc_tv:tc_tvs) (res_ty:res_tys)
586 | Just tv <- tcGetTyVar_maybe res_ty, not (tv `elem` used)
587 = tv : choose_univs (tv:used) tc_tvs res_tys
589 = tc_tv : choose_univs used tc_tvs res_tys
592 argStrictness :: Bool -- True <=> -funbox-strict_fields
594 -> [TcType] -> [StrictnessMark]
595 argStrictness unbox_strict tycon bangs arg_tys
596 = ASSERT( length bangs == length arg_tys )
597 zipWith (chooseBoxingStrategy unbox_strict tycon) arg_tys bangs
599 -- We attempt to unbox/unpack a strict field when either:
600 -- (i) The field is marked '!!', or
601 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
603 -- We have turned off unboxing of newtypes because coercions make unboxing
604 -- and reboxing more complicated
605 chooseBoxingStrategy :: Bool -> TyCon -> TcType -> HsBang -> StrictnessMark
606 chooseBoxingStrategy unbox_strict_fields tycon arg_ty bang
608 HsNoBang -> NotMarkedStrict
609 HsStrict | unbox_strict_fields && can_unbox -> MarkedUnboxed
610 HsUnbox | can_unbox -> MarkedUnboxed
611 other -> MarkedStrict
613 can_unbox = case splitTyConApp_maybe arg_ty of
615 Just (arg_tycon, _) -> not (isNewTyCon arg_tycon) && not (isRecursiveTyCon tycon) &&
616 isProductTyCon arg_tycon
619 %************************************************************************
621 \subsection{Dependency analysis}
623 %************************************************************************
625 Validity checking is done once the mutually-recursive knot has been
626 tied, so we can look at things freely.
629 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
630 checkCycleErrs tyclss
634 = do { mappM_ recClsErr cls_cycles
635 ; failM } -- Give up now, because later checkValidTyCl
636 -- will loop if the synonym is recursive
638 cls_cycles = calcClassCycles tyclss
640 checkValidTyCl :: TyClDecl Name -> TcM ()
641 -- We do the validity check over declarations, rather than TyThings
642 -- only so that we can add a nice context with tcAddDeclCtxt
644 = tcAddDeclCtxt decl $
645 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
646 ; traceTc (text "Validity of" <+> ppr thing)
648 ATyCon tc -> checkValidTyCon tc
649 AClass cl -> checkValidClass cl
650 ; traceTc (text "Done validity of" <+> ppr thing)
653 -------------------------
654 -- For data types declared with record syntax, we require
655 -- that each constructor that has a field 'f'
656 -- (a) has the same result type
657 -- (b) has the same type for 'f'
658 -- module alpha conversion of the quantified type variables
659 -- of the constructor.
661 checkValidTyCon :: TyCon -> TcM ()
664 = checkValidType syn_ctxt syn_rhs
666 = -- Check the context on the data decl
667 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc) `thenM_`
669 -- Check arg types of data constructors
670 mappM_ (checkValidDataCon tc) data_cons `thenM_`
672 -- Check that fields with the same name share a type
673 mappM_ check_fields groups
676 syn_ctxt = TySynCtxt name
678 syn_rhs = synTyConRhs tc
679 data_cons = tyConDataCons tc
681 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
682 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
683 get_fields con = dataConFieldLabels con `zip` repeat con
684 -- dataConFieldLabels may return the empty list, which is fine
686 -- See Note [GADT record selectors] in MkId.lhs
687 -- We must check (a) that the named field has the same
688 -- type in each constructor
689 -- (b) that those constructors have the same result type
691 -- However, the constructors may have differently named type variable
692 -- and (worse) we don't know how the correspond to each other. E.g.
693 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
694 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
696 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
697 -- result type against other candidates' types BOTH WAYS ROUND.
698 -- If they magically agrees, take the substitution and
699 -- apply them to the latter ones, and see if they match perfectly.
700 check_fields fields@((label, con1) : other_fields)
701 -- These fields all have the same name, but are from
702 -- different constructors in the data type
703 = recoverM (return ()) $ mapM_ checkOne other_fields
704 -- Check that all the fields in the group have the same type
705 -- NB: this check assumes that all the constructors of a given
706 -- data type use the same type variables
708 tvs1 = mkVarSet (dataConAllTyVars con1)
709 res1 = dataConResTys con1
710 fty1 = dataConFieldType con1 label
712 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
713 = do { checkFieldCompat label con1 con2 tvs1 res1 res2 fty1 fty2
714 ; checkFieldCompat label con2 con1 tvs2 res2 res1 fty2 fty1 }
716 tvs2 = mkVarSet (dataConAllTyVars con2)
717 res2 = dataConResTys con2
718 fty2 = dataConFieldType con2 label
720 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
721 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
722 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
724 mb_subst1 = tcMatchTys tvs1 res1 res2
725 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
727 -------------------------------
728 checkValidDataCon :: TyCon -> DataCon -> TcM ()
729 checkValidDataCon tc con
730 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
731 addErrCtxt (dataConCtxt con) $
732 do { checkTc (dataConTyCon con == tc) (badDataConTyCon con)
733 ; checkValidType ctxt (dataConUserType con) }
735 ctxt = ConArgCtxt (dataConName con)
737 -------------------------------
738 checkValidClass :: Class -> TcM ()
740 = do { -- CHECK ARITY 1 FOR HASKELL 1.4
741 gla_exts <- doptM Opt_GlasgowExts
743 -- Check that the class is unary, unless GlaExs
744 ; checkTc (notNull tyvars) (nullaryClassErr cls)
745 ; checkTc (gla_exts || unary) (classArityErr cls)
747 -- Check the super-classes
748 ; checkValidTheta (ClassSCCtxt (className cls)) theta
750 -- Check the class operations
751 ; mappM_ (check_op gla_exts) op_stuff
753 -- Check that if the class has generic methods, then the
754 -- class has only one parameter. We can't do generic
755 -- multi-parameter type classes!
756 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
758 -- Check that the class has no associated types, unless GlaExs
759 ; checkTc (gla_exts || no_ats) (badATDecl cls)
762 (tyvars, theta, _, op_stuff) = classBigSig cls
763 unary = isSingleton tyvars
764 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
765 no_ats = True -- !!!TODO: determine whether the class has ATs -=chak
767 check_op gla_exts (sel_id, dm)
768 = addErrCtxt (classOpCtxt sel_id tau) $ do
769 { checkValidTheta SigmaCtxt (tail theta)
770 -- The 'tail' removes the initial (C a) from the
771 -- class itself, leaving just the method type
773 ; checkValidType (FunSigCtxt op_name) tau
775 -- Check that the type mentions at least one of
776 -- the class type variables
777 ; checkTc (any (`elemVarSet` tyVarsOfType tau) tyvars)
778 (noClassTyVarErr cls sel_id)
780 -- Check that for a generic method, the type of
781 -- the method is sufficiently simple
782 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
783 (badGenericMethodType op_name op_ty)
786 op_name = idName sel_id
787 op_ty = idType sel_id
788 (_,theta1,tau1) = tcSplitSigmaTy op_ty
789 (_,theta2,tau2) = tcSplitSigmaTy tau1
790 (theta,tau) | gla_exts = (theta1 ++ theta2, tau2)
791 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
792 -- Ugh! The function might have a type like
793 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
794 -- With -fglasgow-exts, we want to allow this, even though the inner
795 -- forall has an (Eq a) constraint. Whereas in general, each constraint
796 -- in the context of a for-all must mention at least one quantified
797 -- type variable. What a mess!
800 ---------------------------------------------------------------------
801 resultTypeMisMatch field_name con1 con2
802 = vcat [sep [ptext SLIT("Constructors") <+> ppr con1 <+> ptext SLIT("and") <+> ppr con2,
803 ptext SLIT("have a common field") <+> quotes (ppr field_name) <> comma],
804 nest 2 $ ptext SLIT("but have different result types")]
805 fieldTypeMisMatch field_name con1 con2
806 = sep [ptext SLIT("Constructors") <+> ppr con1 <+> ptext SLIT("and") <+> ppr con2,
807 ptext SLIT("give different types for field"), quotes (ppr field_name)]
809 dataConCtxt con = ptext SLIT("In the definition of data constructor") <+> quotes (ppr con)
811 classOpCtxt sel_id tau = sep [ptext SLIT("When checking the class method:"),
812 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
815 = ptext SLIT("No parameters for class") <+> quotes (ppr cls)
818 = vcat [ptext SLIT("Too many parameters for class") <+> quotes (ppr cls),
819 parens (ptext SLIT("Use -fglasgow-exts to allow multi-parameter classes"))]
821 noClassTyVarErr clas op
822 = sep [ptext SLIT("The class method") <+> quotes (ppr op),
823 ptext SLIT("mentions none of the type variables of the class") <+>
824 ppr clas <+> hsep (map ppr (classTyVars clas))]
826 genericMultiParamErr clas
827 = ptext SLIT("The multi-parameter class") <+> quotes (ppr clas) <+>
828 ptext SLIT("cannot have generic methods")
830 badGenericMethodType op op_ty
831 = hang (ptext SLIT("Generic method type is too complex"))
832 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
833 ptext SLIT("You can only use type variables, arrows, lists, and tuples")])
836 = setSrcSpan (getLoc (head sorted_decls)) $
837 addErr (sep [ptext SLIT("Cycle in type synonym declarations:"),
838 nest 2 (vcat (map ppr_decl sorted_decls))])
840 sorted_decls = sortLocated syn_decls
841 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
844 = setSrcSpan (getLoc (head sorted_decls)) $
845 addErr (sep [ptext SLIT("Cycle in class declarations (via superclasses):"),
846 nest 2 (vcat (map ppr_decl sorted_decls))])
848 sorted_decls = sortLocated cls_decls
849 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
851 sortLocated :: [Located a] -> [Located a]
852 sortLocated things = sortLe le things
854 le (L l1 _) (L l2 _) = l1 <= l2
856 badDataConTyCon data_con
857 = hang (ptext SLIT("Data constructor") <+> quotes (ppr data_con) <+>
858 ptext SLIT("returns type") <+> quotes (ppr (dataConTyCon data_con)))
859 2 (ptext SLIT("instead of its parent type"))
862 = vcat [ ptext SLIT("Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
863 , nest 2 (parens $ ptext SLIT("Use -fglasgow-exts to allow GADTs")) ]
865 badStupidTheta tc_name
866 = ptext SLIT("A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
868 newtypeConError tycon n
869 = sep [ptext SLIT("A newtype must have exactly one constructor,"),
870 nest 2 $ ptext SLIT("but") <+> quotes (ppr tycon) <+> ptext SLIT("has") <+> speakN n ]
873 = sep [ptext SLIT("A newtype constructor cannot have an existential context,"),
874 nest 2 $ ptext SLIT("but") <+> quotes (ppr con) <+> ptext SLIT("does")]
876 newtypeFieldErr con_name n_flds
877 = sep [ptext SLIT("The constructor of a newtype must have exactly one field"),
878 nest 2 $ ptext SLIT("but") <+> quotes (ppr con_name) <+> ptext SLIT("has") <+> speakN n_flds]
881 = vcat [ ptext SLIT("Illegal associated type declaration in") <+> quotes (ppr cl_name)
882 , nest 2 (parens $ ptext SLIT("Use -fglasgow-exts to allow ATs")) ]
884 emptyConDeclsErr tycon
885 = sep [quotes (ppr tycon) <+> ptext SLIT("has no constructors"),
886 nest 2 $ ptext SLIT("(-fglasgow-exts permits this)")]