2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
4 \section[TcInstDecls]{Typechecking instance declarations}
12 #include "HsVersions.h"
14 import HsSyn ( HsDecl(..), InstDecl(..), HsType(..),
15 HsBinds(..), MonoBinds(..), GRHSsAndBinds(..), GRHS(..),
16 HsExpr(..), InPat(..), HsLit(..),
18 collectMonoBinders, andMonoBinds
20 import RnHsSyn ( RenamedHsBinds, RenamedMonoBinds,
21 RenamedInstDecl, RenamedFixityDecl, RenamedHsExpr,
22 RenamedSig, RenamedSpecInstSig, RenamedHsDecl
24 import TcHsSyn ( TcHsBinds,
25 TcMonoBinds, TcExpr, TcIdOcc(..), TcIdBndr,
26 tcIdType, maybeBoxedPrimType,
28 mkHsDictLam, mkHsDictApp )
30 import TcBinds ( tcPragmaSigs, sigThetaCtxt )
31 import TcClassDcl ( tcMethodBind, badMethodErr )
33 import RnMonad ( RnNameSupply )
34 import Inst ( Inst, InstOrigin(..), InstanceMapper,
35 instToId, newDicts, newMethod, LIE, emptyLIE, plusLIE )
36 import PragmaInfo ( PragmaInfo(..) )
37 import TcDeriv ( tcDeriving )
38 import TcEnv ( tcLookupClass, newLocalId, tcGetGlobalTyVars,
39 tcExtendGlobalValEnv, tcAddImportedIdInfo
41 import TcInstUtil ( InstInfo(..), mkInstanceRelatedIds, buildInstanceEnvs, classDataCon )
42 import TcKind ( TcKind, unifyKind )
43 import TcMatches ( tcMatchesFun )
44 import TcMonoType ( tcTyVarScope, tcContext, tcHsTypeKind, tcHsType )
45 import TcSimplify ( tcSimplifyAndCheck )
46 import TcType ( TcType, TcTyVar, TcTyVarSet,
48 tcInstSigTyVars, tcInstType, tcInstSigTcType,
49 tcInstTheta, tcInstTcType
51 import Unify ( unifyTauTy, unifyTauTyLists )
54 import Bag ( emptyBag, unitBag, unionBags, unionManyBags,
55 concatBag, foldBag, bagToList, listToBag,
58 import CmdLineOpts ( opt_GlasgowExts,
59 opt_SpecialiseOverloaded, opt_WarnMissingMethods
61 import Class ( classBigSig, classTyCon, Class )
62 import Id ( idType, replacePragmaInfo,
63 isNullaryDataCon, dataConArgTys, Id )
64 import ListSetOps ( minusList )
65 import Maybes ( maybeToBool, expectJust, seqMaybe, catMaybes )
66 import Name ( nameOccName, getSrcLoc, mkLocalName,
67 isLocallyDefined, Module,
70 import PrelVals ( nO_METHOD_BINDING_ERROR_ID )
71 import PprType ( pprParendGenType, pprConstraint )
72 import SrcLoc ( SrcLoc, noSrcLoc )
73 import TyCon ( tyConDataCons, isSynTyCon, isDataTyCon, tyConDerivings )
74 import Type ( Type, ThetaType, mkTyVarTys, isUnpointedType,
75 splitSigmaTy, splitAppTys, isTyVarTy, matchTy, mkSigmaTy,
76 splitTyConApp_maybe, getTyVar, splitDictTy_maybe,
77 splitAlgTyConApp_maybe, splitRhoTy, isSynTy,
80 import TyVar ( zipTyVarEnv, mkTyVarSet, tyVarSetToList, TyVar )
81 import TysPrim ( byteArrayPrimTyCon, mutableByteArrayPrimTyCon )
82 import TysWiredIn ( stringTy )
83 import Unique ( Unique, cCallableClassKey, cReturnableClassKey, Uniquable(..) )
84 import Util ( zipEqual, removeDups )
88 Typechecking instance declarations is done in two passes. The first
89 pass, made by @tcInstDecls1@, collects information to be used in the
92 This pre-processed info includes the as-yet-unprocessed bindings
93 inside the instance declaration. These are type-checked in the second
94 pass, when the class-instance envs and GVE contain all the info from
95 all the instance and value decls. Indeed that's the reason we need
96 two passes over the instance decls.
99 Here is the overall algorithm.
100 Assume that we have an instance declaration
102 instance c => k (t tvs) where b
106 $LIE_c$ is the LIE for the context of class $c$
108 $betas_bar$ is the free variables in the class method type, excluding the
111 $LIE_cop$ is the LIE constraining a particular class method
113 $tau_cop$ is the tau type of a class method
115 $LIE_i$ is the LIE for the context of instance $i$
117 $X$ is the instance constructor tycon
119 $gammas_bar$ is the set of type variables of the instance
121 $LIE_iop$ is the LIE for a particular class method instance
123 $tau_iop$ is the tau type for this instance of a class method
125 $alpha$ is the class variable
127 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
129 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
132 ToDo: Update the list above with names actually in the code.
136 First, make the LIEs for the class and instance contexts, which means
137 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
138 and make LIElistI and LIEI.
140 Then process each method in turn.
142 order the instance methods according to the ordering of the class methods
144 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
146 Create final dictionary function from bindings generated already
148 df = lambda inst_tyvars
155 in <op1,op2,...,opn,sd1,...,sdm>
157 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
158 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
162 tcInstDecls1 :: TcEnv s -- Contains IdInfo for dfun ids
164 -> Module -- module name for deriving
165 -> RnNameSupply -- for renaming derivings
166 -> TcM s (Bag InstInfo,
170 tcInstDecls1 unf_env decls mod_name rn_name_supply
171 = -- Do the ordinary instance declarations
172 mapNF_Tc (tcInstDecl1 unf_env mod_name)
173 [inst_decl | InstD inst_decl <- decls] `thenNF_Tc` \ inst_info_bags ->
175 decl_inst_info = unionManyBags inst_info_bags
177 -- Handle "derived" instances; note that we only do derivings
178 -- for things in this module; we ignore deriving decls from
180 tcDeriving mod_name rn_name_supply decl_inst_info
181 `thenTc` \ (deriv_inst_info, deriv_binds, ddump_deriv) ->
184 full_inst_info = deriv_inst_info `unionBags` decl_inst_info
186 returnTc (full_inst_info, deriv_binds, ddump_deriv)
189 tcInstDecl1 :: TcEnv s -> Module -> RenamedInstDecl -> NF_TcM s (Bag InstInfo)
191 tcInstDecl1 unf_env mod_name (InstDecl poly_ty binds uprags (Just dfun_name) src_loc)
192 = -- Prime error recovery, set source location
193 recoverNF_Tc (returnNF_Tc emptyBag) $
194 tcAddSrcLoc src_loc $
196 -- Type-check all the stuff before the "where"
197 tcHsType poly_ty `thenTc` \ poly_ty' ->
199 (tyvars, theta, dict_ty) = splitSigmaTy poly_ty'
200 (clas, inst_tys) = case splitDictTy_maybe dict_ty of
201 Nothing -> pprPanic "tcInstDecl1" (ppr poly_ty)
205 -- Check for respectable instance type
206 scrutiniseInstanceType clas inst_tys `thenTc_`
208 -- Make the dfun id and constant-method ids
210 (dfun_id, dfun_theta) = mkInstanceRelatedIds dfun_name
211 clas tyvars inst_tys theta
212 -- Add info from interface file
213 final_dfun_id = tcAddImportedIdInfo unf_env dfun_id
215 returnTc (unitBag (InstInfo clas tyvars inst_tys theta
216 dfun_theta final_dfun_id
217 binds src_loc uprags))
221 %************************************************************************
223 \subsection{Type-checking instance declarations, pass 2}
225 %************************************************************************
228 tcInstDecls2 :: Bag InstInfo
229 -> NF_TcM s (LIE s, TcMonoBinds s)
231 tcInstDecls2 inst_decls
232 = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
234 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
235 tc2 `thenNF_Tc` \ (lie2, binds2) ->
236 returnNF_Tc (lie1 `plusLIE` lie2,
237 binds1 `AndMonoBinds` binds2)
241 ======= New documentation starts here (Sept 92) ==============
243 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
244 the dictionary function for this instance declaration. For example
246 instance Foo a => Foo [a] where
250 might generate something like
252 dfun.Foo.List dFoo_a = let op1 x = ...
258 HOWEVER, if the instance decl has no context, then it returns a
259 bigger @HsBinds@ with declarations for each method. For example
261 instance Foo [a] where
267 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
268 const.Foo.op1.List a x = ...
269 const.Foo.op2.List a y = ...
271 This group may be mutually recursive, because (for example) there may
272 be no method supplied for op2 in which case we'll get
274 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
276 that is, the default method applied to the dictionary at this type.
278 What we actually produce in either case is:
280 AbsBinds [a] [dfun_theta_dicts]
281 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
282 { d = (sd1,sd2, ..., op1, op2, ...)
287 The "maybe" says that we only ask AbsBinds to make global constant methods
288 if the dfun_theta is empty.
291 For an instance declaration, say,
293 instance (C1 a, C2 b) => C (T a b) where
296 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
297 function whose type is
299 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
301 Notice that we pass it the superclass dictionaries at the instance type; this
302 is the ``Mark Jones optimisation''. The stuff before the "=>" here
303 is the @dfun_theta@ below.
305 First comes the easy case of a non-local instance decl.
308 tcInstDecl2 :: InstInfo -> NF_TcM s (LIE s, TcMonoBinds s)
310 tcInstDecl2 (InstInfo clas inst_tyvars inst_tys
311 inst_decl_theta dfun_theta
314 | not (isLocallyDefined dfun_id)
315 = returnNF_Tc (emptyLIE, EmptyMonoBinds)
318 -- I deleted this "optimisation" because when importing these
319 -- instance decls the renamer would look for the dfun bindings and they weren't there.
320 -- This would be fixable, but it seems simpler just to produce a tiny void binding instead,
321 -- even though it's never used.
323 -- This case deals with CCallable etc, which don't need any bindings
325 = returnNF_Tc (emptyLIE, EmptyBinds)
329 = -- Prime error recovery
330 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
333 -- Get the class signature
335 origin = InstanceDeclOrigin
337 sc_theta, sc_sel_ids,
338 op_sel_ids, defm_ids) = classBigSig clas
341 -- Instantiate the instance decl with tc-style type variables
342 tcInstSigTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
343 mapNF_Tc (tcInstType tenv) inst_tys `thenNF_Tc` \ inst_tys' ->
344 tcInstTheta tenv dfun_theta `thenNF_Tc` \ dfun_theta' ->
345 tcInstTheta tenv inst_decl_theta `thenNF_Tc` \ inst_decl_theta' ->
347 -- Instantiate the super-class context with inst_tys
349 tcInstTheta (zipTyVarEnv class_tyvars inst_tys') sc_theta `thenNF_Tc` \ sc_theta' ->
351 -- Create dictionary Ids from the specified instance contexts.
352 newDicts origin sc_theta' `thenNF_Tc` \ (sc_dicts, sc_dict_ids) ->
353 newDicts origin dfun_theta' `thenNF_Tc` \ (dfun_arg_dicts, dfun_arg_dicts_ids) ->
354 newDicts origin inst_decl_theta' `thenNF_Tc` \ (inst_decl_dicts, _) ->
355 newDicts origin [(clas,inst_tys')] `thenNF_Tc` \ (this_dict, [this_dict_id]) ->
357 -- Now process any INLINE or SPECIALIZE pragmas for the methods
358 -- ...[NB May 97; all ignored except INLINE]
359 tcPragmaSigs uprags `thenTc` \ (prag_fn, spec_binds, spec_lie) ->
361 -- Check that all the method bindings come from this class
363 check_from_this_class (bndr, loc)
364 | nameOccName bndr `elem` sel_names = returnNF_Tc ()
365 | otherwise = tcAddSrcLoc loc $
366 addErrTc (badMethodErr bndr clas)
367 sel_names = map getOccName op_sel_ids
368 bndrs = bagToList (collectMonoBinders monobinds)
370 mapNF_Tc check_from_this_class bndrs `thenNF_Tc_`
372 tcExtendGlobalValEnv (catMaybes defm_ids) (
374 -- Default-method Ids may be mentioned in synthesised RHSs
375 mapAndUnzip3Tc (tcInstMethodBind clas inst_tys' inst_tyvars' monobinds)
376 (op_sel_ids `zip` defm_ids)
377 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_lies_w_ids) ->
379 -- Check the overloading constraints of the methods and superclasses
380 mapNF_Tc zonkSigTyVar inst_tyvars' `thenNF_Tc` \ zonked_inst_tyvars ->
383 inst_tyvars_set = mkTyVarSet zonked_inst_tyvars
385 (meth_lies, meth_ids) = unzip meth_lies_w_ids
387 -- These insts are in scope; quite a few, eh?
388 avail_insts = this_dict `plusLIE`
389 dfun_arg_dicts `plusLIE`
391 unionManyBags meth_lies
393 tcAddErrCtxt superClassCtxt $
394 tcAddErrCtxtM (sigThetaCtxt sc_dicts) $
397 -- Deal with the LIE arising from the method bindings
398 tcSimplifyAndCheck (text "inst decl1a")
399 inst_tyvars_set -- Local tyvars
401 (unionManyBags insts_needed_s) -- Need to get defns for all these
402 `thenTc` \ (const_lie1, op_binds) ->
404 -- Deal with the super-class bindings
405 -- Ignore errors because they come from the *next* tcSimplify
407 tcSimplifyAndCheck (text "inst decl1b")
409 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
410 -- get bound by just selecting from this_dict!!
412 ) `thenTc` \ (const_lie2, sc_binds) ->
415 -- Check that we *could* construct the superclass dictionaries,
416 -- even though we are *actually* going to pass the superclass dicts in;
417 -- the check ensures that the caller will never have a problem building
419 tcSimplifyAndCheck (text "inst decl1c")
420 inst_tyvars_set -- Local tyvars
421 inst_decl_dicts -- The instance dictionaries available
422 sc_dicts -- The superclass dicationaries reqd
424 -- Ignore the result; we're only doing
425 -- this to make sure it can be done.
427 -- Create the result bindings
429 const_lie = const_lie1 `plusLIE` const_lie2
430 lie_binds = op_binds `AndMonoBinds` sc_binds
432 dict_constr = classDataCon clas
434 con_app = foldl HsApp (TyApp (HsVar (RealId dict_constr)) inst_tys')
435 (map HsVar (sc_dict_ids ++ meth_ids))
436 -- We don't produce a binding for the dict_constr; instead we
437 -- rely on the simplifier to unfold this saturated application
439 dict_bind = VarMonoBind this_dict_id con_app
440 method_binds = andMonoBinds method_binds_s
446 [(inst_tyvars', RealId dfun_id, this_dict_id)]
447 (lie_binds `AndMonoBinds`
448 method_binds `AndMonoBinds`
451 returnTc (const_lie `plusLIE` spec_lie,
452 main_bind `AndMonoBinds` spec_binds)
456 %************************************************************************
458 \subsection{Processing each method}
460 %************************************************************************
465 -> [TcType s] -- Instance types
466 -> [TcTyVar s] -- and their free (sig) tyvars
467 -> RenamedMonoBinds -- Method binding
468 -> (Id, Maybe Id) -- Selector id and default-method id
469 -> TcM s (TcMonoBinds s, LIE s, (LIE s, TcIdOcc s))
471 tcInstMethodBind clas inst_tys inst_tyvars meth_binds (sel_id, maybe_dm_id)
472 = tcGetSrcLoc `thenNF_Tc` \ loc ->
473 tcGetUnique `thenNF_Tc` \ uniq ->
475 meth_occ = getOccName sel_id
476 default_meth_name = mkLocalName uniq meth_occ loc
477 maybe_meth_bind = find meth_occ meth_binds
478 the_meth_bind = case maybe_meth_bind of
480 Nothing -> mk_default_bind default_meth_name loc
483 -- Warn if no method binding, only if -fwarn-missing-methods
485 warnTc (opt_WarnMissingMethods &&
486 not (maybeToBool maybe_meth_bind) &&
487 not (maybeToBool maybe_dm_id))
488 (omittedMethodWarn sel_id clas) `thenNF_Tc_`
490 -- Typecheck the method binding
491 tcMethodBind clas origin inst_tys inst_tyvars sel_id the_meth_bind
493 origin = InstanceDeclOrigin -- Poor
495 find occ EmptyMonoBinds = Nothing
496 find occ (AndMonoBinds b1 b2) = find occ b1 `seqMaybe` find occ b2
498 find occ b@(FunMonoBind op_name _ _ _) | nameOccName op_name == occ = Just b
499 | otherwise = Nothing
500 find occ b@(PatMonoBind (VarPatIn op_name) _ _) | nameOccName op_name == occ = Just b
501 | otherwise = Nothing
502 find occ other = panic "Urk! Bad instance method binding"
505 mk_default_bind local_meth_name loc
506 = PatMonoBind (VarPatIn local_meth_name)
507 (GRHSsAndBindsIn (unguardedRHS (default_expr loc) loc) EmptyBinds)
511 = case maybe_dm_id of
512 Just dm_id -> HsVar (getName dm_id) -- There's a default method
513 Nothing -> error_expr loc -- No default method
516 = HsApp (HsVar (getName nO_METHOD_BINDING_ERROR_ID))
517 (HsLit (HsString (_PK_ (error_msg loc))))
519 error_msg loc = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
525 %************************************************************************
527 \subsection{Type-checking specialise instance pragmas}
529 %************************************************************************
533 tcSpecInstSigs :: E -> CE -> TCE
534 -> Bag InstInfo -- inst decls seen (declared and derived)
535 -> [RenamedSpecInstSig] -- specialise instance upragmas
536 -> TcM (Bag InstInfo) -- new, overlapped, inst decls
538 tcSpecInstSigs e ce tce inst_infos []
541 tcSpecInstSigs e ce tce inst_infos sigs
542 = buildInstanceEnvs inst_infos `thenTc` \ inst_mapper ->
543 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ spec_inst_infos ->
544 returnTc spec_inst_infos
546 tc_inst_spec_sigs inst_mapper []
547 = returnNF_Tc emptyBag
548 tc_inst_spec_sigs inst_mapper (sig:sigs)
549 = tcSpecInstSig e ce tce inst_infos inst_mapper sig `thenNF_Tc` \ info_sig ->
550 tc_inst_spec_sigs inst_mapper sigs `thenNF_Tc` \ info_sigs ->
551 returnNF_Tc (info_sig `unionBags` info_sigs)
553 tcSpecInstSig :: E -> CE -> TCE
556 -> RenamedSpecInstSig
557 -> NF_TcM (Bag InstInfo)
559 tcSpecInstSig e ce tce inst_infos inst_mapper (SpecInstSig class_name ty src_loc)
560 = recoverTc emptyBag (
561 tcAddSrcLoc src_loc (
563 clas = lookupCE ce class_name -- Renamer ensures this can't fail
565 -- Make some new type variables, named as in the specialised instance type
566 ty_names = extractHsTyNames ???is_tyvarish_name??? ty
567 (tmpl_e,inst_tmpls,inst_tmpl_tys) = mkTVE ty_names
569 babyTcMtoTcM (tcInstanceType ce tce tmpl_e True src_loc ty)
570 `thenTc` \ inst_ty ->
572 maybe_tycon = case splitAlgTyConApp_maybe inst_ty of
573 Just (tc,_,_) -> Just tc
576 maybe_unspec_inst = lookup_unspec_inst clas maybe_tycon inst_infos
578 -- Check that we have a local instance declaration to specialise
579 checkMaybeTc maybe_unspec_inst
580 (specInstUnspecInstNotFoundErr clas inst_ty src_loc) `thenTc_`
582 -- Create tvs to substitute for tmpls while simplifying the context
583 copyTyVars inst_tmpls `thenNF_Tc` \ (tv_e, inst_tvs, inst_tv_tys) ->
585 Just (InstInfo _ unspec_tyvars unspec_inst_ty unspec_theta
586 _ _ binds _ uprag) = maybe_unspec_inst
588 subst = case matchTy unspec_inst_ty inst_ty of
590 Nothing -> panic "tcSpecInstSig:matchTy"
592 subst_theta = instantiateThetaTy subst unspec_theta
593 subst_tv_theta = instantiateThetaTy tv_e subst_theta
595 mk_spec_origin clas ty
596 = InstanceSpecOrigin inst_mapper clas ty src_loc
597 -- I'm VERY SUSPICIOUS ABOUT THIS
598 -- the inst-mapper is in a knot at this point so it's no good
599 -- looking at it in tcSimplify...
601 tcSimplifyThetas mk_spec_origin subst_tv_theta
602 `thenTc` \ simpl_tv_theta ->
604 simpl_theta = [ (clas, tv_to_tmpl tv) | (clas, tv) <- simpl_tv_theta ]
606 tv_tmpl_map = zipEqual "tcSpecInstSig" inst_tv_tys inst_tmpl_tys
607 tv_to_tmpl tv = assoc "tcSpecInstSig" tv_tmpl_map tv
609 mkInstanceRelatedIds clas inst_tmpls inst_ty simpl_theta uprag
610 `thenNF_Tc` \ (dfun_id, dfun_theta, const_meth_ids) ->
612 getSwitchCheckerTc `thenNF_Tc` \ sw_chkr ->
613 (if sw_chkr SpecialiseTrace then
614 pprTrace "Specialised Instance: "
615 (vcat [hsep [if null simpl_theta then empty else ppr simpl_theta,
616 if null simpl_theta then empty else ptext SLIT("=>"),
618 pprParendGenType inst_ty],
619 hsep [ptext SLIT(" derived from:"),
620 if null unspec_theta then empty else ppr unspec_theta,
621 if null unspec_theta then empty else ptext SLIT("=>"),
623 pprParendGenType unspec_inst_ty]])
626 returnTc (unitBag (InstInfo clas inst_tmpls inst_ty simpl_theta
628 binds src_loc uprag))
632 lookup_unspec_inst clas maybe_tycon inst_infos
633 = case filter (match_info match_inst_ty) (bagToList inst_infos) of
635 (info:_) -> Just info
637 match_info match_ty (InstInfo inst_clas _ inst_ty _ _ _ _ _ from_here _ _ _)
638 = from_here && clas == inst_clas &&
639 match_ty inst_ty && is_plain_instance inst_ty
641 match_inst_ty = case maybe_tycon of
642 Just tycon -> match_tycon tycon
645 match_tycon tycon inst_ty = case (splitAlgTyConApp_maybe inst_ty) of
646 Just (inst_tc,_,_) -> tycon == inst_tc
649 match_fun inst_ty = isFunType inst_ty
652 is_plain_instance inst_ty
653 = case (splitAlgTyConApp_maybe inst_ty) of
654 Just (_,tys,_) -> all isTyVarTemplateTy tys
655 Nothing -> case maybeUnpackFunTy inst_ty of
656 Just (arg, res) -> isTyVarTemplateTy arg && isTyVarTemplateTy res
657 Nothing -> error "TcInstDecls:is_plain_instance"
662 Checking for a decent instance type
663 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
664 @scrutiniseInstanceType@ checks the type {\em and} its syntactic constraints:
665 it must normally look like: @instance Foo (Tycon a b c ...) ...@
667 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
668 flag is on, or (2)~the instance is imported (they must have been
669 compiled elsewhere). In these cases, we let them go through anyway.
671 We can also have instances for functions: @instance Foo (a -> b) ...@.
674 scrutiniseInstanceType clas inst_taus
675 | -- CCALL CHECK (a).... urgh!
676 -- To verify that a user declaration of a CCallable/CReturnable
677 -- instance is OK, we must be able to see the constructor(s)
678 -- of the instance type (see next guard.)
680 -- We flag this separately to give a more precise error msg.
682 (uniqueOf clas == cCallableClassKey && not constructors_visible) ||
683 (uniqueOf clas == cReturnableClassKey && not constructors_visible)
684 = failWithTc (invisibleDataConPrimCCallErr clas first_inst_tau)
687 -- A user declaration of a CCallable/CReturnable instance
688 -- must be for a "boxed primitive" type.
689 (uniqueOf clas == cCallableClassKey && not (ccallable_type first_inst_tau)) ||
690 (uniqueOf clas == cReturnableClassKey && not (creturnable_type first_inst_tau))
691 = failWithTc (nonBoxedPrimCCallErr clas first_inst_tau)
694 -- It is obviously illegal to have an explicit instance
695 -- for something that we are also planning to `derive'
696 | clas `elem` (tyConDerivings inst_tycon)
697 = failWithTc (derivingWhenInstanceExistsErr clas first_inst_tau)
698 -- Kind check will have ensured inst_taus is of length 1
700 -- ALL TYPE VARIABLES => bad
701 | all isTyVarTy inst_taus
702 = failWithTc (instTypeErr clas inst_taus (text "all the instance types are type variables"))
704 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
705 | not opt_GlasgowExts
706 && not (length inst_taus == 1 &&
707 maybeToBool tyconapp_maybe &&
708 not (isSynTyCon inst_tycon) &&
709 all isTyVarTy arg_tys &&
710 length (tyVarSetToList (tyVarsOfTypes arg_tys)) == length arg_tys
711 -- This last condition checks that all the type variables are distinct
713 = failWithTc (instTypeErr clas inst_taus
714 (text "the instance type must be of form (T a b c)" $$
715 text "where T is not a synonym, and a,b,c are distinct type variables")
722 tyconapp_maybe = splitTyConApp_maybe first_inst_tau
723 Just (inst_tycon, arg_tys) = tyconapp_maybe
724 (first_inst_tau : _) = inst_taus
726 constructors_visible =
727 case splitAlgTyConApp_maybe first_inst_tau of
728 Just (_,_,[]) -> False
729 everything_else -> True
731 -- These conditions come directly from what the DsCCall is capable of.
732 -- Totally grotesque. Green card should solve this.
734 ccallable_type ty = isUnpointedType ty || -- Allow CCallable Int# etc
735 maybeToBool (maybeBoxedPrimType ty) || -- Ditto Int etc
739 byte_arr_thing = case splitAlgTyConApp_maybe ty of
740 Just (tycon, ty_args, [data_con]) | isDataTyCon tycon ->
741 length data_con_arg_tys == 2 &&
742 maybeToBool maybe_arg2_tycon &&
743 (arg2_tycon == byteArrayPrimTyCon ||
744 arg2_tycon == mutableByteArrayPrimTyCon)
746 data_con_arg_tys = dataConArgTys data_con ty_args
747 (data_con_arg_ty1 : data_con_arg_ty2 : _) = data_con_arg_tys
748 maybe_arg2_tycon = splitTyConApp_maybe data_con_arg_ty2
749 Just (arg2_tycon,_) = maybe_arg2_tycon
753 creturnable_type ty = maybeToBool (maybeBoxedPrimType ty) ||
754 -- Or, a data type with a single nullary constructor
755 case (splitAlgTyConApp_maybe ty) of
756 Just (tycon, tys_applied, [data_con])
757 -> isNullaryDataCon data_con
763 instTypeErr clas tys msg
764 = sep [ptext SLIT("Illegal instance declaration for") <+> quotes (pprConstraint clas tys),
768 instBndrErr bndr clas
769 = hsep [ptext SLIT("Class"), quotes (ppr clas), ptext SLIT("does not have a method"), quotes (ppr bndr)]
771 derivingWhenInstanceExistsErr clas tycon
772 = hang (hsep [ptext SLIT("Deriving class"),
774 ptext SLIT("type"), quotes (ppr tycon)])
775 4 (ptext SLIT("when an explicit instance exists"))
777 nonBoxedPrimCCallErr clas inst_ty
778 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
779 4 (hsep [ ptext SLIT("class"), ppr clas, ptext SLIT("type"),
782 omittedMethodWarn sel_id clas
783 = sep [ptext SLIT("Warning: no explicit method nor default method for") <+> quotes (ppr sel_id),
784 ptext SLIT("in an instance declaration for") <+> quotes (ppr clas)]
787 Declaring CCallable & CReturnable instances in a module different
788 from where the type was defined. Caused by importing data type
789 abstractly (either programmatically or by the renamer being over-eager
792 invisibleDataConPrimCCallErr clas inst_ty
793 = hang (hsep [ptext SLIT("Constructors for"), quotes (ppr inst_ty),
794 ptext SLIT("not visible when checking"),
795 quotes (ppr clas), ptext SLIT("instance")])
796 4 (hsep [text "(Try either importing", ppr inst_ty,
797 text "non-abstractly or compile using -fno-prune-tydecls ..)"])
799 instMethodNotInClassErr occ clas
800 = hang (ptext SLIT("Instance mentions a method not in the class"))
801 4 (hsep [ptext SLIT("class") <+> quotes (ppr clas),
802 ptext SLIT("method") <+> quotes (ppr occ)])
804 patMonoBindsCtxt pbind
805 = hang (ptext SLIT("In a pattern binding:"))
808 methodSigCtxt name ty
809 = hang (hsep [ptext SLIT("When matching the definition of class method"),
810 quotes (ppr name), ptext SLIT("to its signature :") ])
813 superClassCtxt = ptext SLIT("From the superclasses of the instance declaration")