2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcInstDecls]{Typechecking instance declarations}
7 #include "HsVersions.h"
17 import HsSyn ( HsDecl(..), InstDecl(..), TyDecl, ClassDecl, DefaultDecl,
18 FixityDecl, IfaceSig, Sig(..),
19 SpecInstSig(..), HsBinds(..),
20 MonoBinds(..), GRHSsAndBinds(..), GRHS(..), Match,
21 InPat(..), OutPat(..), HsExpr(..), HsLit(..),
22 Stmt, DoOrListComp, ArithSeqInfo, Fake, Fixity,
24 SYN_IE(RecFlag), recursive, nonRecursive, collectMonoBinders,
27 import RnHsSyn ( SYN_IE(RenamedHsBinds), SYN_IE(RenamedMonoBinds),
28 SYN_IE(RenamedInstDecl), SYN_IE(RenamedFixityDecl), SYN_IE(RenamedHsExpr),
29 SYN_IE(RenamedSig), SYN_IE(RenamedSpecInstSig), SYN_IE(RenamedHsDecl)
31 import TcHsSyn ( SYN_IE(TcHsBinds),
32 SYN_IE(TcMonoBinds), SYN_IE(TcExpr), tcIdType,
34 mkHsDictLam, mkHsDictApp )
36 import TcBinds ( tcPragmaSigs )
37 import TcClassDcl ( tcMethodBind )
39 import RnMonad ( SYN_IE(RnNameSupply) )
40 import Inst ( Inst, InstOrigin(..), SYN_IE(InstanceMapper),
41 instToId, newDicts, newMethod, SYN_IE(LIE), emptyLIE, plusLIE )
42 import PragmaInfo ( PragmaInfo(..) )
43 import TcDeriv ( tcDeriving )
44 import TcEnv ( tcLookupClass, newLocalId, tcExtendGlobalTyVars, tcGetGlobalTyVars,
45 tcExtendGlobalValEnv, tcAddImportedIdInfo
47 import SpecEnv ( SpecEnv )
48 import TcGRHSs ( tcGRHSsAndBinds )
49 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs )
50 import TcKind ( TcKind, unifyKind )
51 import TcMatches ( tcMatchesFun )
52 import TcMonoType ( tcTyVarScope, tcContext, tcHsTypeKind )
53 import TcSimplify ( tcSimplifyAndCheck )
54 import TcType ( TcIdOcc(..), SYN_IE(TcIdBndr), SYN_IE(TcType), SYN_IE(TcTyVar), SYN_IE(TcTyVarSet),
55 tcInstSigTyVars, tcInstType, tcInstSigTcType,
56 tcInstTheta, tcInstTcType, tcInstSigType
58 import Unify ( unifyTauTy, unifyTauTyLists )
61 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
62 concatBag, foldBag, bagToList, listToBag,
64 import CmdLineOpts ( opt_GlasgowExts,
65 opt_PprUserLength, opt_SpecialiseOverloaded,
66 opt_WarnMissingMethods
68 import Class ( GenClass,
70 classDefaultMethodId, SYN_IE(Class)
72 import Id ( GenId, idType, replacePragmaInfo,
73 isNullaryDataCon, dataConArgTys, SYN_IE(Id) )
74 import ListSetOps ( minusList )
75 import Maybes ( maybeToBool, expectJust, seqMaybe, catMaybes )
76 import Name ( nameOccName, getSrcLoc, mkLocalName,
77 isLocallyDefined, OccName, Name{--O only-}, SYN_IE(Module),
80 import PrelVals ( nO_EXPLICIT_METHOD_ERROR_ID, nO_DEFAULT_METHOD_ERROR_ID )
81 import PprType ( GenType, GenTyVar, GenClass, TyCon,
85 import SrcLoc ( SrcLoc, noSrcLoc )
87 import TyCon ( isSynTyCon, isDataTyCon, derivedClasses )
88 import Type ( GenType(..), SYN_IE(ThetaType), mkTyVarTys, isPrimType,
89 splitSigmaTy, splitAppTys, isTyVarTy, matchTy, mkSigmaTy,
90 getTyCon_maybe, maybeAppTyCon, SYN_IE(Type), getTyVar,
91 maybeBoxedPrimType, maybeAppDataTyCon, splitRhoTy, eqTy
93 import TyVar ( GenTyVar, SYN_IE(GenTyVarSet), tyVarSetToList,
94 mkTyVarSet, unionTyVarSets, SYN_IE(TyVar) )
95 import TysPrim ( byteArrayPrimTyCon, mutableByteArrayPrimTyCon )
96 import TysWiredIn ( stringTy )
97 import Unique ( Unique, cCallableClassKey, cReturnableClassKey, Uniquable(..) )
98 import Util ( zipEqual, panic, pprPanic, pprTrace, removeDups, Ord3(..)
99 #if __GLASGOW_HASKELL__ < 202
105 Typechecking instance declarations is done in two passes. The first
106 pass, made by @tcInstDecls1@, collects information to be used in the
109 This pre-processed info includes the as-yet-unprocessed bindings
110 inside the instance declaration. These are type-checked in the second
111 pass, when the class-instance envs and GVE contain all the info from
112 all the instance and value decls. Indeed that's the reason we need
113 two passes over the instance decls.
116 Here is the overall algorithm.
117 Assume that we have an instance declaration
119 instance c => k (t tvs) where b
123 $LIE_c$ is the LIE for the context of class $c$
125 $betas_bar$ is the free variables in the class method type, excluding the
128 $LIE_cop$ is the LIE constraining a particular class method
130 $tau_cop$ is the tau type of a class method
132 $LIE_i$ is the LIE for the context of instance $i$
134 $X$ is the instance constructor tycon
136 $gammas_bar$ is the set of type variables of the instance
138 $LIE_iop$ is the LIE for a particular class method instance
140 $tau_iop$ is the tau type for this instance of a class method
142 $alpha$ is the class variable
144 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
146 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
149 ToDo: Update the list above with names actually in the code.
153 First, make the LIEs for the class and instance contexts, which means
154 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
155 and make LIElistI and LIEI.
157 Then process each method in turn.
159 order the instance methods according to the ordering of the class methods
161 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
163 Create final dictionary function from bindings generated already
165 df = lambda inst_tyvars
172 in <op1,op2,...,opn,sd1,...,sdm>
174 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
175 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
179 tcInstDecls1 :: TcEnv s -- Contains IdInfo for dfun ids
181 -> Module -- module name for deriving
182 -> RnNameSupply -- for renaming derivings
183 -> TcM s (Bag InstInfo,
187 tcInstDecls1 unf_env decls mod_name rn_name_supply
188 = -- Do the ordinary instance declarations
189 mapNF_Tc (tcInstDecl1 unf_env mod_name)
190 [inst_decl | InstD inst_decl <- decls] `thenNF_Tc` \ inst_info_bags ->
192 decl_inst_info = unionManyBags inst_info_bags
194 -- Handle "derived" instances; note that we only do derivings
195 -- for things in this module; we ignore deriving decls from
197 tcDeriving mod_name rn_name_supply decl_inst_info
198 `thenTc` \ (deriv_inst_info, deriv_binds, ddump_deriv) ->
201 full_inst_info = deriv_inst_info `unionBags` decl_inst_info
203 returnTc (full_inst_info, deriv_binds, ddump_deriv)
206 tcInstDecl1 :: TcEnv s -> Module -> RenamedInstDecl -> NF_TcM s (Bag InstInfo)
208 tcInstDecl1 unf_env mod_name (InstDecl poly_ty binds uprags (Just dfun_name) src_loc)
209 = -- Prime error recovery, set source location
210 recoverNF_Tc (returnNF_Tc emptyBag) $
211 tcAddSrcLoc src_loc $
214 tcLookupClass class_name `thenTc` \ (clas_kind, clas) ->
216 -- Typecheck the context and instance type
217 tcTyVarScope tyvar_names (\ tyvars ->
218 tcContext context `thenTc` \ theta ->
219 tcHsTypeKind inst_ty `thenTc` \ (tau_kind, tau) ->
220 unifyKind clas_kind tau_kind `thenTc_`
221 returnTc (tyvars, theta, tau)
222 ) `thenTc` \ (inst_tyvars, inst_theta, inst_tau) ->
224 -- Check for respectable instance type
225 scrutiniseInstanceType dfun_name clas inst_tau
226 `thenTc` \ (inst_tycon,arg_tys) ->
228 -- Make the dfun id and constant-method ids
230 (dfun_id, dfun_theta) = mkInstanceRelatedIds dfun_name
231 clas inst_tyvars inst_tau inst_theta
232 -- Add info from interface file
233 final_dfun_id = tcAddImportedIdInfo unf_env dfun_id
235 returnTc (unitBag (InstInfo clas inst_tyvars inst_tau inst_theta
236 dfun_theta final_dfun_id
237 binds src_loc uprags))
239 (tyvar_names, context, dict_ty) = case poly_ty of
240 HsForAllTy tvs cxt dict_ty -> (tvs, cxt, dict_ty)
241 other -> ([], [], poly_ty)
242 (class_name, inst_ty) = case dict_ty of
243 MonoDictTy cls ty -> (cls,ty)
244 other -> pprPanic "Malformed instance decl" (ppr PprDebug poly_ty)
248 %************************************************************************
250 \subsection{Type-checking instance declarations, pass 2}
252 %************************************************************************
255 tcInstDecls2 :: Bag InstInfo
256 -> NF_TcM s (LIE s, TcMonoBinds s)
258 tcInstDecls2 inst_decls
259 = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
261 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
262 tc2 `thenNF_Tc` \ (lie2, binds2) ->
263 returnNF_Tc (lie1 `plusLIE` lie2,
264 binds1 `AndMonoBinds` binds2)
268 ======= New documentation starts here (Sept 92) ==============
270 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
271 the dictionary function for this instance declaration. For example
273 instance Foo a => Foo [a] where
277 might generate something like
279 dfun.Foo.List dFoo_a = let op1 x = ...
285 HOWEVER, if the instance decl has no context, then it returns a
286 bigger @HsBinds@ with declarations for each method. For example
288 instance Foo [a] where
294 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
295 const.Foo.op1.List a x = ...
296 const.Foo.op2.List a y = ...
298 This group may be mutually recursive, because (for example) there may
299 be no method supplied for op2 in which case we'll get
301 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
303 that is, the default method applied to the dictionary at this type.
305 What we actually produce in either case is:
307 AbsBinds [a] [dfun_theta_dicts]
308 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
309 { d = (sd1,sd2, ..., op1, op2, ...)
314 The "maybe" says that we only ask AbsBinds to make global constant methods
315 if the dfun_theta is empty.
318 For an instance declaration, say,
320 instance (C1 a, C2 b) => C (T a b) where
323 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
324 function whose type is
326 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
328 Notice that we pass it the superclass dictionaries at the instance type; this
329 is the ``Mark Jones optimisation''. The stuff before the "=>" here
330 is the @dfun_theta@ below.
332 First comes the easy case of a non-local instance decl.
335 tcInstDecl2 :: InstInfo -> NF_TcM s (LIE s, TcMonoBinds s)
337 tcInstDecl2 (InstInfo clas inst_tyvars inst_ty
338 inst_decl_theta dfun_theta
341 | not (isLocallyDefined dfun_id)
342 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
345 -- I deleted this "optimisation" because when importing these
346 -- instance decls the renamer would look for the dfun bindings and they weren't there.
347 -- This would be fixable, but it seems simpler just to produce a tiny void binding instead,
348 -- even though it's never used.
350 -- This case deals with CCallable etc, which don't need any bindings
352 = returnNF_Tc (emptyLIE, EmptyBinds)
356 = -- Prime error recovery
357 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
360 -- Get the class signature
361 tcInstSigTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
363 origin = InstanceDeclOrigin
365 super_classes, sc_sel_ids,
366 op_sel_ids, defm_ids) = classBigSig clas
368 tcInstType tenv inst_ty `thenNF_Tc` \ inst_ty' ->
369 tcInstTheta tenv dfun_theta `thenNF_Tc` \ dfun_theta' ->
370 tcInstTheta tenv inst_decl_theta `thenNF_Tc` \ inst_decl_theta' ->
372 sc_theta' = super_classes `zip` repeat inst_ty'
374 -- Create dictionary Ids from the specified instance contexts.
375 newDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
376 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
377 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
378 newDicts origin [(clas,inst_ty')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
380 -- Now process any INLINE or SPECIALIZE pragmas for the methods
381 -- ...[NB May 97; all ignored except INLINE]
382 tcPragmaSigs uprags `thenTc` \ (prag_fn, spec_binds, spec_lie) ->
384 -- Check the method bindings
386 inst_tyvars_set' = mkTyVarSet inst_tyvars'
387 check_from_this_class (bndr, loc)
388 | nameOccName bndr `elem` sel_names = returnTc ()
389 | otherwise = recoverTc (returnTc ()) $
391 failTc (instBndrErr bndr clas)
392 sel_names = map getOccName op_sel_ids
394 mapTc check_from_this_class (bagToList (collectMonoBinders monobinds)) `thenTc_`
395 tcExtendGlobalTyVars inst_tyvars_set' (
396 tcExtendGlobalValEnv (catMaybes defm_ids) $
397 -- Default-method Ids may be mentioned in synthesised RHSs
398 mapAndUnzip3Tc (tcInstMethodBind clas inst_ty' monobinds)
399 (op_sel_ids `zip` defm_ids)
400 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
402 -- Check the overloading constraints of the methods and superclasses
404 (meth_lies, meth_ids) = unzip meth_lies_w_ids
405 avail_insts -- These insts are in scope; quite a few, eh?
406 = this_dict `plusLIE` dfun_arg_dicts `plusLIE` unionManyBags meth_lies
408 tcAddErrCtxt bindSigCtxt (
410 inst_tyvars_set' -- Local tyvars
412 (sc_dicts `unionBags`
413 unionManyBags insts_needed_s) -- Need to get defns for all these
414 ) `thenTc` \ (const_lie, super_binds) ->
416 -- Check that we *could* construct the superclass dictionaries,
417 -- even though we are *actually* going to pass the superclass dicts in;
418 -- the check ensures that the caller will never have a problem building
420 tcAddErrCtxt superClassSigCtxt (
422 inst_tyvars_set' -- Local tyvars
423 inst_decl_dicts -- The instance dictionaries available
424 sc_dicts -- The superclass dicationaries reqd
426 -- Ignore the result; we're only doing
427 -- this to make sure it can be done.
429 -- Create the result bindings
431 dict_bind = VarMonoBind this_dict_id (Dictionary sc_dict_ids meth_ids)
432 method_binds = andMonoBinds method_binds_s
438 [(inst_tyvars', RealId dfun_id, this_dict_id)]
439 (super_binds `AndMonoBinds`
440 method_binds `AndMonoBinds`
443 returnTc (const_lie `plusLIE` spec_lie,
444 main_bind `AndMonoBinds` spec_binds)
448 %************************************************************************
450 \subsection{Processing each method}
452 %************************************************************************
457 -> TcType s -- Instance type
458 -> RenamedMonoBinds -- Method binding
459 -> (Id, Maybe Id) -- Selector id and default-method id
460 -> TcM s (TcMonoBinds s, LIE s, (LIE s, TcIdOcc s))
462 tcInstMethodBind clas inst_ty meth_binds (sel_id, maybe_dm_id)
463 = tcGetSrcLoc `thenNF_Tc` \ loc ->
464 tcGetUnique `thenNF_Tc` \ uniq ->
466 meth_occ = getOccName sel_id
467 default_meth_name = mkLocalName uniq meth_occ loc
468 maybe_meth_bind = find meth_occ meth_binds
469 the_meth_bind = case maybe_meth_bind of
471 Nothing -> mk_default_bind default_meth_name
474 -- Warn if no method binding, only if -fwarn-missing-methods
476 warnTc (opt_WarnMissingMethods &&
477 not (maybeToBool maybe_meth_bind) &&
478 not (maybeToBool maybe_dm_id))
479 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
481 -- Typecheck the method binding
482 tcMethodBind clas origin inst_ty sel_id the_meth_bind
484 origin = InstanceDeclOrigin -- Poor
486 find occ EmptyMonoBinds = Nothing
487 find occ (AndMonoBinds b1 b2) = find occ b1 `seqMaybe` find occ b2
489 find occ b@(FunMonoBind op_name _ _ _) | nameOccName op_name == occ = Just b
490 | otherwise = Nothing
491 find occ b@(PatMonoBind (VarPatIn op_name) _ _) | nameOccName op_name == occ = Just b
492 | otherwise = Nothing
493 find occ other = panic "Urk! Bad instance method binding"
496 mk_default_bind local_meth_name
497 = PatMonoBind (VarPatIn local_meth_name)
498 (GRHSsAndBindsIn [OtherwiseGRHS default_expr noSrcLoc] EmptyBinds)
501 default_expr = case maybe_dm_id of
502 Just dm_id -> HsVar (getName dm_id) -- There's a default method
503 Nothing -> error_expr -- No default method
505 error_expr = HsApp (HsVar (getName nO_DEFAULT_METHOD_ERROR_ID))
506 (HsLit (HsString (_PK_ error_msg)))
508 error_msg = show (hcat [ppr (PprForUser opt_PprUserLength) (getSrcLoc sel_id), text "|",
509 ppr (PprForUser opt_PprUserLength) sel_id
515 %************************************************************************
517 \subsection{Type-checking specialise instance pragmas}
519 %************************************************************************
523 tcSpecInstSigs :: E -> CE -> TCE
524 -> Bag InstInfo -- inst decls seen (declared and derived)
525 -> [RenamedSpecInstSig] -- specialise instance upragmas
526 -> TcM (Bag InstInfo) -- new, overlapped, inst decls
528 tcSpecInstSigs e ce tce inst_infos []
531 tcSpecInstSigs e ce tce inst_infos sigs
532 = buildInstanceEnvs inst_infos `thenTc` \ inst_mapper ->
533 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ spec_inst_infos ->
534 returnTc spec_inst_infos
536 tc_inst_spec_sigs inst_mapper []
537 = returnNF_Tc emptyBag
538 tc_inst_spec_sigs inst_mapper (sig:sigs)
539 = tcSpecInstSig e ce tce inst_infos inst_mapper sig `thenNF_Tc` \ info_sig ->
540 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ info_sigs ->
541 returnNF_Tc (info_sig `unionBags` info_sigs)
543 tcSpecInstSig :: E -> CE -> TCE
546 -> RenamedSpecInstSig
547 -> NF_TcM (Bag InstInfo)
549 tcSpecInstSig e ce tce inst_infos inst_mapper (SpecInstSig class_name ty src_loc)
550 = recoverTc emptyBag (
551 tcAddSrcLoc src_loc (
553 clas = lookupCE ce class_name -- Renamer ensures this can't fail
555 -- Make some new type variables, named as in the specialised instance type
556 ty_names = extractHsTyNames ???is_tyvarish_name??? ty
557 (tmpl_e,inst_tmpls,inst_tmpl_tys) = mkTVE ty_names
559 babyTcMtoTcM (tcInstanceType ce tce tmpl_e True src_loc ty)
560 `thenTc` \ inst_ty ->
562 maybe_tycon = case maybeAppDataTyCon inst_ty of
563 Just (tc,_,_) -> Just tc
566 maybe_unspec_inst = lookup_unspec_inst clas maybe_tycon inst_infos
568 -- Check that we have a local instance declaration to specialise
569 checkMaybeTc maybe_unspec_inst
570 (specInstUnspecInstNotFoundErr clas inst_ty src_loc) `thenTc_`
572 -- Create tvs to substitute for tmpls while simplifying the context
573 copyTyVars inst_tmpls `thenNF_Tc` \ (tv_e, inst_tvs, inst_tv_tys) ->
575 Just (InstInfo _ unspec_tyvars unspec_inst_ty unspec_theta
576 _ _ binds _ uprag) = maybe_unspec_inst
578 subst = case matchTy unspec_inst_ty inst_ty of
580 Nothing -> panic "tcSpecInstSig:matchTy"
582 subst_theta = instantiateThetaTy subst unspec_theta
583 subst_tv_theta = instantiateThetaTy tv_e subst_theta
585 mk_spec_origin clas ty
586 = InstanceSpecOrigin inst_mapper clas ty src_loc
587 -- I'm VERY SUSPICIOUS ABOUT THIS
588 -- the inst-mapper is in a knot at this point so it's no good
589 -- looking at it in tcSimplify...
591 tcSimplifyThetas mk_spec_origin subst_tv_theta
592 `thenTc` \ simpl_tv_theta ->
594 simpl_theta = [ (clas, tv_to_tmpl tv) | (clas, tv) <- simpl_tv_theta ]
596 tv_tmpl_map = zipEqual "tcSpecInstSig" inst_tv_tys inst_tmpl_tys
597 tv_to_tmpl tv = assoc "tcSpecInstSig" tv_tmpl_map tv
600 clas inst_tmpls inst_ty simpl_theta uprag
601 `thenNF_Tc` \ (dfun_id, dfun_theta, const_meth_ids) ->
603 getSwitchCheckerTc `thenNF_Tc` \ sw_chkr ->
604 (if sw_chkr SpecialiseTrace then
605 pprTrace "Specialised Instance: "
606 (vcat [hsep [if null simpl_theta then empty else ppr PprDebug simpl_theta,
607 if null simpl_theta then empty else ptext SLIT("=>"),
609 pprParendGenType PprDebug inst_ty],
610 hsep [ptext SLIT(" derived from:"),
611 if null unspec_theta then empty else ppr PprDebug unspec_theta,
612 if null unspec_theta then empty else ptext SLIT("=>"),
614 pprParendGenType PprDebug unspec_inst_ty]])
617 returnTc (unitBag (InstInfo clas inst_tmpls inst_ty simpl_theta
619 binds src_loc uprag))
623 lookup_unspec_inst clas maybe_tycon inst_infos
624 = case filter (match_info match_inst_ty) (bagToList inst_infos) of
626 (info:_) -> Just info
628 match_info match_ty (InstInfo inst_clas _ inst_ty _ _ _ _ _ from_here _ _ _)
629 = from_here && clas == inst_clas &&
630 match_ty inst_ty && is_plain_instance inst_ty
632 match_inst_ty = case maybe_tycon of
633 Just tycon -> match_tycon tycon
636 match_tycon tycon inst_ty = case (maybeAppDataTyCon inst_ty) of
637 Just (inst_tc,_,_) -> tycon == inst_tc
640 match_fun inst_ty = isFunType inst_ty
643 is_plain_instance inst_ty
644 = case (maybeAppDataTyCon inst_ty) of
645 Just (_,tys,_) -> all isTyVarTemplateTy tys
646 Nothing -> case maybeUnpackFunTy inst_ty of
647 Just (arg, res) -> isTyVarTemplateTy arg && isTyVarTemplateTy res
648 Nothing -> error "TcInstDecls:is_plain_instance"
653 Checking for a decent instance type
654 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
655 @scrutiniseInstanceType@ checks the type {\em and} its syntactic constraints:
656 it must normally look like: @instance Foo (Tycon a b c ...) ...@
658 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
659 flag is on, or (2)~the instance is imported (they must have been
660 compiled elsewhere). In these cases, we let them go through anyway.
662 We can also have instances for functions: @instance Foo (a -> b) ...@.
665 scrutiniseInstanceType dfun_name clas inst_tau
667 | not (maybeToBool inst_tycon_maybe) || isSynTyCon inst_tycon
668 = failTc (instTypeErr inst_tau)
670 -- IMPORTED INSTANCES ARE OK (but see tcInstDecl1)
671 | not (isLocallyDefined dfun_name)
672 = returnTc (inst_tycon,arg_tys)
675 | not (opt_GlasgowExts ||
676 (all isTyVarTy arg_tys && null tyvar_dups)
678 = failTc (instTypeErr inst_tau)
681 -- It is obviously illegal to have an explicit instance
682 -- for something that we are also planning to `derive'
683 -- Though we can have an explicit instance which is more
684 -- specific than the derived instance
685 | clas `elem` (derivedClasses inst_tycon)
686 && all isTyVarTy arg_tys
687 = failTc (derivingWhenInstanceExistsErr clas inst_tycon)
690 -- A user declaration of a CCallable/CReturnable instance
691 -- must be for a "boxed primitive" type.
692 (uniqueOf clas == cCallableClassKey && not (ccallable_type inst_tau)) ||
693 (uniqueOf clas == cReturnableClassKey && not (creturnable_type inst_tau))
694 = failTc (nonBoxedPrimCCallErr clas inst_tau)
697 = returnTc (inst_tycon,arg_tys)
700 (possible_tycon, arg_tys) = splitAppTys inst_tau
701 inst_tycon_maybe = getTyCon_maybe possible_tycon
702 inst_tycon = expectJust "tcInstDecls1:inst_tycon" inst_tycon_maybe
703 (_, tyvar_dups) = removeDups cmp (map (getTyVar "tcInstDecls1:getTyVarTy") arg_tys)
705 -- These conditions come directly from what the DsCCall is capable of.
706 -- Totally grotesque. Green card should solve this.
708 ccallable_type ty = isPrimType ty || -- Allow CCallable Int# etc
709 maybeToBool (maybeBoxedPrimType ty) || -- Ditto Int etc
710 ty `eqTy` stringTy ||
713 byte_arr_thing = case maybeAppDataTyCon ty of
714 Just (tycon, ty_args, [data_con]) | isDataTyCon tycon ->
715 length data_con_arg_tys == 2 &&
716 maybeToBool maybe_arg2_tycon &&
717 (arg2_tycon == byteArrayPrimTyCon ||
718 arg2_tycon == mutableByteArrayPrimTyCon)
720 data_con_arg_tys = dataConArgTys data_con ty_args
721 (data_con_arg_ty1 : data_con_arg_ty2 : _) = data_con_arg_tys
722 maybe_arg2_tycon = maybeAppTyCon data_con_arg_ty2
723 Just (arg2_tycon,_) = maybe_arg2_tycon
727 creturnable_type ty = maybeToBool (maybeBoxedPrimType ty) ||
728 -- Or, a data type with a single nullary constructor
729 case (maybeAppDataTyCon ty) of
730 Just (tycon, tys_applied, [data_con])
731 -> isNullaryDataCon data_con
739 SynTy tc _ _ -> hsep [ptext SLIT("The type synonym"), ppr sty tc, rest_of_msg]
740 TyVarTy tv -> hsep [ptext SLIT("The type variable"), ppr sty tv, rest_of_msg]
741 other -> sep [ptext SLIT("The type"), nest 4 (ppr sty ty), rest_of_msg]
743 rest_of_msg = ptext SLIT("cannot be used as an instance type")
745 instBndrErr bndr clas sty
746 = hsep [ptext SLIT("Class"), ppr sty clas, ptext SLIT("does not have a method"), ppr sty bndr]
748 derivingWhenInstanceExistsErr clas tycon sty
749 = hang (hsep [ptext SLIT("Deriving class"),
751 ptext SLIT("type"), ppr sty tycon])
752 4 (ptext SLIT("when an explicit instance exists"))
754 nonBoxedPrimCCallErr clas inst_ty sty
755 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
756 4 (hsep [ ptext SLIT("class"), ppr sty clas, ptext SLIT("type"),
759 omittedMethodWarn sel_id clas sty
760 = sep [ptext SLIT("Warning: no explicit method nor default method for") <+> ppr sty sel_id,
761 ptext SLIT("in an instance declaration for") <+> ppr sty clas]
763 instMethodNotInClassErr occ clas sty
764 = hang (ptext SLIT("Instance mentions a method not in the class"))
765 4 (hsep [ptext SLIT("class"), ppr sty clas, ptext SLIT("method"),
768 patMonoBindsCtxt pbind sty
769 = hang (ptext SLIT("In a pattern binding:"))
772 methodSigCtxt name ty sty
773 = hang (hsep [ptext SLIT("When matching the definition of class method"),
774 ppr sty name, ptext SLIT("to its signature :") ])
778 = ptext SLIT("When checking methods of an instance declaration")
780 superClassSigCtxt sty
781 = ptext SLIT("When checking superclass constraints of an instance declaration")