import TcBinds
import TcTyClsDecls
import TcClassDcl
+import TcPat( addInlinePrags )
import TcRnMonad
import TcMType
import TcType
import InstEnv
import FamInst
import FamInstEnv
+import MkCore ( nO_METHOD_BINDING_ERROR_ID )
import TcDeriv
import TcEnv
import RnSource ( addTcgDUs )
-import TcSimplify( simplifySuperClass )
import TcHsType
import TcUnify
import Type
import DataCon
import Class
import Var
-import VarSet ( emptyVarSet )
+import VarSet
import CoreUtils ( mkPiTypes )
import CoreUnfold ( mkDFunUnfolding )
-import CoreSyn ( Expr(Var) )
+import CoreSyn ( Expr(Var), DFunArg(..), CoreExpr )
import Id
import MkId
import Name
Note [Single-method classes]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the class has just one method (or, more accurately, just one element
-of {superclasses + methods}), then we still use the *same* strategy
+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:
+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)
MkC :: forall a. (a->a) -> C a
MkC = /\a.\op. op |> (sym Co:C a)
- df :: forall a. C a => C [a]
- {-# NOINLINE df DFun[ $cop_list ] #-}
- df = /\a. \d. MkC ($cop_list a d)
+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>.
- $cop_list :: forall a. C a => [a] -> [a]
- $cop_list = <blah>
+Instead, we simply rely on the fact that casts are cheap:
-The "constructor" MkC expands to a cast, as does the class-op selector.
-The RULE works just like for multi-field dictionaries:
+ $df :: forall a. C a => C [a]
+ {-# INLINE df #} -- NB: INLINE this
+ $df = /\a. \d. MkC [a] ($cop_list a d)
+ = $cop_list |> forall a. C a -> (sym (Co:C [a]))
- * (df a d) returns (Just (MkC,..,[$cop_list a d]))
- to exprIsConApp_Maybe
+ $cop_list :: forall a. C a => [a] -> [a]
+ $cop_list = <blah>
- * The RULE for op picks the right result
+So if we see
+ (op ($df a d))
+we'll inline 'op' and '$df', since both are simply casts, and
+good things happen.
-This is a bit of a hack, because (df a d) isn't *really* a constructor
-application. But it works just fine in this case, exprIsConApp_maybe
-is otherwise used only when we hit a case expression which will have
-a real data constructor in it.
+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).
-The biggest reason for doing it this way, apart from uniformity, is
-that we want to be very careful when we have
+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
+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)
-The danger is that we'll get something like
- op_list :: C a => [a] -> [a]
- op_list = /\a.\d. $cop_list a d
-and then we'll eta expand, and then we'll inline TOO EARLY. This happened in
-Trac #3772 and I spent far too long fiddling around trying to fix it.
-Look at the test for Trac #3772.
+ $fC[] :: C a => C [a]
+ -- Ordinary DFun
+ $fC[] a d = MkC ($cp1 a d) ($cgen a d)
- (Note: re-reading the above, I can't see how using the
- uniform story solves the problem.)
+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]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
; 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
+ ; clas_decls = filter (isClassDecl . unLoc) tycl_decls
; implicit_things = concatMap implicitTyThings at_idx_tycons
; aux_binds = mkRecSelBinds at_idx_tycons
}
-- 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
+ -- try the deriving stuff, because that may give
-- more errors still
- ; (deriv_inst_info, deriv_binds, deriv_dus)
+ ; (deriv_inst_info, deriv_binds, deriv_dus, deriv_tys, deriv_ty_insts)
<- tcDeriving tycl_decls inst_decls deriv_decls
- ; gbl_env <- addInsts deriv_inst_info getGblEnv
- ; return ( addTcgDUs gbl_env deriv_dus,
+
+ -- Extend the global environment also with the generated datatypes for
+ -- the generic representation
+ ; gbl_env <- addFamInsts (map ATyCon deriv_ty_insts) $
+ tcExtendGlobalEnv (map ATyCon (deriv_tys ++ deriv_ty_insts)) $
+ addInsts deriv_inst_info getGblEnv
+-- ; traceTc "Generic deriving" (vcat (map pprInstInfo deriv_inst_info))
+ ; return ( addTcgDUs gbl_env deriv_dus,
generic_inst_info ++ deriv_inst_info ++ local_info,
aux_binds `plusHsValBinds` deriv_binds)
}}}
; 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) <- checkValidInstance poly_ty tyvars theta tau
+ ; (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 []) $
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
-- Done
; return (dm_binds `unionBags` unionManyBags inst_binds_s) }
-
-tcInstDecl2 :: InstInfo Name -> TcM (LHsBinds Id)
-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}
See Note [Default methods and instances]
the default method Ids replete with their INLINE pragmas. Urk.
\begin{code}
-tc_inst_decl2 :: Id -> InstBindings Name -> TcM (LHsBinds Id)
--- Returns a binding for the dfun
-tc_inst_decl2 dfun_id inst_binds
- = 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
- -- Create dictionary Ids from the specified instance contexts.
- ; dfun_ev_vars <- newEvVars dfun_theta'
- ; self_dict <- newSelfDict 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 "self = df d1 .. dn",
- -- to use in each method binding
- -- Why? See Note [Subtle interaction of recursion and overlap]
- ; let self_ev_bind = EvBind self_dict $
- EvDFunApp dfun_id (mkTyVarTys inst_tyvars') dfun_ev_vars
+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 { -- Instantiate the instance decl with skolem constants
+ ; (inst_tyvars, dfun_theta, inst_head) <- tcSkolDFunType (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_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 <- tcSpecInstPrags dfun_id inst_binds
+ ; spec_info@(spec_inst_prags,_) <- tcSpecInstPrags dfun_id ibinds
-- Typecheck the methods
; (meth_ids, meth_binds)
- <- tcExtendTyVarEnv inst_tyvars' $
- tcInstanceMethods dfun_id clas inst_tyvars' dfun_ev_vars
- inst_tys' self_ev_bind spec_info
- op_items inst_binds
-
- -- Figure out bindings for the superclass context
- ; let tc_sc = tcSuperClass inst_tyvars' dfun_ev_vars self_ev_bind
- (sc_eqs, sc_dicts) = splitAt (classSCNEqs clas) sc_theta'
- ; (sc_dict_ids, sc_binds) <- ASSERT( equalLength sc_sels sc_dicts )
- ASSERT( all isEqPred sc_eqs )
- mapAndUnzipM tc_sc (sc_sels `zip` sc_dicts)
-
- -- NOT FINISHED!
- ; (_eq_sc_binds, sc_eq_vars) <- checkConstraints InstSkol emptyVarSet
- inst_tyvars' dfun_ev_vars $
- emitWanteds ScOrigin sc_eqs
+ <- 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
- dict_bind = mkVarBind self_dict dict_rhs
- dict_rhs = foldl mk_app inst_constr dict_and_meth_ids
- dict_and_meth_ids = sc_dict_ids ++ meth_ids
- inst_constr = L loc $ wrapId (mkWpEvVarApps sc_eq_vars
- <.> 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.
+ -- 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))
- 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 = mkWpEvVarApps dfun_ev_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
+ 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 = dfun_id
- `setIdUnfolding` mkDFunUnfolding inst_ty (map Var dict_and_meth_ids)
- -- Not right for equality superclasses
- `setInlinePragma` dfunInlinePragma
-
- (spec_inst_prags, _) = spec_info
- main_bind = AbsBinds { abs_tvs = inst_tyvars'
+ 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,
+ , 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 `unionBags`
- listToBag sc_binds)
+ ; return (unitBag (L loc main_bind) `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 (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
+ find _ [] = Nothing
+ find i (ev:evs) | pred `tcEqPred` evVarPred ev = Just (ev, i)
+ | otherwise = find (i+1) evs
------------------------------
-tcSpecInstPrags :: DFunId -> InstBindings Name
+tcSpecInstPrags :: DFunId -> InstBindings Name
-> TcM ([Located TcSpecPrag], PragFun)
tcSpecInstPrags _ (NewTypeDerived {})
= return ([], \_ -> [])
filter isSpecInstLSig uprags
-- The filter removes the pragmas for methods
; return (spec_inst_prags, mkPragFun uprags binds) }
-
-------------------------------
-tcSuperClass :: [TyVar] -> [EvVar]
- -> EvBind
- -> (Id, PredType) -> 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 tyvars dicts
- self_ev_bind@(EvBind self_dict _)
- (sc_sel, sc_pred)
- = do { (ev_binds, wanted, sc_dict)
- <- newImplication InstSkol emptyVarSet tyvars dicts $
- emitWanted ScOrigin sc_pred
-
- ; simplifySuperClass self_dict wanted
- -- We include self_dict in the 'givens'; the simplifier
- -- is clever enough to stop sc_pred geting bound by just
- -- selecting from self_dict!!
-
- ; uniq <- newUnique
- ; let sc_op_ty = mkForAllTys tyvars $ mkPiTypes dicts (varType sc_dict)
- sc_op_name = mkDerivedInternalName mkClassOpAuxOcc uniq
- (getName sc_sel)
- sc_op_id = mkLocalId sc_op_name sc_op_ty
- sc_op_bind = VarBind { var_id = sc_op_id, var_inline = False
- , var_rhs = L noSrcSpan $ wrapId sc_wrapper sc_dict }
- sc_wrapper = mkWpTyLams tyvars
- <.> mkWpLams dicts
- <.> mkWpLet (EvBinds (unitBag self_ev_bind))
- <.> mkWpLet ev_binds
-
- ; return (sc_op_id, noLoc sc_op_bind) }
\end{code}
-Note [Recursive superclasses]
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-See Trac #1470 for why we would *like* to add "self_dict" to the
-available instances here. But we can't do so because then the superclases
-get satisfied by selection from self_dict, and that leads to an immediate
-loop. What we need is to add self_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
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 <- tcSubType (SpecPragOrigin name) (SigSkol SpecInstCtxt)
- (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) 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)
tcInstanceMethods :: DFunId -> Class -> [TcTyVar]
-> [EvVar]
-> [TcType]
- -> EvBind -- "This" and its binding
- -> ([Located TcSpecPrag], PragFun)
+ -> ([Located TcSpecPrag], PragFun)
-> [(Id, DefMeth)]
-> InstBindings Name
-> TcM ([Id], [LHsBind Id])
-- The returned inst_meth_ids all have types starting
-- forall tvs. theta => ...
tcInstanceMethods dfun_id clas tyvars dfun_ev_vars inst_tys
- self_dict_ev (spec_inst_prags, prag_fn)
+ (spec_inst_prags, prag_fn)
op_items (VanillaInst binds _ standalone_deriv)
= mapAndUnzipM tc_item op_items
where
----------------------
tc_body :: Id -> Bool -> LHsBind Name -> TcM (TcId, LHsBind Id)
tc_body sel_id generated_code rn_bind
- = add_meth_ctxt 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
- ; (meth_id1, spec_prags) <- tcPrags NonRecursive False True
- meth_id (prag_fn (idName 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
- mb_dict_ev
- meth_id1 local_meth_id
- meth_sig_fn
- (SpecPrags (spec_inst_prags ++ spec_prags))
+ 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)
+
+ -- JPM: This is probably not that simple...
+ tc_default sel_id (GenDefMeth dm_name) = tc_default sel_id (DefMeth dm_name)
+{-
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
= 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
+ -- 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
- EvBind self_dict _ = self_dict_ev
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 }
+ , 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
- , SpecPrags spec_inst_prags)]
- , abs_ev_binds = EvBinds (unitBag self_dict_ev)
+ , 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
; 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
-- instance C [c] where { op = <rhs> }
-- In <rhs>, 'c' is scope but 'b' is not!
- mb_dict_ev = if null tyvars then Nothing else Just self_dict_ev
- -- Only need the self_dict stuff if there are type
- -- variables involved; otherwise overlap is not possible
- -- See Note [Subtle interaction of recursion and overlap]
- -- in TcInstDcls
-
- -- 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 generated_code rn_bind thing
- | generated_code = addLandmarkErrCtxt (derivBindCtxt clas inst_tys rn_bind) 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 _)
+ _ op_items (NewTypeDerived coi _)
-- Running example:
-- class Show b => Foo a b where
-- by the constraint solver, since the <context> may be
-- user-specified.
- = do { rep_d_stuff <- checkConstraints InstSkol emptyVarSet tyvars dfun_ev_vars $
+ = do { rep_d_stuff <- checkConstraints InstSkol tyvars dfun_ev_vars $
emitWanted ScOrigin rep_pred
; mapAndUnzipM (tc_item rep_d_stuff) op_items }
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
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
projects / ghc-hetmet.git / blobdiff