2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcInstDecls]{Typechecking instance declarations}
7 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
9 #include "HsVersions.h"
12 import TcBinds ( mkPragFun, tcPrags, badBootDeclErr )
13 import TcTyClsDecls ( tcIdxTyInstDecl )
14 import TcClassDcl ( tcMethodBind, mkMethodBind, badMethodErr,
15 tcClassDecl2, getGenericInstances )
17 import TcMType ( tcSkolSigType, checkValidInstance, checkValidInstHead )
18 import TcType ( mkClassPred, tcSplitSigmaTy, tcSplitDFunHead,
19 SkolemInfo(InstSkol), tcSplitDFunTy, mkFunTy )
20 import Inst ( newDictBndr, newDictBndrs, instToId, showLIE,
21 getOverlapFlag, tcExtendLocalInstEnv )
22 import InstEnv ( mkLocalInstance, instanceDFunId )
23 import TcDeriv ( tcDeriving )
24 import TcEnv ( InstInfo(..), InstBindings(..),
25 newDFunName, tcExtendIdEnv, tcExtendGlobalEnv
27 import TcHsType ( kcHsSigType, tcHsKindedType )
28 import TcUnify ( checkSigTyVars )
29 import TcSimplify ( tcSimplifySuperClasses )
30 import Type ( zipOpenTvSubst, substTheta, mkTyConApp, mkTyVarTy,
31 splitFunTys, TyThing )
32 import Coercion ( mkSymCoercion )
33 import TyCon ( TyCon, newTyConCo, tyConTyVars )
34 import DataCon ( classDataCon, dataConTyCon, dataConInstArgTys )
35 import Class ( classBigSig )
36 import Var ( TyVar, Id, idName, idType, tyVarKind )
37 import Id ( mkSysLocal )
38 import UniqSupply ( uniqsFromSupply, splitUniqSupply )
39 import MkId ( mkDictFunId )
40 import Name ( Name, getSrcLoc )
41 import Maybe ( catMaybes )
42 import SrcLoc ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
43 import ListSetOps ( minusList )
46 import BasicTypes ( Activation( AlwaysActive ), InlineSpec(..) )
47 import HscTypes ( implicitTyThings )
51 Typechecking instance declarations is done in two passes. The first
52 pass, made by @tcInstDecls1@, collects information to be used in the
55 This pre-processed info includes the as-yet-unprocessed bindings
56 inside the instance declaration. These are type-checked in the second
57 pass, when the class-instance envs and GVE contain all the info from
58 all the instance and value decls. Indeed that's the reason we need
59 two passes over the instance decls.
61 Here is the overall algorithm.
62 Assume that we have an instance declaration
64 instance c => k (t tvs) where b
68 $LIE_c$ is the LIE for the context of class $c$
70 $betas_bar$ is the free variables in the class method type, excluding the
73 $LIE_cop$ is the LIE constraining a particular class method
75 $tau_cop$ is the tau type of a class method
77 $LIE_i$ is the LIE for the context of instance $i$
79 $X$ is the instance constructor tycon
81 $gammas_bar$ is the set of type variables of the instance
83 $LIE_iop$ is the LIE for a particular class method instance
85 $tau_iop$ is the tau type for this instance of a class method
87 $alpha$ is the class variable
89 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
91 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
94 ToDo: Update the list above with names actually in the code.
98 First, make the LIEs for the class and instance contexts, which means
99 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
100 and make LIElistI and LIEI.
102 Then process each method in turn.
104 order the instance methods according to the ordering of the class methods
106 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
108 Create final dictionary function from bindings generated already
110 df = lambda inst_tyvars
117 in <op1,op2,...,opn,sd1,...,sdm>
119 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
120 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
124 %************************************************************************
126 \subsection{Extracting instance decls}
128 %************************************************************************
130 Gather up the instance declarations from their various sources
133 tcInstDecls1 -- Deal with both source-code and imported instance decls
134 :: [LTyClDecl Name] -- For deriving stuff
135 -> [LInstDecl Name] -- Source code instance decls
136 -> TcM (TcGblEnv, -- The full inst env
137 [InstInfo], -- Source-code instance decls to process;
138 -- contains all dfuns for this module
139 HsValBinds Name) -- Supporting bindings for derived instances
141 tcInstDecls1 tycl_decls inst_decls
143 do { -- Stop if addInstInfos etc discovers any errors
144 -- (they recover, so that we get more than one error each
147 -- (1) Do the ordinary instance declarations and instances of
149 ; let { idxty_decls = filter (isIdxTyDecl . unLoc) tycl_decls }
150 ; local_info_tycons <- mappM tcLocalInstDecl1 inst_decls
151 ; idxty_info_tycons <- mappM tcIdxTyInstDecl idxty_decls
153 ; let { (local_infos,
154 local_tycons) = unzip local_info_tycons
156 idxty_tycons) = unzip idxty_info_tycons
157 ; local_idxty_info = concat local_infos ++ catMaybes idxty_infos
158 ; local_idxty_tycon = concat local_tycons ++
159 catMaybes idxty_tycons
160 ; clas_decls = filter (isClassDecl.unLoc) tycl_decls
161 ; implicit_things = concatMap implicitTyThings local_idxty_tycon
164 -- (2) Add the tycons of associated types and their implicit
165 -- tythings to the global environment
166 ; tcExtendGlobalEnv (local_idxty_tycon ++ implicit_things) $ do {
168 -- (3) Instances from generic class declarations
169 ; generic_inst_info <- getGenericInstances clas_decls
171 -- Next, construct the instance environment so far, consisting
173 -- a) local instance decls
174 -- b) generic instances
175 ; addInsts local_idxty_info $ do {
176 ; addInsts generic_inst_info $ do {
178 -- (4) Compute instances from "deriving" clauses;
179 -- This stuff computes a context for the derived instance
180 -- decl, so it needs to know about all the instances possible
181 ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls
182 ; addInsts deriv_inst_info $ do {
184 ; gbl_env <- getGblEnv
186 generic_inst_info ++ deriv_inst_info ++ local_idxty_info,
190 addInsts :: [InstInfo] -> TcM a -> TcM a
191 addInsts infos thing_inside
192 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
196 tcLocalInstDecl1 :: LInstDecl Name
197 -> TcM ([InstInfo], [TyThing]) -- [] if there was an error
198 -- A source-file instance declaration
199 -- Type-check all the stuff before the "where"
201 -- We check for respectable instance type, and context
202 tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
203 = -- Prime error recovery, set source location
204 recoverM (returnM ([], [])) $
206 addErrCtxt (instDeclCtxt1 poly_ty) $
208 do { is_boot <- tcIsHsBoot
209 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
212 -- Typecheck the instance type itself. We can't use
213 -- tcHsSigType, because it's not a valid user type.
214 ; kinded_ty <- kcHsSigType poly_ty
215 ; poly_ty' <- tcHsKindedType kinded_ty
216 ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
218 -- Now, check the validity of the instance.
219 ; (clas, inst_tys) <- checkValidInstHead tau
220 ; checkValidInstance tyvars theta clas inst_tys
222 -- Next, process any associated types.
223 ; idxty_info_tycons <- mappM tcIdxTyInstDecl ats
225 -- Finally, construct the Core representation of the instance.
226 -- (This no longer includes the associated types.)
227 ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
228 ; overlap_flag <- getOverlapFlag
229 ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
230 ispec = mkLocalInstance dfun overlap_flag
232 idxty_tycons) = unzip idxty_info_tycons
234 ; return ([InstInfo { iSpec = ispec,
235 iBinds = VanillaInst binds uprags }] ++
236 catMaybes idxty_infos,
237 catMaybes idxty_tycons)
242 %************************************************************************
244 \subsection{Type-checking instance declarations, pass 2}
246 %************************************************************************
249 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
250 -> TcM (LHsBinds Id, TcLclEnv)
251 -- (a) From each class declaration,
252 -- generate any default-method bindings
253 -- (b) From each instance decl
254 -- generate the dfun binding
256 tcInstDecls2 tycl_decls inst_decls
257 = do { -- (a) Default methods from class decls
258 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
259 filter (isClassDecl.unLoc) tycl_decls
260 ; tcExtendIdEnv (concat dm_ids_s) $ do
262 -- (b) instance declarations
263 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
266 ; let binds = unionManyBags dm_binds_s `unionBags`
267 unionManyBags inst_binds_s
268 ; tcl_env <- getLclEnv -- Default method Ids in here
269 ; returnM (binds, tcl_env) }
272 ======= New documentation starts here (Sept 92) ==============
274 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
275 the dictionary function for this instance declaration. For example
277 instance Foo a => Foo [a] where
281 might generate something like
283 dfun.Foo.List dFoo_a = let op1 x = ...
289 HOWEVER, if the instance decl has no context, then it returns a
290 bigger @HsBinds@ with declarations for each method. For example
292 instance Foo [a] where
298 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
299 const.Foo.op1.List a x = ...
300 const.Foo.op2.List a y = ...
302 This group may be mutually recursive, because (for example) there may
303 be no method supplied for op2 in which case we'll get
305 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
307 that is, the default method applied to the dictionary at this type.
309 What we actually produce in either case is:
311 AbsBinds [a] [dfun_theta_dicts]
312 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
313 { d = (sd1,sd2, ..., op1, op2, ...)
318 The "maybe" says that we only ask AbsBinds to make global constant methods
319 if the dfun_theta is empty.
322 For an instance declaration, say,
324 instance (C1 a, C2 b) => C (T a b) where
327 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
328 function whose type is
330 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
332 Notice that we pass it the superclass dictionaries at the instance type; this
333 is the ``Mark Jones optimisation''. The stuff before the "=>" here
334 is the @dfun_theta@ below.
336 First comes the easy case of a non-local instance decl.
340 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
341 -- Returns a binding for the dfun
343 ------------------------
344 -- Derived newtype instances
346 -- We need to make a copy of the dictionary we are deriving from
347 -- because we may need to change some of the superclass dictionaries
348 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
350 -- In the case of a newtype, things are rather easy
351 -- class Show a => Foo a b where ...
352 -- newtype T a = MkT (Tree [a]) deriving( Foo Int )
353 -- The newtype gives an FC axiom looking like
354 -- axiom CoT a :: T a :=: Tree [a]
356 -- So all need is to generate a binding looking like
357 -- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
358 -- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
359 -- case df `cast` (Foo Int (sym (CoT a))) of
360 -- Foo _ op1 .. opn -> Foo ds op1 .. opn
362 tcInstDecl2 (InstInfo { iSpec = ispec,
363 iBinds = NewTypeDerived tycon rep_tys })
364 = do { let dfun_id = instanceDFunId ispec
365 rigid_info = InstSkol dfun_id
366 origin = SigOrigin rigid_info
367 inst_ty = idType dfun_id
368 ; inst_loc <- getInstLoc origin
369 ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
370 ; dicts <- newDictBndrs inst_loc theta
371 ; uniqs <- newUniqueSupply
372 ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
373 ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
374 ; let (rep_dict_id:sc_dict_ids)
375 | null dicts = [instToId this_dict]
376 | otherwise = map instToId dicts
378 -- (Here, we are relying on the order of dictionary
379 -- arguments built by NewTypeDerived in TcDeriv.)
381 wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
383 -- we need to find the kind that this class applies to
384 -- and drop trailing tvs appropriately
385 cls_kind = tyVarKind (head (reverse (tyConTyVars cls_tycon)))
386 the_tvs = drop_tail (length (fst (splitFunTys cls_kind))) tvs
388 coerced_rep_dict = mkHsCoerce (co_fn the_tvs cls_tycon cls_inst_tys) (HsVar rep_dict_id)
390 body | null sc_dict_ids = coerced_rep_dict
391 | otherwise = HsCase (noLoc coerced_rep_dict) $
392 MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
393 in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
395 the_match = mkSimpleMatch [noLoc the_pat] the_rhs
396 the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
398 (uniqs1, uniqs2) = splitUniqSupply uniqs
400 op_ids = zipWith (mkSysLocal FSLIT("op"))
401 (uniqsFromSupply uniqs1) op_tys
403 dict_ids = zipWith (mkSysLocal FSLIT("dict"))
404 (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
406 the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
407 pat_dicts = dict_ids,
408 pat_binds = emptyLHsBinds,
409 pat_args = PrefixCon (map nlVarPat op_ids),
412 cls_data_con = classDataCon cls
413 cls_tycon = dataConTyCon cls_data_con
414 cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
416 n_dict_args = if length dicts == 0 then 0 else length dicts - 1
417 op_tys = drop n_dict_args cls_arg_tys
419 dict = mkHsCoerce wrap_fn body
420 ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
422 -- For newtype T a = MkT <ty>
423 -- The returned coercion has kind :: C (T a):=:C <ty>
424 co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
425 = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
426 [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
429 drop_tail n l = take (length l - n) l
431 ------------------------
432 -- Ordinary instances
434 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
436 dfun_id = instanceDFunId ispec
437 rigid_info = InstSkol dfun_id
438 inst_ty = idType dfun_id
440 -- Prime error recovery
441 recoverM (returnM emptyLHsBinds) $
442 setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
443 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
445 -- Instantiate the instance decl with skolem constants
446 tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
447 -- These inst_tyvars' scope over the 'where' part
448 -- Those tyvars are inside the dfun_id's type, which is a bit
449 -- bizarre, but OK so long as you realise it!
451 (clas, inst_tys') = tcSplitDFunHead inst_head'
452 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
454 -- Instantiate the super-class context with inst_tys
455 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
456 origin = SigOrigin rigid_info
458 -- Create dictionary Ids from the specified instance contexts.
459 getInstLoc InstScOrigin `thenM` \ sc_loc ->
460 newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
461 getInstLoc origin `thenM` \ inst_loc ->
462 newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
463 newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
464 -- Default-method Ids may be mentioned in synthesised RHSs,
465 -- but they'll already be in the environment.
467 -- Typecheck the methods
468 let -- These insts are in scope; quite a few, eh?
469 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
471 tcMethods origin clas inst_tyvars'
472 dfun_theta' inst_tys' avail_insts
473 op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
475 -- Figure out bindings for the superclass context
476 -- Don't include this_dict in the 'givens', else
477 -- sc_dicts get bound by just selecting from this_dict!!
478 addErrCtxt superClassCtxt
479 (tcSimplifySuperClasses inst_tyvars'
481 sc_dicts) `thenM` \ sc_binds ->
483 -- It's possible that the superclass stuff might unified one
484 -- of the inst_tyavars' with something in the envt
485 checkSigTyVars inst_tyvars' `thenM_`
487 -- Deal with 'SPECIALISE instance' pragmas
488 tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
490 -- Create the result bindings
492 dict_constr = classDataCon clas
493 scs_and_meths = map instToId sc_dicts ++ meth_ids
494 this_dict_id = instToId this_dict
495 inline_prag | null dfun_arg_dicts = []
496 | otherwise = [InlinePrag (Inline AlwaysActive True)]
497 -- Always inline the dfun; this is an experimental decision
498 -- because it makes a big performance difference sometimes.
499 -- Often it means we can do the method selection, and then
500 -- inline the method as well. Marcin's idea; see comments below.
502 -- BUT: don't inline it if it's a constant dictionary;
503 -- we'll get all the benefit without inlining, and we get
504 -- a **lot** of code duplication if we inline it
506 -- See Note [Inline dfuns] below
509 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
510 -- We don't produce a binding for the dict_constr; instead we
511 -- rely on the simplifier to unfold this saturated application
512 -- We do this rather than generate an HsCon directly, because
513 -- it means that the special cases (e.g. dictionary with only one
514 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
515 -- than needing to be repeated here.
517 dict_bind = noLoc (VarBind this_dict_id dict_rhs)
518 all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
520 main_bind = noLoc $ AbsBinds
522 (map instToId dfun_arg_dicts)
523 [(inst_tyvars', dfun_id, this_dict_id,
524 inline_prag ++ prags)]
527 showLIE (text "instance") `thenM_`
528 returnM (unitBag main_bind)
531 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
532 avail_insts op_items monobinds uprags
533 = -- Check that all the method bindings come from this class
535 sel_names = [idName sel_id | (sel_id, _) <- op_items]
536 bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
538 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
540 -- Make the method bindings
542 mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
544 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
546 -- And type check them
547 -- It's really worth making meth_insts available to the tcMethodBind
548 -- Consider instance Monad (ST s) where
549 -- {-# INLINE (>>) #-}
550 -- (>>) = ...(>>=)...
551 -- If we don't include meth_insts, we end up with bindings like this:
552 -- rec { dict = MkD then bind ...
553 -- then = inline_me (... (GHC.Base.>>= dict) ...)
555 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
556 -- and (b) the inline_me prevents us inlining the >>= selector, which
557 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
558 -- is not inlined across modules. Rather ironic since this does not
559 -- happen without the INLINE pragma!
561 -- Solution: make meth_insts available, so that 'then' refers directly
562 -- to the local 'bind' rather than going via the dictionary.
564 -- BUT WATCH OUT! If the method type mentions the class variable, then
565 -- this optimisation is not right. Consider
569 -- instance C Int where
571 -- The occurrence of 'op' on the rhs gives rise to a constraint
573 -- The trouble is that the 'meth_inst' for op, which is 'available', also
574 -- looks like 'op at Int'. But they are not the same.
576 prag_fn = mkPragFun uprags
577 all_insts = avail_insts ++ catMaybes meth_insts
578 sig_fn n = Just [] -- No scoped type variables, but every method has
579 -- a type signature, in effect, so that we check
580 -- the method has the right type
581 tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
582 meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
585 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
587 returnM (meth_ids, unionManyBags meth_binds_s)
591 ------------------------------
592 [Inline dfuns] Inlining dfuns unconditionally
593 ------------------------------
595 The code above unconditionally inlines dict funs. Here's why.
596 Consider this program:
598 test :: Int -> Int -> Bool
599 test x y = (x,y) == (y,x) || test y x
600 -- Recursive to avoid making it inline.
602 This needs the (Eq (Int,Int)) instance. If we inline that dfun
603 the code we end up with is good:
606 \r -> case ==# [ww ww1] of wild {
607 PrelBase.False -> Test.$wtest ww1 ww;
609 case ==# [ww1 ww] of wild1 {
610 PrelBase.False -> Test.$wtest ww1 ww;
611 PrelBase.True -> PrelBase.True [];
614 Test.test = \r [w w1]
617 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
620 If we don't inline the dfun, the code is not nearly as good:
622 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
623 PrelBase.:DEq tpl1 tpl2 -> tpl2;
628 let { y = PrelBase.I#! [ww1]; } in
629 let { x = PrelBase.I#! [ww]; } in
630 let { sat_slx = PrelTup.(,)! [y x]; } in
631 let { sat_sly = PrelTup.(,)! [x y];
633 case == sat_sly sat_slx of wild {
634 PrelBase.False -> Test.$wtest ww1 ww;
635 PrelBase.True -> PrelBase.True [];
642 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
645 Why doesn't GHC inline $fEq? Because it looks big:
647 PrelTup.zdfEqZ1T{-rcX-}
648 = \ @ a{-reT-} :: * @ b{-reS-} :: *
649 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
650 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
652 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
653 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
655 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
656 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
658 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
659 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
660 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
662 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
664 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
666 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
667 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
671 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
672 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
673 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
674 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
676 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
678 and it's not as bad as it seems, because it's further dramatically
679 simplified: only zeze2 is extracted and its body is simplified.
682 %************************************************************************
684 \subsection{Error messages}
686 %************************************************************************
689 instDeclCtxt1 hs_inst_ty
690 = inst_decl_ctxt (case unLoc hs_inst_ty of
691 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
692 HsPredTy pred -> ppr pred
693 other -> ppr hs_inst_ty) -- Don't expect this
694 instDeclCtxt2 dfun_ty
695 = inst_decl_ctxt (ppr (mkClassPred cls tys))
697 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
699 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
701 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")