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
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 inst_env dfuns
226 = getDOptsTc `thenTc` \ dflags ->
228 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
230 addErrsTc errs `thenNF_Tc_`
231 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
234 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
238 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
239 -- Deal with a single instance declaration
240 tcInstDecl1 decl@(InstDecl poly_ty binds uprags maybe_dfun_name src_loc)
241 = -- Prime error recovery, set source location
242 recoverNF_Tc (returnNF_Tc []) $
243 tcAddSrcLoc src_loc $
245 -- Type-check all the stuff before the "where"
246 traceTc (text "Starting inst" <+> ppr poly_ty) `thenTc_`
247 tcAddErrCtxt (instDeclCtxt poly_ty) (
249 ) `thenTc` \ poly_ty' ->
251 (tyvars, theta, clas, inst_tys) = tcSplitDFunTy poly_ty'
254 traceTc (text "Check validity") `thenTc_`
255 (case maybe_dfun_name of
256 Nothing -> -- A source-file instance declaration
258 -- Check for respectable instance type, and context
259 -- but only do this for non-imported instance decls.
260 -- Imported ones should have been checked already, and may indeed
261 -- contain something illegal in normal Haskell, notably
262 -- instance CCallable [Char]
263 getDOptsTc `thenTc` \ dflags ->
264 checkInstValidity dflags theta clas inst_tys `thenTc_`
266 -- Make the dfun id and return it
267 traceTc (text "new name") `thenTc_`
268 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
269 returnNF_Tc (True, dfun_name)
271 Just dfun_name -> -- An interface-file instance declaration
273 returnNF_Tc (False, dfun_name)
274 ) `thenNF_Tc` \ (is_local, dfun_name) ->
276 traceTc (text "Name" <+> ppr dfun_name) `thenTc_`
278 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
280 returnTc [InstInfo { iDFunId = dfun_id,
281 iBinds = binds, iPrags = uprags }]
285 %************************************************************************
287 \subsection{Extracting generic instance declaration from class declarations}
289 %************************************************************************
291 @getGenericInstances@ extracts the generic instance declarations from a class
292 declaration. For exmaple
297 op{ x+y } (Inl v) = ...
298 op{ x+y } (Inr v) = ...
299 op{ x*y } (v :*: w) = ...
302 gives rise to the instance declarations
304 instance C (x+y) where
308 instance C (x*y) where
316 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
317 getGenericInstances class_decls
318 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
320 gen_inst_info = concat gen_inst_infos
322 if null gen_inst_info then
325 getDOptsTc `thenTc` \ dflags ->
326 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
327 (vcat (map pprInstInfo gen_inst_info)))
329 returnTc gen_inst_info
331 get_generics decl@(ClassDecl {tcdMeths = Nothing})
332 = returnTc [] -- Imported class decls
334 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
336 = returnTc [] -- The comon case: no generic default methods
338 | otherwise -- A local class decl with generic default methods
339 = recoverNF_Tc (returnNF_Tc []) $
341 tcLookupClass class_name `thenTc` \ clas ->
343 -- Make an InstInfo out of each group
344 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
346 -- Check that there is only one InstInfo for each type constructor
347 -- The main way this can fail is if you write
348 -- f {| a+b |} ... = ...
349 -- f {| x+y |} ... = ...
350 -- Then at this point we'll have an InstInfo for each
352 tc_inst_infos :: [(TyCon, InstInfo)]
353 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
355 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
357 get_uniq (tc,_) = getUnique tc
359 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
361 -- Check that there is an InstInfo for each generic type constructor
363 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
365 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
370 -- Group the declarations by type pattern
371 groups :: [(RenamedHsType, RenamedMonoBinds)]
372 groups = assocElts (getGenericBinds def_methods)
375 ---------------------------------
376 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
377 -- Takes a group of method bindings, finds the generic ones, and returns
378 -- them in finite map indexed by the type parameter in the definition.
380 getGenericBinds EmptyMonoBinds = emptyAssoc
381 getGenericBinds (AndMonoBinds m1 m2)
382 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
384 getGenericBinds (FunMonoBind id infixop matches loc)
385 = mapAssoc wrap (foldl add emptyAssoc matches)
386 -- Using foldl not foldr is vital, else
387 -- we reverse the order of the bindings!
389 add env match = case maybeGenericMatch match of
391 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
393 wrap ms = FunMonoBind id infixop ms loc
395 ---------------------------------
396 mkGenericInstance :: Class -> SrcLoc
397 -> (RenamedHsType, RenamedMonoBinds)
400 mkGenericInstance clas loc (hs_ty, binds)
401 -- Make a generic instance declaration
402 -- For example: instance (C a, C b) => C (a+b) where { binds }
404 = -- Extract the universally quantified type variables
406 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
408 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
410 -- Type-check the instance type, and check its form
411 tcHsSigType hs_ty `thenTc` \ inst_ty ->
412 checkTc (validGenericInstanceType inst_ty)
413 (badGenericInstanceType binds) `thenTc_`
415 -- Make the dictionary function.
416 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
418 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
420 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
423 returnTc (InstInfo { iDFunId = dfun_id,
424 iBinds = binds, iPrags = [] })
428 %************************************************************************
430 \subsection{Type-checking instance declarations, pass 2}
432 %************************************************************************
435 tcInstDecls2 :: [InstInfo]
436 -> NF_TcM (LIE, TcMonoBinds)
438 tcInstDecls2 inst_decls
439 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
440 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
441 (map tcInstDecl2 inst_decls)
443 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
444 tc2 `thenNF_Tc` \ (lie2, binds2) ->
445 returnNF_Tc (lie1 `plusLIE` lie2,
446 binds1 `AndMonoBinds` binds2)
449 ======= New documentation starts here (Sept 92) ==============
451 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
452 the dictionary function for this instance declaration. For example
454 instance Foo a => Foo [a] where
458 might generate something like
460 dfun.Foo.List dFoo_a = let op1 x = ...
466 HOWEVER, if the instance decl has no context, then it returns a
467 bigger @HsBinds@ with declarations for each method. For example
469 instance Foo [a] where
475 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
476 const.Foo.op1.List a x = ...
477 const.Foo.op2.List a y = ...
479 This group may be mutually recursive, because (for example) there may
480 be no method supplied for op2 in which case we'll get
482 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
484 that is, the default method applied to the dictionary at this type.
486 What we actually produce in either case is:
488 AbsBinds [a] [dfun_theta_dicts]
489 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
490 { d = (sd1,sd2, ..., op1, op2, ...)
495 The "maybe" says that we only ask AbsBinds to make global constant methods
496 if the dfun_theta is empty.
499 For an instance declaration, say,
501 instance (C1 a, C2 b) => C (T a b) where
504 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
505 function whose type is
507 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
509 Notice that we pass it the superclass dictionaries at the instance type; this
510 is the ``Mark Jones optimisation''. The stuff before the "=>" here
511 is the @dfun_theta@ below.
513 First comes the easy case of a non-local instance decl.
517 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
518 -- tcInstDecl2 is called *only* on InstInfos
520 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
521 iBinds = monobinds, iPrags = uprags })
522 = -- Prime error recovery
523 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
524 tcAddSrcLoc (getSrcLoc dfun_id) $
525 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
527 -- Instantiate the instance decl with tc-style type variables
529 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
531 tcInstTyVars inst_tyvars `thenNF_Tc` \ (inst_tyvars', _, tenv) ->
533 inst_tys' = map (substTy tenv) inst_tys
534 dfun_theta' = substTheta tenv dfun_theta
535 origin = InstanceDeclOrigin
537 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
539 dm_ids = [dm_id | (_, DefMeth dm_id) <- op_items]
540 sel_names = [idName sel_id | (sel_id, _) <- op_items]
542 -- Instantiate the super-class context with inst_tys
543 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
545 -- Find any definitions in monobinds that aren't from the class
546 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
548 -- Check that all the method bindings come from this class
549 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
551 -- Create dictionary Ids from the specified instance contexts.
552 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
553 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
554 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
556 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
557 -- The type variable from the dict fun actually scope
558 -- over the bindings. They were gotten from
559 -- the original instance declaration
560 tcExtendGlobalValEnv dm_ids (
561 -- Default-method Ids may be mentioned in synthesised RHSs
563 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
565 monobinds uprags True)
567 )) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
569 -- Deal with SPECIALISE instance pragmas by making them
570 -- look like SPECIALISE pragmas for the dfun
572 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
574 tcExtendGlobalValEnv [dfun_id] (
575 tcSpecSigs dfun_prags
576 ) `thenTc` \ (prag_binds, prag_lie) ->
578 -- Check the overloading constraints of the methods and superclasses
580 -- These insts are in scope; quite a few, eh?
581 avail_insts = [this_dict] ++
586 methods_lie = plusLIEs insts_needed_s
589 -- Simplify the constraints from methods
590 tcAddErrCtxt methodCtxt (
592 (ptext SLIT("instance declaration context"))
596 ) `thenTc` \ (const_lie1, lie_binds1) ->
598 -- Figure out bindings for the superclass context
599 tcAddErrCtxt superClassCtxt (
601 (ptext SLIT("instance declaration context"))
603 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
604 -- get bound by just selecting from this_dict!!
606 ) `thenTc` \ (const_lie2, lie_binds2) ->
608 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
610 -- Create the result bindings
612 dict_constr = classDataCon clas
613 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
614 this_dict_id = instToId this_dict
615 inlines = unitNameSet (idName dfun_id)
616 -- Always inline the dfun; this is an experimental decision
617 -- because it makes a big performance difference sometimes.
618 -- Often it means we can do the method selection, and then
619 -- inline the method as well. Marcin's idea; see comments below.
623 = -- Blatant special case for CCallable, CReturnable
624 -- If the dictionary is empty then we should never
625 -- select anything from it, so we make its RHS just
626 -- emit an error message. This in turn means that we don't
627 -- mention the constructor, which doesn't exist for CCallable, CReturnable
628 -- Hardly beautiful, but only three extra lines.
629 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
630 (HsLit (HsString msg))
632 | otherwise -- The common case
633 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
634 -- We don't produce a binding for the dict_constr; instead we
635 -- rely on the simplifier to unfold this saturated application
636 -- We do this rather than generate an HsCon directly, because
637 -- it means that the special cases (e.g. dictionary with only one
638 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
639 -- than needing to be repeated here.
642 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
644 dict_bind = VarMonoBind this_dict_id dict_rhs
645 method_binds = andMonoBindList method_binds_s
650 (map instToId dfun_arg_dicts)
651 [(inst_tyvars', dfun_id, this_dict_id)]
653 (lie_binds1 `AndMonoBinds`
654 lie_binds2 `AndMonoBinds`
655 method_binds `AndMonoBinds`
658 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
659 main_bind `AndMonoBinds` prag_binds)
662 ------------------------------
663 Inlining dfuns unconditionally
664 ------------------------------
666 The code above unconditionally inlines dict funs. Here's why.
667 Consider this program:
669 test :: Int -> Int -> Bool
670 test x y = (x,y) == (y,x) || test y x
671 -- Recursive to avoid making it inline.
673 This needs the (Eq (Int,Int)) instance. If we inline that dfun
674 the code we end up with is good:
677 \r -> case ==# [ww ww1] of wild {
678 PrelBase.False -> Test.$wtest ww1 ww;
680 case ==# [ww1 ww] of wild1 {
681 PrelBase.False -> Test.$wtest ww1 ww;
682 PrelBase.True -> PrelBase.True [];
685 Test.test = \r [w w1]
688 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
691 If we don't inline the dfun, the code is not nearly as good:
693 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
694 PrelBase.:DEq tpl1 tpl2 -> tpl2;
699 let { y = PrelBase.I#! [ww1]; } in
700 let { x = PrelBase.I#! [ww]; } in
701 let { sat_slx = PrelTup.(,)! [y x]; } in
702 let { sat_sly = PrelTup.(,)! [x y];
704 case == sat_sly sat_slx of wild {
705 PrelBase.False -> Test.$wtest ww1 ww;
706 PrelBase.True -> PrelBase.True [];
713 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
716 Why doesn't GHC inline $fEq? Because it looks big:
718 PrelTup.zdfEqZ1T{-rcX-}
719 = \ @ a{-reT-} :: * @ b{-reS-} :: *
720 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
721 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
723 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
724 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
726 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
727 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
729 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
730 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
731 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
733 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
735 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
737 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
738 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
742 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
743 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
744 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
745 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
747 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
749 and it's not as bad as it seems, because it's further dramatically
750 simplified: only zeze2 is extracted and its body is simplified.
753 %************************************************************************
755 \subsection{Checking for a decent instance type}
757 %************************************************************************
759 @scrutiniseInstanceHead@ checks the type {\em and} its syntactic constraints:
760 it must normally look like: @instance Foo (Tycon a b c ...) ...@
762 The exceptions to this syntactic checking: (1)~if the @GlasgowExts@
763 flag is on, or (2)~the instance is imported (they must have been
764 compiled elsewhere). In these cases, we let them go through anyway.
766 We can also have instances for functions: @instance Foo (a -> b) ...@.
769 checkInstValidity dflags theta clas inst_tys
770 | null errs = returnTc ()
771 | otherwise = addErrsTc errs `thenNF_Tc_` failTc
773 errs = checkInstHead dflags theta clas inst_tys ++
774 [err | pred <- theta, err <- checkInstConstraint dflags pred]
776 checkInstConstraint dflags pred
777 -- Checks whether a predicate is legal in the
778 -- context of an instance declaration
780 | otherwise = [instConstraintErr pred]
782 ok = inheritablePred pred &&
783 (isTyVarClassPred pred || arbitrary_preds_ok)
785 arbitrary_preds_ok = dopt Opt_AllowUndecidableInstances dflags
788 checkInstHead dflags theta clas inst_taus
790 -- A user declaration of a CCallable/CReturnable instance
791 -- must be for a "boxed primitive" type.
792 (clas `hasKey` cCallableClassKey
793 && not (ccallable_type dflags first_inst_tau))
795 (clas `hasKey` cReturnableClassKey
796 && not (creturnable_type first_inst_tau))
797 = [nonBoxedPrimCCallErr clas first_inst_tau]
799 -- If GlasgowExts then check at least one isn't a type variable
800 | dopt Opt_GlasgowExts dflags
801 = -- GlasgowExts case
802 check_tyvars dflags clas inst_taus ++ check_fundeps dflags theta clas inst_taus
804 -- WITH HASKELL 1.4, MUST HAVE C (T a b c)
805 | not (length inst_taus == 1 &&
806 maybeToBool maybe_tycon_app && -- Yes, there's a type constuctor
807 not (isSynTyCon tycon) && -- ...but not a synonym
808 all tcIsTyVarTy arg_tys && -- Applied to type variables
809 length (varSetElems (tyVarsOfTypes arg_tys)) == length arg_tys
810 -- This last condition checks that all the type variables are distinct
812 = [instTypeErr clas inst_taus
813 (text "the instance type must be of form (T a b c)" $$
814 text "where T is not a synonym, and a,b,c are distinct type variables")]
820 (first_inst_tau : _) = inst_taus
822 -- Stuff for algebraic or -> type
823 maybe_tycon_app = tcSplitTyConApp_maybe first_inst_tau
824 Just (tycon, arg_tys) = maybe_tycon_app
826 ccallable_type dflags ty = isFFIArgumentTy dflags PlayRisky ty
827 creturnable_type ty = isFFIImportResultTy dflags ty
829 check_tyvars dflags clas inst_taus
830 -- Check that at least one isn't a type variable
831 -- unless -fallow-undecideable-instances
832 | dopt Opt_AllowUndecidableInstances dflags = []
833 | not (all tcIsTyVarTy inst_taus) = []
834 | otherwise = [the_err]
836 the_err = instTypeErr clas inst_taus msg
837 msg = ptext SLIT("There must be at least one non-type-variable in the instance head")
838 $$ ptext SLIT("Use -fallow-undecidable-instances to lift this restriction")
840 check_fundeps dflags theta clas inst_taus
841 | checkInstFDs theta clas inst_taus = []
842 | otherwise = [the_err]
844 the_err = instTypeErr clas inst_taus msg
845 msg = ptext SLIT("the instance types do not agree with the functional dependencies of the class")
849 %************************************************************************
851 \subsection{Error messages}
853 %************************************************************************
856 tcAddDeclCtxt decl thing_inside
857 = tcAddSrcLoc (tcdLoc decl) $
862 ClassDecl {} -> "class"
863 TySynonym {} -> "type synonym"
864 TyData {tcdND = NewType} -> "newtype"
865 TyData {tcdND = DataType} -> "data type"
867 ctxt = hsep [ptext SLIT("In the"), text thing,
868 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
870 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
872 doc = case inst_ty of
873 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
874 HsPredTy pred -> ppr pred
875 other -> ppr inst_ty -- Don't expect this
879 instConstraintErr pred
880 = hang (ptext SLIT("Illegal constraint") <+>
881 quotes (pprPred pred) <+>
882 ptext SLIT("in instance context"))
883 4 (ptext SLIT("(Instance contexts must constrain only type variables)"))
885 badGenericInstanceType binds
886 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
889 missingGenericInstances missing
890 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
894 dupGenericInsts tc_inst_infos
895 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
896 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
897 ptext SLIT("All the type patterns for a generic type constructor must be identical")
900 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
902 instTypeErr clas tys msg
903 = sep [ptext SLIT("Illegal instance declaration for") <+>
904 quotes (pprClassPred clas tys),
908 nonBoxedPrimCCallErr clas inst_ty
909 = hang (ptext SLIT("Unacceptable instance type for ccall-ish class"))
910 4 (pprClassPred clas [inst_ty])
912 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
913 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")