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 ( emptyNameSet, 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 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
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 dfuns infos
226 = getDOptsTc `thenTc` \ dflags ->
228 (inst_env', errs) = extendInstEnv dflags dfuns infos
230 addErrsTc errs `thenNF_Tc_`
235 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
236 -- Deal with a single instance declaration
237 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
238 = -- Prime error recovery, set source location
239 recoverNF_Tc (returnNF_Tc []) $
240 tcAddSrcLoc src_loc $
242 -- Type-check all the stuff before the "where"
243 tcAddErrCtxt (instDeclCtxt poly_ty) (
245 ) `thenTc` \ poly_ty' ->
247 (tyvars, theta, clas, inst_tys) = splitDFunTy poly_ty'
250 (case maybe_dfun_name of
251 Nothing -> -- A source-file instance declaration
253 -- Check for respectable instance type, and context
254 -- but only do this for non-imported instance decls.
255 -- Imported ones should have been checked already, and may indeed
256 -- contain something illegal in normal Haskell, notably
257 -- instance CCallable [Char]
258 getDOptsTc `thenTc` \ dflags ->
259 checkInstValidity dflags theta clas inst_tys `thenTc_`
261 -- Make the dfun id and return it
262 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
263 returnNF_Tc (True, dfun_name)
265 Just dfun_name -> -- An interface-file instance declaration
267 returnNF_Tc (False, dfun_name)
268 ) `thenNF_Tc` \ (is_local, dfun_name) ->
271 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
273 returnTc [InstInfo { iDFunId = dfun_id,
274 iBinds = binds, iPrags = uprags }]
278 %************************************************************************
280 \subsection{Extracting generic instance declaration from class declarations}
282 %************************************************************************
284 @getGenericInstances@ extracts the generic instance declarations from a class
285 declaration. For exmaple
290 op{ x+y } (Inl v) = ...
291 op{ x+y } (Inr v) = ...
292 op{ x*y } (v :*: w) = ...
295 gives rise to the instance declarations
297 instance C (x+y) where
301 instance C (x*y) where
309 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
310 getGenericInstances class_decls
311 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
313 gen_inst_info = concat gen_inst_infos
315 if null gen_inst_info then
318 getDOptsTc `thenTc` \ dflags ->
319 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
320 (vcat (map pprInstInfo gen_inst_info)))
322 returnTc gen_inst_info
324 get_generics decl@(ClassDecl {tcdMeths = Nothing})
325 = returnTc [] -- Imported class decls
327 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
329 = returnTc [] -- The comon case: no generic default methods
331 | otherwise -- A local class decl with generic default methods
332 = recoverNF_Tc (returnNF_Tc []) $
334 tcLookupClass class_name `thenTc` \ clas ->
336 -- Make an InstInfo out of each group
337 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
339 -- Check that there is only one InstInfo for each type constructor
340 -- The main way this can fail is if you write
341 -- f {| a+b |} ... = ...
342 -- f {| x+y |} ... = ...
343 -- Then at this point we'll have an InstInfo for each
345 tc_inst_infos :: [(TyCon, InstInfo)]
346 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
348 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
350 get_uniq (tc,_) = getUnique tc
352 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
354 -- Check that there is an InstInfo for each generic type constructor
356 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
358 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
363 -- Group the declarations by type pattern
364 groups :: [(RenamedHsType, RenamedMonoBinds)]
365 groups = assocElts (getGenericBinds def_methods)
368 ---------------------------------
369 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
370 -- Takes a group of method bindings, finds the generic ones, and returns
371 -- them in finite map indexed by the type parameter in the definition.
373 getGenericBinds EmptyMonoBinds = emptyAssoc
374 getGenericBinds (AndMonoBinds m1 m2)
375 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
377 getGenericBinds (FunMonoBind id infixop matches loc)
378 = mapAssoc wrap (foldl add emptyAssoc matches)
379 -- Using foldl not foldr is vital, else
380 -- we reverse the order of the bindings!
382 add env match = case maybeGenericMatch match of
384 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
386 wrap ms = FunMonoBind id infixop ms loc
388 ---------------------------------
389 mkGenericInstance :: Class -> SrcLoc
390 -> (RenamedHsType, RenamedMonoBinds)
393 mkGenericInstance clas loc (hs_ty, binds)
394 -- Make a generic instance declaration
395 -- For example: instance (C a, C b) => C (a+b) where { binds }
397 = -- Extract the universally quantified type variables
399 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
401 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
403 -- Type-check the instance type, and check its form
404 tcHsSigType hs_ty `thenTc` \ inst_ty ->
405 checkTc (validGenericInstanceType inst_ty)
406 (badGenericInstanceType binds) `thenTc_`
408 -- Make the dictionary function.
409 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
411 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
413 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
416 returnTc (InstInfo { iDFunId = dfun_id,
417 iBinds = binds, iPrags = [] })
421 %************************************************************************
423 \subsection{Type-checking instance declarations, pass 2}
425 %************************************************************************
428 tcInstDecls2 :: [InstInfo]
429 -> NF_TcM (LIE, TcMonoBinds)
431 tcInstDecls2 inst_decls
432 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
433 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
434 (map tcInstDecl2 inst_decls)
436 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
437 tc2 `thenNF_Tc` \ (lie2, binds2) ->
438 returnNF_Tc (lie1 `plusLIE` lie2,
439 binds1 `AndMonoBinds` binds2)
442 ======= New documentation starts here (Sept 92) ==============
444 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
445 the dictionary function for this instance declaration. For example
447 instance Foo a => Foo [a] where
451 might generate something like
453 dfun.Foo.List dFoo_a = let op1 x = ...
459 HOWEVER, if the instance decl has no context, then it returns a
460 bigger @HsBinds@ with declarations for each method. For example
462 instance Foo [a] where
468 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
469 const.Foo.op1.List a x = ...
470 const.Foo.op2.List a y = ...
472 This group may be mutually recursive, because (for example) there may
473 be no method supplied for op2 in which case we'll get
475 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
477 that is, the default method applied to the dictionary at this type.
479 What we actually produce in either case is:
481 AbsBinds [a] [dfun_theta_dicts]
482 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
483 { d = (sd1,sd2, ..., op1, op2, ...)
488 The "maybe" says that we only ask AbsBinds to make global constant methods
489 if the dfun_theta is empty.
492 For an instance declaration, say,
494 instance (C1 a, C2 b) => C (T a b) where
497 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
498 function whose type is
500 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
502 Notice that we pass it the superclass dictionaries at the instance type; this
503 is the ``Mark Jones optimisation''. The stuff before the "=>" here
504 is the @dfun_theta@ below.
506 First comes the easy case of a non-local instance decl.
510 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
511 -- tcInstDecl2 is called *only* on InstInfos
513 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
514 iBinds = monobinds, iPrags = uprags })
515 = -- Prime error recovery
516 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
517 tcAddSrcLoc (getSrcLoc dfun_id) $
518 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
520 -- Instantiate the instance decl with tc-style type variables
521 tcInstType (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
523 (clas, inst_tys') = splitDictTy dict_ty'
524 origin = InstanceDeclOrigin
526 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
528 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
529 sel_names = [idName sel_id | (sel_id, _) <- op_items]
531 -- Instantiate the super-class context with inst_tys
532 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
534 -- Find any definitions in monobinds that aren't from the class
535 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
537 -- The type variable from the dict fun actually scope
538 -- over the bindings. They were gotten from
539 -- the original instance declaration
540 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
542 -- Check that all the method bindings come from this class
543 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
545 -- Create dictionary Ids from the specified instance contexts.
546 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
547 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
548 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
550 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
551 tcExtendGlobalValEnv dm_ids (
552 -- Default-method Ids may be mentioned in synthesised RHSs
554 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
556 monobinds uprags True)
558 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
560 -- Deal with SPECIALISE instance pragmas by making them
561 -- look like SPECIALISE pragmas for the dfun
563 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
565 tcExtendGlobalValEnv [dfun_id] (
566 tcSpecSigs dfun_prags
567 ) `thenTc` \ (prag_binds, prag_lie) ->
569 -- Check the overloading constraints of the methods and superclasses
571 -- These insts are in scope; quite a few, eh?
572 avail_insts = [this_dict] ++
577 methods_lie = plusLIEs insts_needed_s
580 -- Simplify the constraints from methods
581 tcAddErrCtxt methodCtxt (
583 (ptext SLIT("instance declaration context"))
587 ) `thenTc` \ (const_lie1, lie_binds1) ->
589 -- Figure out bindings for the superclass context
590 tcAddErrCtxt superClassCtxt (
592 (ptext SLIT("instance declaration context"))
594 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
595 -- get bound by just selecting from this_dict!!
597 ) `thenTc` \ (const_lie2, lie_binds2) ->
599 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
601 -- Create the result bindings
603 dict_constr = classDataCon clas
604 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
605 this_dict_id = instToId this_dict
606 inlines = unitNameSet (idName dfun_id)
607 -- Always inline the dfun; this is an experimental decision
608 -- because it makes a big performance difference sometimes.
609 -- Often it means we can do the method selection, and then
610 -- inline the method as well. Marcin's idea; see comments below.
614 = -- Blatant special case for CCallable, CReturnable
615 -- If the dictionary is empty then we should never
616 -- select anything from it, so we make its RHS just
617 -- emit an error message. This in turn means that we don't
618 -- mention the constructor, which doesn't exist for CCallable, CReturnable
619 -- Hardly beautiful, but only three extra lines.
620 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
621 (HsLit (HsString msg))
623 | otherwise -- The common case
624 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
625 -- We don't produce a binding for the dict_constr; instead we
626 -- rely on the simplifier to unfold this saturated application
627 -- We do this rather than generate an HsCon directly, because
628 -- it means that the special cases (e.g. dictionary with only one
629 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
630 -- than needing to be repeated here.
633 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
635 dict_bind = VarMonoBind this_dict_id dict_rhs
636 method_binds = andMonoBindList method_binds_s
641 (map instToId dfun_arg_dicts)
642 [(inst_tyvars', dfun_id, this_dict_id)]
644 (lie_binds1 `AndMonoBinds`
645 lie_binds2 `AndMonoBinds`
646 method_binds `AndMonoBinds`
649 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
650 main_bind `AndMonoBinds` prag_binds)
653 ------------------------------
654 Inlining dfuns unconditionally
655 ------------------------------
657 The code above unconditionally inlines dict funs. Here's why.
658 Consider this program:
660 test :: Int -> Int -> Bool
661 test x y = (x,y) == (y,x) || test y x
662 -- Recursive to avoid making it inline.
664 This needs the (Eq (Int,Int)) instance. If we inline that dfun
665 the code we end up with is good:
668 \r -> case ==# [ww ww1] of wild {
669 PrelBase.False -> Test.$wtest ww1 ww;
671 case ==# [ww1 ww] of wild1 {
672 PrelBase.False -> Test.$wtest ww1 ww;
673 PrelBase.True -> PrelBase.True [];
676 Test.test = \r [w w1]
679 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
682 If we don't inline the dfun, the code is not nearly as good:
684 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
685 PrelBase.:DEq tpl1 tpl2 -> tpl2;
690 let { y = PrelBase.I#! [ww1]; } in
691 let { x = PrelBase.I#! [ww]; } in
692 let { sat_slx = PrelTup.(,)! [y x]; } in
693 let { sat_sly = PrelTup.(,)! [x y];
695 case == sat_sly sat_slx of wild {
696 PrelBase.False -> Test.$wtest ww1 ww;
697 PrelBase.True -> PrelBase.True [];
704 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
707 Why doesn't GHC inline $fEq? Because it looks big:
709 PrelTup.zdfEqZ1T{-rcX-}
710 = \ @ a{-reT-} :: * @ b{-reS-} :: *
711 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
712 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
714 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
715 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
717 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
718 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
720 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
721 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
722 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
724 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
726 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
728 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
729 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
733 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
734 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
735 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
736 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
738 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
740 and it's not as bad as it seems, because it's further dramatically
741 simplified: only zeze2 is extracted and its body is simplified.
744 %************************************************************************
746 \subsection{Checking for a decent instance type}
748 %************************************************************************
750 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
751 it must normally look like: @instance Foo (Tycon a b c ...) ...@
753 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
754 flag is on, or (2)~the instance is imported (they must have been
755 compiled elsewhere). In these cases, we let them go through anyway.
757 We can also have instances for functions: @instance Foo (a -> b) ...@.
760 checkInstValidity dflags theta clas inst_tys
761 | null errs = returnTc ()
762 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
764 errs = checkInstHead dflags theta clas inst_tys ++
765 [err | pred <- theta, err <- checkInstConstraint dflags pred]
767 checkInstConstraint dflags pred
768 -- Checks whether a predicate is legal in the
769 -- context of an instance declaration
771 | otherwise = [instConstraintErr pred]
773 ok = inheritablePred pred &&
774 (isTyVarClassPred pred || arbitrary_preds_ok)
776 arbitrary_preds_ok = dopt Opt_AllowUndecidableInstances dflags
779 checkInstHead dflags theta clas inst_taus
781 -- A user declaration of a CCallable/CReturnable instance
782 -- must be for a "boxed primitive" type.
783 (clas `hasKey` cCallableClassKey
784 && not (ccallable_type dflags first_inst_tau))
786 (clas `hasKey` cReturnableClassKey
787 && not (creturnable_type first_inst_tau))
788 = [nonBoxedPrimCCallErr clas first_inst_tau]
790 -- If GlasgowExts then check at least one isn't a type variable
791 | dopt Opt_GlasgowExts dflags
792 = -- GlasgowExts case
793 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
795 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
796 | not (length inst_taus == 1 &&
797 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
798 not (isSynTyCon tycon) && -- ...but not a synonym
799 all isTyVarTy arg_tys && -- Applied to type variables
800 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
801 -- This last condition checks that all the type variables are distinct
803 = [instTypeErr clas inst_taus
804 (text "the instance type must be of form (T a b c)" $$
805 text "where T is not a synonym, and a,b,c are distinct type variables")]
811 (first_inst_tau : _) = inst_taus
813 -- Stuff for algebraic or -> type
814 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
815 Just (tycon, arg_tys) = maybe_tycon_app
817 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
818 creturnable_type ty = isFFIImportResultTy dflags ty
820 check_tyvars dflags clas inst_taus
821 -- Check that at least one isn't a type variable
822 -- unless -fallow-undecideable-instances
823 | dopt Opt_AllowUndecidableInstances dflags = []
824 | not (all isTyVarTy inst_taus) = []
825 | otherwise = [the_err]
827 the_err = instTypeErr clas inst_taus msg
828 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
829 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
831 check_fundeps dflags theta clas inst_taus
832 | checkInstFDs theta clas inst_taus = []
833 | otherwise = [the_err]
835 the_err = instTypeErr clas inst_taus msg
836 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
840 %************************************************************************
842 \subsection{Error messages}
844 %************************************************************************
847 tcAddDeclCtxt decl thing_inside
848 = tcAddSrcLoc (tcdLoc decl) $
853 ClassDecl {} -> "class"
854 TySynonym {} -> "type synonym"
855 TyData {tcdND = NewType} -> "newtype"
856 TyData {tcdND = DataType} -> "data type"
858 ctxt = hsep [ptext SLIT("In the"), text thing,
859 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
861 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
863 doc = case inst_ty of
864 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
865 HsPredTy pred -> ppr pred
866 other -> ppr inst_ty -- Don't expect this
870 instConstraintErr pred
871 = hang (ptext SLIT("Illegal constraint") <+>
872 quotes (pprPred pred) <+>
873 ptext SLIT("in instance context"))
874 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
876 badGenericInstanceType binds
877 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
880 missingGenericInstances missing
881 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
885 dupGenericInsts tc_inst_infos
886 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
887 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
888 ptext SLIT("All the type patterns for a generic type constructor must be identical")
891 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
893 instTypeErr clas tys msg
894 = sep [ptext SLIT("Illegal instance declaration for") <+>
895 quotes (pprClassPred clas tys),
899 nonBoxedPrimCCallErr clas inst_ty
900 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
901 4 (pprClassPred clas [inst_ty])
903 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
904 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")