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(ATyCon) )
32 import Coercion ( mkSymCoercion )
33 import TyCon ( TyCon, tyConName, newTyConCo, tyConTyVars,
34 isAssocTyCon, tyConFamInst_maybe )
35 import DataCon ( classDataCon, dataConTyCon, dataConInstArgTys )
36 import Class ( classBigSig )
37 import Var ( TyVar, Id, idName, idType, tyVarKind )
38 import Id ( mkSysLocal )
39 import UniqSupply ( uniqsFromSupply, splitUniqSupply )
40 import MkId ( mkDictFunId )
41 import Name ( Name, getSrcLoc )
42 import Maybe ( isNothing, fromJust, catMaybes )
44 import SrcLoc ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
45 import ListSetOps ( minusList )
48 import BasicTypes ( Activation( AlwaysActive ), InlineSpec(..) )
49 import HscTypes ( implicitTyThings )
53 Typechecking instance declarations is done in two passes. The first
54 pass, made by @tcInstDecls1@, collects information to be used in the
57 This pre-processed info includes the as-yet-unprocessed bindings
58 inside the instance declaration. These are type-checked in the second
59 pass, when the class-instance envs and GVE contain all the info from
60 all the instance and value decls. Indeed that's the reason we need
61 two passes over the instance decls.
63 Here is the overall algorithm.
64 Assume that we have an instance declaration
66 instance c => k (t tvs) where b
70 $LIE_c$ is the LIE for the context of class $c$
72 $betas_bar$ is the free variables in the class method type, excluding the
75 $LIE_cop$ is the LIE constraining a particular class method
77 $tau_cop$ is the tau type of a class method
79 $LIE_i$ is the LIE for the context of instance $i$
81 $X$ is the instance constructor tycon
83 $gammas_bar$ is the set of type variables of the instance
85 $LIE_iop$ is the LIE for a particular class method instance
87 $tau_iop$ is the tau type for this instance of a class method
89 $alpha$ is the class variable
91 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
93 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
96 ToDo: Update the list above with names actually in the code.
100 First, make the LIEs for the class and instance contexts, which means
101 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
102 and make LIElistI and LIEI.
104 Then process each method in turn.
106 order the instance methods according to the ordering of the class methods
108 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
110 Create final dictionary function from bindings generated already
112 df = lambda inst_tyvars
119 in <op1,op2,...,opn,sd1,...,sdm>
121 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
122 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
126 %************************************************************************
128 \subsection{Extracting instance decls}
130 %************************************************************************
132 Gather up the instance declarations from their various sources
135 tcInstDecls1 -- Deal with both source-code and imported instance decls
136 :: [LTyClDecl Name] -- For deriving stuff
137 -> [LInstDecl Name] -- Source code instance decls
138 -> TcM (TcGblEnv, -- The full inst env
139 [InstInfo], -- Source-code instance decls to process;
140 -- contains all dfuns for this module
141 HsValBinds Name) -- Supporting bindings for derived instances
143 tcInstDecls1 tycl_decls inst_decls
145 do { -- Stop if addInstInfos etc discovers any errors
146 -- (they recover, so that we get more than one error each
149 -- (1) Do the ordinary instance declarations and instances of
151 ; let { idxty_decls = filter (isIdxTyDecl . unLoc) tycl_decls }
152 ; local_info_tycons <- mappM tcLocalInstDecl1 inst_decls
153 ; idxty_info_tycons <- mappM tcIdxTyInstDeclTL idxty_decls
155 ; let { (local_infos,
156 local_tycons) = unzip local_info_tycons
158 idxty_tycons) = unzip idxty_info_tycons
159 ; local_idxty_info = concat local_infos ++ catMaybes idxty_infos
160 ; local_idxty_tycon = concat local_tycons ++
161 catMaybes idxty_tycons
162 ; clas_decls = filter (isClassDecl.unLoc) tycl_decls
163 ; implicit_things = concatMap implicitTyThings local_idxty_tycon
166 -- (2) Add the tycons of associated types and their implicit
167 -- tythings to the global environment
168 ; tcExtendGlobalEnv (local_idxty_tycon ++ implicit_things) $ do {
170 -- (3) Instances from generic class declarations
171 ; generic_inst_info <- getGenericInstances clas_decls
173 -- Next, construct the instance environment so far, consisting
175 -- a) local instance decls
176 -- b) generic instances
177 ; addInsts local_idxty_info $ do {
178 ; addInsts generic_inst_info $ do {
180 -- (4) Compute instances from "deriving" clauses;
181 -- This stuff computes a context for the derived instance
182 -- decl, so it needs to know about all the instances possible
183 ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls
184 ; addInsts deriv_inst_info $ do {
186 ; gbl_env <- getGblEnv
188 generic_inst_info ++ deriv_inst_info ++ local_idxty_info,
192 -- Make sure that toplevel type instance are not for associated types.
193 -- !!!TODO: Need to perform this check for the InstInfo structures of type
195 tcIdxTyInstDeclTL ldecl@(L loc decl) =
196 do { (info, tything) <- tcIdxTyInstDecl ldecl
198 when (isAssocFamily tything) $
199 addErr $ assocInClassErr (tcdName decl)
200 ; return (info, tything)
202 isAssocFamily (Just (ATyCon tycon)) =
203 case tyConFamInst_maybe tycon of
204 Nothing -> panic "isAssocFamily: no family?!?"
205 Just (fam, _) -> isAssocTyCon fam
206 isAssocFamily (Just _ ) = panic "isAssocFamily: no tycon?!?"
207 isAssocFamily Nothing = False
209 assocInClassErr name =
210 ptext SLIT("Associated type must be inside class instance") <+>
213 addInsts :: [InstInfo] -> TcM a -> TcM a
214 addInsts infos thing_inside
215 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
219 tcLocalInstDecl1 :: LInstDecl Name
220 -> TcM ([InstInfo], [TyThing]) -- [] if there was an error
221 -- A source-file instance declaration
222 -- Type-check all the stuff before the "where"
224 -- We check for respectable instance type, and context
225 tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
226 = -- Prime error recovery, set source location
227 recoverM (returnM ([], [])) $
229 addErrCtxt (instDeclCtxt1 poly_ty) $
231 do { is_boot <- tcIsHsBoot
232 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
235 -- Typecheck the instance type itself. We can't use
236 -- tcHsSigType, because it's not a valid user type.
237 ; kinded_ty <- kcHsSigType poly_ty
238 ; poly_ty' <- tcHsKindedType kinded_ty
239 ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
241 -- Now, check the validity of the instance.
242 ; (clas, inst_tys) <- checkValidInstHead tau
243 ; checkValidInstance tyvars theta clas inst_tys
245 -- Next, process any associated types.
246 ; idxty_info_tycons <- mappM tcIdxTyInstDecl ats
248 -- Finally, construct the Core representation of the instance.
249 -- (This no longer includes the associated types.)
250 ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
251 ; overlap_flag <- getOverlapFlag
252 ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
253 ispec = mkLocalInstance dfun overlap_flag
255 idxty_tycons) = unzip idxty_info_tycons
257 ; return ([InstInfo { iSpec = ispec,
258 iBinds = VanillaInst binds uprags }] ++
259 catMaybes idxty_infos,
260 catMaybes idxty_tycons)
265 %************************************************************************
267 \subsection{Type-checking instance declarations, pass 2}
269 %************************************************************************
272 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
273 -> TcM (LHsBinds Id, TcLclEnv)
274 -- (a) From each class declaration,
275 -- generate any default-method bindings
276 -- (b) From each instance decl
277 -- generate the dfun binding
279 tcInstDecls2 tycl_decls inst_decls
280 = do { -- (a) Default methods from class decls
281 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
282 filter (isClassDecl.unLoc) tycl_decls
283 ; tcExtendIdEnv (concat dm_ids_s) $ do
285 -- (b) instance declarations
286 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
289 ; let binds = unionManyBags dm_binds_s `unionBags`
290 unionManyBags inst_binds_s
291 ; tcl_env <- getLclEnv -- Default method Ids in here
292 ; returnM (binds, tcl_env) }
295 ======= New documentation starts here (Sept 92) ==============
297 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
298 the dictionary function for this instance declaration. For example
300 instance Foo a => Foo [a] where
304 might generate something like
306 dfun.Foo.List dFoo_a = let op1 x = ...
312 HOWEVER, if the instance decl has no context, then it returns a
313 bigger @HsBinds@ with declarations for each method. For example
315 instance Foo [a] where
321 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
322 const.Foo.op1.List a x = ...
323 const.Foo.op2.List a y = ...
325 This group may be mutually recursive, because (for example) there may
326 be no method supplied for op2 in which case we'll get
328 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
330 that is, the default method applied to the dictionary at this type.
332 What we actually produce in either case is:
334 AbsBinds [a] [dfun_theta_dicts]
335 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
336 { d = (sd1,sd2, ..., op1, op2, ...)
341 The "maybe" says that we only ask AbsBinds to make global constant methods
342 if the dfun_theta is empty.
345 For an instance declaration, say,
347 instance (C1 a, C2 b) => C (T a b) where
350 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
351 function whose type is
353 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
355 Notice that we pass it the superclass dictionaries at the instance type; this
356 is the ``Mark Jones optimisation''. The stuff before the "=>" here
357 is the @dfun_theta@ below.
359 First comes the easy case of a non-local instance decl.
363 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
364 -- Returns a binding for the dfun
366 ------------------------
367 -- Derived newtype instances
369 -- We need to make a copy of the dictionary we are deriving from
370 -- because we may need to change some of the superclass dictionaries
371 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
373 -- In the case of a newtype, things are rather easy
374 -- class Show a => Foo a b where ...
375 -- newtype T a = MkT (Tree [a]) deriving( Foo Int )
376 -- The newtype gives an FC axiom looking like
377 -- axiom CoT a :: T a :=: Tree [a]
379 -- So all need is to generate a binding looking like
380 -- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
381 -- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
382 -- case df `cast` (Foo Int (sym (CoT a))) of
383 -- Foo _ op1 .. opn -> Foo ds op1 .. opn
385 tcInstDecl2 (InstInfo { iSpec = ispec,
386 iBinds = NewTypeDerived tycon rep_tys })
387 = do { let dfun_id = instanceDFunId ispec
388 rigid_info = InstSkol dfun_id
389 origin = SigOrigin rigid_info
390 inst_ty = idType dfun_id
391 ; inst_loc <- getInstLoc origin
392 ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
393 ; dicts <- newDictBndrs inst_loc theta
394 ; uniqs <- newUniqueSupply
395 ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
396 ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
397 ; let (rep_dict_id:sc_dict_ids)
398 | null dicts = [instToId this_dict]
399 | otherwise = map instToId dicts
401 -- (Here, we are relying on the order of dictionary
402 -- arguments built by NewTypeDerived in TcDeriv.)
404 wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
406 -- we need to find the kind that this class applies to
407 -- and drop trailing tvs appropriately
408 cls_kind = tyVarKind (head (reverse (tyConTyVars cls_tycon)))
409 the_tvs = drop_tail (length (fst (splitFunTys cls_kind))) tvs
411 coerced_rep_dict = mkHsCoerce (co_fn the_tvs cls_tycon cls_inst_tys) (HsVar rep_dict_id)
413 body | null sc_dict_ids = coerced_rep_dict
414 | otherwise = HsCase (noLoc coerced_rep_dict) $
415 MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
416 in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
418 the_match = mkSimpleMatch [noLoc the_pat] the_rhs
419 the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
421 (uniqs1, uniqs2) = splitUniqSupply uniqs
423 op_ids = zipWith (mkSysLocal FSLIT("op"))
424 (uniqsFromSupply uniqs1) op_tys
426 dict_ids = zipWith (mkSysLocal FSLIT("dict"))
427 (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
429 the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
430 pat_dicts = dict_ids,
431 pat_binds = emptyLHsBinds,
432 pat_args = PrefixCon (map nlVarPat op_ids),
435 cls_data_con = classDataCon cls
436 cls_tycon = dataConTyCon cls_data_con
437 cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
439 n_dict_args = if length dicts == 0 then 0 else length dicts - 1
440 op_tys = drop n_dict_args cls_arg_tys
442 dict = mkHsCoerce wrap_fn body
443 ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
445 -- For newtype T a = MkT <ty>
446 -- The returned coercion has kind :: C (T a):=:C <ty>
447 co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
448 = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
449 [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
452 drop_tail n l = take (length l - n) l
454 ------------------------
455 -- Ordinary instances
457 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
459 dfun_id = instanceDFunId ispec
460 rigid_info = InstSkol dfun_id
461 inst_ty = idType dfun_id
463 -- Prime error recovery
464 recoverM (returnM emptyLHsBinds) $
465 setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
466 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
468 -- Instantiate the instance decl with skolem constants
469 tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
470 -- These inst_tyvars' scope over the 'where' part
471 -- Those tyvars are inside the dfun_id's type, which is a bit
472 -- bizarre, but OK so long as you realise it!
474 (clas, inst_tys') = tcSplitDFunHead inst_head'
475 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
477 -- Instantiate the super-class context with inst_tys
478 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
479 origin = SigOrigin rigid_info
481 -- Create dictionary Ids from the specified instance contexts.
482 getInstLoc InstScOrigin `thenM` \ sc_loc ->
483 newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
484 getInstLoc origin `thenM` \ inst_loc ->
485 newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
486 newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
487 -- Default-method Ids may be mentioned in synthesised RHSs,
488 -- but they'll already be in the environment.
490 -- Typecheck the methods
491 let -- These insts are in scope; quite a few, eh?
492 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
494 tcMethods origin clas inst_tyvars'
495 dfun_theta' inst_tys' avail_insts
496 op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
498 -- Figure out bindings for the superclass context
499 -- Don't include this_dict in the 'givens', else
500 -- sc_dicts get bound by just selecting from this_dict!!
501 addErrCtxt superClassCtxt
502 (tcSimplifySuperClasses inst_tyvars'
504 sc_dicts) `thenM` \ sc_binds ->
506 -- It's possible that the superclass stuff might unified one
507 -- of the inst_tyavars' with something in the envt
508 checkSigTyVars inst_tyvars' `thenM_`
510 -- Deal with 'SPECIALISE instance' pragmas
511 tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
513 -- Create the result bindings
515 dict_constr = classDataCon clas
516 scs_and_meths = map instToId sc_dicts ++ meth_ids
517 this_dict_id = instToId this_dict
518 inline_prag | null dfun_arg_dicts = []
519 | otherwise = [InlinePrag (Inline AlwaysActive True)]
520 -- Always inline the dfun; this is an experimental decision
521 -- because it makes a big performance difference sometimes.
522 -- Often it means we can do the method selection, and then
523 -- inline the method as well. Marcin's idea; see comments below.
525 -- BUT: don't inline it if it's a constant dictionary;
526 -- we'll get all the benefit without inlining, and we get
527 -- a **lot** of code duplication if we inline it
529 -- See Note [Inline dfuns] below
532 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
533 -- We don't produce a binding for the dict_constr; instead we
534 -- rely on the simplifier to unfold this saturated application
535 -- We do this rather than generate an HsCon directly, because
536 -- it means that the special cases (e.g. dictionary with only one
537 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
538 -- than needing to be repeated here.
540 dict_bind = noLoc (VarBind this_dict_id dict_rhs)
541 all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
543 main_bind = noLoc $ AbsBinds
545 (map instToId dfun_arg_dicts)
546 [(inst_tyvars', dfun_id, this_dict_id,
547 inline_prag ++ prags)]
550 showLIE (text "instance") `thenM_`
551 returnM (unitBag main_bind)
554 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
555 avail_insts op_items monobinds uprags
556 = -- Check that all the method bindings come from this class
558 sel_names = [idName sel_id | (sel_id, _) <- op_items]
559 bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
561 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
563 -- Make the method bindings
565 mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
567 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
569 -- And type check them
570 -- It's really worth making meth_insts available to the tcMethodBind
571 -- Consider instance Monad (ST s) where
572 -- {-# INLINE (>>) #-}
573 -- (>>) = ...(>>=)...
574 -- If we don't include meth_insts, we end up with bindings like this:
575 -- rec { dict = MkD then bind ...
576 -- then = inline_me (... (GHC.Base.>>= dict) ...)
578 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
579 -- and (b) the inline_me prevents us inlining the >>= selector, which
580 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
581 -- is not inlined across modules. Rather ironic since this does not
582 -- happen without the INLINE pragma!
584 -- Solution: make meth_insts available, so that 'then' refers directly
585 -- to the local 'bind' rather than going via the dictionary.
587 -- BUT WATCH OUT! If the method type mentions the class variable, then
588 -- this optimisation is not right. Consider
592 -- instance C Int where
594 -- The occurrence of 'op' on the rhs gives rise to a constraint
596 -- The trouble is that the 'meth_inst' for op, which is 'available', also
597 -- looks like 'op at Int'. But they are not the same.
599 prag_fn = mkPragFun uprags
600 all_insts = avail_insts ++ catMaybes meth_insts
601 sig_fn n = Just [] -- No scoped type variables, but every method has
602 -- a type signature, in effect, so that we check
603 -- the method has the right type
604 tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
605 meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
608 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
610 returnM (meth_ids, unionManyBags meth_binds_s)
614 ------------------------------
615 [Inline dfuns] Inlining dfuns unconditionally
616 ------------------------------
618 The code above unconditionally inlines dict funs. Here's why.
619 Consider this program:
621 test :: Int -> Int -> Bool
622 test x y = (x,y) == (y,x) || test y x
623 -- Recursive to avoid making it inline.
625 This needs the (Eq (Int,Int)) instance. If we inline that dfun
626 the code we end up with is good:
629 \r -> case ==# [ww ww1] of wild {
630 PrelBase.False -> Test.$wtest ww1 ww;
632 case ==# [ww1 ww] of wild1 {
633 PrelBase.False -> Test.$wtest ww1 ww;
634 PrelBase.True -> PrelBase.True [];
637 Test.test = \r [w w1]
640 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
643 If we don't inline the dfun, the code is not nearly as good:
645 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
646 PrelBase.:DEq tpl1 tpl2 -> tpl2;
651 let { y = PrelBase.I#! [ww1]; } in
652 let { x = PrelBase.I#! [ww]; } in
653 let { sat_slx = PrelTup.(,)! [y x]; } in
654 let { sat_sly = PrelTup.(,)! [x y];
656 case == sat_sly sat_slx of wild {
657 PrelBase.False -> Test.$wtest ww1 ww;
658 PrelBase.True -> PrelBase.True [];
665 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
668 Why doesn't GHC inline $fEq? Because it looks big:
670 PrelTup.zdfEqZ1T{-rcX-}
671 = \ @ a{-reT-} :: * @ b{-reS-} :: *
672 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
673 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
675 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
676 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
678 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
679 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
681 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
682 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
683 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
685 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
687 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
689 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
690 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
694 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
695 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
696 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
697 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
699 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
701 and it's not as bad as it seems, because it's further dramatically
702 simplified: only zeze2 is extracted and its body is simplified.
705 %************************************************************************
707 \subsection{Error messages}
709 %************************************************************************
712 instDeclCtxt1 hs_inst_ty
713 = inst_decl_ctxt (case unLoc hs_inst_ty of
714 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
715 HsPredTy pred -> ppr pred
716 other -> ppr hs_inst_ty) -- Don't expect this
717 instDeclCtxt2 dfun_ty
718 = inst_decl_ctxt (ppr (mkClassPred cls tys))
720 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
722 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
724 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")