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, pprInstEnv )
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 traceTc (text "inst env before" <+> pprInstEnv inst_env0) `thenNF_Tc_`
200 traceTc (vcat [text "imp" <+> ppr imported_dfuns,
201 text "hst" <+> ppr hst_dfuns,
202 text "local" <+> hsep (map pprInstInfo local_inst_info),
203 text "gen" <+> hsep (map pprInstInfo generic_inst_info)]) `thenNF_Tc_`
204 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
205 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
206 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
207 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
209 -- (3) Compute instances from "deriving" clauses;
210 -- note that we only do derivings for things in this module;
211 -- we ignore deriving decls from interfaces!
212 -- This stuff computes a context for the derived instance decl, so it
213 -- needs to know about all the instances possible; hecne inst_env4
214 tcDeriving prs mod inst_env4 get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) ->
215 traceTc (vcat [text "deriv" <+> hsep (map pprInstInfo deriv_inst_info)]) `thenNF_Tc_`
216 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
218 traceTc (text "inst env after" <+> pprInstEnv final_inst_env) `thenNF_Tc_`
221 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
224 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
225 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
227 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
228 addInstDFuns dfuns infos
229 = getDOptsTc `thenTc` \ dflags ->
231 (inst_env', errs) = extendInstEnv dflags dfuns infos
233 traceTc (text "addInstDFuns" <+> vcat errs) `thenNF_Tc_`
234 addErrsTc errs `thenNF_Tc_`
239 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
240 -- Deal with a single instance declaration
241 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
242 = -- Prime error recovery, set source location
243 recoverNF_Tc (returnNF_Tc []) $
244 tcAddSrcLoc src_loc $
246 -- Type-check all the stuff before the "where"
247 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
249 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
252 (case maybe_dfun_name of
253 Nothing -> -- A source-file instance declaration
255 -- Check for respectable instance type, and context
256 -- but only do this for non-imported instance decls.
257 -- Imported ones should have been checked already, and may indeed
258 -- contain something illegal in normal Haskell, notably
259 -- instance CCallable [Char]
260 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
261 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
263 -- Make the dfun id and return it
264 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
265 returnNF_Tc (True, dfun_name)
267 Just dfun_name -> -- An interface-file instance declaration
269 returnNF_Tc (False, dfun_name)
270 ) `thenNF_Tc` \ (is_local, dfun_name) ->
273 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
275 returnTc [InstInfo { iLocal = is_local, iDFunId = dfun_id,
276 iBinds = binds, iPrags = uprags }]
280 %************************************************************************
282 \subsection{Extracting generic instance declaration from class declarations}
284 %************************************************************************
286 @getGenericInstances@ extracts the generic instance declarations from a class
287 declaration. For exmaple
292 op{ x+y } (Inl v) = ...
293 op{ x+y } (Inr v) = ...
294 op{ x*y } (v :*: w) = ...
297 gives rise to the instance declarations
299 instance C (x+y) where
303 instance C (x*y) where
311 getGenericInstances :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
312 getGenericInstances mod class_decls
313 = mapTc (get_generics mod) class_decls `thenTc` \ gen_inst_infos ->
315 gen_inst_info = concat gen_inst_infos
317 getDOptsTc `thenTc` \ dflags ->
318 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
319 (vcat (map pprInstInfo gen_inst_info)))
321 returnTc gen_inst_info
323 get_generics mod decl@(ClassDecl context class_name tyvar_names
324 fundeps class_sigs def_methods
327 = returnTc [] -- The comon case:
328 -- no generic default methods, or
329 -- its an imported class decl (=> has no methods at all)
331 | otherwise -- A local class decl with generic default methods
332 = recoverNF_Tc (returnNF_Tc []) $
334 tcLookupClass class_name `thenTc` \ clas ->
336 -- Make an InstInfo out of each group
337 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
339 -- Check that there is only one InstInfo for each type constructor
340 -- The main way this can fail is if you write
341 -- f {| a+b |} ... = ...
342 -- f {| x+y |} ... = ...
343 -- Then at this point we'll have an InstInfo for each
345 tc_inst_infos :: [(TyCon, InstInfo)]
346 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
348 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
350 get_uniq (tc,_) = getUnique tc
352 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
354 -- Check that there is an InstInfo for each generic type constructor
356 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
358 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
363 -- Group the declarations by type pattern
364 groups :: [(RenamedHsType, RenamedMonoBinds)]
365 groups = assocElts (getGenericBinds def_methods)
368 ---------------------------------
369 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
370 -- Takes a group of method bindings, finds the generic ones, and returns
371 -- them in finite map indexed by the type parameter in the definition.
373 getGenericBinds EmptyMonoBinds = emptyAssoc
374 getGenericBinds (AndMonoBinds m1 m2)
375 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
377 getGenericBinds (FunMonoBind id infixop matches loc)
378 = mapAssoc wrap (foldl add emptyAssoc matches)
379 -- Using foldl not foldr is vital, else
380 -- we reverse the order of the bindings!
382 add env match = case maybeGenericMatch match of
384 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
386 wrap ms = FunMonoBind id infixop ms loc
388 ---------------------------------
389 mkGenericInstance :: Module -> Class -> SrcLoc
390 -> (RenamedHsType, RenamedMonoBinds)
393 mkGenericInstance mod clas loc (hs_ty, binds)
394 -- Make a generic instance declaration
395 -- For example: instance (C a, C b) => C (a+b) where { binds }
397 = -- Extract the universally quantified type variables
398 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
399 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
400 tcExtendTyVarEnv tyvars $
402 -- Type-check the instance type, and check its form
403 tcHsSigType hs_ty `thenTc` \ inst_ty ->
404 checkTc (validGenericInstanceType inst_ty)
405 (badGenericInstanceType binds) `thenTc_`
407 -- Make the dictionary function.
408 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
410 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
412 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
415 returnTc (InstInfo { iLocal = True, iDFunId = dfun_id,
416 iBinds = binds, iPrags = [] })
420 %************************************************************************
422 \subsection{Type-checking instance declarations, pass 2}
424 %************************************************************************
427 tcInstDecls2 :: [InstInfo]
428 -> NF_TcM (LIE, TcMonoBinds)
430 tcInstDecls2 inst_decls
431 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
432 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
433 (map tcInstDecl2 inst_decls)
435 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
436 tc2 `thenNF_Tc` \ (lie2, binds2) ->
437 returnNF_Tc (lie1 `plusLIE` lie2,
438 binds1 `AndMonoBinds` binds2)
441 ======= New documentation starts here (Sept 92) ==============
443 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
444 the dictionary function for this instance declaration. For example
446 instance Foo a => Foo [a] where
450 might generate something like
452 dfun.Foo.List dFoo_a = let op1 x = ...
458 HOWEVER, if the instance decl has no context, then it returns a
459 bigger @HsBinds@ with declarations for each method. For example
461 instance Foo [a] where
467 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
468 const.Foo.op1.List a x = ...
469 const.Foo.op2.List a y = ...
471 This group may be mutually recursive, because (for example) there may
472 be no method supplied for op2 in which case we'll get
474 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
476 that is, the default method applied to the dictionary at this type.
478 What we actually produce in either case is:
480 AbsBinds [a] [dfun_theta_dicts]
481 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
482 { d = (sd1,sd2, ..., op1, op2, ...)
487 The "maybe" says that we only ask AbsBinds to make global constant methods
488 if the dfun_theta is empty.
491 For an instance declaration, say,
493 instance (C1 a, C2 b) => C (T a b) where
496 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
497 function whose type is
499 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
501 Notice that we pass it the superclass dictionaries at the instance type; this
502 is the ``Mark Jones optimisation''. The stuff before the "=>" here
503 is the @dfun_theta@ below.
505 First comes the easy case of a non-local instance decl.
508 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
510 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
511 iBinds = monobinds, iPrags = uprags })
513 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
516 = -- Prime error recovery
517 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
518 tcAddSrcLoc (getSrcLoc dfun_id) $
520 -- Instantiate the instance decl with tc-style type variables
521 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
523 (clas, inst_tys') = splitDictTy dict_ty'
524 origin = InstanceDeclOrigin
526 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
528 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
529 sel_names = [idName sel_id | (sel_id, _) <- op_items]
531 -- Instantiate the super-class context with inst_tys
532 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
534 -- Find any definitions in monobinds that aren't from the class
535 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
537 -- The type variable from the dict fun actually scope
538 -- over the bindings. They were gotten from
539 -- the original instance declaration
540 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
542 -- Check that all the method bindings come from this class
543 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
545 -- Create dictionary Ids from the specified instance contexts.
546 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
547 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
548 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
550 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
551 tcExtendGlobalValEnv dm_ids (
552 -- Default-method Ids may be mentioned in synthesised RHSs
554 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
556 monobinds uprags True)
558 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
560 -- Deal with SPECIALISE instance pragmas by making them
561 -- look like SPECIALISE pragmas for the dfun
563 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
565 tcExtendGlobalValEnv [dfun_id] (
566 tcSpecSigs dfun_prags
567 ) `thenTc` \ (prag_binds, prag_lie) ->
569 -- Check the overloading constraints of the methods and superclasses
571 -- tcMethodBind has checked that the class_tyvars havn't
572 -- been unified with each other or another type, but we must
573 -- still zonk them before passing them to tcSimplifyAndCheck
574 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
576 inst_tyvars_set = mkVarSet zonked_inst_tyvars
578 (meth_lies, meth_ids) = unzip meth_lies_w_ids
580 -- These insts are in scope; quite a few, eh?
581 avail_insts = this_dict `plusLIE`
582 dfun_arg_dicts `plusLIE`
584 unionManyBags meth_lies
586 methods_lie = plusLIEs insts_needed_s
589 -- Simplify the constraints from methods
590 tcAddErrCtxt methodCtxt (
592 (ptext SLIT("instance declaration context"))
593 inst_tyvars_set -- Local tyvars
596 ) `thenTc` \ (const_lie1, lie_binds1) ->
598 -- Figure out bindings for the superclass context
599 tcAddErrCtxt superClassCtxt (
601 (ptext SLIT("instance declaration context"))
603 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
604 -- get bound by just selecting from this_dict!!
606 ) `thenTc` \ (const_lie2, lie_binds2) ->
609 -- Create the result bindings
611 dict_constr = classDataCon clas
612 scs_and_meths = sc_dict_ids ++ meth_ids
616 = -- Blatant special case for CCallable, CReturnable
617 -- If the dictionary is empty then we should never
618 -- select anything from it, so we make its RHS just
619 -- emit an error message. This in turn means that we don't
620 -- mention the constructor, which doesn't exist for CCallable, CReturnable
621 -- Hardly beautiful, but only three extra lines.
622 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
623 (HsLit (HsString msg))
625 | otherwise -- The common case
626 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
627 -- We don't produce a binding for the dict_constr; instead we
628 -- rely on the simplifier to unfold this saturated application
629 -- We do this rather than generate an HsCon directly, because
630 -- it means that the special cases (e.g. dictionary with only one
631 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
632 -- than needing to be repeated here.
635 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
637 dict_bind = VarMonoBind this_dict_id dict_rhs
638 method_binds = andMonoBindList method_binds_s
644 [(inst_tyvars', dfun_id, this_dict_id)]
645 emptyNameSet -- No inlines (yet)
646 (lie_binds1 `AndMonoBinds`
647 lie_binds2 `AndMonoBinds`
648 method_binds `AndMonoBinds`
651 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
652 main_bind `AndMonoBinds` prag_binds)
656 %************************************************************************
658 \subsection{Checking for a decent instance type}
660 %************************************************************************
662 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
663 it must normally look like: @instance Foo (Tycon a b c ...) ...@
665 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
666 flag is on, or (2)~the instance is imported (they must have been
667 compiled elsewhere). In these cases, we let them go through anyway.
669 We can also have instances for functions: @instance Foo (a -> b) ...@.
672 scrutiniseInstanceConstraint pred
673 = getDOptsTc `thenTc` \ dflags -> case () of
675 | dopt Opt_AllowUndecidableInstances dflags
678 | Just (clas,tys) <- getClassTys_maybe pred,
683 -> addErrTc (instConstraintErr pred)
685 scrutiniseInstanceHead clas inst_taus
686 = getDOptsTc `thenTc` \ dflags -> case () of
689 -- A user declaration of a CCallable/CReturnable instance
690 -- must be for a "boxed primitive" type.
691 (clas `hasKey` cCallableClassKey
692 && not (ccallable_type dflags first_inst_tau))
694 (clas `hasKey` cReturnableClassKey
695 && not (creturnable_type first_inst_tau))
696 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
698 -- Allow anything for AllowUndecidableInstances
699 | dopt Opt_AllowUndecidableInstances dflags
702 -- If GlasgowExts then check at least one isn't a type variable
703 | dopt Opt_GlasgowExts dflags
704 -> if all isTyVarTy inst_taus
705 then addErrTc (instTypeErr clas inst_taus
706 (text "There must be at least one non-type-variable in the instance head"))
709 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
710 | not (length inst_taus == 1 &&
711 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
712 not (isSynTyCon tycon) && -- ...but not a synonym
713 all isTyVarTy arg_tys && -- Applied to type variables
714 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
715 -- This last condition checks that all the type variables are distinct
717 -> addErrTc (instTypeErr clas inst_taus
718 (text "the instance type must be of form (T a b c)" $$
719 text "where T is not a synonym, and a,b,c are distinct type variables")
726 (first_inst_tau : _) = inst_taus
728 -- Stuff for algebraic or -> type
729 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
730 Just (tycon, arg_tys) = maybe_tycon_app
732 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
733 creturnable_type ty = isFFIResultTy ty
737 %************************************************************************
739 \subsection{Error messages}
741 %************************************************************************
744 tcAddDeclCtxt decl thing_inside
751 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
752 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
753 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
754 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
756 ctxt = hsep [ptext SLIT("In the"), text thing,
757 ptext SLIT("declaration for"), quotes (ppr name)]
761 instConstraintErr pred
762 = hang (ptext SLIT("Illegal constraint") <+>
763 quotes (pprPred pred) <+>
764 ptext SLIT("in instance context"))
765 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
767 badGenericInstanceType binds
768 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
771 missingGenericInstances missing
772 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
776 dupGenericInsts tc_inst_infos
777 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
778 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
779 ptext SLIT("All the type patterns for a generic type constructor must be identical")
782 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
784 instTypeErr clas tys msg
785 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
789 nonBoxedPrimCCallErr clas inst_ty
790 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
791 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
794 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
795 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")