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, 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 ( tcInstSigTyVars, checkValidTheta, checkValidInstHead, instTypeErr,
27 UserTypeCtxt(..), SourceTyCtxt(..) )
28 import TcType ( tcSplitDFunTy, mkClassPred, mkTyVarTy, mkTyVarTys,
29 tcSplitSigmaTy, tcSplitPredTy_maybe, getClassPredTys,
32 import Inst ( InstOrigin(..),
34 LIE, mkLIE, emptyLIE, plusLIE, plusLIEs )
35 import TcDeriv ( tcDeriving )
36 import TcEnv ( TcEnv, tcExtendGlobalValEnv,
37 tcExtendTyVarEnvForMeths,
38 tcAddImportedIdInfo, tcLookupClass,
39 InstInfo(..), pprInstInfo, simpleInstInfoTyCon,
40 simpleInstInfoTy, newDFunName,
43 import InstEnv ( InstEnv, extendInstEnv )
44 import PprType ( pprClassPred )
45 import TcMonoType ( tcHsTyVars, kcHsSigType, tcHsType, tcHsSigType )
46 import TcUnify ( checkSigTyVars )
47 import TcSimplify ( tcSimplifyCheck )
48 import HscTypes ( HomeSymbolTable, DFunId,
49 ModDetails(..), PackageInstEnv, PersistentRenamerState
52 import Subst ( substTy, substTheta )
53 import DataCon ( classDataCon )
54 import Class ( Class, classBigSig )
55 import Var ( idName, idType )
56 import VarSet ( emptyVarSet )
57 import Id ( setIdLocalExported )
58 import MkId ( mkDictFunId )
59 import FunDeps ( checkInstFDs )
60 import Generics ( validGenericInstanceType )
61 import Module ( Module, foldModuleEnv )
62 import Name ( getSrcLoc )
63 import NameSet ( unitNameSet, emptyNameSet, nameSetToList )
64 import PrelInfo ( eRROR_ID )
65 import TyCon ( TyCon )
66 import Subst ( mkTopTyVarSubst, substTheta )
67 import TysWiredIn ( genericTyCons )
69 import SrcLoc ( SrcLoc )
70 import Unique ( Uniquable(..) )
71 import Util ( lengthExceeds )
72 import BasicTypes ( NewOrData(..), Fixity )
73 import ErrUtils ( dumpIfSet_dyn )
74 import ListSetOps ( Assoc, emptyAssoc, plusAssoc_C, mapAssoc,
75 assocElts, extendAssoc_C,
76 equivClassesByUniq, minusList
78 import List ( partition )
82 Typechecking instance declarations is done in two passes. The first
83 pass, made by @tcInstDecls1@, collects information to be used in the
86 This pre-processed info includes the as-yet-unprocessed bindings
87 inside the instance declaration. These are type-checked in the second
88 pass, when the class-instance envs and GVE contain all the info from
89 all the instance and value decls. Indeed that's the reason we need
90 two passes over the instance decls.
93 Here is the overall algorithm.
94 Assume that we have an instance declaration
96 instance c => k (t tvs) where b
100 $LIE_c$ is the LIE for the context of class $c$
102 $betas_bar$ is the free variables in the class method type, excluding the
105 $LIE_cop$ is the LIE constraining a particular class method
107 $tau_cop$ is the tau type of a class method
109 $LIE_i$ is the LIE for the context of instance $i$
111 $X$ is the instance constructor tycon
113 $gammas_bar$ is the set of type variables of the instance
115 $LIE_iop$ is the LIE for a particular class method instance
117 $tau_iop$ is the tau type for this instance of a class method
119 $alpha$ is the class variable
121 $LIE_cop' = LIE_cop [X gammas_bar / alpha, fresh betas_bar]$
123 $tau_cop' = tau_cop [X gammas_bar / alpha, fresh betas_bar]$
126 ToDo: Update the list above with names actually in the code.
130 First, make the LIEs for the class and instance contexts, which means
131 instantiate $thetaC [X inst_tyvars / alpha ]$, yielding LIElistC' and LIEC',
132 and make LIElistI and LIEI.
134 Then process each method in turn.
136 order the instance methods according to the ordering of the class methods
138 express LIEC' in terms of LIEI, yielding $dbinds_super$ or an error
140 Create final dictionary function from bindings generated already
142 df = lambda inst_tyvars
149 in <op1,op2,...,opn,sd1,...,sdm>
151 Here, Bop1 \ldots Bopn bind the methods op1 \ldots opn,
152 and $dbinds_super$ bind the superclass dictionaries sd1 \ldots sdm.
156 %************************************************************************
158 \subsection{Extracting instance decls}
160 %************************************************************************
162 Gather up the instance declarations from their various sources
165 tcInstDecls1 :: PackageInstEnv
166 -> PersistentRenamerState
167 -> HomeSymbolTable -- Contains instances
168 -> TcEnv -- Contains IdInfo for dfun ids
169 -> (Name -> Maybe Fixity) -- for deriving Show and Read
170 -> Module -- Module for deriving
172 -> TcM (PackageInstEnv, InstEnv, [InstInfo], RenamedHsBinds)
174 tcInstDecls1 inst_env0 prs hst unf_env get_fixity this_mod decls
176 inst_decls = [inst_decl | InstD inst_decl <- decls]
177 tycl_decls = [decl | TyClD decl <- decls]
178 clas_decls = filter isClassDecl tycl_decls
180 -- (1) Do the ordinary instance declarations
181 mapNF_Tc tcInstDecl1 inst_decls `thenNF_Tc` \ inst_infos ->
183 -- (2) Instances from generic class declarations
184 getGenericInstances clas_decls `thenTc` \ generic_inst_info ->
186 -- Next, construct the instance environment so far, consisting of
187 -- a) cached non-home-package InstEnv (gotten from pcs) pcs_insts pcs
188 -- b) imported instance decls (not in the home package) inst_env1
189 -- c) other modules in this package (gotten from hst) inst_env2
190 -- d) local instance decls inst_env3
191 -- e) generic instances inst_env4
192 -- The result of (b) replaces the cached InstEnv in the PCS
194 (local_inst_info, imported_inst_info)
195 = partition (isLocalThing this_mod . iDFunId) (concat inst_infos)
197 imported_dfuns = map (tcAddImportedIdInfo unf_env . iDFunId)
199 hst_dfuns = foldModuleEnv ((++) . md_insts) [] hst
202 -- pprTrace "tcInstDecls" (vcat [ppr imported_dfuns, ppr hst_dfuns]) $
204 addInstDFuns inst_env0 imported_dfuns `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; hecne 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
271 Just dfun_name -> -- An interface-file instance declaration
272 returnNF_Tc dfun_name
273 ) `thenNF_Tc` \ dfun_name ->
275 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys theta
277 returnTc [InstInfo { iDFunId = dfun_id, 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 `thenTc` \ 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]
418 dfun_id = mkDictFunId dfun_name clas tyvars inst_tys inst_theta
421 returnTc (InstInfo { iDFunId = dfun_id,
422 iBinds = binds, iPrags = [] })
426 %************************************************************************
428 \subsection{Type-checking instance declarations, pass 2}
430 %************************************************************************
433 tcInstDecls2 :: [InstInfo]
434 -> NF_TcM (LIE, TcMonoBinds)
436 tcInstDecls2 inst_decls
437 -- = foldBag combine tcInstDecl2 (returnNF_Tc (emptyLIE, EmptyMonoBinds)) inst_decls
438 = foldr combine (returnNF_Tc (emptyLIE, EmptyMonoBinds))
439 (map tcInstDecl2 inst_decls)
441 combine tc1 tc2 = tc1 `thenNF_Tc` \ (lie1, binds1) ->
442 tc2 `thenNF_Tc` \ (lie2, binds2) ->
443 returnNF_Tc (lie1 `plusLIE` lie2,
444 binds1 `AndMonoBinds` binds2)
447 ======= New documentation starts here (Sept 92) ==============
449 The main purpose of @tcInstDecl2@ is to return a @HsBinds@ which defines
450 the dictionary function for this instance declaration. For example
452 instance Foo a => Foo [a] where
456 might generate something like
458 dfun.Foo.List dFoo_a = let op1 x = ...
464 HOWEVER, if the instance decl has no context, then it returns a
465 bigger @HsBinds@ with declarations for each method. For example
467 instance Foo [a] where
473 dfun.Foo.List a = Dict [Foo.op1.List a, Foo.op2.List a]
474 const.Foo.op1.List a x = ...
475 const.Foo.op2.List a y = ...
477 This group may be mutually recursive, because (for example) there may
478 be no method supplied for op2 in which case we'll get
480 const.Foo.op2.List a = default.Foo.op2 (dfun.Foo.List a)
482 that is, the default method applied to the dictionary at this type.
484 What we actually produce in either case is:
486 AbsBinds [a] [dfun_theta_dicts]
487 [(dfun.Foo.List, d)] ++ (maybe) [(const.Foo.op1.List, op1), ...]
488 { d = (sd1,sd2, ..., op1, op2, ...)
493 The "maybe" says that we only ask AbsBinds to make global constant methods
494 if the dfun_theta is empty.
497 For an instance declaration, say,
499 instance (C1 a, C2 b) => C (T a b) where
502 where the {\em immediate} superclasses of C are D1, D2, we build a dictionary
503 function whose type is
505 (C1 a, C2 b, D1 (T a b), D2 (T a b)) => C (T a b)
507 Notice that we pass it the superclass dictionaries at the instance type; this
508 is the ``Mark Jones optimisation''. The stuff before the "=>" here
509 is the @dfun_theta@ below.
511 First comes the easy case of a non-local instance decl.
515 tcInstDecl2 :: InstInfo -> NF_TcM (LIE, TcMonoBinds)
516 -- tcInstDecl2 is called *only* on InstInfos
518 tcInstDecl2 (InstInfo { iDFunId = dfun_id,
519 iBinds = monobinds, iPrags = uprags })
520 = -- Prime error recovery
521 recoverNF_Tc (returnNF_Tc (emptyLIE, EmptyMonoBinds)) $
522 tcAddSrcLoc (getSrcLoc dfun_id) $
523 tcAddErrCtxt (instDeclCtxt (toHsType (idType dfun_id))) $
525 -- Instantiate the instance decl with tc-style type variables
527 (inst_tyvars, dfun_theta, clas, inst_tys) = tcSplitDFunTy (idType dfun_id)
529 tcInstSigTyVars InstTv inst_tyvars `thenNF_Tc` \ inst_tyvars' ->
531 tenv = mkTopTyVarSubst inst_tyvars (mkTyVarTys inst_tyvars')
532 inst_tys' = map (substTy tenv) inst_tys
533 dfun_theta' = substTheta tenv dfun_theta
534 origin = InstanceDeclOrigin
536 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
538 sel_names = [idName sel_id | (sel_id, _) <- op_items]
540 -- Instantiate the super-class context with inst_tys
541 sc_theta' = substTheta (mkTopTyVarSubst class_tyvars inst_tys') sc_theta
543 -- Find any definitions in monobinds that aren't from the class
544 bad_bndrs = collectMonoBinders monobinds `minusList` sel_names
546 -- Check that all the method bindings come from this class
547 mapTc (addErrTc . badMethodErr clas) bad_bndrs `thenNF_Tc_`
549 -- Create dictionary Ids from the specified instance contexts.
550 newDicts origin sc_theta' `thenNF_Tc` \ sc_dicts ->
551 newDicts origin dfun_theta' `thenNF_Tc` \ dfun_arg_dicts ->
552 newDicts origin [mkClassPred clas inst_tys'] `thenNF_Tc` \ [this_dict] ->
554 tcExtendTyVarEnvForMeths inst_tyvars inst_tyvars' (
555 -- The type variable from the dict fun actually scope
556 -- over the bindings. They were gotten from
557 -- the original instance declaration
559 -- Default-method Ids may be mentioned in synthesised RHSs,
560 -- but they'll already be in the environment.
562 mapAndUnzip3Tc (tcMethodBind clas origin inst_tyvars' inst_tys'
564 monobinds uprags True)
566 ) `thenTc` \ (method_binds_s, insts_needed_s, meth_insts) ->
568 -- Deal with SPECIALISE instance pragmas by making them
569 -- look like SPECIALISE pragmas for the dfun
571 dfun_prags = [SpecSig (idName dfun_id) ty loc | SpecInstSig ty loc <- uprags]
573 tcExtendGlobalValEnv [dfun_id] (
574 tcSpecSigs dfun_prags
575 ) `thenTc` \ (prag_binds, prag_lie) ->
577 -- Check the overloading constraints of the methods and superclasses
579 -- These insts are in scope; quite a few, eh?
580 avail_insts = [this_dict] ++
585 methods_lie = plusLIEs insts_needed_s
588 -- Simplify the constraints from methods
589 tcAddErrCtxt methodCtxt (
591 (ptext SLIT("instance declaration context"))
595 ) `thenTc` \ (const_lie1, lie_binds1) ->
597 -- Figure out bindings for the superclass context
598 tcAddErrCtxt superClassCtxt (
600 (ptext SLIT("instance declaration context"))
602 dfun_arg_dicts -- NB! Don't include this_dict here, else the sc_dicts
603 -- get bound by just selecting from this_dict!!
605 ) `thenTc` \ (const_lie2, lie_binds2) ->
607 checkSigTyVars inst_tyvars' emptyVarSet `thenNF_Tc` \ zonked_inst_tyvars ->
609 -- Create the result bindings
611 local_dfun_id = setIdLocalExported dfun_id
612 -- Reason for setIdLocalExported: see notes with MkId.mkDictFunId
614 dict_constr = classDataCon clas
615 scs_and_meths = map instToId (sc_dicts ++ meth_insts)
616 this_dict_id = instToId this_dict
617 inlines | null dfun_arg_dicts = emptyNameSet
618 | otherwise = 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.
624 -- BUT: don't inline it if it's a constant dictionary;
625 -- we'll get all the benefit without inlining, and we get
626 -- a **lot** of code duplication if we inline it
630 = -- Blatant special case for CCallable, CReturnable
631 -- If the dictionary is empty then we should never
632 -- select anything from it, so we make its RHS just
633 -- emit an error message. This in turn means that we don't
634 -- mention the constructor, which doesn't exist for CCallable, CReturnable
635 -- Hardly beautiful, but only three extra lines.
636 HsApp (TyApp (HsVar eRROR_ID) [idType this_dict_id])
637 (HsLit (HsString msg))
639 | otherwise -- The common case
640 = mkHsConApp dict_constr inst_tys' (map HsVar scs_and_meths)
641 -- We don't produce a binding for the dict_constr; instead we
642 -- rely on the simplifier to unfold this saturated application
643 -- We do this rather than generate an HsCon directly, because
644 -- it means that the special cases (e.g. dictionary with only one
645 -- member) are dealt with by the common MkId.mkDataConWrapId code rather
646 -- than needing to be repeated here.
649 msg = _PK_ ("Compiler error: bad dictionary " ++ showSDoc (ppr clas))
651 dict_bind = VarMonoBind this_dict_id dict_rhs
652 method_binds = andMonoBindList method_binds_s
657 (map instToId dfun_arg_dicts)
658 [(inst_tyvars', local_dfun_id, this_dict_id)]
660 (lie_binds1 `AndMonoBinds`
661 lie_binds2 `AndMonoBinds`
662 method_binds `AndMonoBinds`
665 returnTc (const_lie1 `plusLIE` const_lie2 `plusLIE` prag_lie,
666 main_bind `AndMonoBinds` prag_binds)
669 ------------------------------
670 Inlining dfuns unconditionally
671 ------------------------------
673 The code above unconditionally inlines dict funs. Here's why.
674 Consider this program:
676 test :: Int -> Int -> Bool
677 test x y = (x,y) == (y,x) || test y x
678 -- Recursive to avoid making it inline.
680 This needs the (Eq (Int,Int)) instance. If we inline that dfun
681 the code we end up with is good:
684 \r -> case ==# [ww ww1] of wild {
685 PrelBase.False -> Test.$wtest ww1 ww;
687 case ==# [ww1 ww] of wild1 {
688 PrelBase.False -> Test.$wtest ww1 ww;
689 PrelBase.True -> PrelBase.True [];
692 Test.test = \r [w w1]
695 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
698 If we don't inline the dfun, the code is not nearly as good:
700 (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl {
701 PrelBase.:DEq tpl1 tpl2 -> tpl2;
706 let { y = PrelBase.I#! [ww1]; } in
707 let { x = PrelBase.I#! [ww]; } in
708 let { sat_slx = PrelTup.(,)! [y x]; } in
709 let { sat_sly = PrelTup.(,)! [x y];
711 case == sat_sly sat_slx of wild {
712 PrelBase.False -> Test.$wtest ww1 ww;
713 PrelBase.True -> PrelBase.True [];
720 case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; };
723 Why doesn't GHC inline $fEq? Because it looks big:
725 PrelTup.zdfEqZ1T{-rcX-}
726 = \ @ a{-reT-} :: * @ b{-reS-} :: *
727 zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}}
728 zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} ->
730 zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-})
731 zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in
733 zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-})
734 zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in
736 zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
737 zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-})
738 ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) ->
740 of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) ->
742 of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) ->
744 (zeze1{-rf3-} a1{-rf2-} b1{-rf1-})
745 (zeze{-rf0-} a2{-reZ-} b2{-reY-})
749 a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-})
750 a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-})
751 b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) ->
752 PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-})
754 PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-})
756 and it's not as bad as it seems, because it's further dramatically
757 simplified: only zeze2 is extracted and its body is simplified.
760 %************************************************************************
762 \subsection{Error messages}
764 %************************************************************************
767 tcAddDeclCtxt decl thing_inside
768 = tcAddSrcLoc (tcdLoc decl) $
773 ClassDecl {} -> "class"
774 TySynonym {} -> "type synonym"
775 TyData {tcdND = NewType} -> "newtype"
776 TyData {tcdND = DataType} -> "data type"
778 ctxt = hsep [ptext SLIT("In the"), text thing,
779 ptext SLIT("declaration for"), quotes (ppr (tcdName decl))]
781 instDeclCtxt inst_ty = ptext SLIT("In the instance declaration for") <+> quotes doc
783 doc = case inst_ty of
784 HsForAllTy _ _ (HsPredTy pred) -> ppr pred
785 HsPredTy pred -> ppr pred
786 other -> ppr inst_ty -- Don't expect this
790 badGenericInstanceType binds
791 = vcat [ptext SLIT("Illegal type pattern in the generic bindings"),
794 missingGenericInstances missing
795 = ptext SLIT("Missing type patterns for") <+> pprQuotedList missing
797 dupGenericInsts tc_inst_infos
798 = vcat [ptext SLIT("More than one type pattern for a single generic type constructor:"),
799 nest 4 (vcat (map ppr_inst_ty tc_inst_infos)),
800 ptext SLIT("All the type patterns for a generic type constructor must be identical")
803 ppr_inst_ty (tc,inst) = ppr (simpleInstInfoTy inst)
805 methodCtxt = ptext SLIT("When checking the methods of an instance declaration")
806 superClassCtxt = ptext SLIT("When checking the super-classes of an instance declaration")