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, badATErr,
15 omittedATWarn, 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, classATs )
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 NameSet ( NameSet, addListToNameSet, emptyNameSet,
43 minusNameSet, nameSetToList )
44 import Maybe ( isNothing, fromJust, catMaybes )
46 import DynFlags ( DynFlag(Opt_WarnMissingMethods) )
47 import SrcLoc ( srcLocSpan, unLoc, noLoc, Located(..), srcSpanStart )
48 import ListSetOps ( minusList )
51 import BasicTypes ( Activation( AlwaysActive ), InlineSpec(..) )
52 import HscTypes ( implicitTyThings )
56 Typechecking instance declarations is done in two passes. The first
57 pass, made by @tcInstDecls1@, collects information to be used in the
60 This pre-processed info includes the as-yet-unprocessed bindings
61 inside the instance declaration. These are type-checked in the second
62 pass, when the class-instance envs and GVE contain all the info from
63 all the instance and value decls. Indeed that's the reason we need
64 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 :: [LTyClDecl Name] -- For deriving stuff
140 -> [LInstDecl Name] -- 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 HsValBinds Name) -- Supporting bindings for derived instances
146 tcInstDecls1 tycl_decls inst_decls
148 do { -- Stop if addInstInfos etc discovers any errors
149 -- (they recover, so that we get more than one error each
152 -- (1) Do the ordinary instance declarations and instances of
154 ; let { idxty_decls = filter (isIdxTyDecl . unLoc) tycl_decls }
155 ; local_info_tycons <- mappM tcLocalInstDecl1 inst_decls
156 ; idxty_info_tycons <- mappM tcIdxTyInstDeclTL idxty_decls
158 ; let { (local_infos,
159 local_tycons) = unzip local_info_tycons
161 idxty_tycons) = unzip idxty_info_tycons
162 ; local_idxty_info = concat local_infos ++ catMaybes idxty_infos
163 ; local_idxty_tycon = concat local_tycons ++
164 catMaybes idxty_tycons
165 ; clas_decls = filter (isClassDecl.unLoc) tycl_decls
166 ; implicit_things = concatMap implicitTyThings local_idxty_tycon
169 -- (2) Add the tycons of associated types and their implicit
170 -- tythings to the global environment
171 ; tcExtendGlobalEnv (local_idxty_tycon ++ implicit_things) $ do {
173 -- (3) Instances from generic class declarations
174 ; generic_inst_info <- getGenericInstances clas_decls
176 -- Next, construct the instance environment so far, consisting
178 -- a) local instance decls
179 -- b) generic instances
180 ; addInsts local_idxty_info $ do {
181 ; addInsts generic_inst_info $ do {
183 -- (4) Compute instances from "deriving" clauses;
184 -- This stuff computes a context for the derived instance
185 -- decl, so it needs to know about all the instances possible
186 ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls
187 ; addInsts deriv_inst_info $ do {
189 ; gbl_env <- getGblEnv
191 generic_inst_info ++ deriv_inst_info ++ local_idxty_info,
195 -- Make sure that toplevel type instance are not for associated types.
196 -- !!!TODO: Need to perform this check for the InstInfo structures of type
198 tcIdxTyInstDeclTL ldecl@(L loc decl) =
199 do { (info, tything) <- tcIdxTyInstDecl ldecl
201 when (isAssocFamily tything) $
202 addErr $ assocInClassErr (tcdName decl)
203 ; return (info, tything)
205 isAssocFamily (Just (ATyCon tycon)) =
206 case tyConFamInst_maybe tycon of
207 Nothing -> panic "isAssocFamily: no family?!?"
208 Just (fam, _) -> isAssocTyCon fam
209 isAssocFamily (Just _ ) = panic "isAssocFamily: no tycon?!?"
210 isAssocFamily Nothing = False
212 assocInClassErr name =
213 ptext SLIT("Associated type must be inside class instance") <+>
216 addInsts :: [InstInfo] -> TcM a -> TcM a
217 addInsts infos thing_inside
218 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
222 tcLocalInstDecl1 :: LInstDecl Name
223 -> TcM ([InstInfo], [TyThing]) -- [] if there was an error
224 -- A source-file instance declaration
225 -- Type-check all the stuff before the "where"
227 -- We check for respectable instance type, and context
228 tcLocalInstDecl1 decl@(L loc (InstDecl poly_ty binds uprags ats))
229 = -- Prime error recovery, set source location
230 recoverM (returnM ([], [])) $
232 addErrCtxt (instDeclCtxt1 poly_ty) $
234 do { is_boot <- tcIsHsBoot
235 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
238 -- Typecheck the instance type itself. We can't use
239 -- tcHsSigType, because it's not a valid user type.
240 ; kinded_ty <- kcHsSigType poly_ty
241 ; poly_ty' <- tcHsKindedType kinded_ty
242 ; let (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
244 -- Next, process any associated types.
245 ; idxty_info_tycons <- mappM tcIdxTyInstDecl ats
247 -- Now, check the validity of the instance.
248 ; (clas, inst_tys) <- checkValidInstHead tau
249 ; checkValidInstance tyvars theta clas inst_tys
250 ; checkValidOrMissingAT clas
252 -- Finally, construct the Core representation of the instance.
253 -- (This no longer includes the associated types.)
254 ; dfun_name <- newDFunName clas inst_tys (srcSpanStart loc)
255 ; overlap_flag <- getOverlapFlag
256 ; let dfun = mkDictFunId dfun_name tyvars theta clas inst_tys
257 ispec = mkLocalInstance dfun overlap_flag
259 idxty_tycons) = unzip idxty_info_tycons
261 ; return ([InstInfo { iSpec = ispec,
262 iBinds = VanillaInst binds uprags }] ++
263 catMaybes idxty_infos,
264 catMaybes idxty_tycons)
267 checkValidOrMissingAT clas
268 = do { let classDefATs = addListToNameSet emptyNameSet
272 definedATs = addListToNameSet emptyNameSet
273 . map (tcdName . unLoc)
275 omitted = classDefATs `minusNameSet` definedATs
276 excess = definedATs `minusNameSet` classDefATs
277 ; mapM_ (addErrTc . badATErr clas) (nameSetToList excess)
278 ; warn <- doptM Opt_WarnMissingMethods
279 ; mapM_ (warnTc warn . omittedATWarn) (nameSetToList omitted)
284 %************************************************************************
286 \subsection{Type-checking instance declarations, pass 2}
288 %************************************************************************
291 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo]
292 -> TcM (LHsBinds Id, TcLclEnv)
293 -- (a) From each class declaration,
294 -- generate any default-method bindings
295 -- (b) From each instance decl
296 -- generate the dfun binding
298 tcInstDecls2 tycl_decls inst_decls
299 = do { -- (a) Default methods from class decls
300 (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $
301 filter (isClassDecl.unLoc) tycl_decls
302 ; tcExtendIdEnv (concat dm_ids_s) $ do
304 -- (b) instance declarations
305 ; inst_binds_s <- mappM tcInstDecl2 inst_decls
308 ; let binds = unionManyBags dm_binds_s `unionBags`
309 unionManyBags inst_binds_s
310 ; tcl_env <- getLclEnv -- Default method Ids in here
311 ; returnM (binds, tcl_env) }
314 ======= New documentation starts here (Sept 92) ==============
316 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
317 the dictionary function for this instance declaration. For example
319 instance Foo a => Foo [a] where
323 might generate something like
325 dfun.Foo.List dFoo_a = let op1 x = ...
331 HOWEVER, if the instance decl has no context, then it returns a
332 bigger @HsBinds@ with declarations for each method. For example
334 instance Foo [a] where
340 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
341 const.Foo.op1.List a x = ...
342 const.Foo.op2.List a y = ...
344 This group may be mutually recursive, because (for example) there may
345 be no method supplied for op2 in which case we'll get
347 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
349 that is, the default method applied to the dictionary at this type.
351 What we actually produce in either case is:
353 AbsBinds [a] [dfun_theta_dicts]
354 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
355 { d = (sd1,sd2, ..., op1, op2, ...)
360 The "maybe" says that we only ask AbsBinds to make global constant methods
361 if the dfun_theta is empty.
364 For an instance declaration, say,
366 instance (C1 a, C2 b) => C (T a b) where
369 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
370 function whose type is
372 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
374 Notice that we pass it the superclass dictionaries at the instance type; this
375 is the ``Mark Jones optimisation''. The stuff before the "=>" here
376 is the @dfun_theta@ below.
378 First comes the easy case of a non-local instance decl.
382 tcInstDecl2 :: InstInfo -> TcM (LHsBinds Id)
383 -- Returns a binding for the dfun
385 ------------------------
386 -- Derived newtype instances
388 -- We need to make a copy of the dictionary we are deriving from
389 -- because we may need to change some of the superclass dictionaries
390 -- see Note [Newtype deriving superclasses] in TcDeriv.lhs
392 -- In the case of a newtype, things are rather easy
393 -- class Show a => Foo a b where ...
394 -- newtype T a = MkT (Tree [a]) deriving( Foo Int )
395 -- The newtype gives an FC axiom looking like
396 -- axiom CoT a :: T a :=: Tree [a]
398 -- So all need is to generate a binding looking like
399 -- dfunFooT :: forall a. (Foo Int (Tree [a], Show (T a)) => Foo Int (T a)
400 -- dfunFooT = /\a. \(ds:Show (T a)) (df:Foo (Tree [a])).
401 -- case df `cast` (Foo Int (sym (CoT a))) of
402 -- Foo _ op1 .. opn -> Foo ds op1 .. opn
404 tcInstDecl2 (InstInfo { iSpec = ispec,
405 iBinds = NewTypeDerived tycon rep_tys })
406 = do { let dfun_id = instanceDFunId ispec
407 rigid_info = InstSkol dfun_id
408 origin = SigOrigin rigid_info
409 inst_ty = idType dfun_id
410 ; inst_loc <- getInstLoc origin
411 ; (tvs, theta, inst_head) <- tcSkolSigType rigid_info inst_ty
412 ; dicts <- newDictBndrs inst_loc theta
413 ; uniqs <- newUniqueSupply
414 ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head
415 ; this_dict <- newDictBndr inst_loc (mkClassPred cls rep_tys)
416 ; let (rep_dict_id:sc_dict_ids)
417 | null dicts = [instToId this_dict]
418 | otherwise = map instToId dicts
420 -- (Here, we are relying on the order of dictionary
421 -- arguments built by NewTypeDerived in TcDeriv.)
423 wrap_fn = mkCoTyLams tvs <.> mkCoLams (rep_dict_id:sc_dict_ids)
425 -- we need to find the kind that this class applies to
426 -- and drop trailing tvs appropriately
427 cls_kind = tyVarKind (head (reverse (tyConTyVars cls_tycon)))
428 the_tvs = drop_tail (length (fst (splitFunTys cls_kind))) tvs
430 coerced_rep_dict = mkHsCoerce (co_fn the_tvs cls_tycon cls_inst_tys) (HsVar rep_dict_id)
432 body | null sc_dict_ids = coerced_rep_dict
433 | otherwise = HsCase (noLoc coerced_rep_dict) $
434 MatchGroup [the_match] (mkFunTy in_dict_ty inst_head)
435 in_dict_ty = mkTyConApp cls_tycon cls_inst_tys
437 the_match = mkSimpleMatch [noLoc the_pat] the_rhs
438 the_rhs = mkHsConApp cls_data_con cls_inst_tys (map HsVar (sc_dict_ids ++ op_ids))
440 (uniqs1, uniqs2) = splitUniqSupply uniqs
442 op_ids = zipWith (mkSysLocal FSLIT("op"))
443 (uniqsFromSupply uniqs1) op_tys
445 dict_ids = zipWith (mkSysLocal FSLIT("dict"))
446 (uniqsFromSupply uniqs2) (map idType sc_dict_ids)
448 the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [],
449 pat_dicts = dict_ids,
450 pat_binds = emptyLHsBinds,
451 pat_args = PrefixCon (map nlVarPat op_ids),
454 cls_data_con = classDataCon cls
455 cls_tycon = dataConTyCon cls_data_con
456 cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys
458 n_dict_args = if length dicts == 0 then 0 else length dicts - 1
459 op_tys = drop n_dict_args cls_arg_tys
461 dict = mkHsCoerce wrap_fn body
462 ; return (unitBag (noLoc $ VarBind dfun_id (noLoc dict))) }
464 -- For newtype T a = MkT <ty>
465 -- The returned coercion has kind :: C (T a):=:C <ty>
466 co_fn tvs cls_tycon cls_inst_tys | Just co_con <- newTyConCo tycon
467 = ExprCoFn (mkTyConApp cls_tycon (drop_tail 1 cls_inst_tys ++
468 [mkSymCoercion (mkTyConApp co_con (map mkTyVarTy tvs))]))
471 drop_tail n l = take (length l - n) l
473 ------------------------
474 -- Ordinary instances
476 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags })
478 dfun_id = instanceDFunId ispec
479 rigid_info = InstSkol dfun_id
480 inst_ty = idType dfun_id
482 -- Prime error recovery
483 recoverM (returnM emptyLHsBinds) $
484 setSrcSpan (srcLocSpan (getSrcLoc dfun_id)) $
485 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
487 -- Instantiate the instance decl with skolem constants
488 tcSkolSigType rigid_info inst_ty `thenM` \ (inst_tyvars', dfun_theta', inst_head') ->
489 -- These inst_tyvars' scope over the 'where' part
490 -- Those tyvars are inside the dfun_id's type, which is a bit
491 -- bizarre, but OK so long as you realise it!
493 (clas, inst_tys') = tcSplitDFunHead inst_head'
494 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
496 -- Instantiate the super-class context with inst_tys
497 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
498 origin = SigOrigin rigid_info
500 -- Create dictionary Ids from the specified instance contexts.
501 getInstLoc InstScOrigin `thenM` \ sc_loc ->
502 newDictBndrs sc_loc sc_theta' `thenM` \ sc_dicts ->
503 getInstLoc origin `thenM` \ inst_loc ->
504 newDictBndrs inst_loc dfun_theta' `thenM` \ dfun_arg_dicts ->
505 newDictBndr inst_loc (mkClassPred clas inst_tys') `thenM` \ this_dict ->
506 -- Default-method Ids may be mentioned in synthesised RHSs,
507 -- but they'll already be in the environment.
509 -- Typecheck the methods
510 let -- These insts are in scope; quite a few, eh?
511 avail_insts = [this_dict] ++ dfun_arg_dicts ++ sc_dicts
513 tcMethods origin clas inst_tyvars'
514 dfun_theta' inst_tys' avail_insts
515 op_items monobinds uprags `thenM` \ (meth_ids, meth_binds) ->
517 -- Figure out bindings for the superclass context
518 -- Don't include this_dict in the 'givens', else
519 -- sc_dicts get bound by just selecting from this_dict!!
520 addErrCtxt superClassCtxt
521 (tcSimplifySuperClasses inst_tyvars'
523 sc_dicts) `thenM` \ sc_binds ->
525 -- It's possible that the superclass stuff might unified one
526 -- of the inst_tyavars' with something in the envt
527 checkSigTyVars inst_tyvars' `thenM_`
529 -- Deal with 'SPECIALISE instance' pragmas
530 tcPrags dfun_id (filter isSpecInstLSig uprags) `thenM` \ prags ->
532 -- Create the result bindings
534 dict_constr = classDataCon clas
535 scs_and_meths = map instToId sc_dicts ++ meth_ids
536 this_dict_id = instToId this_dict
537 inline_prag | null dfun_arg_dicts = []
538 | otherwise = [InlinePrag (Inline AlwaysActive True)]
539 -- Always inline the dfun; this is an experimental decision
540 -- because it makes a big performance difference sometimes.
541 -- Often it means we can do the method selection, and then
542 -- inline the method as well. Marcin's idea; see comments below.
544 -- BUT: don't inline it if it's a constant dictionary;
545 -- we'll get all the benefit without inlining, and we get
546 -- a **lot** of code duplication if we inline it
548 -- See Note [Inline dfuns] below
551 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
552 -- We don't produce a binding for the dict_constr; instead we
553 -- rely on the simplifier to unfold this saturated application
554 -- We do this rather than generate an HsCon directly, because
555 -- it means that the special cases (e.g. dictionary with only one
556 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
557 -- than needing to be repeated here.
559 dict_bind = noLoc (VarBind this_dict_id dict_rhs)
560 all_binds = dict_bind `consBag` (sc_binds `unionBags` meth_binds)
562 main_bind = noLoc $ AbsBinds
564 (map instToId dfun_arg_dicts)
565 [(inst_tyvars', dfun_id, this_dict_id,
566 inline_prag ++ prags)]
569 showLIE (text "instance") `thenM_`
570 returnM (unitBag main_bind)
573 tcMethods origin clas inst_tyvars' dfun_theta' inst_tys'
574 avail_insts op_items monobinds uprags
575 = -- Check that all the method bindings come from this class
577 sel_names = [idName sel_id | (sel_id, _) <- op_items]
578 bad_bndrs = collectHsBindBinders monobinds `minusList` sel_names
580 mappM (addErrTc . badMethodErr clas) bad_bndrs `thenM_`
582 -- Make the method bindings
584 mk_method_bind = mkMethodBind origin clas inst_tys' monobinds
586 mapAndUnzipM mk_method_bind op_items `thenM` \ (meth_insts, meth_infos) ->
588 -- And type check them
589 -- It's really worth making meth_insts available to the tcMethodBind
590 -- Consider instance Monad (ST s) where
591 -- {-# INLINE (>>) #-}
592 -- (>>) = ...(>>=)...
593 -- If we don't include meth_insts, we end up with bindings like this:
594 -- rec { dict = MkD then bind ...
595 -- then = inline_me (... (GHC.Base.>>= dict) ...)
597 -- The trouble is that (a) 'then' and 'dict' are mutually recursive,
598 -- and (b) the inline_me prevents us inlining the >>= selector, which
599 -- would unravel the loop. Result: (>>) ends up as a loop breaker, and
600 -- is not inlined across modules. Rather ironic since this does not
601 -- happen without the INLINE pragma!
603 -- Solution: make meth_insts available, so that 'then' refers directly
604 -- to the local 'bind' rather than going via the dictionary.
606 -- BUT WATCH OUT! If the method type mentions the class variable, then
607 -- this optimisation is not right. Consider
611 -- instance C Int where
613 -- The occurrence of 'op' on the rhs gives rise to a constraint
615 -- The trouble is that the 'meth_inst' for op, which is 'available', also
616 -- looks like 'op at Int'. But they are not the same.
618 prag_fn = mkPragFun uprags
619 all_insts = avail_insts ++ catMaybes meth_insts
620 sig_fn n = Just [] -- No scoped type variables, but every method has
621 -- a type signature, in effect, so that we check
622 -- the method has the right type
623 tc_method_bind = tcMethodBind inst_tyvars' dfun_theta' all_insts sig_fn prag_fn
624 meth_ids = [meth_id | (_,meth_id,_) <- meth_infos]
627 mapM tc_method_bind meth_infos `thenM` \ meth_binds_s ->
629 returnM (meth_ids, unionManyBags meth_binds_s)
633 ------------------------------
634 [Inline dfuns] Inlining dfuns unconditionally
635 ------------------------------
637 The code above unconditionally inlines dict funs. Here's why.
638 Consider this program:
640 test :: Int -> Int -> Bool
641 test x y = (x,y) == (y,x) || test y x
642 -- Recursive to avoid making it inline.
644 This needs the (Eq (Int,Int)) instance. If we inline that dfun
645 the code we end up with is good:
648 \r -> case ==# [ww ww1] of wild {
649 PrelBase.False -> Test.$wtest ww1 ww;
651 case ==# [ww1 ww] of wild1 {
652 PrelBase.False -> Test.$wtest ww1 ww;
653 PrelBase.True -> PrelBase.True [];
656 Test.test = \r [w w1]
659 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
662 If we don't inline the dfun, the code is not nearly as good:
664 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
665 PrelBase.:DEq tpl1 tpl2 -> tpl2;
670 let { y = PrelBase.I#! [ww1]; } in
671 let { x = PrelBase.I#! [ww]; } in
672 let { sat_slx = PrelTup.(,)! [y x]; } in
673 let { sat_sly = PrelTup.(,)! [x y];
675 case == sat_sly sat_slx of wild {
676 PrelBase.False -> Test.$wtest ww1 ww;
677 PrelBase.True -> PrelBase.True [];
684 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
687 Why doesn't GHC inline $fEq? Because it looks big:
689 PrelTup.zdfEqZ1T{-rcX-}
690 = \ @ a{-reT-} :: * @ b{-reS-} :: *
691 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
692 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
694 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
695 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
697 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
698 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
700 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
701 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
702 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
704 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
706 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
708 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
709 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
713 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
714 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
715 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
716 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
718 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
720 and it's not as bad as it seems, because it's further dramatically
721 simplified: only zeze2 is extracted and its body is simplified.
724 %************************************************************************
726 \subsection{Error messages}
728 %************************************************************************
731 instDeclCtxt1 hs_inst_ty
732 = inst_decl_ctxt (case unLoc hs_inst_ty of
733 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
734 HsPredTy pred -> ppr pred
735 other -> ppr hs_inst_ty) -- Don't expect this
736 instDeclCtxt2 dfun_ty
737 = inst_decl_ctxt (ppr (mkClassPred cls tys))
739 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
741 inst_decl_ctxt doc = ptext SLIT("In the instance declaration for") <+> quotes doc
743 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")