X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcInstDcls.lhs;h=d4d8d2fbc543e6133eee500eb3955fdcca77a9e6;hp=193736dd8e47567440e43cf1e49fa551f5d54cc3;hb=HEAD;hpb=4f597914955e1eeb08243f8b0743387703fc62b6 diff --git a/compiler/typecheck/TcInstDcls.lhs b/compiler/typecheck/TcInstDcls.lhs index 193736d..d4d8d2f 100644 --- a/compiler/typecheck/TcInstDcls.lhs +++ b/compiler/typecheck/TcInstDcls.lhs @@ -12,26 +12,32 @@ import HsSyn import TcBinds import TcTyClsDecls import TcClassDcl +import TcPat( addInlinePrags ) import TcRnMonad import TcMType import TcType +import BuildTyCl import Inst import InstEnv import FamInst import FamInstEnv import TcDeriv import TcEnv -import RnEnv ( lookupImportedName ) +import RnSource ( addTcgDUs ) import TcHsType import TcUnify -import TcSimplify +import MkCore ( nO_METHOD_BINDING_ERROR_ID ) import Type import Coercion import TyCon -import TypeRep import DataCon import Class import Var +import Pair +import VarSet +import CoreUtils ( mkPiTypes ) +import CoreUnfold ( mkDFunUnfolding ) +import CoreSyn ( Expr(Var), DFunArg(..), CoreExpr ) import Id import MkId import Name @@ -40,12 +46,11 @@ import DynFlags import SrcLoc import Util import Outputable -import Maybes import Bag import BasicTypes import HscTypes import FastString - +import Maybes ( orElse ) import Data.Maybe import Control.Monad import Data.List @@ -92,40 +97,40 @@ Running example: -- A top-level definition for each instance method -- Here op1_i, op2_i are the "instance method Ids" + -- The INLINE pragma comes from the user pragma {-# INLINE [2] op1_i #-} -- From the instance decl bindings op1_i, op2_i :: forall a. C a => forall b. Ix b => [a] -> b -> b op1_i = /\a. \(d:C a). - let local_op1 :: forall a. (C a, C [a]) - => forall b. Ix b => [a] -> b -> b + let this :: C [a] + this = df_i a d -- Note [Subtle interaction of recursion and overlap] + + local_op1 :: forall b. Ix b => [a] -> b -> b local_op1 = -- Source code; run the type checker on this -- NB: Type variable 'a' (but not 'b') is in scope in -- Note [Tricky type variable scoping] - in local_op1 a d (df_i a d) + in local_op1 a d op2_i = /\a \d:C a. $dmop2 [a] (df_i a d) -- The dictionary function itself - {-# INLINE df_i #-} -- Always inline dictionary functions + {-# NOINLINE CONLIKE df_i #-} -- Never inline dictionary functions df_i :: forall a. C a -> C [a] - df_i = /\a. \d:C a. letrec d' = MkC (op1_i a d) - ($dmop2 [a] d') - in d' + df_i = /\a. \d:C a. MkC (op1_i a d) (op2_i a d) -- But see Note [Default methods in instances] -- We can't apply the type checker to the default-method call -* The dictionary function itself is inlined as vigorously as we - possibly can, so that we expose that dictionary constructor to - selectors as much as poss. That is why the op_i stuff is in - *separate* bindings, so that the df_i binding is small enough - to inline. See Note [Inline dfuns unconditionally]. + -- Use a RULE to short-circuit applications of the class ops + {-# RULE "op1@C[a]" forall a, d:C a. + op1 [a] (df_i d) = op1_i a d #-} +Note [Instances and loop breakers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * Note that df_i may be mutually recursive with both op1_i and op2_i. It's crucial that df_i is not chosen as the loop breaker, even though op1_i has a (user-specified) INLINE pragma. - Not even once! Else op1_i, op2_i may be inlined into df_i. * Instead the idea is to inline df_i into op1_i, which may then select methods from the MkC record, and thereby break the recursion with @@ -136,8 +141,142 @@ Running example: * If op1_i is marked INLINE by the user there's a danger that we won't inline df_i in it, and that in turn means that (since it'll be a loop-breaker because df_i isn't), op1_i will ironically never be - inlined. We need to fix this somehow -- perhaps allowing inlining - of INLINE funcitons inside other INLINE functions. + inlined. But this is OK: the recursion breaking happens by way of + a RULE (the magic ClassOp rule above), and RULES work inside InlineRule + unfoldings. See Note [RULEs enabled in SimplGently] in SimplUtils + +Note [ClassOp/DFun selection] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +One thing we see a lot is stuff like + op2 (df d1 d2) +where 'op2' is a ClassOp and 'df' is DFun. Now, we could inline *both* +'op2' and 'df' to get + case (MkD ($cop1 d1 d2) ($cop2 d1 d2) ... of + MkD _ op2 _ _ _ -> op2 +And that will reduce to ($cop2 d1 d2) which is what we wanted. + +But it's tricky to make this work in practice, because it requires us to +inline both 'op2' and 'df'. But neither is keen to inline without having +seen the other's result; and it's very easy to get code bloat (from the +big intermediate) if you inline a bit too much. + +Instead we use a cunning trick. + * We arrange that 'df' and 'op2' NEVER inline. + + * We arrange that 'df' is ALWAYS defined in the sylised form + df d1 d2 = MkD ($cop1 d1 d2) ($cop2 d1 d2) ... + + * We give 'df' a magical unfolding (DFunUnfolding [$cop1, $cop2, ..]) + that lists its methods. + + * We make CoreUnfold.exprIsConApp_maybe spot a DFunUnfolding and return + a suitable constructor application -- inlining df "on the fly" as it + were. + + * We give the ClassOp 'op2' a BuiltinRule that extracts the right piece + iff its argument satisfies exprIsConApp_maybe. This is done in + MkId mkDictSelId + + * We make 'df' CONLIKE, so that shared uses stil match; eg + let d = df d1 d2 + in ...(op2 d)...(op1 d)... + +Note [Single-method classes] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If the class has just one method (or, more accurately, just one element +of {superclasses + methods}), then we use a different strategy. + + class C a where op :: a -> a + instance C a => C [a] where op = + +We translate the class decl into a newtype, which just gives a +top-level axiom. The "constructor" MkC expands to a cast, as does the +class-op selector. + + axiom Co:C a :: C a ~ (a->a) + + op :: forall a. C a -> (a -> a) + op a d = d |> (Co:C a) + + MkC :: forall a. (a->a) -> C a + MkC = /\a.\op. op |> (sym Co:C a) + +The clever RULE stuff doesn't work now, because ($df a d) isn't +a constructor application, so exprIsConApp_maybe won't return +Just . + +Instead, we simply rely on the fact that casts are cheap: + + $df :: forall a. C a => C [a] + {-# INLINE df #-} -- NB: INLINE this + $df = /\a. \d. MkC [a] ($cop_list a d) + = $cop_list |> forall a. C a -> (sym (Co:C [a])) + + $cop_list :: forall a. C a => [a] -> [a] + $cop_list = + +So if we see + (op ($df a d)) +we'll inline 'op' and '$df', since both are simply casts, and +good things happen. + +Why do we use this different strategy? Because otherwise we +end up with non-inlined dictionaries that look like + $df = $cop |> blah +which adds an extra indirection to every use, which seems stupid. See +Trac #4138 for an example (although the regression reported there +wasn't due to the indirction). + +There is an awkward wrinkle though: we want to be very +careful when we have + instance C a => C [a] where + {-# INLINE op #-} + op = ... +then we'll get an INLINE pragma on $cop_list but it's important that +$cop_list only inlines when it's applied to *two* arguments (the +dictionary and the list argument). So we nust not eta-expand $df +above. We ensure that this doesn't happen by putting an INLINE +pragma on the dfun itself; after all, it ends up being just a cast. + +There is one more dark corner to the INLINE story, even more deeply +buried. Consider this (Trac #3772): + + class DeepSeq a => C a where + gen :: Int -> a + + instance C a => C [a] where + gen n = ... + + class DeepSeq a where + deepSeq :: a -> b -> b + + instance DeepSeq a => DeepSeq [a] where + {-# INLINE deepSeq #-} + deepSeq xs b = foldr deepSeq b xs + +That gives rise to these defns: + + $cdeepSeq :: DeepSeq a -> [a] -> b -> b + -- User INLINE( 3 args )! + $cdeepSeq a (d:DS a) b (x:[a]) (y:b) = ... + + $fDeepSeq[] :: DeepSeq a -> DeepSeq [a] + -- DFun (with auto INLINE pragma) + $fDeepSeq[] a d = $cdeepSeq a d |> blah + + $cp1 a d :: C a => DeepSep [a] + -- We don't want to eta-expand this, lest + -- $cdeepSeq gets inlined in it! + $cp1 a d = $fDeepSep[] a (scsel a d) + + $fC[] :: C a => C [a] + -- Ordinary DFun + $fC[] a d = MkC ($cp1 a d) ($cgen a d) + +Here $cp1 is the code that generates the superclass for C [a]. The +issue is this: we must not eta-expand $cp1 either, or else $fDeepSeq[] +and then $cdeepSeq will inline there, which is definitely wrong. Like +on the dfun, we solve this by adding an INLINE pragma to $cp1. Note [Subtle interaction of recursion and overlap] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -146,7 +285,7 @@ Consider this instance C a => C [a] where op1 x = op2 x ++ op2 x op2 x = ... - intance C [Int] where + instance C [Int] where ... When type-checking the C [a] instance, we need a C [a] dictionary (for @@ -174,11 +313,12 @@ See the overlapping instances for RegexContext, and the fact that they call 'nullFail' just like the example above. The DoCon package also does the same thing; it shows up in module Fraction.hs -Conclusion: when typechecking the methods in a C [a] instance, we want -to have C [a] available. That is why we have the strange local let in -the definition of op1_i in the example above. We can typecheck the -defintion of local_op1, and then supply the "this" argument via an -explicit call to the dfun (which in turn will be inlined). +Conclusion: when typechecking the methods in a C [a] instance, we want to +treat the 'a' as an *existential* type variable, in the sense described +by Note [Binding when looking up instances]. That is why isOverlappableTyVar +responds True to an InstSkol, which is the kind of skolem we use in +tcInstDecl2. + Note [Tricky type variable scoping] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -198,93 +338,6 @@ which brings appropriate tyvars into scope. This happens for both and for , but that doesn't matter: the *renamer* will have complained if 'b' is mentioned in . -Note [Inline dfuns unconditionally] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The code above unconditionally inlines dict funs. Here's why. -Consider this program: - - test :: Int -> Int -> Bool - test x y = (x,y) == (y,x) || test y x - -- Recursive to avoid making it inline. - -This needs the (Eq (Int,Int)) instance. If we inline that dfun -the code we end up with is good: - - Test.$wtest = - \r -> case ==# [ww ww1] of wild { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> - case ==# [ww1 ww] of wild1 { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> PrelBase.True []; - }; - }; - Test.test = \r [w w1] - case w of w2 { - PrelBase.I# ww -> - case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; }; - }; - -If we don't inline the dfun, the code is not nearly as good: - - (==) = case PrelTup.$fEq(,) PrelBase.$fEqInt PrelBase.$fEqInt of tpl { - PrelBase.:DEq tpl1 tpl2 -> tpl2; - }; - - Test.$wtest = - \r [ww ww1] - let { y = PrelBase.I#! [ww1]; } in - let { x = PrelBase.I#! [ww]; } in - let { sat_slx = PrelTup.(,)! [y x]; } in - let { sat_sly = PrelTup.(,)! [x y]; - } in - case == sat_sly sat_slx of wild { - PrelBase.False -> Test.$wtest ww1 ww; - PrelBase.True -> PrelBase.True []; - }; - - Test.test = - \r [w w1] - case w of w2 { - PrelBase.I# ww -> - case w1 of w3 { PrelBase.I# ww1 -> Test.$wtest ww ww1; }; - }; - -Why didn't GHC inline $fEq in those days? Because it looked big: - - PrelTup.zdfEqZ1T{-rcX-} - = \ @ a{-reT-} :: * @ b{-reS-} :: * - zddEq{-rf6-} _Ks :: {PrelBase.Eq{-23-} a{-reT-}} - zddEq1{-rf7-} _Ks :: {PrelBase.Eq{-23-} b{-reS-}} -> - let { - zeze{-rf0-} _Kl :: (b{-reS-} -> b{-reS-} -> PrelBase.Bool{-3c-}) - zeze{-rf0-} = PrelBase.zeze{-01L-}@ b{-reS-} zddEq1{-rf7-} } in - let { - zeze1{-rf3-} _Kl :: (a{-reT-} -> a{-reT-} -> PrelBase.Bool{-3c-}) - zeze1{-rf3-} = PrelBase.zeze{-01L-} @ a{-reT-} zddEq{-rf6-} } in - let { - zeze2{-reN-} :: ((a{-reT-}, b{-reS-}) -> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-}) - zeze2{-reN-} = \ ds{-rf5-} _Ks :: (a{-reT-}, b{-reS-}) - ds1{-rf4-} _Ks :: (a{-reT-}, b{-reS-}) -> - case ds{-rf5-} - of wild{-reW-} _Kd { (a1{-rf2-} _Ks, a2{-reZ-} _Ks) -> - case ds1{-rf4-} - of wild1{-reX-} _Kd { (b1{-rf1-} _Ks, b2{-reY-} _Ks) -> - PrelBase.zaza{-r4e-} - (zeze1{-rf3-} a1{-rf2-} b1{-rf1-}) - (zeze{-rf0-} a2{-reZ-} b2{-reY-}) - } - } } in - let { - a1{-reR-} :: ((a{-reT-}, b{-reS-})-> (a{-reT-}, b{-reS-})-> PrelBase.Bool{-3c-}) - a1{-reR-} = \ a2{-reV-} _Ks :: (a{-reT-}, b{-reS-}) - b1{-reU-} _Ks :: (a{-reT-}, b{-reS-}) -> - PrelBase.not{-r6I-} (zeze2{-reN-} a2{-reV-} b1{-reU-}) - } in - PrelBase.zdwZCDEq{-r8J-} @ (a{-reT-}, b{-reS-}) a1{-reR-} zeze2{-reN-}) - -and it's not as bad as it seems, because it's further dramatically -simplified: only zeze2 is extracted and its body is simplified. %************************************************************************ @@ -312,88 +365,63 @@ tcInstDecls1 tycl_decls inst_decls deriv_decls -- round) -- (1) Do class and family instance declarations - ; let { idxty_decls = filter (isFamInstDecl . unLoc) tycl_decls } + ; idx_tycons <- mapAndRecoverM (tcFamInstDecl TopLevel) $ + filter (isFamInstDecl . unLoc) tycl_decls ; local_info_tycons <- mapAndRecoverM tcLocalInstDecl1 inst_decls - ; idx_tycons <- mapAndRecoverM tcIdxTyInstDeclTL idxty_decls ; let { (local_info, at_tycons_s) = unzip local_info_tycons - ; at_idx_tycon = concat at_tycons_s ++ idx_tycons - ; clas_decls = filter (isClassDecl.unLoc) tycl_decls - ; implicit_things = concatMap implicitTyThings at_idx_tycon - } + ; at_idx_tycons = concat at_tycons_s ++ idx_tycons + ; implicit_things = concatMap implicitTyConThings at_idx_tycons + ; aux_binds = mkRecSelBinds at_idx_tycons } -- (2) Add the tycons of indexed types and their implicit -- tythings to the global environment - ; tcExtendGlobalEnv (at_idx_tycon ++ implicit_things) $ do { + ; tcExtendGlobalEnv (map ATyCon at_idx_tycons ++ implicit_things) $ do { - -- (3) Instances from generic class declarations - ; generic_inst_info <- getGenericInstances clas_decls -- Next, construct the instance environment so far, consisting -- of - -- a) local instance decls - -- b) generic instances - -- c) local family instance decls - ; addInsts local_info $ do { - ; addInsts generic_inst_info $ do { - ; addFamInsts at_idx_tycon $ do { - - -- (4) Compute instances from "deriving" clauses; + -- (a) local instance decls + -- (b) local family instance decls + ; addInsts local_info $ + addFamInsts at_idx_tycons $ do { + + -- (3) Compute instances from "deriving" clauses; -- This stuff computes a context for the derived instance -- decl, so it needs to know about all the instances possible -- NB: class instance declarations can contain derivings as -- part of associated data type declarations - failIfErrsM -- If the addInsts stuff gave any errors, don't - -- try the deriving stuff, becuase that may give - -- more errors still - ; (deriv_inst_info, deriv_binds) <- tcDeriving tycl_decls inst_decls - deriv_decls - ; addInsts deriv_inst_info $ do { - - ; gbl_env <- getGblEnv - ; return (gbl_env, - generic_inst_info ++ deriv_inst_info ++ local_info, - deriv_binds) - }}}}}} - where - -- Make sure that toplevel type instance are not for associated types. - -- !!!TODO: Need to perform this check for the TyThing of type functions, - -- too. - tcIdxTyInstDeclTL ldecl@(L loc decl) = - do { tything <- tcFamInstDecl ldecl - ; setSrcSpan loc $ - when (isAssocFamily tything) $ - addErr $ assocInClassErr (tcdName decl) - ; return tything - } - isAssocFamily (ATyCon tycon) = - case tyConFamInst_maybe tycon of - Nothing -> panic "isAssocFamily: no family?!?" - Just (fam, _) -> isTyConAssoc fam - isAssocFamily _ = panic "isAssocFamily: no tycon?!?" - -assocInClassErr :: Name -> SDoc -assocInClassErr name = - ptext (sLit "Associated type") <+> quotes (ppr name) <+> - ptext (sLit "must be inside a class instance") + failIfErrsM -- If the addInsts stuff gave any errors, don't + -- try the deriving stuff, because that may give + -- more errors still + ; (deriv_inst_info, deriv_binds, deriv_dus, deriv_tys, deriv_ty_insts) + <- tcDeriving tycl_decls inst_decls deriv_decls + + -- Extend the global environment also with the generated datatypes for + -- the generic representation + ; let all_tycons = map ATyCon (deriv_tys ++ deriv_ty_insts) + ; gbl_env <- tcExtendGlobalEnv all_tycons $ + tcExtendGlobalEnv (concatMap implicitTyThings all_tycons) $ + addFamInsts deriv_ty_insts $ + addInsts deriv_inst_info getGblEnv + ; return ( addTcgDUs gbl_env deriv_dus, + deriv_inst_info ++ local_info, + aux_binds `plusHsValBinds` deriv_binds) + }}} addInsts :: [InstInfo Name] -> TcM a -> TcM a addInsts infos thing_inside = tcExtendLocalInstEnv (map iSpec infos) thing_inside -addFamInsts :: [TyThing] -> TcM a -> TcM a +addFamInsts :: [TyCon] -> TcM a -> TcM a addFamInsts tycons thing_inside - = tcExtendLocalFamInstEnv (map mkLocalFamInstTyThing tycons) thing_inside - where - mkLocalFamInstTyThing (ATyCon tycon) = mkLocalFamInst tycon - mkLocalFamInstTyThing tything = pprPanic "TcInstDcls.addFamInsts" - (ppr tything) + = tcExtendLocalFamInstEnv (map mkLocalFamInst tycons) thing_inside \end{code} \begin{code} tcLocalInstDecl1 :: LInstDecl Name - -> TcM (InstInfo Name, [TyThing]) + -> TcM (InstInfo Name, [TyCon]) -- A source-file instance declaration -- Type-check all the stuff before the "where" -- @@ -406,15 +434,13 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) ; checkTc (not is_boot || (isEmptyLHsBinds binds && null uprags)) badBootDeclErr - ; (tyvars, theta, tau) <- tcHsInstHead poly_ty - - -- Now, check the validity of the instance. - ; (clas, inst_tys) <- checkValidInstHead tau - ; checkValidInstance tyvars theta clas inst_tys + ; (tyvars, theta, clas, inst_tys) <- tcHsInstHead poly_ty + ; checkValidInstance poly_ty tyvars theta clas inst_tys -- Next, process any associated types. ; idx_tycons <- recoverM (return []) $ - do { idx_tycons <- checkNoErrs $ mapAndRecoverM tcFamInstDecl ats + do { idx_tycons <- checkNoErrs $ + mapAndRecoverM (tcFamInstDecl NotTopLevel) ats ; checkValidAndMissingATs clas (tyvars, inst_tys) (zip ats idx_tycons) ; return idx_tycons } @@ -429,8 +455,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) dfun = mkDictFunId dfun_name tyvars theta' clas inst_tys ispec = mkLocalInstance dfun overlap_flag - ; return (InstInfo { iSpec = ispec, - iBinds = VanillaInst binds uprags }, + ; return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags False }, idx_tycons) } where @@ -440,7 +465,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) checkValidAndMissingATs :: Class -> ([TyVar], [TcType]) -- instance types -> [(LTyClDecl Name, -- source form of AT - TyThing)] -- Core form of AT + TyCon)] -- Core form of AT -> TcM () checkValidAndMissingATs clas inst_tys ats = do { -- Issue a warning for each class AT that is not defined in this @@ -458,12 +483,11 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) ; mapM_ (checkIndexes clas inst_tys) ats } - checkIndexes clas inst_tys (hsAT, ATyCon tycon) = + checkIndexes clas inst_tys (hsAT, tycon) -- !!!TODO: check that this does the Right Thing for indexed synonyms, too! - checkIndexes' clas inst_tys hsAT - (tyConTyVars tycon, - snd . fromJust . tyConFamInst_maybe $ tycon) - checkIndexes _ _ _ = panic "checkIndexes" + = checkIndexes' clas inst_tys hsAT + (tyConTyVars tycon, + snd . fromJust . tyConFamInst_maybe $ tycon) checkIndexes' clas (instTvs, instTys) hsAT (atTvs, atTys) = let atName = tcdName . unLoc $ hsAT @@ -472,11 +496,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) addErrCtxt (atInstCtxt atName) $ case find ((atName ==) . tyConName) (classATs clas) of Nothing -> addErrTc $ badATErr clas atName -- not in this class - Just atDecl -> - case assocTyConArgPoss_maybe atDecl of - Nothing -> panic "checkIndexes': AT has no args poss?!?" - Just poss -> - + Just atycon -> -- The following is tricky! We need to deal with three -- complications: (1) The AT possibly only uses a subset of -- the class parameters as indexes and those it uses may be in @@ -484,6 +504,13 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) -- which must be type variables; and (3) variables in AT and -- instance head will be different `Name's even if their -- source lexemes are identical. + -- + -- e.g. class C a b c where + -- data D b a :: * -> * -- NB (1) b a, omits c + -- instance C [x] Bool Char where + -- data D Bool [x] v = MkD x [v] -- NB (2) v + -- -- NB (3) the x in 'instance C...' have differnt + -- -- Names to x's in 'data D...' -- -- Re (1), `poss' contains a permutation vector to extract the -- class parameters in the right order. @@ -497,7 +524,19 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) -- instance types with the instance type variable sharing its -- source lexeme. -- - let relevantInstTys = map (instTys !!) poss + let poss :: [Int] + -- For *associated* type families, gives the position + -- of that 'TyVar' in the class argument list (0-indexed) + -- e.g. class C a b c where { type F c a :: *->* } + -- Then we get Just [2,0] + poss = catMaybes [ tv `elemIndex` classTyVars clas + | tv <- tyConTyVars atycon] + -- We will get Nothings for the "extra" type + -- variables in an associated data type + -- e.g. class C a where { data D a :: *->* } + -- here D gets arity 2 and has two tyvars + + relevantInstTys = map (instTys !!) poss instArgs = map Just relevantInstTys ++ repeat Nothing -- extra arguments renaming = substSameTyVar atTvs instTvs @@ -508,8 +547,8 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) | isTyVarTy ty = return () | otherwise = addErrTc $ mustBeVarArgErr ty checkIndex ty (Just instTy) - | ty `tcEqType` instTy = return () - | otherwise = addErrTc $ wrongATArgErr ty instTy + | ty `eqType` instTy = return () + | otherwise = addErrTc $ wrongATArgErr ty instTy listToNameSet = addListToNameSet emptyNameSet @@ -522,7 +561,182 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) tv1 `sameLexeme` tv2 = nameOccName (tyVarName tv1) == nameOccName (tyVarName tv2) in - extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement + TcType.extendTvSubst (substSameTyVar tvs replacingTvs) tv replacement +\end{code} + + +%************************************************************************ +%* * + Type checking family instances +%* * +%************************************************************************ + +Family instances are somewhat of a hybrid. They are processed together with +class instance heads, but can contain data constructors and hence they share a +lot of kinding and type checking code with ordinary algebraic data types (and +GADTs). + +\begin{code} +tcFamInstDecl :: TopLevelFlag -> LTyClDecl Name -> TcM TyCon +tcFamInstDecl top_lvl (L loc decl) + = -- Prime error recovery, set source location + setSrcSpan loc $ + tcAddDeclCtxt decl $ + do { -- type family instances require -XTypeFamilies + -- and can't (currently) be in an hs-boot file + ; type_families <- xoptM Opt_TypeFamilies + ; is_boot <- tcIsHsBoot -- Are we compiling an hs-boot file? + ; checkTc type_families $ badFamInstDecl (tcdLName decl) + ; checkTc (not is_boot) $ badBootFamInstDeclErr + + -- Perform kind and type checking + ; tc <- tcFamInstDecl1 decl + ; checkValidTyCon tc -- Remember to check validity; + -- no recursion to worry about here + + -- Check that toplevel type instances are not for associated types. + ; when (isTopLevel top_lvl && isAssocFamily tc) + (addErr $ assocInClassErr (tcdName decl)) + + ; return tc } + +isAssocFamily :: TyCon -> Bool -- Is an assocaited type +isAssocFamily tycon + = case tyConFamInst_maybe tycon of + Nothing -> panic "isAssocFamily: no family?!?" + Just (fam, _) -> isTyConAssoc fam + +assocInClassErr :: Name -> SDoc +assocInClassErr name + = ptext (sLit "Associated type") <+> quotes (ppr name) <+> + ptext (sLit "must be inside a class instance") + + + +tcFamInstDecl1 :: TyClDecl Name -> TcM TyCon + + -- "type instance" +tcFamInstDecl1 (decl@TySynonym {tcdLName = L loc tc_name}) + = kcIdxTyPats decl $ \k_tvs k_typats resKind family -> + do { -- check that the family declaration is for a synonym + checkTc (isFamilyTyCon family) (notFamily family) + ; checkTc (isSynTyCon family) (wrongKindOfFamily family) + + ; -- (1) kind check the right-hand side of the type equation + ; k_rhs <- kcCheckLHsType (tcdSynRhs decl) (EK resKind EkUnk) + -- ToDo: the ExpKind could be better + + -- we need the exact same number of type parameters as the family + -- declaration + ; let famArity = tyConArity family + ; checkTc (length k_typats == famArity) $ + wrongNumberOfParmsErr famArity + + -- (2) type check type equation + ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars + ; t_typats <- mapM tcHsKindedType k_typats + ; t_rhs <- tcHsKindedType k_rhs + + -- (3) check the well-formedness of the instance + ; checkValidTypeInst t_typats t_rhs + + -- (4) construct representation tycon + ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc + ; buildSynTyCon rep_tc_name t_tvs (SynonymTyCon t_rhs) + (typeKind t_rhs) + NoParentTyCon (Just (family, t_typats)) + }} + + -- "newtype instance" and "data instance" +tcFamInstDecl1 (decl@TyData {tcdND = new_or_data, tcdLName = L loc tc_name, + tcdCons = cons}) + = kcIdxTyPats decl $ \k_tvs k_typats resKind fam_tycon -> + do { -- check that the family declaration is for the right kind + checkTc (isFamilyTyCon fam_tycon) (notFamily fam_tycon) + ; checkTc (isAlgTyCon fam_tycon) (wrongKindOfFamily fam_tycon) + + ; -- (1) kind check the data declaration as usual + ; k_decl <- kcDataDecl decl k_tvs + ; let k_ctxt = tcdCtxt k_decl + k_cons = tcdCons k_decl + + -- result kind must be '*' (otherwise, we have too few patterns) + ; checkTc (isLiftedTypeKind resKind) $ tooFewParmsErr (tyConArity fam_tycon) + + -- (2) type check indexed data type declaration + ; tcTyVarBndrs k_tvs $ \t_tvs -> do { -- turn kinded into proper tyvars + + -- kind check the type indexes and the context + ; t_typats <- mapM tcHsKindedType k_typats + ; stupid_theta <- tcHsKindedContext k_ctxt + + -- (3) Check that + -- (a) left-hand side contains no type family applications + -- (vanilla synonyms are fine, though, and we checked for + -- foralls earlier) + ; mapM_ checkTyFamFreeness t_typats + + ; dataDeclChecks tc_name new_or_data stupid_theta k_cons + + -- (4) construct representation tycon + ; rep_tc_name <- newFamInstTyConName tc_name t_typats loc + ; let ex_ok = True -- Existentials ok for type families! + ; fixM (\ rep_tycon -> do + { let orig_res_ty = mkTyConApp fam_tycon t_typats + ; data_cons <- tcConDecls ex_ok rep_tycon + (t_tvs, orig_res_ty) k_cons + ; tc_rhs <- + case new_or_data of + DataType -> return (mkDataTyConRhs data_cons) + NewType -> ASSERT( not (null data_cons) ) + mkNewTyConRhs rep_tc_name rep_tycon (head data_cons) + ; buildAlgTyCon rep_tc_name t_tvs stupid_theta tc_rhs Recursive + h98_syntax NoParentTyCon (Just (fam_tycon, t_typats)) + -- We always assume that indexed types are recursive. Why? + -- (1) Due to their open nature, we can never be sure that a + -- further instance might not introduce a new recursive + -- dependency. (2) They are always valid loop breakers as + -- they involve a coercion. + }) + }} + where + h98_syntax = case cons of -- All constructors have same shape + L _ (ConDecl { con_res = ResTyGADT _ }) : _ -> False + _ -> True + +tcFamInstDecl1 d = pprPanic "tcFamInstDecl1" (ppr d) + +-- Kind checking of indexed types +-- - + +-- Kind check type patterns and kind annotate the embedded type variables. +-- +-- * Here we check that a type instance matches its kind signature, but we do +-- not check whether there is a pattern for each type index; the latter +-- check is only required for type synonym instances. + +kcIdxTyPats :: TyClDecl Name + -> ([LHsTyVarBndr Name] -> [LHsType Name] -> Kind -> TyCon -> TcM a) + -- ^^kinded tvs ^^kinded ty pats ^^res kind + -> TcM a +kcIdxTyPats decl thing_inside + = kcHsTyVars (tcdTyVars decl) $ \tvs -> + do { let tc_name = tcdLName decl + ; fam_tycon <- tcLookupLocatedTyCon tc_name + ; let { (kinds, resKind) = splitKindFunTys (tyConKind fam_tycon) + ; hs_typats = fromJust $ tcdTyPats decl } + + -- we may not have more parameters than the kind indicates + ; checkTc (length kinds >= length hs_typats) $ + tooManyParmsErr (tcdLName decl) + + -- type functions can have a higher-kinded result + ; let resultKind = mkArrowKinds (drop (length hs_typats) kinds) resKind + ; typats <- zipWithM kcCheckLHsType hs_typats + [ EK kind (EkArg (ppr tc_name) n) + | (kind,n) <- kinds `zip` [1..]] + ; thing_inside tvs typats resultKind fam_tycon + } \end{code} @@ -534,7 +748,7 @@ tcLocalInstDecl1 (L loc (InstDecl poly_ty binds uprags ats)) \begin{code} tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name] - -> TcM (LHsBinds Id, TcLclEnv) + -> TcM (LHsBinds Id) -- (a) From each class declaration, -- generate any default-method bindings -- (b) From each instance decl @@ -542,269 +756,288 @@ tcInstDecls2 :: [LTyClDecl Name] -> [InstInfo Name] tcInstDecls2 tycl_decls inst_decls = do { -- (a) Default methods from class decls - (dm_binds_s, dm_ids_s) <- mapAndUnzipM tcClassDecl2 $ - filter (isClassDecl.unLoc) tycl_decls - ; tcExtendIdEnv (concat dm_ids_s) $ do - + let class_decls = filter (isClassDecl . unLoc) tycl_decls + ; dm_binds_s <- mapM tcClassDecl2 class_decls + ; let dm_binds = unionManyBags dm_binds_s + -- (b) instance declarations - ; inst_binds_s <- mapM tcInstDecl2 inst_decls + ; let dm_ids = collectHsBindsBinders dm_binds + -- Add the default method Ids (again) + -- See Note [Default methods and instances] + ; inst_binds_s <- tcExtendIdEnv dm_ids $ + mapM tcInstDecl2 inst_decls -- Done - ; let binds = unionManyBags dm_binds_s `unionBags` - unionManyBags inst_binds_s - ; tcl_env <- getLclEnv -- Default method Ids in here - ; return (binds, tcl_env) } + ; return (dm_binds `unionBags` unionManyBags inst_binds_s) } \end{code} +See Note [Default methods and instances] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The default method Ids are already in the type environment (see Note +[Default method Ids and Template Haskell] in TcTyClsDcls), BUT they +don't have their InlinePragmas yet. Usually that would not matter, +because the simplifier propagates information from binding site to +use. But, unusually, when compiling instance decls we *copy* the +INLINE pragma from the default method to the method for that +particular operation (see Note [INLINE and default methods] below). + +So right here in tcInstDecl2 we must re-extend the type envt with +the default method Ids replete with their INLINE pragmas. Urk. \begin{code} -tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id) --- Returns a binding for the dfun ------------------------- --- Derived newtype instances; surprisingly tricky! --- --- class Show a => Foo a b where ... --- newtype N a = MkN (Tree [a]) deriving( Foo Int ) --- --- The newtype gives an FC axiom looking like --- axiom CoN a :: N a :=: Tree [a] --- (see Note [Newtype coercions] in TyCon for this unusual form of axiom) --- --- So all need is to generate a binding looking like: --- dfunFooT :: forall a. (Foo Int (Tree [a], Show (N a)) => Foo Int (N a) --- dfunFooT = /\a. \(ds:Show (N a)) (df:Foo (Tree [a])). --- case df `cast` (Foo Int (sym (CoN a))) of --- Foo _ op1 .. opn -> Foo ds op1 .. opn --- --- If there are no superclasses, matters are simpler, because we don't need the case --- see Note [Newtype deriving superclasses] in TcDeriv.lhs - -tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = NewTypeDerived }) - = do { let dfun_id = instanceDFunId ispec - rigid_info = InstSkol - origin = SigOrigin rigid_info - inst_ty = idType dfun_id - ; (tvs, theta, inst_head_ty) <- tcSkolSigType rigid_info inst_ty - -- inst_head_ty is a PredType - - ; let (cls, cls_inst_tys) = tcSplitDFunHead inst_head_ty - (class_tyvars, sc_theta, _, _) = classBigSig cls - cls_tycon = classTyCon cls - sc_theta' = substTheta (zipOpenTvSubst class_tyvars cls_inst_tys) sc_theta - - Just (initial_cls_inst_tys, last_ty) = snocView cls_inst_tys - (nt_tycon, tc_args) = tcSplitTyConApp last_ty -- Can't fail - rep_ty = newTyConInstRhs nt_tycon tc_args - - rep_pred = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty]) - -- In our example, rep_pred is (Foo Int (Tree [a])) - the_coercion = make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args - -- Coercion of kind (Foo Int (Tree [a]) ~ Foo Int (N a) - - ; inst_loc <- getInstLoc origin - ; sc_loc <- getInstLoc InstScOrigin - ; dfun_dicts <- newDictBndrs inst_loc theta - ; sc_dicts <- newDictBndrs sc_loc sc_theta' - ; this_dict <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys) - ; rep_dict <- newDictBndr inst_loc rep_pred - - -- Figure out bindings for the superclass context from dfun_dicts - -- Don't include this_dict in the 'givens', else - -- wanted_sc_insts get bound by just selecting from this_dict!! - ; sc_binds <- addErrCtxt superClassCtxt $ - tcSimplifySuperClasses inst_loc dfun_dicts (rep_dict:sc_dicts) - - ; let coerced_rep_dict = wrapId the_coercion (instToId rep_dict) - - ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict - ; let dict_bind = noLoc $ VarBind (instToId this_dict) (noLoc body) - - ; return (unitBag $ noLoc $ - AbsBinds tvs (map instToVar dfun_dicts) - [(tvs, dfun_id, instToId this_dict, [])] - (dict_bind `consBag` sc_binds)) } - where - ----------------------- - -- make_coercion - -- The inst_head looks like (C s1 .. sm (T a1 .. ak)) - -- But we want the coercion (C s1 .. sm (sym (CoT a1 .. ak))) - -- with kind (C s1 .. sm (T a1 .. ak) :=: C s1 .. sm ) - -- where rep_ty is the (eta-reduced) type rep of T - -- So we just replace T with CoT, and insert a 'sym' - -- NB: we know that k will be >= arity of CoT, because the latter fully eta-reduced - - make_coercion cls_tycon initial_cls_inst_tys nt_tycon tc_args - | Just co_con <- newTyConCo_maybe nt_tycon - , let co = mkSymCoercion (mkTyConApp co_con tc_args) - = WpCast (mkTyConApp cls_tycon (initial_cls_inst_tys ++ [co])) - | otherwise -- The newtype is transparent; no need for a cast - = idHsWrapper - - ----------------------- - -- (make_body C tys scs coreced_rep_dict) - -- returns - -- (case coerced_rep_dict of { C _ ops -> C scs ops }) - -- But if there are no superclasses, it returns just coerced_rep_dict - -- See Note [Newtype deriving superclasses] in TcDeriv.lhs - - make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict - | null sc_dicts -- Case (a) - = return coerced_rep_dict - | otherwise -- Case (b) - = do { op_ids <- newSysLocalIds (fsLit "op") op_tys - ; dummy_sc_dict_ids <- newSysLocalIds (fsLit "sc") (map idType sc_dict_ids) - ; let the_pat = ConPatOut { pat_con = noLoc cls_data_con, pat_tvs = [], - pat_dicts = dummy_sc_dict_ids, - pat_binds = emptyLHsBinds, - pat_args = PrefixCon (map nlVarPat op_ids), - pat_ty = pat_ty} - the_match = mkSimpleMatch [noLoc the_pat] the_rhs - the_rhs = mkHsConApp cls_data_con cls_inst_tys $ - map HsVar (sc_dict_ids ++ op_ids) - - -- Warning: this HsCase scrutinises a value with a PredTy, which is - -- never otherwise seen in Haskell source code. It'd be - -- nicer to generate Core directly! - ; return (HsCase (noLoc coerced_rep_dict) $ - MatchGroup [the_match] (mkFunTy pat_ty pat_ty)) } - where - sc_dict_ids = map instToId sc_dicts - pat_ty = mkTyConApp cls_tycon cls_inst_tys - cls_data_con = head (tyConDataCons cls_tycon) - cls_arg_tys = dataConInstArgTys cls_data_con cls_inst_tys - op_tys = dropList sc_dict_ids cls_arg_tys - ------------------------- --- Ordinary instances - -tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = VanillaInst monobinds uprags }) - = let - dfun_id = instanceDFunId ispec - rigid_info = InstSkol - inst_ty = idType dfun_id - loc = getSrcSpan dfun_id - in - -- Prime error recovery - recoverM (return emptyLHsBinds) $ +tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id) + -- Returns a binding for the dfun +tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = ibinds }) + = recoverM (return emptyLHsBinds) $ setSrcSpan loc $ - addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ do + addErrCtxt (instDeclCtxt2 (idType dfun_id)) $ + do { -- Instantiate the instance decl with skolem constants + ; (inst_tyvars, dfun_theta, inst_head) <- tcSkolDFunType (idType dfun_id) + -- We instantiate the dfun_id with superSkolems. + -- See Note [Subtle interaction of recursion and overlap] + -- and Note [Binding when looking up instances] + ; let (clas, inst_tys) = tcSplitDFunHead inst_head + (class_tyvars, sc_theta, _, op_items) = classBigSig clas + sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys) sc_theta + n_ty_args = length inst_tyvars + n_silent = dfunNSilent dfun_id + (silent_theta, orig_theta) = splitAt n_silent dfun_theta + + ; silent_ev_vars <- mapM newSilentGiven silent_theta + ; orig_ev_vars <- newEvVars orig_theta + ; let dfun_ev_vars = silent_ev_vars ++ orig_ev_vars + + ; (sc_dicts, sc_args) + <- mapAndUnzipM (tcSuperClass n_ty_args dfun_ev_vars) sc_theta' + + -- Check that any superclasses gotten from a silent arguemnt + -- can be deduced from the originally-specified dfun arguments + ; ct_loc <- getCtLoc ScOrigin + ; _ <- checkConstraints skol_info inst_tyvars orig_ev_vars $ + emitFlats $ listToBag $ + [ mkEvVarX sc ct_loc | sc <- sc_dicts, isSilentEvVar sc ] + + -- Deal with 'SPECIALISE instance' pragmas + -- See Note [SPECIALISE instance pragmas] + ; spec_info@(spec_inst_prags,_) <- tcSpecInstPrags dfun_id ibinds - -- Instantiate the instance decl with skolem constants - (inst_tyvars', dfun_theta', inst_head') <- tcSkolSigType rigid_info inst_ty - -- These inst_tyvars' scope over the 'where' part + -- Typecheck the methods + ; (meth_ids, meth_binds) + <- tcExtendTyVarEnv inst_tyvars $ + -- The inst_tyvars scope over the 'where' part -- Those tyvars are inside the dfun_id's type, which is a bit -- bizarre, but OK so long as you realise it! - let - (clas, inst_tys') = tcSplitDFunHead inst_head' - (class_tyvars, sc_theta, _, op_items) = classBigSig clas - - -- Instantiate the super-class context with inst_tys - sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta - (eq_sc_theta',dict_sc_theta') = partition isEqPred sc_theta' - origin = SigOrigin rigid_info - (eq_dfun_theta',dict_dfun_theta') = partition isEqPred dfun_theta' - - -- Create dictionary Ids from the specified instance contexts. - sc_loc <- getInstLoc InstScOrigin - sc_dicts <- newDictBndrs sc_loc dict_sc_theta' - inst_loc <- getInstLoc origin - sc_covars <- mkMetaCoVars eq_sc_theta' - wanted_sc_eqs <- mkEqInsts eq_sc_theta' (map mkWantedCo sc_covars) - dfun_covars <- mkCoVars eq_dfun_theta' - dfun_eqs <- mkEqInsts eq_dfun_theta' (map mkGivenCo $ mkTyVarTys dfun_covars) - dfun_dicts <- newDictBndrs inst_loc dict_dfun_theta' - this_dict <- newDictBndr inst_loc (mkClassPred clas inst_tys') - -- Default-method Ids may be mentioned in synthesised RHSs, - -- but they'll already be in the environment. - - -- Typecheck the methods - let -- These insts are in scope; quite a few, eh? - dfun_insts = dfun_eqs ++ dfun_dicts - wanted_sc_insts = wanted_sc_eqs ++ sc_dicts - this_dict_id = instToId this_dict - sc_dict_ids = map instToId sc_dicts - dfun_dict_ids = map instToId dfun_dicts - prag_fn = mkPragFun uprags - tc_meth = tcInstanceMethod loc clas inst_tyvars' - (dfun_covars ++ dfun_dict_ids) - dfun_theta' inst_tys' - this_dict_id dfun_id - prag_fn monobinds - (meth_exprs, meth_binds) <- mapAndUnzipM tc_meth op_items - - -- Figure out bindings for the superclass context - -- Don't include this_dict in the 'givens', else - -- wanted_sc_insts get bound by just selecting from this_dict!! - sc_binds <- addErrCtxt superClassCtxt $ - tcSimplifySuperClasses inst_loc dfun_insts - wanted_sc_insts - -- Note [Recursive superclasses] - - -- It's possible that the superclass stuff might unified one - -- of the inst_tyavars' with something in the envt - checkSigTyVars inst_tyvars' - - -- Deal with 'SPECIALISE instance' pragmas - prags <- tcPrags dfun_id (filter isSpecInstLSig uprags) - - -- Create the result bindings - let - dict_constr = classDataCon clas - inline_prag | null dfun_insts = [] - | otherwise = [L loc (InlinePrag (Inline AlwaysActive True))] - -- Always inline the dfun; this is an experimental decision - -- because it makes a big performance difference sometimes. - -- Often it means we can do the method selection, and then - -- inline the method as well. Marcin's idea; see comments below. - -- - -- BUT: don't inline it if it's a constant dictionary; - -- we'll get all the benefit without inlining, and we get - -- a **lot** of code duplication if we inline it - -- - -- See Note [Inline dfuns] below - - dict_rhs = mkHsConApp dict_constr (inst_tys' ++ mkTyVarTys sc_covars) - (map HsVar sc_dict_ids ++ meth_exprs) - -- We don't produce a binding for the dict_constr; instead we - -- rely on the simplifier to unfold this saturated application - -- We do this rather than generate an HsCon directly, because - -- it means that the special cases (e.g. dictionary with only one - -- member) are dealt with by the common MkId.mkDataConWrapId code rather - -- than needing to be repeated here. - - dict_bind = noLoc (VarBind this_dict_id dict_rhs) - - main_bind = noLoc $ AbsBinds - (inst_tyvars' ++ dfun_covars) - dfun_dict_ids - [(inst_tyvars' ++ dfun_covars, dfun_id, this_dict_id, inline_prag ++ prags)] - (dict_bind `consBag` sc_binds) - - showLIE (text "instance") - return (main_bind `consBag` unionManyBags meth_binds) - -mkCoVars :: [PredType] -> TcM [TyVar] -mkCoVars = newCoVars . map unEqPred - where - unEqPred (EqPred ty1 ty2) = (ty1, ty2) - unEqPred _ = panic "TcInstDcls.mkCoVars" - -mkMetaCoVars :: [PredType] -> TcM [TyVar] -mkMetaCoVars = mapM eqPredToCoVar + tcInstanceMethods dfun_id clas inst_tyvars dfun_ev_vars + inst_tys spec_info + op_items ibinds + + -- Create the result bindings + ; self_dict <- newEvVar (ClassP clas inst_tys) + ; let class_tc = classTyCon clas + [dict_constr] = tyConDataCons class_tc + dict_bind = mkVarBind self_dict dict_rhs + dict_rhs = foldl mk_app inst_constr $ + map HsVar sc_dicts ++ map (wrapId arg_wrapper) meth_ids + inst_constr = L loc $ wrapId (mkWpTyApps inst_tys) + (dataConWrapId dict_constr) + -- We don't produce a binding for the dict_constr; instead we + -- rely on the simplifier to unfold this saturated application + -- We do this rather than generate an HsCon directly, because + -- it means that the special cases (e.g. dictionary with only one + -- member) are dealt with by the common MkId.mkDataConWrapId + -- code rather than needing to be repeated here. + + mk_app :: LHsExpr Id -> HsExpr Id -> LHsExpr Id + mk_app fun arg = L loc (HsApp fun (L loc arg)) + + arg_wrapper = mkWpEvVarApps dfun_ev_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars) + + -- Do not inline the dfun; instead give it a magic DFunFunfolding + -- See Note [ClassOp/DFun selection] + -- See also note [Single-method classes] + dfun_id_w_fun + | isNewTyCon class_tc + = dfun_id `setInlinePragma` alwaysInlinePragma { inl_sat = Just 0 } + | otherwise + = dfun_id `setIdUnfolding` mkDFunUnfolding dfun_ty (sc_args ++ meth_args) + `setInlinePragma` dfunInlinePragma + meth_args = map (DFunPolyArg . Var) meth_ids + + main_bind = AbsBinds { abs_tvs = inst_tyvars + , abs_ev_vars = dfun_ev_vars + , abs_exports = [(inst_tyvars, dfun_id_w_fun, self_dict, + SpecPrags spec_inst_prags)] + , abs_ev_binds = emptyTcEvBinds + , abs_binds = unitBag dict_bind } + + ; return (unitBag (L loc main_bind) `unionBags` + listToBag meth_binds) + } + where + skol_info = InstSkol + dfun_ty = idType dfun_id + dfun_id = instanceDFunId ispec + loc = getSrcSpan dfun_id + +------------------------------ +tcSuperClass :: Int -> [EvVar] -> PredType -> TcM (EvVar, DFunArg CoreExpr) +-- All superclasses should be either +-- (a) be one of the arguments to the dfun, of +-- (b) be a constant, soluble at top level +tcSuperClass n_ty_args ev_vars pred + | Just (ev, i) <- find n_ty_args ev_vars + = return (ev, DFunLamArg i) + | otherwise + = ASSERT2( isEmptyVarSet (tyVarsOfPred pred), ppr pred) -- Constant! + do { sc_dict <- emitWanted ScOrigin pred + ; return (sc_dict, DFunConstArg (Var sc_dict)) } where - eqPredToCoVar (EqPred ty1 ty2) = newMetaCoVar ty1 ty2 - eqPredToCoVar _ = panic "TcInstDcls.mkMetaCoVars" + find _ [] = Nothing + find i (ev:evs) | pred `eqPred` evVarPred ev = Just (ev, i) + | otherwise = find (i+1) evs + +------------------------------ +tcSpecInstPrags :: DFunId -> InstBindings Name + -> TcM ([Located TcSpecPrag], PragFun) +tcSpecInstPrags _ (NewTypeDerived {}) + = return ([], \_ -> []) +tcSpecInstPrags dfun_id (VanillaInst binds uprags _) + = do { spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) $ + filter isSpecInstLSig uprags + -- The filter removes the pragmas for methods + ; return (spec_inst_prags, mkPragFun uprags binds) } \end{code} -Note [Recursive superclasses] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -See Trac #1470 for why we would *like* to add "this_dict" to the -available instances here. But we can't do so because then the superclases -get satisfied by selection from this_dict, and that leads to an immediate -loop. What we need is to add this_dict to Avails without adding its -superclasses, and we currently have no way to do that. +Note [Silent Superclass Arguments] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider the following (extreme) situation: + class C a => D a where ... + instance D [a] => D [a] where ... +Although this looks wrong (assume D [a] to prove D [a]), it is only a +more extreme case of what happens with recursive dictionaries. + +To implement the dfun we must generate code for the superclass C [a], +which we can get by superclass selection from the supplied argument! +So we’d generate: + dfun :: forall a. D [a] -> D [a] + dfun = \d::D [a] -> MkD (scsel d) .. + +However this means that if we later encounter a situation where +we have a [Wanted] dw::D [a] we could solve it thus: + dw := dfun dw +Although recursive, this binding would pass the TcSMonadisGoodRecEv +check because it appears as guarded. But in reality, it will make a +bottom superclass. The trouble is that isGoodRecEv can't "see" the +superclass-selection inside dfun. + +Our solution to this problem is to change the way ‘dfuns’ are created +for instances, so that we pass as first arguments to the dfun some +``silent superclass arguments’’, which are the immediate superclasses +of the dictionary we are trying to construct. In our example: + dfun :: forall a. (C [a], D [a] -> D [a] + dfun = \(dc::C [a]) (dd::D [a]) -> DOrd dc ... + +This gives us: + + ----------------------------------------------------------- + DFun Superclass Invariant + ~~~~~~~~~~~~~~~~~~~~~~~~ + In the body of a DFun, every superclass argument to the + returned dictionary is + either * one of the arguments of the DFun, + or * constant, bound at top level + ----------------------------------------------------------- + +This means that no superclass is hidden inside a dfun application, so +the counting argument in isGoodRecEv (more dfun calls than superclass +selections) works correctly. + +The extra arguments required to satisfy the DFun Superclass Invariant +always come first, and are called the "silent" arguments. DFun types +are built (only) by MkId.mkDictFunId, so that is where we decide +what silent arguments are to be added. + +This net effect is that it is safe to treat a dfun application as +wrapping a dictionary constructor around its arguments (in particular, +a dfun never picks superclasses from the arguments under the dictionary +constructor). + +In our example, if we had [Wanted] dw :: D [a] we would get via the instance: + dw := dfun d1 d2 + [Wanted] (d1 :: C [a]) + [Wanted] (d2 :: D [a]) + [Derived] (d :: D [a]) + [Derived] (scd :: C [a]) scd := scsel d + [Derived] (scd2 :: C [a]) scd2 := scsel d2 + +And now, though we *can* solve: + d2 := dw +we will get an isGoodRecEv failure when we try to solve: + d1 := scsel d + or + d1 := scsel d2 + +Test case SCLoop tests this fix. + +Note [SPECIALISE instance pragmas] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + + instance (Ix a, Ix b) => Ix (a,b) where + {-# SPECIALISE instance Ix (Int,Int) #-} + range (x,y) = ... + +We do *not* want to make a specialised version of the dictionary +function. Rather, we want specialised versions of each method. +Thus we should generate something like this: + + $dfIx :: (Ix a, Ix x) => Ix (a,b) + {- DFUN [$crange, ...] -} + $dfIx da db = Ix ($crange da db) (...other methods...) + + $dfIxPair :: (Ix a, Ix x) => Ix (a,b) + {- DFUN [$crangePair, ...] -} + $dfIxPair = Ix ($crangePair da db) (...other methods...) + + $crange :: (Ix a, Ix b) -> ((a,b),(a,b)) -> [(a,b)] + {-# SPECIALISE $crange :: ((Int,Int),(Int,Int)) -> [(Int,Int)] #-} + $crange da db = + + {-# RULE range ($dfIx da db) = $crange da db #-} + +Note that + + * The RULE is unaffected by the specialisation. We don't want to + specialise $dfIx, because then it would need a specialised RULE + which is a pain. The single RULE works fine at all specialisations. + See Note [How instance declarations are translated] above + + * Instead, we want to specialise the *method*, $crange + +In practice, rather than faking up a SPECIALISE pragama for each +method (which is painful, since we'd have to figure out its +specialised type), we call tcSpecPrag *as if* were going to specialise +$dfIx -- you can see that in the call to tcSpecInst. That generates a +SpecPrag which, as it turns out, can be used unchanged for each method. +The "it turns out" bit is delicate, but it works fine! +\begin{code} +tcSpecInst :: Id -> Sig Name -> TcM TcSpecPrag +tcSpecInst dfun_id prag@(SpecInstSig hs_ty) + = addErrCtxt (spec_ctxt prag) $ + do { let name = idName dfun_id + ; (tyvars, theta, clas, tys) <- tcHsInstHead hs_ty + ; let (_, spec_dfun_ty) = mkDictFunTy tyvars theta clas tys + + ; co_fn <- tcSubType (SpecPragOrigin name) SpecInstCtxt + (idType dfun_id) spec_dfun_ty + ; return (SpecPrag dfun_id co_fn defaultInlinePragma) } + where + spec_ctxt prag = hang (ptext (sLit "In the SPECIALISE pragma")) 2 (ppr prag) + +tcSpecInst _ _ = panic "tcSpecInst" +\end{code} %************************************************************************ %* * @@ -821,140 +1054,354 @@ tcInstanceMethod - Use tcValBinds to do the checking \begin{code} -tcInstanceMethod :: SrcSpan -> Class -> [TcTyVar] -> [Var] - -> TcThetaType -> [TcType] - -> Id -> Id - -> TcPragFun -> LHsBinds Name - -> (Id, DefMeth) - -> TcM (HsExpr Id, LHsBinds Id) +tcInstanceMethods :: DFunId -> Class -> [TcTyVar] + -> [EvVar] + -> [TcType] + -> ([Located TcSpecPrag], PragFun) + -> [(Id, DefMeth)] + -> InstBindings Name + -> TcM ([Id], [LHsBind Id]) -- The returned inst_meth_ids all have types starting -- forall tvs. theta => ... - -tcInstanceMethod loc clas tyvars dfun_lam_vars theta inst_tys - this_dict_id dfun_id - prag_fn binds_in (sel_id, dm_info) - = do { uniq <- newUnique - ; let local_meth_name = mkInternalName uniq sel_occ loc -- Same OccName - tc_body = tcInstanceMethodBody clas tyvars dfun_lam_vars theta inst_tys - this_dict_id dfun_id sel_id - prags local_meth_name - - ; case (findMethodBind sel_name local_meth_name binds_in, dm_info) of - -- There is a user-supplied method binding, so use it - (Just user_bind, _) -> tc_body user_bind - - -- The user didn't supply a method binding, so we have to make - -- up a default binding, in a way depending on the default-method info - - (Nothing, GenDefMeth) -> do -- Derivable type classes stuff - { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name - ; tc_body meth_bind } - - (Nothing, NoDefMeth) -> do -- No default method in the class - { warn <- doptM Opt_WarnMissingMethods - ; warnTc (warn -- Warn only if -fwarn-missing-methods - && reportIfUnused (getOccName sel_id)) - -- Don't warn about _foo methods - omitted_meth_warn - ; return (error_rhs, emptyBag) } - - (Nothing, DefMeth) -> do -- An polymorphic default method - { -- Build the typechecked version directly, - -- without calling typecheck_method; - -- see Note [Default methods in instances] - dm_name <- lookupImportedName (mkDefMethRdrName sel_name) - -- Might not be imported, but will be an OrigName - ; dm_id <- tcLookupId dm_name - ; return (wrapId dm_wrapper dm_id, emptyBag) } } +tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys + (spec_inst_prags, prag_fn) + op_items (VanillaInst binds _ standalone_deriv) + = mapAndUnzipM tc_item op_items where - sel_name = idName sel_id - sel_occ = nameOccName sel_name - prags = prag_fn sel_name - - error_rhs = HsApp (mkLHsWrap (WpTyApp meth_tau) error_id) error_msg - meth_tau = funResultTy (applyTys (idType sel_id) inst_tys) - error_id = L loc (HsVar nO_METHOD_BINDING_ERROR_ID) - error_msg = L loc (HsLit (HsStringPrim (mkFastString error_string))) - error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ]) - - dm_wrapper = WpApp this_dict_id <.> mkWpTyApps inst_tys - - omitted_meth_warn :: SDoc - omitted_meth_warn = ptext (sLit "No explicit method nor default method for") - <+> quotes (ppr sel_id) - ---------------- -tcInstanceMethodBody :: Class -> [TcTyVar] -> [Var] - -> TcThetaType -> [TcType] - -> Id -> Id -> Id - -> [LSig Name] -> Name -> LHsBind Name - -> TcM (HsExpr Id, LHsBinds Id) -tcInstanceMethodBody clas tyvars dfun_lam_vars theta inst_tys - this_dict_id dfun_id sel_id - prags local_meth_name bind@(L loc _) - = do { uniq <- newUnique - ; let (sel_tyvars,sel_rho) = tcSplitForAllTys (idType sel_id) - rho_ty = ASSERT( length sel_tyvars == length inst_tys ) - substTyWith sel_tyvars inst_tys sel_rho - - (first_pred, meth_tau) = tcSplitPredFunTy_maybe rho_ty - `orElse` pprPanic "tcInstanceMethod" (ppr sel_id) - - meth_name = mkInternalName uniq (getOccName local_meth_name) loc - meth_ty = mkSigmaTy tyvars theta meth_tau - meth_id = mkLocalId meth_name meth_ty - - local_meth_ty = mkSigmaTy tyvars (theta ++ [first_pred]) meth_tau - local_meth_id = mkLocalId local_meth_name local_meth_ty - - tv_names = map tyVarName tyvars - - -- The first predicate should be of form (C a b) - -- where C is the class in question - ; MASSERT( case getClassPredTys_maybe first_pred of - { Just (clas1, _tys) -> clas == clas1 ; Nothing -> False } ) - - ; local_meth_bind <- tcMethodBind tv_names prags local_meth_id bind - - ; let full_bind = unitBag $ L loc $ - VarBind meth_id $ L loc $ - mkHsWrap (mkWpTyLams tyvars <.> mkWpLams dfun_lam_vars) $ - HsLet (HsValBinds (ValBindsOut [(NonRecursive, local_meth_bind)] [])) $ L loc $ - mkHsWrap (WpLet this_dict_bind <.> WpApp this_dict_id) $ - wrapId meth_wrapper local_meth_id - this_dict_bind = unitBag $ L loc $ - VarBind this_dict_id $ L loc $ - wrapId meth_wrapper dfun_id - - ; return (wrapId meth_wrapper meth_id, full_bind) } + ---------------------- + tc_item :: (Id, DefMeth) -> TcM (Id, LHsBind Id) + tc_item (sel_id, dm_info) + = case findMethodBind (idName sel_id) binds of + Just user_bind -> tc_body sel_id standalone_deriv user_bind + Nothing -> tc_default sel_id dm_info + + ---------------------- + tc_body :: Id -> Bool -> LHsBind Name -> TcM (TcId, LHsBind Id) + tc_body sel_id generated_code rn_bind + = add_meth_ctxt sel_id generated_code rn_bind $ + do { (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars + inst_tys sel_id + ; let prags = prag_fn (idName sel_id) + ; meth_id1 <- addInlinePrags meth_id prags + ; spec_prags <- tcSpecPrags meth_id1 prags + ; bind <- tcInstanceMethodBody InstSkol + tyvars dfun_ev_vars + meth_id1 local_meth_id meth_sig_fn + (mk_meth_spec_prags meth_id1 spec_prags) + rn_bind + ; return (meth_id1, bind) } + + ---------------------- + tc_default :: Id -> DefMeth -> TcM (TcId, LHsBind Id) + + tc_default sel_id (GenDefMeth dm_name) + = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id dm_name + ; tc_body sel_id False {- Not generated code? -} meth_bind } +{- + tc_default sel_id GenDefMeth -- Derivable type classes stuff + = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id + ; tc_body sel_id False {- Not generated code? -} meth_bind } +-} + tc_default sel_id NoDefMeth -- No default method at all + = do { warnMissingMethod sel_id + ; (meth_id, _) <- mkMethIds clas tyvars dfun_ev_vars + inst_tys sel_id + ; return (meth_id, mkVarBind meth_id $ + mkLHsWrap lam_wrapper error_rhs) } + where + error_rhs = L loc $ HsApp error_fun error_msg + error_fun = L loc $ wrapId (WpTyApp meth_tau) nO_METHOD_BINDING_ERROR_ID + error_msg = L loc (HsLit (HsStringPrim (mkFastString error_string))) + meth_tau = funResultTy (applyTys (idType sel_id) inst_tys) + error_string = showSDoc (hcat [ppr loc, text "|", ppr sel_id ]) + lam_wrapper = mkWpTyLams tyvars <.> mkWpLams dfun_ev_vars + + tc_default sel_id (DefMeth dm_name) -- A polymorphic default method + = do { -- Build the typechecked version directly, + -- without calling typecheck_method; + -- see Note [Default methods in instances] + -- Generate /\as.\ds. let self = df as ds + -- in $dm inst_tys self + -- The 'let' is necessary only because HsSyn doesn't allow + -- you to apply a function to a dictionary *expression*. + + ; self_dict <- newEvVar (ClassP clas inst_tys) + ; let self_ev_bind = EvBind self_dict $ + EvDFunApp dfun_id (mkTyVarTys tyvars) dfun_ev_vars + + ; (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars + inst_tys sel_id + ; dm_id <- tcLookupId dm_name + ; let dm_inline_prag = idInlinePragma dm_id + rhs = HsWrap (mkWpEvVarApps [self_dict] <.> mkWpTyApps inst_tys) $ + HsVar dm_id + + meth_bind = L loc $ VarBind { var_id = local_meth_id + , var_rhs = L loc rhs + , var_inline = False } + meth_id1 = meth_id `setInlinePragma` dm_inline_prag + -- Copy the inline pragma (if any) from the default + -- method to this version. Note [INLINE and default methods] + + bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars + , abs_exports = [( tyvars, meth_id1, local_meth_id + , mk_meth_spec_prags meth_id1 [])] + , abs_ev_binds = EvBinds (unitBag self_ev_bind) + , abs_binds = unitBag meth_bind } + -- Default methods in an instance declaration can't have their own + -- INLINE or SPECIALISE pragmas. It'd be possible to allow them, but + -- currently they are rejected with + -- "INLINE pragma lacks an accompanying binding" + + ; return (meth_id1, L loc bind) } + + ---------------------- + mk_meth_spec_prags :: Id -> [LTcSpecPrag] -> TcSpecPrags + -- Adapt the SPECIALISE pragmas to work for this method Id + -- There are two sources: + -- * spec_inst_prags: {-# SPECIALISE instance :: #-} + -- These ones have the dfun inside, but [perhaps surprisingly] + -- the correct wrapper + -- * spec_prags_for_me: {-# SPECIALISE op :: #-} + mk_meth_spec_prags meth_id spec_prags_for_me + = SpecPrags (spec_prags_for_me ++ + [ L loc (SpecPrag meth_id wrap inl) + | L loc (SpecPrag _ wrap inl) <- spec_inst_prags]) + + loc = getSrcSpan dfun_id + meth_sig_fn _ = Just ([],loc) -- The 'Just' says "yes, there's a type sig" + -- But there are no scoped type variables from local_method_id + -- Only the ones from the instance decl itself, which are already + -- in scope. Example: + -- class C a where { op :: forall b. Eq b => ... } + -- instance C [c] where { op = } + -- In , 'c' is scope but 'b' is not! + + -- For instance decls that come from standalone deriving clauses + -- we want to print out the full source code if there's an error + -- because otherwise the user won't see the code at all + add_meth_ctxt sel_id generated_code rn_bind thing + | generated_code = addLandmarkErrCtxt (derivBindCtxt sel_id clas inst_tys rn_bind) thing + | otherwise = thing + + +tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys + _ op_items (NewTypeDerived coi _) + +-- Running example: +-- class Show b => Foo a b where +-- op :: a -> b -> b +-- newtype N a = MkN (Tree [a]) +-- deriving instance (Show p, Foo Int p) => Foo Int (N p) +-- -- NB: standalone deriving clause means +-- -- that the contex is user-specified +-- Hence op :: forall a b. Foo a b => a -> b -> b +-- +-- We're going to make an instance like +-- instance (Show p, Foo Int p) => Foo Int (N p) +-- op = $copT +-- +-- $copT :: forall p. (Show p, Foo Int p) => Int -> N p -> N p +-- $copT p (d1:Show p) (d2:Foo Int p) +-- = op Int (Tree [p]) rep_d |> op_co +-- where +-- rep_d :: Foo Int (Tree [p]) = ...d1...d2... +-- op_co :: (Int -> Tree [p] -> Tree [p]) ~ (Int -> T p -> T p) +-- We get op_co by substituting [Int/a] and [co/b] in type for op +-- where co : [p] ~ T p +-- +-- Notice that the dictionary bindings "..d1..d2.." must be generated +-- by the constraint solver, since the may be +-- user-specified. + + = do { rep_d_stuff <- checkConstraints InstSkol tyvars dfun_ev_vars $ + emitWanted ScOrigin rep_pred + + ; mapAndUnzipM (tc_item rep_d_stuff) op_items } + where + loc = getSrcSpan dfun_id + + inst_tvs = fst (tcSplitForAllTys (idType dfun_id)) + Just (init_inst_tys, _) = snocView inst_tys + rep_ty = pFst (coercionKind co) -- [p] + rep_pred = mkClassPred clas (init_inst_tys ++ [rep_ty]) + + -- co : [p] ~ T p + co = substCoWithTys inst_tvs (mkTyVarTys tyvars) $ + mkSymCo coi + + ---------------- + tc_item :: (TcEvBinds, EvVar) -> (Id, DefMeth) -> TcM (TcId, LHsBind TcId) + tc_item (rep_ev_binds, rep_d) (sel_id, _) + = do { (meth_id, local_meth_id) <- mkMethIds clas tyvars dfun_ev_vars + inst_tys sel_id + + ; let meth_rhs = wrapId (mk_op_wrapper sel_id rep_d) sel_id + meth_bind = VarBind { var_id = local_meth_id + , var_rhs = L loc meth_rhs + , var_inline = False } + + bind = AbsBinds { abs_tvs = tyvars, abs_ev_vars = dfun_ev_vars + , abs_exports = [(tyvars, meth_id, + local_meth_id, noSpecPrags)] + , abs_ev_binds = rep_ev_binds + , abs_binds = unitBag $ L loc meth_bind } + + ; return (meth_id, L loc bind) } + + ---------------- + mk_op_wrapper :: Id -> EvVar -> HsWrapper + mk_op_wrapper sel_id rep_d + = WpCast (liftCoSubstWith sel_tvs (map mkReflCo init_inst_tys ++ [co]) + local_meth_ty) + <.> WpEvApp (EvId rep_d) + <.> mkWpTyApps (init_inst_tys ++ [rep_ty]) + where + (sel_tvs, sel_rho) = tcSplitForAllTys (idType sel_id) + (_, local_meth_ty) = tcSplitPredFunTy_maybe sel_rho + `orElse` pprPanic "tcInstanceMethods" (ppr sel_id) + +---------------------- +mkMethIds :: Class -> [TcTyVar] -> [EvVar] -> [TcType] -> Id -> TcM (TcId, TcId) +mkMethIds clas tyvars dfun_ev_vars inst_tys sel_id + = do { uniq <- newUnique + ; let meth_name = mkDerivedInternalName mkClassOpAuxOcc uniq sel_name + ; local_meth_name <- newLocalName sel_name + -- Base the local_meth_name on the selector name, becuase + -- type errors from tcInstanceMethodBody come from here + + ; let meth_id = mkLocalId meth_name meth_ty + local_meth_id = mkLocalId local_meth_name local_meth_ty + ; return (meth_id, local_meth_id) } where - meth_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys tyvars) + local_meth_ty = instantiateMethod clas sel_id inst_tys + meth_ty = mkForAllTys tyvars $ mkPiTypes dfun_ev_vars local_meth_ty + sel_name = idName sel_id +---------------------- wrapId :: HsWrapper -> id -> HsExpr id wrapId wrapper id = mkHsWrap wrapper (HsVar id) + +derivBindCtxt :: Id -> Class -> [Type ] -> LHsBind Name -> SDoc +derivBindCtxt sel_id clas tys _bind + = vcat [ ptext (sLit "When typechecking the code for ") <+> quotes (ppr sel_id) + , nest 2 (ptext (sLit "in a standalone derived instance for") + <+> quotes (pprClassPred clas tys) <> colon) + , nest 2 $ ptext (sLit "To see the code I am typechecking, use -ddump-deriv") ] + +-- Too voluminous +-- , nest 2 $ pprSetDepth AllTheWay $ ppr bind ] + +warnMissingMethod :: Id -> TcM () +warnMissingMethod sel_id + = do { warn <- doptM Opt_WarnMissingMethods + ; warnTc (warn -- Warn only if -fwarn-missing-methods + && not (startsWithUnderscore (getOccName sel_id))) + -- Don't warn about _foo methods + (ptext (sLit "No explicit method nor default method for") + <+> quotes (ppr sel_id)) } \end{code} +Note [Export helper functions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +We arrange to export the "helper functions" of an instance declaration, +so that they are not subject to preInlineUnconditionally, even if their +RHS is trivial. Reason: they are mentioned in the DFunUnfolding of +the dict fun as Ids, not as CoreExprs, so we can't substitute a +non-variable for them. + +We could change this by making DFunUnfoldings have CoreExprs, but it +seems a bit simpler this way. + Note [Default methods in instances] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this class Baz v x where foo :: x -> x - foo y = y + foo y = instance Baz Int Int From the class decl we get $dmfoo :: forall v x. Baz v x => x -> x + $dmfoo y = + +Notice that the type is ambiguous. That's fine, though. The instance +decl generates + + $dBazIntInt = MkBaz fooIntInt + fooIntInt = $dmfoo Int Int $dBazIntInt + +BUT this does mean we must generate the dictionary translation of +fooIntInt directly, rather than generating source-code and +type-checking it. That was the bug in Trac #1061. In any case it's +less work to generate the translated version! + +Note [INLINE and default methods] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Default methods need special case. They are supposed to behave rather like +macros. For exmample + + class Foo a where + op1, op2 :: Bool -> a -> a + + {-# INLINE op1 #-} + op1 b x = op2 (not b) x + + instance Foo Int where + -- op1 via default method + op2 b x = + +The instance declaration should behave + + just as if 'op1' had been defined with the + code, and INLINE pragma, from its original + definition. + +That is, just as if you'd written -Notice that the type is ambiguous. That's fine, though. The instance decl generates + instance Foo Int where + op2 b x = - $dBazIntInt = MkBaz ($dmfoo Int Int $dBazIntInt) + {-# INLINE op1 #-} + op1 b x = op2 (not b) x -BUT this does mean we must generate the dictionary translation directly, rather -than generating source-code and type-checking it. That was the bug ing -Trac #1061. In any case it's less work to generate the translated version! +So for the above example we generate: + + + {-# INLINE $dmop1 #-} + -- $dmop1 has an InlineCompulsory unfolding + $dmop1 d b x = op2 d (not b) x + + $fFooInt = MkD $cop1 $cop2 + + {-# INLINE $cop1 #-} + $cop1 = $dmop1 $fFooInt + + $cop2 = + +Note carefullly: + +* We *copy* any INLINE pragma from the default method $dmop1 to the + instance $cop1. Otherwise we'll just inline the former in the + latter and stop, which isn't what the user expected + +* Regardless of its pragma, we give the default method an + unfolding with an InlineCompulsory source. That means + that it'll be inlined at every use site, notably in + each instance declaration, such as $cop1. This inlining + must happen even though + a) $dmop1 is not saturated in $cop1 + b) $cop1 itself has an INLINE pragma + + It's vital that $dmop1 *is* inlined in this way, to allow the mutual + recursion between $fooInt and $cop1 to be broken + +* To communicate the need for an InlineCompulsory to the desugarer + (which makes the Unfoldings), we use the IsDefaultMethod constructor + in TcSpecPrags. %************************************************************************ @@ -979,9 +1426,6 @@ instDeclCtxt2 dfun_ty inst_decl_ctxt :: SDoc -> SDoc inst_decl_ctxt doc = ptext (sLit "In the instance declaration for") <+> quotes doc -superClassCtxt :: SDoc -superClassCtxt = ptext (sLit "When checking the super-classes of an instance declaration") - atInstCtxt :: Name -> SDoc atInstCtxt name = ptext (sLit "In the associated type instance for") <+> quotes (ppr name) @@ -996,7 +1440,40 @@ mustBeVarArgErr ty = wrongATArgErr :: Type -> Type -> SDoc wrongATArgErr ty instTy = sep [ ptext (sLit "Type indexes must match class instance head") - , ptext (sLit "Found") <+> ppr ty <+> ptext (sLit "but expected") <+> - ppr instTy + , ptext (sLit "Found") <+> quotes (ppr ty) + <+> ptext (sLit "but expected") <+> quotes (ppr instTy) ] + +tooManyParmsErr :: Located Name -> SDoc +tooManyParmsErr tc_name + = ptext (sLit "Family instance has too many parameters:") <+> + quotes (ppr tc_name) + +tooFewParmsErr :: Arity -> SDoc +tooFewParmsErr arity + = ptext (sLit "Family instance has too few parameters; expected") <+> + ppr arity + +wrongNumberOfParmsErr :: Arity -> SDoc +wrongNumberOfParmsErr exp_arity + = ptext (sLit "Number of parameters must match family declaration; expected") + <+> ppr exp_arity + +badBootFamInstDeclErr :: SDoc +badBootFamInstDeclErr + = ptext (sLit "Illegal family instance in hs-boot file") + +notFamily :: TyCon -> SDoc +notFamily tycon + = vcat [ ptext (sLit "Illegal family instance for") <+> quotes (ppr tycon) + , nest 2 $ parens (ppr tycon <+> ptext (sLit "is not an indexed type family"))] + +wrongKindOfFamily :: TyCon -> SDoc +wrongKindOfFamily family + = ptext (sLit "Wrong category of family instance; declaration was for a") + <+> kindOfFamily + where + kindOfFamily | isSynTyCon family = ptext (sLit "type synonym") + | isAlgTyCon family = ptext (sLit "data type") + | otherwise = pprPanic "wrongKindOfFamily" (ppr family) \end{code}