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(..) )
14 import HsSyn ( HsDecl(..), InstDecl(..), TyClDecl(..), HsType(..),
15 MonoBinds(..), HsExpr(..), HsLit(..), Sig(..), HsTyVarBndr(..),
16 andMonoBindList, collectMonoBinders,
17 isClassDecl, isIfaceInstDecl, toHsType
19 import RnHsSyn ( RenamedHsBinds, RenamedInstDecl, RenamedHsDecl,
20 RenamedMonoBinds, RenamedTyClDecl, RenamedHsType,
21 extractHsTyVars, maybeGenericMatch
23 import TcHsSyn ( TcMonoBinds, mkHsConApp )
24 import TcBinds ( tcSpecSigs )
25 import TcClassDcl ( tcMethodBind, badMethodErr )
27 import TcMType ( tcInstSigTyVars, checkValidTheta, checkValidInstHead, instTypeErr,
28 UserTypeCtxt(..), SourceTyCtxt(..) )
29 import TcType ( tcSplitDFunTy, mkClassPred, mkTyVarTy, mkTyVarTys,
30 tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys,
33 import Inst ( InstOrigin(..),
35 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
36 import TcDeriv ( tcDeriving )
37 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
38 tcExtendTyVarEnvForMeths, tcLookupId,
39 tcAddImportedIdInfo, tcLookupClass,
40 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
41 simpleInstInfoTy, newDFunName,
44 import InstEnv ( InstEnv, extendInstEnv )
45 import PprType ( pprClassPred )
46 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType )
47 import TcUnify ( checkSigTyVars )
48 import TcSimplify ( tcSimplifyCheck )
49 import HscTypes ( HomeSymbolTable, DFunId,
50 ModDetails(..), PackageInstEnv, PersistentRenamerState
53 import Subst ( substTy, substTheta )
54 import DataCon ( classDataCon )
55 import Class ( Class, classBigSig )
56 import Var ( idName, idType )
57 import VarSet ( emptyVarSet )
58 import Id ( setIdLocalExported )
59 import MkId ( mkDictFunId )
60 import FunDeps ( checkInstFDs )
61 import Generics ( validGenericInstanceType )
62 import Module ( Module, foldModuleEnv )
63 import Name ( getSrcLoc )
64 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
65 import PrelInfo ( eRROR_ID )
66 import TyCon ( TyCon )
67 import Subst ( mkTopTyVarSubst, substTheta )
68 import TysWiredIn ( genericTyCons )
70 import SrcLoc ( SrcLoc )
71 import Unique ( Uniquable(..) )
72 import Util ( lengthExceeds )
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
180 (imported_inst_ds, local_inst_ds) = partition isIfaceInstDecl inst_decls
182 -- (1) Do the ordinary instance declarations
183 mapNF_Tc tcInstDecl1 local_inst_ds `thenNF_Tc` \ local_inst_infos ->
184 mapNF_Tc tcInstDecl1 imported_inst_ds `thenNF_Tc` \ imported_inst_infos ->
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) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
191 -- b) imported instance decls (not in the home package) inst_env1
192 -- c) other modules in this package (gotten from hst) inst_env2
193 -- d) local instance decls inst_env3
194 -- e) generic instances inst_env4
195 -- The result of (b) replaces the cached InstEnv in the PCS
197 local_inst_info = concat local_inst_infos
198 imported_inst_info = concat imported_inst_infos
199 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
202 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
204 addInstInfos inst_env0 imported_inst_info `thenNF_Tc` \ inst_env1 ->
205 addInstDFuns inst_env1 hst_dfuns `thenNF_Tc` \ inst_env2 ->
206 addInstInfos inst_env2 local_inst_info `thenNF_Tc` \ inst_env3 ->
207 addInstInfos inst_env3 generic_inst_info `thenNF_Tc` \ inst_env4 ->
209 -- (3) Compute instances from "deriving" clauses;
210 -- note that we only do derivings for things in this module;
211 -- we ignore deriving decls from interfaces!
212 -- This stuff computes a context for the derived instance decl, so it
213 -- needs to know about all the instances possible; hence inst_env4
214 tcDeriving prs this_mod inst_env4 get_fixity tycl_decls
215 `thenTc` \ (deriv_inst_info, deriv_binds) ->
216 addInstInfos inst_env4 deriv_inst_info `thenNF_Tc` \ final_inst_env ->
220 generic_inst_info ++ deriv_inst_info ++ local_inst_info,
223 addInstInfos :: InstEnv -> [InstInfo] -> NF_TcM InstEnv
224 addInstInfos inst_env infos = addInstDFuns inst_env (map iDFunId infos)
226 addInstDFuns :: InstEnv -> [DFunId] -> NF_TcM InstEnv
227 addInstDFuns inst_env dfuns
228 = getDOptsTc `thenTc` \ dflags ->
230 (inst_env', errs) = extendInstEnv dflags inst_env dfuns
232 addErrsTc errs `thenNF_Tc_`
233 traceTc (text "Adding instances:" <+> vcat (map pp dfuns)) `thenTc_`
236 pp dfun = ppr dfun <+> dcolon <+> ppr (idType dfun)
240 tcInstDecl1 :: RenamedInstDecl -> NF_TcM [InstInfo]
241 -- Deal with a single instance declaration
242 -- Type-check all the stuff before the "where"
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 $
247 tcAddErrCtxt (instDeclCtxt poly_ty) $
249 -- Typecheck the instance type itself. We can't use
250 -- tcHsSigType, because it's not a valid user type.
251 kcHsSigType poly_ty `thenTc_`
252 tcHsType poly_ty `thenTc` \ poly_ty' ->
254 (tyvars, theta, tau) = tcSplitSigmaTy poly_ty'
255 (clas,inst_tys) = case tcSplitPredTy_maybe tau of { Just st -> getClassPredTys st }
256 -- The checkValidInstHead makes sure these splits succeed
258 (case maybe_dfun_name of
259 Nothing -> -- A source-file instance declaration
260 -- Check for respectable instance type, and context
261 -- but only do this for non-imported instance decls.
262 -- Imported ones should have been checked already, and may indeed
263 -- contain something illegal in normal Haskell, notably
264 -- instance CCallable [Char]
265 checkValidTheta InstThetaCtxt theta `thenTc_`
266 checkValidInstHead tau `thenTc_`
267 checkTc (checkInstFDs theta clas inst_tys)
268 (instTypeErr (pprClassPred clas inst_tys) msg) `thenTc_`
269 newDFunName clas inst_tys src_loc `thenTc` \ dfun_name ->
270 returnTc (mkDictFunId dfun_name clas tyvars inst_tys theta)
272 Just dfun_name -> -- An interface-file instance declaration
273 -- Should be in scope by now, because we should
274 -- have sucked in its interface-file definition
275 -- So it will be replete with its unfolding etc
277 ) `thenNF_Tc` \ dfun_id ->
278 returnTc [InstInfo { iDFunId = dfun_id, iBinds = binds, iPrags = uprags }]
280 msg = parens (ptext SLIT("the instance types do not agree with the functional dependencies of the class"))
284 %************************************************************************
286 \subsection{Extracting generic instance declaration from class declarations}
288 %************************************************************************
290 @getGenericInstances@ extracts the generic instance declarations from a class
291 declaration. For exmaple
296 op{ x+y } (Inl v) = ...
297 op{ x+y } (Inr v) = ...
298 op{ x*y } (v :*: w) = ...
301 gives rise to the instance declarations
303 instance C (x+y) where
307 instance C (x*y) where
315 getGenericInstances :: [RenamedTyClDecl] -> TcM [InstInfo]
316 getGenericInstances class_decls
317 = mapTc get_generics class_decls `thenTc` \ gen_inst_infos ->
319 gen_inst_info = concat gen_inst_infos
321 if null gen_inst_info then
324 getDOptsTc `thenTc` \ dflags ->
325 ioToTc (dumpIfSet_dyn dflags Opt_D_dump_deriv "Generic instances"
326 (vcat (map pprInstInfo gen_inst_info)))
328 returnTc gen_inst_info
330 get_generics decl@(ClassDecl {tcdMeths = Nothing})
331 = returnTc [] -- Imported class decls
333 get_generics decl@(ClassDecl {tcdName = class_name, tcdMeths = Just def_methods, tcdLoc = loc})
335 = returnTc [] -- The comon case: no generic default methods
337 | otherwise -- A source class decl with generic default methods
338 = recoverNF_Tc (returnNF_Tc []) $
340 tcLookupClass class_name `thenTc` \ clas ->
342 -- Make an InstInfo out of each group
343 mapTc (mkGenericInstance clas loc) groups `thenTc` \ inst_infos ->
345 -- Check that there is only one InstInfo for each type constructor
346 -- The main way this can fail is if you write
347 -- f {| a+b |} ... = ...
348 -- f {| x+y |} ... = ...
349 -- Then at this point we'll have an InstInfo for each
351 tc_inst_infos :: [(TyCon, InstInfo)]
352 tc_inst_infos = [(simpleInstInfoTyCon i, i) | i <- inst_infos]
354 bad_groups = [group | group <- equivClassesByUniq get_uniq tc_inst_infos,
355 group `lengthExceeds` 1]
356 get_uniq (tc,_) = getUnique tc
358 mapTc (addErrTc . dupGenericInsts) bad_groups `thenTc_`
360 -- Check that there is an InstInfo for each generic type constructor
362 missing = genericTyCons `minusList` [tc | (tc,_) <- tc_inst_infos]
364 checkTc (null missing) (missingGenericInstances missing) `thenTc_`
369 -- Group the declarations by type pattern
370 groups :: [(RenamedHsType, RenamedMonoBinds)]
371 groups = assocElts (getGenericBinds def_methods)
374 ---------------------------------
375 getGenericBinds :: RenamedMonoBinds -> Assoc RenamedHsType RenamedMonoBinds
376 -- Takes a group of method bindings, finds the generic ones, and returns
377 -- them in finite map indexed by the type parameter in the definition.
379 getGenericBinds EmptyMonoBinds = emptyAssoc
380 getGenericBinds (AndMonoBinds m1 m2)
381 = plusAssoc_C AndMonoBinds (getGenericBinds m1) (getGenericBinds m2)
383 getGenericBinds (FunMonoBind id infixop matches loc)
384 = mapAssoc wrap (foldl add emptyAssoc matches)
385 -- Using foldl not foldr is vital, else
386 -- we reverse the order of the bindings!
388 add env match = case maybeGenericMatch match of
390 Just (ty, match') -> extendAssoc_C (++) env (ty, [match'])
392 wrap ms = FunMonoBind id infixop ms loc
394 ---------------------------------
395 mkGenericInstance :: Class -> SrcLoc
396 -> (RenamedHsType, RenamedMonoBinds)
399 mkGenericInstance clas loc (hs_ty, binds)
400 -- Make a generic instance declaration
401 -- For example: instance (C a, C b) => C (a+b) where { binds }
403 = -- Extract the universally quantified type variables
405 sig_tvs = map UserTyVar (nameSetToList (extractHsTyVars hs_ty))
407 tcHsTyVars sig_tvs (kcHsSigType hs_ty) $ \ tyvars ->
409 -- Type-check the instance type, and check its form
410 tcHsSigType GenPatCtxt hs_ty `thenTc` \ inst_ty ->
411 checkTc (validGenericInstanceType inst_ty)
412 (badGenericInstanceType binds) `thenTc_`
414 -- Make the dictionary function.
415 newDFunName clas [inst_ty] loc `thenNF_Tc` \ dfun_name ->
417 inst_theta = [mkClassPred clas [mkTyVarTy tv] | tv <- tyvars]
419 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
422 returnTc (InstInfo { iDFunId = dfun_id,
423 iBinds = binds, iPrags = [] })
427 %************************************************************************
429 \subsection{Type-checking instance declarations, pass 2}
431 %************************************************************************
434 tcInstDecls2 :: [InstInfo]
435 -> NF_TcM (LIE, TcMonoBinds)
437 tcInstDecls2 inst_decls
438 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
439 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
440 (map tcInstDecl2 inst_decls)
442 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
443 tc2 `thenNF_Tc` \ (lie2, binds2) ->
444 returnNF_Tc (lie1 `plusLIE` lie2,
445 binds1 `AndMonoBinds` binds2)
448 ======= New documentation starts here (Sept 92) ==============
450 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
451 the dictionary function for this instance declaration. For example
453 instance Foo a => Foo [a] where
457 might generate something like
459 dfun.Foo.List dFoo_a = let op1 x = ...
465 HOWEVER, if the instance decl has no context, then it returns a
466 bigger @HsBinds@ with declarations for each method. For example
468 instance Foo [a] where
474 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
475 const.Foo.op1.List a x = ...
476 const.Foo.op2.List a y = ...
478 This group may be mutually recursive, because (for example) there may
479 be no method supplied for op2 in which case we'll get
481 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
483 that is, the default method applied to the dictionary at this type.
485 What we actually produce in either case is:
487 AbsBinds [a] [dfun_theta_dicts]
488 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
489 { d = (sd1,sd2, ..., op1, op2, ...)
494 The "maybe" says that we only ask AbsBinds to make global constant methods
495 if the dfun_theta is empty.
498 For an instance declaration, say,
500 instance (C1 a, C2 b) => C (T a b) where
503 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
504 function whose type is
506 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
508 Notice that we pass it the superclass dictionaries at the instance type; this
509 is the ``Mark Jones optimisation''. The stuff before the "=>" here
510 is the @dfun_theta@ below.
512 First comes the easy case of a non-local instance decl.
516 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
517 -- tcInstDecl2 is called *only* on InstInfos
519 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
520 iBinds = monobinds, iPrags = uprags })
521 = -- Prime error recovery
522 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
523 tcAddSrcLoc (getSrcLoc dfun_id) $
524 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
526 -- Instantiate the instance decl with tc-style type variables
528 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
530 tcInstSigTyVars InstTv inst_tyvars `thenNF_Tc` \ inst_tyvars' ->
532 tenv = mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars')
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 sel_names = [idName sel_id | (sel_id, _) <- op_items]
541 -- Instantiate the super-class context with inst_tys
542 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
544 -- Find any definitions in monobinds that aren't from the class
545 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
547 -- Check that all the method bindings come from this class
548 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
550 -- Create dictionary Ids from the specified instance contexts.
551 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
552 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
553 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
555 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
556 -- The type variable from the dict fun actually scope
557 -- over the bindings. They were gotten from
558 -- the original instance declaration
560 -- Default-method Ids may be mentioned in synthesised RHSs,
561 -- but they'll already be in the environment.
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 local_dfun_id = setIdLocalExported dfun_id
613 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
615 dict_constr = classDataCon clas
616 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
617 this_dict_id = instToId this_dict
618 inlines | null dfun_arg_dicts = emptyNameSet
619 | otherwise = unitNameSet (idName dfun_id)
620 -- Always inline the dfun; this is an experimental decision
621 -- because it makes a big performance difference sometimes.
622 -- Often it means we can do the method selection, and then
623 -- inline the method as well. Marcin's idea; see comments below.
625 -- BUT: don't inline it if it's a constant dictionary;
626 -- we'll get all the benefit without inlining, and we get
627 -- a **lot** of code duplication if we inline it
631 = -- Blatant special case for CCallable, CReturnable
632 -- If the dictionary is empty then we should never
633 -- select anything from it, so we make its RHS just
634 -- emit an error message. This in turn means that we don't
635 -- mention the constructor, which doesn't exist for CCallable, CReturnable
636 -- Hardly beautiful, but only three extra lines.
637 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
638 (HsLit (HsString msg))
640 | otherwise -- The common case
641 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
642 -- We don't produce a binding for the dict_constr; instead we
643 -- rely on the simplifier to unfold this saturated application
644 -- We do this rather than generate an HsCon directly, because
645 -- it means that the special cases (e.g. dictionary with only one
646 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
647 -- than needing to be repeated here.
650 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
652 dict_bind = VarMonoBind this_dict_id dict_rhs
653 method_binds = andMonoBindList method_binds_s
658 (map instToId dfun_arg_dicts)
659 [(inst_tyvars', local_dfun_id, this_dict_id)]
661 (lie_binds1 `AndMonoBinds`
662 lie_binds2 `AndMonoBinds`
663 method_binds `AndMonoBinds`
666 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
667 main_bind `AndMonoBinds` prag_binds)
670 ------------------------------
671 Inlining dfuns unconditionally
672 ------------------------------
674 The code above unconditionally inlines dict funs. Here's why.
675 Consider this program:
677 test :: Int -> Int -> Bool
678 test x y = (x,y) == (y,x) || test y x
679 -- Recursive to avoid making it inline.
681 This needs the (Eq (Int,Int)) instance. If we inline that dfun
682 the code we end up with is good:
685 \r -> case ==# [ww ww1] of wild {
686 PrelBase.False -> Test.$wtest ww1 ww;
688 case ==# [ww1 ww] of wild1 {
689 PrelBase.False -> Test.$wtest ww1 ww;
690 PrelBase.True -> PrelBase.True [];
693 Test.test = \r [w w1]
696 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
699 If we don't inline the dfun, the code is not nearly as good:
701 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
702 PrelBase.:DEq tpl1 tpl2 -> tpl2;
707 let { y = PrelBase.I#! [ww1]; } in
708 let { x = PrelBase.I#! [ww]; } in
709 let { sat_slx = PrelTup.(,)! [y x]; } in
710 let { sat_sly = PrelTup.(,)! [x y];
712 case == sat_sly sat_slx of wild {
713 PrelBase.False -> Test.$wtest ww1 ww;
714 PrelBase.True -> PrelBase.True [];
721 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
724 Why doesn't GHC inline $fEq? Because it looks big:
726 PrelTup.zdfEqZ1T{-rcX-}
727 = \ @ a{-reT-} :: * @ b{-reS-} :: *
728 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
729 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
731 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
732 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
734 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
735 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
737 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
738 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
739 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
741 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
743 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
745 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
746 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
750 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
751 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
752 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
753 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
755 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
757 and it's not as bad as it seems, because it's further dramatically
758 simplified: only zeze2 is extracted and its body is simplified.
761 %************************************************************************
763 \subsection{Error messages}
765 %************************************************************************
768 tcAddDeclCtxt decl thing_inside
769 = tcAddSrcLoc (tcdLoc decl) $
774 ClassDecl {} -> "class"
775 TySynonym {} -> "type synonym"
776 TyData {tcdND = NewType} -> "newtype"
777 TyData {tcdND = DataType} -> "data type"
779 ctxt = hsep [ptext SLIT("In the"), text thing,
780 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
782 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
784 doc = case inst_ty of
785 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
786 HsPredTy pred -> ppr pred
787 other -> ppr inst_ty -- Don't expect this
791 badGenericInstanceType binds
792 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
795 missingGenericInstances missing
796 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
798 dupGenericInsts tc_inst_infos
799 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
800 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
801 ptext SLIT("All the type patterns for a generic type constructor must be identical")
804 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
806 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
807 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")