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(..),
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 ( tcTyVars, 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
398 tcTyVars (nameSetToList (extractHsTyVars hs_ty))
399 (kcHsSigType hs_ty) `thenTc` \ tyvars ->
400 tcExtendTyVarEnv tyvars $
402 -- Type-check the instance type, and check its form
403 tcHsSigType hs_ty `thenTc` \ inst_ty ->
404 checkTc (validGenericInstanceType inst_ty)
405 (badGenericInstanceType binds) `thenTc_`
407 -- Make the dictionary function.
408 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
410 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
412 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
415 returnTc (InstInfo { iDFunId = dfun_id,
416 iBinds = binds, iPrags = [] })
420 %************************************************************************
422 \subsection{Type-checking instance declarations, pass 2}
424 %************************************************************************
427 tcInstDecls2 :: [InstInfo]
428 -> NF_TcM (LIE, TcMonoBinds)
430 tcInstDecls2 inst_decls
431 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
432 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
433 (map tcInstDecl2 inst_decls)
435 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
436 tc2 `thenNF_Tc` \ (lie2, binds2) ->
437 returnNF_Tc (lie1 `plusLIE` lie2,
438 binds1 `AndMonoBinds` binds2)
441 ======= New documentation starts here (Sept 92) ==============
443 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
444 the dictionary function for this instance declaration. For example
446 instance Foo a => Foo [a] where
450 might generate something like
452 dfun.Foo.List dFoo_a = let op1 x = ...
458 HOWEVER, if the instance decl has no context, then it returns a
459 bigger @HsBinds@ with declarations for each method. For example
461 instance Foo [a] where
467 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
468 const.Foo.op1.List a x = ...
469 const.Foo.op2.List a y = ...
471 This group may be mutually recursive, because (for example) there may
472 be no method supplied for op2 in which case we'll get
474 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
476 that is, the default method applied to the dictionary at this type.
478 What we actually produce in either case is:
480 AbsBinds [a] [dfun_theta_dicts]
481 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
482 { d = (sd1,sd2, ..., op1, op2, ...)
487 The "maybe" says that we only ask AbsBinds to make global constant methods
488 if the dfun_theta is empty.
491 For an instance declaration, say,
493 instance (C1 a, C2 b) => C (T a b) where
496 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
497 function whose type is
499 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
501 Notice that we pass it the superclass dictionaries at the instance type; this
502 is the ``Mark Jones optimisation''. The stuff before the "=>" here
503 is the @dfun_theta@ below.
505 First comes the easy case of a non-local instance decl.
509 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
510 -- tcInstDecl2 is called *only* on InstInfos
512 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
513 iBinds = monobinds, iPrags = uprags })
514 = -- Prime error recovery
515 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
516 tcAddSrcLoc (getSrcLoc dfun_id) $
517 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
519 -- Instantiate the instance decl with tc-style type variables
520 tcInstType (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', dict_ty') ->
522 (clas, inst_tys') = splitDictTy dict_ty'
523 origin = InstanceDeclOrigin
525 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
527 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
528 sel_names = [idName sel_id | (sel_id, _) <- op_items]
530 -- Instantiate the super-class context with inst_tys
531 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
533 -- Find any definitions in monobinds that aren't from the class
534 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
536 -- The type variable from the dict fun actually scope
537 -- over the bindings. They were gotten from
538 -- the original instance declaration
539 (inst_tyvars, _) = splitForAllTys (idType dfun_id)
541 -- Check that all the method bindings come from this class
542 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
544 -- Create dictionary Ids from the specified instance contexts.
545 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
546 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
547 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
549 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
550 tcExtendGlobalValEnv dm_ids (
551 -- Default-method Ids may be mentioned in synthesised RHSs
553 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
555 monobinds uprags True)
557 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
559 -- Deal with SPECIALISE instance pragmas by making them
560 -- look like SPECIALISE pragmas for the dfun
562 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
564 tcExtendGlobalValEnv [dfun_id] (
565 tcSpecSigs dfun_prags
566 ) `thenTc` \ (prag_binds, prag_lie) ->
568 -- Check the overloading constraints of the methods and superclasses
570 -- These insts are in scope; quite a few, eh?
571 avail_insts = [this_dict] ++
576 methods_lie = plusLIEs insts_needed_s
579 -- Simplify the constraints from methods
580 tcAddErrCtxt methodCtxt (
582 (ptext SLIT("instance declaration context"))
586 ) `thenTc` \ (const_lie1, lie_binds1) ->
588 -- Figure out bindings for the superclass context
589 tcAddErrCtxt superClassCtxt (
591 (ptext SLIT("instance declaration context"))
593 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
594 -- get bound by just selecting from this_dict!!
596 ) `thenTc` \ (const_lie2, lie_binds2) ->
598 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
600 -- Create the result bindings
602 dict_constr = classDataCon clas
603 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
604 this_dict_id = instToId this_dict
605 inlines = unitNameSet (idName dfun_id)
606 -- Always inline the dfun; this is an experimental decision
607 -- because it makes a big performance difference sometimes.
608 -- Often it means we can do the method selection, and then
609 -- inline the method as well. Marcin's idea; see comments below.
613 = -- Blatant special case for CCallable, CReturnable
614 -- If the dictionary is empty then we should never
615 -- select anything from it, so we make its RHS just
616 -- emit an error message. This in turn means that we don't
617 -- mention the constructor, which doesn't exist for CCallable, CReturnable
618 -- Hardly beautiful, but only three extra lines.
619 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
620 (HsLit (HsString msg))
622 | otherwise -- The common case
623 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
624 -- We don't produce a binding for the dict_constr; instead we
625 -- rely on the simplifier to unfold this saturated application
626 -- We do this rather than generate an HsCon directly, because
627 -- it means that the special cases (e.g. dictionary with only one
628 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
629 -- than needing to be repeated here.
632 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
634 dict_bind = VarMonoBind this_dict_id dict_rhs
635 method_binds = andMonoBindList method_binds_s
640 (map instToId dfun_arg_dicts)
641 [(inst_tyvars', dfun_id, this_dict_id)]
643 (lie_binds1 `AndMonoBinds`
644 lie_binds2 `AndMonoBinds`
645 method_binds `AndMonoBinds`
648 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
649 main_bind `AndMonoBinds` prag_binds)
652 ------------------------------
653 Inlining dfuns unconditionally
654 ------------------------------
656 The code above unconditionally inlines dict funs. Here's why.
657 Consider this program:
659 test :: Int -> Int -> Bool
660 test x y = (x,y) == (y,x) || test y x
661 -- Recursive to avoid making it inline.
663 This needs the (Eq (Int,Int)) instance. If we inline that dfun
664 the code we end up with is good:
667 \r -> case ==# [ww ww1] of wild {
668 PrelBase.False -> Test.$wtest ww1 ww;
670 case ==# [ww1 ww] of wild1 {
671 PrelBase.False -> Test.$wtest ww1 ww;
672 PrelBase.True -> PrelBase.True [];
675 Test.test = \r [w w1]
678 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
681 If we don't inline the dfun, the code is not nearly as good:
683 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
684 PrelBase.:DEq tpl1 tpl2 -> tpl2;
689 let { y = PrelBase.I#! [ww1]; } in
690 let { x = PrelBase.I#! [ww]; } in
691 let { sat_slx = PrelTup.(,)! [y x]; } in
692 let { sat_sly = PrelTup.(,)! [x y];
694 case == sat_sly sat_slx of wild {
695 PrelBase.False -> Test.$wtest ww1 ww;
696 PrelBase.True -> PrelBase.True [];
703 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
706 Why doesn't GHC inline $fEq? Because it looks big:
708 PrelTup.zdfEqZ1T{-rcX-}
709 = \ @ a{-reT-} :: * @ b{-reS-} :: *
710 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
711 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
713 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
714 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
716 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
717 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
719 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
720 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
721 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
723 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
725 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
727 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
728 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
732 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
733 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
734 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
735 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
737 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
739 and it's not as bad as it seems, because it's further dramatically
740 simplified: only zeze2 is extracted and its body is simplified.
743 %************************************************************************
745 \subsection{Checking for a decent instance type}
747 %************************************************************************
749 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
750 it must normally look like: @instance Foo (Tycon a b c ...) ...@
752 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
753 flag is on, or (2)~the instance is imported (they must have been
754 compiled elsewhere). In these cases, we let them go through anyway.
756 We can also have instances for functions: @instance Foo (a -> b) ...@.
759 checkInstValidity dflags theta clas inst_tys
760 | null errs = returnTc ()
761 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
763 errs = checkInstHead dflags theta clas inst_tys ++
764 [err | pred <- theta, err <- checkInstConstraint dflags pred]
766 checkInstConstraint dflags pred
767 -- Checks whether a predicate is legal in the
768 -- context of an instance declaration
770 | otherwise = [instConstraintErr pred]
772 ok = inheritablePred pred &&
773 (isTyVarClassPred pred || arbitrary_preds_ok)
775 arbitrary_preds_ok = dopt Opt_AllowUndecidableInstances dflags
778 checkInstHead dflags theta clas inst_taus
780 -- A user declaration of a CCallable/CReturnable instance
781 -- must be for a "boxed primitive" type.
782 (clas `hasKey` cCallableClassKey
783 && not (ccallable_type dflags first_inst_tau))
785 (clas `hasKey` cReturnableClassKey
786 && not (creturnable_type first_inst_tau))
787 = [nonBoxedPrimCCallErr clas first_inst_tau]
789 -- If GlasgowExts then check at least one isn't a type variable
790 | dopt Opt_GlasgowExts dflags
791 = -- GlasgowExts case
792 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
794 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
795 | not (length inst_taus == 1 &&
796 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
797 not (isSynTyCon tycon) && -- ...but not a synonym
798 all isTyVarTy arg_tys && -- Applied to type variables
799 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
800 -- This last condition checks that all the type variables are distinct
802 = [instTypeErr clas inst_taus
803 (text "the instance type must be of form (T a b c)" $$
804 text "where T is not a synonym, and a,b,c are distinct type variables")]
810 (first_inst_tau : _) = inst_taus
812 -- Stuff for algebraic or -> type
813 maybe_tycon_app = splitTyConApp_maybe first_inst_tau
814 Just (tycon, arg_tys) = maybe_tycon_app
816 ccallable_type dflags ty = isFFIArgumentTy dflags False {- Not safe call -} ty
817 creturnable_type ty = isFFIImportResultTy dflags ty
819 check_tyvars dflags clas inst_taus
820 -- Check that at least one isn't a type variable
821 -- unless -fallow-undecideable-instances
822 | dopt Opt_AllowUndecidableInstances dflags = []
823 | not (all isTyVarTy inst_taus) = []
824 | otherwise = [the_err]
826 the_err = instTypeErr clas inst_taus msg
827 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
828 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
830 check_fundeps dflags theta clas inst_taus
831 | checkInstFDs theta clas inst_taus = []
832 | otherwise = [the_err]
834 the_err = instTypeErr clas inst_taus msg
835 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
839 %************************************************************************
841 \subsection{Error messages}
843 %************************************************************************
846 tcAddDeclCtxt decl thing_inside
847 = tcAddSrcLoc (tcdLoc decl) $
852 ClassDecl {} -> "class"
853 TySynonym {} -> "type synonym"
854 TyData {tcdND = NewType} -> "newtype"
855 TyData {tcdND = DataType} -> "data type"
857 ctxt = hsep [ptext SLIT("In the"), text thing,
858 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
860 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
862 doc = case inst_ty of
863 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
864 HsPredTy pred -> ppr pred
865 other -> ppr inst_ty -- Don't expect this
869 instConstraintErr pred
870 = hang (ptext SLIT("Illegal constraint") <+>
871 quotes (pprPred pred) <+>
872 ptext SLIT("in instance context"))
873 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
875 badGenericInstanceType binds
876 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
879 missingGenericInstances missing
880 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
884 dupGenericInsts tc_inst_infos
885 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
886 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
887 ptext SLIT("All the type patterns for a generic type constructor must be identical")
890 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
892 instTypeErr clas tys msg
893 = sep [ptext SLIT("Illegal instance declaration for") <+>
894 quotes (pprClassPred clas tys),
898 nonBoxedPrimCCallErr clas inst_ty
899 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
900 4 (pprClassPred clas [inst_ty])
902 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
903 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")