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, isClassDecl, toHsType
18 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl,
19 RenamedMonoBinds, RenamedTyClDecl, RenamedHsType,
20 extractHsTyVars, maybeGenericMatch
22 import TcHsSyn ( TcMonoBinds, mkHsConApp )
23 import TcBinds ( tcSpecSigs )
24 import TcClassDcl ( tcMethodBind, badMethodErr )
26 import TcMType ( tcInstTyVars, checkValidTheta, checkValidInstHead, instTypeErr,
27 UserTypeCtxt(..), SourceTyCtxt(..) )
28 import TcType ( tcSplitDFunTy, mkClassPred, mkTyVarTy,
29 tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys
31 import Inst ( InstOrigin(..),
33 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
34 import TcDeriv ( tcDeriving )
35 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
36 tcExtendTyVarEnvForMeths,
37 tcAddImportedIdInfo, tcLookupClass,
38 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
39 simpleInstInfoTy, newDFunName,
42 import InstEnv ( InstEnv, extendInstEnv )
43 import PprType ( pprClassPred )
44 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType, checkSigTyVars )
45 import TcSimplify ( tcSimplifyCheck )
46 import HscTypes ( HomeSymbolTable, DFunId,
47 ModDetails(..), PackageInstEnv, PersistentRenamerState
50 import Subst ( substTy, substTheta )
51 import DataCon ( classDataCon )
52 import Class ( Class, DefMeth(..), classBigSig )
53 import Var ( idName, idType )
54 import VarSet ( emptyVarSet )
55 import MkId ( mkDictFunId )
56 import FunDeps ( checkInstFDs )
57 import Generics ( validGenericInstanceType )
58 import Module ( Module, foldModuleEnv )
59 import Name ( getSrcLoc )
60 import NameSet ( unitNameSet, nameSetToList )
61 import PrelInfo ( eRROR_ID )
62 import TyCon ( TyCon )
63 import Subst ( mkTopTyVarSubst, substTheta )
64 import TysWiredIn ( genericTyCons )
66 import SrcLoc ( SrcLoc )
67 import Unique ( Uniquable(..) )
68 import BasicTypes ( NewOrData(..), Fixity )
69 import ErrUtils ( dumpIfSet_dyn )
70 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
71 assocElts, extendAssoc_C,
72 equivClassesByUniq, minusList
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
176 -- (1) Do the ordinary instance declarations
177 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
179 -- (2) Instances from generic class declarations
180 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
182 -- Next, construct the instance environment so far, consisting of
183 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
184 -- b) imported instance decls (not in the home package) inst_env1
185 -- c) other modules in this package (gotten from hst) inst_env2
186 -- d) local instance decls inst_env3
187 -- e) generic instances inst_env4
188 -- The result of (b) replaces the cached InstEnv in the PCS
190 (local_inst_info, imported_inst_info)
191 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
193 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
195 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
198 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
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 this_mod inst_env4 get_fixity tycl_decls
211 `thenTc` \ (deriv_inst_info, deriv_binds) ->
212 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
216 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
219 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
220 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
222 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
223 addInstDFuns inst_env dfuns
224 = getDOptsTc `thenTc` \ dflags ->
226 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
228 addErrsTc errs `thenNF_Tc_`
229 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
232 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
236 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
237 -- Deal with a single instance declaration
238 -- Type-check all the stuff before the "where"
239 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
240 = -- Prime error recovery, set source location
241 recoverNF_Tc (returnNF_Tc []) $
242 tcAddSrcLoc src_loc $
243 tcAddErrCtxt (instDeclCtxt poly_ty) $
245 -- Typecheck the instance type itself. We can't use
246 -- tcHsSigType, because it's not a valid user type.
247 kcHsSigType poly_ty `thenTc_`
248 tcHsType poly_ty `thenTc` \ poly_ty' ->
250 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
251 (clas,inst_tys) = case tcSplitPredTy_maybe tau of { Just st -> getClassPredTys st }
252 -- The checkValidInstHead makes sure these splits succeed
254 (case maybe_dfun_name of
255 Nothing -> -- A source-file instance declaration
256 -- Check for respectable instance type, and context
257 -- but only do this for non-imported instance decls.
258 -- Imported ones should have been checked already, and may indeed
259 -- contain something illegal in normal Haskell, notably
260 -- instance CCallable [Char]
261 checkValidTheta InstThetaCtxt theta `thenTc_`
262 checkValidInstHead tau `thenTc_`
263 checkTc (checkInstFDs theta clas inst_tys)
264 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
265 newDFunName clas inst_tys src_loc
267 Just dfun_name -> -- An interface-file instance declaration
268 returnNF_Tc dfun_name
269 ) `thenNF_Tc` \ dfun_name ->
271 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
273 returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
275 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
279 %************************************************************************
281 \subsection{Extracting generic instance declaration from class declarations}
283 %************************************************************************
285 @getGenericInstances@ extracts the generic instance declarations from a class
286 declaration. For exmaple
291 op{ x+y } (Inl v) = ...
292 op{ x+y } (Inr v) = ...
293 op{ x*y } (v :*: w) = ...
296 gives rise to the instance declarations
298 instance C (x+y) where
302 instance C (x*y) where
310 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
311 getGenericInstances class_decls
312 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
314 gen_inst_info = concat gen_inst_infos
316 if null gen_inst_info then
319 getDOptsTc `thenTc` \ dflags ->
320 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
321 (vcat (map pprInstInfo gen_inst_info)))
323 returnTc gen_inst_info
325 get_generics decl@(ClassDecl {tcdMeths = Nothing})
326 = returnTc [] -- Imported class decls
328 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
330 = returnTc [] -- The comon case: no generic default methods
332 | otherwise -- A local class decl with generic default methods
333 = recoverNF_Tc (returnNF_Tc []) $
335 tcLookupClass class_name `thenTc` \ clas ->
337 -- Make an InstInfo out of each group
338 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
340 -- Check that there is only one InstInfo for each type constructor
341 -- The main way this can fail is if you write
342 -- f {| a+b |} ... = ...
343 -- f {| x+y |} ... = ...
344 -- Then at this point we'll have an InstInfo for each
346 tc_inst_infos :: [(TyCon, InstInfo)]
347 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
349 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
351 get_uniq (tc,_) = getUnique tc
353 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
355 -- Check that there is an InstInfo for each generic type constructor
357 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
359 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
364 -- Group the declarations by type pattern
365 groups :: [(RenamedHsType, RenamedMonoBinds)]
366 groups = assocElts (getGenericBinds def_methods)
369 ---------------------------------
370 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
371 -- Takes a group of method bindings, finds the generic ones, and returns
372 -- them in finite map indexed by the type parameter in the definition.
374 getGenericBinds EmptyMonoBinds = emptyAssoc
375 getGenericBinds (AndMonoBinds m1 m2)
376 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
378 getGenericBinds (FunMonoBind id infixop matches loc)
379 = mapAssoc wrap (foldl add emptyAssoc matches)
380 -- Using foldl not foldr is vital, else
381 -- we reverse the order of the bindings!
383 add env match = case maybeGenericMatch match of
385 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
387 wrap ms = FunMonoBind id infixop ms loc
389 ---------------------------------
390 mkGenericInstance :: Class -> SrcLoc
391 -> (RenamedHsType, RenamedMonoBinds)
394 mkGenericInstance clas loc (hs_ty, binds)
395 -- Make a generic instance declaration
396 -- For example: instance (C a, C b) => C (a+b) where { binds }
398 = -- Extract the universally quantified type variables
400 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
402 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
404 -- Type-check the instance type, and check its form
405 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
406 checkTc (validGenericInstanceType inst_ty)
407 (badGenericInstanceType binds) `thenTc_`
409 -- Make the dictionary function.
410 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
412 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
414 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
417 returnTc (InstInfo { iDFunId = dfun_id,
418 iBinds = binds, iPrags = [] })
422 %************************************************************************
424 \subsection{Type-checking instance declarations, pass 2}
426 %************************************************************************
429 tcInstDecls2 :: [InstInfo]
430 -> NF_TcM (LIE, TcMonoBinds)
432 tcInstDecls2 inst_decls
433 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
434 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
435 (map tcInstDecl2 inst_decls)
437 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
438 tc2 `thenNF_Tc` \ (lie2, binds2) ->
439 returnNF_Tc (lie1 `plusLIE` lie2,
440 binds1 `AndMonoBinds` binds2)
443 ======= New documentation starts here (Sept 92) ==============
445 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
446 the dictionary function for this instance declaration. For example
448 instance Foo a => Foo [a] where
452 might generate something like
454 dfun.Foo.List dFoo_a = let op1 x = ...
460 HOWEVER, if the instance decl has no context, then it returns a
461 bigger @HsBinds@ with declarations for each method. For example
463 instance Foo [a] where
469 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
470 const.Foo.op1.List a x = ...
471 const.Foo.op2.List a y = ...
473 This group may be mutually recursive, because (for example) there may
474 be no method supplied for op2 in which case we'll get
476 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
478 that is, the default method applied to the dictionary at this type.
480 What we actually produce in either case is:
482 AbsBinds [a] [dfun_theta_dicts]
483 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
484 { d = (sd1,sd2, ..., op1, op2, ...)
489 The "maybe" says that we only ask AbsBinds to make global constant methods
490 if the dfun_theta is empty.
493 For an instance declaration, say,
495 instance (C1 a, C2 b) => C (T a b) where
498 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
499 function whose type is
501 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
503 Notice that we pass it the superclass dictionaries at the instance type; this
504 is the ``Mark Jones optimisation''. The stuff before the "=>" here
505 is the @dfun_theta@ below.
507 First comes the easy case of a non-local instance decl.
511 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
512 -- tcInstDecl2 is called *only* on InstInfos
514 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
515 iBinds = monobinds, iPrags = uprags })
516 = -- Prime error recovery
517 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
518 tcAddSrcLoc (getSrcLoc dfun_id) $
519 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
521 -- Instantiate the instance decl with tc-style type variables
523 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
525 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
527 inst_tys' = map (substTy tenv) inst_tys
528 dfun_theta' = substTheta tenv dfun_theta
529 origin = InstanceDeclOrigin
531 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
533 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
534 sel_names = [idName sel_id | (sel_id, _) <- op_items]
536 -- Instantiate the super-class context with inst_tys
537 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
539 -- Find any definitions in monobinds that aren't from the class
540 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
542 -- Check that all the method bindings come from this class
543 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
545 -- Create dictionary Ids from the specified instance contexts.
546 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
547 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
548 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
550 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
551 -- The type variable from the dict fun actually scope
552 -- over the bindings. They were gotten from
553 -- the original instance declaration
554 tcExtendGlobalValEnv dm_ids (
555 -- Default-method Ids may be mentioned in synthesised RHSs
557 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
559 monobinds uprags True)
561 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
563 -- Deal with SPECIALISE instance pragmas by making them
564 -- look like SPECIALISE pragmas for the dfun
566 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
568 tcExtendGlobalValEnv [dfun_id] (
569 tcSpecSigs dfun_prags
570 ) `thenTc` \ (prag_binds, prag_lie) ->
572 -- Check the overloading constraints of the methods and superclasses
574 -- These insts are in scope; quite a few, eh?
575 avail_insts = [this_dict] ++
580 methods_lie = plusLIEs insts_needed_s
583 -- Simplify the constraints from methods
584 tcAddErrCtxt methodCtxt (
586 (ptext SLIT("instance declaration context"))
590 ) `thenTc` \ (const_lie1, lie_binds1) ->
592 -- Figure out bindings for the superclass context
593 tcAddErrCtxt superClassCtxt (
595 (ptext SLIT("instance declaration context"))
597 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
598 -- get bound by just selecting from this_dict!!
600 ) `thenTc` \ (const_lie2, lie_binds2) ->
602 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
604 -- Create the result bindings
606 dict_constr = classDataCon clas
607 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
608 this_dict_id = instToId this_dict
609 inlines = unitNameSet (idName dfun_id)
610 -- Always inline the dfun; this is an experimental decision
611 -- because it makes a big performance difference sometimes.
612 -- Often it means we can do the method selection, and then
613 -- inline the method as well. Marcin's idea; see comments below.
617 = -- Blatant special case for CCallable, CReturnable
618 -- If the dictionary is empty then we should never
619 -- select anything from it, so we make its RHS just
620 -- emit an error message. This in turn means that we don't
621 -- mention the constructor, which doesn't exist for CCallable, CReturnable
622 -- Hardly beautiful, but only three extra lines.
623 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
624 (HsLit (HsString msg))
626 | otherwise -- The common case
627 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
628 -- We don't produce a binding for the dict_constr; instead we
629 -- rely on the simplifier to unfold this saturated application
630 -- We do this rather than generate an HsCon directly, because
631 -- it means that the special cases (e.g. dictionary with only one
632 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
633 -- than needing to be repeated here.
636 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
638 dict_bind = VarMonoBind this_dict_id dict_rhs
639 method_binds = andMonoBindList method_binds_s
644 (map instToId dfun_arg_dicts)
645 [(inst_tyvars', dfun_id, this_dict_id)]
647 (lie_binds1 `AndMonoBinds`
648 lie_binds2 `AndMonoBinds`
649 method_binds `AndMonoBinds`
652 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
653 main_bind `AndMonoBinds` prag_binds)
656 ------------------------------
657 Inlining dfuns unconditionally
658 ------------------------------
660 The code above unconditionally inlines dict funs. Here's why.
661 Consider this program:
663 test :: Int -> Int -> Bool
664 test x y = (x,y) == (y,x) || test y x
665 -- Recursive to avoid making it inline.
667 This needs the (Eq (Int,Int)) instance. If we inline that dfun
668 the code we end up with is good:
671 \r -> case ==# [ww ww1] of wild {
672 PrelBase.False -> Test.$wtest ww1 ww;
674 case ==# [ww1 ww] of wild1 {
675 PrelBase.False -> Test.$wtest ww1 ww;
676 PrelBase.True -> PrelBase.True [];
679 Test.test = \r [w w1]
682 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
685 If we don't inline the dfun, the code is not nearly as good:
687 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
688 PrelBase.:DEq tpl1 tpl2 -> tpl2;
693 let { y = PrelBase.I#! [ww1]; } in
694 let { x = PrelBase.I#! [ww]; } in
695 let { sat_slx = PrelTup.(,)! [y x]; } in
696 let { sat_sly = PrelTup.(,)! [x y];
698 case == sat_sly sat_slx of wild {
699 PrelBase.False -> Test.$wtest ww1 ww;
700 PrelBase.True -> PrelBase.True [];
707 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
710 Why doesn't GHC inline $fEq? Because it looks big:
712 PrelTup.zdfEqZ1T{-rcX-}
713 = \ @ a{-reT-} :: * @ b{-reS-} :: *
714 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
715 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
717 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
718 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
720 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
721 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
723 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
724 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
725 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
727 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
729 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
731 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
732 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
736 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
737 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
738 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
739 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
741 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
743 and it's not as bad as it seems, because it's further dramatically
744 simplified: only zeze2 is extracted and its body is simplified.
747 %************************************************************************
749 \subsection{Error messages}
751 %************************************************************************
754 tcAddDeclCtxt decl thing_inside
755 = tcAddSrcLoc (tcdLoc decl) $
760 ClassDecl {} -> "class"
761 TySynonym {} -> "type synonym"
762 TyData {tcdND = NewType} -> "newtype"
763 TyData {tcdND = DataType} -> "data type"
765 ctxt = hsep [ptext SLIT("In the"), text thing,
766 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
768 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
770 doc = case inst_ty of
771 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
772 HsPredTy pred -> ppr pred
773 other -> ppr inst_ty -- Don't expect this
777 badGenericInstanceType binds
778 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
781 missingGenericInstances missing
782 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
784 dupGenericInsts tc_inst_infos
785 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
786 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
787 ptext SLIT("All the type patterns for a generic type constructor must be identical")
790 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
792 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
793 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")