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,
60 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
171 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
173 tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod decls
175 inst_decls = [inst_decl | InstD inst_decl <- decls]
176 tycl_decls = [decl | TyClD decl <- decls]
177 clas_decls = filter isClassDecl tycl_decls
179 -- (1) Do the ordinary instance declarations
180 mapNF_Tc (tcInstDecl1 mod unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
182 -- (2) Instances from generic class declarations
183 getGenericInstances mod clas_decls `thenTc` \ generic_inst_info ->
185 -- Next, construct the instance environment so far, consisting of
186 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
187 -- b) imported instance decls (not in the home package) inst_env1
188 -- c) other modules in this package (gotten from hst) inst_env2
189 -- d) local instance decls inst_env3
190 -- e) generic instances inst_env4
191 -- The result of (b) replaces the cached InstEnv in the PCS
193 (local_inst_info, imported_inst_info) = partition iLocal (concat inst_infos)
195 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
197 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
199 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
200 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
201 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
202 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
204 -- (3) Compute instances from "deriving" clauses;
205 -- note that we only do derivings for things in this module;
206 -- we ignore deriving decls from interfaces!
207 -- This stuff computes a context for the derived instance decl, so it
208 -- needs to know about all the instances possible; hecne inst_env4
209 tcDeriving prs mod inst_env4 get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) ->
210 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
214 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
217 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
218 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
220 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
221 addInstDFuns dfuns infos
222 = getDOptsTc `thenTc` \ dflags ->
223 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
224 addErrsTc errs `thenNF_Tc_`
232 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
233 -- Deal with a single instance declaration
234 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
235 = -- Prime error recovery, set source location
236 recoverNF_Tc (returnNF_Tc []) $
237 tcAddSrcLoc src_loc $
239 -- Type-check all the stuff before the "where"
240 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
242 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
245 (case maybe_dfun_name of
246 Nothing -> -- A source-file instance declaration
248 -- Check for respectable instance type, and context
249 -- but only do this for non-imported instance decls.
250 -- Imported ones should have been checked already, and may indeed
251 -- contain something illegal in normal Haskell, notably
252 -- instance CCallable [Char]
253 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
254 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
256 -- Make the dfun id and return it
257 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
258 returnNF_Tc (True, dfun_name)
260 Just dfun_name -> -- An interface-file instance declaration
262 returnNF_Tc (False, dfun_name)
263 ) `thenNF_Tc` \ (is_local, dfun_name) ->
266 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
268 returnTc [InstInfo { iLocal = is_local, iDFunId = dfun_id,
269 iBinds = binds, iPrags = uprags }]
273 %************************************************************************
275 \subsection{Extracting generic instance declaration from class declarations}
277 %************************************************************************
279 @getGenericInstances@ extracts the generic instance declarations from a class
280 declaration. For exmaple
285 op{ x+y } (Inl v) = ...
286 op{ x+y } (Inr v) = ...
287 op{ x*y } (v :*: w) = ...
290 gives rise to the instance declarations
292 instance C (x+y) where
296 instance C (x*y) where
304 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
305 getGenericInstances mod class_decls
306 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
308 gen_inst_info = concat gen_inst_infos
310 getDOptsTc `thenTc` \ dflags ->
311 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
312 (vcat (map pprInstInfo gen_inst_info)))
314 returnTc gen_inst_info
316 get_generics mod decl@(ClassDecl context class_name tyvar_names
317 fundeps class_sigs def_methods
320 = returnTc [] -- The comon case:
321 -- no generic default methods, or
322 -- its an imported class decl (=> has no methods at all)
324 | otherwise -- A local class decl with generic default methods
325 = recoverNF_Tc (returnNF_Tc []) $
327 tcLookupClass class_name `thenTc` \ clas ->
329 -- Make an InstInfo out of each group
330 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
332 -- Check that there is only one InstInfo for each type constructor
333 -- The main way this can fail is if you write
334 -- f {| a+b |} ... = ...
335 -- f {| x+y |} ... = ...
336 -- Then at this point we'll have an InstInfo for each
338 tc_inst_infos :: [(TyCon, InstInfo)]
339 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
341 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
343 get_uniq (tc,_) = getUnique tc
345 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
347 -- Check that there is an InstInfo for each generic type constructor
349 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
351 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
356 -- Group the declarations by type pattern
357 groups :: [(RenamedHsType, RenamedMonoBinds)]
358 groups = assocElts (getGenericBinds def_methods)
361 ---------------------------------
362 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
363 -- Takes a group of method bindings, finds the generic ones, and returns
364 -- them in finite map indexed by the type parameter in the definition.
366 getGenericBinds EmptyMonoBinds = emptyAssoc
367 getGenericBinds (AndMonoBinds m1 m2)
368 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
370 getGenericBinds (FunMonoBind id infixop matches loc)
371 = mapAssoc wrap (foldl add emptyAssoc matches)
372 -- Using foldl not foldr is vital, else
373 -- we reverse the order of the bindings!
375 add env match = case maybeGenericMatch match of
377 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
379 wrap ms = FunMonoBind id infixop ms loc
381 ---------------------------------
382 mkGenericInstance :: Module -> Class -> SrcLoc
383 -> (RenamedHsType, RenamedMonoBinds)
386 mkGenericInstance mod clas loc (hs_ty, binds)
387 -- Make a generic instance declaration
388 -- For example: instance (C a, C b) => C (a+b) where { binds }
390 = -- Extract the universally quantified type variables
391 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
392 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
393 tcExtendTyVarEnv tyvars $
395 -- Type-check the instance type, and check its form
396 tcHsSigType hs_ty `thenTc` \ inst_ty ->
397 checkTc (validGenericInstanceType inst_ty)
398 (badGenericInstanceType binds) `thenTc_`
400 -- Make the dictionary function.
401 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
403 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
405 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
408 returnTc (InstInfo { iLocal = True, iDFunId = dfun_id,
409 iBinds = binds, iPrags = [] })
413 %************************************************************************
415 \subsection{Type-checking instance declarations, pass 2}
417 %************************************************************************
420 tcInstDecls2 :: [InstInfo]
421 -> NF_TcM (LIE, TcMonoBinds)
423 tcInstDecls2 inst_decls
424 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
425 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
426 (map tcInstDecl2 inst_decls)
428 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
429 tc2 `thenNF_Tc` \ (lie2, binds2) ->
430 returnNF_Tc (lie1 `plusLIE` lie2,
431 binds1 `AndMonoBinds` binds2)
434 ======= New documentation starts here (Sept 92) ==============
436 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
437 the dictionary function for this instance declaration. For example
439 instance Foo a => Foo [a] where
443 might generate something like
445 dfun.Foo.List dFoo_a = let op1 x = ...
451 HOWEVER, if the instance decl has no context, then it returns a
452 bigger @HsBinds@ with declarations for each method. For example
454 instance Foo [a] where
460 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
461 const.Foo.op1.List a x = ...
462 const.Foo.op2.List a y = ...
464 This group may be mutually recursive, because (for example) there may
465 be no method supplied for op2 in which case we'll get
467 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
469 that is, the default method applied to the dictionary at this type.
471 What we actually produce in either case is:
473 AbsBinds [a] [dfun_theta_dicts]
474 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
475 { d = (sd1,sd2, ..., op1, op2, ...)
480 The "maybe" says that we only ask AbsBinds to make global constant methods
481 if the dfun_theta is empty.
484 For an instance declaration, say,
486 instance (C1 a, C2 b) => C (T a b) where
489 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
490 function whose type is
492 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
494 Notice that we pass it the superclass dictionaries at the instance type; this
495 is the ``Mark Jones optimisation''. The stuff before the "=>" here
496 is the @dfun_theta@ below.
498 First comes the easy case of a non-local instance decl.
501 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
503 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
504 iBinds = monobinds, iPrags = uprags })
506 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
509 = -- Prime error recovery
510 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
511 tcAddSrcLoc (getSrcLoc dfun_id) $
513 -- Instantiate the instance decl with tc-style type variables
514 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
516 (clas, inst_tys') = splitDictTy dict_ty'
517 origin = InstanceDeclOrigin
519 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
521 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
522 sel_names = [idName sel_id | (sel_id, _) <- op_items]
524 -- Instantiate the super-class context with inst_tys
525 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
527 -- Find any definitions in monobinds that aren't from the class
528 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
530 -- The type variable from the dict fun actually scope
531 -- over the bindings. They were gotten from
532 -- the original instance declaration
533 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
535 -- Check that all the method bindings come from this class
536 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
538 -- Create dictionary Ids from the specified instance contexts.
539 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
540 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
541 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
543 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
544 tcExtendGlobalValEnv dm_ids (
545 -- Default-method Ids may be mentioned in synthesised RHSs
547 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
549 monobinds uprags True)
551 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
553 -- Deal with SPECIALISE instance pragmas by making them
554 -- look like SPECIALISE pragmas for the dfun
556 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
558 tcExtendGlobalValEnv [dfun_id] (
559 tcSpecSigs dfun_prags
560 ) `thenTc` \ (prag_binds, prag_lie) ->
562 -- Check the overloading constraints of the methods and superclasses
564 -- tcMethodBind has checked that the class_tyvars havn't
565 -- been unified with each other or another type, but we must
566 -- still zonk them before passing them to tcSimplifyAndCheck
567 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
569 inst_tyvars_set = mkVarSet zonked_inst_tyvars
571 (meth_lies, meth_ids) = unzip meth_lies_w_ids
573 -- These insts are in scope; quite a few, eh?
574 avail_insts = this_dict `plusLIE`
575 dfun_arg_dicts `plusLIE`
577 unionManyBags meth_lies
579 methods_lie = plusLIEs insts_needed_s
582 -- Simplify the constraints from methods
583 tcAddErrCtxt methodCtxt (
585 (ptext SLIT("instance declaration context"))
586 inst_tyvars_set -- Local tyvars
589 ) `thenTc` \ (const_lie1, lie_binds1) ->
591 -- Figure out bindings for the superclass context
592 tcAddErrCtxt superClassCtxt (
594 (ptext SLIT("instance declaration context"))
596 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
597 -- get bound by just selecting from this_dict!!
599 ) `thenTc` \ (const_lie2, lie_binds2) ->
602 -- Create the result bindings
604 dict_constr = classDataCon clas
605 scs_and_meths = sc_dict_ids ++ meth_ids
609 = -- Blatant special case for CCallable, CReturnable
610 -- If the dictionary is empty then we should never
611 -- select anything from it, so we make its RHS just
612 -- emit an error message. This in turn means that we don't
613 -- mention the constructor, which doesn't exist for CCallable, CReturnable
614 -- Hardly beautiful, but only three extra lines.
615 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
616 (HsLit (HsString msg))
618 | otherwise -- The common case
619 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
620 -- We don't produce a binding for the dict_constr; instead we
621 -- rely on the simplifier to unfold this saturated application
622 -- We do this rather than generate an HsCon directly, because
623 -- it means that the special cases (e.g. dictionary with only one
624 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
625 -- than needing to be repeated here.
628 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
630 dict_bind = VarMonoBind this_dict_id dict_rhs
631 method_binds = andMonoBindList method_binds_s
637 [(inst_tyvars', dfun_id, this_dict_id)]
638 emptyNameSet -- No inlines (yet)
639 (lie_binds1 `AndMonoBinds`
640 lie_binds2 `AndMonoBinds`
641 method_binds `AndMonoBinds`
644 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
645 main_bind `AndMonoBinds` prag_binds)
649 %************************************************************************
651 \subsection{Checking for a decent instance type}
653 %************************************************************************
655 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
656 it must normally look like: @instance Foo (Tycon a b c ...) ...@
658 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
659 flag is on, or (2)~the instance is imported (they must have been
660 compiled elsewhere). In these cases, we let them go through anyway.
662 We can also have instances for functions: @instance Foo (a -> b) ...@.
665 scrutiniseInstanceConstraint pred
666 = getDOptsTc `thenTc` \ dflags -> case () of
668 | dopt Opt_AllowUndecidableInstances dflags
671 | Just (clas,tys) <- getClassTys_maybe pred,
676 -> addErrTc (instConstraintErr pred)
678 scrutiniseInstanceHead clas inst_taus
679 = getDOptsTc `thenTc` \ dflags -> case () of
682 -- A user declaration of a CCallable/CReturnable instance
683 -- must be for a "boxed primitive" type.
684 (clas `hasKey` cCallableClassKey
685 && not (ccallable_type dflags first_inst_tau))
687 (clas `hasKey` cReturnableClassKey
688 && not (creturnable_type first_inst_tau))
689 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
691 -- Allow anything for AllowUndecidableInstances
692 | dopt Opt_AllowUndecidableInstances dflags
695 -- If GlasgowExts then check at least one isn't a type variable
696 | dopt Opt_GlasgowExts dflags
697 -> if all isTyVarTy inst_taus
698 then addErrTc (instTypeErr clas inst_taus
699 (text "There must be at least one non-type-variable in the instance head"))
702 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
703 | not (length inst_taus == 1 &&
704 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
705 not (isSynTyCon tycon) && -- ...but not a synonym
706 all isTyVarTy arg_tys && -- Applied to type variables
707 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
708 -- This last condition checks that all the type variables are distinct
710 -> addErrTc (instTypeErr clas inst_taus
711 (text "the instance type must be of form (T a b c)" $$
712 text "where T is not a synonym, and a,b,c are distinct type variables")
719 (first_inst_tau : _) = inst_taus
721 -- Stuff for algebraic or -> type
722 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
723 Just (tycon, arg_tys) = maybe_tycon_app
725 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
726 creturnable_type ty = isFFIResultTy ty
730 %************************************************************************
732 \subsection{Error messages}
734 %************************************************************************
737 tcAddDeclCtxt decl thing_inside
744 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
745 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
746 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
747 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
749 ctxt = hsep [ptext SLIT("In the"), text thing,
750 ptext SLIT("declaration for"), quotes (ppr name)]
754 instConstraintErr pred
755 = hang (ptext SLIT("Illegal constraint") <+>
756 quotes (pprPred pred) <+>
757 ptext SLIT("in instance context"))
758 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
760 badGenericInstanceType binds
761 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
764 missingGenericInstances missing
765 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
769 dupGenericInsts tc_inst_infos
770 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
771 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
772 ptext SLIT("All the type patterns for a generic type constructor must be identical")
775 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
777 instTypeErr clas tys msg
778 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
782 nonBoxedPrimCCallErr clas inst_ty
783 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
784 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
787 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
788 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")