import TcBinds
import TcTyClsDecls
import TcClassDcl
+import TcPat( addInlinePrags )
+import TcSimplify( simplifyTop )
import TcRnMonad
import TcMType
import TcType
import InstEnv
import FamInst
import FamInstEnv
+import MkCore ( nO_METHOD_BINDING_ERROR_ID )
import TcDeriv
import TcEnv
-import RnEnv ( lookupGlobalOccRn )
import RnSource ( addTcgDUs )
import TcHsType
import TcUnify
-import TcSimplify
import Type
import Coercion
import TyCon
import DataCon
import Class
import Var
+import VarSet
+import CoreUtils ( mkPiTypes )
import CoreUnfold ( mkDFunUnfolding )
-import PrelNames ( inlineIdName )
+import CoreSyn ( Expr(Var), DFunArg(..), CoreExpr )
import Id
import MkId
import Name
import BasicTypes
import HscTypes
import FastString
-
+import Maybes ( orElse )
import Data.Maybe
import Control.Monad
import Data.List
{-# RULE "op1@C[a]" forall a, d:C a.
op1 [a] (df_i d) = op1_i a d #-}
-* We want to inline the dictionary function itself as vigorously as we
- possibly can, so that we expose that dictionary constructor to
- selectors as much as poss. We don't actually inline it; rather, we
- use a Builtin RULE for the ClassOps (see MkId.mkDictSelId) to short
- circuit such applications. But the RULE only applies if it can "see"
- the dfun's DFunUnfolding.
-
+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.
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, $cop2, ..])
+ that lists its methods.
+
+ * We make CoreUnfold.exprIsConApp_maybe spot a DFunUnfolding and return
+ a suitable constructor application -- inlining df "on the fly" as it
+ were.
+
+ * We give the ClassOp 'op2' a BuiltinRule that extracts the right piece
+ iff its argument satisfies exprIsConApp_maybe. This is done in
+ MkId mkDictSelId
+
+ * We make 'df' CONLIKE, so that shared uses stil match; eg
+ let d = df d1 d2
+ in ...(op2 d)...(op1 d)...
+
+Note [Single-method classes]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If the class has just one method (or, more accurately, just one element
+of {superclasses + methods}), then we use a different strategy.
+
+ class C a where op :: a -> a
+ instance C a => C [a] where op = <blah>
+
+We translate the class decl into a newtype, which just gives a
+top-level axiom. The "constructor" MkC expands to a cast, as does the
+class-op selector.
+
+ axiom Co:C a :: C a ~ (a->a)
+
+ op :: forall a. C a -> (a -> a)
+ op a d = d |> (Co:C a)
+
+ MkC :: forall a. (a->a) -> C a
+ MkC = /\a.\op. op |> (sym Co:C a)
+
+The clever RULE stuff doesn't work now, because ($df a d) isn't
+a constructor application, so exprIsConApp_maybe won't return
+Just <blah>.
+
+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]
+ $cop_list = <blah>
+
+So if we see
+ (op ($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]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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
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
-definition for 'this' in the definition of op1_i in the example above.
-We can typecheck the defintion of local_op1, and when doing tcSimplifyCheck
-we supply 'this' as a given dictionary. Only needed, though, if there
-are some type variables involved; otherwise there can be no overlap and
-none of this arises.
+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]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- 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_tycons = concat at_tycons_s ++ idx_tycons
; clas_decls = filter (isClassDecl.unLoc) tycl_decls
; implicit_things = concatMap implicitTyThings at_idx_tycons
- ; aux_binds = mkAuxBinds at_idx_tycons
+ ; aux_binds = mkRecSelBinds at_idx_tycons
}
-- (2) Add the tycons of indexed types and their implicit
-- Next, construct the instance environment so far, consisting
-- of
- -- a) local instance decls
- -- b) generic instances
- -- c) local family instance decls
+ -- (a) local instance decls
+ -- (b) generic instances
+ -- (c) local family instance decls
; addInsts local_info $
addInsts generic_inst_info $
addFamInsts at_idx_tycons $ do {
generic_inst_info ++ deriv_inst_info ++ local_info,
aux_binds `plusHsValBinds` 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")
addInsts :: [InstInfo Name] -> TcM a -> TcM a
addInsts infos thing_inside
; 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 }
dfun = mkDictFunId dfun_name tyvars theta' clas inst_tys
ispec = mkLocalInstance dfun overlap_flag
- ; return (InstInfo { iSpec = ispec,
- iBinds = VanillaInst binds uprags False },
+ ; return (InstInfo { iSpec = ispec, iBinds = VanillaInst binds uprags False },
idx_tycons)
}
where
case find ((atName ==) . tyConName) (classATs clas) of
Nothing -> addErrTc $ badATErr clas atName -- not in this class
Just atycon ->
- case assocTyConArgPoss_maybe atycon of
- Nothing -> panic "checkIndexes': AT has no args poss?!?"
- Just poss ->
-
-- 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
-- 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
\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
tcInstDecls2 tycl_decls inst_decls
= do { -- (a) Default methods from class decls
let class_decls = filter (isClassDecl . unLoc) tycl_decls
- ; (dm_ids_s, dm_binds_s) <- mapAndUnzipM tcClassDecl2 class_decls
+ ; dm_binds_s <- mapM tcClassDecl2 class_decls
+ ; let dm_binds = unionManyBags dm_binds_s
- ; tcExtendIdEnv (concat dm_ids_s) $ do
-
-- (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
tcInstDecl2 (InstInfo { iSpec = ispec, iBinds = ibinds })
= recoverM (return emptyLHsBinds) $
setSrcSpan loc $
addErrCtxt (instDeclCtxt2 (idType dfun_id)) $
- tc_inst_decl2 dfun_id ibinds
- where
- dfun_id = instanceDFunId ispec
- loc = getSrcSpan dfun_id
-\end{code}
-
-
-\begin{code}
-tc_inst_decl2 :: Id -> InstBindings 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
-
-tc_inst_decl2 dfun_id (NewTypeDerived coi)
- = do { let rigid_info = InstSkol
- origin = SigOrigin rigid_info
- inst_ty = idType dfun_id
- inst_tvs = fst (tcSplitForAllTys inst_ty)
- ; (inst_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
-
- (rep_ty, wrapper)
- = case coi of
- IdCo -> (last_ty, idHsWrapper)
- ACo co -> (snd (coercionKind co'), WpCast (mk_full_coercion co'))
- where
- co' = substTyWith inst_tvs (mkTyVarTys inst_tvs') co
- -- NB: the free variable of coi are bound by the
- -- universally quantified variables of the dfun_id
- -- This is weird, and maybe we should make NewTypeDerived
- -- carry a type-variable list too; but it works fine
-
- -----------------------
- -- mk_full_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 <rep_ty>)
- -- 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
-
- mk_full_coercion co = mkTyConApp cls_tycon
- (initial_cls_inst_tys ++ [mkSymCoercion co])
- -- Full coercion : (Foo Int (Tree [a]) ~ Foo Int (N a)
-
- rep_pred = mkClassPred cls (initial_cls_inst_tys ++ [rep_ty])
- -- In our example, rep_pred is (Foo Int (Tree [a]))
-
- ; sc_loc <- getInstLoc InstScOrigin
- ; sc_dicts <- newDictBndrs sc_loc sc_theta'
- ; inst_loc <- getInstLoc origin
- ; dfun_dicts <- newDictBndrs inst_loc theta
- ; rep_dict <- newDictBndr inst_loc rep_pred
- ; this_dict <- newDictBndr inst_loc (mkClassPred cls cls_inst_tys)
-
- -- Figure out bindings for the superclass context from dfun_dicts
- -- Don't include this_dict in the 'givens', else
- -- sc_dicts get bound by just selecting from this_dict!!
- ; sc_binds <- addErrCtxt superClassCtxt $
- tcSimplifySuperClasses inst_loc this_dict dfun_dicts
- (rep_dict:sc_dicts)
-
- -- It's possible that the superclass stuff might unified something
- -- in the envt with one of the clas_tyvars
- ; checkSigTyVars inst_tvs'
-
- ; let coerced_rep_dict = wrapId wrapper (instToId rep_dict)
-
- ; body <- make_body cls_tycon cls_inst_tys sc_dicts coerced_rep_dict
- ; let dict_bind = mkVarBind (instToId this_dict) (noLoc body)
-
- ; return (unitBag $ noLoc $
- AbsBinds inst_tvs' (map instToVar dfun_dicts)
- [(inst_tvs', dfun_id, instToId this_dict, [])]
- (dict_bind `consBag` sc_binds)) }
- where
- -----------------------
- -- (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
-
-tc_inst_decl2 dfun_id (VanillaInst monobinds uprags standalone_deriv)
- = do { let rigid_info = InstSkol
- inst_ty = idType dfun_id
- loc = getSrcSpan dfun_id
-
- -- 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
- -- 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, sc_sels, op_items) = classBigSig clas
-
- -- Instantiate the super-class context with inst_tys
- sc_theta' = substTheta (zipOpenTvSubst class_tyvars inst_tys') sc_theta
- origin = SigOrigin rigid_info
-
- -- Create dictionary Ids from the specified instance contexts.
- ; inst_loc <- getInstLoc origin
- ; dfun_dicts <- newDictBndrs inst_loc dfun_theta' -- Includes equalities
- ; 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.
-
-
- -- Cook up a binding for "this = df d1 .. dn",
- -- to use in each method binding
- -- Need to clone the dict in case it is floated out, and
- -- then clashes with its friends
- ; cloned_this <- cloneDict this_dict
- ; let cloned_this_bind = mkVarBind (instToId cloned_this) $
- L loc $ wrapId app_wrapper dfun_id
- app_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
- dfun_lam_vars = map instToVar dfun_dicts -- Includes equalities
- nested_this_pair
- | null inst_tyvars' && null dfun_theta' = (this_dict, emptyBag)
- | otherwise = (cloned_this, unitBag cloned_this_bind)
+ do { -- Instantiate the instance decl with skolem constants
+ ; (inst_tyvars, dfun_theta, inst_head) <- tcSkolSigType skol_info (idType dfun_id)
+ ; 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_binds, sc_dicts, sc_args)
+ <- mapAndUnzip3M (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 $
+ emitConstraints $ listToBag $
+ [ WcEvVar (WantedEvVar sc ct_loc)
+ | sc <- sc_dicts, isSilentEvVar sc ]
-- Deal with 'SPECIALISE instance' pragmas
-- See Note [SPECIALISE instance pragmas]
- ; let spec_inst_sigs = filter isSpecInstLSig uprags
- -- The filter removes the pragmas for methods
- ; spec_inst_prags <- mapM (wrapLocM (tcSpecInst dfun_id)) spec_inst_sigs
+ ; spec_info <- tcSpecInstPrags dfun_id ibinds
-- Typecheck the methods
- ; let prag_fn = mkPragFun uprags
- tc_meth = tcInstanceMethod loc standalone_deriv
- clas inst_tyvars'
- dfun_dicts inst_tys'
- nested_this_pair
- prag_fn spec_inst_prags monobinds
-
- ; (meth_ids, meth_binds) <- tcExtendTyVarEnv inst_tyvars' $
- mapAndUnzipM tc_meth op_items
-
- -- Figure out bindings for the superclass context
- ; sc_loc <- getInstLoc InstScOrigin
- ; sc_dicts <- newDictOccs sc_loc sc_theta' -- These are wanted
- ; let tc_sc = tcSuperClass inst_loc inst_tyvars' dfun_dicts nested_this_pair
- ; (sc_ids, sc_binds) <- mapAndUnzipM tc_sc (sc_sels `zip` sc_dicts)
-
- -- It's possible that the superclass stuff might unified
- -- something in the envt with one of the inst_tyvars'
- ; checkSigTyVars inst_tyvars'
+ ; (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!
+ tcInstanceMethods dfun_id clas inst_tyvars dfun_ev_vars
+ inst_tys spec_info
+ op_items ibinds
-- Create the result bindings
- ; let dict_constr = classDataCon clas
- this_dict_id = instToId this_dict
- dict_bind = mkVarBind this_dict_id dict_rhs
- dict_rhs = foldl mk_app inst_constr (sc_ids ++ meth_ids)
- inst_constr = L loc $ wrapId (mkWpTyApps inst_tys')
- (dataConWrapId dict_constr)
+ ; 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 -> Id -> LHsExpr Id
- mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id)))
- arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
-
- dfun_id_w_fun = dfun_id
- `setIdUnfolding` mkDFunUnfolding dict_constr (sc_ids ++ meth_ids)
- `setInlinePragma` dfunInlinePragma
-
- main_bind = noLoc $ AbsBinds
- inst_tyvars'
- dfun_lam_vars
- [(inst_tyvars', dfun_id_w_fun, this_dict_id, spec_inst_prags)]
- (unitBag dict_bind)
-
- ; showLIE (text "instance")
- ; return (unitBag main_bind `unionBags`
- listToBag meth_binds `unionBags`
- listToBag sc_binds) }
+ -- 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`
+ unionManyBags sc_binds `unionBags`
+ listToBag meth_binds)
+ }
+ where
+ skol_info = InstSkol -- See Note [Subtle interaction of recursion and overlap]
+ dfun_ty = idType dfun_id
+ dfun_id = instanceDFunId ispec
+ loc = getSrcSpan dfun_id
+------------------------------
+tcSuperClass :: Int -> [EvVar] -> PredType -> TcM (LHsBinds Id, Id, DFunArg CoreExpr)
+tcSuperClass n_ty_args ev_vars pred
+ | Just (ev, i) <- find n_ty_args ev_vars
+ = return (emptyBag, ev, DFunLamArg i)
+ | otherwise
+ = ASSERT2( isEmptyVarSet (tyVarsOfPred pred), ppr pred)
+ do { sc_dict <- newWantedEvVar pred
+ ; loc <- getCtLoc ScOrigin
+ ; ev_binds <- simplifyTop (unitBag (WcEvVar (WantedEvVar sc_dict loc)))
+ ; let ev_wrap = WpLet (EvBinds ev_binds)
+ sc_bind = mkVarBind sc_dict (noLoc $ (wrapId ev_wrap sc_dict))
+ ; return (unitBag sc_bind, sc_dict, DFunConstArg (Var sc_dict)) }
+ -- It's very important to solve the superclass constraint *in isolation*
+ -- so that it isn't generated by superclass selection from something else
+ -- We then generate the (also rather degenerate) top-level binding:
+ -- sc_dict = let sc_dict = <blah> in sc_dict
+ -- where <blah> is generated by solving the implication constraint
+ where
+ find _ [] = Nothing
+ find i (ev:evs) | pred `tcEqPred` evVarPred ev = Just (ev, i)
+ | otherwise = find (i+1) evs
------------------------------
-tcSuperClass :: InstLoc -> [TyVar] -> [Inst]
- -> (Inst, LHsBinds Id)
- -> (Id, Inst) -> TcM (Id, LHsBind Id)
--- Build a top level decl like
--- sc_op = /\a \d. let this = ... in
--- let sc = ... in
--- sc
--- The "this" part is just-in-case (discarded if not used)
--- See Note [Recursive superclasses]
-tcSuperClass inst_loc tyvars dicts (this_dict, this_bind)
- (sc_sel, sc_dict)
- = addErrCtxt superClassCtxt $
- do { sc_binds <- tcSimplifySuperClasses inst_loc
- this_dict dicts [sc_dict]
- -- Don't include this_dict in the 'givens', else
- -- sc_dicts get bound by just selecting from this_dict!!
-
- ; uniq <- newUnique
- ; let sc_op_ty = mkSigmaTy tyvars (map dictPred dicts)
- (mkPredTy (dictPred sc_dict))
- sc_op_name = mkDerivedInternalName mkClassOpAuxOcc uniq
- (getName sc_sel)
- sc_op_id = mkLocalId sc_op_name sc_op_ty
- sc_id = instToVar sc_dict
- sc_op_bind = AbsBinds tyvars
- (map instToVar dicts)
- [(tyvars, sc_op_id, sc_id, [])]
- (this_bind `unionBags` sc_binds)
-
- ; return (sc_op_id, noLoc sc_op_bind) }
+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
The "it turns out" bit is delicate, but it works fine!
\begin{code}
-tcSpecInst :: Id -> Sig Name -> TcM SpecPrag
+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, tau) <- tcHsInstHead hs_ty
- ; let spec_ty = mkSigmaTy tyvars theta tau
- ; co_fn <- tcSubExp (SpecPragOrigin name) (idType dfun_id) spec_ty
- ; return (SpecPrag co_fn defaultInlinePragma) }
+ ; (tyvars, theta, clas, tys) <- tcHsInstHead hs_ty
+ ; let (_, spec_dfun_ty) = mkDictFunTy tyvars theta clas tys
+
+ ; co_fn <- tcSubType (SpecPragOrigin name) (SigSkol 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)
- Use tcValBinds to do the checking
\begin{code}
-tcInstanceMethod :: SrcSpan -> Bool -> Class -> [TcTyVar] -> [Inst]
- -> [TcType]
- -> (Inst, LHsBinds Id) -- "This" and its binding
- -> TcPragFun -- Local prags
- -> [LSpecPrag] -- Arising from 'SPECLALISE instance'
- -> LHsBinds Name
- -> (Id, DefMeth)
- -> TcM (Id, LHsBind 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 standalone_deriv clas tyvars dfun_dicts inst_tys
- (this_dict, this_dict_bind)
- prag_fn spec_inst_prags binds_in (sel_id, dm_info)
- = 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 local_meth_ty = instantiateMethod clas sel_id inst_tys
- meth_ty = mkSigmaTy tyvars (map dictPred dfun_dicts) local_meth_ty
- meth_id = mkLocalId meth_name meth_ty
- local_meth_id = mkLocalId local_meth_name local_meth_ty
-
- --------------
- tc_body rn_bind
- = add_meth_ctxt rn_bind $
- do { (meth_id1, spec_prags) <- tcPrags NonRecursive False True
- meth_id (prag_fn sel_name)
- ; tcInstanceMethodBody (instLoc this_dict)
- tyvars dfun_dicts
- ([this_dict], this_dict_bind)
- meth_id1 local_meth_id
- meth_sig_fn
- (spec_inst_prags ++ spec_prags)
- rn_bind }
-
- --------------
- tc_default :: DefMeth -> TcM (Id, LHsBind Id)
- -- 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
-
- tc_default NoDefMeth -- No default method at all
- = do { warnMissingMethod sel_id
- ; return (meth_id, mkVarBind meth_id $
- mkLHsWrap lam_wrapper error_rhs) }
-
- tc_default GenDefMeth -- Derivable type classes stuff
- = do { meth_bind <- mkGenericDefMethBind clas inst_tys sel_id local_meth_name
- ; tc_body meth_bind }
-
- tc_default DefMeth -- An polymorphic default method
- = do { -- Build the typechecked version directly,
- -- without calling typecheck_method;
- -- see Note [Default methods in instances]
- -- Generate /\as.\ds. let this = df as ds
- -- in $dm inst_tys this
- -- The 'let' is necessary only because HsSyn doesn't allow
- -- you to apply a function to a dictionary *expression*.
- dm_name <- lookupGlobalOccRn (mkDefMethRdrName sel_name)
- -- Might not be imported, but will be an OrigName
- ; dm_id <- tcLookupId dm_name
- ; inline_id <- tcLookupId inlineIdName
- ; let dm_inline_prag = idInlinePragma dm_id
- dm_app = HsWrap (WpApp (instToId this_dict) <.> mkWpTyApps inst_tys) $
- HsVar dm_id
- rhs | isInlinePragma dm_inline_prag -- See Note [INLINE and default methods]
- = HsApp (L loc (HsWrap (WpTyApp local_meth_ty) (HsVar inline_id)))
- (L loc dm_app)
- | otherwise = dm_app
-
- 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_dicts = dfun_lam_vars
- , abs_exports = [( tyvars, meth_id1
- , local_meth_id, spec_inst_prags)]
- , abs_binds = this_dict_bind `unionBags` 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) }
-
- ; case findMethodBind sel_name local_meth_name binds_in of
- Just user_bind -> tc_body user_bind -- User-supplied method binding
- Nothing -> tc_default dm_info -- None supplied
- }
+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
-
- meth_sig_fn _ = Just [] -- The 'Just' says "yes, there's a type sig"
+ ----------------------
+ 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 -- 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 :: <blah> #-}
+ -- These ones have the dfun inside, but [perhaps surprisingly]
+ -- the correct wrapper
+ -- * spec_prags_for_me: {-# SPECIALISE op :: <blah> #-}
+ 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:
-- instance C [c] where { op = <rhs> }
-- In <rhs>, 'c' is scope but 'b' is not!
- 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 ])
-
- dfun_lam_vars = map instToVar dfun_dicts
- lam_wrapper = mkWpTyLams tyvars <.> mkWpLams dfun_lam_vars
-
- -- For instance decls that come from standalone deriving clauses
+ -- 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 rn_bind thing
- | standalone_deriv = addLandmarkErrCtxt (derivBindCtxt clas inst_tys rn_bind) thing
- | otherwise = thing
+ 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 <context> 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 = fst (coercionKind co) -- [p]
+ rep_pred = mkClassPred clas (init_inst_tys ++ [rep_ty])
+
+ -- co : [p] ~ T p
+ co = substTyWith inst_tvs (mkTyVarTys tyvars) $
+ case coi of { IdCo ty -> ty ;
+ ACo co -> mkSymCoercion co }
+
+ ----------------
+ 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 (substTyWith sel_tvs (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
+ 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 :: Class -> [Type ] -> LHsBind Name -> SDoc
-derivBindCtxt clas tys bind
- = vcat [ ptext (sLit "When typechecking a standalone-derived method for")
- <+> quotes (pprClassPred clas tys) <> colon
- , nest 2 $ pprSetDepth AllTheWay $ ppr bind ]
+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
$dmfoo :: forall v x. Baz v x => x -> x
$dmfoo y = <blah>
-Notice that the type is ambiguous. That's fine, though. The instance decl generates
+Notice that the type is ambiguous. That's fine, though. The instance
+decl generates
$dBazIntInt = MkBaz fooIntInt
fooIntInt = $dmfoo Int Int $dBazIntInt
Note [INLINE and default methods]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-We *copy* any INLINE pragma from the default method to the instance.
-Example:
+Default methods need special case. They are supposed to behave rather like
+macros. For exmample
+
class Foo a where
op1, op2 :: Bool -> a -> a
op1 b x = op2 (not b) x
instance Foo Int where
+ -- op1 via default method
op2 b x = <blah>
+
+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
+
+ instance Foo Int where
+ op2 b x = <blah>
+
+ {-# INLINE op1 #-}
+ op1 b x = op2 (not b) x
+
+So for the above example we generate:
-Then 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 = inline $dmop1 $fFooInt
+ $cop1 = $dmop1 $fFooInt
$cop2 = <blah>
-Note carefully:
- a) We copy $dmop1's inline pragma to $cop1. Otherwise
- we'll just inline the former in the latter and stop, which
- isn't what the user expected
+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
- b) We use the magic 'inline' Id to ensure that $dmop1 really is
- inlined in $cop1, even though the latter itself has an INLINE pragma
- That is important to allow the mutual recursion between $fooInt and
- $cop1 to be broken
+* 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
-This is all regrettably delicate.
+ 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.
%************************************************************************
instDeclCtxt2 dfun_ty
= inst_decl_ctxt (ppr (mkClassPred cls tys))
where
- (_,cls,tys) = tcSplitDFunTy dfun_ty
+ (_,_,cls,tys) = tcSplitDFunTy 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)