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 TcClassDcl ( tcMethodBind, mkMethodBind, badMethodErr,
14 tcClassDecl2, getGenericInstances )
16 import TcMType ( tcSkolSigType, checkValidInstance, checkValidInstHead )
17 import TcType ( mkClassPred, tcSplitSigmaTy, tcSplitDFunHead,
18 SkolemInfo(InstSkol), tcSplitDFunTy, mkFunTy )
19 import Inst ( newDictBndr, newDictBndrs, instToId, showLIE,
20 getOverlapFlag, tcExtendLocalInstEnv )
21 import InstEnv ( mkLocalInstance, instanceDFunId )
22 import TcDeriv ( tcDeriving )
23 import TcEnv ( InstInfo(..), InstBindings(..),
24 newDFunName, tcExtendIdEnv
26 import TcHsType ( kcHsSigType, tcHsKindedType )
27 import TcUnify ( checkSigTyVars )
28 import TcSimplify ( tcSimplifySuperClasses )
29 import Type ( zipOpenTvSubst, substTheta, mkTyConApp, mkTyVarTy,
31 import Coercion ( mkSymCoercion )
32 import TyCon ( TyCon, newTyConCo, tyConTyVars )
33 import DataCon ( classDataCon, dataConTyCon, dataConInstArgTys )
34 import Class ( classBigSig )
35 import Var ( TyVar, Id, idName, idType, tyVarKind )
36 import Id ( mkSysLocal )
37 import UniqSupply ( uniqsFromSupply, splitUniqSupply )
38 import MkId ( mkDictFunId )
39 import Name ( Name, getSrcLoc )
40 import Maybe ( catMaybes )
41 import SrcLoc ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
42 import ListSetOps ( minusList )
45 import BasicTypes ( Activation( AlwaysActive ), InlineSpec(..) )
49 Typechecking instance declarations is done in two passes. The first
50 pass, made by @tcInstDecls1@, collects information to be used in the
53 This pre-processed info includes the as-yet-unprocessed bindings
54 inside the instance declaration. These are type-checked in the second
55 pass, when the class-instance envs and GVE contain all the info from
56 all the instance and value decls. Indeed that's the reason we need
57 two passes over the instance decls.
59 Here is the overall algorithm.
60 Assume that we have an instance declaration
62 instance c => k (t tvs) where b
66 $LIE_c$ is the LIE for the context of class $c$
68 $betas_bar$ is the free variables in the class method type, excluding the
71 $LIE_cop$ is the LIE constraining a particular class method
73 $tau_cop$ is the tau type of a class method
75 $LIE_i$ is the LIE for the context of instance $i$
77 $X$ is the instance constructor tycon
79 $gammas_bar$ is the set of type variables of the instance
81 $LIE_iop$ is the LIE for a particular class method instance
83 $tau_iop$ is the tau type for this instance of a class method
85 $alpha$ is the class variable
87 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
89 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
92 ToDo: Update the list above with names actually in the code.
96 First, make the LIEs for the class and instance contexts, which means
97 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
98 and make LIElistI and LIEI.
100 Then process each method in turn.
102 order the instance methods according to the ordering of the class methods
104 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
106 Create final dictionary function from bindings generated already
108 df = lambda inst_tyvars
115 in <op1,op2,...,opn,sd1,...,sdm>
117 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
118 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
122 %************************************************************************
124 \subsection{Extracting instance decls}
126 %************************************************************************
128 Gather up the instance declarations from their various sources
131 tcInstDecls1 -- Deal with both source-code and imported instance decls
132 :: [LTyClDecl Name] -- For deriving stuff
133 -> [LInstDecl Name] -- Source code instance decls
134 -> TcM (TcGblEnv, -- The full inst env
135 [InstInfo], -- Source-code instance decls to process;
136 -- contains all dfuns for this module
137 HsValBinds Name) -- Supporting bindings for derived instances
139 tcInstDecls1 tycl_decls inst_decls
141 -- Stop if addInstInfos etc discovers any errors
142 -- (they recover, so that we get more than one error each round)
144 -- (1) Do the ordinary instance declarations
145 mappM tcLocalInstDecl1 inst_decls `thenM` \ local_inst_infos ->
148 local_inst_info = catMaybes local_inst_infos
149 clas_decls = filter (isClassDecl.unLoc) tycl_decls
151 -- (2) Instances from generic class declarations
152 getGenericInstances clas_decls `thenM` \ generic_inst_info ->
154 -- Next, construct the instance environment so far, consisting of
155 -- a) local instance decls
156 -- b) generic instances
157 addInsts local_inst_info $
158 addInsts generic_inst_info $
160 -- (3) Compute instances from "deriving" clauses;
161 -- This stuff computes a context for the derived instance decl, so it
162 -- needs to know about all the instances possible; hence inst_env4
163 tcDeriving tycl_decls `thenM` \ (deriv_inst_info, deriv_binds) ->
164 addInsts deriv_inst_info $
166 getGblEnv `thenM` \ gbl_env ->
168 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
171 addInsts :: [InstInfo] -> TcM a -> TcM a
172 addInsts infos thing_inside
173 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
177 tcLocalInstDecl1 :: LInstDecl Name
178 -> TcM (Maybe InstInfo) -- Nothing if there was an error
179 -- A source-file instance declaration
180 -- Type-check all the stuff before the "where"
182 -- We check for respectable instance type, and context
183 tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
184 -- !!!TODO: Handle the `ats' parameter!!! -=chak
185 = -- Prime error recovery, set source location
186 recoverM (returnM Nothing) $
188 addErrCtxt (instDeclCtxt1 poly_ty) $
190 do { is_boot <- tcIsHsBoot
191 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
194 -- Typecheck the instance type itself. We can't use
195 -- tcHsSigType, because it's not a valid user type.
196 ; kinded_ty <- kcHsSigType poly_ty
197 ; poly_ty' <- tcHsKindedType kinded_ty
198 ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
200 ; (clas, inst_tys) <- checkValidInstHead tau
201 ; checkValidInstance tyvars theta clas inst_tys
203 ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
204 ; overlap_flag <- getOverlapFlag
205 ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
206 ispec = mkLocalInstance dfun overlap_flag
208 ; return (Just (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags })) }
212 %************************************************************************
214 \subsection{Type-checking instance declarations, pass 2}
216 %************************************************************************
219 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
220 -> TcM (LHsBinds Id, TcLclEnv)
221 -- (a) From each class declaration,
222 -- generate any default-method bindings
223 -- (b) From each instance decl
224 -- generate the dfun binding
226 tcInstDecls2 tycl_decls inst_decls
227 = do { -- (a) Default methods from class decls
228 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
229 filter (isClassDecl.unLoc) tycl_decls
230 ; tcExtendIdEnv (concat dm_ids_s) $ do
232 -- (b) instance declarations
233 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
236 ; let binds = unionManyBags dm_binds_s `unionBags`
237 unionManyBags inst_binds_s
238 ; tcl_env <- getLclEnv -- Default method Ids in here
239 ; returnM (binds, tcl_env) }
242 ======= New documentation starts here (Sept 92) ==============
244 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
245 the dictionary function for this instance declaration. For example
247 instance Foo a => Foo [a] where
251 might generate something like
253 dfun.Foo.List dFoo_a = let op1 x = ...
259 HOWEVER, if the instance decl has no context, then it returns a
260 bigger @HsBinds@ with declarations for each method. For example
262 instance Foo [a] where
268 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
269 const.Foo.op1.List a x = ...
270 const.Foo.op2.List a y = ...
272 This group may be mutually recursive, because (for example) there may
273 be no method supplied for op2 in which case we'll get
275 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
277 that is, the default method applied to the dictionary at this type.
279 What we actually produce in either case is:
281 AbsBinds [a] [dfun_theta_dicts]
282 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
283 { d = (sd1,sd2, ..., op1, op2, ...)
288 The "maybe" says that we only ask AbsBinds to make global constant methods
289 if the dfun_theta is empty.
292 For an instance declaration, say,
294 instance (C1 a, C2 b) => C (T a b) where
297 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
298 function whose type is
300 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
302 Notice that we pass it the superclass dictionaries at the instance type; this
303 is the ``Mark Jones optimisation''. The stuff before the "=>" here
304 is the @dfun_theta@ below.
306 First comes the easy case of a non-local instance decl.
310 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
311 -- Returns a binding for the dfun
313 ------------------------
314 -- Derived newtype instances
316 -- We need to make a copy of the dictionary we are deriving from
317 -- because we may need to change some of the superclass dictionaries
318 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
320 -- In the case of a newtype, things are rather easy
321 -- class Show a => Foo a b where ...
322 -- newtype T a = MkT (Tree [a]) deriving( Foo Int )
323 -- The newtype gives an FC axiom looking like
324 -- axiom CoT a :: T a :=: Tree [a]
326 -- So all need is to generate a binding looking like
327 -- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
328 -- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
329 -- case df `cast` (Foo Int (sym (CoT a))) of
330 -- Foo _ op1 .. opn -> Foo ds op1 .. opn
332 tcInstDecl2 (InstInfo { iSpec = ispec,
333 iBinds = NewTypeDerived tycon rep_tys })
334 = do { let dfun_id = instanceDFunId ispec
335 rigid_info = InstSkol dfun_id
336 origin = SigOrigin rigid_info
337 inst_ty = idType dfun_id
338 ; inst_loc <- getInstLoc origin
339 ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
340 ; dicts <- newDictBndrs inst_loc theta
341 ; uniqs <- newUniqueSupply
342 ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
343 ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
344 ; let (rep_dict_id:sc_dict_ids)
345 | null dicts = [instToId this_dict]
346 | otherwise = map instToId dicts
348 -- (Here, we are relying on the order of dictionary
349 -- arguments built by NewTypeDerived in TcDeriv.)
351 wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
353 -- we need to find the kind that this class applies to
354 -- and drop trailing tvs appropriately
355 cls_kind = tyVarKind (head (reverse (tyConTyVars cls_tycon)))
356 the_tvs = drop_tail (length (fst (splitFunTys cls_kind))) tvs
358 coerced_rep_dict = mkHsCoerce (co_fn the_tvs cls_tycon cls_inst_tys) (HsVar rep_dict_id)
360 body | null sc_dict_ids = coerced_rep_dict
361 | otherwise = HsCase (noLoc coerced_rep_dict) $
362 MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
363 in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
365 the_match = mkSimpleMatch [noLoc the_pat] the_rhs
366 the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
368 (uniqs1, uniqs2) = splitUniqSupply uniqs
370 op_ids = zipWith (mkSysLocal FSLIT("op"))
371 (uniqsFromSupply uniqs1) op_tys
373 dict_ids = zipWith (mkSysLocal FSLIT("dict"))
374 (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
376 the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
377 pat_dicts = dict_ids,
378 pat_binds = emptyLHsBinds,
379 pat_args = PrefixCon (map nlVarPat op_ids),
382 cls_data_con = classDataCon cls
383 cls_tycon = dataConTyCon cls_data_con
384 cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
386 n_dict_args = if length dicts == 0 then 0 else length dicts - 1
387 op_tys = drop n_dict_args cls_arg_tys
389 dict = mkHsCoerce wrap_fn body
390 ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
392 -- For newtype T a = MkT <ty>
393 -- The returned coercion has kind :: C (T a):=:C <ty>
394 co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
395 = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
396 [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
399 drop_tail n l = take (length l - n) l
401 ------------------------
402 -- Ordinary instances
404 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
406 dfun_id = instanceDFunId ispec
407 rigid_info = InstSkol dfun_id
408 inst_ty = idType dfun_id
410 -- Prime error recovery
411 recoverM (returnM emptyLHsBinds) $
412 setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
413 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
415 -- Instantiate the instance decl with skolem constants
416 tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
417 -- These inst_tyvars' scope over the 'where' part
418 -- Those tyvars are inside the dfun_id's type, which is a bit
419 -- bizarre, but OK so long as you realise it!
421 (clas, inst_tys') = tcSplitDFunHead inst_head'
422 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
424 -- Instantiate the super-class context with inst_tys
425 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
426 origin = SigOrigin rigid_info
428 -- Create dictionary Ids from the specified instance contexts.
429 getInstLoc InstScOrigin `thenM` \ sc_loc ->
430 newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
431 getInstLoc origin `thenM` \ inst_loc ->
432 newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
433 newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
434 -- Default-method Ids may be mentioned in synthesised RHSs,
435 -- but they'll already be in the environment.
437 -- Typecheck the methods
438 let -- These insts are in scope; quite a few, eh?
439 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
441 tcMethods origin clas inst_tyvars'
442 dfun_theta' inst_tys' avail_insts
443 op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
445 -- Figure out bindings for the superclass context
446 -- Don't include this_dict in the 'givens', else
447 -- sc_dicts get bound by just selecting from this_dict!!
448 addErrCtxt superClassCtxt
449 (tcSimplifySuperClasses inst_tyvars'
451 sc_dicts) `thenM` \ sc_binds ->
453 -- It's possible that the superclass stuff might unified one
454 -- of the inst_tyavars' with something in the envt
455 checkSigTyVars inst_tyvars' `thenM_`
457 -- Deal with 'SPECIALISE instance' pragmas
458 tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
460 -- Create the result bindings
462 dict_constr = classDataCon clas
463 scs_and_meths = map instToId sc_dicts ++ meth_ids
464 this_dict_id = instToId this_dict
465 inline_prag | null dfun_arg_dicts = []
466 | otherwise = [InlinePrag (Inline AlwaysActive True)]
467 -- Always inline the dfun; this is an experimental decision
468 -- because it makes a big performance difference sometimes.
469 -- Often it means we can do the method selection, and then
470 -- inline the method as well. Marcin's idea; see comments below.
472 -- BUT: don't inline it if it's a constant dictionary;
473 -- we'll get all the benefit without inlining, and we get
474 -- a **lot** of code duplication if we inline it
476 -- See Note [Inline dfuns] below
479 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
480 -- We don't produce a binding for the dict_constr; instead we
481 -- rely on the simplifier to unfold this saturated application
482 -- We do this rather than generate an HsCon directly, because
483 -- it means that the special cases (e.g. dictionary with only one
484 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
485 -- than needing to be repeated here.
487 dict_bind = noLoc (VarBind this_dict_id dict_rhs)
488 all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
490 main_bind = noLoc $ AbsBinds
492 (map instToId dfun_arg_dicts)
493 [(inst_tyvars', dfun_id, this_dict_id,
494 inline_prag ++ prags)]
497 showLIE (text "instance") `thenM_`
498 returnM (unitBag main_bind)
501 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
502 avail_insts op_items monobinds uprags
503 = -- Check that all the method bindings come from this class
505 sel_names = [idName sel_id | (sel_id, _) <- op_items]
506 bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
508 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
510 -- Make the method bindings
512 mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
514 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
516 -- And type check them
517 -- It's really worth making meth_insts available to the tcMethodBind
518 -- Consider instance Monad (ST s) where
519 -- {-# INLINE (>>) #-}
520 -- (>>) = ...(>>=)...
521 -- If we don't include meth_insts, we end up with bindings like this:
522 -- rec { dict = MkD then bind ...
523 -- then = inline_me (... (GHC.Base.>>= dict) ...)
525 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
526 -- and (b) the inline_me prevents us inlining the >>= selector, which
527 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
528 -- is not inlined across modules. Rather ironic since this does not
529 -- happen without the INLINE pragma!
531 -- Solution: make meth_insts available, so that 'then' refers directly
532 -- to the local 'bind' rather than going via the dictionary.
534 -- BUT WATCH OUT! If the method type mentions the class variable, then
535 -- this optimisation is not right. Consider
539 -- instance C Int where
541 -- The occurrence of 'op' on the rhs gives rise to a constraint
543 -- The trouble is that the 'meth_inst' for op, which is 'available', also
544 -- looks like 'op at Int'. But they are not the same.
546 prag_fn = mkPragFun uprags
547 all_insts = avail_insts ++ catMaybes meth_insts
548 sig_fn n = Just [] -- No scoped type variables, but every method has
549 -- a type signature, in effect, so that we check
550 -- the method has the right type
551 tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
552 meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
555 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
557 returnM (meth_ids, unionManyBags meth_binds_s)
561 ------------------------------
562 [Inline dfuns] Inlining dfuns unconditionally
563 ------------------------------
565 The code above unconditionally inlines dict funs. Here's why.
566 Consider this program:
568 test :: Int -> Int -> Bool
569 test x y = (x,y) == (y,x) || test y x
570 -- Recursive to avoid making it inline.
572 This needs the (Eq (Int,Int)) instance. If we inline that dfun
573 the code we end up with is good:
576 \r -> case ==# [ww ww1] of wild {
577 PrelBase.False -> Test.$wtest ww1 ww;
579 case ==# [ww1 ww] of wild1 {
580 PrelBase.False -> Test.$wtest ww1 ww;
581 PrelBase.True -> PrelBase.True [];
584 Test.test = \r [w w1]
587 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
590 If we don't inline the dfun, the code is not nearly as good:
592 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
593 PrelBase.:DEq tpl1 tpl2 -> tpl2;
598 let { y = PrelBase.I#! [ww1]; } in
599 let { x = PrelBase.I#! [ww]; } in
600 let { sat_slx = PrelTup.(,)! [y x]; } in
601 let { sat_sly = PrelTup.(,)! [x y];
603 case == sat_sly sat_slx of wild {
604 PrelBase.False -> Test.$wtest ww1 ww;
605 PrelBase.True -> PrelBase.True [];
612 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
615 Why doesn't GHC inline $fEq? Because it looks big:
617 PrelTup.zdfEqZ1T{-rcX-}
618 = \ @ a{-reT-} :: * @ b{-reS-} :: *
619 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
620 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
622 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
623 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
625 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
626 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
628 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
629 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
630 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
632 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
634 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
636 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
637 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
641 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
642 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
643 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
644 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
646 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
648 and it's not as bad as it seems, because it's further dramatically
649 simplified: only zeze2 is extracted and its body is simplified.
652 %************************************************************************
654 \subsection{Error messages}
656 %************************************************************************
659 instDeclCtxt1 hs_inst_ty
660 = inst_decl_ctxt (case unLoc hs_inst_ty of
661 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
662 HsPredTy pred -> ppr pred
663 other -> ppr hs_inst_ty) -- Don't expect this
664 instDeclCtxt2 dfun_ty
665 = inst_decl_ctxt (ppr (mkClassPred cls tys))
667 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
669 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
671 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")