import SrcLoc
import Util
import Outputable
-import Maybes
import Bag
import BasicTypes
import HscTypes
{-# 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 = <rhs>
-- Source code; run the type checker on this
-- NB: Type variable 'a' (but not 'b') is in scope in <rhs>
-- 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)
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).
+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 variales involved; otherwise there can be no overlap and
+none of this arises.
Note [Tricky type variable scoping]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- newtype N a = MkN (Tree [a]) deriving( Foo Int )
--
-- The newtype gives an FC axiom looking like
--- axiom CoN a :: N a :=: Tree [a]
+-- 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:
rigid_info = InstSkol
origin = SigOrigin rigid_info
inst_ty = idType dfun_id
- ; (tvs, theta, inst_head_ty) <- tcSkolSigType rigid_info 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
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'
+ ; inst_loc <- getInstLoc origin
+ ; dfun_dicts <- newDictBndrs inst_loc 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_dicts get bound by just selecting from this_dict!!
; sc_binds <- addErrCtxt superClassCtxt $
- tcSimplifySuperClasses inst_loc dfun_dicts (rep_dict:sc_dicts)
+ 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 the_coercion (instToId 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, [])]
+ AbsBinds inst_tvs' (map instToVar dfun_dicts)
+ [(inst_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 <rep_ty>)
+ -- 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
-- 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')
+ sc_loc <- getInstLoc InstScOrigin
+ sc_dicts <- newDictOccs sc_loc sc_theta' -- These are wanted
+ 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.
-- 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
+ let this_dict_id = instToId this_dict
+ dfun_lam_vars = map instToVar dfun_dicts -- Includes equalities
+ prag_fn = mkPragFun uprags
+ tc_meth = tcInstanceMethod loc clas inst_tyvars'
+ dfun_dicts
+ dfun_theta' inst_tys'
+ this_dict dfun_id
+ prag_fn monobinds
+ (meth_exprs, meth_binds) <- tcExtendTyVarEnv inst_tyvars' $
+ 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_dicts get bound by just selecting from this_dict!!
sc_binds <- addErrCtxt superClassCtxt $
- tcSimplifySuperClasses inst_loc dfun_insts
- wanted_sc_insts
+ tcSimplifySuperClasses inst_loc this_dict dfun_dicts sc_dicts
-- Note [Recursive superclasses]
- -- It's possible that the superclass stuff might unified one
- -- of the inst_tyavars' with something in the envt
+ -- It's possible that the superclass stuff might unified something
+ -- in the envt with one of the inst_tyvars'
checkSigTyVars inst_tyvars'
-- Deal with 'SPECIALISE instance' pragmas
-- Create the result bindings
let
dict_constr = classDataCon clas
- inline_prag | null dfun_insts = []
+ inline_prag | null dfun_dicts = []
| otherwise = [L loc (InlinePrag (Inline AlwaysActive True))]
-- Always inline the dfun; this is an experimental decision
-- because it makes a big performance difference sometimes.
--
-- See Note [Inline dfuns] below
- dict_rhs = mkHsConApp dict_constr (inst_tys' ++ mkTyVarTys sc_covars)
- (map HsVar sc_dict_ids ++ meth_exprs)
+ sc_dict_vars = map instToVar sc_dicts
+ dict_bind = L loc (VarBind this_dict_id dict_rhs)
+ dict_rhs = foldl (\ f a -> L loc (HsApp f (L loc a))) inst_constr meth_exprs
+ inst_constr = L loc $ wrapId (mkWpApps sc_dict_vars <.> 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
-- 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)]
+ inst_tyvars'
+ dfun_lam_vars
+ [(inst_tyvars', 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
- where
- eqPredToCoVar (EqPred ty1 ty2) = newMetaCoVar ty1 ty2
- eqPredToCoVar _ = panic "TcInstDcls.mkMetaCoVars"
\end{code}
Note [Recursive superclasses]
- Use tcValBinds to do the checking
\begin{code}
-tcInstanceMethod :: SrcSpan -> Class -> [TcTyVar] -> [Var]
+tcInstanceMethod :: SrcSpan -> Class -> [TcTyVar] -> [Inst]
-> TcThetaType -> [TcType]
- -> Id -> Id
+ -> Inst -> Id
-> TcPragFun -> LHsBinds Name
-> (Id, DefMeth)
-> TcM (HsExpr Id, LHsBinds 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
+tcInstanceMethod loc clas tyvars dfun_dicts theta inst_tys
+ this_dict dfun_id prag_fn binds_in (sel_id, dm_info)
+ = do { cloned_this <- cloneDict this_dict
+ -- Need to clone the dict in case it is floated out, and
+ -- then clashes with its friends
+ ; uniq1 <- newUnique
+ ; let local_meth_name = mkInternalName uniq1 sel_occ loc -- Same OccName
+ this_dict_bind = L loc $ VarBind (instToId cloned_this) $
+ L loc $ wrapId meth_wrapper dfun_id
+ mb_this_bind | null tyvars = Nothing
+ | otherwise = Just (cloned_this, this_dict_bind)
+ -- Only need the this_dict stuff if there are type variables
+ -- involved; otherwise overlap is not possible
+ -- See Note [Subtle interaction of recursion and overlap]
+
+ tc_body rn_bind = do { (meth_id, tc_binds) <- tcInstanceMethodBody
+ InstSkol clas tyvars dfun_dicts theta inst_tys
+ mb_this_bind sel_id
+ local_meth_name
+ meth_sig_fn meth_prag_fn rn_bind
+ ; return (wrapId meth_wrapper meth_id, tc_binds) }
; case (findMethodBind sel_name local_meth_name binds_in, dm_info) of
-- There is a user-supplied method binding, so use it
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)
+ this_dict_id = instToId this_dict
+
+ meth_prag_fn _ = prag_fn sel_name
+ meth_sig_fn _ = Just [] -- 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 = <rhs> }
+ -- In <rhs>, 'c' is scope but 'b' is not!
+
+ error_rhs = 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 ])
dm_wrapper = WpApp this_dict_id <.> mkWpTyApps inst_tys
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) }
- where
+ dfun_lam_vars = map instToVar dfun_dicts
meth_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys tyvars)
+
wrapId :: HsWrapper -> id -> HsExpr id
wrapId wrapper id = mkHsWrap wrapper (HsVar id)
\end{code}