X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypes%2FFunDeps.lhs;h=af42ee98a674e65b6dec47fd27ca3d25ec63bc8e;hb=69e62273a69dbfd974c6a721176438b1b03345d2;hp=f8a9fbafb16b3694f6af1fb1f798670736197cf7;hpb=92cee1fc0f88395d566888cdab8fdfdd2fb906a2;p=ghc-hetmet.git diff --git a/ghc/compiler/types/FunDeps.lhs b/ghc/compiler/types/FunDeps.lhs index f8a9fba..af42ee9 100644 --- a/ghc/compiler/types/FunDeps.lhs +++ b/ghc/compiler/types/FunDeps.lhs @@ -8,25 +8,28 @@ It's better to read it as: "if we know these, then we're going to know these" \begin{code} module FunDeps ( Equation, pprEquation, pprEquationDoc, - oclose, grow, improve, checkInstFDs, checkClsFD, pprFundeps + oclose, grow, improve, + checkInstFDs, checkFunDeps, + pprFundeps ) where #include "HsVersions.h" -import Name ( getSrcLoc ) -import Var ( Id, TyVar ) +import Name ( Name, getSrcLoc ) +import Var ( TyVar ) import Class ( Class, FunDep, classTvsFds ) -import Subst ( mkSubst, emptyInScopeSet, substTy ) -import TcType ( Type, ThetaType, SourceType(..), PredType, - predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred, - unifyTyListsX, unifyExtendTysX, tcEqType - ) -import PprType ( ) +import Unify ( tcUnifyTys, BindFlag(..) ) +import Type ( substTys, notElemTvSubst ) +import TcType ( Type, ThetaType, PredType(..), tcEqType, + predTyUnique, mkClassPred, tyVarsOfTypes, tyVarsOfPred ) +import InstEnv ( Instance(..), InstEnv, instanceHead, classInstances, + instanceCantMatch, roughMatchTcs ) import VarSet import VarEnv import Outputable +import Util ( notNull ) import List ( tails ) -import Maybes ( maybeToBool ) +import Maybe ( isJust ) import ListSetOps ( equivClassesByUniq ) \end{code} @@ -148,35 +151,39 @@ grow preds fixed_tvs \begin{code} ---------- -type Equation = (TyVarSet, Type, Type) -- These two types should be equal, for some - -- substitution of the tyvars in the tyvar set - -- For example, ({a,b}, (a,Int,b), (Int,z,Bool)) - -- We unify z with Int, but since a and b are quantified we do nothing to them - -- We usually act on an equation by instantiating the quantified type varaibles - -- to fresh type variables, and then calling the standard unifier. - -- - -- INVARIANT: they aren't already equal - -- - +type Equation = (TyVarSet, [(Type, Type)]) +-- These pairs of types should be equal, for some +-- substitution of the tyvars in the tyvar set +-- INVARIANT: corresponding types aren't already equal + +-- It's important that we have a *list* of pairs of types. Consider +-- class C a b c | a -> b c where ... +-- instance C Int x x where ... +-- Then, given the constraint (C Int Bool v) we should improve v to Bool, +-- via the equation ({x}, [(Bool,x), (v,x)]) +-- This would not happen if the class had looked like +-- class C a b c | a -> b, a -> c + +-- To "execute" the equation, make fresh type variable for each tyvar in the set, +-- instantiate the two types with these fresh variables, and then unify. +-- +-- For example, ({a,b}, (a,Int,b), (Int,z,Bool)) +-- We unify z with Int, but since a and b are quantified we do nothing to them +-- We usually act on an equation by instantiating the quantified type varaibles +-- to fresh type variables, and then calling the standard unifier. pprEquationDoc (eqn, doc) = vcat [pprEquation eqn, nest 2 doc] -pprEquation (qtvs, t1, t2) = ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)) - <+> ppr t1 <+> ptext SLIT(":=:") <+> ppr t2 +pprEquation (qtvs, pairs) + = vcat [ptext SLIT("forall") <+> braces (pprWithCommas ppr (varSetElems qtvs)), + nest 2 (vcat [ ppr t1 <+> ptext SLIT(":=:") <+> ppr t2 | (t1,t2) <- pairs])] ---------- -improve :: InstEnv Id -- Gives instances for given class +improve :: (Class -> [Instance]) -- Gives instances for given class -> [(PredType,SDoc)] -- Current constraints; doc says where they come from -> [(Equation,SDoc)] -- Derived equalities that must also hold -- (NB the above INVARIANT for type Equation) -- The SDoc explains why the equation holds (for error messages) - -type InstEnv a = Class -> [(TyVarSet, [Type], a)] --- This is a bit clumsy, because InstEnv is really --- defined in module InstEnv. However, we don't want --- to define it (and ClsInstEnv) here because InstEnv --- is their home. Nor do we want to make a recursive --- module group (InstEnv imports stuff from FunDeps). \end{code} Given a bunch of predicates that must hold, such as @@ -214,12 +221,14 @@ improve inst_env preds eqn <- checkGroup inst_env group ] ---------- -checkGroup :: InstEnv Id -> [(PredType,SDoc)] -> [(Equation, SDoc)] +checkGroup :: (Class -> [Instance]) + -> [(PredType,SDoc)] + -> [(Equation, SDoc)] -- 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'), mkEqnMsg p1 p2) + [ ((emptyVarSet, [(ty,ty')]), mkEqnMsg p1 p2) | p2@(IParam _ ty', _) <- ips, not (ty `tcEqType` ty')] checkGroup inst_env clss@((ClassP cls _, _) : _) @@ -240,7 +249,7 @@ checkGroup inst_env clss@((ClassP cls _, _) : _) where (cls_tvs, cls_fds) = classTvsFds cls - cls_inst_env = inst_env cls + instances = inst_env cls -- NOTE that we iterate over the fds first; they are typically -- empty, which aborts the rest of the loop. @@ -256,12 +265,17 @@ checkGroup inst_env clss@((ClassP cls _, _) : _) instance_eqns :: [(Equation,SDoc)] instance_eqns -- This group comes from comparing with instance decls = [ (eqn, mkEqnMsg p1 p2) - | fd <- cls_fds, - (qtvs, tys1, dfun_id) <- cls_inst_env, - let p1 = (mkClassPred cls tys1, - ptext SLIT("arising from the instance declaration at") <+> ppr (getSrcLoc dfun_id)), + | fd <- cls_fds, -- Iterate through the fundeps first, + -- because there often are none! p2@(ClassP _ tys2, _) <- clss, - eqn <- checkClsFD qtvs fd cls_tvs tys1 tys2 + 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)) ] mkEqnMsg (pred1,from1) (pred2,from2) @@ -280,6 +294,7 @@ checkClsFD qtvs fd clas_tvs tys1 tys2 -- to make the types match. For example, given -- class C a b | a->b where ... -- instance C (Maybe x) (Tree x) where .. +-- -- and an Inst of form (C (Maybe t1) t2), -- then we will call checkClsFD with -- @@ -287,31 +302,54 @@ checkClsFD qtvs fd clas_tvs tys1 tys2 -- tys2 = [Maybe t1, t2] -- -- We can instantiate x to t1, and then we want to force --- Tree x [t1/x] :=: t2 - --- We use 'unify' even though we are often only matching --- unifyTyListsX will only bind variables in qtvs, so it's OK! - = case unifyTyListsX qtvs ls1 ls2 of - Nothing -> [] - Just unif -> -- pprTrace "checkFD" (vcat [ppr_fd fd, - -- ppr (varSetElems qtvs) <+> (ppr ls1 $$ ppr ls2), - -- ppr unif]) $ - [ (qtvs', substTy full_unif r1, substTy full_unif r2) - | (r1,r2) <- rs1 `zip` rs2, - not (maybeToBool (unifyExtendTysX qtvs unif r1 r2))] - -- Don't include any equations that already hold - -- taking account of the fact that any qtvs that aren't - -- already instantiated can be instantiated to anything at all - -- NB: qtvs, not qtvs' because unifyExtendTysX only tries to - -- look template tyvars up in the substitution +-- (Tree x) [t1/x] :=: t2 +-- +-- This function is also used when matching two Insts (rather than an Inst +-- against an instance decl. In that case, qtvs is empty, and we are doing +-- an equality check +-- +-- This function is also used by InstEnv.badFunDeps, which needs to *unify* +-- For the one-sided matching case, the qtvs are just from the template, +-- so we get matching +-- + = ASSERT2( length tys1 == length tys2 && + length tys1 == length clas_tvs + , ppr tys1 <+> ppr tys2 ) + + case tcUnifyTys bind_fn ls1 ls2 of + Nothing -> [] + Just subst | isJust (tcUnifyTys bind_fn rs1' rs2') + -- Don't include any equations that already hold. + -- Reason: then we know if any actual improvement has happened, + -- in which case we need to iterate the solver + -- In making this check we must taking account of the fact that any + -- qtvs that aren't already instantiated can be instantiated to anything + -- at all + -> [] + + | otherwise -- Aha! A useful equation + -> [ (qtvs', zip rs1' rs2')] + -- We could avoid this substTy stuff by producing the eqn + -- (qtvs, ls1++rs1, ls2++rs2) + -- which will re-do the ls1/ls2 unification when the equation is + -- executed. What we're doing instead is recording the partial + -- work of the ls1/ls2 unification leaving a smaller unification problem where - full_unif = mkSubst emptyInScopeSet unif - -- No for-alls in sight; hmm - - qtvs' = filterVarSet (\v -> not (v `elemSubstEnv` unif)) qtvs + rs1' = substTys subst rs1 + rs2' = substTys subst rs2 + qtvs' = filterVarSet (`notElemTvSubst` subst) qtvs -- qtvs' are the quantified type variables -- that have not been substituted out + -- + -- Eg. class C a b | a -> b + -- instance C Int [y] + -- Given constraint C Int z + -- we generate the equation + -- ({y}, [y], z) where + bind_fn tv | tv `elemVarSet` qtvs = BindMe + | otherwise = Skolem + (ls1, rs1) = instFD fd clas_tvs tys1 (ls2, rs2) = instFD fd clas_tvs tys2 @@ -340,6 +378,87 @@ checkInstFDs theta clas inst_taus (ls,rs) = instFD fd tyvars inst_taus \end{code} + +%************************************************************************ +%* * + Check that a new instance decl is OK wrt fundeps +%* * +%************************************************************************ + +Here is the bad case: + class C a b | a->b where ... + instance C Int Bool where ... + instance C Int Char where ... + +The point is that a->b, so Int in the first parameter must uniquely +determine the second. In general, given the same class decl, and given + + instance C s1 s2 where ... + instance C t1 t2 where ... + +Then the criterion is: if U=unify(s1,t1) then U(s2) = U(t2). + +Matters are a little more complicated if there are free variables in +the s2/t2. + + class D a b c | a -> b + instance D a b => D [(a,a)] [b] Int + instance D a b => D [a] [b] Bool + +The instance decls don't overlap, because the third parameter keeps +them separate. But we want to make sure that given any constraint + D s1 s2 s3 +if s1 matches + + +\begin{code} +checkFunDeps :: (InstEnv, InstEnv) -> Instance + -> Maybe [Instance] -- Nothing <=> ok + -- Just dfs <=> conflict with dfs +-- Check wheher adding DFunId would break functional-dependency constraints +-- Used only for instance decls defined in the module being compiled +checkFunDeps inst_envs ispec + | null bad_fundeps = Nothing + | otherwise = Just bad_fundeps + where + (ins_tvs, _, clas, ins_tys) = instanceHead ispec + ins_tv_set = mkVarSet ins_tvs + cls_inst_env = classInstances inst_envs clas + bad_fundeps = badFunDeps cls_inst_env clas ins_tv_set ins_tys + +badFunDeps :: [Instance] -> Class + -> TyVarSet -> [Type] -- Proposed new instance type + -> [Instance] +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, + 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), + notNull (checkClsFD (tvs `unionVarSet` ins_tv_set) + fd clas_tvs tys ins_tys) + ] + where + (clas_tvs, fds) = classTvsFds clas + rough_tcs = roughMatchTcs 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 ... +-- For each instance .... => C ta tb tc +-- we want to match only on the types ta, tb; so our +-- rough-match thing must similarly be filtered. +-- Hence, we Nothing-ise the tb type right here +trimRoughMatchTcs clas_tvs (ltvs,_) mb_tcs + = zipWith select clas_tvs mb_tcs + where + select clas_tv mb_tc | clas_tv `elem` ltvs = mb_tc + | otherwise = Nothing +\end{code} + + %************************************************************************ %* * \subsection{Miscellaneous} @@ -353,3 +472,4 @@ pprFundeps fds = hsep (ptext SLIT("|") : punctuate comma (map ppr_fd fds)) ppr_fd (us, vs) = hsep [interppSP us, ptext SLIT("->"), interppSP vs] \end{code} +