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 Id ( setIdLocalExported )
56 import MkId ( mkDictFunId )
57 import FunDeps ( checkInstFDs )
58 import Generics ( validGenericInstanceType )
59 import Module ( Module, foldModuleEnv )
60 import Name ( getSrcLoc )
61 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
62 import PrelInfo ( eRROR_ID )
63 import TyCon ( TyCon )
64 import Subst ( mkTopTyVarSubst, substTheta )
65 import TysWiredIn ( genericTyCons )
67 import SrcLoc ( SrcLoc )
68 import Unique ( Uniquable(..) )
69 import BasicTypes ( NewOrData(..), Fixity )
70 import ErrUtils ( dumpIfSet_dyn )
71 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
72 assocElts, extendAssoc_C,
73 equivClassesByUniq, minusList
75 import List ( partition )
79 Typechecking instance declarations is done in two passes. The first
80 pass, made by @tcInstDecls1@, collects information to be used in the
83 This pre-processed info includes the as-yet-unprocessed bindings
84 inside the instance declaration. These are type-checked in the second
85 pass, when the class-instance envs and GVE contain all the info from
86 all the instance and value decls. Indeed that's the reason we need
87 two passes over the instance decls.
90 Here is the overall algorithm.
91 Assume that we have an instance declaration
93 instance c => k (t tvs) where b
97 $LIE_c$ is the LIE for the context of class $c$
99 $betas_bar$ is the free variables in the class method type, excluding the
102 $LIE_cop$ is the LIE constraining a particular class method
104 $tau_cop$ is the tau type of a class method
106 $LIE_i$ is the LIE for the context of instance $i$
108 $X$ is the instance constructor tycon
110 $gammas_bar$ is the set of type variables of the instance
112 $LIE_iop$ is the LIE for a particular class method instance
114 $tau_iop$ is the tau type for this instance of a class method
116 $alpha$ is the class variable
118 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
120 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
123 ToDo: Update the list above with names actually in the code.
127 First, make the LIEs for the class and instance contexts, which means
128 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
129 and make LIElistI and LIEI.
131 Then process each method in turn.
133 order the instance methods according to the ordering of the class methods
135 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
137 Create final dictionary function from bindings generated already
139 df = lambda inst_tyvars
146 in <op1,op2,...,opn,sd1,...,sdm>
148 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
149 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
153 %************************************************************************
155 \subsection{Extracting instance decls}
157 %************************************************************************
159 Gather up the instance declarations from their various sources
162 tcInstDecls1 :: PackageInstEnv
163 -> PersistentRenamerState
164 -> HomeSymbolTable -- Contains instances
165 -> TcEnv -- Contains IdInfo for dfun ids
166 -> (Name -> Maybe Fixity) -- for deriving Show and Read
167 -> Module -- Module for deriving
169 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
171 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
173 inst_decls = [inst_decl | InstD inst_decl <- decls]
174 tycl_decls = [decl | TyClD decl <- decls]
175 clas_decls = filter isClassDecl tycl_decls
177 -- (1) Do the ordinary instance declarations
178 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
180 -- (2) Instances from generic class declarations
181 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
183 -- Next, construct the instance environment so far, consisting of
184 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
185 -- b) imported instance decls (not in the home package) inst_env1
186 -- c) other modules in this package (gotten from hst) inst_env2
187 -- d) local instance decls inst_env3
188 -- e) generic instances inst_env4
189 -- The result of (b) replaces the cached InstEnv in the PCS
191 (local_inst_info, imported_inst_info)
192 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
194 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
196 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
199 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
201 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
202 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
203 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
204 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
206 -- (3) Compute instances from "deriving" clauses;
207 -- note that we only do derivings for things in this module;
208 -- we ignore deriving decls from interfaces!
209 -- This stuff computes a context for the derived instance decl, so it
210 -- needs to know about all the instances possible; hecne inst_env4
211 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
212 `thenTc` \ (deriv_inst_info, deriv_binds) ->
213 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
217 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
220 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
221 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
223 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
224 addInstDFuns inst_env dfuns
225 = getDOptsTc `thenTc` \ dflags ->
227 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
229 addErrsTc errs `thenNF_Tc_`
230 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
233 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
237 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
238 -- Deal with a single instance declaration
239 -- Type-check all the stuff before the "where"
240 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
241 = -- Prime error recovery, set source location
242 recoverNF_Tc (returnNF_Tc []) $
243 tcAddSrcLoc src_loc $
244 tcAddErrCtxt (instDeclCtxt poly_ty) $
246 -- Typecheck the instance type itself. We can't use
247 -- tcHsSigType, because it's not a valid user type.
248 kcHsSigType poly_ty `thenTc_`
249 tcHsType poly_ty `thenTc` \ poly_ty' ->
251 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
252 (clas,inst_tys) = case tcSplitPredTy_maybe tau of { Just st -> getClassPredTys st }
253 -- The checkValidInstHead makes sure these splits succeed
255 (case maybe_dfun_name of
256 Nothing -> -- A source-file instance declaration
257 -- Check for respectable instance type, and context
258 -- but only do this for non-imported instance decls.
259 -- Imported ones should have been checked already, and may indeed
260 -- contain something illegal in normal Haskell, notably
261 -- instance CCallable [Char]
262 checkValidTheta InstThetaCtxt theta `thenTc_`
263 checkValidInstHead tau `thenTc_`
264 checkTc (checkInstFDs theta clas inst_tys)
265 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
266 newDFunName clas inst_tys src_loc
268 Just dfun_name -> -- An interface-file instance declaration
269 returnNF_Tc dfun_name
270 ) `thenNF_Tc` \ dfun_name ->
272 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
274 returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
276 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
280 %************************************************************************
282 \subsection{Extracting generic instance declaration from class declarations}
284 %************************************************************************
286 @getGenericInstances@ extracts the generic instance declarations from a class
287 declaration. For exmaple
292 op{ x+y } (Inl v) = ...
293 op{ x+y } (Inr v) = ...
294 op{ x*y } (v :*: w) = ...
297 gives rise to the instance declarations
299 instance C (x+y) where
303 instance C (x*y) where
311 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
312 getGenericInstances class_decls
313 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
315 gen_inst_info = concat gen_inst_infos
317 if null gen_inst_info then
320 getDOptsTc `thenTc` \ dflags ->
321 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
322 (vcat (map pprInstInfo gen_inst_info)))
324 returnTc gen_inst_info
326 get_generics decl@(ClassDecl {tcdMeths = Nothing})
327 = returnTc [] -- Imported class decls
329 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
331 = returnTc [] -- The comon case: no generic default methods
333 | otherwise -- A source class decl with generic default methods
334 = recoverNF_Tc (returnNF_Tc []) $
336 tcLookupClass class_name `thenTc` \ clas ->
338 -- Make an InstInfo out of each group
339 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
341 -- Check that there is only one InstInfo for each type constructor
342 -- The main way this can fail is if you write
343 -- f {| a+b |} ... = ...
344 -- f {| x+y |} ... = ...
345 -- Then at this point we'll have an InstInfo for each
347 tc_inst_infos :: [(TyCon, InstInfo)]
348 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
350 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
352 get_uniq (tc,_) = getUnique tc
354 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
356 -- Check that there is an InstInfo for each generic type constructor
358 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
360 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
365 -- Group the declarations by type pattern
366 groups :: [(RenamedHsType, RenamedMonoBinds)]
367 groups = assocElts (getGenericBinds def_methods)
370 ---------------------------------
371 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
372 -- Takes a group of method bindings, finds the generic ones, and returns
373 -- them in finite map indexed by the type parameter in the definition.
375 getGenericBinds EmptyMonoBinds = emptyAssoc
376 getGenericBinds (AndMonoBinds m1 m2)
377 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
379 getGenericBinds (FunMonoBind id infixop matches loc)
380 = mapAssoc wrap (foldl add emptyAssoc matches)
381 -- Using foldl not foldr is vital, else
382 -- we reverse the order of the bindings!
384 add env match = case maybeGenericMatch match of
386 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
388 wrap ms = FunMonoBind id infixop ms loc
390 ---------------------------------
391 mkGenericInstance :: Class -> SrcLoc
392 -> (RenamedHsType, RenamedMonoBinds)
395 mkGenericInstance clas loc (hs_ty, binds)
396 -- Make a generic instance declaration
397 -- For example: instance (C a, C b) => C (a+b) where { binds }
399 = -- Extract the universally quantified type variables
401 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
403 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
405 -- Type-check the instance type, and check its form
406 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
407 checkTc (validGenericInstanceType inst_ty)
408 (badGenericInstanceType binds) `thenTc_`
410 -- Make the dictionary function.
411 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
413 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
415 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
418 returnTc (InstInfo { iDFunId = dfun_id,
419 iBinds = binds, iPrags = [] })
423 %************************************************************************
425 \subsection{Type-checking instance declarations, pass 2}
427 %************************************************************************
430 tcInstDecls2 :: [InstInfo]
431 -> NF_TcM (LIE, TcMonoBinds)
433 tcInstDecls2 inst_decls
434 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
435 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
436 (map tcInstDecl2 inst_decls)
438 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
439 tc2 `thenNF_Tc` \ (lie2, binds2) ->
440 returnNF_Tc (lie1 `plusLIE` lie2,
441 binds1 `AndMonoBinds` binds2)
444 ======= New documentation starts here (Sept 92) ==============
446 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
447 the dictionary function for this instance declaration. For example
449 instance Foo a => Foo [a] where
453 might generate something like
455 dfun.Foo.List dFoo_a = let op1 x = ...
461 HOWEVER, if the instance decl has no context, then it returns a
462 bigger @HsBinds@ with declarations for each method. For example
464 instance Foo [a] where
470 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
471 const.Foo.op1.List a x = ...
472 const.Foo.op2.List a y = ...
474 This group may be mutually recursive, because (for example) there may
475 be no method supplied for op2 in which case we'll get
477 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
479 that is, the default method applied to the dictionary at this type.
481 What we actually produce in either case is:
483 AbsBinds [a] [dfun_theta_dicts]
484 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
485 { d = (sd1,sd2, ..., op1, op2, ...)
490 The "maybe" says that we only ask AbsBinds to make global constant methods
491 if the dfun_theta is empty.
494 For an instance declaration, say,
496 instance (C1 a, C2 b) => C (T a b) where
499 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
500 function whose type is
502 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
504 Notice that we pass it the superclass dictionaries at the instance type; this
505 is the ``Mark Jones optimisation''. The stuff before the "=>" here
506 is the @dfun_theta@ below.
508 First comes the easy case of a non-local instance decl.
512 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
513 -- tcInstDecl2 is called *only* on InstInfos
515 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
516 iBinds = monobinds, iPrags = uprags })
517 = -- Prime error recovery
518 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
519 tcAddSrcLoc (getSrcLoc dfun_id) $
520 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
522 -- Instantiate the instance decl with tc-style type variables
524 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
526 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
528 inst_tys' = map (substTy tenv) inst_tys
529 dfun_theta' = substTheta tenv dfun_theta
530 origin = InstanceDeclOrigin
532 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
534 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
535 sel_names = [idName sel_id | (sel_id, _) <- op_items]
537 -- Instantiate the super-class context with inst_tys
538 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
540 -- Find any definitions in monobinds that aren't from the class
541 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
543 -- Check that all the method bindings come from this class
544 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
546 -- Create dictionary Ids from the specified instance contexts.
547 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
548 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
549 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
551 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
552 -- The type variable from the dict fun actually scope
553 -- over the bindings. They were gotten from
554 -- the original instance declaration
555 tcExtendGlobalValEnv dm_ids (
556 -- Default-method Ids may be mentioned in synthesised RHSs
558 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
560 monobinds uprags True)
562 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
564 -- Deal with SPECIALISE instance pragmas by making them
565 -- look like SPECIALISE pragmas for the dfun
567 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
569 tcExtendGlobalValEnv [dfun_id] (
570 tcSpecSigs dfun_prags
571 ) `thenTc` \ (prag_binds, prag_lie) ->
573 -- Check the overloading constraints of the methods and superclasses
575 -- These insts are in scope; quite a few, eh?
576 avail_insts = [this_dict] ++
581 methods_lie = plusLIEs insts_needed_s
584 -- Simplify the constraints from methods
585 tcAddErrCtxt methodCtxt (
587 (ptext SLIT("instance declaration context"))
591 ) `thenTc` \ (const_lie1, lie_binds1) ->
593 -- Figure out bindings for the superclass context
594 tcAddErrCtxt superClassCtxt (
596 (ptext SLIT("instance declaration context"))
598 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
599 -- get bound by just selecting from this_dict!!
601 ) `thenTc` \ (const_lie2, lie_binds2) ->
603 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
605 -- Create the result bindings
607 local_dfun_id = setIdLocalExported dfun_id
608 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
610 dict_constr = classDataCon clas
611 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
612 this_dict_id = instToId this_dict
613 inlines | null dfun_arg_dicts = emptyNameSet
614 | otherwise = unitNameSet (idName dfun_id)
615 -- Always inline the dfun; this is an experimental decision
616 -- because it makes a big performance difference sometimes.
617 -- Often it means we can do the method selection, and then
618 -- inline the method as well. Marcin's idea; see comments below.
620 -- BUT: don't inline it if it's a constant dictionary;
621 -- we'll get all the benefit without inlining, and we get
622 -- a **lot** of code duplication if we inline it
626 = -- Blatant special case for CCallable, CReturnable
627 -- If the dictionary is empty then we should never
628 -- select anything from it, so we make its RHS just
629 -- emit an error message. This in turn means that we don't
630 -- mention the constructor, which doesn't exist for CCallable, CReturnable
631 -- Hardly beautiful, but only three extra lines.
632 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
633 (HsLit (HsString msg))
635 | otherwise -- The common case
636 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
637 -- We don't produce a binding for the dict_constr; instead we
638 -- rely on the simplifier to unfold this saturated application
639 -- We do this rather than generate an HsCon directly, because
640 -- it means that the special cases (e.g. dictionary with only one
641 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
642 -- than needing to be repeated here.
645 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
647 dict_bind = VarMonoBind this_dict_id dict_rhs
648 method_binds = andMonoBindList method_binds_s
653 (map instToId dfun_arg_dicts)
654 [(inst_tyvars', local_dfun_id, this_dict_id)]
656 (lie_binds1 `AndMonoBinds`
657 lie_binds2 `AndMonoBinds`
658 method_binds `AndMonoBinds`
661 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
662 main_bind `AndMonoBinds` prag_binds)
665 ------------------------------
666 Inlining dfuns unconditionally
667 ------------------------------
669 The code above unconditionally inlines dict funs. Here's why.
670 Consider this program:
672 test :: Int -> Int -> Bool
673 test x y = (x,y) == (y,x) || test y x
674 -- Recursive to avoid making it inline.
676 This needs the (Eq (Int,Int)) instance. If we inline that dfun
677 the code we end up with is good:
680 \r -> case ==# [ww ww1] of wild {
681 PrelBase.False -> Test.$wtest ww1 ww;
683 case ==# [ww1 ww] of wild1 {
684 PrelBase.False -> Test.$wtest ww1 ww;
685 PrelBase.True -> PrelBase.True [];
688 Test.test = \r [w w1]
691 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
694 If we don't inline the dfun, the code is not nearly as good:
696 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
697 PrelBase.:DEq tpl1 tpl2 -> tpl2;
702 let { y = PrelBase.I#! [ww1]; } in
703 let { x = PrelBase.I#! [ww]; } in
704 let { sat_slx = PrelTup.(,)! [y x]; } in
705 let { sat_sly = PrelTup.(,)! [x y];
707 case == sat_sly sat_slx of wild {
708 PrelBase.False -> Test.$wtest ww1 ww;
709 PrelBase.True -> PrelBase.True [];
716 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
719 Why doesn't GHC inline $fEq? Because it looks big:
721 PrelTup.zdfEqZ1T{-rcX-}
722 = \ @ a{-reT-} :: * @ b{-reS-} :: *
723 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
724 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
726 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
727 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
729 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
730 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
732 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
733 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
734 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
736 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
738 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
740 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
741 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
745 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
746 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
747 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
748 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
750 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
752 and it's not as bad as it seems, because it's further dramatically
753 simplified: only zeze2 is extracted and its body is simplified.
756 %************************************************************************
758 \subsection{Error messages}
760 %************************************************************************
763 tcAddDeclCtxt decl thing_inside
764 = tcAddSrcLoc (tcdLoc decl) $
769 ClassDecl {} -> "class"
770 TySynonym {} -> "type synonym"
771 TyData {tcdND = NewType} -> "newtype"
772 TyData {tcdND = DataType} -> "data type"
774 ctxt = hsep [ptext SLIT("In the"), text thing,
775 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
777 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
779 doc = case inst_ty of
780 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
781 HsPredTy pred -> ppr pred
782 other -> ppr inst_ty -- Don't expect this
786 badGenericInstanceType binds
787 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
790 missingGenericInstances missing
791 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
793 dupGenericInsts tc_inst_infos
794 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
795 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
796 ptext SLIT("All the type patterns for a generic type constructor must be identical")
799 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
801 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
802 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")