X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypes%2FInstEnv.lhs;h=965ba55e55cd42e211441ae0ac780614852ccce0;hb=c9ba9f57aba0f91918d292ee3d05763791bcf5db;hp=ad2bd1f9b5a099f72e48656f2e3713287184bde7;hpb=01e0566e61e4222600c7ba0a2d35d6102fd1afb5;p=ghc-hetmet.git diff --git a/ghc/compiler/types/InstEnv.lhs b/ghc/compiler/types/InstEnv.lhs index ad2bd1f..965ba55 100644 --- a/ghc/compiler/types/InstEnv.lhs +++ b/ghc/compiler/types/InstEnv.lhs @@ -7,32 +7,31 @@ The bits common to TcInstDcls and TcDeriv. \begin{code} module InstEnv ( - DFunId, ClsInstEnv, InstEnv, + DFunId, InstEnv, - emptyInstEnv, extendInstEnv, - lookupInstEnv, InstLookupResult(..), - classInstEnv, simpleDFunClassTyCon + emptyInstEnv, extendInstEnv, extendInstEnvList, + lookupInstEnv, instEnvElts, + classInstances, simpleDFunClassTyCon, checkFunDeps ) where #include "HsVersions.h" -import Class ( Class ) -import Var ( Id ) -import VarSet ( TyVarSet, unionVarSet, mkVarSet ) -import VarEnv ( TyVarSubstEnv ) -import Maybes ( MaybeErr(..), returnMaB, failMaB, thenMaB, maybeToBool ) -import Name ( getSrcLoc ) -import Type ( Type, splitTyConApp_maybe, - splitSigmaTy, splitDFunTy, tyVarsOfTypes +import Class ( Class, classTvsFds ) +import Var ( Id, isTcTyVar ) +import VarSet +import Type ( TvSubst ) +import TcType ( Type, tcTyConAppTyCon, tcIsTyVarTy, + tcSplitDFunTy, tyVarsOfTypes, isExistentialTyVar ) -import PprType ( ) +import Unify ( tcMatchTys, tcUnifyTys, BindFlag(..) ) +import FunDeps ( checkClsFD ) import TyCon ( TyCon ) import Outputable -import Unify ( matchTys, unifyTyListsX ) -import UniqFM ( UniqFM, lookupWithDefaultUFM, addToUFM, emptyUFM ) +import UniqFM ( UniqFM, lookupUFM, emptyUFM, addToUFM_C, eltsUFM ) import Id ( idType ) -import ErrUtils ( Message ) import CmdLineOpts +import Util ( notNull ) +import Maybe ( isJust ) \end{code} @@ -42,20 +41,88 @@ import CmdLineOpts %* * %************************************************************************ +A @ClsInstEnv@ all the instances of that class. The @Id@ inside a +ClsInstEnv mapping is the dfun for that instance. + +If class C maps to a list containing the item ([a,b], [t1,t2,t3], dfun), then + + forall a b, C t1 t2 t3 can be constructed by dfun + +or, to put it another way, we have + + instance (...) => C t1 t2 t3, witnessed by dfun + \begin{code} type DFunId = Id +type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class + +data ClsInstEnv + = ClsIE [InstEnvElt] -- The instances for a particular class, in any order + Bool -- True <=> there is an instance of form C a b c + -- If *not* then the common case of looking up + -- (C a b c) can fail immediately + -- NB: use tcIsTyVarTy: don't look through newtypes!! + +type InstEnvElt = (TyVarSet, [Type], DFunId) + +-- INVARIANTS: +-- * [a,b] must be a superset of the free vars of [t1,t2,t3] +-- +-- * The dfun must itself be quantified over [a,b] +-- +-- * The template type variables [a,b] are distinct in each item +-- of a ClsInstEnv (so we can safely unify them) + +-- Thus, the @ClassInstEnv@ for @Eq@ might contain the following entry: +-- [a] ===> dfun_Eq_List :: forall a. Eq a => Eq [a] +-- The "a" in the pattern must be one of the forall'd variables in +-- the dfun type. -type InstEnv = UniqFM ClsInstEnv -- Maps Class to instances for that class -type ClsInstEnv = [(TyVarSet, [Type], DFunId)] -- The instances for a particular class +emptyInstEnv :: InstEnv +emptyInstEnv = emptyUFM + +instEnvElts :: InstEnv -> [InstEnvElt] +instEnvElts ie = [elt | ClsIE elts _ <- eltsUFM ie, elt <- elts] + +classInstances :: (InstEnv,InstEnv) -> Class -> [InstEnvElt] +classInstances (pkg_ie, home_ie) cls + = get home_ie ++ get pkg_ie + where + get env = case lookupUFM env cls of + Just (ClsIE insts _) -> insts + Nothing -> [] + +extendInstEnvList :: InstEnv -> [DFunId] -> InstEnv +extendInstEnvList inst_env dfuns = foldl extendInstEnv inst_env dfuns + +extendInstEnv :: InstEnv -> DFunId -> InstEnv +extendInstEnv inst_env dfun_id + = addToUFM_C add inst_env clas (ClsIE [ins_item] ins_tyvar) + where + add (ClsIE cur_insts cur_tyvar) _ = ClsIE (ins_item : cur_insts) + (ins_tyvar || cur_tyvar) + (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun_id) + ins_tv_set = mkVarSet ins_tvs + ins_item = (ins_tv_set, ins_tys, dfun_id) + ins_tyvar = all tcIsTyVarTy ins_tys + +#ifdef UNUSED +pprInstEnv :: InstEnv -> SDoc +pprInstEnv env + = vcat [ brackets (pprWithCommas ppr (varSetElems tyvars)) <+> + brackets (pprWithCommas ppr tys) <+> ppr dfun + | ClsIE cls_inst_env _ <- eltsUFM env + , (tyvars, tys, dfun) <- cls_inst_env + ] +#endif simpleDFunClassTyCon :: DFunId -> (Class, TyCon) simpleDFunClassTyCon dfun = (clas, tycon) where - (_,_,clas,[ty]) = splitDFunTy (idType dfun) - tycon = case splitTyConApp_maybe ty of - Just (tycon,_) -> tycon + (_,_,clas,[ty]) = tcSplitDFunTy (idType dfun) + tycon = tcTyConAppTyCon ty \end{code} %************************************************************************ @@ -64,40 +131,6 @@ simpleDFunClassTyCon dfun %* * %************************************************************************ -The actual type declarations are in HscTypes. - -\begin{code} -emptyInstEnv :: InstEnv -emptyInstEnv = emptyUFM - -classInstEnv :: InstEnv -> Class -> ClsInstEnv -classInstEnv env cls = lookupWithDefaultUFM env [] cls -\end{code} - -A @ClsInstEnv@ lives inside a class, and identifies all the instances -of that class. The @Id@ inside a ClsInstEnv mapping is the dfun for -that instance. - -If class C maps to a list containing the item ([a,b], [t1,t2,t3], dfun), then - - forall a b, C t1 t2 t3 can be constructed by dfun - -or, to put it another way, we have - - instance (...) => C t1 t2 t3, witnessed by dfun - -There is an important consistency constraint in the elements of a ClsInstEnv: - - * [a,b] must be a superset of the free vars of [t1,t2,t3] - - * The dfun must itself be quantified over [a,b] - -Thus, the @ClassInstEnv@ for @Eq@ might contain the following entry: - [a] ===> dfun_Eq_List :: forall a. Eq a => Eq [a] -The "a" in the pattern must be one of the forall'd variables in -the dfun type. - - Notes on overlapping instances ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -211,126 +244,191 @@ exists. --Jeff +BUT NOTE [Nov 2001]: we must actually *unify* not reverse-match in +this test. Suppose the instance envt had + ..., forall a b. C a a b, ..., forall a b c. C a b c, ... +(still most specific first) +Now suppose we are looking for (C x y Int), where x and y are unconstrained. + C x y Int doesn't match the template {a,b} C a a b +but neither does + C a a b match the template {x,y} C x y Int +But still x and y might subsequently be unified so they *do* match. + +Simple story: unify, don't match. + + +%************************************************************************ +%* * +\subsection{Looking up an instance} +%* * +%************************************************************************ @lookupInstEnv@ looks up in a @InstEnv@, using a one-way match. Since the env is kept ordered, the first match must be the only one. The thing we are looking up can have an arbitrary "flexi" part. \begin{code} -lookupInstEnv :: InstEnv -- The envt - -> Class -> [Type] -- Key - -> InstLookupResult - -data InstLookupResult - = FoundInst -- There is a (template,substitution) pair - -- that makes the template match the key, - -- and no template is an instance of the key - TyVarSubstEnv Id - - | NoMatch Bool -- Boolean is true iff there is at least one - -- template that matches the key. - -- (but there are other template(s) that are - -- instances of the key, so we don't report - -- FoundInst) - -- The NoMatch True case happens when we look up +lookupInstEnv :: DynFlags + -> (InstEnv -- External package inst-env + ,InstEnv) -- Home-package inst-env + -> Class -> [Type] -- What we are looking for + -> ([(TvSubst, InstEnvElt)], -- Successful matches + [Id]) -- These don't match but do unify + -- The second component of the tuple happens when we look up -- Foo [a] -- in an InstEnv that has entries for -- Foo [Int] -- Foo [b] -- Then which we choose would depend on the way in which 'a' - -- is instantiated. So we say there is no match, but identify - -- it as ambiguous case in the hope of giving a better error msg. - -- See the notes above from Jeff Lewis - -lookupInstEnv env key_cls key_tys - = find (classInstEnv env key_cls) + -- is instantiated. So we report that Foo [b] is a match (mapping b->a) + -- but Foo [Int] is a unifier. This gives the caller a better chance of + -- giving a suitable error messagen + +lookupInstEnv dflags (pkg_ie, home_ie) cls tys + | not (null all_unifs) = (all_matches, all_unifs) -- This is always an error situation, + -- so don't attempt to pune the matches + | otherwise = (pruned_matches, []) + where + all_tvs = all tcIsTyVarTy tys + incoherent_ok = dopt Opt_AllowIncoherentInstances dflags + overlap_ok = dopt Opt_AllowOverlappingInstances dflags + (home_matches, home_unifs) = lookup_inst_env home_ie cls tys all_tvs + (pkg_matches, pkg_unifs) = lookup_inst_env pkg_ie cls tys all_tvs + all_matches = home_matches ++ pkg_matches + all_unifs | incoherent_ok = [] -- Don't worry about these if incoherent is ok! + | otherwise = home_unifs ++ pkg_unifs + + pruned_matches | overlap_ok = foldr insert_overlapping [] all_matches + | otherwise = all_matches + +lookup_inst_env :: InstEnv -- The envt + -> Class -> [Type] -- What we are looking for + -> Bool -- All the [Type] are tyvars + -> ([(TvSubst, InstEnvElt)], -- Successful matches + [Id]) -- These don't match but do unify +lookup_inst_env env key_cls key_tys key_all_tvs + = case lookupUFM env key_cls of + Nothing -> ([],[]) -- No instances for this class + Just (ClsIE insts has_tv_insts) + | key_all_tvs && not has_tv_insts -> ([],[]) -- Short cut for common case + -- The thing we are looking up is of form (C a b c), and + -- the ClsIE has no instances of that form, so don't bother to search + | otherwise -> find insts [] [] where - key_vars = tyVarsOfTypes key_tys - - find [] = NoMatch False - find ((tpl_tyvars, tpl, val) : rest) - = case matchTys tpl_tyvars tpl key_tys of - Nothing -> - case matchTys key_vars key_tys tpl of - Nothing -> find rest - Just (_, _) -> NoMatch (any_match rest) - Just (subst, leftovers) -> ASSERT( null leftovers ) - FoundInst subst val - - any_match rest = or [ maybeToBool (matchTys tvs tpl key_tys) - | (tvs,tpl,_) <- rest - ] + find [] ms us = (ms, us) + find (item@(tpl_tyvars, tpl, dfun_id) : rest) ms us + = case tcMatchTys tpl_tyvars tpl key_tys of + Just subst -> find rest ((subst,item):ms) us + Nothing + -- Does not match, so next check whether the things unify + -- [see notes about overlapping instances above] + -> ASSERT2( not (tyVarsOfTypes key_tys `intersectsVarSet` tpl_tyvars), + (ppr key_cls <+> ppr key_tys <+> ppr key_all_tvs) $$ + (ppr dfun_id <+> ppr tpl_tyvars <+> ppr tpl) + ) + -- Unification will break badly if the variables overlap + -- They shouldn't because we allocate separate uniques for them + case tcUnifyTys bind_fn tpl key_tys of + Just _ -> find rest ms (dfun_id:us) + Nothing -> find rest ms us + + bind_fn tv | isTcTyVar tv && isExistentialTyVar tv = Skolem + | otherwise = BindMe + -- The key_tys can contain skolem constants, and we can guarantee that those + -- are never going to be instantiated to anything, so we should not involve + -- them in the unification test. Example: + -- class Foo a where { op :: a -> Int } + -- instance Foo a => Foo [a] -- NB overlap + -- instance Foo [Int] -- NB overlap + -- data T = forall a. Foo a => MkT a + -- f :: T -> Int + -- f (MkT x) = op [x,x] + -- The op [x,x] means we need (Foo [a]). Without the filterVarSet we'd + -- complain, saying that the choice of instance depended on the instantiation + -- of 'a'; but of course it isn't *going* to be instantiated. + -- + -- We do this only for pattern-bound skolems. For example we reject + -- g :: forall a => [a] -> Int + -- g x = op x + -- on the grounds that the correct instance depends on the instantiation of 'a' + +insert_overlapping :: (TvSubst, InstEnvElt) -> [(TvSubst, InstEnvElt)] + -> [(TvSubst, InstEnvElt)] +-- Add a new solution, knocking out strictly less specific ones +insert_overlapping new_item [] = [new_item] +insert_overlapping new_item (item:items) + | new_beats_old && old_beats_new = item : insert_overlapping new_item items + -- Duplicate => keep both for error report + | new_beats_old = insert_overlapping new_item items + -- Keep new one + | old_beats_new = item : items + -- Keep old one + | otherwise = item : insert_overlapping new_item items + -- Keep both + where + new_beats_old = new_item `beats` item + old_beats_new = item `beats` new_item + + (_, (tvs1, tys1, _)) `beats` (_, (tvs2, tys2, _)) + = isJust (tcMatchTys tvs2 tys2 tys1) -- A beats B if A is more specific than B + -- I.e. if B can be instantiated to match A \end{code} -@addToClsInstEnv@ extends a @ClsInstEnv@, checking for overlaps. -A boolean flag controls overlap reporting. +%************************************************************************ +%* * + Functional dependencies +%* * +%************************************************************************ + +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 -True => overlap is permitted, but only if one template matches the other; - not if they unify but neither is \begin{code} -extendInstEnv :: DynFlags -> InstEnv -> [DFunId] -> (InstEnv, [Message]) - -- Similar, but all we have is the DFuns -extendInstEnv dflags env infos - = go env [] infos - where - go env msgs [] = (env, msgs) - go env msgs (dfun:dfuns) = case addToInstEnv dflags env dfun of - Succeeded new_env -> go new_env msgs dfuns - Failed dfun' -> go env (msg:msgs) dfuns - where - msg = dupInstErr dfun dfun' - - -dupInstErr dfun1 dfun2 - -- Overlapping/duplicate instances for given class; msg could be more glamourous - = hang (ptext SLIT("Duplicate or overlapping instance declarations:")) - 2 (ppr_dfun dfun1 $$ ppr_dfun dfun2) +checkFunDeps :: (InstEnv, InstEnv) -> DFunId + -> Maybe [DFunId] -- Nothing <=> ok + -- Just dfs <=> conflict with dfs +-- Check wheher adding DFunId would break functional-dependency constraints +checkFunDeps inst_envs dfun + | null bad_fundeps = Nothing + | otherwise = Just bad_fundeps where - ppr_dfun dfun = ppr (getSrcLoc dfun) <> colon <+> ppr tau - where - (_,_,tau) = splitSigmaTy (idType dfun) - -addToInstEnv :: DynFlags - -> InstEnv -> DFunId - -> MaybeErr InstEnv -- Success... - DFunId -- Failure: Offending overlap - -addToInstEnv dflags inst_env dfun_id - = case insert_into (classInstEnv inst_env clas) of - Failed stuff -> Failed stuff - Succeeded new_env -> Succeeded (addToUFM inst_env clas new_env) - + (ins_tvs, _, clas, ins_tys) = tcSplitDFunTy (idType dfun) + 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 :: [InstEnvElt] -> Class + -> TyVarSet -> [Type] -- Proposed new instance type + -> [DFunId] +badFunDeps cls_inst_env clas ins_tv_set ins_tys + = [ dfun_id | fd <- fds, + (tvs, tys, dfun_id) <- cls_inst_env, + notNull (checkClsFD (tvs `unionVarSet` ins_tv_set) fd clas_tvs tys ins_tys) + ] where - (ins_tvs, _, clas, ins_tys) = splitDFunTy (idType dfun_id) - - ins_tv_set = mkVarSet ins_tvs - ins_item = (ins_tv_set, ins_tys, dfun_id) - - insert_into [] = returnMaB [ins_item] - insert_into env@(cur_item@(tpl_tvs, tpl_tys, val) : rest) - - -- FAIL if: - -- (a) they are the same, or - -- (b) they unify, and any sort of overlap is prohibited, - -- (c) they unify but neither is more specific than t'other - | identical - || (unifiable && not (dopt Opt_AllowOverlappingInstances dflags)) - || (unifiable && not (ins_item_more_specific || cur_item_more_specific)) - = failMaB val - - -- New item is an instance of current item, so drop it here - | ins_item_more_specific = returnMaB (ins_item : env) - - -- Otherwise carry on - | otherwise = insert_into rest `thenMaB` \ rest' -> - returnMaB (cur_item : rest') - where - unifiable = maybeToBool (unifyTyListsX (ins_tv_set `unionVarSet` tpl_tvs) tpl_tys ins_tys) - ins_item_more_specific = maybeToBool (matchTys tpl_tvs tpl_tys ins_tys) - cur_item_more_specific = maybeToBool (matchTys ins_tv_set ins_tys tpl_tys) - identical = ins_item_more_specific && cur_item_more_specific + (clas_tvs, fds) = classTvsFds clas \end{code} - -