X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypes%2FFunDeps.lhs;h=665f2311f0b580f10920cef71fce0f2266551b58;hb=ede4d6f3d1c7ec99c2bbf2148fcb56588a649979;hp=5ece0471884ec94b704736a60133a1328c7ce17f;hpb=1c64864faf17b32ecaefa37fe8aa8fac5304f830;p=ghc-hetmet.git diff --git a/compiler/types/FunDeps.lhs b/compiler/types/FunDeps.lhs index 5ece047..665f231 100644 --- a/compiler/types/FunDeps.lhs +++ b/compiler/types/FunDeps.lhs @@ -1,37 +1,33 @@ - +% +% (c) The University of Glasgow 2006 % (c) The GRASP/AQUA Project, Glasgow University, 2000 % -\section[FunDeps]{FunDeps - functional dependencies} + +FunDeps - functional dependencies 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, + oclose, grow, improveOne, checkInstCoverage, checkFunDeps, pprFundeps ) where #include "HsVersions.h" -import Name ( Name, getSrcLoc ) -import Var ( TyVar ) -import Class ( Class, FunDep, pprFundeps, classTvsFds ) -import TcGadt ( tcUnifyTys, BindFlag(..) ) -import Type ( substTys, notElemTvSubst ) -import Coercion ( isEqPred ) -import TcType ( Type, PredType(..), tcEqType, - predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred ) -import InstEnv ( Instance(..), InstEnv, instanceHead, classInstances, - instanceCantMatch, roughMatchTcs ) +import Name +import Var +import Class +import TcGadt +import TcType +import InstEnv import VarSet import VarEnv import Outputable -import Util ( notNull ) -import List ( tails ) -import Maybe ( isJust ) -import ListSetOps ( equivClassesByUniq ) +import Util +import Data.Maybe ( isJust ) \end{code} @@ -124,24 +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} %************************************************************************ @@ -152,7 +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 @@ -177,16 +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 @@ -219,81 +223,68 @@ 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 - ----------- -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 +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 + = [ ((emptyVarSet, [(ty,ty2)]), pred, p2) + | p2@(IParam ip2 ty2, _) <- preds + , ip==ip2 + , not (ty `tcEqType` ty2)] + +improveOne inst_env pred@(ClassP cls tys, _) preds + | tys `lengthAtLeast` 2 + = 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 - + -- instance declaration. See tcfail143.hs for an example where (cls_tvs, cls_fds) = classTvsFds cls instances = inst_env cls + rough_tcs = roughMatchTcs tys -- 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 + = [ (eqn, pred, p2) + | fd <- cls_fds + , p2@(ClassP cls2 tys2, _) <- preds + , cls == cls2 + , eqn <- checkClsFD emptyVarSet fd cls_tvs tys 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, + = [ (eqn, p_inst, pred) + | 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)) + , let rough_fd_tcs = trimRoughMatchTcs cls_tvs fd rough_tcs + , ispec@(Instance { is_tvs = qtvs, is_tys = tys_inst, + is_tcs = mb_tcs_inst }) <- instances + , not (instanceCantMatch mb_tcs_inst rough_fd_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") + <+> ppr (getSrcLoc ispec)) ] ----------- + +improveOne inst_env eq_pred preds + = [] + + checkClsFD :: TyVarSet -- Quantified type variables; see note below -> FunDep TyVar -> [TyVar] -- One functional dependency from the class -> [Type] -> [Type]