2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcInstDecls]{Typechecking instance declarations}
7 module TcInstDcls ( tcInstDecls1, tcInstDecls2, tcAddDeclCtxt ) where
9 #include "HsVersions.h"
12 import CmdLineOpts ( DynFlag(..) )
14 import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..), HsType(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), HsTyVarBndr(..),
16 andMonoBindList, collectMonoBinders, isClassDecl, toHsType
18 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl,
19 RenamedMonoBinds, RenamedTyClDecl, RenamedHsType,
20 extractHsTyVars, maybeGenericMatch
22 import TcHsSyn ( TcMonoBinds, mkHsConApp )
23 import TcBinds ( tcSpecSigs )
24 import TcClassDcl ( tcMethodBind, badMethodErr )
26 import TcMType ( tcInstTyVars, checkValidTheta, checkValidInstHead, instTypeErr,
27 UserTypeCtxt(..), SourceTyCtxt(..) )
28 import TcType ( tcSplitDFunTy, mkClassPred, mkTyVarTy,
29 tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys
31 import Inst ( InstOrigin(..),
33 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
34 import TcDeriv ( tcDeriving )
35 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
36 tcExtendTyVarEnvForMeths,
37 tcAddImportedIdInfo, tcLookupClass,
38 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
39 simpleInstInfoTy, newDFunName,
42 import InstEnv ( InstEnv, extendInstEnv )
43 import PprType ( pprClassPred )
44 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType, checkSigTyVars )
45 import TcSimplify ( tcSimplifyCheck )
46 import HscTypes ( HomeSymbolTable, DFunId,
47 ModDetails(..), PackageInstEnv, PersistentRenamerState
50 import Subst ( substTy, substTheta )
51 import DataCon ( classDataCon )
52 import Class ( Class, DefMeth(..), classBigSig )
53 import Var ( idName, idType )
54 import VarSet ( emptyVarSet )
55 import Id ( setIdLocalExported )
56 import MkId ( mkDictFunId )
57 import FunDeps ( checkInstFDs )
58 import Generics ( validGenericInstanceType )
59 import Module ( Module, foldModuleEnv )
60 import Name ( getSrcLoc )
61 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
62 import PrelInfo ( eRROR_ID )
63 import TyCon ( TyCon )
64 import Subst ( mkTopTyVarSubst, substTheta )
65 import TysWiredIn ( genericTyCons )
67 import SrcLoc ( SrcLoc )
68 import Unique ( Uniquable(..) )
69 import Util ( lengthExceeds )
70 import BasicTypes ( NewOrData(..), Fixity )
71 import ErrUtils ( dumpIfSet_dyn )
72 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
73 assocElts, extendAssoc_C,
74 equivClassesByUniq, minusList
76 import List ( partition )
80 Typechecking instance declarations is done in two passes. The first
81 pass, made by @tcInstDecls1@, collects information to be used in the
84 This pre-processed info includes the as-yet-unprocessed bindings
85 inside the instance declaration. These are type-checked in the second
86 pass, when the class-instance envs and GVE contain all the info from
87 all the instance and value decls. Indeed that's the reason we need
88 two passes over the instance decls.
91 Here is the overall algorithm.
92 Assume that we have an instance declaration
94 instance c => k (t tvs) where b
98 $LIE_c$ is the LIE for the context of class $c$
100 $betas_bar$ is the free variables in the class method type, excluding the
103 $LIE_cop$ is the LIE constraining a particular class method
105 $tau_cop$ is the tau type of a class method
107 $LIE_i$ is the LIE for the context of instance $i$
109 $X$ is the instance constructor tycon
111 $gammas_bar$ is the set of type variables of the instance
113 $LIE_iop$ is the LIE for a particular class method instance
115 $tau_iop$ is the tau type for this instance of a class method
117 $alpha$ is the class variable
119 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
121 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
124 ToDo: Update the list above with names actually in the code.
128 First, make the LIEs for the class and instance contexts, which means
129 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
130 and make LIElistI and LIEI.
132 Then process each method in turn.
134 order the instance methods according to the ordering of the class methods
136 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
138 Create final dictionary function from bindings generated already
140 df = lambda inst_tyvars
147 in <op1,op2,...,opn,sd1,...,sdm>
149 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
150 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
154 %************************************************************************
156 \subsection{Extracting instance decls}
158 %************************************************************************
160 Gather up the instance declarations from their various sources
163 tcInstDecls1 :: PackageInstEnv
164 -> PersistentRenamerState
165 -> HomeSymbolTable -- Contains instances
166 -> TcEnv -- Contains IdInfo for dfun ids
167 -> (Name -> Maybe Fixity) -- for deriving Show and Read
168 -> Module -- Module for deriving
170 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
172 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
174 inst_decls = [inst_decl | InstD inst_decl <- decls]
175 tycl_decls = [decl | TyClD decl <- decls]
176 clas_decls = filter isClassDecl tycl_decls
178 -- (1) Do the ordinary instance declarations
179 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
181 -- (2) Instances from generic class declarations
182 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
184 -- Next, construct the instance environment so far, consisting of
185 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
186 -- b) imported instance decls (not in the home package) inst_env1
187 -- c) other modules in this package (gotten from hst) inst_env2
188 -- d) local instance decls inst_env3
189 -- e) generic instances inst_env4
190 -- The result of (b) replaces the cached InstEnv in the PCS
192 (local_inst_info, imported_inst_info)
193 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
195 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
197 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
200 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
202 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
203 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
204 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
205 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
207 -- (3) Compute instances from "deriving" clauses;
208 -- note that we only do derivings for things in this module;
209 -- we ignore deriving decls from interfaces!
210 -- This stuff computes a context for the derived instance decl, so it
211 -- needs to know about all the instances possible; hecne inst_env4
212 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
213 `thenTc` \ (deriv_inst_info, deriv_binds) ->
214 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
218 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
221 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
222 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
224 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
225 addInstDFuns inst_env dfuns
226 = getDOptsTc `thenTc` \ dflags ->
228 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
230 addErrsTc errs `thenNF_Tc_`
231 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
234 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
238 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
239 -- Deal with a single instance declaration
240 -- Type-check all the stuff before the "where"
241 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
242 = -- Prime error recovery, set source location
243 recoverNF_Tc (returnNF_Tc []) $
244 tcAddSrcLoc src_loc $
245 tcAddErrCtxt (instDeclCtxt poly_ty) $
247 -- Typecheck the instance type itself. We can't use
248 -- tcHsSigType, because it's not a valid user type.
249 kcHsSigType poly_ty `thenTc_`
250 tcHsType poly_ty `thenTc` \ poly_ty' ->
252 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
253 (clas,inst_tys) = case tcSplitPredTy_maybe tau of { Just st -> getClassPredTys st }
254 -- The checkValidInstHead makes sure these splits succeed
256 (case maybe_dfun_name of
257 Nothing -> -- A source-file instance declaration
258 -- Check for respectable instance type, and context
259 -- but only do this for non-imported instance decls.
260 -- Imported ones should have been checked already, and may indeed
261 -- contain something illegal in normal Haskell, notably
262 -- instance CCallable [Char]
263 checkValidTheta InstThetaCtxt theta `thenTc_`
264 checkValidInstHead tau `thenTc_`
265 checkTc (checkInstFDs theta clas inst_tys)
266 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
267 newDFunName clas inst_tys src_loc
269 Just dfun_name -> -- An interface-file instance declaration
270 returnNF_Tc dfun_name
271 ) `thenNF_Tc` \ dfun_name ->
273 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
275 returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
277 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
281 %************************************************************************
283 \subsection{Extracting generic instance declaration from class declarations}
285 %************************************************************************
287 @getGenericInstances@ extracts the generic instance declarations from a class
288 declaration. For exmaple
293 op{ x+y } (Inl v) = ...
294 op{ x+y } (Inr v) = ...
295 op{ x*y } (v :*: w) = ...
298 gives rise to the instance declarations
300 instance C (x+y) where
304 instance C (x*y) where
312 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
313 getGenericInstances class_decls
314 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
316 gen_inst_info = concat gen_inst_infos
318 if null gen_inst_info then
321 getDOptsTc `thenTc` \ dflags ->
322 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
323 (vcat (map pprInstInfo gen_inst_info)))
325 returnTc gen_inst_info
327 get_generics decl@(ClassDecl {tcdMeths = Nothing})
328 = returnTc [] -- Imported class decls
330 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
332 = returnTc [] -- The comon case: no generic default methods
334 | otherwise -- A source class decl with generic default methods
335 = recoverNF_Tc (returnNF_Tc []) $
337 tcLookupClass class_name `thenTc` \ clas ->
339 -- Make an InstInfo out of each group
340 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
342 -- Check that there is only one InstInfo for each type constructor
343 -- The main way this can fail is if you write
344 -- f {| a+b |} ... = ...
345 -- f {| x+y |} ... = ...
346 -- Then at this point we'll have an InstInfo for each
348 tc_inst_infos :: [(TyCon, InstInfo)]
349 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
351 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
352 group `lengthExceeds` 1]
353 get_uniq (tc,_) = getUnique tc
355 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
357 -- Check that there is an InstInfo for each generic type constructor
359 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
361 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
366 -- Group the declarations by type pattern
367 groups :: [(RenamedHsType, RenamedMonoBinds)]
368 groups = assocElts (getGenericBinds def_methods)
371 ---------------------------------
372 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
373 -- Takes a group of method bindings, finds the generic ones, and returns
374 -- them in finite map indexed by the type parameter in the definition.
376 getGenericBinds EmptyMonoBinds = emptyAssoc
377 getGenericBinds (AndMonoBinds m1 m2)
378 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
380 getGenericBinds (FunMonoBind id infixop matches loc)
381 = mapAssoc wrap (foldl add emptyAssoc matches)
382 -- Using foldl not foldr is vital, else
383 -- we reverse the order of the bindings!
385 add env match = case maybeGenericMatch match of
387 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
389 wrap ms = FunMonoBind id infixop ms loc
391 ---------------------------------
392 mkGenericInstance :: Class -> SrcLoc
393 -> (RenamedHsType, RenamedMonoBinds)
396 mkGenericInstance clas loc (hs_ty, binds)
397 -- Make a generic instance declaration
398 -- For example: instance (C a, C b) => C (a+b) where { binds }
400 = -- Extract the universally quantified type variables
402 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
404 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
406 -- Type-check the instance type, and check its form
407 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
408 checkTc (validGenericInstanceType inst_ty)
409 (badGenericInstanceType binds) `thenTc_`
411 -- Make the dictionary function.
412 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
414 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
416 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
419 returnTc (InstInfo { iDFunId = dfun_id,
420 iBinds = binds, iPrags = [] })
424 %************************************************************************
426 \subsection{Type-checking instance declarations, pass 2}
428 %************************************************************************
431 tcInstDecls2 :: [InstInfo]
432 -> NF_TcM (LIE, TcMonoBinds)
434 tcInstDecls2 inst_decls
435 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
436 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
437 (map tcInstDecl2 inst_decls)
439 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
440 tc2 `thenNF_Tc` \ (lie2, binds2) ->
441 returnNF_Tc (lie1 `plusLIE` lie2,
442 binds1 `AndMonoBinds` binds2)
445 ======= New documentation starts here (Sept 92) ==============
447 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
448 the dictionary function for this instance declaration. For example
450 instance Foo a => Foo [a] where
454 might generate something like
456 dfun.Foo.List dFoo_a = let op1 x = ...
462 HOWEVER, if the instance decl has no context, then it returns a
463 bigger @HsBinds@ with declarations for each method. For example
465 instance Foo [a] where
471 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
472 const.Foo.op1.List a x = ...
473 const.Foo.op2.List a y = ...
475 This group may be mutually recursive, because (for example) there may
476 be no method supplied for op2 in which case we'll get
478 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
480 that is, the default method applied to the dictionary at this type.
482 What we actually produce in either case is:
484 AbsBinds [a] [dfun_theta_dicts]
485 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
486 { d = (sd1,sd2, ..., op1, op2, ...)
491 The "maybe" says that we only ask AbsBinds to make global constant methods
492 if the dfun_theta is empty.
495 For an instance declaration, say,
497 instance (C1 a, C2 b) => C (T a b) where
500 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
501 function whose type is
503 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
505 Notice that we pass it the superclass dictionaries at the instance type; this
506 is the ``Mark Jones optimisation''. The stuff before the "=>" here
507 is the @dfun_theta@ below.
509 First comes the easy case of a non-local instance decl.
513 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
514 -- tcInstDecl2 is called *only* on InstInfos
516 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
517 iBinds = monobinds, iPrags = uprags })
518 = -- Prime error recovery
519 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
520 tcAddSrcLoc (getSrcLoc dfun_id) $
521 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
523 -- Instantiate the instance decl with tc-style type variables
525 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
527 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
529 inst_tys' = map (substTy tenv) inst_tys
530 dfun_theta' = substTheta tenv dfun_theta
531 origin = InstanceDeclOrigin
533 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
535 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
536 sel_names = [idName sel_id | (sel_id, _) <- op_items]
538 -- Instantiate the super-class context with inst_tys
539 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
541 -- Find any definitions in monobinds that aren't from the class
542 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
544 -- Check that all the method bindings come from this class
545 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
547 -- Create dictionary Ids from the specified instance contexts.
548 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
549 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
550 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
552 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
553 -- The type variable from the dict fun actually scope
554 -- over the bindings. They were gotten from
555 -- the original instance declaration
556 tcExtendGlobalValEnv dm_ids (
557 -- Default-method Ids may be mentioned in synthesised RHSs
559 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
561 monobinds uprags True)
563 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
565 -- Deal with SPECIALISE instance pragmas by making them
566 -- look like SPECIALISE pragmas for the dfun
568 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
570 tcExtendGlobalValEnv [dfun_id] (
571 tcSpecSigs dfun_prags
572 ) `thenTc` \ (prag_binds, prag_lie) ->
574 -- Check the overloading constraints of the methods and superclasses
576 -- These insts are in scope; quite a few, eh?
577 avail_insts = [this_dict] ++
582 methods_lie = plusLIEs insts_needed_s
585 -- Simplify the constraints from methods
586 tcAddErrCtxt methodCtxt (
588 (ptext SLIT("instance declaration context"))
592 ) `thenTc` \ (const_lie1, lie_binds1) ->
594 -- Figure out bindings for the superclass context
595 tcAddErrCtxt superClassCtxt (
597 (ptext SLIT("instance declaration context"))
599 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
600 -- get bound by just selecting from this_dict!!
602 ) `thenTc` \ (const_lie2, lie_binds2) ->
604 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
606 -- Create the result bindings
608 local_dfun_id = setIdLocalExported dfun_id
609 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
611 dict_constr = classDataCon clas
612 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
613 this_dict_id = instToId this_dict
614 inlines | null dfun_arg_dicts = emptyNameSet
615 | otherwise = unitNameSet (idName dfun_id)
616 -- Always inline the dfun; this is an experimental decision
617 -- because it makes a big performance difference sometimes.
618 -- Often it means we can do the method selection, and then
619 -- inline the method as well. Marcin's idea; see comments below.
621 -- BUT: don't inline it if it's a constant dictionary;
622 -- we'll get all the benefit without inlining, and we get
623 -- a **lot** of code duplication if we inline it
627 = -- Blatant special case for CCallable, CReturnable
628 -- If the dictionary is empty then we should never
629 -- select anything from it, so we make its RHS just
630 -- emit an error message. This in turn means that we don't
631 -- mention the constructor, which doesn't exist for CCallable, CReturnable
632 -- Hardly beautiful, but only three extra lines.
633 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
634 (HsLit (HsString msg))
636 | otherwise -- The common case
637 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
638 -- We don't produce a binding for the dict_constr; instead we
639 -- rely on the simplifier to unfold this saturated application
640 -- We do this rather than generate an HsCon directly, because
641 -- it means that the special cases (e.g. dictionary with only one
642 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
643 -- than needing to be repeated here.
646 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
648 dict_bind = VarMonoBind this_dict_id dict_rhs
649 method_binds = andMonoBindList method_binds_s
654 (map instToId dfun_arg_dicts)
655 [(inst_tyvars', local_dfun_id, this_dict_id)]
657 (lie_binds1 `AndMonoBinds`
658 lie_binds2 `AndMonoBinds`
659 method_binds `AndMonoBinds`
662 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
663 main_bind `AndMonoBinds` prag_binds)
666 ------------------------------
667 Inlining dfuns unconditionally
668 ------------------------------
670 The code above unconditionally inlines dict funs. Here's why.
671 Consider this program:
673 test :: Int -> Int -> Bool
674 test x y = (x,y) == (y,x) || test y x
675 -- Recursive to avoid making it inline.
677 This needs the (Eq (Int,Int)) instance. If we inline that dfun
678 the code we end up with is good:
681 \r -> case ==# [ww ww1] of wild {
682 PrelBase.False -> Test.$wtest ww1 ww;
684 case ==# [ww1 ww] of wild1 {
685 PrelBase.False -> Test.$wtest ww1 ww;
686 PrelBase.True -> PrelBase.True [];
689 Test.test = \r [w w1]
692 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
695 If we don't inline the dfun, the code is not nearly as good:
697 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
698 PrelBase.:DEq tpl1 tpl2 -> tpl2;
703 let { y = PrelBase.I#! [ww1]; } in
704 let { x = PrelBase.I#! [ww]; } in
705 let { sat_slx = PrelTup.(,)! [y x]; } in
706 let { sat_sly = PrelTup.(,)! [x y];
708 case == sat_sly sat_slx of wild {
709 PrelBase.False -> Test.$wtest ww1 ww;
710 PrelBase.True -> PrelBase.True [];
717 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
720 Why doesn't GHC inline $fEq? Because it looks big:
722 PrelTup.zdfEqZ1T{-rcX-}
723 = \ @ a{-reT-} :: * @ b{-reS-} :: *
724 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
725 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
727 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
728 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
730 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
731 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
733 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
734 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
735 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
737 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
739 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
741 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
742 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
746 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
747 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
748 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
749 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
751 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
753 and it's not as bad as it seems, because it's further dramatically
754 simplified: only zeze2 is extracted and its body is simplified.
757 %************************************************************************
759 \subsection{Error messages}
761 %************************************************************************
764 tcAddDeclCtxt decl thing_inside
765 = tcAddSrcLoc (tcdLoc decl) $
770 ClassDecl {} -> "class"
771 TySynonym {} -> "type synonym"
772 TyData {tcdND = NewType} -> "newtype"
773 TyData {tcdND = DataType} -> "data type"
775 ctxt = hsep [ptext SLIT("In the"), text thing,
776 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
778 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
780 doc = case inst_ty of
781 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
782 HsPredTy pred -> ppr pred
783 other -> ppr inst_ty -- Don't expect this
787 badGenericInstanceType binds
788 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
791 missingGenericInstances missing
792 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
794 dupGenericInsts tc_inst_infos
795 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
796 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
797 ptext SLIT("All the type patterns for a generic type constructor must be identical")
800 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
802 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
803 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")