2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 TcInstDecls: Typechecking instance declarations
9 module TcInstDcls ( tcInstDecls1, tcInstDecls2 ) where
15 import TcPat( addInlinePrags )
26 import RnSource ( addTcgDUs )
29 import MkCore ( nO_METHOD_BINDING_ERROR_ID )
38 import CoreUtils ( mkPiTypes )
39 import CoreUnfold ( mkDFunUnfolding )
40 import CoreSyn ( Expr(Var), DFunArg(..), CoreExpr )
53 import Maybes ( orElse )
58 #include "HsVersions.h"
61 Typechecking instance declarations is done in two passes. The first
62 pass, made by @tcInstDecls1@, collects information to be used in the
65 This pre-processed info includes the as-yet-unprocessed bindings
66 inside the instance declaration. These are type-checked in the second
67 pass, when the class-instance envs and GVE contain all the info from
68 all the instance and value decls. Indeed that's the reason we need
69 two passes over the instance decls.
72 Note [How instance declarations are translated]
73 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
74 Here is how we translation instance declarations into Core
78 op1, op2 :: Ix b => a -> b -> b
82 {-# INLINE [2] op1 #-}
86 op1,op2 :: forall a. C a => forall b. Ix b => a -> b -> b
90 -- Default methods get the 'self' dictionary as argument
91 -- so they can call other methods at the same type
92 -- Default methods get the same type as their method selector
93 $dmop2 :: forall a. C a => forall b. Ix b => a -> b -> b
94 $dmop2 = /\a. \(d:C a). /\b. \(d2: Ix b). <dm-rhs>
95 -- NB: type variables 'a' and 'b' are *both* in scope in <dm-rhs>
96 -- Note [Tricky type variable scoping]
98 -- A top-level definition for each instance method
99 -- Here op1_i, op2_i are the "instance method Ids"
100 -- The INLINE pragma comes from the user pragma
101 {-# INLINE [2] op1_i #-} -- From the instance decl bindings
102 op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b
103 op1_i = /\a. \(d:C a).
106 -- Note [Subtle interaction of recursion and overlap]
108 local_op1 :: forall b. Ix b => [a] -> b -> b
110 -- Source code; run the type checker on this
111 -- NB: Type variable 'a' (but not 'b') is in scope in <rhs>
112 -- Note [Tricky type variable scoping]
116 op2_i = /\a \d:C a. $dmop2 [a] (df_i a d)
118 -- The dictionary function itself
119 {-# NOINLINE CONLIKE df_i #-} -- Never inline dictionary functions
120 df_i :: forall a. C a -> C [a]
121 df_i = /\a. \d:C a. MkC (op1_i a d) (op2_i a d)
122 -- But see Note [Default methods in instances]
123 -- We can't apply the type checker to the default-method call
125 -- Use a RULE to short-circuit applications of the class ops
126 {-# RULE "op1@C[a]" forall a, d:C a.
127 op1 [a] (df_i d) = op1_i a d #-}
129 Note [Instances and loop breakers]
130 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
131 * Note that df_i may be mutually recursive with both op1_i and op2_i.
132 It's crucial that df_i is not chosen as the loop breaker, even
133 though op1_i has a (user-specified) INLINE pragma.
135 * Instead the idea is to inline df_i into op1_i, which may then select
136 methods from the MkC record, and thereby break the recursion with
137 df_i, leaving a *self*-recurisve op1_i. (If op1_i doesn't call op at
138 the same type, it won't mention df_i, so there won't be recursion in
141 * If op1_i is marked INLINE by the user there's a danger that we won't
142 inline df_i in it, and that in turn means that (since it'll be a
143 loop-breaker because df_i isn't), op1_i will ironically never be
144 inlined. But this is OK: the recursion breaking happens by way of
145 a RULE (the magic ClassOp rule above), and RULES work inside InlineRule
146 unfoldings. See Note [RULEs enabled in SimplGently] in SimplUtils
148 Note [ClassOp/DFun selection]
149 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
150 One thing we see a lot is stuff like
152 where 'op2' is a ClassOp and 'df' is DFun. Now, we could inline *both*
153 'op2' and 'df' to get
154 case (MkD ($cop1 d1 d2) ($cop2 d1 d2) ... of
155 MkD _ op2 _ _ _ -> op2
156 And that will reduce to ($cop2 d1 d2) which is what we wanted.
158 But it's tricky to make this work in practice, because it requires us to
159 inline both 'op2' and 'df'. But neither is keen to inline without having
160 seen the other's result; and it's very easy to get code bloat (from the
161 big intermediate) if you inline a bit too much.
163 Instead we use a cunning trick.
164 * We arrange that 'df' and 'op2' NEVER inline.
166 * We arrange that 'df' is ALWAYS defined in the sylised form
167 df d1 d2 = MkD ($cop1 d1 d2) ($cop2 d1 d2) ...
169 * We give 'df' a magical unfolding (DFunUnfolding [$cop1, $cop2, ..])
170 that lists its methods.
172 * We make CoreUnfold.exprIsConApp_maybe spot a DFunUnfolding and return
173 a suitable constructor application -- inlining df "on the fly" as it
176 * We give the ClassOp 'op2' a BuiltinRule that extracts the right piece
177 iff its argument satisfies exprIsConApp_maybe. This is done in
180 * We make 'df' CONLIKE, so that shared uses stil match; eg
182 in ...(op2 d)...(op1 d)...
184 Note [Single-method classes]
185 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
186 If the class has just one method (or, more accurately, just one element
187 of {superclasses + methods}), then we use a different strategy.
189 class C a where op :: a -> a
190 instance C a => C [a] where op = <blah>
192 We translate the class decl into a newtype, which just gives a
193 top-level axiom. The "constructor" MkC expands to a cast, as does the
196 axiom Co:C a :: C a ~ (a->a)
198 op :: forall a. C a -> (a -> a)
199 op a d = d |> (Co:C a)
201 MkC :: forall a. (a->a) -> C a
202 MkC = /\a.\op. op |> (sym Co:C a)
204 The clever RULE stuff doesn't work now, because ($df a d) isn't
205 a constructor application, so exprIsConApp_maybe won't return
208 Instead, we simply rely on the fact that casts are cheap:
210 $df :: forall a. C a => C [a]
211 {-# INLINE df #-} -- NB: INLINE this
212 $df = /\a. \d. MkC [a] ($cop_list a d)
213 = $cop_list |> forall a. C a -> (sym (Co:C [a]))
215 $cop_list :: forall a. C a => [a] -> [a]
220 we'll inline 'op' and '$df', since both are simply casts, and
223 Why do we use this different strategy? Because otherwise we
224 end up with non-inlined dictionaries that look like
226 which adds an extra indirection to every use, which seems stupid. See
227 Trac #4138 for an example (although the regression reported there
228 wasn't due to the indirction).
230 There is an awkward wrinkle though: we want to be very
232 instance C a => C [a] where
235 then we'll get an INLINE pragma on $cop_list but it's important that
236 $cop_list only inlines when it's applied to *two* arguments (the
237 dictionary and the list argument). So we nust not eta-expand $df
238 above. We ensure that this doesn't happen by putting an INLINE
239 pragma on the dfun itself; after all, it ends up being just a cast.
241 There is one more dark corner to the INLINE story, even more deeply
242 buried. Consider this (Trac #3772):
244 class DeepSeq a => C a where
247 instance C a => C [a] where
250 class DeepSeq a where
251 deepSeq :: a -> b -> b
253 instance DeepSeq a => DeepSeq [a] where
254 {-# INLINE deepSeq #-}
255 deepSeq xs b = foldr deepSeq b xs
257 That gives rise to these defns:
259 $cdeepSeq :: DeepSeq a -> [a] -> b -> b
260 -- User INLINE( 3 args )!
261 $cdeepSeq a (d:DS a) b (x:[a]) (y:b) = ...
263 $fDeepSeq[] :: DeepSeq a -> DeepSeq [a]
264 -- DFun (with auto INLINE pragma)
265 $fDeepSeq[] a d = $cdeepSeq a d |> blah
267 $cp1 a d :: C a => DeepSep [a]
268 -- We don't want to eta-expand this, lest
269 -- $cdeepSeq gets inlined in it!
270 $cp1 a d = $fDeepSep[] a (scsel a d)
272 $fC[] :: C a => C [a]
274 $fC[] a d = MkC ($cp1 a d) ($cgen a d)
276 Here $cp1 is the code that generates the superclass for C [a]. The
277 issue is this: we must not eta-expand $cp1 either, or else $fDeepSeq[]
278 and then $cdeepSeq will inline there, which is definitely wrong. Like
279 on the dfun, we solve this by adding an INLINE pragma to $cp1.
281 Note [Subtle interaction of recursion and overlap]
282 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
284 class C a where { op1,op2 :: a -> a }
285 instance C a => C [a] where
286 op1 x = op2 x ++ op2 x
288 instance C [Int] where
291 When type-checking the C [a] instance, we need a C [a] dictionary (for
292 the call of op2). If we look up in the instance environment, we find
293 an overlap. And in *general* the right thing is to complain (see Note
294 [Overlapping instances] in InstEnv). But in *this* case it's wrong to
295 complain, because we just want to delegate to the op2 of this same
298 Why is this justified? Because we generate a (C [a]) constraint in
299 a context in which 'a' cannot be instantiated to anything that matches
300 other overlapping instances, or else we would not be excecuting this
301 version of op1 in the first place.
303 It might even be a bit disguised:
305 nullFail :: C [a] => [a] -> [a]
306 nullFail x = op2 x ++ op2 x
308 instance C a => C [a] where
311 Precisely this is used in package 'regex-base', module Context.hs.
312 See the overlapping instances for RegexContext, and the fact that they
313 call 'nullFail' just like the example above. The DoCon package also
314 does the same thing; it shows up in module Fraction.hs
316 Conclusion: when typechecking the methods in a C [a] instance, we want to
317 treat the 'a' as an *existential* type variable, in the sense described
318 by Note [Binding when looking up instances]. That is why isOverlappableTyVar
319 responds True to an InstSkol, which is the kind of skolem we use in
323 Note [Tricky type variable scoping]
324 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
327 op1, op2 :: Ix b => a -> b -> b
330 instance C a => C [a]
331 {-# INLINE [2] op1 #-}
334 note that 'a' and 'b' are *both* in scope in <dm-rhs>, but only 'a' is
335 in scope in <rhs>. In particular, we must make sure that 'b' is in
336 scope when typechecking <dm-rhs>. This is achieved by subFunTys,
337 which brings appropriate tyvars into scope. This happens for both
338 <dm-rhs> and for <rhs>, but that doesn't matter: the *renamer* will have
339 complained if 'b' is mentioned in <rhs>.
343 %************************************************************************
345 \subsection{Extracting instance decls}
347 %************************************************************************
349 Gather up the instance declarations from their various sources
352 tcInstDecls1 -- Deal with both source-code and imported instance decls
353 :: [LTyClDecl Name] -- For deriving stuff
354 -> [LInstDecl Name] -- Source code instance decls
355 -> [LDerivDecl Name] -- Source code stand-alone deriving decls
356 -> TcM (TcGblEnv, -- The full inst env
357 [InstInfo Name], -- Source-code instance decls to process;
358 -- contains all dfuns for this module
359 HsValBinds Name) -- Supporting bindings for derived instances
361 tcInstDecls1 tycl_decls inst_decls deriv_decls
363 do { -- Stop if addInstInfos etc discovers any errors
364 -- (they recover, so that we get more than one error each
367 -- (1) Do class and family instance declarations
368 ; idx_tycons <- mapAndRecoverM (tcFamInstDecl TopLevel) $
369 filter (isFamInstDecl . unLoc) tycl_decls
370 ; local_info_tycons <- mapAndRecoverM tcLocalInstDecl1 inst_decls
373 at_tycons_s) = unzip local_info_tycons
374 ; at_idx_tycons = concat at_tycons_s ++ idx_tycons
375 ; implicit_things = concatMap implicitTyConThings at_idx_tycons
376 ; aux_binds = mkRecSelBinds at_idx_tycons }
378 -- (2) Add the tycons of indexed types and their implicit
379 -- tythings to the global environment
380 ; tcExtendGlobalEnv (map ATyCon at_idx_tycons ++ implicit_things) $ do {
383 -- Next, construct the instance environment so far, consisting
385 -- (a) local instance decls
386 -- (b) local family instance decls
387 ; addInsts local_info $
388 addFamInsts at_idx_tycons $ do {
390 -- (3) Compute instances from "deriving" clauses;
391 -- This stuff computes a context for the derived instance
392 -- decl, so it needs to know about all the instances possible
393 -- NB: class instance declarations can contain derivings as
394 -- part of associated data type declarations
395 failIfErrsM -- If the addInsts stuff gave any errors, don't
396 -- try the deriving stuff, because that may give
398 ; (deriv_inst_info, deriv_binds, deriv_dus, deriv_tys, deriv_ty_insts)
399 <- tcDeriving tycl_decls inst_decls deriv_decls
401 -- Extend the global environment also with the generated datatypes for
402 -- the generic representation
403 ; let all_tycons = map ATyCon (deriv_tys ++ deriv_ty_insts)
404 ; gbl_env <- tcExtendGlobalEnv all_tycons $
405 tcExtendGlobalEnv (concatMap implicitTyThings all_tycons) $
406 addFamInsts deriv_ty_insts $
407 addInsts deriv_inst_info getGblEnv
408 ; return ( addTcgDUs gbl_env deriv_dus,
409 deriv_inst_info ++ local_info,
410 aux_binds `plusHsValBinds` deriv_binds)
413 addInsts :: [InstInfo Name] -> TcM a -> TcM a
414 addInsts infos thing_inside
415 = tcExtendLocalInstEnv (map iSpec infos) thing_inside
417 addFamInsts :: [TyCon] -> TcM a -> TcM a
418 addFamInsts tycons thing_inside
419 = tcExtendLocalFamInstEnv (map mkLocalFamInst tycons) thing_inside
423 tcLocalInstDecl1 :: LInstDecl Name
424 -> TcM (InstInfo Name, [TyCon])
425 -- A source-file instance declaration
426 -- Type-check all the stuff before the "where"
428 -- We check for respectable instance type, and context
429 tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats))
431 addErrCtxt (instDeclCtxt1 poly_ty) $
433 do { is_boot <- tcIsHsBoot
434 ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags))
437 ; (tyvars, theta, clas, inst_tys) <- tcHsInstHead poly_ty
438 ; checkValidInstance poly_ty tyvars theta clas inst_tys
440 -- Next, process any associated types.
441 ; idx_tycons <- recoverM (return []) $
442 do { idx_tycons <- checkNoErrs $
443 mapAndRecoverM (tcFamInstDecl NotTopLevel) ats
444 ; checkValidAndMissingATs clas (tyvars, inst_tys)
446 ; return idx_tycons }
448 -- Finally, construct the Core representation of the instance.
449 -- (This no longer includes the associated types.)
450 ; dfun_name <- newDFunName clas inst_tys (getLoc poly_ty)
451 -- Dfun location is that of instance *header*
452 ; overlap_flag <- getOverlapFlag
453 ; let (eq_theta,dict_theta) = partition isEqPred theta
454 theta' = eq_theta ++ dict_theta
455 dfun = mkDictFunId dfun_name tyvars theta' clas inst_tys
456 ispec = mkLocalInstance dfun overlap_flag
458 ; return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags False },
462 -- We pass in the source form and the type checked form of the ATs. We
463 -- really need the source form only to be able to produce more informative
465 checkValidAndMissingATs :: Class
466 -> ([TyVar], [TcType]) -- instance types
467 -> [(LTyClDecl Name, -- source form of AT
468 TyCon)] -- Core form of AT
470 checkValidAndMissingATs clas inst_tys ats
471 = do { -- Issue a warning for each class AT that is not defined in this
473 ; let class_ats = map tyConName (classATs clas)
474 defined_ats = listToNameSet . map (tcdName.unLoc.fst) $ ats
475 omitted = filterOut (`elemNameSet` defined_ats) class_ats
476 ; warn <- doptM Opt_WarnMissingMethods
477 ; mapM_ (warnTc warn . omittedATWarn) omitted
479 -- Ensure that all AT indexes that correspond to class parameters
480 -- coincide with the types in the instance head. All remaining
481 -- AT arguments must be variables. Also raise an error for any
482 -- type instances that are not associated with this class.
483 ; mapM_ (checkIndexes clas inst_tys) ats
486 checkIndexes clas inst_tys (hsAT, tycon)
487 -- !!!TODO: check that this does the Right Thing for indexed synonyms, too!
488 = checkIndexes' clas inst_tys hsAT
490 snd . fromJust . tyConFamInst_maybe $ tycon)
492 checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys)
493 = let atName = tcdName . unLoc $ hsAT
495 setSrcSpan (getLoc hsAT) $
496 addErrCtxt (atInstCtxt atName) $
497 case find ((atName ==) . tyConName) (classATs clas) of
498 Nothing -> addErrTc $ badATErr clas atName -- not in this class
500 -- The following is tricky! We need to deal with three
501 -- complications: (1) The AT possibly only uses a subset of
502 -- the class parameters as indexes and those it uses may be in
503 -- a different order; (2) the AT may have extra arguments,
504 -- which must be type variables; and (3) variables in AT and
505 -- instance head will be different `Name's even if their
506 -- source lexemes are identical.
508 -- e.g. class C a b c where
509 -- data D b a :: * -> * -- NB (1) b a, omits c
510 -- instance C [x] Bool Char where
511 -- data D Bool [x] v = MkD x [v] -- NB (2) v
512 -- -- NB (3) the x in 'instance C...' have differnt
513 -- -- Names to x's in 'data D...'
515 -- Re (1), `poss' contains a permutation vector to extract the
516 -- class parameters in the right order.
518 -- Re (2), we wrap the (permuted) class parameters in a Maybe
519 -- type and use Nothing for any extra AT arguments. (First
520 -- equation of `checkIndex' below.)
522 -- Re (3), we replace any type variable in the AT parameters
523 -- that has the same source lexeme as some variable in the
524 -- instance types with the instance type variable sharing its
528 -- For *associated* type families, gives the position
529 -- of that 'TyVar' in the class argument list (0-indexed)
530 -- e.g. class C a b c where { type F c a :: *->* }
531 -- Then we get Just [2,0]
532 poss = catMaybes [ tv `elemIndex` classTyVars clas
533 | tv <- tyConTyVars atycon]
534 -- We will get Nothings for the "extra" type
535 -- variables in an associated data type
536 -- e.g. class C a where { data D a :: *->* }
537 -- here D gets arity 2 and has two tyvars
539 relevantInstTys = map (instTys !!) poss
540 instArgs = map Just relevantInstTys ++
541 repeat Nothing -- extra arguments
542 renaming = substSameTyVar atTvs instTvs
544 zipWithM_ checkIndex (substTys renaming atTys) instArgs
546 checkIndex ty Nothing
547 | isTyVarTy ty = return ()
548 | otherwise = addErrTc $ mustBeVarArgErr ty
549 checkIndex ty (Just instTy)
550 | ty `eqType` instTy = return ()
551 | otherwise = addErrTc $ wrongATArgErr ty instTy
553 listToNameSet = addListToNameSet emptyNameSet
555 substSameTyVar [] _ = emptyTvSubst
556 substSameTyVar (tv:tvs) replacingTvs =
557 let replacement = case find (tv `sameLexeme`) replacingTvs of
558 Nothing -> mkTyVarTy tv
559 Just rtv -> mkTyVarTy rtv
561 tv1 `sameLexeme` tv2 =
562 nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2)
564 TcType.extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement
568 %************************************************************************
570 Type checking family instances
572 %************************************************************************
574 Family instances are somewhat of a hybrid. They are processed together with
575 class instance heads, but can contain data constructors and hence they share a
576 lot of kinding and type checking code with ordinary algebraic data types (and
580 tcFamInstDecl :: TopLevelFlag -> LTyClDecl Name -> TcM TyCon
581 tcFamInstDecl top_lvl (L loc decl)
582 = -- Prime error recovery, set source location
585 do { -- type family instances require -XTypeFamilies
586 -- and can't (currently) be in an hs-boot file
587 ; type_families <- xoptM Opt_TypeFamilies
588 ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file?
589 ; checkTc type_families $ badFamInstDecl (tcdLName decl)
590 ; checkTc (not is_boot) $ badBootFamInstDeclErr
592 -- Perform kind and type checking
593 ; tc <- tcFamInstDecl1 decl
594 ; checkValidTyCon tc -- Remember to check validity;
595 -- no recursion to worry about here
597 -- Check that toplevel type instances are not for associated types.
598 ; when (isTopLevel top_lvl && isAssocFamily tc)
599 (addErr $ assocInClassErr (tcdName decl))
603 isAssocFamily :: TyCon -> Bool -- Is an assocaited type
605 = case tyConFamInst_maybe tycon of
606 Nothing -> panic "isAssocFamily: no family?!?"
607 Just (fam, _) -> isTyConAssoc fam
609 assocInClassErr :: Name -> SDoc
611 = ptext (sLit "Associated type") <+> quotes (ppr name) <+>
612 ptext (sLit "must be inside a class instance")
616 tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon
619 tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name})
620 = kcIdxTyPats decl $ \k_tvs k_typats resKind family ->
621 do { -- check that the family declaration is for a synonym
622 checkTc (isFamilyTyCon family) (notFamily family)
623 ; checkTc (isSynTyCon family) (wrongKindOfFamily family)
625 ; -- (1) kind check the right-hand side of the type equation
626 ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk)
627 -- ToDo: the ExpKind could be better
629 -- we need the exact same number of type parameters as the family
631 ; let famArity = tyConArity family
632 ; checkTc (length k_typats == famArity) $
633 wrongNumberOfParmsErr famArity
635 -- (2) type check type equation
636 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
637 ; t_typats <- mapM tcHsKindedType k_typats
638 ; t_rhs <- tcHsKindedType k_rhs
640 -- (3) check the well-formedness of the instance
641 ; checkValidTypeInst t_typats t_rhs
643 -- (4) construct representation tycon
644 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
645 ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs)
647 NoParentTyCon (Just (family, t_typats))
650 -- "newtype instance" and "data instance"
651 tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name,
653 = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon ->
654 do { -- check that the family declaration is for the right kind
655 checkTc (isFamilyTyCon fam_tycon) (notFamily fam_tycon)
656 ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon)
658 ; -- (1) kind check the data declaration as usual
659 ; k_decl <- kcDataDecl decl k_tvs
660 ; let k_ctxt = tcdCtxt k_decl
661 k_cons = tcdCons k_decl
663 -- result kind must be '*' (otherwise, we have too few patterns)
664 ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon)
666 -- (2) type check indexed data type declaration
667 ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars
669 -- kind check the type indexes and the context
670 ; t_typats <- mapM tcHsKindedType k_typats
671 ; stupid_theta <- tcHsKindedContext k_ctxt
674 -- (a) left-hand side contains no type family applications
675 -- (vanilla synonyms are fine, though, and we checked for
677 ; mapM_ checkTyFamFreeness t_typats
679 ; dataDeclChecks tc_name new_or_data stupid_theta k_cons
681 -- (4) construct representation tycon
682 ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc
683 ; let ex_ok = True -- Existentials ok for type families!
684 ; fixM (\ rep_tycon -> do
685 { let orig_res_ty = mkTyConApp fam_tycon t_typats
686 ; data_cons <- tcConDecls ex_ok rep_tycon
687 (t_tvs, orig_res_ty) k_cons
690 DataType -> return (mkDataTyConRhs data_cons)
691 NewType -> ASSERT( not (null data_cons) )
692 mkNewTyConRhs rep_tc_name rep_tycon (head data_cons)
693 ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive
694 h98_syntax NoParentTyCon (Just (fam_tycon, t_typats))
695 -- We always assume that indexed types are recursive. Why?
696 -- (1) Due to their open nature, we can never be sure that a
697 -- further instance might not introduce a new recursive
698 -- dependency. (2) They are always valid loop breakers as
699 -- they involve a coercion.
703 h98_syntax = case cons of -- All constructors have same shape
704 L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False
707 tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d)
709 -- Kind checking of indexed types
712 -- Kind check type patterns and kind annotate the embedded type variables.
714 -- * Here we check that a type instance matches its kind signature, but we do
715 -- not check whether there is a pattern for each type index; the latter
716 -- check is only required for type synonym instances.
718 kcIdxTyPats :: TyClDecl Name
719 -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a)
720 -- ^^kinded tvs ^^kinded ty pats ^^res kind
722 kcIdxTyPats decl thing_inside
723 = kcHsTyVars (tcdTyVars decl) $ \tvs ->
724 do { let tc_name = tcdLName decl
725 ; fam_tycon <- tcLookupLocatedTyCon tc_name
726 ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon)
727 ; hs_typats = fromJust $ tcdTyPats decl }
729 -- we may not have more parameters than the kind indicates
730 ; checkTc (length kinds >= length hs_typats) $
731 tooManyParmsErr (tcdLName decl)
733 -- type functions can have a higher-kinded result
734 ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind
735 ; typats <- zipWithM kcCheckLHsType hs_typats
736 [ EK kind (EkArg (ppr tc_name) n)
737 | (kind,n) <- kinds `zip` [1..]]
738 ; thing_inside tvs typats resultKind fam_tycon
743 %************************************************************************
745 Type-checking instance declarations, pass 2
747 %************************************************************************
750 tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name]
752 -- (a) From each class declaration,
753 -- generate any default-method bindings
754 -- (b) From each instance decl
755 -- generate the dfun binding
757 tcInstDecls2 tycl_decls inst_decls
758 = do { -- (a) Default methods from class decls
759 let class_decls = filter (isClassDecl . unLoc) tycl_decls
760 ; dm_binds_s <- mapM tcClassDecl2 class_decls
761 ; let dm_binds = unionManyBags dm_binds_s
763 -- (b) instance declarations
764 ; let dm_ids = collectHsBindsBinders dm_binds
765 -- Add the default method Ids (again)
766 -- See Note [Default methods and instances]
767 ; inst_binds_s <- tcExtendIdEnv dm_ids $
768 mapM tcInstDecl2 inst_decls
771 ; return (dm_binds `unionBags` unionManyBags inst_binds_s) }
774 See Note [Default methods and instances]
775 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
776 The default method Ids are already in the type environment (see Note
777 [Default method Ids and Template Haskell] in TcTyClsDcls), BUT they
778 don't have their InlinePragmas yet. Usually that would not matter,
779 because the simplifier propagates information from binding site to
780 use. But, unusually, when compiling instance decls we *copy* the
781 INLINE pragma from the default method to the method for that
782 particular operation (see Note [INLINE and default methods] below).
784 So right here in tcInstDecl2 we must re-extend the type envt with
785 the default method Ids replete with their INLINE pragmas. Urk.
789 tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
790 -- Returns a binding for the dfun
791 tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = ibinds })
792 = recoverM (return emptyLHsBinds) $
794 addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
795 do { -- Instantiate the instance decl with skolem constants
796 ; (inst_tyvars, dfun_theta, inst_head) <- tcSkolDFunType (idType dfun_id)
797 -- We instantiate the dfun_id with superSkolems.
798 -- See Note [Subtle interaction of recursion and overlap]
799 -- and Note [Binding when looking up instances]
800 ; let (clas, inst_tys) = tcSplitDFunHead inst_head
801 (class_tyvars, sc_theta, _, op_items) = classBigSig clas
802 sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys) sc_theta
803 n_ty_args = length inst_tyvars
804 n_silent = dfunNSilent dfun_id
805 (silent_theta, orig_theta) = splitAt n_silent dfun_theta
807 ; silent_ev_vars <- mapM newSilentGiven silent_theta
808 ; orig_ev_vars <- newEvVars orig_theta
809 ; let dfun_ev_vars = silent_ev_vars ++ orig_ev_vars
811 ; (sc_dicts, sc_args)
812 <- mapAndUnzipM (tcSuperClass n_ty_args dfun_ev_vars) sc_theta'
814 -- Check that any superclasses gotten from a silent arguemnt
815 -- can be deduced from the originally-specified dfun arguments
816 ; ct_loc <- getCtLoc ScOrigin
817 ; _ <- checkConstraints skol_info inst_tyvars orig_ev_vars $
818 emitFlats $ listToBag $
819 [ mkEvVarX sc ct_loc | sc <- sc_dicts, isSilentEvVar sc ]
821 -- Deal with 'SPECIALISE instance' pragmas
822 -- See Note [SPECIALISE instance pragmas]
823 ; spec_info@(spec_inst_prags,_) <- tcSpecInstPrags dfun_id ibinds
825 -- Typecheck the methods
826 ; (meth_ids, meth_binds)
827 <- tcExtendTyVarEnv inst_tyvars $
828 -- The inst_tyvars scope over the 'where' part
829 -- Those tyvars are inside the dfun_id's type, which is a bit
830 -- bizarre, but OK so long as you realise it!
831 tcInstanceMethods dfun_id clas inst_tyvars dfun_ev_vars
835 -- Create the result bindings
836 ; self_dict <- newEvVar (ClassP clas inst_tys)
837 ; let class_tc = classTyCon clas
838 [dict_constr] = tyConDataCons class_tc
839 dict_bind = mkVarBind self_dict dict_rhs
840 dict_rhs = foldl mk_app inst_constr $
841 map HsVar sc_dicts ++ map (wrapId arg_wrapper) meth_ids
842 inst_constr = L loc $ wrapId (mkWpTyApps inst_tys)
843 (dataConWrapId dict_constr)
844 -- We don't produce a binding for the dict_constr; instead we
845 -- rely on the simplifier to unfold this saturated application
846 -- We do this rather than generate an HsCon directly, because
847 -- it means that the special cases (e.g. dictionary with only one
848 -- member) are dealt with by the common MkId.mkDataConWrapId
849 -- code rather than needing to be repeated here.
851 mk_app :: LHsExpr Id -> HsExpr Id -> LHsExpr Id
852 mk_app fun arg = L loc (HsApp fun (L loc arg))
854 arg_wrapper = mkWpEvVarApps dfun_ev_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars)
856 -- Do not inline the dfun; instead give it a magic DFunFunfolding
857 -- See Note [ClassOp/DFun selection]
858 -- See also note [Single-method classes]
860 | isNewTyCon class_tc
861 = dfun_id `setInlinePragma` alwaysInlinePragma { inl_sat = Just 0 }
863 = dfun_id `setIdUnfolding` mkDFunUnfolding dfun_ty (sc_args ++ meth_args)
864 `setInlinePragma` dfunInlinePragma
865 meth_args = map (DFunPolyArg . Var) meth_ids
867 main_bind = AbsBinds { abs_tvs = inst_tyvars
868 , abs_ev_vars = dfun_ev_vars
869 , abs_exports = [(inst_tyvars, dfun_id_w_fun, self_dict,
870 SpecPrags spec_inst_prags)]
871 , abs_ev_binds = emptyTcEvBinds
872 , abs_binds = unitBag dict_bind }
874 ; return (unitBag (L loc main_bind) `unionBags`
875 listToBag meth_binds)
879 dfun_ty = idType dfun_id
880 dfun_id = instanceDFunId ispec
881 loc = getSrcSpan dfun_id
883 ------------------------------
884 tcSuperClass :: Int -> [EvVar] -> PredType -> TcM (EvVar, DFunArg CoreExpr)
885 -- All superclasses should be either
886 -- (a) be one of the arguments to the dfun, of
887 -- (b) be a constant, soluble at top level
888 tcSuperClass n_ty_args ev_vars pred
889 | Just (ev, i) <- find n_ty_args ev_vars
890 = return (ev, DFunLamArg i)
892 = ASSERT2( isEmptyVarSet (tyVarsOfPred pred), ppr pred) -- Constant!
893 do { sc_dict <- emitWanted ScOrigin pred
894 ; return (sc_dict, DFunConstArg (Var sc_dict)) }
897 find i (ev:evs) | pred `eqPred` evVarPred ev = Just (ev, i)
898 | otherwise = find (i+1) evs
900 ------------------------------
901 tcSpecInstPrags :: DFunId -> InstBindings Name
902 -> TcM ([Located TcSpecPrag], PragFun)
903 tcSpecInstPrags _ (NewTypeDerived {})
904 = return ([], \_ -> [])
905 tcSpecInstPrags dfun_id (VanillaInst binds uprags _)
906 = do { spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) $
907 filter isSpecInstLSig uprags
908 -- The filter removes the pragmas for methods
909 ; return (spec_inst_prags, mkPragFun uprags binds) }
912 Note [Silent Superclass Arguments]
913 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
914 Consider the following (extreme) situation:
915 class C a => D a where ...
916 instance D [a] => D [a] where ...
917 Although this looks wrong (assume D [a] to prove D [a]), it is only a
918 more extreme case of what happens with recursive dictionaries.
920 To implement the dfun we must generate code for the superclass C [a],
921 which we can get by superclass selection from the supplied argument!
923 dfun :: forall a. D [a] -> D [a]
924 dfun = \d::D [a] -> MkD (scsel d) ..
926 However this means that if we later encounter a situation where
927 we have a [Wanted] dw::D [a] we could solve it thus:
929 Although recursive, this binding would pass the TcSMonadisGoodRecEv
930 check because it appears as guarded. But in reality, it will make a
931 bottom superclass. The trouble is that isGoodRecEv can't "see" the
932 superclass-selection inside dfun.
934 Our solution to this problem is to change the way ‘dfuns’ are created
935 for instances, so that we pass as first arguments to the dfun some
936 ``silent superclass arguments’’, which are the immediate superclasses
937 of the dictionary we are trying to construct. In our example:
938 dfun :: forall a. (C [a], D [a] -> D [a]
939 dfun = \(dc::C [a]) (dd::D [a]) -> DOrd dc ...
943 -----------------------------------------------------------
944 DFun Superclass Invariant
945 ~~~~~~~~~~~~~~~~~~~~~~~~
946 In the body of a DFun, every superclass argument to the
947 returned dictionary is
948 either * one of the arguments of the DFun,
949 or * constant, bound at top level
950 -----------------------------------------------------------
952 This means that no superclass is hidden inside a dfun application, so
953 the counting argument in isGoodRecEv (more dfun calls than superclass
954 selections) works correctly.
956 The extra arguments required to satisfy the DFun Superclass Invariant
957 always come first, and are called the "silent" arguments. DFun types
958 are built (only) by MkId.mkDictFunId, so that is where we decide
959 what silent arguments are to be added.
961 This net effect is that it is safe to treat a dfun application as
962 wrapping a dictionary constructor around its arguments (in particular,
963 a dfun never picks superclasses from the arguments under the dictionary
966 In our example, if we had [Wanted] dw :: D [a] we would get via the instance:
968 [Wanted] (d1 :: C [a])
969 [Wanted] (d2 :: D [a])
970 [Derived] (d :: D [a])
971 [Derived] (scd :: C [a]) scd := scsel d
972 [Derived] (scd2 :: C [a]) scd2 := scsel d2
974 And now, though we *can* solve:
976 we will get an isGoodRecEv failure when we try to solve:
981 Test case SCLoop tests this fix.
983 Note [SPECIALISE instance pragmas]
984 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
987 instance (Ix a, Ix b) => Ix (a,b) where
988 {-# SPECIALISE instance Ix (Int,Int) #-}
991 We do *not* want to make a specialised version of the dictionary
992 function. Rather, we want specialised versions of each method.
993 Thus we should generate something like this:
995 $dfIx :: (Ix a, Ix x) => Ix (a,b)
996 {- DFUN [$crange, ...] -}
997 $dfIx da db = Ix ($crange da db) (...other methods...)
999 $dfIxPair :: (Ix a, Ix x) => Ix (a,b)
1000 {- DFUN [$crangePair, ...] -}
1001 $dfIxPair = Ix ($crangePair da db) (...other methods...)
1003 $crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)]
1004 {-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-}
1005 $crange da db = <blah>
1007 {-# RULE range ($dfIx da db) = $crange da db #-}
1011 * The RULE is unaffected by the specialisation. We don't want to
1012 specialise $dfIx, because then it would need a specialised RULE
1013 which is a pain. The single RULE works fine at all specialisations.
1014 See Note [How instance declarations are translated] above
1016 * Instead, we want to specialise the *method*, $crange
1018 In practice, rather than faking up a SPECIALISE pragama for each
1019 method (which is painful, since we'd have to figure out its
1020 specialised type), we call tcSpecPrag *as if* were going to specialise
1021 $dfIx -- you can see that in the call to tcSpecInst. That generates a
1022 SpecPrag which, as it turns out, can be used unchanged for each method.
1023 The "it turns out" bit is delicate, but it works fine!
1026 tcSpecInst :: Id -> Sig Name -> TcM TcSpecPrag
1027 tcSpecInst dfun_id prag@(SpecInstSig hs_ty)
1028 = addErrCtxt (spec_ctxt prag) $
1029 do { let name = idName dfun_id
1030 ; (tyvars, theta, clas, tys) <- tcHsInstHead hs_ty
1031 ; let (_, spec_dfun_ty) = mkDictFunTy tyvars theta clas tys
1033 ; co_fn <- tcSubType (SpecPragOrigin name) SpecInstCtxt
1034 (idType dfun_id) spec_dfun_ty
1035 ; return (SpecPrag dfun_id co_fn defaultInlinePragma) }
1037 spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag)
1039 tcSpecInst _ _ = panic "tcSpecInst"
1042 %************************************************************************
1044 Type-checking an instance method
1046 %************************************************************************
1049 - Make the method bindings, as a [(NonRec, HsBinds)], one per method
1050 - Remembering to use fresh Name (the instance method Name) as the binder
1051 - Bring the instance method Ids into scope, for the benefit of tcInstSig
1052 - Use sig_fn mapping instance method Name -> instance tyvars
1054 - Use tcValBinds to do the checking
1057 tcInstanceMethods :: DFunId -> Class -> [TcTyVar]
1060 -> ([Located TcSpecPrag], PragFun)
1062 -> InstBindings Name
1063 -> TcM ([Id], [LHsBind Id])
1064 -- The returned inst_meth_ids all have types starting
1065 -- forall tvs. theta => ...
1066 tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys
1067 (spec_inst_prags, prag_fn)
1068 op_items (VanillaInst binds _ standalone_deriv)
1069 = mapAndUnzipM tc_item op_items
1071 ----------------------
1072 tc_item :: (Id, DefMeth) -> TcM (Id, LHsBind Id)
1073 tc_item (sel_id, dm_info)
1074 = case findMethodBind (idName sel_id) binds of
1075 Just user_bind -> tc_body sel_id standalone_deriv user_bind
1076 Nothing -> tc_default sel_id dm_info
1078 ----------------------
1079 tc_body :: Id -> Bool -> LHsBind Name -> TcM (TcId, LHsBind Id)
1080 tc_body sel_id generated_code rn_bind
1081 = add_meth_ctxt sel_id generated_code rn_bind $
1082 do { (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars
1084 ; let prags = prag_fn (idName sel_id)
1085 ; meth_id1 <- addInlinePrags meth_id prags
1086 ; spec_prags <- tcSpecPrags meth_id1 prags
1087 ; bind <- tcInstanceMethodBody InstSkol
1089 meth_id1 local_meth_id meth_sig_fn
1090 (mk_meth_spec_prags meth_id1 spec_prags)
1092 ; return (meth_id1, bind) }
1094 ----------------------
1095 tc_default :: Id -> DefMeth -> TcM (TcId, LHsBind Id)
1097 tc_default sel_id (GenDefMeth dm_name)
1098 = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id dm_name
1099 ; tc_body sel_id False {- Not generated code? -} meth_bind }
1101 tc_default sel_id GenDefMeth -- Derivable type classes stuff
1102 = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id
1103 ; tc_body sel_id False {- Not generated code? -} meth_bind }
1105 tc_default sel_id NoDefMeth -- No default method at all
1106 = do { warnMissingMethod sel_id
1107 ; (meth_id, _) <- mkMethIds clas tyvars dfun_ev_vars
1109 ; return (meth_id, mkVarBind meth_id $
1110 mkLHsWrap lam_wrapper error_rhs) }
1112 error_rhs = L loc $ HsApp error_fun error_msg
1113 error_fun = L loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID
1114 error_msg = L loc (HsLit (HsStringPrim (mkFastString error_string)))
1115 meth_tau = funResultTy (applyTys (idType sel_id) inst_tys)
1116 error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ])
1117 lam_wrapper = mkWpTyLams tyvars <.> mkWpLams dfun_ev_vars
1119 tc_default sel_id (DefMeth dm_name) -- A polymorphic default method
1120 = do { -- Build the typechecked version directly,
1121 -- without calling typecheck_method;
1122 -- see Note [Default methods in instances]
1123 -- Generate /\as.\ds. let self = df as ds
1124 -- in $dm inst_tys self
1125 -- The 'let' is necessary only because HsSyn doesn't allow
1126 -- you to apply a function to a dictionary *expression*.
1128 ; self_dict <- newEvVar (ClassP clas inst_tys)
1129 ; let self_ev_bind = EvBind self_dict $
1130 EvDFunApp dfun_id (mkTyVarTys tyvars) dfun_ev_vars
1132 ; (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars
1134 ; dm_id <- tcLookupId dm_name
1135 ; let dm_inline_prag = idInlinePragma dm_id
1136 rhs = HsWrap (mkWpEvVarApps [self_dict] <.> mkWpTyApps inst_tys) $
1139 meth_bind = L loc $ VarBind { var_id = local_meth_id
1140 , var_rhs = L loc rhs
1141 , var_inline = False }
1142 meth_id1 = meth_id `setInlinePragma` dm_inline_prag
1143 -- Copy the inline pragma (if any) from the default
1144 -- method to this version. Note [INLINE and default methods]
1146 bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
1147 , abs_exports = [( tyvars, meth_id1, local_meth_id
1148 , mk_meth_spec_prags meth_id1 [])]
1149 , abs_ev_binds = EvBinds (unitBag self_ev_bind)
1150 , abs_binds = unitBag meth_bind }
1151 -- Default methods in an instance declaration can't have their own
1152 -- INLINE or SPECIALISE pragmas. It'd be possible to allow them, but
1153 -- currently they are rejected with
1154 -- "INLINE pragma lacks an accompanying binding"
1156 ; return (meth_id1, L loc bind) }
1158 ----------------------
1159 mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> TcSpecPrags
1160 -- Adapt the SPECIALISE pragmas to work for this method Id
1161 -- There are two sources:
1162 -- * spec_inst_prags: {-# SPECIALISE instance :: <blah> #-}
1163 -- These ones have the dfun inside, but [perhaps surprisingly]
1164 -- the correct wrapper
1165 -- * spec_prags_for_me: {-# SPECIALISE op :: <blah> #-}
1166 mk_meth_spec_prags meth_id spec_prags_for_me
1167 = SpecPrags (spec_prags_for_me ++
1168 [ L loc (SpecPrag meth_id wrap inl)
1169 | L loc (SpecPrag _ wrap inl) <- spec_inst_prags])
1171 loc = getSrcSpan dfun_id
1172 meth_sig_fn _ = Just ([],loc) -- The 'Just' says "yes, there's a type sig"
1173 -- But there are no scoped type variables from local_method_id
1174 -- Only the ones from the instance decl itself, which are already
1175 -- in scope. Example:
1176 -- class C a where { op :: forall b. Eq b => ... }
1177 -- instance C [c] where { op = <rhs> }
1178 -- In <rhs>, 'c' is scope but 'b' is not!
1180 -- For instance decls that come from standalone deriving clauses
1181 -- we want to print out the full source code if there's an error
1182 -- because otherwise the user won't see the code at all
1183 add_meth_ctxt sel_id generated_code rn_bind thing
1184 | generated_code = addLandmarkErrCtxt (derivBindCtxt sel_id clas inst_tys rn_bind) thing
1188 tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys
1189 _ op_items (NewTypeDerived coi _)
1192 -- class Show b => Foo a b where
1193 -- op :: a -> b -> b
1194 -- newtype N a = MkN (Tree [a])
1195 -- deriving instance (Show p, Foo Int p) => Foo Int (N p)
1196 -- -- NB: standalone deriving clause means
1197 -- -- that the contex is user-specified
1198 -- Hence op :: forall a b. Foo a b => a -> b -> b
1200 -- We're going to make an instance like
1201 -- instance (Show p, Foo Int p) => Foo Int (N p)
1204 -- $copT :: forall p. (Show p, Foo Int p) => Int -> N p -> N p
1205 -- $copT p (d1:Show p) (d2:Foo Int p)
1206 -- = op Int (Tree [p]) rep_d |> op_co
1208 -- rep_d :: Foo Int (Tree [p]) = ...d1...d2...
1209 -- op_co :: (Int -> Tree [p] -> Tree [p]) ~ (Int -> T p -> T p)
1210 -- We get op_co by substituting [Int/a] and [co/b] in type for op
1211 -- where co : [p] ~ T p
1213 -- Notice that the dictionary bindings "..d1..d2.." must be generated
1214 -- by the constraint solver, since the <context> may be
1217 = do { rep_d_stuff <- checkConstraints InstSkol tyvars dfun_ev_vars $
1218 emitWanted ScOrigin rep_pred
1220 ; mapAndUnzipM (tc_item rep_d_stuff) op_items }
1222 loc = getSrcSpan dfun_id
1224 inst_tvs = fst (tcSplitForAllTys (idType dfun_id))
1225 Just (init_inst_tys, _) = snocView inst_tys
1226 rep_ty = pFst (coercionKind co) -- [p]
1227 rep_pred = mkClassPred clas (init_inst_tys ++ [rep_ty])
1230 co = substCoWithTys inst_tvs (mkTyVarTys tyvars) $
1234 tc_item :: (TcEvBinds, EvVar) -> (Id, DefMeth) -> TcM (TcId, LHsBind TcId)
1235 tc_item (rep_ev_binds, rep_d) (sel_id, _)
1236 = do { (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars
1239 ; let meth_rhs = wrapId (mk_op_wrapper sel_id rep_d) sel_id
1240 meth_bind = VarBind { var_id = local_meth_id
1241 , var_rhs = L loc meth_rhs
1242 , var_inline = False }
1244 bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars
1245 , abs_exports = [(tyvars, meth_id,
1246 local_meth_id, noSpecPrags)]
1247 , abs_ev_binds = rep_ev_binds
1248 , abs_binds = unitBag $ L loc meth_bind }
1250 ; return (meth_id, L loc bind) }
1253 mk_op_wrapper :: Id -> EvVar -> HsWrapper
1254 mk_op_wrapper sel_id rep_d
1255 = WpCast (liftCoSubstWith sel_tvs (map mkReflCo init_inst_tys ++ [co])
1257 <.> WpEvApp (EvId rep_d)
1258 <.> mkWpTyApps (init_inst_tys ++ [rep_ty])
1260 (sel_tvs, sel_rho) = tcSplitForAllTys (idType sel_id)
1261 (_, local_meth_ty) = tcSplitPredFunTy_maybe sel_rho
1262 `orElse` pprPanic "tcInstanceMethods" (ppr sel_id)
1264 ----------------------
1265 mkMethIds :: Class -> [TcTyVar] -> [EvVar] -> [TcType] -> Id -> TcM (TcId, TcId)
1266 mkMethIds clas tyvars dfun_ev_vars inst_tys sel_id
1267 = do { uniq <- newUnique
1268 ; let meth_name = mkDerivedInternalName mkClassOpAuxOcc uniq sel_name
1269 ; local_meth_name <- newLocalName sel_name
1270 -- Base the local_meth_name on the selector name, becuase
1271 -- type errors from tcInstanceMethodBody come from here
1273 ; let meth_id = mkLocalId meth_name meth_ty
1274 local_meth_id = mkLocalId local_meth_name local_meth_ty
1275 ; return (meth_id, local_meth_id) }
1277 local_meth_ty = instantiateMethod clas sel_id inst_tys
1278 meth_ty = mkForAllTys tyvars $ mkPiTypes dfun_ev_vars local_meth_ty
1279 sel_name = idName sel_id
1281 ----------------------
1282 wrapId :: HsWrapper -> id -> HsExpr id
1283 wrapId wrapper id = mkHsWrap wrapper (HsVar id)
1285 derivBindCtxt :: Id -> Class -> [Type ] -> LHsBind Name -> SDoc
1286 derivBindCtxt sel_id clas tys _bind
1287 = vcat [ ptext (sLit "When typechecking the code for ") <+> quotes (ppr sel_id)
1288 , nest 2 (ptext (sLit "in a standalone derived instance for")
1289 <+> quotes (pprClassPred clas tys) <> colon)
1290 , nest 2 $ ptext (sLit "To see the code I am typechecking, use -ddump-deriv") ]
1293 -- , nest 2 $ pprSetDepth AllTheWay $ ppr bind ]
1295 warnMissingMethod :: Id -> TcM ()
1296 warnMissingMethod sel_id
1297 = do { warn <- doptM Opt_WarnMissingMethods
1298 ; warnTc (warn -- Warn only if -fwarn-missing-methods
1299 && not (startsWithUnderscore (getOccName sel_id)))
1300 -- Don't warn about _foo methods
1301 (ptext (sLit "No explicit method nor default method for")
1302 <+> quotes (ppr sel_id)) }
1305 Note [Export helper functions]
1306 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1307 We arrange to export the "helper functions" of an instance declaration,
1308 so that they are not subject to preInlineUnconditionally, even if their
1309 RHS is trivial. Reason: they are mentioned in the DFunUnfolding of
1310 the dict fun as Ids, not as CoreExprs, so we can't substitute a
1311 non-variable for them.
1313 We could change this by making DFunUnfoldings have CoreExprs, but it
1314 seems a bit simpler this way.
1316 Note [Default methods in instances]
1317 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1324 instance Baz Int Int
1326 From the class decl we get
1328 $dmfoo :: forall v x. Baz v x => x -> x
1331 Notice that the type is ambiguous. That's fine, though. The instance
1334 $dBazIntInt = MkBaz fooIntInt
1335 fooIntInt = $dmfoo Int Int $dBazIntInt
1337 BUT this does mean we must generate the dictionary translation of
1338 fooIntInt directly, rather than generating source-code and
1339 type-checking it. That was the bug in Trac #1061. In any case it's
1340 less work to generate the translated version!
1342 Note [INLINE and default methods]
1343 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1344 Default methods need special case. They are supposed to behave rather like
1345 macros. For exmample
1348 op1, op2 :: Bool -> a -> a
1351 op1 b x = op2 (not b) x
1353 instance Foo Int where
1354 -- op1 via default method
1357 The instance declaration should behave
1359 just as if 'op1' had been defined with the
1360 code, and INLINE pragma, from its original
1363 That is, just as if you'd written
1365 instance Foo Int where
1369 op1 b x = op2 (not b) x
1371 So for the above example we generate:
1374 {-# INLINE $dmop1 #-}
1375 -- $dmop1 has an InlineCompulsory unfolding
1376 $dmop1 d b x = op2 d (not b) x
1378 $fFooInt = MkD $cop1 $cop2
1380 {-# INLINE $cop1 #-}
1381 $cop1 = $dmop1 $fFooInt
1387 * We *copy* any INLINE pragma from the default method $dmop1 to the
1388 instance $cop1. Otherwise we'll just inline the former in the
1389 latter and stop, which isn't what the user expected
1391 * Regardless of its pragma, we give the default method an
1392 unfolding with an InlineCompulsory source. That means
1393 that it'll be inlined at every use site, notably in
1394 each instance declaration, such as $cop1. This inlining
1395 must happen even though
1396 a) $dmop1 is not saturated in $cop1
1397 b) $cop1 itself has an INLINE pragma
1399 It's vital that $dmop1 *is* inlined in this way, to allow the mutual
1400 recursion between $fooInt and $cop1 to be broken
1402 * To communicate the need for an InlineCompulsory to the desugarer
1403 (which makes the Unfoldings), we use the IsDefaultMethod constructor
1407 %************************************************************************
1409 \subsection{Error messages}
1411 %************************************************************************
1414 instDeclCtxt1 :: LHsType Name -> SDoc
1415 instDeclCtxt1 hs_inst_ty
1416 = inst_decl_ctxt (case unLoc hs_inst_ty of
1417 HsForAllTy _ _ _ (L _ (HsPredTy pred)) -> ppr pred
1418 HsPredTy pred -> ppr pred
1419 _ -> ppr hs_inst_ty) -- Don't expect this
1420 instDeclCtxt2 :: Type -> SDoc
1421 instDeclCtxt2 dfun_ty
1422 = inst_decl_ctxt (ppr (mkClassPred cls tys))
1424 (_,_,cls,tys) = tcSplitDFunTy dfun_ty
1426 inst_decl_ctxt :: SDoc -> SDoc
1427 inst_decl_ctxt doc = ptext (sLit "In the instance declaration for") <+> quotes doc
1429 atInstCtxt :: Name -> SDoc
1430 atInstCtxt name = ptext (sLit "In the associated type instance for") <+>
1433 mustBeVarArgErr :: Type -> SDoc
1434 mustBeVarArgErr ty =
1435 sep [ ptext (sLit "Arguments that do not correspond to a class parameter") <+>
1436 ptext (sLit "must be variables")
1437 , ptext (sLit "Instead of a variable, found") <+> ppr ty
1440 wrongATArgErr :: Type -> Type -> SDoc
1441 wrongATArgErr ty instTy =
1442 sep [ ptext (sLit "Type indexes must match class instance head")
1443 , ptext (sLit "Found") <+> quotes (ppr ty)
1444 <+> ptext (sLit "but expected") <+> quotes (ppr instTy)
1447 tooManyParmsErr :: Located Name -> SDoc
1448 tooManyParmsErr tc_name
1449 = ptext (sLit "Family instance has too many parameters:") <+>
1450 quotes (ppr tc_name)
1452 tooFewParmsErr :: Arity -> SDoc
1453 tooFewParmsErr arity
1454 = ptext (sLit "Family instance has too few parameters; expected") <+>
1457 wrongNumberOfParmsErr :: Arity -> SDoc
1458 wrongNumberOfParmsErr exp_arity
1459 = ptext (sLit "Number of parameters must match family declaration; expected")
1462 badBootFamInstDeclErr :: SDoc
1463 badBootFamInstDeclErr
1464 = ptext (sLit "Illegal family instance in hs-boot file")
1466 notFamily :: TyCon -> SDoc
1468 = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon)
1469 , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))]
1471 wrongKindOfFamily :: TyCon -> SDoc
1472 wrongKindOfFamily family
1473 = ptext (sLit "Wrong category of family instance; declaration was for a")
1476 kindOfFamily | isSynTyCon family = ptext (sLit "type synonym")
1477 | isAlgTyCon family = ptext (sLit "data type")
1478 | otherwise = pprPanic "wrongKindOfFamily" (ppr family)