2 % (c) The University of Glasgow 2006
3 % (c) The AQUA Project, Glasgow University, 1996-1998
6 TcTyClsDecls: Typecheck type and class declarations
10 tcTyAndClassDecls, tcFamInstDecl, mkAuxBinds
13 #include "HsVersions.h"
28 import TysWiredIn ( unitTy )
36 import MkId ( rEC_SEL_ERROR_ID )
52 import Unique ( mkBuiltinUnique )
57 import Control.Monad ( mplus )
61 %************************************************************************
63 \subsection{Type checking for type and class declarations}
65 %************************************************************************
69 Consider a mutually-recursive group, binding
70 a type constructor T and a class C.
72 Step 1: getInitialKind
73 Construct a KindEnv by binding T and C to a kind variable
76 In that environment, do a kind check
78 Step 3: Zonk the kinds
80 Step 4: buildTyConOrClass
81 Construct an environment binding T to a TyCon and C to a Class.
82 a) Their kinds comes from zonking the relevant kind variable
83 b) Their arity (for synonyms) comes direct from the decl
84 c) The funcional dependencies come from the decl
85 d) The rest comes a knot-tied binding of T and C, returned from Step 4
86 e) The variances of the tycons in the group is calculated from
90 In this environment, walk over the decls, constructing the TyCons and Classes.
91 This uses in a strict way items (a)-(c) above, which is why they must
92 be constructed in Step 4. Feed the results back to Step 4.
93 For this step, pass the is-recursive flag as the wimp-out flag
97 Step 6: Extend environment
98 We extend the type environment with bindings not only for the TyCons and Classes,
99 but also for their "implicit Ids" like data constructors and class selectors
101 Step 7: checkValidTyCl
102 For a recursive group only, check all the decls again, just
103 to check all the side conditions on validity. We could not
104 do this before because we were in a mutually recursive knot.
106 Identification of recursive TyCons
107 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
108 The knot-tying parameters: @rec_details_list@ is an alist mapping @Name@s to
111 Identifying a TyCon as recursive serves two purposes
113 1. Avoid infinite types. Non-recursive newtypes are treated as
114 "transparent", like type synonyms, after the type checker. If we did
115 this for all newtypes, we'd get infinite types. So we figure out for
116 each newtype whether it is "recursive", and add a coercion if so. In
117 effect, we are trying to "cut the loops" by identifying a loop-breaker.
119 2. Avoid infinite unboxing. This is nothing to do with newtypes.
123 Well, this function diverges, but we don't want the strictness analyser
124 to diverge. But the strictness analyser will diverge because it looks
125 deeper and deeper into the structure of T. (I believe there are
126 examples where the function does something sane, and the strictness
127 analyser still diverges, but I can't see one now.)
129 Now, concerning (1), the FC2 branch currently adds a coercion for ALL
130 newtypes. I did this as an experiment, to try to expose cases in which
131 the coercions got in the way of optimisations. If it turns out that we
132 can indeed always use a coercion, then we don't risk recursive types,
133 and don't need to figure out what the loop breakers are.
135 For newtype *families* though, we will always have a coercion, so they
136 are always loop breakers! So you can easily adjust the current
137 algorithm by simply treating all newtype families as loop breakers (and
138 indeed type families). I think.
141 tcTyAndClassDecls :: ModDetails -> [LTyClDecl Name]
142 -> TcM (TcGblEnv, -- Input env extended by types and classes
143 -- and their implicit Ids,DataCons
144 HsValBinds Name) -- Renamed bindings for record selectors
145 -- Fails if there are any errors
147 tcTyAndClassDecls boot_details allDecls
148 = checkNoErrs $ -- The code recovers internally, but if anything gave rise to
149 -- an error we'd better stop now, to avoid a cascade
150 do { -- Omit instances of type families; they are handled together
151 -- with the *heads* of class instances
152 ; let decls = filter (not . isFamInstDecl . unLoc) allDecls
154 -- First check for cyclic type synonysm or classes
155 -- See notes with checkCycleErrs
156 ; checkCycleErrs decls
158 ; traceTc (text "tcTyAndCl" <+> ppr mod)
159 ; (syn_tycons, alg_tyclss) <- fixM (\ ~(_rec_syn_tycons, rec_alg_tyclss) ->
160 do { let { -- Seperate ordinary synonyms from all other type and
161 -- class declarations and add all associated type
162 -- declarations from type classes. The latter is
163 -- required so that the temporary environment for the
164 -- knot includes all associated family declarations.
165 ; (syn_decls, alg_decls) = partition (isSynDecl . unLoc)
167 ; alg_at_decls = concatMap addATs alg_decls
169 -- Extend the global env with the knot-tied results
170 -- for data types and classes
172 -- We must populate the environment with the loop-tied
173 -- T's right away, because the kind checker may "fault
174 -- in" some type constructors that recursively
176 ; let gbl_things = mkGlobalThings alg_at_decls rec_alg_tyclss
177 ; tcExtendRecEnv gbl_things $ do
179 -- Kind-check the declarations
180 { (kc_syn_decls, kc_alg_decls) <- kcTyClDecls syn_decls alg_decls
182 ; let { -- Calculate rec-flag
183 ; calc_rec = calcRecFlags boot_details rec_alg_tyclss
184 ; tc_decl = addLocM (tcTyClDecl calc_rec) }
186 -- Type-check the type synonyms, and extend the envt
187 ; syn_tycons <- tcSynDecls kc_syn_decls
188 ; tcExtendGlobalEnv syn_tycons $ do
190 -- Type-check the data types and classes
191 { alg_tyclss <- mapM tc_decl kc_alg_decls
192 ; return (syn_tycons, concat alg_tyclss)
194 -- Finished with knot-tying now
195 -- Extend the environment with the finished things
196 ; tcExtendGlobalEnv (syn_tycons ++ alg_tyclss) $ do
198 -- Perform the validity check
199 { traceTc (text "ready for validity check")
200 ; mapM_ (addLocM checkValidTyCl) decls
201 ; traceTc (text "done")
203 -- Add the implicit things;
204 -- we want them in the environment because
205 -- they may be mentioned in interface files
206 -- NB: All associated types and their implicit things will be added a
207 -- second time here. This doesn't matter as the definitions are
209 ; let { implicit_things = concatMap implicitTyThings alg_tyclss
210 ; aux_binds = mkAuxBinds alg_tyclss }
211 ; traceTc ((text "Adding" <+> ppr alg_tyclss)
212 $$ (text "and" <+> ppr implicit_things))
213 ; env <- tcExtendGlobalEnv implicit_things getGblEnv
214 ; return (env, aux_binds) }
217 -- Pull associated types out of class declarations, to tie them into the
219 -- NB: We put them in the same place in the list as `tcTyClDecl' will
220 -- eventually put the matching `TyThing's. That's crucial; otherwise,
221 -- the two argument lists of `mkGlobalThings' don't match up.
222 addATs decl@(L _ (ClassDecl {tcdATs = ats})) = decl : ats
225 mkGlobalThings :: [LTyClDecl Name] -- The decls
226 -> [TyThing] -- Knot-tied, in 1-1 correspondence with the decls
228 -- Driven by the Decls, and treating the TyThings lazily
229 -- make a TypeEnv for the new things
230 mkGlobalThings decls things
231 = map mk_thing (decls `zipLazy` things)
233 mk_thing (L _ (ClassDecl {tcdLName = L _ name}), ~(AClass cl))
235 mk_thing (L _ decl, ~(ATyCon tc))
236 = (tcdName decl, ATyCon tc)
240 %************************************************************************
242 Type checking family instances
244 %************************************************************************
246 Family instances are somewhat of a hybrid. They are processed together with
247 class instance heads, but can contain data constructors and hence they share a
248 lot of kinding and type checking code with ordinary algebraic data types (and
252 tcFamInstDecl :: LTyClDecl Name -> TcM TyThing
253 tcFamInstDecl (L loc decl)
254 = -- Prime error recovery, set source location
257 do { -- type families require -XTypeFamilies and can't be in an
259 ; type_families <- doptM Opt_TypeFamilies
260 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
261 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
262 ; checkTc (not is_boot) $ badBootFamInstDeclErr
264 -- Perform kind and type checking
265 ; tc <- tcFamInstDecl1 decl
266 ; checkValidTyCon tc -- Remember to check validity;
267 -- no recursion to worry about here
268 ; return (ATyCon tc) }
270 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
273 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
274 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
275 do { -- check that the family declaration is for a synonym
276 unless (isSynTyCon family) $
277 addErr (wrongKindOfFamily family)
279 ; -- (1) kind check the right-hand side of the type equation
280 ; k_rhs <- kcCheckHsType (tcdSynRhs decl) resKind
282 -- we need the exact same number of type parameters as the family
284 ; let famArity = tyConArity family
285 ; checkTc (length k_typats == famArity) $
286 wrongNumberOfParmsErr famArity
288 -- (2) type check type equation
289 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
290 ; t_typats <- mapM tcHsKindedType k_typats
291 ; t_rhs <- tcHsKindedType k_rhs
293 -- (3) check the well-formedness of the instance
294 ; checkValidTypeInst t_typats t_rhs
296 -- (4) construct representation tycon
297 ; rep_tc_name <- newFamInstTyConName tc_name loc
298 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
299 (typeKind t_rhs) (Just (family, t_typats))
302 -- "newtype instance" and "data instance"
303 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
305 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
306 do { -- check that the family declaration is for the right kind
307 unless (isAlgTyCon fam_tycon) $
308 addErr (wrongKindOfFamily fam_tycon)
310 ; -- (1) kind check the data declaration as usual
311 ; k_decl <- kcDataDecl decl k_tvs
312 ; let k_ctxt = tcdCtxt k_decl
313 k_cons = tcdCons k_decl
315 -- result kind must be '*' (otherwise, we have too few patterns)
316 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
318 -- (2) type check indexed data type declaration
319 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
320 ; unbox_strict <- doptM Opt_UnboxStrictFields
322 -- kind check the type indexes and the context
323 ; t_typats <- mapM tcHsKindedType k_typats
324 ; stupid_theta <- tcHsKindedContext k_ctxt
327 -- (a) left-hand side contains no type family applications
328 -- (vanilla synonyms are fine, though, and we checked for
330 ; mapM_ checkTyFamFreeness t_typats
332 -- (b) a newtype has exactly one constructor
333 ; checkTc (new_or_data == DataType || isSingleton k_cons) $
334 newtypeConError tc_name (length k_cons)
336 -- (4) construct representation tycon
337 ; rep_tc_name <- newFamInstTyConName tc_name loc
338 ; let ex_ok = True -- Existentials ok for type families!
339 ; fixM (\ rep_tycon -> do
340 { let orig_res_ty = mkTyConApp fam_tycon t_typats
341 ; data_cons <- tcConDecls unbox_strict ex_ok rep_tycon
342 (t_tvs, orig_res_ty) k_cons
345 DataType -> return (mkDataTyConRhs data_cons)
346 NewType -> ASSERT( not (null data_cons) )
347 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
348 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
349 False h98_syntax (Just (fam_tycon, t_typats))
350 -- We always assume that indexed types are recursive. Why?
351 -- (1) Due to their open nature, we can never be sure that a
352 -- further instance might not introduce a new recursive
353 -- dependency. (2) They are always valid loop breakers as
354 -- they involve a coercion.
358 h98_syntax = case cons of -- All constructors have same shape
359 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
362 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
364 -- Kind checking of indexed types
367 -- Kind check type patterns and kind annotate the embedded type variables.
369 -- * Here we check that a type instance matches its kind signature, but we do
370 -- not check whether there is a pattern for each type index; the latter
371 -- check is only required for type synonym instances.
373 kcIdxTyPats :: TyClDecl Name
374 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
375 -- ^^kinded tvs ^^kinded ty pats ^^res kind
377 kcIdxTyPats decl thing_inside
378 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
379 do { fam_tycon <- tcLookupLocatedTyCon (tcdLName decl)
380 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
381 ; hs_typats = fromJust $ tcdTyPats decl }
383 -- we may not have more parameters than the kind indicates
384 ; checkTc (length kinds >= length hs_typats) $
385 tooManyParmsErr (tcdLName decl)
387 -- type functions can have a higher-kinded result
388 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
389 ; typats <- zipWithM kcCheckHsType hs_typats kinds
390 ; thing_inside tvs typats resultKind fam_tycon
396 %************************************************************************
400 %************************************************************************
402 We need to kind check all types in the mutually recursive group
403 before we know the kind of the type variables. For example:
406 op :: D b => a -> b -> b
409 bop :: (Monad c) => ...
411 Here, the kind of the locally-polymorphic type variable "b"
412 depends on *all the uses of class D*. For example, the use of
413 Monad c in bop's type signature means that D must have kind Type->Type.
415 However type synonyms work differently. They can have kinds which don't
416 just involve (->) and *:
417 type R = Int# -- Kind #
418 type S a = Array# a -- Kind * -> #
419 type T a b = (# a,b #) -- Kind * -> * -> (# a,b #)
420 So we must infer their kinds from their right-hand sides *first* and then
421 use them, whereas for the mutually recursive data types D we bring into
422 scope kind bindings D -> k, where k is a kind variable, and do inference.
426 This treatment of type synonyms only applies to Haskell 98-style synonyms.
427 General type functions can be recursive, and hence, appear in `alg_decls'.
429 The kind of a type family is solely determinded by its kind signature;
430 hence, only kind signatures participate in the construction of the initial
431 kind environment (as constructed by `getInitialKind'). In fact, we ignore
432 instances of families altogether in the following. However, we need to
433 include the kinds of associated families into the construction of the
434 initial kind environment. (This is handled by `allDecls').
437 kcTyClDecls :: [LTyClDecl Name] -> [Located (TyClDecl Name)]
438 -> TcM ([LTyClDecl Name], [Located (TyClDecl Name)])
439 kcTyClDecls syn_decls alg_decls
440 = do { -- First extend the kind env with each data type, class, and
441 -- indexed type, mapping them to a type variable
442 let initialKindDecls = concat [allDecls decl | L _ decl <- alg_decls]
443 ; alg_kinds <- mapM getInitialKind initialKindDecls
444 ; tcExtendKindEnv alg_kinds $ do
446 -- Now kind-check the type synonyms, in dependency order
447 -- We do these differently to data type and classes,
448 -- because a type synonym can be an unboxed type
450 -- and a kind variable can't unify with UnboxedTypeKind
451 -- So we infer their kinds in dependency order
452 { (kc_syn_decls, syn_kinds) <- kcSynDecls (calcSynCycles syn_decls)
453 ; tcExtendKindEnv syn_kinds $ do
455 -- Now kind-check the data type, class, and kind signatures,
456 -- returning kind-annotated decls; we don't kind-check
457 -- instances of indexed types yet, but leave this to
459 { kc_alg_decls <- mapM (wrapLocM kcTyClDecl)
460 (filter (not . isFamInstDecl . unLoc) alg_decls)
462 ; return (kc_syn_decls, kc_alg_decls) }}}
464 -- get all declarations relevant for determining the initial kind
466 allDecls (decl@ClassDecl {tcdATs = ats}) = decl : [ at
469 allDecls decl | isFamInstDecl decl = []
472 ------------------------------------------------------------------------
473 getInitialKind :: TyClDecl Name -> TcM (Name, TcKind)
474 -- Only for data type, class, and indexed type declarations
475 -- Get as much info as possible from the data, class, or indexed type decl,
476 -- so as to maximise usefulness of error messages
478 = do { arg_kinds <- mapM (mk_arg_kind . unLoc) (tyClDeclTyVars decl)
479 ; res_kind <- mk_res_kind decl
480 ; return (tcdName decl, mkArrowKinds arg_kinds res_kind) }
482 mk_arg_kind (UserTyVar _) = newKindVar
483 mk_arg_kind (KindedTyVar _ kind) = return kind
485 mk_res_kind (TyFamily { tcdKind = Just kind }) = return kind
486 mk_res_kind (TyData { tcdKindSig = Just kind }) = return kind
487 -- On GADT-style declarations we allow a kind signature
488 -- data T :: *->* where { ... }
489 mk_res_kind _ = return liftedTypeKind
493 kcSynDecls :: [SCC (LTyClDecl Name)]
494 -> TcM ([LTyClDecl Name], -- Kind-annotated decls
495 [(Name,TcKind)]) -- Kind bindings
498 kcSynDecls (group : groups)
499 = do { (decl, nk) <- kcSynDecl group
500 ; (decls, nks) <- tcExtendKindEnv [nk] (kcSynDecls groups)
501 ; return (decl:decls, nk:nks) }
504 kcSynDecl :: SCC (LTyClDecl Name)
505 -> TcM (LTyClDecl Name, -- Kind-annotated decls
506 (Name,TcKind)) -- Kind bindings
507 kcSynDecl (AcyclicSCC (L loc decl))
508 = tcAddDeclCtxt decl $
509 kcHsTyVars (tcdTyVars decl) (\ k_tvs ->
510 do { traceTc (text "kcd1" <+> ppr (unLoc (tcdLName decl)) <+> brackets (ppr (tcdTyVars decl))
511 <+> brackets (ppr k_tvs))
512 ; (k_rhs, rhs_kind) <- kcHsType (tcdSynRhs decl)
513 ; traceTc (text "kcd2" <+> ppr (unLoc (tcdLName decl)))
514 ; let tc_kind = foldr (mkArrowKind . kindedTyVarKind) rhs_kind k_tvs
515 ; return (L loc (decl { tcdTyVars = k_tvs, tcdSynRhs = k_rhs }),
516 (unLoc (tcdLName decl), tc_kind)) })
518 kcSynDecl (CyclicSCC decls)
519 = do { recSynErr decls; failM } -- Fail here to avoid error cascade
520 -- of out-of-scope tycons
522 kindedTyVarKind :: LHsTyVarBndr Name -> Kind
523 kindedTyVarKind (L _ (KindedTyVar _ k)) = k
524 kindedTyVarKind x = pprPanic "kindedTyVarKind" (ppr x)
526 ------------------------------------------------------------------------
527 kcTyClDecl :: TyClDecl Name -> TcM (TyClDecl Name)
528 -- Not used for type synonyms (see kcSynDecl)
530 kcTyClDecl decl@(TyData {})
531 = ASSERT( not . isFamInstDecl $ decl ) -- must not be a family instance
532 kcTyClDeclBody decl $
535 kcTyClDecl decl@(TyFamily {})
536 = kcFamilyDecl [] decl -- the empty list signals a toplevel decl
538 kcTyClDecl decl@(ClassDecl {tcdCtxt = ctxt, tcdSigs = sigs, tcdATs = ats})
539 = kcTyClDeclBody decl $ \ tvs' ->
540 do { ctxt' <- kcHsContext ctxt
541 ; ats' <- mapM (wrapLocM (kcFamilyDecl tvs')) ats
542 ; sigs' <- mapM (wrapLocM kc_sig) sigs
543 ; return (decl {tcdTyVars = tvs', tcdCtxt = ctxt', tcdSigs = sigs',
546 kc_sig (TypeSig nm op_ty) = do { op_ty' <- kcHsLiftedSigType op_ty
547 ; return (TypeSig nm op_ty') }
548 kc_sig other_sig = return other_sig
550 kcTyClDecl decl@(ForeignType {})
553 kcTyClDecl (TySynonym {}) = panic "kcTyClDecl TySynonym"
555 kcTyClDeclBody :: TyClDecl Name
556 -> ([LHsTyVarBndr Name] -> TcM a)
558 -- getInitialKind has made a suitably-shaped kind for the type or class
559 -- Unpack it, and attribute those kinds to the type variables
560 -- Extend the env with bindings for the tyvars, taken from
561 -- the kind of the tycon/class. Give it to the thing inside, and
562 -- check the result kind matches
563 kcTyClDeclBody decl thing_inside
564 = tcAddDeclCtxt decl $
565 do { tc_ty_thing <- tcLookupLocated (tcdLName decl)
566 ; let tc_kind = case tc_ty_thing of
568 _ -> pprPanic "kcTyClDeclBody" (ppr tc_ty_thing)
569 (kinds, _) = splitKindFunTys tc_kind
570 hs_tvs = tcdTyVars decl
571 kinded_tvs = ASSERT( length kinds >= length hs_tvs )
572 [ L loc (KindedTyVar (hsTyVarName tv) k)
573 | (L loc tv, k) <- zip hs_tvs kinds]
574 ; tcExtendKindEnvTvs kinded_tvs (thing_inside kinded_tvs) }
576 -- Kind check a data declaration, assuming that we already extended the
577 -- kind environment with the type variables of the left-hand side (these
578 -- kinded type variables are also passed as the second parameter).
580 kcDataDecl :: TyClDecl Name -> [LHsTyVarBndr Name] -> TcM (TyClDecl Name)
581 kcDataDecl decl@(TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdCons = cons})
583 = do { ctxt' <- kcHsContext ctxt
584 ; cons' <- mapM (wrapLocM kc_con_decl) cons
585 ; return (decl {tcdTyVars = tvs, tcdCtxt = ctxt', tcdCons = cons'}) }
587 -- doc comments are typechecked to Nothing here
588 kc_con_decl (ConDecl name expl ex_tvs ex_ctxt details res _) = do
589 kcHsTyVars ex_tvs $ \ex_tvs' -> do
590 ex_ctxt' <- kcHsContext ex_ctxt
591 details' <- kc_con_details details
593 ResTyH98 -> return ResTyH98
594 ResTyGADT ty -> do { ty' <- kcHsSigType ty; return (ResTyGADT ty') }
595 return (ConDecl name expl ex_tvs' ex_ctxt' details' res' Nothing)
597 kc_con_details (PrefixCon btys)
598 = do { btys' <- mapM kc_larg_ty btys
599 ; return (PrefixCon btys') }
600 kc_con_details (InfixCon bty1 bty2)
601 = do { bty1' <- kc_larg_ty bty1
602 ; bty2' <- kc_larg_ty bty2
603 ; return (InfixCon bty1' bty2') }
604 kc_con_details (RecCon fields)
605 = do { fields' <- mapM kc_field fields
606 ; return (RecCon fields') }
608 kc_field (ConDeclField fld bty d) = do { bty' <- kc_larg_ty bty
609 ; return (ConDeclField fld bty' d) }
611 kc_larg_ty bty = case new_or_data of
612 DataType -> kcHsSigType bty
613 NewType -> kcHsLiftedSigType bty
614 -- Can't allow an unlifted type for newtypes, because we're effectively
615 -- going to remove the constructor while coercing it to a lifted type.
616 -- And newtypes can't be bang'd
617 kcDataDecl d _ = pprPanic "kcDataDecl" (ppr d)
619 -- Kind check a family declaration or type family default declaration.
621 kcFamilyDecl :: [LHsTyVarBndr Name] -- tyvars of enclosing class decl if any
622 -> TyClDecl Name -> TcM (TyClDecl Name)
623 kcFamilyDecl classTvs decl@(TyFamily {tcdKind = kind})
624 = kcTyClDeclBody decl $ \tvs' ->
625 do { mapM_ unifyClassParmKinds tvs'
626 ; return (decl {tcdTyVars = tvs',
627 tcdKind = kind `mplus` Just liftedTypeKind})
628 -- default result kind is '*'
631 unifyClassParmKinds (L _ (KindedTyVar n k))
632 | Just classParmKind <- lookup n classTyKinds = unifyKind k classParmKind
633 | otherwise = return ()
634 unifyClassParmKinds x = pprPanic "kcFamilyDecl/unifyClassParmKinds" (ppr x)
635 classTyKinds = [(n, k) | L _ (KindedTyVar n k) <- classTvs]
636 kcFamilyDecl _ (TySynonym {}) -- type family defaults
637 = panic "TcTyClsDecls.kcFamilyDecl: not implemented yet"
638 kcFamilyDecl _ d = pprPanic "kcFamilyDecl" (ppr d)
642 %************************************************************************
644 \subsection{Type checking}
646 %************************************************************************
649 tcSynDecls :: [LTyClDecl Name] -> TcM [TyThing]
650 tcSynDecls [] = return []
651 tcSynDecls (decl : decls)
652 = do { syn_tc <- addLocM tcSynDecl decl
653 ; syn_tcs <- tcExtendGlobalEnv [syn_tc] (tcSynDecls decls)
654 ; return (syn_tc : syn_tcs) }
657 tcSynDecl :: TyClDecl Name -> TcM TyThing
659 (TySynonym {tcdLName = L _ tc_name, tcdTyVars = tvs, tcdSynRhs = rhs_ty})
660 = tcTyVarBndrs tvs $ \ tvs' -> do
661 { traceTc (text "tcd1" <+> ppr tc_name)
662 ; rhs_ty' <- tcHsKindedType rhs_ty
663 ; tycon <- buildSynTyCon tc_name tvs' (SynonymTyCon rhs_ty')
664 (typeKind rhs_ty') Nothing
665 ; return (ATyCon tycon)
667 tcSynDecl d = pprPanic "tcSynDecl" (ppr d)
670 tcTyClDecl :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
672 tcTyClDecl calc_isrec decl
673 = tcAddDeclCtxt decl (tcTyClDecl1 calc_isrec decl)
675 -- "type family" declarations
676 tcTyClDecl1 :: (Name -> RecFlag) -> TyClDecl Name -> TcM [TyThing]
677 tcTyClDecl1 _calc_isrec
678 (TyFamily {tcdFlavour = TypeFamily,
679 tcdLName = L _ tc_name, tcdTyVars = tvs,
680 tcdKind = Just kind}) -- NB: kind at latest added during kind checking
681 = tcTyVarBndrs tvs $ \ tvs' -> do
682 { traceTc (text "type family: " <+> ppr tc_name)
684 -- Check that we don't use families without -XTypeFamilies
685 ; idx_tys <- doptM Opt_TypeFamilies
686 ; checkTc idx_tys $ badFamInstDecl tc_name
688 -- Check for no type indices
689 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
691 ; tycon <- buildSynTyCon tc_name tvs' (OpenSynTyCon kind Nothing) kind Nothing
692 ; return [ATyCon tycon]
695 -- "data family" declaration
696 tcTyClDecl1 _calc_isrec
697 (TyFamily {tcdFlavour = DataFamily,
698 tcdLName = L _ tc_name, tcdTyVars = tvs, tcdKind = mb_kind})
699 = tcTyVarBndrs tvs $ \ tvs' -> do
700 { traceTc (text "data family: " <+> ppr tc_name)
701 ; extra_tvs <- tcDataKindSig mb_kind
702 ; let final_tvs = tvs' ++ extra_tvs -- we may not need these
705 -- Check that we don't use families without -XTypeFamilies
706 ; idx_tys <- doptM Opt_TypeFamilies
707 ; checkTc idx_tys $ badFamInstDecl tc_name
709 -- Check for no type indices
710 ; checkTc (not (null tvs)) (noIndexTypes tc_name)
712 ; tycon <- buildAlgTyCon tc_name final_tvs []
713 mkOpenDataTyConRhs Recursive False True Nothing
714 ; return [ATyCon tycon]
717 -- "newtype" and "data"
718 -- NB: not used for newtype/data instances (whether associated or not)
719 tcTyClDecl1 calc_isrec
720 (TyData {tcdND = new_or_data, tcdCtxt = ctxt, tcdTyVars = tvs,
721 tcdLName = L _ tc_name, tcdKindSig = mb_ksig, tcdCons = cons})
722 = tcTyVarBndrs tvs $ \ tvs' -> do
723 { extra_tvs <- tcDataKindSig mb_ksig
724 ; let final_tvs = tvs' ++ extra_tvs
725 ; stupid_theta <- tcHsKindedContext ctxt
726 ; want_generic <- doptM Opt_Generics
727 ; unbox_strict <- doptM Opt_UnboxStrictFields
728 ; empty_data_decls <- doptM Opt_EmptyDataDecls
729 ; kind_signatures <- doptM Opt_KindSignatures
730 ; existential_ok <- doptM Opt_ExistentialQuantification
731 ; gadt_ok <- doptM Opt_GADTs
732 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
733 ; let ex_ok = existential_ok || gadt_ok -- Data cons can have existential context
735 -- Check that we don't use GADT syntax in H98 world
736 ; checkTc (gadt_ok || h98_syntax) (badGadtDecl tc_name)
738 -- Check that we don't use kind signatures without Glasgow extensions
739 ; checkTc (kind_signatures || isNothing mb_ksig) (badSigTyDecl tc_name)
741 -- Check that the stupid theta is empty for a GADT-style declaration
742 ; checkTc (null stupid_theta || h98_syntax) (badStupidTheta tc_name)
744 -- Check that a newtype has exactly one constructor
745 -- Do this before checking for empty data decls, so that
746 -- we don't suggest -XEmptyDataDecls for newtypes
747 ; checkTc (new_or_data == DataType || isSingleton cons)
748 (newtypeConError tc_name (length cons))
750 -- Check that there's at least one condecl,
751 -- or else we're reading an hs-boot file, or -XEmptyDataDecls
752 ; checkTc (not (null cons) || empty_data_decls || is_boot)
753 (emptyConDeclsErr tc_name)
755 ; tycon <- fixM (\ tycon -> do
756 { let res_ty = mkTyConApp tycon (mkTyVarTys final_tvs)
757 ; data_cons <- tcConDecls unbox_strict ex_ok
758 tycon (final_tvs, res_ty) cons
760 if null cons && is_boot -- In a hs-boot file, empty cons means
761 then return AbstractTyCon -- "don't know"; hence Abstract
762 else case new_or_data of
763 DataType -> return (mkDataTyConRhs data_cons)
764 NewType -> ASSERT( not (null data_cons) )
765 mkNewTyConRhs tc_name tycon (head data_cons)
766 ; buildAlgTyCon tc_name final_tvs stupid_theta tc_rhs is_rec
767 (want_generic && canDoGenerics data_cons) h98_syntax Nothing
769 ; return [ATyCon tycon]
772 is_rec = calc_isrec tc_name
773 h98_syntax = case cons of -- All constructors have same shape
774 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
777 tcTyClDecl1 calc_isrec
778 (ClassDecl {tcdLName = L _ class_name, tcdTyVars = tvs,
779 tcdCtxt = ctxt, tcdMeths = meths,
780 tcdFDs = fundeps, tcdSigs = sigs, tcdATs = ats} )
781 = tcTyVarBndrs tvs $ \ tvs' -> do
782 { ctxt' <- tcHsKindedContext ctxt
783 ; fds' <- mapM (addLocM tc_fundep) fundeps
784 ; atss <- mapM (addLocM (tcTyClDecl1 (const Recursive))) ats
785 -- NB: 'ats' only contains "type family" and "data family"
786 -- declarations as well as type family defaults
787 ; let ats' = map (setAssocFamilyPermutation tvs') (concat atss)
788 ; sig_stuff <- tcClassSigs class_name sigs meths
789 ; clas <- fixM (\ clas ->
790 let -- This little knot is just so we can get
791 -- hold of the name of the class TyCon, which we
792 -- need to look up its recursiveness
793 tycon_name = tyConName (classTyCon clas)
794 tc_isrec = calc_isrec tycon_name
796 buildClass False {- Must include unfoldings for selectors -}
797 class_name tvs' ctxt' fds' ats'
799 ; return (AClass clas : ats')
800 -- NB: Order is important due to the call to `mkGlobalThings' when
801 -- tying the the type and class declaration type checking knot.
804 tc_fundep (tvs1, tvs2) = do { tvs1' <- mapM tcLookupTyVar tvs1 ;
805 ; tvs2' <- mapM tcLookupTyVar tvs2 ;
806 ; return (tvs1', tvs2') }
809 (ForeignType {tcdLName = L _ tc_name, tcdExtName = tc_ext_name})
810 = return [ATyCon (mkForeignTyCon tc_name tc_ext_name liftedTypeKind 0)]
812 tcTyClDecl1 _ d = pprPanic "tcTyClDecl1" (ppr d)
814 -----------------------------------
815 tcConDecls :: Bool -> Bool -> TyCon -> ([TyVar], Type)
816 -> [LConDecl Name] -> TcM [DataCon]
817 tcConDecls unbox ex_ok rep_tycon res_tmpl cons
818 = mapM (addLocM (tcConDecl unbox ex_ok rep_tycon res_tmpl)) cons
820 tcConDecl :: Bool -- True <=> -funbox-strict_fields
821 -> Bool -- True <=> -XExistentialQuantificaton or -XGADTs
822 -> TyCon -- Representation tycon
823 -> ([TyVar], Type) -- Return type template (with its template tyvars)
827 tcConDecl unbox_strict existential_ok rep_tycon res_tmpl -- Data types
828 (ConDecl name _ tvs ctxt details res_ty _)
829 = addErrCtxt (dataConCtxt name) $
830 tcTyVarBndrs tvs $ \ tvs' -> do
831 { ctxt' <- tcHsKindedContext ctxt
832 ; checkTc (existential_ok || (null tvs && null (unLoc ctxt)))
833 (badExistential name)
834 ; (univ_tvs, ex_tvs, eq_preds, res_ty') <- tcResultType res_tmpl tvs' res_ty
836 tc_datacon is_infix field_lbls btys
837 = do { (arg_tys, stricts) <- mapAndUnzipM (tcConArg unbox_strict) btys
838 ; buildDataCon (unLoc name) is_infix
840 univ_tvs ex_tvs eq_preds ctxt' arg_tys
842 -- NB: we put data_tc, the type constructor gotten from the
843 -- constructor type signature into the data constructor;
844 -- that way checkValidDataCon can complain if it's wrong.
847 PrefixCon btys -> tc_datacon False [] btys
848 InfixCon bty1 bty2 -> tc_datacon True [] [bty1,bty2]
849 RecCon fields -> tc_datacon False field_names btys
851 field_names = map (unLoc . cd_fld_name) fields
852 btys = map cd_fld_type fields
856 -- data instance T (b,c) where
857 -- TI :: forall e. e -> T (e,e)
859 -- The representation tycon looks like this:
860 -- data :R7T b c where
861 -- TI :: forall b1 c1. (b1 ~ c1) => b1 -> :R7T b1 c1
862 -- In this case orig_res_ty = T (e,e)
864 tcResultType :: ([TyVar], Type) -- Template for result type; e.g.
865 -- data instance T [a] b c = ...
866 -- gives template ([a,b,c], T [a] b c)
867 -> [TyVar] -- where MkT :: forall x y z. ...
869 -> TcM ([TyVar], -- Universal
870 [TyVar], -- Existential (distinct OccNames from univs)
871 [(TyVar,Type)], -- Equality predicates
872 Type) -- Typechecked return type
873 -- We don't check that the TyCon given in the ResTy is
874 -- the same as the parent tycon, becuase we are in the middle
875 -- of a recursive knot; so it's postponed until checkValidDataCon
877 tcResultType (tmpl_tvs, res_ty) dc_tvs ResTyH98
878 = return (tmpl_tvs, dc_tvs, [], res_ty)
879 -- In H98 syntax the dc_tvs are the existential ones
880 -- data T a b c = forall d e. MkT ...
881 -- The {a,b,c} are tc_tvs, and {d,e} are dc_tvs
883 tcResultType (tmpl_tvs, res_tmpl) dc_tvs (ResTyGADT res_ty)
884 -- E.g. data T [a] b c where
885 -- MkT :: forall x y z. T [(x,y)] z z
887 -- Univ tyvars Eq-spec
891 -- Existentials are the leftover type vars: [x,y]
892 -- So we return ([a,b,z], [x,y], [a~(x,y),b~z], T [(x,y)] z z)
893 = do { res_ty' <- tcHsKindedType res_ty
894 ; let Just subst = tcMatchTy (mkVarSet tmpl_tvs) res_tmpl res_ty'
896 -- /Lazily/ figure out the univ_tvs etc
897 -- Each univ_tv is either a dc_tv or a tmpl_tv
898 (univ_tvs, eq_spec) = foldr choose ([], []) tidy_tmpl_tvs
899 choose tmpl (univs, eqs)
900 | Just ty <- lookupTyVar subst tmpl
901 = case tcGetTyVar_maybe ty of
902 Just tv | not (tv `elem` univs)
904 _other -> (tmpl:univs, (tmpl,ty):eqs)
905 | otherwise = pprPanic "tcResultType" (ppr res_ty)
906 ex_tvs = dc_tvs `minusList` univ_tvs
908 ; return (univ_tvs, ex_tvs, eq_spec, res_ty') }
910 -- NB: tmpl_tvs and dc_tvs are distinct, but
911 -- we want them to be *visibly* distinct, both for
912 -- interface files and general confusion. So rename
913 -- the tc_tvs, since they are not used yet (no
914 -- consequential renaming needed)
915 (_, tidy_tmpl_tvs) = mapAccumL tidy_one init_occ_env tmpl_tvs
916 init_occ_env = initTidyOccEnv (map getOccName dc_tvs)
917 tidy_one env tv = (env', setTyVarName tv (tidyNameOcc name occ'))
920 (env', occ') = tidyOccName env (getOccName name)
923 tcConArg :: Bool -- True <=> -funbox-strict_fields
925 -> TcM (TcType, StrictnessMark)
926 tcConArg unbox_strict bty
927 = do { arg_ty <- tcHsBangType bty
928 ; let bang = getBangStrictness bty
929 ; return (arg_ty, chooseBoxingStrategy unbox_strict arg_ty bang) }
931 -- We attempt to unbox/unpack a strict field when either:
932 -- (i) The field is marked '!!', or
933 -- (ii) The field is marked '!', and the -funbox-strict-fields flag is on.
935 -- We have turned off unboxing of newtypes because coercions make unboxing
936 -- and reboxing more complicated
937 chooseBoxingStrategy :: Bool -> TcType -> HsBang -> StrictnessMark
938 chooseBoxingStrategy unbox_strict_fields arg_ty bang
940 HsNoBang -> NotMarkedStrict
941 HsStrict | unbox_strict_fields
942 && can_unbox arg_ty -> MarkedUnboxed
943 HsUnbox | can_unbox arg_ty -> MarkedUnboxed
946 -- we can unbox if the type is a chain of newtypes with a product tycon
948 can_unbox arg_ty = case splitTyConApp_maybe arg_ty of
950 Just (arg_tycon, tycon_args) ->
951 not (isRecursiveTyCon arg_tycon) && -- Note [Recusive unboxing]
952 isProductTyCon arg_tycon &&
953 (if isNewTyCon arg_tycon then
954 can_unbox (newTyConInstRhs arg_tycon tycon_args)
958 Note [Recursive unboxing]
959 ~~~~~~~~~~~~~~~~~~~~~~~~~
960 Be careful not to try to unbox this!
962 But it's the *argument* type that matters. This is fine:
964 because Int is non-recursive.
967 %************************************************************************
971 %************************************************************************
973 Validity checking is done once the mutually-recursive knot has been
974 tied, so we can look at things freely.
977 checkCycleErrs :: [LTyClDecl Name] -> TcM ()
978 checkCycleErrs tyclss
982 = do { mapM_ recClsErr cls_cycles
983 ; failM } -- Give up now, because later checkValidTyCl
984 -- will loop if the synonym is recursive
986 cls_cycles = calcClassCycles tyclss
988 checkValidTyCl :: TyClDecl Name -> TcM ()
989 -- We do the validity check over declarations, rather than TyThings
990 -- only so that we can add a nice context with tcAddDeclCtxt
992 = tcAddDeclCtxt decl $
993 do { thing <- tcLookupLocatedGlobal (tcdLName decl)
994 ; traceTc (text "Validity of" <+> ppr thing)
996 ATyCon tc -> checkValidTyCon tc
997 AClass cl -> checkValidClass cl
998 _ -> panic "checkValidTyCl"
999 ; traceTc (text "Done validity of" <+> ppr thing)
1002 -------------------------
1003 -- For data types declared with record syntax, we require
1004 -- that each constructor that has a field 'f'
1005 -- (a) has the same result type
1006 -- (b) has the same type for 'f'
1007 -- module alpha conversion of the quantified type variables
1008 -- of the constructor.
1010 -- Note that we allow existentials to match becuase the
1011 -- fields can never meet. E.g
1013 -- T1 { f1 :: b, f2 :: a, f3 ::Int } :: T
1014 -- T2 { f1 :: c, f2 :: c, f3 ::Int } :: T
1015 -- Here we do not complain about f1,f2 because they are existential
1017 checkValidTyCon :: TyCon -> TcM ()
1020 = case synTyConRhs tc of
1021 OpenSynTyCon _ _ -> return ()
1022 SynonymTyCon ty -> checkValidType syn_ctxt ty
1024 = do -- Check the context on the data decl
1025 checkValidTheta (DataTyCtxt name) (tyConStupidTheta tc)
1027 -- Check arg types of data constructors
1028 mapM_ (checkValidDataCon tc) data_cons
1030 -- Check that fields with the same name share a type
1031 mapM_ check_fields groups
1034 syn_ctxt = TySynCtxt name
1036 data_cons = tyConDataCons tc
1038 groups = equivClasses cmp_fld (concatMap get_fields data_cons)
1039 cmp_fld (f1,_) (f2,_) = f1 `compare` f2
1040 get_fields con = dataConFieldLabels con `zip` repeat con
1041 -- dataConFieldLabels may return the empty list, which is fine
1043 -- See Note [GADT record selectors] in MkId.lhs
1044 -- We must check (a) that the named field has the same
1045 -- type in each constructor
1046 -- (b) that those constructors have the same result type
1048 -- However, the constructors may have differently named type variable
1049 -- and (worse) we don't know how the correspond to each other. E.g.
1050 -- C1 :: forall a b. { f :: a, g :: b } -> T a b
1051 -- C2 :: forall d c. { f :: c, g :: c } -> T c d
1053 -- So what we do is to ust Unify.tcMatchTys to compare the first candidate's
1054 -- result type against other candidates' types BOTH WAYS ROUND.
1055 -- If they magically agrees, take the substitution and
1056 -- apply them to the latter ones, and see if they match perfectly.
1057 check_fields ((label, con1) : other_fields)
1058 -- These fields all have the same name, but are from
1059 -- different constructors in the data type
1060 = recoverM (return ()) $ mapM_ checkOne other_fields
1061 -- Check that all the fields in the group have the same type
1062 -- NB: this check assumes that all the constructors of a given
1063 -- data type use the same type variables
1065 (tvs1, _, _, res1) = dataConSig con1
1067 fty1 = dataConFieldType con1 label
1069 checkOne (_, con2) -- Do it bothways to ensure they are structurally identical
1070 = do { checkFieldCompat label con1 con2 ts1 res1 res2 fty1 fty2
1071 ; checkFieldCompat label con2 con1 ts2 res2 res1 fty2 fty1 }
1073 (tvs2, _, _, res2) = dataConSig con2
1075 fty2 = dataConFieldType con2 label
1076 check_fields [] = panic "checkValidTyCon/check_fields []"
1078 checkFieldCompat :: Name -> DataCon -> DataCon -> TyVarSet
1079 -> Type -> Type -> Type -> Type -> TcM ()
1080 checkFieldCompat fld con1 con2 tvs1 res1 res2 fty1 fty2
1081 = do { checkTc (isJust mb_subst1) (resultTypeMisMatch fld con1 con2)
1082 ; checkTc (isJust mb_subst2) (fieldTypeMisMatch fld con1 con2) }
1084 mb_subst1 = tcMatchTy tvs1 res1 res2
1085 mb_subst2 = tcMatchTyX tvs1 (expectJust "checkFieldCompat" mb_subst1) fty1 fty2
1087 -------------------------------
1088 checkValidDataCon :: TyCon -> DataCon -> TcM ()
1089 checkValidDataCon tc con
1090 = setSrcSpan (srcLocSpan (getSrcLoc con)) $
1091 addErrCtxt (dataConCtxt con) $
1092 do { let tc_tvs = tyConTyVars tc
1093 res_ty_tmpl = mkFamilyTyConApp tc (mkTyVarTys tc_tvs)
1094 actual_res_ty = dataConOrigResTy con
1095 ; checkTc (isJust (tcMatchTy (mkVarSet tc_tvs)
1098 (badDataConTyCon con res_ty_tmpl actual_res_ty)
1099 ; checkValidMonoType (dataConOrigResTy con)
1100 -- Disallow MkT :: T (forall a. a->a)
1101 -- Reason: it's really the argument of an equality constraint
1102 ; checkValidType ctxt (dataConUserType con)
1103 ; when (isNewTyCon tc) (checkNewDataCon con)
1106 ctxt = ConArgCtxt (dataConName con)
1108 -------------------------------
1109 checkNewDataCon :: DataCon -> TcM ()
1110 -- Checks for the data constructor of a newtype
1112 = do { checkTc (isSingleton arg_tys) (newtypeFieldErr con (length arg_tys))
1114 ; checkTc (null eq_spec) (newtypePredError con)
1115 -- Return type is (T a b c)
1116 ; checkTc (null ex_tvs && null eq_theta && null dict_theta) (newtypeExError con)
1118 ; checkTc (not (any isMarkedStrict (dataConStrictMarks con)))
1119 (newtypeStrictError con)
1123 (_univ_tvs, ex_tvs, eq_spec, eq_theta, dict_theta, arg_tys, _res_ty) = dataConFullSig con
1125 -------------------------------
1126 checkValidClass :: Class -> TcM ()
1128 = do { constrained_class_methods <- doptM Opt_ConstrainedClassMethods
1129 ; multi_param_type_classes <- doptM Opt_MultiParamTypeClasses
1130 ; fundep_classes <- doptM Opt_FunctionalDependencies
1132 -- Check that the class is unary, unless GlaExs
1133 ; checkTc (notNull tyvars) (nullaryClassErr cls)
1134 ; checkTc (multi_param_type_classes || unary) (classArityErr cls)
1135 ; checkTc (fundep_classes || null fundeps) (classFunDepsErr cls)
1137 -- Check the super-classes
1138 ; checkValidTheta (ClassSCCtxt (className cls)) theta
1140 -- Check the class operations
1141 ; mapM_ (check_op constrained_class_methods) op_stuff
1143 -- Check that if the class has generic methods, then the
1144 -- class has only one parameter. We can't do generic
1145 -- multi-parameter type classes!
1146 ; checkTc (unary || no_generics) (genericMultiParamErr cls)
1149 (tyvars, fundeps, theta, _, _, op_stuff) = classExtraBigSig cls
1150 unary = isSingleton tyvars
1151 no_generics = null [() | (_, GenDefMeth) <- op_stuff]
1153 check_op constrained_class_methods (sel_id, dm)
1154 = addErrCtxt (classOpCtxt sel_id tau) $ do
1155 { checkValidTheta SigmaCtxt (tail theta)
1156 -- The 'tail' removes the initial (C a) from the
1157 -- class itself, leaving just the method type
1159 ; traceTc (text "class op type" <+> ppr op_ty <+> ppr tau)
1160 ; checkValidType (FunSigCtxt op_name) tau
1162 -- Check that the type mentions at least one of
1163 -- the class type variables...or at least one reachable
1164 -- from one of the class variables. Example: tc223
1165 -- class Error e => Game b mv e | b -> mv e where
1166 -- newBoard :: MonadState b m => m ()
1167 -- Here, MonadState has a fundep m->b, so newBoard is fine
1168 ; let grown_tyvars = grow theta (mkVarSet tyvars)
1169 ; checkTc (tyVarsOfType tau `intersectsVarSet` grown_tyvars)
1170 (noClassTyVarErr cls sel_id)
1172 -- Check that for a generic method, the type of
1173 -- the method is sufficiently simple
1174 ; checkTc (dm /= GenDefMeth || validGenericMethodType tau)
1175 (badGenericMethodType op_name op_ty)
1178 op_name = idName sel_id
1179 op_ty = idType sel_id
1180 (_,theta1,tau1) = tcSplitSigmaTy op_ty
1181 (_,theta2,tau2) = tcSplitSigmaTy tau1
1182 (theta,tau) | constrained_class_methods = (theta1 ++ theta2, tau2)
1183 | otherwise = (theta1, mkPhiTy (tail theta1) tau1)
1184 -- Ugh! The function might have a type like
1185 -- op :: forall a. C a => forall b. (Eq b, Eq a) => tau2
1186 -- With -XConstrainedClassMethods, we want to allow this, even though the inner
1187 -- forall has an (Eq a) constraint. Whereas in general, each constraint
1188 -- in the context of a for-all must mention at least one quantified
1189 -- type variable. What a mess!
1193 %************************************************************************
1195 Building record selectors
1197 %************************************************************************
1200 mkAuxBinds :: [TyThing] -> HsValBinds Name
1201 mkAuxBinds ty_things
1202 = ValBindsOut [(NonRecursive, b) | b <- binds] sigs
1204 (sigs, binds) = unzip rec_sels
1205 rec_sels = map mkRecSelBind [ (tc,fld)
1206 | ATyCon tc <- ty_things
1207 , fld <- tyConFields tc ]
1210 mkRecSelBind :: (TyCon, FieldLabel) -> (LSig Name, LHsBinds Name)
1211 mkRecSelBind (tycon, sel_name)
1212 = (L loc (IdSig sel_id), unitBag (L loc sel_bind))
1214 loc = getSrcSpan tycon
1215 sel_id = Var.mkLocalVar rec_details sel_name sel_ty vanillaIdInfo
1216 rec_details = RecSelId { sel_tycon = tycon, sel_naughty = is_naughty }
1218 -- Find a representative constructor, con1
1219 all_cons = tyConDataCons tycon
1220 cons_w_field = [ con | con <- all_cons
1221 , sel_name `elem` dataConFieldLabels con ]
1222 con1 = ASSERT( not (null cons_w_field) ) head cons_w_field
1224 -- Selector type; Note [Polymorphic selectors]
1225 field_ty = dataConFieldType con1 sel_name
1226 (field_tvs, field_theta, field_tau)
1227 | is_naughty = ([], [], unitTy)
1228 | otherwise = tcSplitSigmaTy field_ty
1229 data_ty = dataConOrigResTy con1
1230 data_tvs = tyVarsOfType data_ty
1231 is_naughty = not (tyVarsOfType field_ty `subVarSet` data_tvs)
1232 sel_ty = mkForAllTys (varSetElems data_tvs ++ field_tvs) $
1233 mkPhiTy (dataConStupidTheta con1) $ -- Urgh!
1234 mkPhiTy field_theta $ -- Urgh!
1235 mkFunTy data_ty field_tau
1237 -- Make the binding: sel (C2 { fld = x }) = x
1238 -- sel (C7 { fld = x }) = x
1239 -- where cons_w_field = [C2,C7]
1240 sel_bind = mkFunBind sel_lname (map mk_match cons_w_field ++ deflt)
1241 mk_match con = mkSimpleMatch [L loc (mk_sel_pat con)]
1243 mk_sel_pat con = ConPatIn (L loc (getName con)) (RecCon rec_fields)
1244 rec_fields = HsRecFields { rec_flds = [rec_field], rec_dotdot = Nothing }
1245 rec_field = HsRecField { hsRecFieldId = sel_lname
1246 , hsRecFieldArg = nlVarPat field_var
1247 , hsRecPun = False }
1248 match_body | is_naughty = ExplicitTuple [] Boxed
1249 | otherwise = HsVar field_var
1250 sel_lname = L loc sel_name
1251 field_var = mkInternalName (mkBuiltinUnique 1) (getOccName sel_name) loc
1253 -- Add catch-all default case unless the case is exhaustive
1254 -- We do this explicitly so that we get a nice error message that
1255 -- mentions this particular record selector
1256 deflt | length cons_w_field == length all_cons = []
1257 | otherwise = [mkSimpleMatch [nlWildPat]
1258 (nlHsApp (nlHsVar (getName rEC_SEL_ERROR_ID))
1260 msg_lit = HsStringPrim $ mkFastString $
1261 occNameString (getOccName sel_name)
1264 tyConFields :: TyCon -> [FieldLabel]
1266 | isAlgTyCon tc = nub (concatMap dataConFieldLabels (tyConDataCons tc))
1270 Note [Polymorphic selectors]
1271 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1272 When a record has a polymorphic field, we pull the foralls out to the front.
1273 data T = MkT { f :: forall a. [a] -> a }
1274 Then f :: forall a. T -> [a] -> a
1275 NOT f :: T -> forall a. [a] -> a
1277 This is horrid. It's only needed in deeply obscure cases, which I hate.
1278 The only case I know is test tc163, which is worth looking at. It's far
1279 from clear that this test should succeed at all!
1281 Note [Naughty record selectors]
1282 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1283 A "naughty" field is one for which we can't define a record
1284 selector, because an existential type variable would escape. For example:
1285 data T = forall a. MkT { x,y::a }
1286 We obviously can't define
1288 Nevertheless we *do* put a RecSelId into the type environment
1289 so that if the user tries to use 'x' as a selector we can bleat
1290 helpfully, rather than saying unhelpfully that 'x' is not in scope.
1291 Hence the sel_naughty flag, to identify record selectors that don't really exist.
1293 In general, a field is naughty if its type mentions a type variable that
1294 isn't in the result type of the constructor.
1296 We make a dummy binding for naughty selectors, so that they can be treated
1297 uniformly, apart from their sel_naughty field. The function is never called.
1299 Note [GADT record selectors]
1300 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1301 For GADTs, we require that all constructors with a common field 'f' have the same
1302 result type (modulo alpha conversion). [Checked in TcTyClsDecls.checkValidTyCon]
1305 T1 { f :: Maybe a } :: T [a]
1306 T2 { f :: Maybe a, y :: b } :: T [a]
1308 and now the selector takes that result type as its argument:
1309 f :: forall a. T [a] -> Maybe a
1311 Details: the "real" types of T1,T2 are:
1312 T1 :: forall r a. (r~[a]) => a -> T r
1313 T2 :: forall r a b. (r~[a]) => a -> b -> T r
1315 So the selector loooks like this:
1316 f :: forall a. T [a] -> Maybe a
1319 T1 c (g:[a]~[c]) (v:Maybe c) -> v `cast` Maybe (right (sym g))
1320 T2 c d (g:[a]~[c]) (v:Maybe c) (w:d) -> v `cast` Maybe (right (sym g))
1322 Note the forall'd tyvars of the selector are just the free tyvars
1323 of the result type; there may be other tyvars in the constructor's
1324 type (e.g. 'b' in T2).
1326 Note the need for casts in the result!
1328 Note [Selector running example]
1329 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1330 It's OK to combine GADTs and type families. Here's a running example:
1332 data instance T [a] where
1333 T1 { fld :: b } :: T [Maybe b]
1335 The representation type looks like this
1337 T1 { fld :: b } :: :R7T (Maybe b)
1339 and there's coercion from the family type to the representation type
1340 :CoR7T a :: T [a] ~ :R7T a
1342 The selector we want for fld looks like this:
1344 fld :: forall b. T [Maybe b] -> b
1345 fld = /\b. \(d::T [Maybe b]).
1346 case d `cast` :CoR7T (Maybe b) of
1349 The scrutinee of the case has type :R7T (Maybe b), which can be
1350 gotten by appying the eq_spec to the univ_tvs of the data con.
1352 %************************************************************************
1356 %************************************************************************
1359 resultTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1360 resultTypeMisMatch field_name con1 con2
1361 = vcat [sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1362 ptext (sLit "have a common field") <+> quotes (ppr field_name) <> comma],
1363 nest 2 $ ptext (sLit "but have different result types")]
1365 fieldTypeMisMatch :: Name -> DataCon -> DataCon -> SDoc
1366 fieldTypeMisMatch field_name con1 con2
1367 = sep [ptext (sLit "Constructors") <+> ppr con1 <+> ptext (sLit "and") <+> ppr con2,
1368 ptext (sLit "give different types for field"), quotes (ppr field_name)]
1370 dataConCtxt :: Outputable a => a -> SDoc
1371 dataConCtxt con = ptext (sLit "In the definition of data constructor") <+> quotes (ppr con)
1373 classOpCtxt :: Var -> Type -> SDoc
1374 classOpCtxt sel_id tau = sep [ptext (sLit "When checking the class method:"),
1375 nest 2 (ppr sel_id <+> dcolon <+> ppr tau)]
1377 nullaryClassErr :: Class -> SDoc
1379 = ptext (sLit "No parameters for class") <+> quotes (ppr cls)
1381 classArityErr :: Class -> SDoc
1383 = vcat [ptext (sLit "Too many parameters for class") <+> quotes (ppr cls),
1384 parens (ptext (sLit "Use -XMultiParamTypeClasses to allow multi-parameter classes"))]
1386 classFunDepsErr :: Class -> SDoc
1388 = vcat [ptext (sLit "Fundeps in class") <+> quotes (ppr cls),
1389 parens (ptext (sLit "Use -XFunctionalDependencies to allow fundeps"))]
1391 noClassTyVarErr :: Class -> Var -> SDoc
1392 noClassTyVarErr clas op
1393 = sep [ptext (sLit "The class method") <+> quotes (ppr op),
1394 ptext (sLit "mentions none of the type variables of the class") <+>
1395 ppr clas <+> hsep (map ppr (classTyVars clas))]
1397 genericMultiParamErr :: Class -> SDoc
1398 genericMultiParamErr clas
1399 = ptext (sLit "The multi-parameter class") <+> quotes (ppr clas) <+>
1400 ptext (sLit "cannot have generic methods")
1402 badGenericMethodType :: Name -> Kind -> SDoc
1403 badGenericMethodType op op_ty
1404 = hang (ptext (sLit "Generic method type is too complex"))
1405 4 (vcat [ppr op <+> dcolon <+> ppr op_ty,
1406 ptext (sLit "You can only use type variables, arrows, lists, and tuples")])
1408 recSynErr :: [LTyClDecl Name] -> TcRn ()
1410 = setSrcSpan (getLoc (head sorted_decls)) $
1411 addErr (sep [ptext (sLit "Cycle in type synonym declarations:"),
1412 nest 2 (vcat (map ppr_decl sorted_decls))])
1414 sorted_decls = sortLocated syn_decls
1415 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr decl
1417 recClsErr :: [Located (TyClDecl Name)] -> TcRn ()
1419 = setSrcSpan (getLoc (head sorted_decls)) $
1420 addErr (sep [ptext (sLit "Cycle in class declarations (via superclasses):"),
1421 nest 2 (vcat (map ppr_decl sorted_decls))])
1423 sorted_decls = sortLocated cls_decls
1424 ppr_decl (L loc decl) = ppr loc <> colon <+> ppr (decl { tcdSigs = [] })
1426 sortLocated :: [Located a] -> [Located a]
1427 sortLocated things = sortLe le things
1429 le (L l1 _) (L l2 _) = l1 <= l2
1431 badDataConTyCon :: DataCon -> Type -> Type -> SDoc
1432 badDataConTyCon data_con res_ty_tmpl actual_res_ty
1433 = hang (ptext (sLit "Data constructor") <+> quotes (ppr data_con) <+>
1434 ptext (sLit "returns type") <+> quotes (ppr actual_res_ty))
1435 2 (ptext (sLit "instead of an instance of its parent type") <+> quotes (ppr res_ty_tmpl))
1437 badGadtDecl :: Name -> SDoc
1439 = vcat [ ptext (sLit "Illegal generalised algebraic data declaration for") <+> quotes (ppr tc_name)
1440 , nest 2 (parens $ ptext (sLit "Use -XGADTs to allow GADTs")) ]
1442 badExistential :: Located Name -> SDoc
1443 badExistential con_name
1444 = hang (ptext (sLit "Data constructor") <+> quotes (ppr con_name) <+>
1445 ptext (sLit "has existential type variables, or a context"))
1446 2 (parens $ ptext (sLit "Use -XExistentialQuantification or -XGADTs to allow this"))
1448 badStupidTheta :: Name -> SDoc
1449 badStupidTheta tc_name
1450 = ptext (sLit "A data type declared in GADT style cannot have a context:") <+> quotes (ppr tc_name)
1452 newtypeConError :: Name -> Int -> SDoc
1453 newtypeConError tycon n
1454 = sep [ptext (sLit "A newtype must have exactly one constructor,"),
1455 nest 2 $ ptext (sLit "but") <+> quotes (ppr tycon) <+> ptext (sLit "has") <+> speakN n ]
1457 newtypeExError :: DataCon -> SDoc
1459 = sep [ptext (sLit "A newtype constructor cannot have an existential context,"),
1460 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1462 newtypeStrictError :: DataCon -> SDoc
1463 newtypeStrictError con
1464 = sep [ptext (sLit "A newtype constructor cannot have a strictness annotation,"),
1465 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does")]
1467 newtypePredError :: DataCon -> SDoc
1468 newtypePredError con
1469 = sep [ptext (sLit "A newtype constructor must have a return type of form T a1 ... an"),
1470 nest 2 $ ptext (sLit "but") <+> quotes (ppr con) <+> ptext (sLit "does not")]
1472 newtypeFieldErr :: DataCon -> Int -> SDoc
1473 newtypeFieldErr con_name n_flds
1474 = sep [ptext (sLit "The constructor of a newtype must have exactly one field"),
1475 nest 2 $ ptext (sLit "but") <+> quotes (ppr con_name) <+> ptext (sLit "has") <+> speakN n_flds]
1477 badSigTyDecl :: Name -> SDoc
1478 badSigTyDecl tc_name
1479 = vcat [ ptext (sLit "Illegal kind signature") <+>
1480 quotes (ppr tc_name)
1481 , nest 2 (parens $ ptext (sLit "Use -XKindSignatures to allow kind signatures")) ]
1483 noIndexTypes :: Name -> SDoc
1484 noIndexTypes tc_name
1485 = ptext (sLit "Type family constructor") <+> quotes (ppr tc_name)
1486 <+> ptext (sLit "must have at least one type index parameter")
1488 badFamInstDecl :: Outputable a => a -> SDoc
1489 badFamInstDecl tc_name
1490 = vcat [ ptext (sLit "Illegal family instance for") <+>
1491 quotes (ppr tc_name)
1492 , nest 2 (parens $ ptext (sLit "Use -XTypeFamilies to allow indexed type families")) ]
1494 tooManyParmsErr :: Located Name -> SDoc
1495 tooManyParmsErr tc_name
1496 = ptext (sLit "Family instance has too many parameters:") <+>
1497 quotes (ppr tc_name)
1499 tooFewParmsErr :: Arity -> SDoc
1500 tooFewParmsErr arity
1501 = ptext (sLit "Family instance has too few parameters; expected") <+>
1504 wrongNumberOfParmsErr :: Arity -> SDoc
1505 wrongNumberOfParmsErr exp_arity
1506 = ptext (sLit "Number of parameters must match family declaration; expected")
1509 badBootFamInstDeclErr :: SDoc
1510 badBootFamInstDeclErr =
1511 ptext (sLit "Illegal family instance in hs-boot file")
1513 wrongKindOfFamily :: TyCon -> SDoc
1514 wrongKindOfFamily family =
1515 ptext (sLit "Wrong category of family instance; declaration was for a") <+>
1518 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1519 | isAlgTyCon family = ptext (sLit "data type")
1520 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)
1522 emptyConDeclsErr :: Name -> SDoc
1523 emptyConDeclsErr tycon
1524 = sep [quotes (ppr tycon) <+> ptext (sLit "has no constructors"),
1525 nest 2 $ ptext (sLit "(-XEmptyDataDecls permits this)")]