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 TcType ( tcInstType )
27 import Inst ( InstOrigin(..),
29 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
30 import TcDeriv ( tcDeriving )
31 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
32 tcExtendTyVarEnvForMeths,
33 tcAddImportedIdInfo, tcLookupClass,
34 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
35 simpleInstInfoTy, newDFunName, tcExtendTyVarEnv,
38 import InstEnv ( InstEnv, extendInstEnv )
39 import TcMonoType ( tcHsTyVars, tcHsSigType, kcHsSigType, checkSigTyVars )
40 import TcSimplify ( tcSimplifyCheck )
41 import HscTypes ( HomeSymbolTable, DFunId,
42 ModDetails(..), PackageInstEnv, PersistentRenamerState
45 import DataCon ( classDataCon )
46 import Class ( Class, DefMeth(..), classBigSig )
47 import Var ( idName, idType )
48 import VarSet ( emptyVarSet )
49 import Maybes ( maybeToBool )
50 import MkId ( mkDictFunId )
51 import FunDeps ( checkInstFDs )
52 import Generics ( validGenericInstanceType )
53 import Module ( Module, foldModuleEnv )
54 import Name ( getSrcLoc )
55 import NameSet ( unitNameSet, nameSetToList )
56 import PrelInfo ( eRROR_ID )
57 import PprType ( pprClassPred, pprPred )
58 import TyCon ( TyCon, isSynTyCon )
59 import Type ( splitDFunTy, isTyVarTy,
60 splitTyConApp_maybe, splitDictTy,
62 tyVarsOfTypes, mkClassPred, mkTyVarTy,
63 isTyVarClassPred, inheritablePred
65 import Subst ( mkTopTyVarSubst, substTheta )
66 import VarSet ( varSetElems )
67 import TysWiredIn ( genericTyCons, isFFIArgumentTy, isFFIImportResultTy )
68 import ForeignCall ( Safety(..) )
69 import PrelNames ( cCallableClassKey, cReturnableClassKey, hasKey )
71 import SrcLoc ( SrcLoc )
72 import VarSet ( varSetElems )
73 import Unique ( Uniquable(..) )
74 import BasicTypes ( NewOrData(..), Fixity )
75 import ErrUtils ( dumpIfSet_dyn )
76 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
77 assocElts, extendAssoc_C,
78 equivClassesByUniq, minusList
80 import List ( partition )
84 Typechecking instance declarations is done in two passes. The first
85 pass, made by @tcInstDecls1@, collects information to be used in the
88 This pre-processed info includes the as-yet-unprocessed bindings
89 inside the instance declaration. These are type-checked in the second
90 pass, when the class-instance envs and GVE contain all the info from
91 all the instance and value decls. Indeed that's the reason we need
92 two passes over the instance decls.
95 Here is the overall algorithm.
96 Assume that we have an instance declaration
98 instance c => k (t tvs) where b
102 $LIE_c$ is the LIE for the context of class $c$
104 $betas_bar$ is the free variables in the class method type, excluding the
107 $LIE_cop$ is the LIE constraining a particular class method
109 $tau_cop$ is the tau type of a class method
111 $LIE_i$ is the LIE for the context of instance $i$
113 $X$ is the instance constructor tycon
115 $gammas_bar$ is the set of type variables of the instance
117 $LIE_iop$ is the LIE for a particular class method instance
119 $tau_iop$ is the tau type for this instance of a class method
121 $alpha$ is the class variable
123 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
125 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
128 ToDo: Update the list above with names actually in the code.
132 First, make the LIEs for the class and instance contexts, which means
133 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
134 and make LIElistI and LIEI.
136 Then process each method in turn.
138 order the instance methods according to the ordering of the class methods
140 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
142 Create final dictionary function from bindings generated already
144 df = lambda inst_tyvars
151 in <op1,op2,...,opn,sd1,...,sdm>
153 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
154 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
158 %************************************************************************
160 \subsection{Extracting instance decls}
162 %************************************************************************
164 Gather up the instance declarations from their various sources
167 tcInstDecls1 :: PackageInstEnv
168 -> PersistentRenamerState
169 -> HomeSymbolTable -- Contains instances
170 -> TcEnv -- Contains IdInfo for dfun ids
171 -> (Name -> Maybe Fixity) -- for deriving Show and Read
172 -> Module -- Module for deriving
174 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
176 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
178 inst_decls = [inst_decl | InstD inst_decl <- decls]
179 tycl_decls = [decl | TyClD decl <- decls]
180 clas_decls = filter isClassDecl tycl_decls
182 -- (1) Do the ordinary instance declarations
183 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
185 -- (2) Instances from generic class declarations
186 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
188 -- Next, construct the instance environment so far, consisting of
189 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
190 -- b) imported instance decls (not in the home package) inst_env1
191 -- c) other modules in this package (gotten from hst) inst_env2
192 -- d) local instance decls inst_env3
193 -- e) generic instances inst_env4
194 -- The result of (b) replaces the cached InstEnv in the PCS
196 (local_inst_info, imported_inst_info)
197 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
199 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
201 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
203 addInstDFuns inst_env0 imported_dfuns `thenNF_Tc` \ inst_env1 ->
204 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
205 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
206 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
208 -- (3) Compute instances from "deriving" clauses;
209 -- note that we only do derivings for things in this module;
210 -- we ignore deriving decls from interfaces!
211 -- This stuff computes a context for the derived instance decl, so it
212 -- needs to know about all the instances possible; hecne inst_env4
213 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
214 `thenTc` \ (deriv_inst_info, deriv_binds) ->
215 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
219 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
222 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
223 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
225 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
226 addInstDFuns dfuns infos
227 = getDOptsTc `thenTc` \ dflags ->
229 (inst_env', errs) = extendInstEnv dflags dfuns infos
231 addErrsTc errs `thenNF_Tc_`
236 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
237 -- Deal with a single instance declaration
238 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
239 = -- Prime error recovery, set source location
240 recoverNF_Tc (returnNF_Tc []) $
241 tcAddSrcLoc src_loc $
243 -- Type-check all the stuff before the "where"
244 tcAddErrCtxt (instDeclCtxt poly_ty) (
246 ) `thenTc` \ poly_ty' ->
248 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
251 (case maybe_dfun_name of
252 Nothing -> -- A source-file instance declaration
254 -- Check for respectable instance type, and context
255 -- but only do this for non-imported instance decls.
256 -- Imported ones should have been checked already, and may indeed
257 -- contain something illegal in normal Haskell, notably
258 -- instance CCallable [Char]
259 getDOptsTc `thenTc` \ dflags ->
260 checkInstValidity dflags theta clas inst_tys `thenTc_`
262 -- Make the dfun id and return it
263 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
264 returnNF_Tc (True, dfun_name)
266 Just dfun_name -> -- An interface-file instance declaration
268 returnNF_Tc (False, dfun_name)
269 ) `thenNF_Tc` \ (is_local, dfun_name) ->
272 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
274 returnTc [InstInfo { iDFunId = dfun_id,
275 iBinds = binds, iPrags = uprags }]
279 %************************************************************************
281 \subsection{Extracting generic instance declaration from class declarations}
283 %************************************************************************
285 @getGenericInstances@ extracts the generic instance declarations from a class
286 declaration. For exmaple
291 op{ x+y } (Inl v) = ...
292 op{ x+y } (Inr v) = ...
293 op{ x*y } (v :*: w) = ...
296 gives rise to the instance declarations
298 instance C (x+y) where
302 instance C (x*y) where
310 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
311 getGenericInstances class_decls
312 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
314 gen_inst_info = concat gen_inst_infos
316 if null gen_inst_info then
319 getDOptsTc `thenTc` \ dflags ->
320 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
321 (vcat (map pprInstInfo gen_inst_info)))
323 returnTc gen_inst_info
325 get_generics decl@(ClassDecl {tcdMeths = Nothing})
326 = returnTc [] -- Imported class decls
328 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
330 = returnTc [] -- The comon case: no generic default methods
332 | otherwise -- A local class decl with generic default methods
333 = recoverNF_Tc (returnNF_Tc []) $
335 tcLookupClass class_name `thenTc` \ clas ->
337 -- Make an InstInfo out of each group
338 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
340 -- Check that there is only one InstInfo for each type constructor
341 -- The main way this can fail is if you write
342 -- f {| a+b |} ... = ...
343 -- f {| x+y |} ... = ...
344 -- Then at this point we'll have an InstInfo for each
346 tc_inst_infos :: [(TyCon, InstInfo)]
347 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
349 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
351 get_uniq (tc,_) = getUnique tc
353 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
355 -- Check that there is an InstInfo for each generic type constructor
357 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
359 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
364 -- Group the declarations by type pattern
365 groups :: [(RenamedHsType, RenamedMonoBinds)]
366 groups = assocElts (getGenericBinds def_methods)
369 ---------------------------------
370 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
371 -- Takes a group of method bindings, finds the generic ones, and returns
372 -- them in finite map indexed by the type parameter in the definition.
374 getGenericBinds EmptyMonoBinds = emptyAssoc
375 getGenericBinds (AndMonoBinds m1 m2)
376 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
378 getGenericBinds (FunMonoBind id infixop matches loc)
379 = mapAssoc wrap (foldl add emptyAssoc matches)
380 -- Using foldl not foldr is vital, else
381 -- we reverse the order of the bindings!
383 add env match = case maybeGenericMatch match of
385 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
387 wrap ms = FunMonoBind id infixop ms loc
389 ---------------------------------
390 mkGenericInstance :: Class -> SrcLoc
391 -> (RenamedHsType, RenamedMonoBinds)
394 mkGenericInstance clas loc (hs_ty, binds)
395 -- Make a generic instance declaration
396 -- For example: instance (C a, C b) => C (a+b) where { binds }
398 = -- Extract the universally quantified type variables
400 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
402 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
404 -- Type-check the instance type, and check its form
405 tcHsSigType hs_ty `thenTc` \ inst_ty ->
406 checkTc (validGenericInstanceType inst_ty)
407 (badGenericInstanceType binds) `thenTc_`
409 -- Make the dictionary function.
410 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
412 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
414 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
417 returnTc (InstInfo { iDFunId = dfun_id,
418 iBinds = binds, iPrags = [] })
422 %************************************************************************
424 \subsection{Type-checking instance declarations, pass 2}
426 %************************************************************************
429 tcInstDecls2 :: [InstInfo]
430 -> NF_TcM (LIE, TcMonoBinds)
432 tcInstDecls2 inst_decls
433 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
434 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
435 (map tcInstDecl2 inst_decls)
437 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
438 tc2 `thenNF_Tc` \ (lie2, binds2) ->
439 returnNF_Tc (lie1 `plusLIE` lie2,
440 binds1 `AndMonoBinds` binds2)
443 ======= New documentation starts here (Sept 92) ==============
445 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
446 the dictionary function for this instance declaration. For example
448 instance Foo a => Foo [a] where
452 might generate something like
454 dfun.Foo.List dFoo_a = let op1 x = ...
460 HOWEVER, if the instance decl has no context, then it returns a
461 bigger @HsBinds@ with declarations for each method. For example
463 instance Foo [a] where
469 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
470 const.Foo.op1.List a x = ...
471 const.Foo.op2.List a y = ...
473 This group may be mutually recursive, because (for example) there may
474 be no method supplied for op2 in which case we'll get
476 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
478 that is, the default method applied to the dictionary at this type.
480 What we actually produce in either case is:
482 AbsBinds [a] [dfun_theta_dicts]
483 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
484 { d = (sd1,sd2, ..., op1, op2, ...)
489 The "maybe" says that we only ask AbsBinds to make global constant methods
490 if the dfun_theta is empty.
493 For an instance declaration, say,
495 instance (C1 a, C2 b) => C (T a b) where
498 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
499 function whose type is
501 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
503 Notice that we pass it the superclass dictionaries at the instance type; this
504 is the ``Mark Jones optimisation''. The stuff before the "=>" here
505 is the @dfun_theta@ below.
507 First comes the easy case of a non-local instance decl.
511 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
512 -- tcInstDecl2 is called *only* on InstInfos
514 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
515 iBinds = monobinds, iPrags = uprags })
516 = -- Prime error recovery
517 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
518 tcAddSrcLoc (getSrcLoc dfun_id) $
519 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
521 -- Instantiate the instance decl with tc-style type variables
522 tcInstType (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
524 (clas, inst_tys') = splitDictTy dict_ty'
525 origin = InstanceDeclOrigin
527 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
529 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
530 sel_names = [idName sel_id | (sel_id, _) <- op_items]
532 -- Instantiate the super-class context with inst_tys
533 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
535 -- Find any definitions in monobinds that aren't from the class
536 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
538 -- The type variable from the dict fun actually scope
539 -- over the bindings. They were gotten from
540 -- the original instance declaration
541 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
543 -- Check that all the method bindings come from this class
544 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
546 -- Create dictionary Ids from the specified instance contexts.
547 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
548 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
549 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
551 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
552 tcExtendGlobalValEnv dm_ids (
553 -- Default-method Ids may be mentioned in synthesised RHSs
555 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
557 monobinds uprags True)
559 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
561 -- Deal with SPECIALISE instance pragmas by making them
562 -- look like SPECIALISE pragmas for the dfun
564 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
566 tcExtendGlobalValEnv [dfun_id] (
567 tcSpecSigs dfun_prags
568 ) `thenTc` \ (prag_binds, prag_lie) ->
570 -- Check the overloading constraints of the methods and superclasses
572 -- These insts are in scope; quite a few, eh?
573 avail_insts = [this_dict] ++
578 methods_lie = plusLIEs insts_needed_s
581 -- Simplify the constraints from methods
582 tcAddErrCtxt methodCtxt (
584 (ptext SLIT("instance declaration context"))
588 ) `thenTc` \ (const_lie1, lie_binds1) ->
590 -- Figure out bindings for the superclass context
591 tcAddErrCtxt superClassCtxt (
593 (ptext SLIT("instance declaration context"))
595 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
596 -- get bound by just selecting from this_dict!!
598 ) `thenTc` \ (const_lie2, lie_binds2) ->
600 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
602 -- Create the result bindings
604 dict_constr = classDataCon clas
605 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
606 this_dict_id = instToId this_dict
607 inlines = unitNameSet (idName dfun_id)
608 -- Always inline the dfun; this is an experimental decision
609 -- because it makes a big performance difference sometimes.
610 -- Often it means we can do the method selection, and then
611 -- inline the method as well. Marcin's idea; see comments below.
615 = -- Blatant special case for CCallable, CReturnable
616 -- If the dictionary is empty then we should never
617 -- select anything from it, so we make its RHS just
618 -- emit an error message. This in turn means that we don't
619 -- mention the constructor, which doesn't exist for CCallable, CReturnable
620 -- Hardly beautiful, but only three extra lines.
621 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
622 (HsLit (HsString msg))
624 | otherwise -- The common case
625 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
626 -- We don't produce a binding for the dict_constr; instead we
627 -- rely on the simplifier to unfold this saturated application
628 -- We do this rather than generate an HsCon directly, because
629 -- it means that the special cases (e.g. dictionary with only one
630 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
631 -- than needing to be repeated here.
634 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
636 dict_bind = VarMonoBind this_dict_id dict_rhs
637 method_binds = andMonoBindList method_binds_s
642 (map instToId dfun_arg_dicts)
643 [(inst_tyvars', dfun_id, this_dict_id)]
645 (lie_binds1 `AndMonoBinds`
646 lie_binds2 `AndMonoBinds`
647 method_binds `AndMonoBinds`
650 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
651 main_bind `AndMonoBinds` prag_binds)
654 ------------------------------
655 Inlining dfuns unconditionally
656 ------------------------------
658 The code above unconditionally inlines dict funs. Here's why.
659 Consider this program:
661 test :: Int -> Int -> Bool
662 test x y = (x,y) == (y,x) || test y x
663 -- Recursive to avoid making it inline.
665 This needs the (Eq (Int,Int)) instance. If we inline that dfun
666 the code we end up with is good:
669 \r -> case ==# [ww ww1] of wild {
670 PrelBase.False -> Test.$wtest ww1 ww;
672 case ==# [ww1 ww] of wild1 {
673 PrelBase.False -> Test.$wtest ww1 ww;
674 PrelBase.True -> PrelBase.True [];
677 Test.test = \r [w w1]
680 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
683 If we don't inline the dfun, the code is not nearly as good:
685 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
686 PrelBase.:DEq tpl1 tpl2 -> tpl2;
691 let { y = PrelBase.I#! [ww1]; } in
692 let { x = PrelBase.I#! [ww]; } in
693 let { sat_slx = PrelTup.(,)! [y x]; } in
694 let { sat_sly = PrelTup.(,)! [x y];
696 case == sat_sly sat_slx of wild {
697 PrelBase.False -> Test.$wtest ww1 ww;
698 PrelBase.True -> PrelBase.True [];
705 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
708 Why doesn't GHC inline $fEq? Because it looks big:
710 PrelTup.zdfEqZ1T{-rcX-}
711 = \ @ a{-reT-} :: * @ b{-reS-} :: *
712 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
713 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
715 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
716 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
718 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
719 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
721 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
722 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
723 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
725 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
727 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
729 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
730 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
734 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
735 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
736 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
737 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
739 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
741 and it's not as bad as it seems, because it's further dramatically
742 simplified: only zeze2 is extracted and its body is simplified.
745 %************************************************************************
747 \subsection{Checking for a decent instance type}
749 %************************************************************************
751 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
752 it must normally look like: @instance Foo (Tycon a b c ...) ...@
754 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
755 flag is on, or (2)~the instance is imported (they must have been
756 compiled elsewhere). In these cases, we let them go through anyway.
758 We can also have instances for functions: @instance Foo (a -> b) ...@.
761 checkInstValidity dflags theta clas inst_tys
762 | null errs = returnTc ()
763 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
765 errs = checkInstHead dflags theta clas inst_tys ++
766 [err | pred <- theta, err <- checkInstConstraint dflags pred]
768 checkInstConstraint dflags pred
769 -- Checks whether a predicate is legal in the
770 -- context of an instance declaration
772 | otherwise = [instConstraintErr pred]
774 ok = inheritablePred pred &&
775 (isTyVarClassPred pred || arbitrary_preds_ok)
777 arbitrary_preds_ok = dopt Opt_AllowUndecidableInstances dflags
780 checkInstHead dflags theta clas inst_taus
782 -- A user declaration of a CCallable/CReturnable instance
783 -- must be for a "boxed primitive" type.
784 (clas `hasKey` cCallableClassKey
785 && not (ccallable_type dflags first_inst_tau))
787 (clas `hasKey` cReturnableClassKey
788 && not (creturnable_type first_inst_tau))
789 = [nonBoxedPrimCCallErr clas first_inst_tau]
791 -- If GlasgowExts then check at least one isn't a type variable
792 | dopt Opt_GlasgowExts dflags
793 = -- GlasgowExts case
794 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
796 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
797 | not (length inst_taus == 1 &&
798 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
799 not (isSynTyCon tycon) && -- ...but not a synonym
800 all isTyVarTy arg_tys && -- Applied to type variables
801 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
802 -- This last condition checks that all the type variables are distinct
804 = [instTypeErr clas inst_taus
805 (text "the instance type must be of form (T a b c)" $$
806 text "where T is not a synonym, and a,b,c are distinct type variables")]
812 (first_inst_tau : _) = inst_taus
814 -- Stuff for algebraic or -> type
815 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
816 Just (tycon, arg_tys) = maybe_tycon_app
818 ccallable_type dflags ty = isFFIArgumentTy dflags PlayRisky ty
819 creturnable_type ty = isFFIImportResultTy dflags ty
821 check_tyvars dflags clas inst_taus
822 -- Check that at least one isn't a type variable
823 -- unless -fallow-undecideable-instances
824 | dopt Opt_AllowUndecidableInstances dflags = []
825 | not (all isTyVarTy inst_taus) = []
826 | otherwise = [the_err]
828 the_err = instTypeErr clas inst_taus msg
829 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
830 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
832 check_fundeps dflags theta clas inst_taus
833 | checkInstFDs theta clas inst_taus = []
834 | otherwise = [the_err]
836 the_err = instTypeErr clas inst_taus msg
837 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
841 %************************************************************************
843 \subsection{Error messages}
845 %************************************************************************
848 tcAddDeclCtxt decl thing_inside
849 = tcAddSrcLoc (tcdLoc decl) $
854 ClassDecl {} -> "class"
855 TySynonym {} -> "type synonym"
856 TyData {tcdND = NewType} -> "newtype"
857 TyData {tcdND = DataType} -> "data type"
859 ctxt = hsep [ptext SLIT("In the"), text thing,
860 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
862 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
864 doc = case inst_ty of
865 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
866 HsPredTy pred -> ppr pred
867 other -> ppr inst_ty -- Don't expect this
871 instConstraintErr pred
872 = hang (ptext SLIT("Illegal constraint") <+>
873 quotes (pprPred pred) <+>
874 ptext SLIT("in instance context"))
875 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
877 badGenericInstanceType binds
878 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
881 missingGenericInstances missing
882 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
886 dupGenericInsts tc_inst_infos
887 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
888 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
889 ptext SLIT("All the type patterns for a generic type constructor must be identical")
892 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
894 instTypeErr clas tys msg
895 = sep [ptext SLIT("Illegal instance declaration for") <+>
896 quotes (pprClassPred clas tys),
900 nonBoxedPrimCCallErr clas inst_ty
901 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
902 4 (pprClassPred clas [inst_ty])
904 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
905 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")