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(..), dopt )
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, UserTypeCtxt(..), SourceTyCtxt(..) )
27 import TcType ( tcSplitDFunTy, tcIsTyVarTy, tcSplitTyConApp_maybe,
28 tyVarsOfTypes, mkClassPred, mkTyVarTy,
29 tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys_maybe
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 TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType, checkSigTyVars )
44 import TcSimplify ( tcSimplifyCheck )
45 import HscTypes ( HomeSymbolTable, DFunId,
46 ModDetails(..), PackageInstEnv, PersistentRenamerState
49 import Subst ( substTy, substTheta )
50 import DataCon ( classDataCon )
51 import Class ( Class, DefMeth(..), classBigSig )
52 import Var ( idName, idType )
53 import VarSet ( emptyVarSet )
54 import Maybes ( maybeToBool )
55 import MkId ( mkDictFunId )
56 import FunDeps ( checkInstFDs )
57 import Generics ( validGenericInstanceType )
58 import Module ( Module, foldModuleEnv )
59 import Name ( getSrcLoc )
60 import NameSet ( unitNameSet, nameSetToList )
61 import PrelInfo ( eRROR_ID )
62 import PprType ( pprClassPred )
63 import TyCon ( TyCon, isSynTyCon )
64 import Subst ( mkTopTyVarSubst, substTheta )
65 import VarSet ( varSetElems )
66 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIImportResultTy )
67 import ForeignCall ( Safety(..) )
68 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
70 import SrcLoc ( SrcLoc )
71 import VarSet ( varSetElems )
72 import Unique ( Uniquable(..) )
73 import BasicTypes ( NewOrData(..), Fixity )
74 import ErrUtils ( dumpIfSet_dyn )
75 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
76 assocElts, extendAssoc_C,
77 equivClassesByUniq, minusList
79 import List ( partition )
83 Typechecking instance declarations is done in two passes. The first
84 pass, made by @tcInstDecls1@, collects information to be used in the
87 This pre-processed info includes the as-yet-unprocessed bindings
88 inside the instance declaration. These are type-checked in the second
89 pass, when the class-instance envs and GVE contain all the info from
90 all the instance and value decls. Indeed that's the reason we need
91 two passes over the instance decls.
94 Here is the overall algorithm.
95 Assume that we have an instance declaration
97 instance c => k (t tvs) where b
101 $LIE_c$ is the LIE for the context of class $c$
103 $betas_bar$ is the free variables in the class method type, excluding the
106 $LIE_cop$ is the LIE constraining a particular class method
108 $tau_cop$ is the tau type of a class method
110 $LIE_i$ is the LIE for the context of instance $i$
112 $X$ is the instance constructor tycon
114 $gammas_bar$ is the set of type variables of the instance
116 $LIE_iop$ is the LIE for a particular class method instance
118 $tau_iop$ is the tau type for this instance of a class method
120 $alpha$ is the class variable
122 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
124 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
127 ToDo: Update the list above with names actually in the code.
131 First, make the LIEs for the class and instance contexts, which means
132 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
133 and make LIElistI and LIEI.
135 Then process each method in turn.
137 order the instance methods according to the ordering of the class methods
139 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
141 Create final dictionary function from bindings generated already
143 df = lambda inst_tyvars
150 in <op1,op2,...,opn,sd1,...,sdm>
152 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
153 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
157 %************************************************************************
159 \subsection{Extracting instance decls}
161 %************************************************************************
163 Gather up the instance declarations from their various sources
166 tcInstDecls1 :: PackageInstEnv
167 -> PersistentRenamerState
168 -> HomeSymbolTable -- Contains instances
169 -> TcEnv -- Contains IdInfo for dfun ids
170 -> (Name -> Maybe Fixity) -- for deriving Show and Read
171 -> Module -- Module for deriving
173 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
175 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
177 inst_decls = [inst_decl | InstD inst_decl <- decls]
178 tycl_decls = [decl | TyClD decl <- decls]
179 clas_decls = filter isClassDecl tycl_decls
181 -- (1) Do the ordinary instance declarations
182 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
184 -- (2) Instances from generic class declarations
185 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
187 -- Next, construct the instance environment so far, consisting of
188 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
189 -- b) imported instance decls (not in the home package) inst_env1
190 -- c) other modules in this package (gotten from hst) inst_env2
191 -- d) local instance decls inst_env3
192 -- e) generic instances inst_env4
193 -- The result of (b) replaces the cached InstEnv in the PCS
195 (local_inst_info, imported_inst_info)
196 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
198 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
200 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
203 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
205 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
206 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
207 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
208 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
210 -- (3) Compute instances from "deriving" clauses;
211 -- note that we only do derivings for things in this module;
212 -- we ignore deriving decls from interfaces!
213 -- This stuff computes a context for the derived instance decl, so it
214 -- needs to know about all the instances possible; hecne inst_env4
215 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
216 `thenTc` \ (deriv_inst_info, deriv_binds) ->
217 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
221 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
224 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
225 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
227 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
228 addInstDFuns inst_env dfuns
229 = getDOptsTc `thenTc` \ dflags ->
231 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
233 addErrsTc errs `thenNF_Tc_`
234 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
237 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
241 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
242 -- Deal with a single instance declaration
243 -- Type-check all the stuff before the "where"
244 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
245 = -- Prime error recovery, set source location
246 recoverNF_Tc (returnNF_Tc []) $
247 tcAddSrcLoc src_loc $
248 tcAddErrCtxt (instDeclCtxt poly_ty) $
250 -- Typecheck the instance type itself. We can't use
251 -- tcHsSigType, because it's not a valid user type.
252 kcHsSigType poly_ty `thenTc_`
253 tcHsType poly_ty `thenTc` \ poly_ty' ->
255 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
256 maybe_cls_tys = case tcSplitPredTy_maybe tau of
257 Just pred -> getClassPredTys_maybe pred
259 Just (clas, inst_tys) = maybe_cls_tys
261 checkTc (maybeToBool maybe_cls_tys) (instHeadErr tau) `thenTc_`
263 (case maybe_dfun_name of
264 Nothing -> -- A source-file instance declaration
266 -- Check for respectable instance type, and context
267 -- but only do this for non-imported instance decls.
268 -- Imported ones should have been checked already, and may indeed
269 -- contain something illegal in normal Haskell, notably
270 -- instance CCallable [Char]
271 getDOptsTc `thenTc` \ dflags ->
272 checkValidTheta InstDeclCtxt theta `thenTc_`
273 checkValidInstHead dflags theta clas inst_tys `thenTc_`
274 newDFunName clas inst_tys src_loc
276 Just dfun_name -> -- An interface-file instance declaration
277 returnNF_Tc dfun_name
278 ) `thenNF_Tc` \ dfun_name ->
281 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
283 returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
287 %************************************************************************
289 \subsection{Extracting generic instance declaration from class declarations}
291 %************************************************************************
293 @getGenericInstances@ extracts the generic instance declarations from a class
294 declaration. For exmaple
299 op{ x+y } (Inl v) = ...
300 op{ x+y } (Inr v) = ...
301 op{ x*y } (v :*: w) = ...
304 gives rise to the instance declarations
306 instance C (x+y) where
310 instance C (x*y) where
318 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
319 getGenericInstances class_decls
320 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
322 gen_inst_info = concat gen_inst_infos
324 if null gen_inst_info then
327 getDOptsTc `thenTc` \ dflags ->
328 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
329 (vcat (map pprInstInfo gen_inst_info)))
331 returnTc gen_inst_info
333 get_generics decl@(ClassDecl {tcdMeths = Nothing})
334 = returnTc [] -- Imported class decls
336 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
338 = returnTc [] -- The comon case: no generic default methods
340 | otherwise -- A local class decl with generic default methods
341 = recoverNF_Tc (returnNF_Tc []) $
343 tcLookupClass class_name `thenTc` \ clas ->
345 -- Make an InstInfo out of each group
346 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
348 -- Check that there is only one InstInfo for each type constructor
349 -- The main way this can fail is if you write
350 -- f {| a+b |} ... = ...
351 -- f {| x+y |} ... = ...
352 -- Then at this point we'll have an InstInfo for each
354 tc_inst_infos :: [(TyCon, InstInfo)]
355 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
357 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
359 get_uniq (tc,_) = getUnique tc
361 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
363 -- Check that there is an InstInfo for each generic type constructor
365 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
367 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
372 -- Group the declarations by type pattern
373 groups :: [(RenamedHsType, RenamedMonoBinds)]
374 groups = assocElts (getGenericBinds def_methods)
377 ---------------------------------
378 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
379 -- Takes a group of method bindings, finds the generic ones, and returns
380 -- them in finite map indexed by the type parameter in the definition.
382 getGenericBinds EmptyMonoBinds = emptyAssoc
383 getGenericBinds (AndMonoBinds m1 m2)
384 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
386 getGenericBinds (FunMonoBind id infixop matches loc)
387 = mapAssoc wrap (foldl add emptyAssoc matches)
388 -- Using foldl not foldr is vital, else
389 -- we reverse the order of the bindings!
391 add env match = case maybeGenericMatch match of
393 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
395 wrap ms = FunMonoBind id infixop ms loc
397 ---------------------------------
398 mkGenericInstance :: Class -> SrcLoc
399 -> (RenamedHsType, RenamedMonoBinds)
402 mkGenericInstance clas loc (hs_ty, binds)
403 -- Make a generic instance declaration
404 -- For example: instance (C a, C b) => C (a+b) where { binds }
406 = -- Extract the universally quantified type variables
408 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
410 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
412 -- Type-check the instance type, and check its form
413 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
414 checkTc (validGenericInstanceType inst_ty)
415 (badGenericInstanceType binds) `thenTc_`
417 -- Make the dictionary function.
418 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
420 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
422 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
425 returnTc (InstInfo { iDFunId = dfun_id,
426 iBinds = binds, iPrags = [] })
430 %************************************************************************
432 \subsection{Type-checking instance declarations, pass 2}
434 %************************************************************************
437 tcInstDecls2 :: [InstInfo]
438 -> NF_TcM (LIE, TcMonoBinds)
440 tcInstDecls2 inst_decls
441 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
442 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
443 (map tcInstDecl2 inst_decls)
445 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
446 tc2 `thenNF_Tc` \ (lie2, binds2) ->
447 returnNF_Tc (lie1 `plusLIE` lie2,
448 binds1 `AndMonoBinds` binds2)
451 ======= New documentation starts here (Sept 92) ==============
453 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
454 the dictionary function for this instance declaration. For example
456 instance Foo a => Foo [a] where
460 might generate something like
462 dfun.Foo.List dFoo_a = let op1 x = ...
468 HOWEVER, if the instance decl has no context, then it returns a
469 bigger @HsBinds@ with declarations for each method. For example
471 instance Foo [a] where
477 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
478 const.Foo.op1.List a x = ...
479 const.Foo.op2.List a y = ...
481 This group may be mutually recursive, because (for example) there may
482 be no method supplied for op2 in which case we'll get
484 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
486 that is, the default method applied to the dictionary at this type.
488 What we actually produce in either case is:
490 AbsBinds [a] [dfun_theta_dicts]
491 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
492 { d = (sd1,sd2, ..., op1, op2, ...)
497 The "maybe" says that we only ask AbsBinds to make global constant methods
498 if the dfun_theta is empty.
501 For an instance declaration, say,
503 instance (C1 a, C2 b) => C (T a b) where
506 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
507 function whose type is
509 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
511 Notice that we pass it the superclass dictionaries at the instance type; this
512 is the ``Mark Jones optimisation''. The stuff before the "=>" here
513 is the @dfun_theta@ below.
515 First comes the easy case of a non-local instance decl.
519 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
520 -- tcInstDecl2 is called *only* on InstInfos
522 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
523 iBinds = monobinds, iPrags = uprags })
524 = -- Prime error recovery
525 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
526 tcAddSrcLoc (getSrcLoc dfun_id) $
527 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
529 -- Instantiate the instance decl with tc-style type variables
531 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
533 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
535 inst_tys' = map (substTy tenv) inst_tys
536 dfun_theta' = substTheta tenv dfun_theta
537 origin = InstanceDeclOrigin
539 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
541 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
542 sel_names = [idName sel_id | (sel_id, _) <- op_items]
544 -- Instantiate the super-class context with inst_tys
545 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
547 -- Find any definitions in monobinds that aren't from the class
548 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
550 -- Check that all the method bindings come from this class
551 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
553 -- Create dictionary Ids from the specified instance contexts.
554 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
555 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
556 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
558 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
559 -- The type variable from the dict fun actually scope
560 -- over the bindings. They were gotten from
561 -- the original instance declaration
562 tcExtendGlobalValEnv dm_ids (
563 -- Default-method Ids may be mentioned in synthesised RHSs
565 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
567 monobinds uprags True)
569 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
571 -- Deal with SPECIALISE instance pragmas by making them
572 -- look like SPECIALISE pragmas for the dfun
574 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
576 tcExtendGlobalValEnv [dfun_id] (
577 tcSpecSigs dfun_prags
578 ) `thenTc` \ (prag_binds, prag_lie) ->
580 -- Check the overloading constraints of the methods and superclasses
582 -- These insts are in scope; quite a few, eh?
583 avail_insts = [this_dict] ++
588 methods_lie = plusLIEs insts_needed_s
591 -- Simplify the constraints from methods
592 tcAddErrCtxt methodCtxt (
594 (ptext SLIT("instance declaration context"))
598 ) `thenTc` \ (const_lie1, lie_binds1) ->
600 -- Figure out bindings for the superclass context
601 tcAddErrCtxt superClassCtxt (
603 (ptext SLIT("instance declaration context"))
605 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
606 -- get bound by just selecting from this_dict!!
608 ) `thenTc` \ (const_lie2, lie_binds2) ->
610 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
612 -- Create the result bindings
614 dict_constr = classDataCon clas
615 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
616 this_dict_id = instToId this_dict
617 inlines = unitNameSet (idName dfun_id)
618 -- Always inline the dfun; this is an experimental decision
619 -- because it makes a big performance difference sometimes.
620 -- Often it means we can do the method selection, and then
621 -- inline the method as well. Marcin's idea; see comments below.
625 = -- Blatant special case for CCallable, CReturnable
626 -- If the dictionary is empty then we should never
627 -- select anything from it, so we make its RHS just
628 -- emit an error message. This in turn means that we don't
629 -- mention the constructor, which doesn't exist for CCallable, CReturnable
630 -- Hardly beautiful, but only three extra lines.
631 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
632 (HsLit (HsString msg))
634 | otherwise -- The common case
635 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
636 -- We don't produce a binding for the dict_constr; instead we
637 -- rely on the simplifier to unfold this saturated application
638 -- We do this rather than generate an HsCon directly, because
639 -- it means that the special cases (e.g. dictionary with only one
640 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
641 -- than needing to be repeated here.
644 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
646 dict_bind = VarMonoBind this_dict_id dict_rhs
647 method_binds = andMonoBindList method_binds_s
652 (map instToId dfun_arg_dicts)
653 [(inst_tyvars', dfun_id, this_dict_id)]
655 (lie_binds1 `AndMonoBinds`
656 lie_binds2 `AndMonoBinds`
657 method_binds `AndMonoBinds`
660 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
661 main_bind `AndMonoBinds` prag_binds)
664 ------------------------------
665 Inlining dfuns unconditionally
666 ------------------------------
668 The code above unconditionally inlines dict funs. Here's why.
669 Consider this program:
671 test :: Int -> Int -> Bool
672 test x y = (x,y) == (y,x) || test y x
673 -- Recursive to avoid making it inline.
675 This needs the (Eq (Int,Int)) instance. If we inline that dfun
676 the code we end up with is good:
679 \r -> case ==# [ww ww1] of wild {
680 PrelBase.False -> Test.$wtest ww1 ww;
682 case ==# [ww1 ww] of wild1 {
683 PrelBase.False -> Test.$wtest ww1 ww;
684 PrelBase.True -> PrelBase.True [];
687 Test.test = \r [w w1]
690 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
693 If we don't inline the dfun, the code is not nearly as good:
695 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
696 PrelBase.:DEq tpl1 tpl2 -> tpl2;
701 let { y = PrelBase.I#! [ww1]; } in
702 let { x = PrelBase.I#! [ww]; } in
703 let { sat_slx = PrelTup.(,)! [y x]; } in
704 let { sat_sly = PrelTup.(,)! [x y];
706 case == sat_sly sat_slx of wild {
707 PrelBase.False -> Test.$wtest ww1 ww;
708 PrelBase.True -> PrelBase.True [];
715 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
718 Why doesn't GHC inline $fEq? Because it looks big:
720 PrelTup.zdfEqZ1T{-rcX-}
721 = \ @ a{-reT-} :: * @ b{-reS-} :: *
722 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
723 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
725 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
726 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
728 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
729 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
731 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
732 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
733 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
735 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
737 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
739 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
740 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
744 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
745 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
746 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
747 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
749 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
751 and it's not as bad as it seems, because it's further dramatically
752 simplified: only zeze2 is extracted and its body is simplified.
755 %************************************************************************
757 \subsection{Checking for a decent instance type}
759 %************************************************************************
761 @checkValidInstHead@ checks the type {\em and} its syntactic constraints:
762 it must normally look like: @instance Foo (Tycon a b c ...) ...@
764 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
765 flag is on, or (2)~the instance is imported (they must have been
766 compiled elsewhere). In these cases, we let them go through anyway.
768 We can also have instances for functions: @instance Foo (a -> b) ...@.
771 checkValidInstHead dflags theta clas inst_tys
772 | null errs = returnTc ()
773 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
775 errs = check_inst_head dflags theta clas inst_tys
777 check_inst_head dflags theta clas inst_taus
779 -- A user declaration of a CCallable/CReturnable instance
780 -- must be for a "boxed primitive" type.
781 (clas `hasKey` cCallableClassKey
782 && not (ccallable_type dflags first_inst_tau))
784 (clas `hasKey` cReturnableClassKey
785 && not (creturnable_type first_inst_tau))
786 = [nonBoxedPrimCCallErr clas first_inst_tau]
788 -- If GlasgowExts then check at least one isn't a type variable
789 | dopt Opt_GlasgowExts dflags
790 = -- GlasgowExts case
791 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
793 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
794 | not (length inst_taus == 1 &&
795 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
796 not (isSynTyCon tycon) && -- ...but not a synonym
797 all tcIsTyVarTy arg_tys && -- Applied to type variables
798 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
799 -- This last condition checks that all the type variables are distinct
801 = [instTypeErr clas inst_taus
802 (text "the instance type must be of form (T a b c)" $$
803 text "where T is not a synonym, and a,b,c are distinct type variables")]
809 (first_inst_tau : _) = inst_taus
811 -- Stuff for algebraic or -> type
812 maybe_tycon_app = tcSplitTyConApp_maybe first_inst_tau
813 Just (tycon, arg_tys) = maybe_tycon_app
815 ccallable_type dflags ty = isFFIArgumentTy dflags PlayRisky ty
816 creturnable_type ty = isFFIImportResultTy dflags ty
818 check_tyvars dflags clas inst_taus
819 -- Check that at least one isn't a type variable
820 -- unless -fallow-undecideable-instances
821 | dopt Opt_AllowUndecidableInstances dflags = []
822 | not (all tcIsTyVarTy inst_taus) = []
823 | otherwise = [the_err]
825 the_err = instTypeErr clas inst_taus msg
826 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
827 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
829 check_fundeps dflags theta clas inst_taus
830 | checkInstFDs theta clas inst_taus = []
831 | otherwise = [the_err]
833 the_err = instTypeErr clas inst_taus msg
834 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
838 %************************************************************************
840 \subsection{Error messages}
842 %************************************************************************
845 tcAddDeclCtxt decl thing_inside
846 = tcAddSrcLoc (tcdLoc decl) $
851 ClassDecl {} -> "class"
852 TySynonym {} -> "type synonym"
853 TyData {tcdND = NewType} -> "newtype"
854 TyData {tcdND = DataType} -> "data type"
856 ctxt = hsep [ptext SLIT("In the"), text thing,
857 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
859 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
861 doc = case inst_ty of
862 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
863 HsPredTy pred -> ppr pred
864 other -> ppr inst_ty -- Don't expect this
868 badGenericInstanceType binds
869 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
872 missingGenericInstances missing
873 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
877 dupGenericInsts tc_inst_infos
878 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
879 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
880 ptext SLIT("All the type patterns for a generic type constructor must be identical")
883 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
886 = vcat [ptext SLIT("Illegal instance head:") <+> ppr ty,
887 ptext SLIT("Instance head must be of form <context> => <class> <types>")]
889 instTypeErr clas tys msg
890 = sep [ptext SLIT("Illegal instance declaration for") <+>
891 quotes (pprClassPred clas tys),
895 nonBoxedPrimCCallErr clas inst_ty
896 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
897 4 (pprClassPred clas [inst_ty])
899 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
900 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")