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 unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
182 -- (2) Instances from generic class declarations
183 getGenericInstances 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 ->
224 (inst_env', errs) = extendInstEnv dflags dfuns infos
226 addErrsTc errs `thenNF_Tc_`
231 tcInstDecl1 :: TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
232 -- Deal with a single instance declaration
233 tcInstDecl1 unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
234 = -- Prime error recovery, set source location
235 recoverNF_Tc (returnNF_Tc []) $
236 tcAddSrcLoc src_loc $
238 -- Type-check all the stuff before the "where"
239 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
241 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
244 (case maybe_dfun_name of
245 Nothing -> -- A source-file instance declaration
247 -- Check for respectable instance type, and context
248 -- but only do this for non-imported instance decls.
249 -- Imported ones should have been checked already, and may indeed
250 -- contain something illegal in normal Haskell, notably
251 -- instance CCallable [Char]
252 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
253 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
255 -- Make the dfun id and return it
256 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
257 returnNF_Tc (True, dfun_name)
259 Just dfun_name -> -- An interface-file instance declaration
261 returnNF_Tc (False, dfun_name)
262 ) `thenNF_Tc` \ (is_local, dfun_name) ->
265 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
267 returnTc [InstInfo { iLocal = is_local, iDFunId = dfun_id,
268 iBinds = binds, iPrags = uprags }]
272 %************************************************************************
274 \subsection{Extracting generic instance declaration from class declarations}
276 %************************************************************************
278 @getGenericInstances@ extracts the generic instance declarations from a class
279 declaration. For exmaple
284 op{ x+y } (Inl v) = ...
285 op{ x+y } (Inr v) = ...
286 op{ x*y } (v :*: w) = ...
289 gives rise to the instance declarations
291 instance C (x+y) where
295 instance C (x*y) where
303 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
304 getGenericInstances class_decls
305 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
307 gen_inst_info = concat gen_inst_infos
309 getDOptsTc `thenTc` \ dflags ->
310 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
311 (vcat (map pprInstInfo gen_inst_info)))
313 returnTc gen_inst_info
315 get_generics decl@(ClassDecl {tcdMeths = Nothing})
316 = returnTc [] -- Imported class decls
318 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
320 = returnTc [] -- The comon case: no generic default methods
322 | otherwise -- A local class decl with generic default methods
323 = recoverNF_Tc (returnNF_Tc []) $
325 tcLookupClass class_name `thenTc` \ clas ->
327 -- Make an InstInfo out of each group
328 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
330 -- Check that there is only one InstInfo for each type constructor
331 -- The main way this can fail is if you write
332 -- f {| a+b |} ... = ...
333 -- f {| x+y |} ... = ...
334 -- Then at this point we'll have an InstInfo for each
336 tc_inst_infos :: [(TyCon, InstInfo)]
337 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
339 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
341 get_uniq (tc,_) = getUnique tc
343 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
345 -- Check that there is an InstInfo for each generic type constructor
347 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
349 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
354 -- Group the declarations by type pattern
355 groups :: [(RenamedHsType, RenamedMonoBinds)]
356 groups = assocElts (getGenericBinds def_methods)
359 ---------------------------------
360 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
361 -- Takes a group of method bindings, finds the generic ones, and returns
362 -- them in finite map indexed by the type parameter in the definition.
364 getGenericBinds EmptyMonoBinds = emptyAssoc
365 getGenericBinds (AndMonoBinds m1 m2)
366 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
368 getGenericBinds (FunMonoBind id infixop matches loc)
369 = mapAssoc wrap (foldl add emptyAssoc matches)
370 -- Using foldl not foldr is vital, else
371 -- we reverse the order of the bindings!
373 add env match = case maybeGenericMatch match of
375 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
377 wrap ms = FunMonoBind id infixop ms loc
379 ---------------------------------
380 mkGenericInstance :: Class -> SrcLoc
381 -> (RenamedHsType, RenamedMonoBinds)
384 mkGenericInstance clas loc (hs_ty, binds)
385 -- Make a generic instance declaration
386 -- For example: instance (C a, C b) => C (a+b) where { binds }
388 = -- Extract the universally quantified type variables
389 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
390 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
391 tcExtendTyVarEnv tyvars $
393 -- Type-check the instance type, and check its form
394 tcHsSigType hs_ty `thenTc` \ inst_ty ->
395 checkTc (validGenericInstanceType inst_ty)
396 (badGenericInstanceType binds) `thenTc_`
398 -- Make the dictionary function.
399 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
401 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
403 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
406 returnTc (InstInfo { iLocal = True, iDFunId = dfun_id,
407 iBinds = binds, iPrags = [] })
411 %************************************************************************
413 \subsection{Type-checking instance declarations, pass 2}
415 %************************************************************************
418 tcInstDecls2 :: [InstInfo]
419 -> NF_TcM (LIE, TcMonoBinds)
421 tcInstDecls2 inst_decls
422 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
423 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
424 (map tcInstDecl2 inst_decls)
426 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
427 tc2 `thenNF_Tc` \ (lie2, binds2) ->
428 returnNF_Tc (lie1 `plusLIE` lie2,
429 binds1 `AndMonoBinds` binds2)
432 ======= New documentation starts here (Sept 92) ==============
434 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
435 the dictionary function for this instance declaration. For example
437 instance Foo a => Foo [a] where
441 might generate something like
443 dfun.Foo.List dFoo_a = let op1 x = ...
449 HOWEVER, if the instance decl has no context, then it returns a
450 bigger @HsBinds@ with declarations for each method. For example
452 instance Foo [a] where
458 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
459 const.Foo.op1.List a x = ...
460 const.Foo.op2.List a y = ...
462 This group may be mutually recursive, because (for example) there may
463 be no method supplied for op2 in which case we'll get
465 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
467 that is, the default method applied to the dictionary at this type.
469 What we actually produce in either case is:
471 AbsBinds [a] [dfun_theta_dicts]
472 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
473 { d = (sd1,sd2, ..., op1, op2, ...)
478 The "maybe" says that we only ask AbsBinds to make global constant methods
479 if the dfun_theta is empty.
482 For an instance declaration, say,
484 instance (C1 a, C2 b) => C (T a b) where
487 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
488 function whose type is
490 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
492 Notice that we pass it the superclass dictionaries at the instance type; this
493 is the ``Mark Jones optimisation''. The stuff before the "=>" here
494 is the @dfun_theta@ below.
496 First comes the easy case of a non-local instance decl.
499 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
501 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
502 iBinds = monobinds, iPrags = uprags })
504 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
507 = -- Prime error recovery
508 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
509 tcAddSrcLoc (getSrcLoc dfun_id) $
511 -- Instantiate the instance decl with tc-style type variables
512 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
514 (clas, inst_tys') = splitDictTy dict_ty'
515 origin = InstanceDeclOrigin
517 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
519 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
520 sel_names = [idName sel_id | (sel_id, _) <- op_items]
522 -- Instantiate the super-class context with inst_tys
523 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
525 -- Find any definitions in monobinds that aren't from the class
526 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
528 -- The type variable from the dict fun actually scope
529 -- over the bindings. They were gotten from
530 -- the original instance declaration
531 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
533 -- Check that all the method bindings come from this class
534 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
536 -- Create dictionary Ids from the specified instance contexts.
537 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
538 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
539 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
541 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
542 tcExtendGlobalValEnv dm_ids (
543 -- Default-method Ids may be mentioned in synthesised RHSs
545 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
547 monobinds uprags True)
549 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
551 -- Deal with SPECIALISE instance pragmas by making them
552 -- look like SPECIALISE pragmas for the dfun
554 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
556 tcExtendGlobalValEnv [dfun_id] (
557 tcSpecSigs dfun_prags
558 ) `thenTc` \ (prag_binds, prag_lie) ->
560 -- Check the overloading constraints of the methods and superclasses
562 -- tcMethodBind has checked that the class_tyvars havn't
563 -- been unified with each other or another type, but we must
564 -- still zonk them before passing them to tcSimplifyAndCheck
565 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
567 inst_tyvars_set = mkVarSet zonked_inst_tyvars
569 (meth_lies, meth_ids) = unzip meth_lies_w_ids
571 -- These insts are in scope; quite a few, eh?
572 avail_insts = this_dict `plusLIE`
573 dfun_arg_dicts `plusLIE`
575 unionManyBags meth_lies
577 methods_lie = plusLIEs insts_needed_s
580 -- Simplify the constraints from methods
581 tcAddErrCtxt methodCtxt (
583 (ptext SLIT("instance declaration context"))
584 inst_tyvars_set -- Local tyvars
587 ) `thenTc` \ (const_lie1, lie_binds1) ->
589 -- Figure out bindings for the superclass context
590 tcAddErrCtxt superClassCtxt (
592 (ptext SLIT("instance declaration context"))
594 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
595 -- get bound by just selecting from this_dict!!
597 ) `thenTc` \ (const_lie2, lie_binds2) ->
600 -- Create the result bindings
602 dict_constr = classDataCon clas
603 scs_and_meths = sc_dict_ids ++ meth_ids
607 = -- Blatant special case for CCallable, CReturnable
608 -- If the dictionary is empty then we should never
609 -- select anything from it, so we make its RHS just
610 -- emit an error message. This in turn means that we don't
611 -- mention the constructor, which doesn't exist for CCallable, CReturnable
612 -- Hardly beautiful, but only three extra lines.
613 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
614 (HsLit (HsString msg))
616 | otherwise -- The common case
617 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
618 -- We don't produce a binding for the dict_constr; instead we
619 -- rely on the simplifier to unfold this saturated application
620 -- We do this rather than generate an HsCon directly, because
621 -- it means that the special cases (e.g. dictionary with only one
622 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
623 -- than needing to be repeated here.
626 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
628 dict_bind = VarMonoBind this_dict_id dict_rhs
629 method_binds = andMonoBindList method_binds_s
635 [(inst_tyvars', dfun_id, this_dict_id)]
636 emptyNameSet -- No inlines (yet)
637 (lie_binds1 `AndMonoBinds`
638 lie_binds2 `AndMonoBinds`
639 method_binds `AndMonoBinds`
642 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
643 main_bind `AndMonoBinds` prag_binds)
647 %************************************************************************
649 \subsection{Checking for a decent instance type}
651 %************************************************************************
653 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
654 it must normally look like: @instance Foo (Tycon a b c ...) ...@
656 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
657 flag is on, or (2)~the instance is imported (they must have been
658 compiled elsewhere). In these cases, we let them go through anyway.
660 We can also have instances for functions: @instance Foo (a -> b) ...@.
663 scrutiniseInstanceConstraint pred
664 = getDOptsTc `thenTc` \ dflags -> case () of
666 | dopt Opt_AllowUndecidableInstances dflags
669 | Just (clas,tys) <- getClassTys_maybe pred,
674 -> addErrTc (instConstraintErr pred)
676 scrutiniseInstanceHead clas inst_taus
677 = getDOptsTc `thenTc` \ dflags -> case () of
680 -- A user declaration of a CCallable/CReturnable instance
681 -- must be for a "boxed primitive" type.
682 (clas `hasKey` cCallableClassKey
683 && not (ccallable_type dflags first_inst_tau))
685 (clas `hasKey` cReturnableClassKey
686 && not (creturnable_type first_inst_tau))
687 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
689 -- Allow anything for AllowUndecidableInstances
690 | dopt Opt_AllowUndecidableInstances dflags
693 -- If GlasgowExts then check at least one isn't a type variable
694 | dopt Opt_GlasgowExts dflags
695 -> if all isTyVarTy inst_taus
696 then addErrTc (instTypeErr clas inst_taus
697 (text "There must be at least one non-type-variable in the instance head"))
700 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
701 | not (length inst_taus == 1 &&
702 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
703 not (isSynTyCon tycon) && -- ...but not a synonym
704 all isTyVarTy arg_tys && -- Applied to type variables
705 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
706 -- This last condition checks that all the type variables are distinct
708 -> addErrTc (instTypeErr clas inst_taus
709 (text "the instance type must be of form (T a b c)" $$
710 text "where T is not a synonym, and a,b,c are distinct type variables")
717 (first_inst_tau : _) = inst_taus
719 -- Stuff for algebraic or -> type
720 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
721 Just (tycon, arg_tys) = maybe_tycon_app
723 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
724 creturnable_type ty = isFFIResultTy ty
728 %************************************************************************
730 \subsection{Error messages}
732 %************************************************************************
735 tcAddDeclCtxt decl thing_inside
736 = tcAddSrcLoc (tcdLoc decl) $
741 ClassDecl {} -> "class"
742 TySynonym {} -> "type synonym"
743 TyData {tcdND = NewType} -> "newtype"
744 TyData {tcdND = DataType} -> "data type"
746 ctxt = hsep [ptext SLIT("In the"), text thing,
747 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
751 instConstraintErr pred
752 = hang (ptext SLIT("Illegal constraint") <+>
753 quotes (pprPred pred) <+>
754 ptext SLIT("in instance context"))
755 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
757 badGenericInstanceType binds
758 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
761 missingGenericInstances missing
762 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
766 dupGenericInsts tc_inst_infos
767 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
768 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
769 ptext SLIT("All the type patterns for a generic type constructor must be identical")
772 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
774 instTypeErr clas tys msg
775 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
779 nonBoxedPrimCCallErr clas inst_ty
780 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
781 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
784 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
785 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")