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 ( tcInstType, tcInstTyVars )
27 import TcType ( tcSplitDFunTy, tcIsTyVarTy, tcSplitTyConApp_maybe,
28 tyVarsOfTypes, mkClassPred, mkTyVarTy,
29 isTyVarClassPred, inheritablePred
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, tcHsSigType, kcHsSigType, 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, pprPred )
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 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
244 = -- Prime error recovery, set source location
245 recoverNF_Tc (returnNF_Tc []) $
246 tcAddSrcLoc src_loc $
248 -- Type-check all the stuff before the "where"
249 traceTc (text "Starting inst" <+> ppr poly_ty) `thenTc_`
250 tcAddErrCtxt (instDeclCtxt poly_ty) (
252 ) `thenTc` \ poly_ty' ->
254 (tyvars, theta, clas, inst_tys) = tcSplitDFunTy poly_ty'
257 traceTc (text "Check validity") `thenTc_`
258 (case maybe_dfun_name of
259 Nothing -> -- A source-file instance declaration
261 -- Check for respectable instance type, and context
262 -- but only do this for non-imported instance decls.
263 -- Imported ones should have been checked already, and may indeed
264 -- contain something illegal in normal Haskell, notably
265 -- instance CCallable [Char]
266 getDOptsTc `thenTc` \ dflags ->
267 checkInstValidity dflags theta clas inst_tys `thenTc_`
269 -- Make the dfun id and return it
270 traceTc (text "new name") `thenTc_`
271 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
272 returnNF_Tc (True, dfun_name)
274 Just dfun_name -> -- An interface-file instance declaration
276 returnNF_Tc (False, dfun_name)
277 ) `thenNF_Tc` \ (is_local, dfun_name) ->
279 traceTc (text "Name" <+> ppr dfun_name) `thenTc_`
281 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
283 returnTc [InstInfo { iDFunId = dfun_id,
284 iBinds = binds, iPrags = uprags }]
288 %************************************************************************
290 \subsection{Extracting generic instance declaration from class declarations}
292 %************************************************************************
294 @getGenericInstances@ extracts the generic instance declarations from a class
295 declaration. For exmaple
300 op{ x+y } (Inl v) = ...
301 op{ x+y } (Inr v) = ...
302 op{ x*y } (v :*: w) = ...
305 gives rise to the instance declarations
307 instance C (x+y) where
311 instance C (x*y) where
319 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
320 getGenericInstances class_decls
321 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
323 gen_inst_info = concat gen_inst_infos
325 if null gen_inst_info then
328 getDOptsTc `thenTc` \ dflags ->
329 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
330 (vcat (map pprInstInfo gen_inst_info)))
332 returnTc gen_inst_info
334 get_generics decl@(ClassDecl {tcdMeths = Nothing})
335 = returnTc [] -- Imported class decls
337 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
339 = returnTc [] -- The comon case: no generic default methods
341 | otherwise -- A local class decl with generic default methods
342 = recoverNF_Tc (returnNF_Tc []) $
344 tcLookupClass class_name `thenTc` \ clas ->
346 -- Make an InstInfo out of each group
347 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
349 -- Check that there is only one InstInfo for each type constructor
350 -- The main way this can fail is if you write
351 -- f {| a+b |} ... = ...
352 -- f {| x+y |} ... = ...
353 -- Then at this point we'll have an InstInfo for each
355 tc_inst_infos :: [(TyCon, InstInfo)]
356 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
358 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
360 get_uniq (tc,_) = getUnique tc
362 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
364 -- Check that there is an InstInfo for each generic type constructor
366 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
368 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
373 -- Group the declarations by type pattern
374 groups :: [(RenamedHsType, RenamedMonoBinds)]
375 groups = assocElts (getGenericBinds def_methods)
378 ---------------------------------
379 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
380 -- Takes a group of method bindings, finds the generic ones, and returns
381 -- them in finite map indexed by the type parameter in the definition.
383 getGenericBinds EmptyMonoBinds = emptyAssoc
384 getGenericBinds (AndMonoBinds m1 m2)
385 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
387 getGenericBinds (FunMonoBind id infixop matches loc)
388 = mapAssoc wrap (foldl add emptyAssoc matches)
389 -- Using foldl not foldr is vital, else
390 -- we reverse the order of the bindings!
392 add env match = case maybeGenericMatch match of
394 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
396 wrap ms = FunMonoBind id infixop ms loc
398 ---------------------------------
399 mkGenericInstance :: Class -> SrcLoc
400 -> (RenamedHsType, RenamedMonoBinds)
403 mkGenericInstance clas loc (hs_ty, binds)
404 -- Make a generic instance declaration
405 -- For example: instance (C a, C b) => C (a+b) where { binds }
407 = -- Extract the universally quantified type variables
409 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
411 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
413 -- Type-check the instance type, and check its form
414 tcHsSigType hs_ty `thenTc` \ inst_ty ->
415 checkTc (validGenericInstanceType inst_ty)
416 (badGenericInstanceType binds) `thenTc_`
418 -- Make the dictionary function.
419 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
421 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
423 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
426 returnTc (InstInfo { iDFunId = dfun_id,
427 iBinds = binds, iPrags = [] })
431 %************************************************************************
433 \subsection{Type-checking instance declarations, pass 2}
435 %************************************************************************
438 tcInstDecls2 :: [InstInfo]
439 -> NF_TcM (LIE, TcMonoBinds)
441 tcInstDecls2 inst_decls
442 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
443 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
444 (map tcInstDecl2 inst_decls)
446 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
447 tc2 `thenNF_Tc` \ (lie2, binds2) ->
448 returnNF_Tc (lie1 `plusLIE` lie2,
449 binds1 `AndMonoBinds` binds2)
452 ======= New documentation starts here (Sept 92) ==============
454 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
455 the dictionary function for this instance declaration. For example
457 instance Foo a => Foo [a] where
461 might generate something like
463 dfun.Foo.List dFoo_a = let op1 x = ...
469 HOWEVER, if the instance decl has no context, then it returns a
470 bigger @HsBinds@ with declarations for each method. For example
472 instance Foo [a] where
478 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
479 const.Foo.op1.List a x = ...
480 const.Foo.op2.List a y = ...
482 This group may be mutually recursive, because (for example) there may
483 be no method supplied for op2 in which case we'll get
485 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
487 that is, the default method applied to the dictionary at this type.
489 What we actually produce in either case is:
491 AbsBinds [a] [dfun_theta_dicts]
492 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
493 { d = (sd1,sd2, ..., op1, op2, ...)
498 The "maybe" says that we only ask AbsBinds to make global constant methods
499 if the dfun_theta is empty.
502 For an instance declaration, say,
504 instance (C1 a, C2 b) => C (T a b) where
507 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
508 function whose type is
510 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
512 Notice that we pass it the superclass dictionaries at the instance type; this
513 is the ``Mark Jones optimisation''. The stuff before the "=>" here
514 is the @dfun_theta@ below.
516 First comes the easy case of a non-local instance decl.
520 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
521 -- tcInstDecl2 is called *only* on InstInfos
523 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
524 iBinds = monobinds, iPrags = uprags })
525 = -- Prime error recovery
526 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
527 tcAddSrcLoc (getSrcLoc dfun_id) $
528 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
530 -- Instantiate the instance decl with tc-style type variables
532 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
534 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
536 inst_tys' = map (substTy tenv) inst_tys
537 dfun_theta' = substTheta tenv dfun_theta
538 origin = InstanceDeclOrigin
540 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
542 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
543 sel_names = [idName sel_id | (sel_id, _) <- op_items]
545 -- Instantiate the super-class context with inst_tys
546 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
548 -- Find any definitions in monobinds that aren't from the class
549 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
551 -- Check that all the method bindings come from this class
552 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
554 -- Create dictionary Ids from the specified instance contexts.
555 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
556 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
557 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
559 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
560 -- The type variable from the dict fun actually scope
561 -- over the bindings. They were gotten from
562 -- the original instance declaration
563 tcExtendGlobalValEnv dm_ids (
564 -- Default-method Ids may be mentioned in synthesised RHSs
566 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
568 monobinds uprags True)
570 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
572 -- Deal with SPECIALISE instance pragmas by making them
573 -- look like SPECIALISE pragmas for the dfun
575 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
577 tcExtendGlobalValEnv [dfun_id] (
578 tcSpecSigs dfun_prags
579 ) `thenTc` \ (prag_binds, prag_lie) ->
581 -- Check the overloading constraints of the methods and superclasses
583 -- These insts are in scope; quite a few, eh?
584 avail_insts = [this_dict] ++
589 methods_lie = plusLIEs insts_needed_s
592 -- Simplify the constraints from methods
593 tcAddErrCtxt methodCtxt (
595 (ptext SLIT("instance declaration context"))
599 ) `thenTc` \ (const_lie1, lie_binds1) ->
601 -- Figure out bindings for the superclass context
602 tcAddErrCtxt superClassCtxt (
604 (ptext SLIT("instance declaration context"))
606 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
607 -- get bound by just selecting from this_dict!!
609 ) `thenTc` \ (const_lie2, lie_binds2) ->
611 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
613 -- Create the result bindings
615 dict_constr = classDataCon clas
616 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
617 this_dict_id = instToId this_dict
618 inlines = unitNameSet (idName dfun_id)
619 -- Always inline the dfun; this is an experimental decision
620 -- because it makes a big performance difference sometimes.
621 -- Often it means we can do the method selection, and then
622 -- inline the method as well. Marcin's idea; see comments below.
626 = -- Blatant special case for CCallable, CReturnable
627 -- If the dictionary is empty then we should never
628 -- select anything from it, so we make its RHS just
629 -- emit an error message. This in turn means that we don't
630 -- mention the constructor, which doesn't exist for CCallable, CReturnable
631 -- Hardly beautiful, but only three extra lines.
632 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
633 (HsLit (HsString msg))
635 | otherwise -- The common case
636 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
637 -- We don't produce a binding for the dict_constr; instead we
638 -- rely on the simplifier to unfold this saturated application
639 -- We do this rather than generate an HsCon directly, because
640 -- it means that the special cases (e.g. dictionary with only one
641 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
642 -- than needing to be repeated here.
645 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
647 dict_bind = VarMonoBind this_dict_id dict_rhs
648 method_binds = andMonoBindList method_binds_s
653 (map instToId dfun_arg_dicts)
654 [(inst_tyvars', dfun_id, this_dict_id)]
656 (lie_binds1 `AndMonoBinds`
657 lie_binds2 `AndMonoBinds`
658 method_binds `AndMonoBinds`
661 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
662 main_bind `AndMonoBinds` prag_binds)
665 ------------------------------
666 Inlining dfuns unconditionally
667 ------------------------------
669 The code above unconditionally inlines dict funs. Here's why.
670 Consider this program:
672 test :: Int -> Int -> Bool
673 test x y = (x,y) == (y,x) || test y x
674 -- Recursive to avoid making it inline.
676 This needs the (Eq (Int,Int)) instance. If we inline that dfun
677 the code we end up with is good:
680 \r -> case ==# [ww ww1] of wild {
681 PrelBase.False -> Test.$wtest ww1 ww;
683 case ==# [ww1 ww] of wild1 {
684 PrelBase.False -> Test.$wtest ww1 ww;
685 PrelBase.True -> PrelBase.True [];
688 Test.test = \r [w w1]
691 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
694 If we don't inline the dfun, the code is not nearly as good:
696 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
697 PrelBase.:DEq tpl1 tpl2 -> tpl2;
702 let { y = PrelBase.I#! [ww1]; } in
703 let { x = PrelBase.I#! [ww]; } in
704 let { sat_slx = PrelTup.(,)! [y x]; } in
705 let { sat_sly = PrelTup.(,)! [x y];
707 case == sat_sly sat_slx of wild {
708 PrelBase.False -> Test.$wtest ww1 ww;
709 PrelBase.True -> PrelBase.True [];
716 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
719 Why doesn't GHC inline $fEq? Because it looks big:
721 PrelTup.zdfEqZ1T{-rcX-}
722 = \ @ a{-reT-} :: * @ b{-reS-} :: *
723 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
724 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
726 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
727 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
729 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
730 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
732 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
733 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
734 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
736 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
738 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
740 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
741 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
745 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
746 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
747 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
748 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
750 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
752 and it's not as bad as it seems, because it's further dramatically
753 simplified: only zeze2 is extracted and its body is simplified.
756 %************************************************************************
758 \subsection{Checking for a decent instance type}
760 %************************************************************************
762 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
763 it must normally look like: @instance Foo (Tycon a b c ...) ...@
765 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
766 flag is on, or (2)~the instance is imported (they must have been
767 compiled elsewhere). In these cases, we let them go through anyway.
769 We can also have instances for functions: @instance Foo (a -> b) ...@.
772 checkInstValidity dflags theta clas inst_tys
773 | null errs = returnTc ()
774 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
776 errs = checkInstHead dflags theta clas inst_tys ++
777 [err | pred <- theta, err <- checkInstConstraint dflags pred]
779 checkInstConstraint dflags pred
780 -- Checks whether a predicate is legal in the
781 -- context of an instance declaration
783 | otherwise = [instConstraintErr pred]
785 ok = inheritablePred pred &&
786 (isTyVarClassPred pred || arbitrary_preds_ok)
788 arbitrary_preds_ok = dopt Opt_AllowUndecidableInstances dflags
791 checkInstHead dflags theta clas inst_taus
793 -- A user declaration of a CCallable/CReturnable instance
794 -- must be for a "boxed primitive" type.
795 (clas `hasKey` cCallableClassKey
796 && not (ccallable_type dflags first_inst_tau))
798 (clas `hasKey` cReturnableClassKey
799 && not (creturnable_type first_inst_tau))
800 = [nonBoxedPrimCCallErr clas first_inst_tau]
802 -- If GlasgowExts then check at least one isn't a type variable
803 | dopt Opt_GlasgowExts dflags
804 = -- GlasgowExts case
805 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
807 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
808 | not (length inst_taus == 1 &&
809 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
810 not (isSynTyCon tycon) && -- ...but not a synonym
811 all tcIsTyVarTy arg_tys && -- Applied to type variables
812 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
813 -- This last condition checks that all the type variables are distinct
815 = [instTypeErr clas inst_taus
816 (text "the instance type must be of form (T a b c)" $$
817 text "where T is not a synonym, and a,b,c are distinct type variables")]
823 (first_inst_tau : _) = inst_taus
825 -- Stuff for algebraic or -> type
826 maybe_tycon_app = tcSplitTyConApp_maybe first_inst_tau
827 Just (tycon, arg_tys) = maybe_tycon_app
829 ccallable_type dflags ty = isFFIArgumentTy dflags PlayRisky ty
830 creturnable_type ty = isFFIImportResultTy dflags ty
832 check_tyvars dflags clas inst_taus
833 -- Check that at least one isn't a type variable
834 -- unless -fallow-undecideable-instances
835 | dopt Opt_AllowUndecidableInstances dflags = []
836 | not (all tcIsTyVarTy inst_taus) = []
837 | otherwise = [the_err]
839 the_err = instTypeErr clas inst_taus msg
840 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
841 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
843 check_fundeps dflags theta clas inst_taus
844 | checkInstFDs theta clas inst_taus = []
845 | otherwise = [the_err]
847 the_err = instTypeErr clas inst_taus msg
848 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
852 %************************************************************************
854 \subsection{Error messages}
856 %************************************************************************
859 tcAddDeclCtxt decl thing_inside
860 = tcAddSrcLoc (tcdLoc decl) $
865 ClassDecl {} -> "class"
866 TySynonym {} -> "type synonym"
867 TyData {tcdND = NewType} -> "newtype"
868 TyData {tcdND = DataType} -> "data type"
870 ctxt = hsep [ptext SLIT("In the"), text thing,
871 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
873 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
875 doc = case inst_ty of
876 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
877 HsPredTy pred -> ppr pred
878 other -> ppr inst_ty -- Don't expect this
882 instConstraintErr pred
883 = hang (ptext SLIT("Illegal constraint") <+>
884 quotes (pprPred pred) <+>
885 ptext SLIT("in instance context"))
886 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
888 badGenericInstanceType binds
889 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
892 missingGenericInstances missing
893 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
897 dupGenericInsts tc_inst_infos
898 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
899 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
900 ptext SLIT("All the type patterns for a generic type constructor must be identical")
903 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
905 instTypeErr clas tys msg
906 = sep [ptext SLIT("Illegal instance declaration for") <+>
907 quotes (pprClassPred clas tys),
911 nonBoxedPrimCCallErr clas inst_ty
912 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
913 4 (pprClassPred clas [inst_ty])
915 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
916 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")