X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=9af92107eeff13ef6aa69079633f61f441469b5e;hb=ecdc15ea7813c43a4d84b7c6554a13c06f210a7e;hp=cad292b1207230ed1c3ed784538a270c5ac107ec;hpb=f4510d27c5883fe7e8570f4dd49d45a8b0122f2c;p=ghc-hetmet.git diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs index cad292b..9af9210 100644 --- a/compiler/types/FunDeps.lhs +++ b/compiler/types/FunDeps.lhs @@ -10,7 +10,7 @@ It's better to read it as: "if we know these, then we're going to know these" \begin{code} module FunDeps ( Equation, pprEquation, - oclose, grow, improve, improveOne, + oclose, grow, improveOne, checkInstCoverage, checkFunDeps, pprFundeps ) where @@ -21,17 +21,12 @@ import Name import Var import Class import TcGadt -import Type -import Coercion import TcType import InstEnv import VarSet import VarEnv import Outputable import Util -import ListSetOps - -import Data.List ( tails ) import Data.Maybe ( isJust ) \end{code} @@ -125,24 +120,43 @@ oclose preds fixed_tvs ] \end{code} +Note [Growing the tau-tvs using constraints] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +(grow preds tvs) is the result of extend the set of tyvars tvs + using all conceivable links from pred + +E.g. tvs = {a}, preds = {H [a] b, K (b,Int) c, Eq e} +Then grow precs tvs = {a,b,c} + +All the type variables from an implicit parameter are added, whether or +not they are mentioned in tvs; see Note [Implicit parameters and ambiguity] +in TcSimplify. + +See also Note [Ambiguity] in TcSimplify + \begin{code} grow :: [PredType] -> TyVarSet -> TyVarSet --- See Note [Ambiguity] in TcSimplify grow preds fixed_tvs - | null preds = fixed_tvs - | otherwise = loop fixed_tvs + | null preds = real_fixed_tvs + | otherwise = loop real_fixed_tvs where + -- Add the implicit parameters; + -- see Note [Implicit parameters and ambiguity] in TcSimplify + real_fixed_tvs = foldr unionVarSet fixed_tvs ip_tvs + loop fixed_tvs | new_fixed_tvs `subVarSet` fixed_tvs = fixed_tvs | otherwise = loop new_fixed_tvs where - new_fixed_tvs = foldl extend fixed_tvs pred_sets + new_fixed_tvs = foldl extend fixed_tvs non_ip_tvs extend fixed_tvs pred_tvs | fixed_tvs `intersectsVarSet` pred_tvs = fixed_tvs `unionVarSet` pred_tvs | otherwise = fixed_tvs - pred_sets = [tyVarsOfPred pred | pred <- preds] + (ip_tvs, non_ip_tvs) = partitionWith get_ip preds + get_ip (IParam _ ty) = Left (tyVarsOfType ty) + get_ip other = Right (tyVarsOfPred other) \end{code} %************************************************************************ @@ -153,7 +167,6 @@ grow preds fixed_tvs \begin{code} ----------- type Equation = (TyVarSet, [(Type, Type)]) -- These pairs of types should be equal, for some -- substitution of the tyvars in the tyvar set @@ -178,16 +191,6 @@ type Equation = (TyVarSet, [(Type, Type)]) pprEquation (qtvs, pairs) = vcat [ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)), nest 2 (vcat [ ppr t1 <+> ptext SLIT(":=:") <+> ppr t2 | (t1,t2) <- pairs])] - ----------- -type Pred_Loc = (PredType, SDoc) -- SDoc says where the Pred comes from - -improve :: (Class -> [Instance]) -- Gives instances for given class - -> [Pred_Loc] -- Current constraints; - -> [(Equation,Pred_Loc,Pred_Loc)] -- Derived equalities that must also hold - -- (NB the above INVARIANT for type Equation) - -- The Pred_Locs explain which two predicates were - -- combined (for error messages) \end{code} Given a bunch of predicates that must hold, such as @@ -220,20 +223,15 @@ NOTA BENE: \begin{code} -improve inst_env preds - = [ eqn | group <- equivClassesByUniq (predTyUnique . fst) (filterEqPreds preds), - eqn <- checkGroup inst_env group ] - where - filterEqPreds = filter (not . isEqPred . fst) - -- Equality predicates don't have uniques - -- In any case, improvement *generates*, rather than - -- *consumes*, equality constraints - -improveOne :: (Class -> [Instance]) - -> Pred_Loc - -> [Pred_Loc] - -> [(Equation,Pred_Loc,Pred_Loc)] +type Pred_Loc = (PredType, SDoc) -- SDoc says where the Pred comes from +improveOne :: (Class -> [Instance]) -- Gives instances for given class + -> Pred_Loc -- Do improvement triggered by this + -> [Pred_Loc] -- Current constraints + -> [(Equation,Pred_Loc,Pred_Loc)] -- Derived equalities that must also hold + -- (NB the above INVARIANT for type Equation) + -- The Pred_Locs explain which two predicates were + -- combined (for error messages) -- Just do improvement triggered by a single, distinguised predicate improveOne inst_env pred@(IParam ip ty, _) preds @@ -273,10 +271,14 @@ improveOne inst_env pred@(ClassP cls tys, _) preds = [ (eqn, p_inst, pred) | fd <- cls_fds -- Iterate through the fundeps first, -- because there often are none! - , let rough_fd_tcs = trimRoughMatchTcs cls_tvs fd rough_tcs + , let trimmed_tcs = trimRoughMatchTcs cls_tvs fd rough_tcs + -- Trim the rough_tcs based on the head of the fundep. + -- Remember that instanceCantMatch treats both argumnents + -- symmetrically, so it's ok to trim the rough_tcs, + -- rather than trimming each inst_tcs in turn , ispec@(Instance { is_tvs = qtvs, is_tys = tys_inst, - is_tcs = mb_tcs_inst }) <- instances - , not (instanceCantMatch mb_tcs_inst rough_tcs) + is_tcs = inst_tcs }) <- instances + , not (instanceCantMatch inst_tcs trimmed_tcs) , eqn <- checkClsFD qtvs fd cls_tvs tys_inst tys , let p_inst = (mkClassPred cls tys_inst, ptext SLIT("arising from the instance declaration at") @@ -286,72 +288,7 @@ improveOne inst_env pred@(ClassP cls tys, _) preds improveOne inst_env eq_pred preds = [] ----------- -checkGroup :: (Class -> [Instance]) - -> [Pred_Loc] - -> [(Equation, Pred_Loc, Pred_Loc)] - -- The preds are all for the same class or implicit param - -checkGroup inst_env (p1@(IParam _ ty, _) : ips) - = -- For implicit parameters, all the types must match - [ ((emptyVarSet, [(ty,ty')]), p1, p2) - | p2@(IParam _ ty', _) <- ips, not (ty `tcEqType` ty')] - -checkGroup inst_env clss@((ClassP cls _, _) : _) - = -- For classes life is more complicated - -- Suppose the class is like - -- classs C as | (l1 -> r1), (l2 -> r2), ... where ... - -- Then FOR EACH PAIR (ClassP c tys1, ClassP c tys2) in the list clss - -- we check whether - -- U l1[tys1/as] = U l2[tys2/as] - -- (where U is a unifier) - -- - -- If so, we return the pair - -- U r1[tys1/as] = U l2[tys2/as] - -- - -- We need to do something very similar comparing each predicate - -- with relevant instance decls - - instance_eqns ++ pairwise_eqns - -- NB: we put the instance equations first. This biases the - -- order so that we first improve individual constraints against the - -- instances (which are perhaps in a library and less likely to be - -- wrong; and THEN perform the pairwise checks. - -- The other way round, it's possible for the pairwise check to succeed - -- and cause a subsequent, misleading failure of one of the pair with an - -- instance declaration. See tcfail143.hs for an exmample - where - (cls_tvs, cls_fds) = classTvsFds cls - instances = inst_env cls - - -- NOTE that we iterate over the fds first; they are typically - -- empty, which aborts the rest of the loop. - pairwise_eqns :: [(Equation,Pred_Loc,Pred_Loc)] - pairwise_eqns -- This group comes from pairwise comparison - = [ (eqn, p1, p2) - | fd <- cls_fds, - p1@(ClassP _ tys1, _) : rest <- tails clss, - p2@(ClassP _ tys2, _) <- rest, - eqn <- checkClsFD emptyVarSet fd cls_tvs tys1 tys2 - ] - - instance_eqns :: [(Equation,Pred_Loc,Pred_Loc)] - instance_eqns -- This group comes from comparing with instance decls - = [ (eqn, p1, p2) - | fd <- cls_fds, -- Iterate through the fundeps first, - -- because there often are none! - p2@(ClassP _ tys2, _) <- clss, - let rough_tcs2 = trimRoughMatchTcs cls_tvs fd (roughMatchTcs tys2), - ispec@(Instance { is_tvs = qtvs, is_tys = tys1, - is_tcs = mb_tcs1 }) <- instances, - not (instanceCantMatch mb_tcs1 rough_tcs2), - eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2, - let p1 = (mkClassPred cls tys1, - ptext SLIT("arising from the instance declaration at") <+> - ppr (getSrcLoc ispec)) - ] ----------- checkClsFD :: TyVarSet -- Quantified type variables; see note below -> FunDep TyVar -> [TyVar] -- One functional dependency from the class -> [Type] -> [Type] @@ -522,11 +459,11 @@ badFunDeps :: [Instance] -> Class badFunDeps cls_insts clas ins_tv_set ins_tys = [ ispec | fd <- fds, -- fds is often empty let trimmed_tcs = trimRoughMatchTcs clas_tvs fd rough_tcs, - ispec@(Instance { is_tcs = mb_tcs, is_tvs = tvs, + ispec@(Instance { is_tcs = inst_tcs, is_tvs = tvs, is_tys = tys }) <- cls_insts, -- Filter out ones that can't possibly match, -- based on the head of the fundep - not (instanceCantMatch trimmed_tcs mb_tcs), + not (instanceCantMatch inst_tcs trimmed_tcs), notNull (checkClsFD (tvs `unionVarSet` ins_tv_set) fd clas_tvs tys ins_tys) ] @@ -536,16 +473,16 @@ badFunDeps cls_insts clas ins_tv_set ins_tys trimRoughMatchTcs :: [TyVar] -> FunDep TyVar -> [Maybe Name] -> [Maybe Name] -- Computing rough_tcs for a particular fundep --- class C a b c | a c -> b where ... +-- class C a b c | a -> b where ... -- For each instance .... => C ta tb tc --- we want to match only on the types ta, tb; so our +-- we want to match only on the types ta, tc; so our -- rough-match thing must similarly be filtered. -- Hence, we Nothing-ise the tb type right here -trimRoughMatchTcs clas_tvs (ltvs,_) mb_tcs +trimRoughMatchTcs clas_tvs (_,rtvs) mb_tcs = zipWith select clas_tvs mb_tcs where - select clas_tv mb_tc | clas_tv `elem` ltvs = mb_tc - | otherwise = Nothing + select clas_tv mb_tc | clas_tv `elem` rtvs = Nothing + | otherwise = mb_tc \end{code}