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
27 import TcHsType ( kcHsSigType, tcHsKindedType )
28 import TcUnify ( checkSigTyVars )
29 import TcSimplify ( tcSimplifySuperClasses )
30 import Type ( zipOpenTvSubst, substTheta, mkTyConApp, mkTyVarTy,
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(..) )
50 Typechecking instance declarations is done in two passes. The first
51 pass, made by @tcInstDecls1@, collects information to be used in the
54 This pre-processed info includes the as-yet-unprocessed bindings
55 inside the instance declaration. These are type-checked in the second
56 pass, when the class-instance envs and GVE contain all the info from
57 all the instance and value decls. Indeed that's the reason we need
58 two passes over the instance decls.
60 Here is the overall algorithm.
61 Assume that we have an instance declaration
63 instance c => k (t tvs) where b
67 $LIE_c$ is the LIE for the context of class $c$
69 $betas_bar$ is the free variables in the class method type, excluding the
72 $LIE_cop$ is the LIE constraining a particular class method
74 $tau_cop$ is the tau type of a class method
76 $LIE_i$ is the LIE for the context of instance $i$
78 $X$ is the instance constructor tycon
80 $gammas_bar$ is the set of type variables of the instance
82 $LIE_iop$ is the LIE for a particular class method instance
84 $tau_iop$ is the tau type for this instance of a class method
86 $alpha$ is the class variable
88 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
90 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
93 ToDo: Update the list above with names actually in the code.
97 First, make the LIEs for the class and instance contexts, which means
98 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
99 and make LIElistI and LIEI.
101 Then process each method in turn.
103 order the instance methods according to the ordering of the class methods
105 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
107 Create final dictionary function from bindings generated already
109 df = lambda inst_tyvars
116 in <op1,op2,...,opn,sd1,...,sdm>
118 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
119 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
123 %************************************************************************
125 \subsection{Extracting instance decls}
127 %************************************************************************
129 Gather up the instance declarations from their various sources
132 tcInstDecls1 -- Deal with both source-code and imported instance decls
133 :: [LTyClDecl Name] -- For deriving stuff
134 -> [LInstDecl Name] -- Source code instance decls
135 -> TcM (TcGblEnv, -- The full inst env
136 [InstInfo], -- Source-code instance decls to process;
137 -- contains all dfuns for this module
138 HsValBinds Name) -- Supporting bindings for derived instances
140 tcInstDecls1 tycl_decls inst_decls
142 do { -- Stop if addInstInfos etc discovers any errors
143 -- (they recover, so that we get more than one error each
146 -- (1) Do the ordinary instance declarations and instances of
148 ; let { idxty_decls = filter (isIdxTyDecl . unLoc) tycl_decls }
149 ; local_inst_infos <- mappM tcLocalInstDecl1 inst_decls
150 ; idxty_inst_infos <- mappM tcIdxTyInstDecl idxty_decls
152 ; let { local_inst_info = concat local_inst_infos ++
153 catMaybes idxty_inst_infos
154 ; clas_decls = filter (isClassDecl.unLoc) tycl_decls }
156 -- (2) Instances from generic class declarations
157 ; generic_inst_info <- getGenericInstances clas_decls
159 -- Next, construct the instance environment so far, consisting
161 -- a) local instance decls
162 -- b) generic instances
163 ; addInsts local_inst_info $ do {
164 ; addInsts generic_inst_info $ do {
166 -- (3) Compute instances from "deriving" clauses;
167 -- This stuff computes a context for the derived instance
168 -- decl, so it needs to know about all the instances possible
169 ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls
170 ; addInsts deriv_inst_info $ do {
172 ; gbl_env <- getGblEnv
174 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
178 addInsts :: [InstInfo] -> TcM a -> TcM a
179 addInsts infos thing_inside
180 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
184 tcLocalInstDecl1 :: LInstDecl Name
185 -> TcM [InstInfo] -- [] if there was an error
186 -- A source-file instance declaration
187 -- Type-check all the stuff before the "where"
189 -- We check for respectable instance type, and context
190 tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
191 = -- Prime error recovery, set source location
192 recoverM (returnM []) $
194 addErrCtxt (instDeclCtxt1 poly_ty) $
196 do { is_boot <- tcIsHsBoot
197 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
200 -- Typecheck the instance type itself. We can't use
201 -- tcHsSigType, because it's not a valid user type.
202 ; kinded_ty <- kcHsSigType poly_ty
203 ; poly_ty' <- tcHsKindedType kinded_ty
204 ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
206 -- Now, check the validity of the instance.
207 ; (clas, inst_tys) <- checkValidInstHead tau
208 ; checkValidInstance tyvars theta clas inst_tys
210 -- Next, process any associated types.
211 ; idxty_inst_info <- mappM tcIdxTyInstDecl ats
213 -- Finally, construct the Core representation of the instance.
214 -- (This no longer includes the associated types.)
215 ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
216 ; overlap_flag <- getOverlapFlag
217 ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
218 ispec = mkLocalInstance dfun overlap_flag
220 ; return $ [InstInfo { iSpec = ispec,
221 iBinds = VanillaInst binds uprags }] ++
222 catMaybes idxty_inst_info }
226 %************************************************************************
228 \subsection{Type-checking instance declarations, pass 2}
230 %************************************************************************
233 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
234 -> TcM (LHsBinds Id, TcLclEnv)
235 -- (a) From each class declaration,
236 -- generate any default-method bindings
237 -- (b) From each instance decl
238 -- generate the dfun binding
240 tcInstDecls2 tycl_decls inst_decls
241 = do { -- (a) Default methods from class decls
242 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
243 filter (isClassDecl.unLoc) tycl_decls
244 ; tcExtendIdEnv (concat dm_ids_s) $ do
246 -- (b) instance declarations
247 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
250 ; let binds = unionManyBags dm_binds_s `unionBags`
251 unionManyBags inst_binds_s
252 ; tcl_env <- getLclEnv -- Default method Ids in here
253 ; returnM (binds, tcl_env) }
256 ======= New documentation starts here (Sept 92) ==============
258 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
259 the dictionary function for this instance declaration. For example
261 instance Foo a => Foo [a] where
265 might generate something like
267 dfun.Foo.List dFoo_a = let op1 x = ...
273 HOWEVER, if the instance decl has no context, then it returns a
274 bigger @HsBinds@ with declarations for each method. For example
276 instance Foo [a] where
282 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
283 const.Foo.op1.List a x = ...
284 const.Foo.op2.List a y = ...
286 This group may be mutually recursive, because (for example) there may
287 be no method supplied for op2 in which case we'll get
289 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
291 that is, the default method applied to the dictionary at this type.
293 What we actually produce in either case is:
295 AbsBinds [a] [dfun_theta_dicts]
296 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
297 { d = (sd1,sd2, ..., op1, op2, ...)
302 The "maybe" says that we only ask AbsBinds to make global constant methods
303 if the dfun_theta is empty.
306 For an instance declaration, say,
308 instance (C1 a, C2 b) => C (T a b) where
311 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
312 function whose type is
314 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
316 Notice that we pass it the superclass dictionaries at the instance type; this
317 is the ``Mark Jones optimisation''. The stuff before the "=>" here
318 is the @dfun_theta@ below.
320 First comes the easy case of a non-local instance decl.
324 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
325 -- Returns a binding for the dfun
327 ------------------------
328 -- Derived newtype instances
330 -- We need to make a copy of the dictionary we are deriving from
331 -- because we may need to change some of the superclass dictionaries
332 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
334 -- In the case of a newtype, things are rather easy
335 -- class Show a => Foo a b where ...
336 -- newtype T a = MkT (Tree [a]) deriving( Foo Int )
337 -- The newtype gives an FC axiom looking like
338 -- axiom CoT a :: T a :=: Tree [a]
340 -- So all need is to generate a binding looking like
341 -- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
342 -- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
343 -- case df `cast` (Foo Int (sym (CoT a))) of
344 -- Foo _ op1 .. opn -> Foo ds op1 .. opn
346 tcInstDecl2 (InstInfo { iSpec = ispec,
347 iBinds = NewTypeDerived tycon rep_tys })
348 = do { let dfun_id = instanceDFunId ispec
349 rigid_info = InstSkol dfun_id
350 origin = SigOrigin rigid_info
351 inst_ty = idType dfun_id
352 ; inst_loc <- getInstLoc origin
353 ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
354 ; dicts <- newDictBndrs inst_loc theta
355 ; uniqs <- newUniqueSupply
356 ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
357 ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
358 ; let (rep_dict_id:sc_dict_ids)
359 | null dicts = [instToId this_dict]
360 | otherwise = map instToId dicts
362 -- (Here, we are relying on the order of dictionary
363 -- arguments built by NewTypeDerived in TcDeriv.)
365 wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
367 -- we need to find the kind that this class applies to
368 -- and drop trailing tvs appropriately
369 cls_kind = tyVarKind (head (reverse (tyConTyVars cls_tycon)))
370 the_tvs = drop_tail (length (fst (splitFunTys cls_kind))) tvs
372 coerced_rep_dict = mkHsCoerce (co_fn the_tvs cls_tycon cls_inst_tys) (HsVar rep_dict_id)
374 body | null sc_dict_ids = coerced_rep_dict
375 | otherwise = HsCase (noLoc coerced_rep_dict) $
376 MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
377 in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
379 the_match = mkSimpleMatch [noLoc the_pat] the_rhs
380 the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
382 (uniqs1, uniqs2) = splitUniqSupply uniqs
384 op_ids = zipWith (mkSysLocal FSLIT("op"))
385 (uniqsFromSupply uniqs1) op_tys
387 dict_ids = zipWith (mkSysLocal FSLIT("dict"))
388 (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
390 the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
391 pat_dicts = dict_ids,
392 pat_binds = emptyLHsBinds,
393 pat_args = PrefixCon (map nlVarPat op_ids),
396 cls_data_con = classDataCon cls
397 cls_tycon = dataConTyCon cls_data_con
398 cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
400 n_dict_args = if length dicts == 0 then 0 else length dicts - 1
401 op_tys = drop n_dict_args cls_arg_tys
403 dict = mkHsCoerce wrap_fn body
404 ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
406 -- For newtype T a = MkT <ty>
407 -- The returned coercion has kind :: C (T a):=:C <ty>
408 co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
409 = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
410 [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
413 drop_tail n l = take (length l - n) l
415 ------------------------
416 -- Ordinary instances
418 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
420 dfun_id = instanceDFunId ispec
421 rigid_info = InstSkol dfun_id
422 inst_ty = idType dfun_id
424 -- Prime error recovery
425 recoverM (returnM emptyLHsBinds) $
426 setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
427 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
429 -- Instantiate the instance decl with skolem constants
430 tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
431 -- These inst_tyvars' scope over the 'where' part
432 -- Those tyvars are inside the dfun_id's type, which is a bit
433 -- bizarre, but OK so long as you realise it!
435 (clas, inst_tys') = tcSplitDFunHead inst_head'
436 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
438 -- Instantiate the super-class context with inst_tys
439 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
440 origin = SigOrigin rigid_info
442 -- Create dictionary Ids from the specified instance contexts.
443 getInstLoc InstScOrigin `thenM` \ sc_loc ->
444 newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
445 getInstLoc origin `thenM` \ inst_loc ->
446 newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
447 newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
448 -- Default-method Ids may be mentioned in synthesised RHSs,
449 -- but they'll already be in the environment.
451 -- Typecheck the methods
452 let -- These insts are in scope; quite a few, eh?
453 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
455 tcMethods origin clas inst_tyvars'
456 dfun_theta' inst_tys' avail_insts
457 op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
459 -- Figure out bindings for the superclass context
460 -- Don't include this_dict in the 'givens', else
461 -- sc_dicts get bound by just selecting from this_dict!!
462 addErrCtxt superClassCtxt
463 (tcSimplifySuperClasses inst_tyvars'
465 sc_dicts) `thenM` \ sc_binds ->
467 -- It's possible that the superclass stuff might unified one
468 -- of the inst_tyavars' with something in the envt
469 checkSigTyVars inst_tyvars' `thenM_`
471 -- Deal with 'SPECIALISE instance' pragmas
472 tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
474 -- Create the result bindings
476 dict_constr = classDataCon clas
477 scs_and_meths = map instToId sc_dicts ++ meth_ids
478 this_dict_id = instToId this_dict
479 inline_prag | null dfun_arg_dicts = []
480 | otherwise = [InlinePrag (Inline AlwaysActive True)]
481 -- Always inline the dfun; this is an experimental decision
482 -- because it makes a big performance difference sometimes.
483 -- Often it means we can do the method selection, and then
484 -- inline the method as well. Marcin's idea; see comments below.
486 -- BUT: don't inline it if it's a constant dictionary;
487 -- we'll get all the benefit without inlining, and we get
488 -- a **lot** of code duplication if we inline it
490 -- See Note [Inline dfuns] below
493 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
494 -- We don't produce a binding for the dict_constr; instead we
495 -- rely on the simplifier to unfold this saturated application
496 -- We do this rather than generate an HsCon directly, because
497 -- it means that the special cases (e.g. dictionary with only one
498 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
499 -- than needing to be repeated here.
501 dict_bind = noLoc (VarBind this_dict_id dict_rhs)
502 all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
504 main_bind = noLoc $ AbsBinds
506 (map instToId dfun_arg_dicts)
507 [(inst_tyvars', dfun_id, this_dict_id,
508 inline_prag ++ prags)]
511 showLIE (text "instance") `thenM_`
512 returnM (unitBag main_bind)
515 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
516 avail_insts op_items monobinds uprags
517 = -- Check that all the method bindings come from this class
519 sel_names = [idName sel_id | (sel_id, _) <- op_items]
520 bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
522 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
524 -- Make the method bindings
526 mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
528 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
530 -- And type check them
531 -- It's really worth making meth_insts available to the tcMethodBind
532 -- Consider instance Monad (ST s) where
533 -- {-# INLINE (>>) #-}
534 -- (>>) = ...(>>=)...
535 -- If we don't include meth_insts, we end up with bindings like this:
536 -- rec { dict = MkD then bind ...
537 -- then = inline_me (... (GHC.Base.>>= dict) ...)
539 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
540 -- and (b) the inline_me prevents us inlining the >>= selector, which
541 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
542 -- is not inlined across modules. Rather ironic since this does not
543 -- happen without the INLINE pragma!
545 -- Solution: make meth_insts available, so that 'then' refers directly
546 -- to the local 'bind' rather than going via the dictionary.
548 -- BUT WATCH OUT! If the method type mentions the class variable, then
549 -- this optimisation is not right. Consider
553 -- instance C Int where
555 -- The occurrence of 'op' on the rhs gives rise to a constraint
557 -- The trouble is that the 'meth_inst' for op, which is 'available', also
558 -- looks like 'op at Int'. But they are not the same.
560 prag_fn = mkPragFun uprags
561 all_insts = avail_insts ++ catMaybes meth_insts
562 sig_fn n = Just [] -- No scoped type variables, but every method has
563 -- a type signature, in effect, so that we check
564 -- the method has the right type
565 tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
566 meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
569 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
571 returnM (meth_ids, unionManyBags meth_binds_s)
575 ------------------------------
576 [Inline dfuns] Inlining dfuns unconditionally
577 ------------------------------
579 The code above unconditionally inlines dict funs. Here's why.
580 Consider this program:
582 test :: Int -> Int -> Bool
583 test x y = (x,y) == (y,x) || test y x
584 -- Recursive to avoid making it inline.
586 This needs the (Eq (Int,Int)) instance. If we inline that dfun
587 the code we end up with is good:
590 \r -> case ==# [ww ww1] of wild {
591 PrelBase.False -> Test.$wtest ww1 ww;
593 case ==# [ww1 ww] of wild1 {
594 PrelBase.False -> Test.$wtest ww1 ww;
595 PrelBase.True -> PrelBase.True [];
598 Test.test = \r [w w1]
601 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
604 If we don't inline the dfun, the code is not nearly as good:
606 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
607 PrelBase.:DEq tpl1 tpl2 -> tpl2;
612 let { y = PrelBase.I#! [ww1]; } in
613 let { x = PrelBase.I#! [ww]; } in
614 let { sat_slx = PrelTup.(,)! [y x]; } in
615 let { sat_sly = PrelTup.(,)! [x y];
617 case == sat_sly sat_slx of wild {
618 PrelBase.False -> Test.$wtest ww1 ww;
619 PrelBase.True -> PrelBase.True [];
626 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
629 Why doesn't GHC inline $fEq? Because it looks big:
631 PrelTup.zdfEqZ1T{-rcX-}
632 = \ @ a{-reT-} :: * @ b{-reS-} :: *
633 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
634 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
636 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
637 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
639 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
640 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
642 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
643 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
644 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
646 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
648 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
650 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
651 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
655 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
656 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
657 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
658 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
660 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
662 and it's not as bad as it seems, because it's further dramatically
663 simplified: only zeze2 is extracted and its body is simplified.
666 %************************************************************************
668 \subsection{Error messages}
670 %************************************************************************
673 instDeclCtxt1 hs_inst_ty
674 = inst_decl_ctxt (case unLoc hs_inst_ty of
675 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
676 HsPredTy pred -> ppr pred
677 other -> ppr hs_inst_ty) -- Don't expect this
678 instDeclCtxt2 dfun_ty
679 = inst_decl_ctxt (ppr (mkClassPred cls tys))
681 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
683 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
685 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")