2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[TcInstDecls]{Typechecking instance declarations}
7 module TcInstDcls ( tcInstDecls1, tcIfaceInstDecls1, addInstDFuns,
8 tcInstDecls2, initInstEnv, tcAddDeclCtxt ) where
10 #include "HsVersions.h"
13 import CmdLineOpts ( DynFlag(..) )
15 import HsSyn ( InstDecl(..), TyClDecl(..), HsType(..),
16 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), HsTyVarBndr(..),
17 andMonoBindList, collectMonoBinders,
20 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl,
21 RenamedMonoBinds, RenamedTyClDecl, RenamedHsType,
22 extractHsTyVars, maybeGenericMatch
24 import TcHsSyn ( TcMonoBinds, mkHsConApp )
25 import TcBinds ( tcSpecSigs )
26 import TcClassDcl ( tcMethodBind, badMethodErr )
28 import TcMType ( tcInstSigType, checkValidTheta, checkValidInstHead, instTypeErr,
29 UserTypeCtxt(..), SourceTyCtxt(..) )
30 import TcType ( mkClassPred, mkTyVarTy, tcSplitForAllTys,
31 tcSplitSigmaTy, getClassPredTys, tcSplitPredTy_maybe,
34 import Inst ( InstOrigin(..), newDicts, instToId,
35 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
36 import TcDeriv ( tcDeriving )
37 import TcEnv ( tcExtendGlobalValEnv,
38 tcExtendTyVarEnvForMeths, tcLookupId, tcLookupClass,
39 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
40 simpleInstInfoTy, newDFunName
42 import InstEnv ( InstEnv, extendInstEnv )
43 import PprType ( pprClassPred )
44 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType )
45 import TcUnify ( checkSigTyVars )
46 import TcSimplify ( tcSimplifyCheck )
47 import HscTypes ( HomeSymbolTable, DFunId, FixityEnv,
48 PersistentCompilerState(..), PersistentRenamerState,
51 import Subst ( substTheta )
52 import DataCon ( classDataCon )
53 import Class ( Class, classBigSig )
54 import Var ( idName, idType )
55 import VarSet ( emptyVarSet )
56 import Id ( setIdLocalExported )
57 import MkId ( mkDictFunId, unsafeCoerceId, eRROR_ID )
58 import FunDeps ( checkInstFDs )
59 import Generics ( validGenericInstanceType )
60 import Module ( Module, foldModuleEnv )
61 import Name ( getSrcLoc )
62 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
63 import TyCon ( TyCon )
64 import Subst ( mkTopTyVarSubst, substTheta )
65 import TysWiredIn ( genericTyCons )
66 import SrcLoc ( SrcLoc )
67 import Unique ( Uniquable(..) )
68 import Util ( lengthExceeds, isSingleton )
69 import BasicTypes ( NewOrData(..) )
70 import ErrUtils ( dumpIfSet_dyn )
71 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
72 assocElts, extendAssoc_C, equivClassesByUniq, minusList
74 import Maybe ( catMaybes )
78 Typechecking instance declarations is done in two passes. The first
79 pass, made by @tcInstDecls1@, collects information to be used in the
82 This pre-processed info includes the as-yet-unprocessed bindings
83 inside the instance declaration. These are type-checked in the second
84 pass, when the class-instance envs and GVE contain all the info from
85 all the instance and value decls. Indeed that's the reason we need
86 two passes over the instance decls.
89 Here is the overall algorithm.
90 Assume that we have an instance declaration
92 instance c => k (t tvs) where b
96 $LIE_c$ is the LIE for the context of class $c$
98 $betas_bar$ is the free variables in the class method type, excluding the
101 $LIE_cop$ is the LIE constraining a particular class method
103 $tau_cop$ is the tau type of a class method
105 $LIE_i$ is the LIE for the context of instance $i$
107 $X$ is the instance constructor tycon
109 $gammas_bar$ is the set of type variables of the instance
111 $LIE_iop$ is the LIE for a particular class method instance
113 $tau_iop$ is the tau type for this instance of a class method
115 $alpha$ is the class variable
117 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
119 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
122 ToDo: Update the list above with names actually in the code.
126 First, make the LIEs for the class and instance contexts, which means
127 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
128 and make LIElistI and LIEI.
130 Then process each method in turn.
132 order the instance methods according to the ordering of the class methods
134 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
136 Create final dictionary function from bindings generated already
138 df = lambda inst_tyvars
145 in <op1,op2,...,opn,sd1,...,sdm>
147 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
148 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
152 %************************************************************************
154 \subsection{Extracting instance decls}
156 %************************************************************************
158 Gather up the instance declarations from their various sources
161 tcInstDecls1 -- Deal with source-code instance decls
162 :: PersistentRenamerState
163 -> InstEnv -- Imported instance envt
164 -> FixityEnv -- for deriving Show and Read
165 -> Module -- Module for deriving
166 -> [RenamedTyClDecl] -- For deriving stuff
167 -> [RenamedInstDecl] -- Source code instance decls
168 -> TcM (InstEnv, -- the full inst env
169 [InstInfo], -- instance decls to process; contains all dfuns
171 RenamedHsBinds) -- derived instances
173 tcInstDecls1 prs inst_env get_fixity this_mod
174 tycl_decls inst_decls
175 -- The incoming inst_env includes all the imported instances already
177 -- Stop if addInstInfos etc discovers any errors
178 -- (they recover, so that we get more than one error each round)
179 -- (1) Do the ordinary instance declarations
180 mapNF_Tc tcLocalInstDecl1 inst_decls `thenNF_Tc` \ local_inst_infos ->
183 local_inst_info = catMaybes local_inst_infos
184 clas_decls = filter isClassDecl tycl_decls
186 -- (2) Instances from generic class declarations
187 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
189 -- Next, construct the instance environment so far, consisting of
190 -- a) imported instance decls (from this module) inst_env1
191 -- b) local instance decls inst_env2
192 -- c) generic instances final_inst_env
193 addInstInfos inst_env local_inst_info `thenNF_Tc` \ inst_env1 ->
194 addInstInfos inst_env1 generic_inst_info `thenNF_Tc` \ inst_env2 ->
196 -- (3) Compute instances from "deriving" clauses;
197 -- note that we only do derivings for things in this module;
198 -- we ignore deriving decls from interfaces!
199 -- This stuff computes a context for the derived instance decl, so it
200 -- needs to know about all the instances possible; hence inst_env4
201 tcDeriving prs this_mod inst_env2
202 get_fixity tycl_decls `thenTc` \ (deriv_inst_info, deriv_binds) ->
203 addInstInfos inst_env2 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
205 returnTc (final_inst_env,
206 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
209 initInstEnv :: PersistentCompilerState -> HomeSymbolTable -> NF_TcM InstEnv
210 -- Initialise the instance environment from the
211 -- persistent compiler state and the home symbol table
214 pkg_inst_env = pcs_insts pcs
215 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
217 addInstDFuns pkg_inst_env hst_dfuns
219 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
220 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
222 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
223 addInstDFuns inst_env dfuns
224 = getDOptsTc `thenNF_Tc` \ dflags ->
226 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
228 addErrsTc errs `thenNF_Tc_`
229 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
232 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
236 tcIfaceInstDecls1 :: [RenamedInstDecl] -> NF_TcM [DFunId]
237 tcIfaceInstDecls1 decls = mapNF_Tc tcIfaceInstDecl1 decls
239 tcIfaceInstDecl1 :: RenamedInstDecl -> NF_TcM DFunId
240 -- An interface-file instance declaration
241 -- Should be in scope by now, because we should
242 -- have sucked in its interface-file definition
243 -- So it will be replete with its unfolding etc
244 tcIfaceInstDecl1 decl@(InstDecl poly_ty binds uprags (Just dfun_name) src_loc)
245 = tcLookupId dfun_name
248 tcLocalInstDecl1 :: RenamedInstDecl
249 -> NF_TcM (Maybe InstInfo) -- Nothing if there was an error
250 -- A source-file instance declaration
251 -- Type-check all the stuff before the "where"
253 -- We 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 tcLocalInstDecl1 decl@(InstDecl poly_ty binds uprags Nothing src_loc)
259 = -- Prime error recovery, set source location
260 recoverNF_Tc (returnNF_Tc Nothing) $
261 tcAddSrcLoc src_loc $
262 tcAddErrCtxt (instDeclCtxt poly_ty) $
264 -- Typecheck the instance type itself. We can't use
265 -- tcHsSigType, because it's not a valid user type.
266 kcHsSigType poly_ty `thenTc_`
267 tcHsType poly_ty `thenTc` \ poly_ty' ->
269 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
271 checkValidTheta InstThetaCtxt theta `thenTc_`
272 checkValidInstHead tau `thenTc` \ (clas,inst_tys) ->
273 checkTc (checkInstFDs theta clas inst_tys)
274 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
275 newDFunName clas inst_tys src_loc `thenNF_Tc` \ dfun_name ->
276 returnTc (Just (InstInfo { iDFunId = mkDictFunId dfun_name clas tyvars inst_tys theta,
277 iBinds = binds, iPrags = uprags }))
279 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
283 %************************************************************************
285 \subsection{Extracting generic instance declaration from class declarations}
287 %************************************************************************
289 @getGenericInstances@ extracts the generic instance declarations from a class
290 declaration. For exmaple
295 op{ x+y } (Inl v) = ...
296 op{ x+y } (Inr v) = ...
297 op{ x*y } (v :*: w) = ...
300 gives rise to the instance declarations
302 instance C (x+y) where
306 instance C (x*y) where
314 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
315 getGenericInstances class_decls
316 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
318 gen_inst_info = concat gen_inst_infos
320 if null gen_inst_info then
323 getDOptsTc `thenNF_Tc` \ dflags ->
324 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
325 (vcat (map pprInstInfo gen_inst_info)))
327 returnTc gen_inst_info
329 get_generics decl@(ClassDecl {tcdMeths = Nothing})
330 = returnTc [] -- Imported class decls
332 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
334 = returnTc [] -- The comon case: no generic default methods
336 | otherwise -- A source class decl with generic default methods
337 = recoverNF_Tc (returnNF_Tc []) $
339 tcLookupClass class_name `thenTc` \ clas ->
341 -- Make an InstInfo out of each group
342 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
344 -- Check that there is only one InstInfo for each type constructor
345 -- The main way this can fail is if you write
346 -- f {| a+b |} ... = ...
347 -- f {| x+y |} ... = ...
348 -- Then at this point we'll have an InstInfo for each
350 tc_inst_infos :: [(TyCon, InstInfo)]
351 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
353 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
354 group `lengthExceeds` 1]
355 get_uniq (tc,_) = getUnique tc
357 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
359 -- Check that there is an InstInfo for each generic type constructor
361 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
363 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
368 -- Group the declarations by type pattern
369 groups :: [(RenamedHsType, RenamedMonoBinds)]
370 groups = assocElts (getGenericBinds def_methods)
373 ---------------------------------
374 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
375 -- Takes a group of method bindings, finds the generic ones, and returns
376 -- them in finite map indexed by the type parameter in the definition.
378 getGenericBinds EmptyMonoBinds = emptyAssoc
379 getGenericBinds (AndMonoBinds m1 m2)
380 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
382 getGenericBinds (FunMonoBind id infixop matches loc)
383 = mapAssoc wrap (foldl add emptyAssoc matches)
384 -- Using foldl not foldr is vital, else
385 -- we reverse the order of the bindings!
387 add env match = case maybeGenericMatch match of
389 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
391 wrap ms = FunMonoBind id infixop ms loc
393 ---------------------------------
394 mkGenericInstance :: Class -> SrcLoc
395 -> (RenamedHsType, RenamedMonoBinds)
398 mkGenericInstance clas loc (hs_ty, binds)
399 -- Make a generic instance declaration
400 -- For example: instance (C a, C b) => C (a+b) where { binds }
402 = -- Extract the universally quantified type variables
404 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
406 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
408 -- Type-check the instance type, and check its form
409 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
410 checkTc (validGenericInstanceType inst_ty)
411 (badGenericInstanceType binds) `thenTc_`
413 -- Make the dictionary function.
414 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
416 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
417 dfun_id = mkDictFunId dfun_name clas tyvars [inst_ty] inst_theta
420 returnTc (InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = [] })
424 %************************************************************************
426 \subsection{Type-checking instance declarations, pass 2}
428 %************************************************************************
431 tcInstDecls2 :: [InstInfo]
432 -> NF_TcM (LIE, TcMonoBinds)
434 tcInstDecls2 inst_decls
435 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
436 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
437 (map tcInstDecl2 inst_decls)
439 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
440 tc2 `thenNF_Tc` \ (lie2, binds2) ->
441 returnNF_Tc (lie1 `plusLIE` lie2,
442 binds1 `AndMonoBinds` binds2)
445 ======= New documentation starts here (Sept 92) ==============
447 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
448 the dictionary function for this instance declaration. For example
450 instance Foo a => Foo [a] where
454 might generate something like
456 dfun.Foo.List dFoo_a = let op1 x = ...
462 HOWEVER, if the instance decl has no context, then it returns a
463 bigger @HsBinds@ with declarations for each method. For example
465 instance Foo [a] where
471 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
472 const.Foo.op1.List a x = ...
473 const.Foo.op2.List a y = ...
475 This group may be mutually recursive, because (for example) there may
476 be no method supplied for op2 in which case we'll get
478 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
480 that is, the default method applied to the dictionary at this type.
482 What we actually produce in either case is:
484 AbsBinds [a] [dfun_theta_dicts]
485 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
486 { d = (sd1,sd2, ..., op1, op2, ...)
491 The "maybe" says that we only ask AbsBinds to make global constant methods
492 if the dfun_theta is empty.
495 For an instance declaration, say,
497 instance (C1 a, C2 b) => C (T a b) where
500 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
501 function whose type is
503 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
505 Notice that we pass it the superclass dictionaries at the instance type; this
506 is the ``Mark Jones optimisation''. The stuff before the "=>" here
507 is the @dfun_theta@ below.
509 First comes the easy case of a non-local instance decl.
513 tcInstDecl2 :: InstInfo -> TcM (LIE, TcMonoBinds)
515 tcInstDecl2 (NewTypeDerived { iDFunId = dfun_id })
516 = tcInstSigType InstTv (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') ->
517 newDicts InstanceDeclOrigin dfun_theta' `thenNF_Tc` \ rep_dicts ->
519 rep_dict_id = ASSERT( isSingleton rep_dicts )
520 instToId (head rep_dicts) -- Derived newtypes have just one dict arg
522 body = TyLam inst_tyvars' $
523 DictLam [rep_dict_id] $
524 (HsVar unsafeCoerceId `TyApp` [idType rep_dict_id, inst_head'])
527 -- You might wonder why we have the 'coerce'. It's because the
528 -- type equality mechanism isn't clever enough; see comments with Type.eqType.
529 -- So Lint complains if we don't have this.
531 returnTc (emptyLIE, VarMonoBind dfun_id body)
533 tcInstDecl2 (InstInfo { iDFunId = dfun_id, iBinds = monobinds, iPrags = uprags })
534 = -- Prime error recovery
535 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
536 tcAddSrcLoc (getSrcLoc dfun_id) $
537 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
539 -- Instantiate the instance decl with tc-style type variables
540 tcInstSigType InstTv (idType dfun_id) `thenNF_Tc` \ (inst_tyvars', dfun_theta', inst_head') ->
542 Just pred = tcSplitPredTy_maybe inst_head'
543 (clas, inst_tys') = getClassPredTys pred
544 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
546 sel_names = [idName sel_id | (sel_id, _) <- op_items]
548 -- Instantiate the super-class context with inst_tys
549 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
551 -- Find any definitions in monobinds that aren't from the class
552 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
553 (inst_tyvars, _) = tcSplitForAllTys (idType dfun_id)
554 origin = InstanceDeclOrigin
556 -- Check that all the method bindings come from this class
557 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
559 -- Create dictionary Ids from the specified instance contexts.
560 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
561 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
562 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
564 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
565 -- The type variable from the dict fun actually scope
566 -- over the bindings. They were gotten from
567 -- the original instance declaration
569 -- Default-method Ids may be mentioned in synthesised RHSs,
570 -- but they'll already be in the environment.
572 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
574 monobinds uprags True)
576 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
578 -- Deal with SPECIALISE instance pragmas by making them
579 -- look like SPECIALISE pragmas for the dfun
581 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
583 tcExtendGlobalValEnv [dfun_id] (
584 tcSpecSigs dfun_prags
585 ) `thenTc` \ (prag_binds, prag_lie) ->
587 -- Check the overloading constraints of the methods and superclasses
589 -- These insts are in scope; quite a few, eh?
590 avail_insts = [this_dict] ++
595 methods_lie = plusLIEs insts_needed_s
598 -- Simplify the constraints from methods
599 tcAddErrCtxt methodCtxt (
601 (ptext SLIT("instance declaration context"))
605 ) `thenTc` \ (const_lie1, lie_binds1) ->
607 -- Figure out bindings for the superclass context
608 tcAddErrCtxt superClassCtxt (
610 (ptext SLIT("instance declaration context"))
612 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
613 -- get bound by just selecting from this_dict!!
615 ) `thenTc` \ (const_lie2, lie_binds2) ->
617 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
619 -- Create the result bindings
621 local_dfun_id = setIdLocalExported dfun_id
622 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
624 dict_constr = classDataCon clas
625 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
626 this_dict_id = instToId this_dict
627 inlines | null dfun_arg_dicts = emptyNameSet
628 | otherwise = unitNameSet (idName dfun_id)
629 -- Always inline the dfun; this is an experimental decision
630 -- because it makes a big performance difference sometimes.
631 -- Often it means we can do the method selection, and then
632 -- inline the method as well. Marcin's idea; see comments below.
634 -- BUT: don't inline it if it's a constant dictionary;
635 -- we'll get all the benefit without inlining, and we get
636 -- a **lot** of code duplication if we inline it
640 = -- Blatant special case for CCallable, CReturnable
641 -- If the dictionary is empty then we should never
642 -- select anything from it, so we make its RHS just
643 -- emit an error message. This in turn means that we don't
644 -- mention the constructor, which doesn't exist for CCallable, CReturnable
645 -- Hardly beautiful, but only three extra lines.
646 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
647 (HsLit (HsString msg))
649 | otherwise -- The common case
650 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
651 -- We don't produce a binding for the dict_constr; instead we
652 -- rely on the simplifier to unfold this saturated application
653 -- We do this rather than generate an HsCon directly, because
654 -- it means that the special cases (e.g. dictionary with only one
655 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
656 -- than needing to be repeated here.
659 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
661 dict_bind = VarMonoBind this_dict_id dict_rhs
662 method_binds = andMonoBindList method_binds_s
667 (map instToId dfun_arg_dicts)
668 [(inst_tyvars', local_dfun_id, this_dict_id)]
670 (lie_binds1 `AndMonoBinds`
671 lie_binds2 `AndMonoBinds`
672 method_binds `AndMonoBinds`
675 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
676 main_bind `AndMonoBinds` prag_binds)
679 ------------------------------
680 Inlining dfuns unconditionally
681 ------------------------------
683 The code above unconditionally inlines dict funs. Here's why.
684 Consider this program:
686 test :: Int -> Int -> Bool
687 test x y = (x,y) == (y,x) || test y x
688 -- Recursive to avoid making it inline.
690 This needs the (Eq (Int,Int)) instance. If we inline that dfun
691 the code we end up with is good:
694 \r -> case ==# [ww ww1] of wild {
695 PrelBase.False -> Test.$wtest ww1 ww;
697 case ==# [ww1 ww] of wild1 {
698 PrelBase.False -> Test.$wtest ww1 ww;
699 PrelBase.True -> PrelBase.True [];
702 Test.test = \r [w w1]
705 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
708 If we don't inline the dfun, the code is not nearly as good:
710 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
711 PrelBase.:DEq tpl1 tpl2 -> tpl2;
716 let { y = PrelBase.I#! [ww1]; } in
717 let { x = PrelBase.I#! [ww]; } in
718 let { sat_slx = PrelTup.(,)! [y x]; } in
719 let { sat_sly = PrelTup.(,)! [x y];
721 case == sat_sly sat_slx of wild {
722 PrelBase.False -> Test.$wtest ww1 ww;
723 PrelBase.True -> PrelBase.True [];
730 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
733 Why doesn't GHC inline $fEq? Because it looks big:
735 PrelTup.zdfEqZ1T{-rcX-}
736 = \ @ a{-reT-} :: * @ b{-reS-} :: *
737 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
738 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
740 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
741 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
743 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
744 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
746 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
747 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
748 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
750 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
752 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
754 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
755 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
759 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
760 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
761 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
762 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
764 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
766 and it's not as bad as it seems, because it's further dramatically
767 simplified: only zeze2 is extracted and its body is simplified.
770 %************************************************************************
772 \subsection{Error messages}
774 %************************************************************************
777 tcAddDeclCtxt decl thing_inside
778 = tcAddSrcLoc (tcdLoc decl) $
783 ClassDecl {} -> "class"
784 TySynonym {} -> "type synonym"
785 TyData {tcdND = NewType} -> "newtype"
786 TyData {tcdND = DataType} -> "data type"
788 ctxt = hsep [ptext SLIT("In the"), text thing,
789 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
791 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
793 doc = case inst_ty of
794 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
795 HsPredTy pred -> ppr pred
796 other -> ppr inst_ty -- Don't expect this
800 badGenericInstanceType binds
801 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
804 missingGenericInstances missing
805 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
807 dupGenericInsts tc_inst_infos
808 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
809 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
810 ptext SLIT("All the type patterns for a generic type constructor must be identical")
813 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
815 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
816 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")