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, classDataCon, 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 Class ( Class, DefMeth(..), classBigSig )
46 import Var ( idName, idType )
47 import Maybes ( maybeToBool )
48 import MkId ( mkDictFunId )
49 import Generics ( validGenericInstanceType )
50 import Module ( Module, foldModuleEnv )
51 import Name ( getSrcLoc )
52 import NameSet ( emptyNameSet, nameSetToList )
53 import PrelInfo ( eRROR_ID )
54 import PprType ( pprConstraint, pprPred )
55 import TyCon ( TyCon, isSynTyCon, tyConDerivings )
56 import Type ( splitDFunTy, isTyVarTy,
57 splitTyConApp_maybe, splitDictTy,
58 splitAlgTyConApp_maybe, splitForAllTys,
59 unUsgTy, tyVarsOfTypes, mkClassPred, mkTyVarTy,
62 import Subst ( mkTopTyVarSubst, substClasses )
63 import VarSet ( mkVarSet, varSetElems )
64 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIResultTy )
65 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
67 import SrcLoc ( SrcLoc )
68 import VarSet ( varSetElems )
69 import Unique ( Uniquable(..) )
70 import BasicTypes ( NewOrData(..), Fixity )
71 import ErrUtils ( dumpIfSet_dyn )
72 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
73 assocElts, extendAssoc_C,
74 equivClassesByUniq, minusList
76 import List ( partition )
80 Typechecking instance declarations is done in two passes. The first
81 pass, made by @tcInstDecls1@, collects information to be used in the
84 This pre-processed info includes the as-yet-unprocessed bindings
85 inside the instance declaration. These are type-checked in the second
86 pass, when the class-instance envs and GVE contain all the info from
87 all the instance and value decls. Indeed that's the reason we need
88 two passes over the instance decls.
91 Here is the overall algorithm.
92 Assume that we have an instance declaration
94 instance c => k (t tvs) where b
98 $LIE_c$ is the LIE for the context of class $c$
100 $betas_bar$ is the free variables in the class method type, excluding the
103 $LIE_cop$ is the LIE constraining a particular class method
105 $tau_cop$ is the tau type of a class method
107 $LIE_i$ is the LIE for the context of instance $i$
109 $X$ is the instance constructor tycon
111 $gammas_bar$ is the set of type variables of the instance
113 $LIE_iop$ is the LIE for a particular class method instance
115 $tau_iop$ is the tau type for this instance of a class method
117 $alpha$ is the class variable
119 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
121 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
124 ToDo: Update the list above with names actually in the code.
128 First, make the LIEs for the class and instance contexts, which means
129 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
130 and make LIElistI and LIEI.
132 Then process each method in turn.
134 order the instance methods according to the ordering of the class methods
136 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
138 Create final dictionary function from bindings generated already
140 df = lambda inst_tyvars
147 in <op1,op2,...,opn,sd1,...,sdm>
149 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
150 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
154 %************************************************************************
156 \subsection{Extracting instance decls}
158 %************************************************************************
160 Gather up the instance declarations from their various sources
163 tcInstDecls1 :: PackageInstEnv
164 -> PersistentRenamerState
165 -> HomeSymbolTable -- Contains instances
166 -> TcEnv -- Contains IdInfo for dfun ids
167 -> (Name -> Maybe Fixity) -- for deriving Show and Read
168 -> Module -- Module for deriving
171 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
173 tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod tycons decls
175 inst_decls = [inst_decl | InstD inst_decl <- decls]
176 clas_decls = [clas_decl | TyClD clas_decl <- decls, isClassDecl clas_decl]
178 -- (1) Do the ordinary instance declarations
179 mapNF_Tc (tcInstDecl1 mod unf_env) inst_decls `thenNF_Tc` \ inst_infos ->
181 -- (2) Instances from generic class declarations
182 getGenericInstances mod clas_decls `thenTc` \ generic_inst_info ->
184 -- Next, construct the instance environment so far, consisting of
185 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
186 -- b) imported instance decls (not in the home package) inst_env1
187 -- c) other modules in this package (gotten from hst) inst_env2
188 -- d) local instance decls inst_env3
189 -- e) generic instances inst_env4
190 -- The result of (b) replaces the cached InstEnv in the PCS
192 (local_inst_info, imported_inst_info) = partition iLocal (concat inst_infos)
194 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
196 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
198 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
199 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
200 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
201 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
203 -- (3) Compute instances from "deriving" clauses;
204 -- note that we only do derivings for things in this module;
205 -- we ignore deriving decls from interfaces!
206 -- This stuff computes a context for the derived instance decl, so it
207 -- needs to know about all the instances possible; hecne inst_env4
208 tcDeriving prs mod inst_env4 get_fixity tycons `thenTc` \ (deriv_inst_info, deriv_binds) ->
209 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
213 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
216 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
217 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
219 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
220 addInstDFuns dfuns infos
221 = getDOptsTc `thenTc` \ dflags ->
222 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
223 addErrsTc errs `thenNF_Tc_`
231 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
232 -- Deal with a single instance declaration
233 tcInstDecl1 mod 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 mod 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 :: Module -> [RenamedTyClDecl] -> TcM [InstInfo]
304 getGenericInstances mod class_decls
305 = mapTc (get_generics mod) 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 mod decl@(ClassDecl context class_name tyvar_names
316 fundeps class_sigs def_methods
319 = returnTc [] -- The comon case:
320 -- no generic default methods, or
321 -- its an imported class decl (=> has no methods at all)
323 | otherwise -- A local class decl with generic default methods
324 = recoverNF_Tc (returnNF_Tc []) $
326 tcLookupClass class_name `thenTc` \ clas ->
328 -- Make an InstInfo out of each group
329 mapTc (mkGenericInstance mod clas loc) groups `thenTc` \ inst_infos ->
331 -- Check that there is only one InstInfo for each type constructor
332 -- The main way this can fail is if you write
333 -- f {| a+b |} ... = ...
334 -- f {| x+y |} ... = ...
335 -- Then at this point we'll have an InstInfo for each
337 tc_inst_infos :: [(TyCon, InstInfo)]
338 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
340 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
342 get_uniq (tc,_) = getUnique tc
344 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
346 -- Check that there is an InstInfo for each generic type constructor
348 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
350 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
355 -- Group the declarations by type pattern
356 groups :: [(RenamedHsType, RenamedMonoBinds)]
357 groups = assocElts (getGenericBinds def_methods)
360 ---------------------------------
361 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
362 -- Takes a group of method bindings, finds the generic ones, and returns
363 -- them in finite map indexed by the type parameter in the definition.
365 getGenericBinds EmptyMonoBinds = emptyAssoc
366 getGenericBinds (AndMonoBinds m1 m2)
367 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
369 getGenericBinds (FunMonoBind id infixop matches loc)
370 = mapAssoc wrap (foldr add emptyAssoc matches)
372 add match env = case maybeGenericMatch match of
374 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
376 wrap ms = FunMonoBind id infixop ms loc
378 ---------------------------------
379 mkGenericInstance :: Module -> Class -> SrcLoc
380 -> (RenamedHsType, RenamedMonoBinds)
383 mkGenericInstance mod clas loc (hs_ty, binds)
384 -- Make a generic instance declaration
385 -- For example: instance (C a, C b) => C (a+b) where { binds }
387 = -- Extract the universally quantified type variables
388 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
389 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
390 tcExtendTyVarEnv tyvars $
392 -- Type-check the instance type, and check its form
393 tcHsSigType hs_ty `thenTc` \ inst_ty ->
394 checkTc (validGenericInstanceType inst_ty)
395 (badGenericInstanceType binds) `thenTc_`
397 -- Make the dictionary function.
398 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
400 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
402 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
405 returnTc (InstInfo { iLocal = True, iDFunId = dfun_id,
406 iBinds = binds, iPrags = [] })
410 %************************************************************************
412 \subsection{Type-checking instance declarations, pass 2}
414 %************************************************************************
417 tcInstDecls2 :: [InstInfo]
418 -> NF_TcM (LIE, TcMonoBinds)
420 tcInstDecls2 inst_decls
421 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
422 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
423 (map tcInstDecl2 inst_decls)
425 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
426 tc2 `thenNF_Tc` \ (lie2, binds2) ->
427 returnNF_Tc (lie1 `plusLIE` lie2,
428 binds1 `AndMonoBinds` binds2)
431 ======= New documentation starts here (Sept 92) ==============
433 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
434 the dictionary function for this instance declaration. For example
436 instance Foo a => Foo [a] where
440 might generate something like
442 dfun.Foo.List dFoo_a = let op1 x = ...
448 HOWEVER, if the instance decl has no context, then it returns a
449 bigger @HsBinds@ with declarations for each method. For example
451 instance Foo [a] where
457 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
458 const.Foo.op1.List a x = ...
459 const.Foo.op2.List a y = ...
461 This group may be mutually recursive, because (for example) there may
462 be no method supplied for op2 in which case we'll get
464 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
466 that is, the default method applied to the dictionary at this type.
468 What we actually produce in either case is:
470 AbsBinds [a] [dfun_theta_dicts]
471 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
472 { d = (sd1,sd2, ..., op1, op2, ...)
477 The "maybe" says that we only ask AbsBinds to make global constant methods
478 if the dfun_theta is empty.
481 For an instance declaration, say,
483 instance (C1 a, C2 b) => C (T a b) where
486 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
487 function whose type is
489 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
491 Notice that we pass it the superclass dictionaries at the instance type; this
492 is the ``Mark Jones optimisation''. The stuff before the "=>" here
493 is the @dfun_theta@ below.
495 First comes the easy case of a non-local instance decl.
498 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
500 tcInstDecl2 (InstInfo { iLocal = is_local, iDFunId = dfun_id,
501 iBinds = monobinds, iPrags = uprags })
503 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
506 = -- Prime error recovery
507 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
508 tcAddSrcLoc (getSrcLoc dfun_id) $
510 -- Instantiate the instance decl with tc-style type variables
511 tcInstId dfun_id `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
513 (clas, inst_tys') = splitDictTy dict_ty'
514 origin = InstanceDeclOrigin
516 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
518 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
519 sel_names = [idName sel_id | (sel_id, _) <- op_items]
521 -- Instantiate the super-class context with inst_tys
522 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
524 -- Find any definitions in monobinds that aren't from the class
525 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
527 -- The type variable from the dict fun actually scope
528 -- over the bindings. They were gotten from
529 -- the original instance declaration
530 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
532 -- Check that all the method bindings come from this class
533 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
535 -- Create dictionary Ids from the specified instance contexts.
536 newClassDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
537 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
538 newClassDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
540 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
541 tcExtendGlobalValEnv dm_ids (
542 -- Default-method Ids may be mentioned in synthesised RHSs
544 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
546 monobinds uprags True)
548 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
550 -- Deal with SPECIALISE instance pragmas by making them
551 -- look like SPECIALISE pragmas for the dfun
553 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
555 tcExtendGlobalValEnv [dfun_id] (
556 tcSpecSigs dfun_prags
557 ) `thenTc` \ (prag_binds, prag_lie) ->
559 -- Check the overloading constraints of the methods and superclasses
561 -- tcMethodBind has checked that the class_tyvars havn't
562 -- been unified with each other or another type, but we must
563 -- still zonk them before passing them to tcSimplifyAndCheck
564 zonkTcSigTyVars inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
566 inst_tyvars_set = mkVarSet zonked_inst_tyvars
568 (meth_lies, meth_ids) = unzip meth_lies_w_ids
570 -- These insts are in scope; quite a few, eh?
571 avail_insts = this_dict `plusLIE`
572 dfun_arg_dicts `plusLIE`
574 unionManyBags meth_lies
576 methods_lie = plusLIEs insts_needed_s
579 -- Ditto method bindings
580 tcAddErrCtxt methodCtxt (
582 (ptext SLIT("instance declaration context"))
583 inst_tyvars_set -- Local tyvars
586 ) `thenTc` \ (const_lie1, lie_binds1) ->
588 -- Now do the simplification again, this time to get the
589 -- bindings; this time we use an enhanced "avails"
590 -- Ignore errors because they come from the *previous* tcSimplify
593 (ptext SLIT("instance declaration context"))
595 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
596 -- get bound by just selecting from this_dict!!
598 ) `thenTc` \ (const_lie2, lie_binds2) ->
601 -- Create the result bindings
603 dict_constr = classDataCon clas
604 scs_and_meths = sc_dict_ids ++ meth_ids
608 = -- Blatant special case for CCallable, CReturnable
609 -- If the dictionary is empty then we should never
610 -- select anything from it, so we make its RHS just
611 -- emit an error message. This in turn means that we don't
612 -- mention the constructor, which doesn't exist for CCallable, CReturnable
613 -- Hardly beautiful, but only three extra lines.
614 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
615 (HsLit (HsString msg))
617 | otherwise -- The common case
618 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
619 -- We don't produce a binding for the dict_constr; instead we
620 -- rely on the simplifier to unfold this saturated application
621 -- We do this rather than generate an HsCon directly, because
622 -- it means that the special cases (e.g. dictionary with only one
623 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
624 -- than needing to be repeated here.
627 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
629 dict_bind = VarMonoBind this_dict_id dict_rhs
630 method_binds = andMonoBindList method_binds_s
636 [(inst_tyvars', dfun_id, this_dict_id)]
637 emptyNameSet -- No inlines (yet)
638 (lie_binds1 `AndMonoBinds`
639 lie_binds2 `AndMonoBinds`
640 method_binds `AndMonoBinds`
643 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
644 main_bind `AndMonoBinds` prag_binds)
648 %************************************************************************
650 \subsection{Checking for a decent instance type}
652 %************************************************************************
654 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
655 it must normally look like: @instance Foo (Tycon a b c ...) ...@
657 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
658 flag is on, or (2)~the instance is imported (they must have been
659 compiled elsewhere). In these cases, we let them go through anyway.
661 We can also have instances for functions: @instance Foo (a -> b) ...@.
664 scrutiniseInstanceConstraint pred
665 = getDOptsTc `thenTc` \ dflags -> case () of
667 | dopt Opt_AllowUndecidableInstances dflags
670 | Just (clas,tys) <- getClassTys_maybe pred,
675 -> addErrTc (instConstraintErr pred)
677 scrutiniseInstanceHead clas inst_taus
678 = getDOptsTc `thenTc` \ dflags -> case () of
681 -- A user declaration of a CCallable/CReturnable instance
682 -- must be for a "boxed primitive" type.
683 (clas `hasKey` cCallableClassKey
684 && not (ccallable_type dflags first_inst_tau))
686 (clas `hasKey` cReturnableClassKey
687 && not (creturnable_type first_inst_tau))
688 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
691 -- It is obviously illegal to have an explicit instance
692 -- for something that we are also planning to `derive'
693 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
694 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
695 -- Kind check will have ensured inst_taus is of length 1
697 -- Allow anything for AllowUndecidableInstances
698 | dopt Opt_AllowUndecidableInstances dflags
701 -- If GlasgowExts then check at least one isn't a type variable
702 | dopt Opt_GlasgowExts dflags
703 -> if all isTyVarTy inst_taus
704 then addErrTc (instTypeErr clas inst_taus
705 (text "There must be at least one non-type-variable in the instance head"))
708 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
709 | not (length inst_taus == 1 &&
710 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
711 not (isSynTyCon tycon) && -- ...but not a synonym
712 all isTyVarTy arg_tys && -- Applied to type variables
713 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
714 -- This last condition checks that all the type variables are distinct
716 -> addErrTc (instTypeErr clas inst_taus
717 (text "the instance type must be of form (T a b c)" $$
718 text "where T is not a synonym, and a,b,c are distinct type variables")
725 (first_inst_tau : _) = inst_taus
727 -- Stuff for algebraic or -> type
728 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
729 Just (tycon, arg_tys) = maybe_tycon_app
731 -- Stuff for an *algebraic* data type
732 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
733 -- The "Alg" part looks through synonyms
734 Just (alg_tycon, _, _) = alg_tycon_app_maybe
736 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
737 creturnable_type ty = isFFIResultTy ty
741 %************************************************************************
743 \subsection{Error messages}
745 %************************************************************************
748 tcAddDeclCtxt decl thing_inside
755 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
756 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
757 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
758 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
760 ctxt = hsep [ptext SLIT("In the"), text thing,
761 ptext SLIT("declaration for"), quotes (ppr name)]
765 instConstraintErr pred
766 = hang (ptext SLIT("Illegal constraint") <+>
767 quotes (pprPred pred) <+>
768 ptext SLIT("in instance context"))
769 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
771 badGenericInstanceType binds
772 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
775 missingGenericInstances missing
776 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
780 dupGenericInsts tc_inst_infos
781 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
782 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
783 ptext SLIT("All the type patterns for a generic type constructor must be identical")
786 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
788 instTypeErr clas tys msg
789 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
793 derivingWhenInstanceExistsErr clas tycon
794 = hang (hsep [ptext SLIT("Deriving class"),
796 ptext SLIT("type"), quotes (ppr tycon)])
797 4 (ptext SLIT("when an explicit instance exists"))
799 nonBoxedPrimCCallErr clas inst_ty
800 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
801 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
804 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")