2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcInstDecls]{Typechecking instance declarations}
7 module TcInstDcls ( tcInstDecls1, tcInstDecls2, tcAddDeclCtxt ) where
9 #include "HsVersions.h"
12 import CmdLineOpts ( DynFlag(..), dopt )
14 import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..),
16 andMonoBindList, collectMonoBinders, isClassDecl
18 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl, RenamedMonoBinds,
19 RenamedTyClDecl, RenamedHsType,
20 extractHsTyVars, maybeGenericMatch
22 import TcHsSyn ( TcMonoBinds, mkHsConApp )
23 import TcBinds ( tcSpecSigs )
24 import TcClassDcl ( tcMethodBind, badMethodErr )
26 import Inst ( InstOrigin(..),
27 newDicts, newClassDicts,
28 LIE, emptyLIE, plusLIE, plusLIEs )
29 import TcDeriv ( tcDeriving )
30 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
31 tcExtendTyVarEnvForMeths,
32 tcAddImportedIdInfo, tcInstId, tcLookupClass,
33 InstInfo(..), pprInstInfo, simpleInstInfoTyCon, simpleInstInfoTy,
34 newDFunName, tcExtendTyVarEnv
36 import InstEnv ( InstEnv, extendInstEnv )
37 import TcMonoType ( tcTyVars, tcHsSigType, kcHsSigType )
38 import TcSimplify ( tcSimplifyAndCheck )
39 import TcType ( zonkTcSigTyVars )
40 import HscTypes ( HomeSymbolTable, DFunId,
41 ModDetails(..), PackageInstEnv, PersistentRenamerState
44 import Bag ( unionManyBags )
45 import DataCon ( classDataCon )
46 import Class ( Class, DefMeth(..), classBigSig )
47 import Var ( idName, idType )
48 import Maybes ( maybeToBool )
49 import MkId ( mkDictFunId )
50 import Generics ( validGenericInstanceType )
51 import Module ( Module, foldModuleEnv )
52 import Name ( getSrcLoc )
53 import NameSet ( emptyNameSet, nameSetToList )
54 import PrelInfo ( eRROR_ID )
55 import PprType ( pprConstraint, pprPred )
56 import TyCon ( TyCon, isSynTyCon )
57 import Type ( splitDFunTy, isTyVarTy,
58 splitTyConApp_maybe, splitDictTy,
59 splitAlgTyConApp_maybe, splitForAllTys,
60 unUsgTy, tyVarsOfTypes, mkClassPred, mkTyVarTy,
63 import Subst ( mkTopTyVarSubst, substClasses )
64 import VarSet ( mkVarSet, varSetElems )
65 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIResultTy )
66 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
68 import SrcLoc ( SrcLoc )
69 import VarSet ( varSetElems )
70 import Unique ( Uniquable(..) )
71 import BasicTypes ( NewOrData(..), Fixity )
72 import ErrUtils ( dumpIfSet_dyn )
73 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
74 assocElts, extendAssoc_C,
75 equivClassesByUniq, minusList
77 import List ( partition )
81 Typechecking instance declarations is done in two passes. The first
82 pass, made by @tcInstDecls1@, collects information to be used in the
85 This pre-processed info includes the as-yet-unprocessed bindings
86 inside the instance declaration. These are type-checked in the second
87 pass, when the class-instance envs and GVE contain all the info from
88 all the instance and value decls. Indeed that's the reason we need
89 two passes over the instance decls.
92 Here is the overall algorithm.
93 Assume that we have an instance declaration
95 instance c => k (t tvs) where b
99 $LIE_c$ is the LIE for the context of class $c$
101 $betas_bar$ is the free variables in the class method type, excluding the
104 $LIE_cop$ is the LIE constraining a particular class method
106 $tau_cop$ is the tau type of a class method
108 $LIE_i$ is the LIE for the context of instance $i$
110 $X$ is the instance constructor tycon
112 $gammas_bar$ is the set of type variables of the instance
114 $LIE_iop$ is the LIE for a particular class method instance
116 $tau_iop$ is the tau type for this instance of a class method
118 $alpha$ is the class variable
120 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
122 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
125 ToDo: Update the list above with names actually in the code.
129 First, make the LIEs for the class and instance contexts, which means
130 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
131 and make LIElistI and LIEI.
133 Then process each method in turn.
135 order the instance methods according to the ordering of the class methods
137 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
139 Create final dictionary function from bindings generated already
141 df = lambda inst_tyvars
148 in <op1,op2,...,opn,sd1,...,sdm>
150 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
151 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
155 %************************************************************************
157 \subsection{Extracting instance decls}
159 %************************************************************************
161 Gather up the instance declarations from their various sources
164 tcInstDecls1 :: PackageInstEnv
165 -> PersistentRenamerState
166 -> HomeSymbolTable -- Contains instances
167 -> TcEnv -- Contains IdInfo for dfun ids
168 -> (Name -> Maybe Fixity) -- for deriving Show and Read
169 -> Module -- Module for deriving
172 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
174 tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod tycons decls
176 inst_decls = [inst_decl | InstD inst_decl <- decls]
177 tycl_decls = [decl | TyClD decl <- decls]
178 clas_decls = filter isClassDecl tycl_decls
180 -- (1) Do the ordinary instance declarations
181 mapNF_Tc (tcInstDecl1 mod unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
183 -- (2) Instances from generic class declarations
184 getGenericInstances mod clas_decls `thenTc` \ generic_inst_info ->
186 -- Next, construct the instance environment so far, consisting of
187 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
188 -- b) imported instance decls (not in the home package) inst_env1
189 -- c) other modules in this package (gotten from hst) inst_env2
190 -- d) local instance decls inst_env3
191 -- e) generic instances inst_env4
192 -- The result of (b) replaces the cached InstEnv in the PCS
194 (local_inst_info, imported_inst_info) = partition iLocal (concat inst_infos)
196 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
198 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
200 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
201 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
202 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
203 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
205 -- (3) Compute instances from "deriving" clauses;
206 -- note that we only do derivings for things in this module;
207 -- we ignore deriving decls from interfaces!
208 -- This stuff computes a context for the derived instance decl, so it
209 -- needs to know about all the instances possible; hecne inst_env4
210 tcDeriving prs mod inst_env4 get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) ->
211 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
215 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
218 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
219 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
221 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
222 addInstDFuns dfuns infos
223 = getDOptsTc `thenTc` \ dflags ->
224 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
225 addErrsTc errs `thenNF_Tc_`
233 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
234 -- Deal with a single instance declaration
235 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
236 = -- Prime error recovery, set source location
237 recoverNF_Tc (returnNF_Tc []) $
238 tcAddSrcLoc src_loc $
240 -- Type-check all the stuff before the "where"
241 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
243 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
246 (case maybe_dfun_name of
247 Nothing -> -- A source-file instance declaration
249 -- Check for respectable instance type, and context
250 -- but only do this for non-imported instance decls.
251 -- Imported ones should have been checked already, and may indeed
252 -- contain something illegal in normal Haskell, notably
253 -- instance CCallable [Char]
254 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
255 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
257 -- Make the dfun id and return it
258 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
259 returnNF_Tc (True, dfun_name)
261 Just dfun_name -> -- An interface-file instance declaration
263 returnNF_Tc (False, dfun_name)
264 ) `thenNF_Tc` \ (is_local, dfun_name) ->
267 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
269 returnTc [InstInfo { iLocal = is_local, iDFunId = dfun_id,
270 iBinds = binds, iPrags = uprags }]
274 %************************************************************************
276 \subsection{Extracting generic instance declaration from class declarations}
278 %************************************************************************
280 @getGenericInstances@ extracts the generic instance declarations from a class
281 declaration. For exmaple
286 op{ x+y } (Inl v) = ...
287 op{ x+y } (Inr v) = ...
288 op{ x*y } (v :*: w) = ...
291 gives rise to the instance declarations
293 instance C (x+y) where
297 instance C (x*y) where
305 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
306 getGenericInstances mod class_decls
307 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
309 gen_inst_info = concat gen_inst_infos
311 getDOptsTc `thenTc` \ dflags ->
312 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
313 (vcat (map pprInstInfo gen_inst_info)))
315 returnTc gen_inst_info
317 get_generics mod decl@(ClassDecl context class_name tyvar_names
318 fundeps class_sigs def_methods
321 = returnTc [] -- The comon case:
322 -- no generic default methods, or
323 -- its an imported class decl (=> has no methods at all)
325 | otherwise -- A local class decl with generic default methods
326 = recoverNF_Tc (returnNF_Tc []) $
328 tcLookupClass class_name `thenTc` \ clas ->
330 -- Make an InstInfo out of each group
331 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
333 -- Check that there is only one InstInfo for each type constructor
334 -- The main way this can fail is if you write
335 -- f {| a+b |} ... = ...
336 -- f {| x+y |} ... = ...
337 -- Then at this point we'll have an InstInfo for each
339 tc_inst_infos :: [(TyCon, InstInfo)]
340 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
342 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
344 get_uniq (tc,_) = getUnique tc
346 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
348 -- Check that there is an InstInfo for each generic type constructor
350 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
352 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
357 -- Group the declarations by type pattern
358 groups :: [(RenamedHsType, RenamedMonoBinds)]
359 groups = assocElts (getGenericBinds def_methods)
362 ---------------------------------
363 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
364 -- Takes a group of method bindings, finds the generic ones, and returns
365 -- them in finite map indexed by the type parameter in the definition.
367 getGenericBinds EmptyMonoBinds = emptyAssoc
368 getGenericBinds (AndMonoBinds m1 m2)
369 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
371 getGenericBinds (FunMonoBind id infixop matches loc)
372 = mapAssoc wrap (foldr add emptyAssoc matches)
374 add match env = case maybeGenericMatch match of
376 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
378 wrap ms = FunMonoBind id infixop ms loc
380 ---------------------------------
381 mkGenericInstance :: Module -> Class -> SrcLoc
382 -> (RenamedHsType, RenamedMonoBinds)
385 mkGenericInstance mod clas loc (hs_ty, binds)
386 -- Make a generic instance declaration
387 -- For example: instance (C a, C b) => C (a+b) where { binds }
389 = -- Extract the universally quantified type variables
390 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
391 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
392 tcExtendTyVarEnv tyvars $
394 -- Type-check the instance type, and check its form
395 tcHsSigType hs_ty `thenTc` \ inst_ty ->
396 checkTc (validGenericInstanceType inst_ty)
397 (badGenericInstanceType binds) `thenTc_`
399 -- Make the dictionary function.
400 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
402 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
404 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
407 returnTc (InstInfo { iLocal = True, iDFunId = dfun_id,
408 iBinds = binds, iPrags = [] })
412 %************************************************************************
414 \subsection{Type-checking instance declarations, pass 2}
416 %************************************************************************
419 tcInstDecls2 :: [InstInfo]
420 -> NF_TcM (LIE, TcMonoBinds)
422 tcInstDecls2 inst_decls
423 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
424 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
425 (map tcInstDecl2 inst_decls)
427 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
428 tc2 `thenNF_Tc` \ (lie2, binds2) ->
429 returnNF_Tc (lie1 `plusLIE` lie2,
430 binds1 `AndMonoBinds` binds2)
433 ======= New documentation starts here (Sept 92) ==============
435 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
436 the dictionary function for this instance declaration. For example
438 instance Foo a => Foo [a] where
442 might generate something like
444 dfun.Foo.List dFoo_a = let op1 x = ...
450 HOWEVER, if the instance decl has no context, then it returns a
451 bigger @HsBinds@ with declarations for each method. For example
453 instance Foo [a] where
459 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
460 const.Foo.op1.List a x = ...
461 const.Foo.op2.List a y = ...
463 This group may be mutually recursive, because (for example) there may
464 be no method supplied for op2 in which case we'll get
466 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
468 that is, the default method applied to the dictionary at this type.
470 What we actually produce in either case is:
472 AbsBinds [a] [dfun_theta_dicts]
473 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
474 { d = (sd1,sd2, ..., op1, op2, ...)
479 The "maybe" says that we only ask AbsBinds to make global constant methods
480 if the dfun_theta is empty.
483 For an instance declaration, say,
485 instance (C1 a, C2 b) => C (T a b) where
488 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
489 function whose type is
491 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
493 Notice that we pass it the superclass dictionaries at the instance type; this
494 is the ``Mark Jones optimisation''. The stuff before the "=>" here
495 is the @dfun_theta@ below.
497 First comes the easy case of a non-local instance decl.
500 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
502 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
503 iBinds = monobinds, iPrags = uprags })
505 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
508 = -- Prime error recovery
509 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
510 tcAddSrcLoc (getSrcLoc dfun_id) $
512 -- Instantiate the instance decl with tc-style type variables
513 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
515 (clas, inst_tys') = splitDictTy dict_ty'
516 origin = InstanceDeclOrigin
518 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
520 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
521 sel_names = [idName sel_id | (sel_id, _) <- op_items]
523 -- Instantiate the super-class context with inst_tys
524 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
526 -- Find any definitions in monobinds that aren't from the class
527 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
529 -- The type variable from the dict fun actually scope
530 -- over the bindings. They were gotten from
531 -- the original instance declaration
532 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
534 -- Check that all the method bindings come from this class
535 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
537 -- Create dictionary Ids from the specified instance contexts.
538 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
539 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
540 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
542 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
543 tcExtendGlobalValEnv dm_ids (
544 -- Default-method Ids may be mentioned in synthesised RHSs
546 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
548 monobinds uprags True)
550 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
552 -- Deal with SPECIALISE instance pragmas by making them
553 -- look like SPECIALISE pragmas for the dfun
555 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
557 tcExtendGlobalValEnv [dfun_id] (
558 tcSpecSigs dfun_prags
559 ) `thenTc` \ (prag_binds, prag_lie) ->
561 -- Check the overloading constraints of the methods and superclasses
563 -- tcMethodBind has checked that the class_tyvars havn't
564 -- been unified with each other or another type, but we must
565 -- still zonk them before passing them to tcSimplifyAndCheck
566 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
568 inst_tyvars_set = mkVarSet zonked_inst_tyvars
570 (meth_lies, meth_ids) = unzip meth_lies_w_ids
572 -- These insts are in scope; quite a few, eh?
573 avail_insts = this_dict `plusLIE`
574 dfun_arg_dicts `plusLIE`
576 unionManyBags meth_lies
578 methods_lie = plusLIEs insts_needed_s
581 -- Ditto method bindings
582 tcAddErrCtxt methodCtxt (
584 (ptext SLIT("instance declaration context"))
585 inst_tyvars_set -- Local tyvars
588 ) `thenTc` \ (const_lie1, lie_binds1) ->
590 -- Now do the simplification again, this time to get the
591 -- bindings; this time we use an enhanced "avails"
592 -- Ignore errors because they come from the *previous* tcSimplify
595 (ptext SLIT("instance declaration context"))
597 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
598 -- get bound by just selecting from this_dict!!
600 ) `thenTc` \ (const_lie2, lie_binds2) ->
603 -- Create the result bindings
605 dict_constr = classDataCon clas
606 scs_and_meths = sc_dict_ids ++ meth_ids
610 = -- Blatant special case for CCallable, CReturnable
611 -- If the dictionary is empty then we should never
612 -- select anything from it, so we make its RHS just
613 -- emit an error message. This in turn means that we don't
614 -- mention the constructor, which doesn't exist for CCallable, CReturnable
615 -- Hardly beautiful, but only three extra lines.
616 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
617 (HsLit (HsString msg))
619 | otherwise -- The common case
620 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
621 -- We don't produce a binding for the dict_constr; instead we
622 -- rely on the simplifier to unfold this saturated application
623 -- We do this rather than generate an HsCon directly, because
624 -- it means that the special cases (e.g. dictionary with only one
625 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
626 -- than needing to be repeated here.
629 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
631 dict_bind = VarMonoBind this_dict_id dict_rhs
632 method_binds = andMonoBindList method_binds_s
638 [(inst_tyvars', dfun_id, this_dict_id)]
639 emptyNameSet -- No inlines (yet)
640 (lie_binds1 `AndMonoBinds`
641 lie_binds2 `AndMonoBinds`
642 method_binds `AndMonoBinds`
645 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
646 main_bind `AndMonoBinds` prag_binds)
650 %************************************************************************
652 \subsection{Checking for a decent instance type}
654 %************************************************************************
656 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
657 it must normally look like: @instance Foo (Tycon a b c ...) ...@
659 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
660 flag is on, or (2)~the instance is imported (they must have been
661 compiled elsewhere). In these cases, we let them go through anyway.
663 We can also have instances for functions: @instance Foo (a -> b) ...@.
666 scrutiniseInstanceConstraint pred
667 = getDOptsTc `thenTc` \ dflags -> case () of
669 | dopt Opt_AllowUndecidableInstances dflags
672 | Just (clas,tys) <- getClassTys_maybe pred,
677 -> addErrTc (instConstraintErr pred)
679 scrutiniseInstanceHead clas inst_taus
680 = getDOptsTc `thenTc` \ dflags -> case () of
683 -- A user declaration of a CCallable/CReturnable instance
684 -- must be for a "boxed primitive" type.
685 (clas `hasKey` cCallableClassKey
686 && not (ccallable_type dflags first_inst_tau))
688 (clas `hasKey` cReturnableClassKey
689 && not (creturnable_type first_inst_tau))
690 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
692 -- Allow anything for AllowUndecidableInstances
693 | dopt Opt_AllowUndecidableInstances dflags
696 -- If GlasgowExts then check at least one isn't a type variable
697 | dopt Opt_GlasgowExts dflags
698 -> if all isTyVarTy inst_taus
699 then addErrTc (instTypeErr clas inst_taus
700 (text "There must be at least one non-type-variable in the instance head"))
703 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
704 | not (length inst_taus == 1 &&
705 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
706 not (isSynTyCon tycon) && -- ...but not a synonym
707 all isTyVarTy arg_tys && -- Applied to type variables
708 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
709 -- This last condition checks that all the type variables are distinct
711 -> addErrTc (instTypeErr clas inst_taus
712 (text "the instance type must be of form (T a b c)" $$
713 text "where T is not a synonym, and a,b,c are distinct type variables")
720 (first_inst_tau : _) = inst_taus
722 -- Stuff for algebraic or -> type
723 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
724 Just (tycon, arg_tys) = maybe_tycon_app
726 -- Stuff for an *algebraic* data type
727 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
728 -- The "Alg" part looks through synonyms
729 Just (alg_tycon, _, _) = alg_tycon_app_maybe
731 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
732 creturnable_type ty = isFFIResultTy ty
736 %************************************************************************
738 \subsection{Error messages}
740 %************************************************************************
743 tcAddDeclCtxt decl thing_inside
750 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
751 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
752 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
753 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
755 ctxt = hsep [ptext SLIT("In the"), text thing,
756 ptext SLIT("declaration for"), quotes (ppr name)]
760 instConstraintErr pred
761 = hang (ptext SLIT("Illegal constraint") <+>
762 quotes (pprPred pred) <+>
763 ptext SLIT("in instance context"))
764 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
766 badGenericInstanceType binds
767 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
770 missingGenericInstances missing
771 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
775 dupGenericInsts tc_inst_infos
776 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
777 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
778 ptext SLIT("All the type patterns for a generic type constructor must be identical")
781 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
783 instTypeErr clas tys msg
784 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
788 nonBoxedPrimCCallErr clas inst_ty
789 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
790 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
793 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")