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(..) )
14 import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..), HsType(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), HsTyVarBndr(..),
16 andMonoBindList, collectMonoBinders,
17 isClassDecl, isIfaceInstDecl, toHsType
19 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl,
20 RenamedMonoBinds, RenamedTyClDecl, RenamedHsType,
21 extractHsTyVars, maybeGenericMatch
23 import TcHsSyn ( TcMonoBinds, mkHsConApp )
24 import TcBinds ( tcSpecSigs )
25 import TcClassDcl ( tcMethodBind, badMethodErr )
27 import TcMType ( tcInstSigType, checkValidTheta, checkValidInstHead, instTypeErr,
28 UserTypeCtxt(..), SourceTyCtxt(..) )
29 import TcType ( mkClassPred, mkTyVarTy, mkTyVarTys, tcSplitForAllTys,
30 tcSplitSigmaTy, getClassPredTys, tcSplitPredTy_maybe,
33 import Inst ( InstOrigin(..), newDicts, instToId,
34 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
35 import TcDeriv ( tcDeriving )
36 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
37 tcExtendTyVarEnvForMeths, tcLookupId, tcLookupClass,
38 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
39 simpleInstInfoTy, newDFunName
41 import InstEnv ( InstEnv, extendInstEnv )
42 import PprType ( pprClassPred )
43 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType )
44 import TcUnify ( checkSigTyVars )
45 import TcSimplify ( tcSimplifyCheck )
46 import HscTypes ( HomeSymbolTable, DFunId,
47 ModDetails(..), PackageInstEnv, PersistentRenamerState
49 import Subst ( substTy, substTheta )
50 import DataCon ( classDataCon )
51 import Class ( Class, classBigSig )
52 import Var ( idName, idType )
53 import VarSet ( emptyVarSet )
54 import Id ( setIdLocalExported )
55 import MkId ( mkDictFunId, unsafeCoerceId, eRROR_ID )
56 import FunDeps ( checkInstFDs )
57 import Generics ( validGenericInstanceType )
58 import Module ( Module, foldModuleEnv )
59 import Name ( getSrcLoc )
60 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
61 import TyCon ( TyCon )
62 import Subst ( mkTopTyVarSubst, substTheta )
63 import TysWiredIn ( genericTyCons )
65 import SrcLoc ( SrcLoc )
66 import Unique ( Uniquable(..) )
67 import Util ( lengthExceeds, isSingleton )
68 import BasicTypes ( NewOrData(..), Fixity )
69 import ErrUtils ( dumpIfSet_dyn )
70 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
71 assocElts, extendAssoc_C, equivClassesByUniq, minusList
73 import Maybe ( catMaybes )
74 import List ( partition )
78 Typechecking instance declarations is done in two passes. The first
79 pass, made by @tcInstDecls1@, collects information to be used in the
82 This pre-processed info includes the as-yet-unprocessed bindings
83 inside the instance declaration. These are type-checked in the second
84 pass, when the class-instance envs and GVE contain all the info from
85 all the instance and value decls. Indeed that's the reason we need
86 two passes over the instance decls.
89 Here is the overall algorithm.
90 Assume that we have an instance declaration
92 instance c => k (t tvs) where b
96 $LIE_c$ is the LIE for the context of class $c$
98 $betas_bar$ is the free variables in the class method type, excluding the
101 $LIE_cop$ is the LIE constraining a particular class method
103 $tau_cop$ is the tau type of a class method
105 $LIE_i$ is the LIE for the context of instance $i$
107 $X$ is the instance constructor tycon
109 $gammas_bar$ is the set of type variables of the instance
111 $LIE_iop$ is the LIE for a particular class method instance
113 $tau_iop$ is the tau type for this instance of a class method
115 $alpha$ is the class variable
117 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
119 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
122 ToDo: Update the list above with names actually in the code.
126 First, make the LIEs for the class and instance contexts, which means
127 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
128 and make LIElistI and LIEI.
130 Then process each method in turn.
132 order the instance methods according to the ordering of the class methods
134 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
136 Create final dictionary function from bindings generated already
138 df = lambda inst_tyvars
145 in <op1,op2,...,opn,sd1,...,sdm>
147 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
148 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
152 %************************************************************************
154 \subsection{Extracting instance decls}
156 %************************************************************************
158 Gather up the instance declarations from their various sources
161 tcInstDecls1 :: PackageInstEnv
162 -> PersistentRenamerState
163 -> HomeSymbolTable -- Contains instances
164 -> TcEnv -- Contains IdInfo for dfun ids
165 -> (Name -> Maybe Fixity) -- for deriving Show and Read
166 -> Module -- Module for deriving
168 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
170 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
172 inst_decls = [inst_decl | InstD inst_decl <- decls]
173 tycl_decls = [decl | TyClD decl <- decls]
174 clas_decls = filter isClassDecl tycl_decls
175 (imported_inst_ds, local_inst_ds) = partition isIfaceInstDecl inst_decls
177 -- (1) Do the ordinary instance declarations
178 mapNF_Tc tcLocalInstDecl1 local_inst_ds `thenNF_Tc` \ local_inst_infos ->
179 mapNF_Tc tcImportedInstDecl1 imported_inst_ds `thenNF_Tc` \ imported_dfuns ->
181 -- (2) Instances from generic class declarations
182 getGenericInstances 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 = catMaybes local_inst_infos
193 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
196 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
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; hence inst_env4
208 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
209 `thenTc` \ (deriv_inst_info, deriv_binds) ->
210 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
214 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
217 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
218 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
220 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
221 addInstDFuns inst_env dfuns
222 = getDOptsTc `thenNF_Tc` \ dflags ->
224 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
226 addErrsTc errs `thenNF_Tc_`
227 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
230 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
234 tcImportedInstDecl1 :: RenamedInstDecl -> NF_TcM DFunId
235 -- An interface-file instance declaration
236 -- Should be in scope by now, because we should
237 -- have sucked in its interface-file definition
238 -- So it will be replete with its unfolding etc
239 tcImportedInstDecl1 decl@(InstDecl poly_ty binds uprags (Just dfun_name) src_loc)
240 = tcLookupId dfun_name
243 tcLocalInstDecl1 :: RenamedInstDecl
244 -> NF_TcM (Maybe InstInfo) -- Nothing if there was an error
245 -- A source-file instance declaration
246 -- Type-check all the stuff before the "where"
248 -- We check for respectable instance type, and context
249 -- but only do this for non-imported instance decls.
250 -- Imported ones should have been checked already, and may indeed
251 -- contain something illegal in normal Haskell, notably
252 -- instance CCallable [Char]
253 tcLocalInstDecl1 decl@(InstDecl poly_ty binds uprags Nothing src_loc)
254 = -- Prime error recovery, set source location
255 recoverNF_Tc (returnNF_Tc Nothing) $
256 tcAddSrcLoc src_loc $
257 tcAddErrCtxt (instDeclCtxt poly_ty) $
259 -- Typecheck the instance type itself. We can't use
260 -- tcHsSigType, because it's not a valid user type.
261 kcHsSigType poly_ty `thenTc_`
262 tcHsType poly_ty `thenTc` \ poly_ty' ->
264 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
266 checkValidTheta InstThetaCtxt theta `thenTc_`
267 checkValidInstHead tau `thenTc` \ (clas,inst_tys) ->
268 checkTc (checkInstFDs theta clas inst_tys)
269 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
270 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
271 returnTc (Just (InstInfo { iDFunId = mkDictFunId dfun_name clas tyvars inst_tys theta,
272 iBinds = binds, iPrags = uprags }))
274 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
278 %************************************************************************
280 \subsection{Extracting generic instance declaration from class declarations}
282 %************************************************************************
284 @getGenericInstances@ extracts the generic instance declarations from a class
285 declaration. For exmaple
290 op{ x+y } (Inl v) = ...
291 op{ x+y } (Inr v) = ...
292 op{ x*y } (v :*: w) = ...
295 gives rise to the instance declarations
297 instance C (x+y) where
301 instance C (x*y) where
309 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
310 getGenericInstances class_decls
311 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
313 gen_inst_info = concat gen_inst_infos
315 if null gen_inst_info then
318 getDOptsTc `thenNF_Tc` \ dflags ->
319 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
320 (vcat (map pprInstInfo gen_inst_info)))
322 returnTc gen_inst_info
324 get_generics decl@(ClassDecl {tcdMeths = Nothing})
325 = returnTc [] -- Imported class decls
327 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
329 = returnTc [] -- The comon case: no generic default methods
331 | otherwise -- A source class decl with generic default methods
332 = recoverNF_Tc (returnNF_Tc []) $
334 tcLookupClass class_name `thenTc` \ clas ->
336 -- Make an InstInfo out of each group
337 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
339 -- Check that there is only one InstInfo for each type constructor
340 -- The main way this can fail is if you write
341 -- f {| a+b |} ... = ...
342 -- f {| x+y |} ... = ...
343 -- Then at this point we'll have an InstInfo for each
345 tc_inst_infos :: [(TyCon, InstInfo)]
346 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
348 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
349 group `lengthExceeds` 1]
350 get_uniq (tc,_) = getUnique tc
352 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
354 -- Check that there is an InstInfo for each generic type constructor
356 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
358 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
363 -- Group the declarations by type pattern
364 groups :: [(RenamedHsType, RenamedMonoBinds)]
365 groups = assocElts (getGenericBinds def_methods)
368 ---------------------------------
369 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
370 -- Takes a group of method bindings, finds the generic ones, and returns
371 -- them in finite map indexed by the type parameter in the definition.
373 getGenericBinds EmptyMonoBinds = emptyAssoc
374 getGenericBinds (AndMonoBinds m1 m2)
375 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
377 getGenericBinds (FunMonoBind id infixop matches loc)
378 = mapAssoc wrap (foldl add emptyAssoc matches)
379 -- Using foldl not foldr is vital, else
380 -- we reverse the order of the bindings!
382 add env match = case maybeGenericMatch match of
384 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
386 wrap ms = FunMonoBind id infixop ms loc
388 ---------------------------------
389 mkGenericInstance :: Class -> SrcLoc
390 -> (RenamedHsType, RenamedMonoBinds)
393 mkGenericInstance clas loc (hs_ty, binds)
394 -- Make a generic instance declaration
395 -- For example: instance (C a, C b) => C (a+b) where { binds }
397 = -- Extract the universally quantified type variables
399 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
401 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
403 -- Type-check the instance type, and check its form
404 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
405 checkTc (validGenericInstanceType inst_ty)
406 (badGenericInstanceType binds) `thenTc_`
408 -- Make the dictionary function.
409 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
411 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
412 dfun_id = mkDictFunId dfun_name clas tyvars [inst_ty] inst_theta
415 returnTc (InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = [] })
419 %************************************************************************
421 \subsection{Type-checking instance declarations, pass 2}
423 %************************************************************************
426 tcInstDecls2 :: [InstInfo]
427 -> NF_TcM (LIE, TcMonoBinds)
429 tcInstDecls2 inst_decls
430 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
431 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
432 (map tcInstDecl2 inst_decls)
434 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
435 tc2 `thenNF_Tc` \ (lie2, binds2) ->
436 returnNF_Tc (lie1 `plusLIE` lie2,
437 binds1 `AndMonoBinds` binds2)
440 ======= New documentation starts here (Sept 92) ==============
442 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
443 the dictionary function for this instance declaration. For example
445 instance Foo a => Foo [a] where
449 might generate something like
451 dfun.Foo.List dFoo_a = let op1 x = ...
457 HOWEVER, if the instance decl has no context, then it returns a
458 bigger @HsBinds@ with declarations for each method. For example
460 instance Foo [a] where
466 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
467 const.Foo.op1.List a x = ...
468 const.Foo.op2.List a y = ...
470 This group may be mutually recursive, because (for example) there may
471 be no method supplied for op2 in which case we'll get
473 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
475 that is, the default method applied to the dictionary at this type.
477 What we actually produce in either case is:
479 AbsBinds [a] [dfun_theta_dicts]
480 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
481 { d = (sd1,sd2, ..., op1, op2, ...)
486 The "maybe" says that we only ask AbsBinds to make global constant methods
487 if the dfun_theta is empty.
490 For an instance declaration, say,
492 instance (C1 a, C2 b) => C (T a b) where
495 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
496 function whose type is
498 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
500 Notice that we pass it the superclass dictionaries at the instance type; this
501 is the ``Mark Jones optimisation''. The stuff before the "=>" here
502 is the @dfun_theta@ below.
504 First comes the easy case of a non-local instance decl.
508 tcInstDecl2 :: InstInfo -> TcM (LIE, TcMonoBinds)
510 tcInstDecl2 (NewTypeDerived { iDFunId = dfun_id })
511 = tcInstSigType InstTv (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') ->
512 newDicts InstanceDeclOrigin dfun_theta' `thenNF_Tc` \ rep_dicts ->
514 rep_dict_id = ASSERT( isSingleton rep_dicts )
515 instToId (head rep_dicts) -- Derived newtypes have just one dict arg
517 body = TyLam inst_tyvars' $
518 DictLam [rep_dict_id] $
519 (HsVar unsafeCoerceId `TyApp` [idType rep_dict_id, inst_head'])
522 -- You might wonder why we have the 'coerce'. It's because the
523 -- type equality mechanism isn't clever enough; see comments with Type.eqType.
524 -- So Lint complains if we don't have this.
526 returnTc (emptyLIE, VarMonoBind dfun_id body)
528 tcInstDecl2 (InstInfo { iDFunId = dfun_id, iBinds = monobinds, iPrags = uprags })
529 = -- Prime error recovery
530 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
531 tcAddSrcLoc (getSrcLoc dfun_id) $
532 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
534 -- Instantiate the instance decl with tc-style type variables
535 tcInstSigType InstTv (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') ->
537 Just pred = tcSplitPredTy_maybe inst_head'
538 (clas, inst_tys') = getClassPredTys pred
539 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
541 sel_names = [idName sel_id | (sel_id, _) <- op_items]
543 -- Instantiate the super-class context with inst_tys
544 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
546 -- Find any definitions in monobinds that aren't from the class
547 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
548 (inst_tyvars, _) = tcSplitForAllTys (idType dfun_id)
549 origin = InstanceDeclOrigin
551 -- Check that all the method bindings come from this class
552 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
554 -- Create dictionary Ids from the specified instance contexts.
555 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
556 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
557 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
559 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
560 -- The type variable from the dict fun actually scope
561 -- over the bindings. They were gotten from
562 -- the original instance declaration
564 -- Default-method Ids may be mentioned in synthesised RHSs,
565 -- but they'll already be in the environment.
567 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
569 monobinds uprags True)
571 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
573 -- Deal with SPECIALISE instance pragmas by making them
574 -- look like SPECIALISE pragmas for the dfun
576 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
578 tcExtendGlobalValEnv [dfun_id] (
579 tcSpecSigs dfun_prags
580 ) `thenTc` \ (prag_binds, prag_lie) ->
582 -- Check the overloading constraints of the methods and superclasses
584 -- These insts are in scope; quite a few, eh?
585 avail_insts = [this_dict] ++
590 methods_lie = plusLIEs insts_needed_s
593 -- Simplify the constraints from methods
594 tcAddErrCtxt methodCtxt (
596 (ptext SLIT("instance declaration context"))
600 ) `thenTc` \ (const_lie1, lie_binds1) ->
602 -- Figure out bindings for the superclass context
603 tcAddErrCtxt superClassCtxt (
605 (ptext SLIT("instance declaration context"))
607 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
608 -- get bound by just selecting from this_dict!!
610 ) `thenTc` \ (const_lie2, lie_binds2) ->
612 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
614 -- Create the result bindings
616 local_dfun_id = setIdLocalExported dfun_id
617 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
619 dict_constr = classDataCon clas
620 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
621 this_dict_id = instToId this_dict
622 inlines | null dfun_arg_dicts = emptyNameSet
623 | otherwise = unitNameSet (idName dfun_id)
624 -- Always inline the dfun; this is an experimental decision
625 -- because it makes a big performance difference sometimes.
626 -- Often it means we can do the method selection, and then
627 -- inline the method as well. Marcin's idea; see comments below.
629 -- BUT: don't inline it if it's a constant dictionary;
630 -- we'll get all the benefit without inlining, and we get
631 -- a **lot** of code duplication if we inline it
635 = -- Blatant special case for CCallable, CReturnable
636 -- If the dictionary is empty then we should never
637 -- select anything from it, so we make its RHS just
638 -- emit an error message. This in turn means that we don't
639 -- mention the constructor, which doesn't exist for CCallable, CReturnable
640 -- Hardly beautiful, but only three extra lines.
641 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
642 (HsLit (HsString msg))
644 | otherwise -- The common case
645 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
646 -- We don't produce a binding for the dict_constr; instead we
647 -- rely on the simplifier to unfold this saturated application
648 -- We do this rather than generate an HsCon directly, because
649 -- it means that the special cases (e.g. dictionary with only one
650 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
651 -- than needing to be repeated here.
654 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
656 dict_bind = VarMonoBind this_dict_id dict_rhs
657 method_binds = andMonoBindList method_binds_s
662 (map instToId dfun_arg_dicts)
663 [(inst_tyvars', local_dfun_id, this_dict_id)]
665 (lie_binds1 `AndMonoBinds`
666 lie_binds2 `AndMonoBinds`
667 method_binds `AndMonoBinds`
670 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
671 main_bind `AndMonoBinds` prag_binds)
674 ------------------------------
675 Inlining dfuns unconditionally
676 ------------------------------
678 The code above unconditionally inlines dict funs. Here's why.
679 Consider this program:
681 test :: Int -> Int -> Bool
682 test x y = (x,y) == (y,x) || test y x
683 -- Recursive to avoid making it inline.
685 This needs the (Eq (Int,Int)) instance. If we inline that dfun
686 the code we end up with is good:
689 \r -> case ==# [ww ww1] of wild {
690 PrelBase.False -> Test.$wtest ww1 ww;
692 case ==# [ww1 ww] of wild1 {
693 PrelBase.False -> Test.$wtest ww1 ww;
694 PrelBase.True -> PrelBase.True [];
697 Test.test = \r [w w1]
700 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
703 If we don't inline the dfun, the code is not nearly as good:
705 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
706 PrelBase.:DEq tpl1 tpl2 -> tpl2;
711 let { y = PrelBase.I#! [ww1]; } in
712 let { x = PrelBase.I#! [ww]; } in
713 let { sat_slx = PrelTup.(,)! [y x]; } in
714 let { sat_sly = PrelTup.(,)! [x y];
716 case == sat_sly sat_slx of wild {
717 PrelBase.False -> Test.$wtest ww1 ww;
718 PrelBase.True -> PrelBase.True [];
725 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
728 Why doesn't GHC inline $fEq? Because it looks big:
730 PrelTup.zdfEqZ1T{-rcX-}
731 = \ @ a{-reT-} :: * @ b{-reS-} :: *
732 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
733 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
735 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
736 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
738 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
739 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
741 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
742 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
743 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
745 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
747 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
749 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
750 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
754 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
755 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
756 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
757 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
759 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
761 and it's not as bad as it seems, because it's further dramatically
762 simplified: only zeze2 is extracted and its body is simplified.
765 %************************************************************************
767 \subsection{Error messages}
769 %************************************************************************
772 tcAddDeclCtxt decl thing_inside
773 = tcAddSrcLoc (tcdLoc decl) $
778 ClassDecl {} -> "class"
779 TySynonym {} -> "type synonym"
780 TyData {tcdND = NewType} -> "newtype"
781 TyData {tcdND = DataType} -> "data type"
783 ctxt = hsep [ptext SLIT("In the"), text thing,
784 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
786 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
788 doc = case inst_ty of
789 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
790 HsPredTy pred -> ppr pred
791 other -> ppr inst_ty -- Don't expect this
795 badGenericInstanceType binds
796 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
799 missingGenericInstances missing
800 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
802 dupGenericInsts tc_inst_infos
803 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
804 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
805 ptext SLIT("All the type patterns for a generic type constructor must be identical")
808 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
810 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
811 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")