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 newDFunName, tcExtendTyVarEnv
35 import InstEnv ( InstInfo(..), InstEnv, pprInstInfo, classDataCon,
36 simpleInstInfoTyCon, simpleInstInfoTy, isLocalInst,
38 import TcMonoType ( tcTyVars, tcHsSigType, kcHsSigType )
39 import TcSimplify ( tcSimplifyAndCheck )
40 import TcType ( zonkTcSigTyVars )
41 import HscTypes ( PersistentCompilerState(..), HomeSymbolTable, DFunId,
42 ModDetails(..), PackageInstEnv, PersistentRenamerState
45 import Bag ( unionManyBags )
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 ( isLocallyDefined )
53 import NameSet ( emptyNameSet, nameSetToList )
54 import PrelInfo ( eRROR_ID )
55 import PprType ( pprConstraint, pprPred )
56 import TyCon ( TyCon, isSynTyCon, tyConDerivings )
57 import Type ( mkTyVarTys, splitDFunTy, isTyVarTy,
58 splitTyConApp_maybe, splitDictTy,
59 splitAlgTyConApp_maybe,
60 unUsgTy, tyVarsOfTypes, mkClassPred, mkTyVarTy,
63 import Subst ( mkTopTyVarSubst, substClasses, substTheta )
64 import VarSet ( mkVarSet, varSetElems )
65 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIResultTy )
66 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
68 import SrcLoc ( SrcLoc )
69 import VarSet ( varSetElems )
70 import Unique ( Uniquable(..) )
71 import BasicTypes ( NewOrData(..), Fixity )
72 import ErrUtils ( dumpIfSet_dyn )
73 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
74 assocElts, extendAssoc_C,
75 equivClassesByUniq, minusList
77 import List ( partition )
81 Typechecking instance declarations is done in two passes. The first
82 pass, made by @tcInstDecls1@, collects information to be used in the
85 This pre-processed info includes the as-yet-unprocessed bindings
86 inside the instance declaration. These are type-checked in the second
87 pass, when the class-instance envs and GVE contain all the info from
88 all the instance and value decls. Indeed that's the reason we need
89 two passes over the instance decls.
92 Here is the overall algorithm.
93 Assume that we have an instance declaration
95 instance c => k (t tvs) where b
99 $LIE_c$ is the LIE for the context of class $c$
101 $betas_bar$ is the free variables in the class method type, excluding the
104 $LIE_cop$ is the LIE constraining a particular class method
106 $tau_cop$ is the tau type of a class method
108 $LIE_i$ is the LIE for the context of instance $i$
110 $X$ is the instance constructor tycon
112 $gammas_bar$ is the set of type variables of the instance
114 $LIE_iop$ is the LIE for a particular class method instance
116 $tau_iop$ is the tau type for this instance of a class method
118 $alpha$ is the class variable
120 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
122 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
125 ToDo: Update the list above with names actually in the code.
129 First, make the LIEs for the class and instance contexts, which means
130 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
131 and make LIElistI and LIEI.
133 Then process each method in turn.
135 order the instance methods according to the ordering of the class methods
137 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
139 Create final dictionary function from bindings generated already
141 df = lambda inst_tyvars
148 in <op1,op2,...,opn,sd1,...,sdm>
150 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
151 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
155 %************************************************************************
157 \subsection{Extracting instance decls}
159 %************************************************************************
161 Gather up the instance declarations from their various sources
164 tcInstDecls1 :: PackageInstEnv
165 -> PersistentRenamerState
166 -> HomeSymbolTable -- Contains instances
167 -> TcEnv -- Contains IdInfo for dfun ids
168 -> (Name -> Maybe Fixity) -- for deriving Show and Read
169 -> Module -- Module for deriving
172 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
174 tcInstDecls1 inst_env0 prs hst unf_env get_fixity mod local_tycons decls
176 inst_decls = [inst_decl | InstD inst_decl <- decls]
177 clas_decls = [clas_decl | TyClD clas_decl <- decls, isClassDecl clas_decl]
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)
194 = partition isLocalInst (concat inst_infos)
196 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
198 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
200 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
201 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
202 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
203 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
205 -- (3) Compute instances from "deriving" clauses;
206 -- note that we only do derivings for things in this module;
207 -- we ignore deriving decls from interfaces!
208 -- This stuff computes a context for the derived instance decl, so it
209 -- needs to know about all the instances possible; hecne inst_env4
210 tcDeriving prs mod inst_env4 get_fixity local_tycons `thenTc` \ (deriv_inst_info, deriv_binds) ->
211 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
215 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
218 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
219 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
221 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
222 addInstDFuns dfuns infos
223 = getDOptsTc `thenTc` \ dflags ->
224 extendInstEnv dflags dfuns infos `bind` \ (inst_env', errs) ->
225 addErrsTc errs `thenNF_Tc_`
233 tcInstDecl1 :: Module -> TcEnv -> RenamedInstDecl -> NF_TcM [InstInfo]
234 -- Deal with a single instance declaration
235 tcInstDecl1 mod unf_env (InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
236 = -- Prime error recovery, set source location
237 recoverNF_Tc (returnNF_Tc []) $
238 tcAddSrcLoc src_loc $
240 -- Type-check all the stuff before the "where"
241 tcHsSigType poly_ty `thenTc` \ poly_ty' ->
243 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
246 (case maybe_dfun_name of
247 Nothing -> -- A source-file instance declaration
249 -- Check for respectable instance type, and context
250 -- but only do this for non-imported instance decls.
251 -- Imported ones should have been checked already, and may indeed
252 -- contain something illegal in normal Haskell, notably
253 -- instance CCallable [Char]
254 scrutiniseInstanceHead clas inst_tys `thenNF_Tc_`
255 mapNF_Tc scrutiniseInstanceConstraint theta `thenNF_Tc_`
257 -- Make the dfun id and return it
258 newDFunName mod clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
259 returnNF_Tc (True, mkDictFunId dfun_name clas tyvars inst_tys theta)
261 Just dfun_name -> -- An interface-file instance declaration
263 returnNF_Tc (False, mkDictFunId dfun_name clas tyvars inst_tys theta)
264 ) `thenNF_Tc` \ (is_local, dfun_id) ->
266 returnTc [InstInfo { iLocal = is_local,
267 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
268 iTheta = theta, iDFunId = dfun_id,
269 iBinds = binds, iLoc = src_loc, 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 bad_groups = [group | group <- equivClassesByUniq get_uniq inst_infos,
340 get_uniq inst = getUnique (simpleInstInfoTyCon inst)
342 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
344 -- Check that there is an InstInfo for each generic type constructor
346 missing = genericTyCons `minusList` map simpleInstInfoTyCon inst_infos
348 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
353 -- Group the declarations by type pattern
354 groups :: [(RenamedHsType, RenamedMonoBinds)]
355 groups = assocElts (getGenericBinds def_methods)
358 ---------------------------------
359 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
360 -- Takes a group of method bindings, finds the generic ones, and returns
361 -- them in finite map indexed by the type parameter in the definition.
363 getGenericBinds EmptyMonoBinds = emptyAssoc
364 getGenericBinds (AndMonoBinds m1 m2)
365 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
367 getGenericBinds (FunMonoBind id infixop matches loc)
368 = mapAssoc wrap (foldr add emptyAssoc matches)
370 add match env = case maybeGenericMatch match of
372 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
374 wrap ms = FunMonoBind id infixop ms loc
376 ---------------------------------
377 mkGenericInstance :: Module -> Class -> SrcLoc
378 -> (RenamedHsType, RenamedMonoBinds)
381 mkGenericInstance mod clas loc (hs_ty, binds)
382 -- Make a generic instance declaration
383 -- For example: instance (C a, C b) => C (a+b) where { binds }
385 = -- Extract the universally quantified type variables
386 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
387 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
388 tcExtendTyVarEnv tyvars $
390 -- Type-check the instance type, and check its form
391 tcHsSigType hs_ty `thenTc` \ inst_ty ->
392 checkTc (validGenericInstanceType inst_ty)
393 (badGenericInstanceType binds) `thenTc_`
395 -- Make the dictionary function.
396 newDFunName mod clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
398 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
400 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
403 returnTc (InstInfo { iLocal = True,
404 iClass = clas, iTyVars = tyvars, iTys = inst_tys,
405 iTheta = inst_theta, iDFunId = dfun_id, iBinds = binds,
406 iLoc = loc, 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 { iClass = clas, iTyVars = inst_tyvars, iTys = inst_tys,
501 iTheta = inst_decl_theta, iDFunId = dfun_id,
502 iBinds = monobinds, iLoc = locn, iPrags = uprags })
503 | not (isLocallyDefined dfun_id)
504 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
507 = -- Prime error recovery
508 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
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 theta found in the original instance decl
523 inst_decl_theta' = substTheta (mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars'))
526 -- Instantiate the super-class context with inst_tys
527 sc_theta' = substClasses (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
529 -- Find any definitions in monobinds that aren't from the class
530 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
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 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
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 -- Ditto method bindings
581 tcAddErrCtxt methodCtxt (
583 (ptext SLIT("instance declaration context"))
584 inst_tyvars_set -- Local tyvars
587 ) `thenTc` \ (const_lie1, lie_binds1) ->
589 -- Check that we *could* construct the superclass dictionaries,
590 -- even though we are *actually* going to pass the superclass dicts in;
591 -- the check ensures that the caller will never have
592 --a problem building them.
593 tcAddErrCtxt superClassCtxt (
595 (ptext SLIT("instance declaration context"))
596 inst_tyvars_set -- Local tyvars
597 inst_decl_dicts -- The instance dictionaries available
598 sc_dicts -- The superclass dicationaries reqd
600 -- Ignore the result; we're only doing
601 -- this to make sure it can be done.
603 -- Now do the simplification again, this time to get the
604 -- bindings; this time we use an enhanced "avails"
605 -- Ignore errors because they come from the *previous* tcSimplify
608 (ptext SLIT("instance declaration context"))
610 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
611 -- get bound by just selecting from this_dict!!
613 ) `thenTc` \ (const_lie2, lie_binds2) ->
616 -- Create the result bindings
618 dict_constr = classDataCon clas
619 scs_and_meths = sc_dict_ids ++ meth_ids
623 = -- Blatant special case for CCallable, CReturnable
624 -- If the dictionary is empty then we should never
625 -- select anything from it, so we make its RHS just
626 -- emit an error message. This in turn means that we don't
627 -- mention the constructor, which doesn't exist for CCallable, CReturnable
628 -- Hardly beautiful, but only three extra lines.
629 HsApp (TyApp (HsVar eRROR_ID) [(unUsgTy . idType) this_dict_id])
630 (HsLit (HsString msg))
632 | otherwise -- The common case
633 = mkHsConApp dict_constr inst_tys' (map HsVar (sc_dict_ids ++ meth_ids))
634 -- We don't produce a binding for the dict_constr; instead we
635 -- rely on the simplifier to unfold this saturated application
636 -- We do this rather than generate an HsCon directly, because
637 -- it means that the special cases (e.g. dictionary with only one
638 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
639 -- than needing to be repeated here.
642 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
644 dict_bind = VarMonoBind this_dict_id dict_rhs
645 method_binds = andMonoBindList method_binds_s
651 [(inst_tyvars', dfun_id, this_dict_id)]
652 emptyNameSet -- No inlines (yet)
653 (lie_binds1 `AndMonoBinds`
654 lie_binds2 `AndMonoBinds`
655 method_binds `AndMonoBinds`
658 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
659 main_bind `AndMonoBinds` prag_binds)
663 %************************************************************************
665 \subsection{Checking for a decent instance type}
667 %************************************************************************
669 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
670 it must normally look like: @instance Foo (Tycon a b c ...) ...@
672 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
673 flag is on, or (2)~the instance is imported (they must have been
674 compiled elsewhere). In these cases, we let them go through anyway.
676 We can also have instances for functions: @instance Foo (a -> b) ...@.
679 scrutiniseInstanceConstraint pred
680 = getDOptsTc `thenTc` \ dflags -> case () of
682 | dopt Opt_AllowUndecidableInstances dflags
685 | Just (clas,tys) <- getClassTys_maybe pred,
690 -> addErrTc (instConstraintErr pred)
692 scrutiniseInstanceHead clas inst_taus
693 = getDOptsTc `thenTc` \ dflags -> case () of
696 -- A user declaration of a CCallable/CReturnable instance
697 -- must be for a "boxed primitive" type.
698 (clas `hasKey` cCallableClassKey
699 && not (ccallable_type dflags first_inst_tau))
701 (clas `hasKey` cReturnableClassKey
702 && not (creturnable_type first_inst_tau))
703 -> addErrTc (nonBoxedPrimCCallErr clas first_inst_tau)
706 -- It is obviously illegal to have an explicit instance
707 -- for something that we are also planning to `derive'
708 | maybeToBool alg_tycon_app_maybe && clas `elem` (tyConDerivings alg_tycon)
709 -> addErrTc (derivingWhenInstanceExistsErr clas first_inst_tau)
710 -- Kind check will have ensured inst_taus is of length 1
712 -- Allow anything for AllowUndecidableInstances
713 | dopt Opt_AllowUndecidableInstances dflags
716 -- If GlasgowExts then check at least one isn't a type variable
717 | dopt Opt_GlasgowExts dflags
718 -> if all isTyVarTy inst_taus
719 then addErrTc (instTypeErr clas inst_taus
720 (text "There must be at least one non-type-variable in the instance head"))
723 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
724 | not (length inst_taus == 1 &&
725 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
726 not (isSynTyCon tycon) && -- ...but not a synonym
727 all isTyVarTy arg_tys && -- Applied to type variables
728 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
729 -- This last condition checks that all the type variables are distinct
731 -> addErrTc (instTypeErr clas inst_taus
732 (text "the instance type must be of form (T a b c)" $$
733 text "where T is not a synonym, and a,b,c are distinct type variables")
740 (first_inst_tau : _) = inst_taus
742 -- Stuff for algebraic or -> type
743 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
744 Just (tycon, arg_tys) = maybe_tycon_app
746 -- Stuff for an *algebraic* data type
747 alg_tycon_app_maybe = splitAlgTyConApp_maybe first_inst_tau
748 -- The "Alg" part looks through synonyms
749 Just (alg_tycon, _, _) = alg_tycon_app_maybe
751 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
752 creturnable_type ty = isFFIResultTy ty
756 %************************************************************************
758 \subsection{Error messages}
760 %************************************************************************
763 tcAddDeclCtxt decl thing_inside
770 (ClassDecl _ name _ _ _ _ _ loc) -> (name, loc, "class")
771 (TySynonym name _ _ loc) -> (name, loc, "type synonym")
772 (TyData NewType _ name _ _ _ _ loc _ _) -> (name, loc, "newtype")
773 (TyData DataType _ name _ _ _ _ loc _ _) -> (name, loc, "data type")
775 ctxt = hsep [ptext SLIT("In the"), text thing,
776 ptext SLIT("declaration for"), quotes (ppr name)]
780 instConstraintErr pred
781 = hang (ptext SLIT("Illegal constraint") <+>
782 quotes (pprPred pred) <+>
783 ptext SLIT("in instance context"))
784 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
786 badGenericInstanceType binds
787 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
790 missingGenericInstances missing
791 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
795 dupGenericInsts inst_infos
796 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
797 nest 4 (vcat (map (ppr . simpleInstInfoTy) inst_infos)),
798 ptext SLIT("All the type patterns for a generic type constructor must be identical")
801 instTypeErr clas tys msg
802 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
806 derivingWhenInstanceExistsErr clas tycon
807 = hang (hsep [ptext SLIT("Deriving class"),
809 ptext SLIT("type"), quotes (ppr tycon)])
810 4 (ptext SLIT("when an explicit instance exists"))
812 nonBoxedPrimCCallErr clas inst_ty
813 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
814 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
817 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
818 superClassCtxt = ptext SLIT("When checking the superclasses of an instance declaration")