| otherwise -- Otherwise we must generate a binding
= do { uniq <- newUnique
; span <- getSrcSpanM
- ; let (eq_givens,dict_givens) = partitionGivenEqInsts givens
+ ; let (eq_givens, dict_givens) = partition isEqInst givens
eq_tyvar_cos = map TyVarTy $ uniqSetToList $ tyVarsOfTypes $ map eqInstType eq_givens
; let name = mkInternalName uniq (mkVarOcc "ic") span
implic_inst = ImplicInst { tci_name = name, tci_reft = reft,
tci_tyvars = all_tvs,
tci_given = (eq_givens ++ dict_givens),
tci_wanted = irreds, tci_loc = loc }
- ; let
- -- only create binder for dict_irreds
- -- we
- (eq_irreds,dict_irreds) = partitionWantedEqInsts irreds
+ ; let -- only create binder for dict_irreds
+ (eq_irreds, dict_irreds) = partition isEqInst irreds
n_dict_irreds = length dict_irreds
dict_irred_ids = map instToId dict_irreds
tup_ty = mkTupleTy Boxed n_dict_irreds (map idType dict_irred_ids)
-- Note [SUPER-CLASS LOOP 1]
\end{code}
+
%************************************************************************
%* *
\subsection[reduce]{@reduce@}
%* *
%************************************************************************
+Note [Ancestor Equalities]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+During context reduction, we add to the wanted equalities also those
+equalities that (transitively) occur in superclass contexts of wanted
+class constraints. Consider the following code
+
+ class a ~ Int => C a
+ instance C Int
+
+If (C a) is wanted, we want to add (a ~ Int), which will be discharged by
+substituting Int for a. Hence, we ultimately want (C Int), which we
+discharge with the explicit instance.
\begin{code}
reduceContext :: RedEnv
text "----------------------"
]))
+ ; let givens = red_givens env
+ (given_eqs0, given_dicts0) = partition isEqInst givens
+ (wanted_eqs0, wanted_dicts) = partition isEqInst wanteds
- ; let givens = red_givens env
- (given_eqs0,given_dicts0) = partitionGivenEqInsts givens
- (wanted_eqs0,wanted_dicts) = partitionWantedEqInsts wanteds
+ -- We want to add as wanted equalities those that (transitively)
+ -- occur in superclass contexts of wanted class constraints.
+ -- See Note [Ancestor Equalities]
+ ; ancestor_eqs <- ancestorEqualities wanted_dicts
+ ; let wanted_eqs = wanted_eqs0 ++ ancestor_eqs
+ ; traceTc $ text "reduceContext: ancestor eqs" <+> ppr ancestor_eqs
- ; wanted_ancestor_eqs <- (mapM wantedAncestorEqualities wanted_dicts >>= \ls -> return (concat ls))
- ; traceTc (text "test wanted SCs" <+> ppr wanted_ancestor_eqs)
- ; let wanted_eqs = wanted_ancestor_eqs ++ wanted_eqs0
+ -- 1. Normalise the *given* *equality* constraints
+ ; (given_eqs, eliminate_skolems) <- normaliseGivens given_eqs0
- ; -- 1. Normalise the *given* *equality* constraints
- (given_eqs,eliminate_skolems) <- normaliseGivens given_eqs0
-
- ; -- 2. Normalise the *given* *dictionary* constraints
+ -- 2. Normalise the *given* *dictionary* constraints
-- wrt. the toplevel and given equations
- (given_dicts,given_binds) <- normaliseGivenDicts given_eqs given_dicts0
+ ; (given_dicts, given_binds) <- normaliseGivenDicts given_eqs
+ given_dicts0
- ; -- 3. Solve the *wanted* *equation* constraints
- eq_irreds0 <- solveWanteds given_eqs wanted_eqs
+ -- 3. Solve the *wanted* *equation* constraints
+ ; eq_irreds0 <- solveWanteds given_eqs wanted_eqs
- -- 4. Normalise the *wanted* equality constraints with respect to each other
+ -- 4. Normalise the *wanted* equality constraints with respect to
+ -- each other
; eq_irreds <- normaliseWanteds eq_irreds0
--- -- Do the real work
--- -- Process non-implication constraints first, so that they are
--- -- available to help solving the implication constraints
--- -- ToDo: seems a bit inefficient and ad-hoc
--- ; let (implics, rest) = partition isImplicInst wanteds
--- ; avails <- reduceList env (rest ++ implics) init_state
-
-- 5. Build the Avail mapping from "given_dicts"
; init_state <- foldlM addGiven emptyAvails given_dicts
; wanted_dicts' <- zonkInsts wanted_dicts
; avails <- reduceList env wanted_dicts' init_state
; (binds, irreds0, needed_givens) <- extractResults avails wanted_dicts'
- ; traceTc (text "reduceContext extractresults" <+> vcat
- [ppr avails,ppr wanted_dicts',ppr binds,ppr needed_givens])
+ ; traceTc $ text "reduceContext extractresults" <+> vcat
+ [ppr avails,ppr wanted_dicts',ppr binds,ppr needed_givens]
- ; -- 7. Normalise the *wanted* *dictionary* constraints
+ -- 7. Normalise the *wanted* *dictionary* constraints
-- wrt. the toplevel and given equations
- (irreds1,normalise_binds1) <- normaliseWantedDicts given_eqs irreds0
+ ; (irreds1,normalise_binds1) <- normaliseWantedDicts given_eqs irreds0
- ; -- 8. Substitute the wanted *equations* in the wanted *dictionaries*
- (irreds,normalise_binds2) <- substEqInDictInsts eq_irreds irreds1
+ -- 8. Substitute the wanted *equations* in the wanted *dictionaries*
+ ; (irreds,normalise_binds2) <- substEqInDictInsts eq_irreds irreds1
- ; -- 9. eliminate the artificial skolem constants introduced in 1.
- eliminate_skolems
+ -- 9. eliminate the artificial skolem constants introduced in 1.
+ ; eliminate_skolems
-- If there was some FD improvement,
-- or new wanted equations have been exposed,
; let improved = availsImproved avails
|| (not $ isEmptyBag normalise_binds1)
|| (not $ isEmptyBag normalise_binds2)
- || (not $ null $ fst $ partitionGivenEqInsts irreds)
+ || (any isEqInst irreds)
; traceTc (text "reduceContext end" <+> (vcat [
text "----------------------",
text "----------------------"
]))
- ; return (improved, given_binds `unionBags` normalise_binds1 `unionBags` normalise_binds2 `unionBags` binds, irreds ++ eq_irreds, needed_givens) }
+ ; return (improved,
+ given_binds `unionBags` normalise_binds1
+ `unionBags` normalise_binds2
+ `unionBags` binds,
+ irreds ++ eq_irreds,
+ needed_givens)
+ }
tcImproveOne :: Avails -> Inst -> TcM ImprovementDone
tcImproveOne avails inst
-- when inferring types.
; let dict_wanteds = filter (not . isEqInst) wanteds
- (extra_eq_givens,extra_dict_givens) = partitionGivenEqInsts extra_givens
+ (extra_eq_givens, extra_dict_givens) = partition isEqInst extra_givens
dict_ids = map instToId extra_dict_givens
-- TOMDO: given equational constraints bug!
-- we need a different evidence for given
where
is_loop pred = any (`tcEqType` mkPredTy pred) dep_tys
-- Note: this compares by *type*, not by Unique
- deps = findAllDeps (unitVarSet (instToId inst)) avail
+ deps = findAllDeps (unitVarSet (instToVar inst)) avail
dep_tys = map idType (varSetElems deps)
findAllDeps :: IdSet -> AvailHow -> IdSet
; addSCs is_loop avails' sc_dict }
where
sc_sel_rhs = L (instSpan dict) (HsWrap co_fn (HsVar sc_sel))
- co_fn = WpApp (instToId dict) <.> mkWpTyApps tys
+ co_fn = WpApp (instToVar dict) <.> mkWpTyApps tys
is_given :: Inst -> Bool
is_given sc_dict = case findAvail avails sc_dict of
Just (Given _) -> True -- Given is cheaper than superclass selection
other -> False
-
-wantedAncestorEqualities :: Inst -> TcM [Inst]
-wantedAncestorEqualities dict
- | isClassDict dict
- = mapM mkWantedEqInst $ filter isEqPred $ bagToList $ wantedAncestorEqualities' (dictPred dict) emptyBag
- | otherwise
- = return []
-
-wantedAncestorEqualities' :: PredType -> Bag PredType -> Bag PredType
-wantedAncestorEqualities' pred bag
- = ASSERT( isClassPred pred )
- let (clas, tys) = getClassPredTys pred
+-- From the a set of insts obtain all equalities that (transitively) occur in
+-- superclass contexts of class constraints (aka the ancestor equalities).
+--
+ancestorEqualities :: [Inst] -> TcM [Inst]
+ancestorEqualities
+ = mapM mkWantedEqInst -- turn only equality predicates..
+ . filter isEqPred -- ..into wanted equality insts
+ . bagToList
+ . addAEsToBag emptyBag -- collect the superclass constraints..
+ . map dictPred -- ..of all predicates in a bag
+ . filter isClassDict
+ where
+ addAEsToBag :: Bag PredType -> [PredType] -> Bag PredType
+ addAEsToBag bag [] = bag
+ addAEsToBag bag (pred:preds)
+ | pred `elemBag` bag = addAEsToBag bag preds
+ | isEqPred pred = addAEsToBag bagWithPred preds
+ | isClassPred pred = addAEsToBag bagWithPred predsWithSCs
+ | otherwise = addAEsToBag bag preds
+ where
+ bagWithPred = bag `snocBag` pred
+ predsWithSCs = preds ++ substTheta (zipTopTvSubst tyvars tys) sc_theta
+ --
(tyvars, sc_theta, _, _) = classBigSig clas
- sc_theta' = substTheta (zipTopTvSubst tyvars tys) sc_theta
- add_sc bag sc_pred
- | elemBag sc_pred bag = bag
- | not (isEqPred sc_pred)
- && not (isClassPred sc_pred)
- = bag
- | isEqPred sc_pred = consBag sc_pred bag
- | otherwise = let bag' = consBag sc_pred bag
- in wantedAncestorEqualities' sc_pred bag'
- in foldl add_sc bag sc_theta'
-
+ (clas, tys) = getClassPredTys pred
\end{code}
+
%************************************************************************
%* *
\section{tcSimplifyTop: defaulting}
projects / ghc-hetmet.git / commitdiff