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"
11 import HsSyn ( InstDecl(..), HsType(..),
12 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..),
13 andMonoBindList, collectMonoBinders,
16 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedTyClDecl )
17 import TcHsSyn ( TcMonoBinds, mkHsConApp )
18 import TcBinds ( tcSpecSigs )
19 import TcClassDcl ( tcMethodBind, mkMethodBind, badMethodErr,
20 tcClassDecl2, getGenericInstances )
22 import TcMType ( tcInstType, checkValidTheta, checkValidInstHead, instTypeErr,
23 checkAmbiguity, SourceTyCtxt(..) )
24 import TcType ( mkClassPred, tcSplitForAllTys, tyVarsOfType,
25 tcSplitSigmaTy, getClassPredTys, tcSplitPredTy_maybe, mkTyVarTys,
26 TyVarDetails(..), tcSplitDFunTy
28 import Inst ( InstOrigin(..), tcInstClassOp, newDicts, instToId,
29 showLIE, tcExtendLocalInstEnv )
30 import TcDeriv ( tcDeriving )
31 import TcEnv ( tcExtendGlobalValEnv, tcExtendTyVarEnv2,
32 InstInfo(..), InstBindings(..),
33 newDFunName, tcExtendLocalValEnv
35 import PprType ( pprClassPred )
36 import TcHsType ( kcHsSigType, tcHsKindedType )
37 import TcUnify ( checkSigTyVars )
38 import TcSimplify ( tcSimplifyCheck, tcSimplifyTop )
39 import Subst ( mkTyVarSubst, substTheta, substTy )
40 import DataCon ( classDataCon )
41 import Class ( classBigSig )
42 import Var ( idName, idType )
44 import MkId ( mkDictFunId, rUNTIME_ERROR_ID )
45 import FunDeps ( checkInstFDs )
46 import Name ( getSrcLoc )
47 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
48 import UnicodeUtil ( stringToUtf8 )
49 import Maybe ( catMaybes )
50 import ListSetOps ( minusList )
55 Typechecking instance declarations is done in two passes. The first
56 pass, made by @tcInstDecls1@, collects information to be used in the
59 This pre-processed info includes the as-yet-unprocessed bindings
60 inside the instance declaration. These are type-checked in the second
61 pass, when the class-instance envs and GVE contain all the info from
62 all the instance and value decls. Indeed that's the reason we need
63 two passes over the instance decls.
66 Here is the overall algorithm.
67 Assume that we have an instance declaration
69 instance c => k (t tvs) where b
73 $LIE_c$ is the LIE for the context of class $c$
75 $betas_bar$ is the free variables in the class method type, excluding the
78 $LIE_cop$ is the LIE constraining a particular class method
80 $tau_cop$ is the tau type of a class method
82 $LIE_i$ is the LIE for the context of instance $i$
84 $X$ is the instance constructor tycon
86 $gammas_bar$ is the set of type variables of the instance
88 $LIE_iop$ is the LIE for a particular class method instance
90 $tau_iop$ is the tau type for this instance of a class method
92 $alpha$ is the class variable
94 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
96 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
99 ToDo: Update the list above with names actually in the code.
103 First, make the LIEs for the class and instance contexts, which means
104 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
105 and make LIElistI and LIEI.
107 Then process each method in turn.
109 order the instance methods according to the ordering of the class methods
111 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
113 Create final dictionary function from bindings generated already
115 df = lambda inst_tyvars
122 in <op1,op2,...,opn,sd1,...,sdm>
124 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
125 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
129 %************************************************************************
131 \subsection{Extracting instance decls}
133 %************************************************************************
135 Gather up the instance declarations from their various sources
138 tcInstDecls1 -- Deal with both source-code and imported instance decls
139 :: [RenamedTyClDecl] -- For deriving stuff
140 -> [RenamedInstDecl] -- Source code instance decls
141 -> TcM (TcGblEnv, -- The full inst env
142 [InstInfo], -- Source-code instance decls to process;
143 -- contains all dfuns for this module
144 RenamedHsBinds) -- Supporting bindings for derived instances
146 tcInstDecls1 tycl_decls inst_decls
148 -- Stop if addInstInfos etc discovers any errors
149 -- (they recover, so that we get more than one error each round)
151 -- (1) Do the ordinary instance declarations
152 mappM tcLocalInstDecl1 inst_decls `thenM` \ local_inst_infos ->
155 local_inst_info = catMaybes local_inst_infos
156 clas_decls = filter isClassDecl tycl_decls
158 -- (2) Instances from generic class declarations
159 getGenericInstances clas_decls `thenM` \ generic_inst_info ->
161 -- Next, construct the instance environment so far, consisting of
162 -- a) local instance decls
163 -- b) generic instances
164 addInsts local_inst_info $
165 addInsts generic_inst_info $
167 -- (3) Compute instances from "deriving" clauses;
168 -- This stuff computes a context for the derived instance decl, so it
169 -- needs to know about all the instances possible; hence inst_env4
170 tcDeriving tycl_decls `thenM` \ (deriv_inst_info, deriv_binds, keep_alive) ->
171 addInsts deriv_inst_info $
173 getGblEnv `thenM` \ gbl_env ->
174 returnM (gbl_env { tcg_keep = tcg_keep gbl_env `unionNameSets` keep_alive },
175 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
178 addInsts :: [InstInfo] -> TcM a -> TcM a
179 addInsts infos thing_inside
180 = tcExtendLocalInstEnv (map iDFunId infos) thing_inside
184 tcLocalInstDecl1 :: RenamedInstDecl
185 -> TcM (Maybe InstInfo) -- Nothing 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 -- but only do this for non-imported instance decls.
191 -- Imported ones should have been checked already, and may indeed
192 -- contain something illegal in normal Haskell, notably
193 -- instance CCallable [Char]
194 tcLocalInstDecl1 decl@(InstDecl poly_ty binds uprags src_loc)
195 = -- Prime error recovery, set source location
196 recoverM (returnM Nothing) $
198 addErrCtxt (instDeclCtxt1 poly_ty) $
200 -- Typecheck the instance type itself. We can't use
201 -- tcHsSigType, because it's not a valid user type.
202 kcHsSigType poly_ty `thenM` \ kinded_ty ->
203 tcHsKindedType kinded_ty `thenM` \ poly_ty' ->
205 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
207 checkValidTheta InstThetaCtxt theta `thenM_`
208 checkAmbiguity tyvars theta (tyVarsOfType tau) `thenM_`
209 checkValidInstHead tau `thenM` \ (clas,inst_tys) ->
210 checkTc (checkInstFDs theta clas inst_tys)
211 (instTypeErr (pprClassPred clas inst_tys) msg) `thenM_`
212 newDFunName clas inst_tys src_loc `thenM` \ dfun_name ->
213 returnM (Just (InstInfo { iDFunId = mkDictFunId dfun_name tyvars theta clas inst_tys,
214 iBinds = VanillaInst binds uprags }))
216 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
220 %************************************************************************
222 \subsection{Type-checking instance declarations, pass 2}
224 %************************************************************************
227 tcInstDecls2 :: [RenamedTyClDecl] -> [InstInfo]
228 -> TcM (TcLclEnv, TcMonoBinds)
229 -- (a) From each class declaration,
230 -- generate any default-method bindings
231 -- (b) From each instance decl
232 -- generate the dfun binding
234 tcInstDecls2 tycl_decls inst_decls
235 = do { -- (a) Default methods from class decls
236 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
237 filter isClassDecl tycl_decls
238 ; tcExtendLocalValEnv (concat dm_ids_s) $ do
240 -- (b) instance declarations
241 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
244 ; tcl_env <- getLclEnv
245 ; returnM (tcl_env, andMonoBindList dm_binds_s `AndMonoBinds`
246 andMonoBindList inst_binds_s) }
249 ======= New documentation starts here (Sept 92) ==============
251 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
252 the dictionary function for this instance declaration. For example
254 instance Foo a => Foo [a] where
258 might generate something like
260 dfun.Foo.List dFoo_a = let op1 x = ...
266 HOWEVER, if the instance decl has no context, then it returns a
267 bigger @HsBinds@ with declarations for each method. For example
269 instance Foo [a] where
275 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
276 const.Foo.op1.List a x = ...
277 const.Foo.op2.List a y = ...
279 This group may be mutually recursive, because (for example) there may
280 be no method supplied for op2 in which case we'll get
282 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
284 that is, the default method applied to the dictionary at this type.
286 What we actually produce in either case is:
288 AbsBinds [a] [dfun_theta_dicts]
289 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
290 { d = (sd1,sd2, ..., op1, op2, ...)
295 The "maybe" says that we only ask AbsBinds to make global constant methods
296 if the dfun_theta is empty.
299 For an instance declaration, say,
301 instance (C1 a, C2 b) => C (T a b) where
304 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
305 function whose type is
307 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
309 Notice that we pass it the superclass dictionaries at the instance type; this
310 is the ``Mark Jones optimisation''. The stuff before the "=>" here
311 is the @dfun_theta@ below.
313 First comes the easy case of a non-local instance decl.
317 tcInstDecl2 :: InstInfo -> TcM TcMonoBinds
319 tcInstDecl2 (InstInfo { iDFunId = dfun_id, iBinds = binds })
320 = -- Prime error recovery
321 recoverM (returnM EmptyMonoBinds) $
322 addSrcLoc (getSrcLoc dfun_id) $
323 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
325 inst_ty = idType dfun_id
326 (inst_tyvars, _) = tcSplitForAllTys inst_ty
327 -- The tyvars of the instance decl scope over the 'where' part
328 -- Those tyvars are inside the dfun_id's type, which is a bit
329 -- bizarre, but OK so long as you realise it!
332 -- Instantiate the instance decl with tc-style type variables
333 tcInstType InstTv inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
335 Just pred = tcSplitPredTy_maybe inst_head'
336 (clas, inst_tys') = getClassPredTys pred
337 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
339 -- Instantiate the super-class context with inst_tys
340 sc_theta' = substTheta (mkTyVarSubst class_tyvars inst_tys') sc_theta
341 origin = InstanceDeclOrigin
343 -- Create dictionary Ids from the specified instance contexts.
344 newDicts origin sc_theta' `thenM` \ sc_dicts ->
345 newDicts origin dfun_theta' `thenM` \ dfun_arg_dicts ->
346 newDicts origin [pred] `thenM` \ [this_dict] ->
347 -- Default-method Ids may be mentioned in synthesised RHSs,
348 -- but they'll already be in the environment.
351 -- Typecheck the methods
352 let -- These insts are in scope; quite a few, eh?
353 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
355 tcMethods clas inst_tyvars inst_tyvars'
356 dfun_theta' inst_tys' avail_insts
357 op_items binds `thenM` \ (meth_ids, meth_binds) ->
359 -- Figure out bindings for the superclass context
360 tcSuperClasses inst_tyvars' dfun_arg_dicts sc_dicts
361 `thenM` \ (zonked_inst_tyvars, sc_binds_inner, sc_binds_outer) ->
363 -- Deal with 'SPECIALISE instance' pragmas by making them
364 -- look like SPECIALISE pragmas for the dfun
366 uprags = case binds of
367 VanillaInst _ uprags -> uprags
369 spec_prags = [ SpecSig (idName dfun_id) ty loc
370 | SpecInstSig ty loc <- uprags ]
371 xtve = inst_tyvars `zip` inst_tyvars'
373 tcExtendGlobalValEnv [dfun_id] (
374 tcExtendTyVarEnv2 xtve $
375 tcSpecSigs spec_prags
376 ) `thenM` \ prag_binds ->
378 -- Create the result bindings
380 dict_constr = classDataCon clas
381 scs_and_meths = map instToId sc_dicts ++ meth_ids
382 this_dict_id = instToId this_dict
383 inlines | null dfun_arg_dicts = emptyNameSet
384 | otherwise = unitNameSet (idName dfun_id)
385 -- Always inline the dfun; this is an experimental decision
386 -- because it makes a big performance difference sometimes.
387 -- Often it means we can do the method selection, and then
388 -- inline the method as well. Marcin's idea; see comments below.
390 -- BUT: don't inline it if it's a constant dictionary;
391 -- we'll get all the benefit without inlining, and we get
392 -- a **lot** of code duplication if we inline it
394 -- See Note [Inline dfuns] below
398 = -- Blatant special case for CCallable, CReturnable
399 -- If the dictionary is empty then we should never
400 -- select anything from it, so we make its RHS just
401 -- emit an error message. This in turn means that we don't
402 -- mention the constructor, which doesn't exist for CCallable, CReturnable
403 -- Hardly beautiful, but only three extra lines.
404 HsApp (TyApp (HsVar rUNTIME_ERROR_ID) [idType this_dict_id])
405 (HsLit (HsStringPrim (mkFastString (stringToUtf8 msg))))
407 | otherwise -- The common case
408 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
409 -- We don't produce a binding for the dict_constr; instead we
410 -- rely on the simplifier to unfold this saturated application
411 -- We do this rather than generate an HsCon directly, because
412 -- it means that the special cases (e.g. dictionary with only one
413 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
414 -- than needing to be repeated here.
417 msg = "Compiler error: bad dictionary " ++ showSDoc (ppr clas)
419 dict_bind = VarMonoBind this_dict_id dict_rhs
420 all_binds = sc_binds_inner `AndMonoBinds` meth_binds `AndMonoBinds` dict_bind
424 (map instToId dfun_arg_dicts)
425 [(inst_tyvars', dfun_id, this_dict_id)]
428 showLIE (text "instance") `thenM_`
429 returnM (main_bind `AndMonoBinds` prag_binds `AndMonoBinds` sc_binds_outer)
432 tcMethods clas inst_tyvars inst_tyvars' dfun_theta' inst_tys'
433 avail_insts op_items (VanillaInst monobinds uprags)
434 = -- Check that all the method bindings come from this class
436 sel_names = [idName sel_id | (sel_id, _) <- op_items]
437 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
439 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
441 -- Make the method bindings
443 mk_method_bind = mkMethodBind InstanceDeclOrigin clas inst_tys' monobinds
445 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
447 -- And type check them
448 -- It's really worth making meth_insts available to the tcMethodBind
449 -- Consider instance Monad (ST s) where
450 -- {-# INLINE (>>) #-}
451 -- (>>) = ...(>>=)...
452 -- If we don't include meth_insts, we end up with bindings like this:
453 -- rec { dict = MkD then bind ...
454 -- then = inline_me (... (GHC.Base.>>= dict) ...)
456 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
457 -- and (b) the inline_me prevents us inlining the >>= selector, which
458 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
459 -- is not inlined across modules. Rather ironic since this does not
460 -- happen without the INLINE pragma!
462 -- Solution: make meth_insts available, so that 'then' refers directly
463 -- to the local 'bind' rather than going via the dictionary.
465 -- BUT WATCH OUT! If the method type mentions the class variable, then
466 -- this optimisation is not right. Consider
470 -- instance C Int where
472 -- The occurrence of 'op' on the rhs gives rise to a constraint
474 -- The trouble is that the 'meth_inst' for op, which is 'available', also
475 -- looks like 'op at Int'. But they are not the same.
477 all_insts = avail_insts ++ catMaybes meth_insts
478 xtve = inst_tyvars `zip` inst_tyvars'
479 tc_method_bind = tcMethodBind xtve inst_tyvars' dfun_theta' all_insts uprags
481 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
483 returnM ([meth_id | (_,meth_id,_) <- meth_infos],
484 andMonoBindList meth_binds_s)
487 -- Derived newtype instances
488 tcMethods clas inst_tyvars inst_tyvars' dfun_theta' inst_tys'
489 avail_insts op_items (NewTypeDerived rep_tys)
490 = getInstLoc InstanceDeclOrigin `thenM` \ inst_loc ->
491 mapAndUnzip3M (do_one inst_loc) op_items `thenM` \ (meth_ids, meth_binds, rhs_insts) ->
494 (ptext SLIT("newtype derived instance"))
495 inst_tyvars' avail_insts rhs_insts `thenM` \ lie_binds ->
497 -- I don't think we have to do the checkSigTyVars thing
499 returnM (meth_ids, lie_binds `AndMonoBinds` andMonoBindList meth_binds)
502 do_one inst_loc (sel_id, _)
503 = -- The binding is like "op @ NewTy = op @ RepTy"
504 -- Make the *binder*, like in mkMethodBind
505 tcInstClassOp inst_loc sel_id inst_tys' `thenM` \ meth_inst ->
507 -- Make the *occurrence on the rhs*
508 tcInstClassOp inst_loc sel_id rep_tys' `thenM` \ rhs_inst ->
510 meth_id = instToId meth_inst
512 return (meth_id, VarMonoBind meth_id (HsVar (instToId rhs_inst)), rhs_inst)
514 -- Instantiate rep_tys with the relevant type variables
515 rep_tys' = map (substTy subst) rep_tys
516 subst = mkTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars')
519 Note: [Superclass loops]
520 ~~~~~~~~~~~~~~~~~~~~~~~~~
521 We have to be very, very careful when generating superclasses, lest we
522 accidentally build a loop. Here's an example:
526 class S a => C a where { opc :: a -> a }
527 class S b => D b where { opd :: b -> b }
535 From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int}
536 Simplifying, we may well get:
537 $dfCInt = :C ds1 (opd dd)
540 Notice that we spot that we can extract ds1 from dd.
542 Alas! Alack! We can do the same for (instance D Int):
544 $dfDInt = :D ds2 (opc dc)
548 And now we've defined the superclass in terms of itself.
551 Solution: treat the superclass context separately, and simplify it
552 all the way down to nothing on its own. Don't toss any 'free' parts
553 out to be simplified together with other bits of context.
554 Hence the tcSimplifyTop below.
556 At a more basic level, don't include this_dict in the context wrt
557 which we simplify sc_dicts, else sc_dicts get bound by just selecting
561 tcSuperClasses inst_tyvars' dfun_arg_dicts sc_dicts
562 = addErrCtxt superClassCtxt $
563 getLIE (tcSimplifyCheck doc inst_tyvars'
565 sc_dicts) `thenM` \ (sc_binds1, sc_lie) ->
567 -- It's possible that the superclass stuff might have done unification
568 checkSigTyVars inst_tyvars' `thenM` \ zonked_inst_tyvars ->
570 -- We must simplify this all the way down
571 -- lest we build superclass loops
572 -- See Note [Superclass loops] above
573 tcSimplifyTop sc_lie `thenM` \ sc_binds2 ->
575 returnM (zonked_inst_tyvars, sc_binds1, sc_binds2)
578 doc = ptext SLIT("instance declaration superclass context")
582 ------------------------------
583 [Inline dfuns] Inlining dfuns unconditionally
584 ------------------------------
586 The code above unconditionally inlines dict funs. Here's why.
587 Consider this program:
589 test :: Int -> Int -> Bool
590 test x y = (x,y) == (y,x) || test y x
591 -- Recursive to avoid making it inline.
593 This needs the (Eq (Int,Int)) instance. If we inline that dfun
594 the code we end up with is good:
597 \r -> case ==# [ww ww1] of wild {
598 PrelBase.False -> Test.$wtest ww1 ww;
600 case ==# [ww1 ww] of wild1 {
601 PrelBase.False -> Test.$wtest ww1 ww;
602 PrelBase.True -> PrelBase.True [];
605 Test.test = \r [w w1]
608 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
611 If we don't inline the dfun, the code is not nearly as good:
613 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
614 PrelBase.:DEq tpl1 tpl2 -> tpl2;
619 let { y = PrelBase.I#! [ww1]; } in
620 let { x = PrelBase.I#! [ww]; } in
621 let { sat_slx = PrelTup.(,)! [y x]; } in
622 let { sat_sly = PrelTup.(,)! [x y];
624 case == sat_sly sat_slx of wild {
625 PrelBase.False -> Test.$wtest ww1 ww;
626 PrelBase.True -> PrelBase.True [];
633 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
636 Why doesn't GHC inline $fEq? Because it looks big:
638 PrelTup.zdfEqZ1T{-rcX-}
639 = \ @ a{-reT-} :: * @ b{-reS-} :: *
640 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
641 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
643 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
644 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
646 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
647 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
649 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
650 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
651 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
653 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
655 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
657 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
658 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
662 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
663 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
664 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
665 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
667 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
669 and it's not as bad as it seems, because it's further dramatically
670 simplified: only zeze2 is extracted and its body is simplified.
673 %************************************************************************
675 \subsection{Error messages}
677 %************************************************************************
680 instDeclCtxt1 hs_inst_ty
681 = inst_decl_ctxt (case hs_inst_ty of
682 HsForAllTy _ _ _ (HsPredTy pred) -> ppr pred
683 HsPredTy pred -> ppr pred
684 other -> ppr hs_inst_ty) -- Don't expect this
685 instDeclCtxt2 dfun_ty
686 = inst_decl_ctxt (ppr (mkClassPred cls tys))
688 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
690 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
692 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")