X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcTyFuns.lhs;h=ba73891fa4945365d6940ad8929a491d28fb3e47;hb=c7ae8f20f93b4e36837fc3ecafccd3f49c95cb6b;hp=82e397f554cd23a23472bda17885983b9277cba8;hpb=583e2422f9f70c8ff69f948a3be788f5d412c862;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcTyFuns.lhs b/compiler/typecheck/TcTyFuns.lhs index 82e397f..ba73891 100644 --- a/compiler/typecheck/TcTyFuns.lhs +++ b/compiler/typecheck/TcTyFuns.lhs @@ -3,16 +3,16 @@ normalisation and entailment checking of equality constraints. \begin{code} module TcTyFuns ( - tcNormaliseFamInst, + -- type normalisation wrt to toplevel equalities only + tcNormaliseFamInst, - normaliseGivenEqs, normaliseGivenDicts, - normaliseWantedEqs, normaliseWantedDicts, - solveWantedEqs, - substEqInDictInsts, - - -- errors - misMatchMsg, failWithMisMatch - ) where + -- instance normalisation wrt to equalities + tcReduceEqs, + + -- errors + misMatchMsg, failWithMisMatch, + +) where #include "HsVersions.h" @@ -30,13 +30,16 @@ import Type import TypeRep ( Type(..) ) import TyCon import HsSyn +import Id import VarEnv +import VarSet import Var import Name import Bag import Outputable import SrcLoc ( Located(..) ) import Maybes +import FastString -- standard import Data.List @@ -46,7 +49,7 @@ import Control.Monad %************************************************************************ %* * - Normalisation of types + Normalisation of types wrt toplevel equality schemata %* * %************************************************************************ @@ -76,7 +79,7 @@ tcUnfoldSynFamInst (TyConApp tycon tys) mkTyConApp coe_tc tys') where tys' = rep_tys ++ restTys - coe_tc = expectJust "TcTyFun.tcUnfoldSynFamInst" + coe_tc = expectJust "TcTyFuns.tcUnfoldSynFamInst" (tyConFamilyCoercion_maybe rep_tc) } where @@ -92,91 +95,12 @@ possible (ie, we treat family instances as a TRS). Also zonk meta variables. then co : ty ~ ty' \begin{code} +-- |Normalise the given type as far as possible with toplevel equalities. +-- This results in a coercion witnessing the type equality, in addition to the +-- normalised type. +-- tcNormaliseFamInst :: TcType -> TcM (CoercionI, TcType) tcNormaliseFamInst = tcGenericNormaliseFamInst tcUnfoldSynFamInst - -tcNormaliseFamInstPred :: TcPredType -> TcM (CoercionI, TcPredType) -tcNormaliseFamInstPred = tcGenericNormaliseFamInstPred tcUnfoldSynFamInst -\end{code} - -An elementary rewrite is a properly oriented equality with associated coercion -that has one of the following two forms: - -(1) co :: F t1..tn ~ t -(2) co :: a ~ t , where t /= F t1..tn and a is a skolem tyvar - -NB: We do *not* use equalities of the form a ~ t where a is a meta tyvar as a -reqrite rule. Instead, such equalities are solved by unification. This is -essential; cf Note [skolemOccurs loop]. - -The following functions takes an equality instance and turns it into an -elementary rewrite if possible. - -\begin{code} -data Rewrite = Rewrite TcType -- lhs of rewrite rule - TcType -- rhs of rewrite rule - TcType -- coercion witnessing the rewrite rule - -eqInstToRewrite :: Inst -> Maybe (Rewrite, Bool) - -- True iff rewrite swapped equality -eqInstToRewrite inst - = ASSERT( isEqInst inst ) - go ty1 ty2 (eqInstType inst) - where - (ty1,ty2) = eqInstTys inst - - -- look through synonyms - go ty1 ty2 co | Just ty1' <- tcView ty1 = go ty1' ty2 co - go ty1 ty2 co | Just ty2' <- tcView ty2 = go ty1 ty2' co - - -- left-to-right rule with type family head - go ty1@(TyConApp con _) ty2 co - | isOpenSynTyCon con - = Just (Rewrite ty1 ty2 co, False) -- not swapped - - -- left-to-right rule with type variable head - go ty1@(TyVarTy tv) ty2 co - | isSkolemTyVar tv - = Just (Rewrite ty1 ty2 co, False) -- not swapped - - -- right-to-left rule with type family head, only after - -- having checked whether we can work left-to-right - go ty1 ty2@(TyConApp con _) co - | isOpenSynTyCon con - = Just (Rewrite ty2 ty1 (mkSymCoercion co), True) -- swapped - - -- right-to-left rule with type variable head, only after - -- having checked whether we can work left-to-right - go ty1 ty2@(TyVarTy tv) co - | isSkolemTyVar tv - = Just (Rewrite ty2 ty1 (mkSymCoercion co), True) -- swapped - - -- this equality is not a rewrite rule => ignore - go _ _ _ = Nothing -\end{code} - -Normalise a type relative to an elementary rewrite implied by an EqInst or an -explicitly given elementary rewrite. - -\begin{code} --- Rewrite by EqInst --- Precondition: the EqInst passes the occurs check -tcEqInstNormaliseFamInst :: Inst -> TcType -> TcM (CoercionI, TcType) -tcEqInstNormaliseFamInst inst ty - = case eqInstToRewrite inst of - Just (rewrite, _) -> tcEqRuleNormaliseFamInst rewrite ty - Nothing -> return (IdCo, ty) - --- Rewrite by equality rewrite rule -tcEqRuleNormaliseFamInst :: Rewrite -- elementary rewrite - -> TcType -- type to rewrite - -> TcM (CoercionI, -- witnessing coercion - TcType) -- rewritten type -tcEqRuleNormaliseFamInst (Rewrite pat rhs co) ty - = tcGenericNormaliseFamInst matchEqRule ty - where - matchEqRule sty | pat `tcEqType` sty = return $ Just (rhs, co) - | otherwise = return $ Nothing \end{code} Generic normalisation of 'Type's and 'PredType's; ie, walk the type term and @@ -231,10 +155,6 @@ tcGenericNormaliseFamInst fun (ForAllTy tyvar ty1) = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1 ; return (mkForAllTyCoI tyvar coi, mkForAllTy tyvar nty1) } -tcGenericNormaliseFamInst fun (NoteTy note ty1) - = do { (coi,nty1) <- tcGenericNormaliseFamInst fun ty1 - ; return (coi, NoteTy note nty1) - } tcGenericNormaliseFamInst fun ty@(TyVarTy tv) | isTcTyVar tv = do { traceTc (text "tcGenericNormaliseFamInst" <+> ppr ty) @@ -279,751 +199,1027 @@ tcGenericNormaliseFamInstPred fun (EqPred ty1 ty2) %************************************************************************ %* * -\section{Normalisation of equality constraints} + Normalisation of instances wrt to equalities %* * %************************************************************************ -Note [Inconsistencies in equality constraints] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We guarantee that we raise an error if we discover any inconsistencies (i.e., -equalities that if presented to the unifer in TcUnify would result in an -error) during normalisation of wanted constraints. This is especially so that -we don't solve wanted constraints under an inconsistent given set. In -particular, we don't want to permit signatures, such as - - bad :: (Int ~ Bool => Int) -> a -> a - \begin{code} -normaliseGivenEqs :: [Inst] -> TcM ([Inst], TcM ()) -normaliseGivenEqs givens - = do { traceTc (text "normaliseGivenEqs <-" <+> ppr givens) - ; (result, deSkolem) <- - rewriteToFixedPoint (Just ("(SkolemOccurs)", skolemOccurs)) - [ ("(ZONK)", dontRerun $ zonkInsts) - , ("(TRIVIAL)", dontRerun $ trivialRule) - , ("(DECOMP)", decompRule) - , ("(TOP)", topRule) - , ("(SUBST)", substRule) -- incl. occurs check - ] givens - ; traceTc (text "normaliseGivenEqs ->" <+> ppr result) - ; return (result, deSkolem) - } -\end{code} - -\begin{code} -normaliseWantedEqs :: [Inst] -> TcM [Inst] -normaliseWantedEqs insts - = do { traceTc (text "normaliseWantedEqs <-" <+> ppr insts) - ; result <- liftM fst $ rewriteToFixedPoint Nothing - [ ("(ZONK)", dontRerun $ zonkInsts) - , ("(TRIVIAL)", dontRerun $ trivialRule) - , ("(DECOMP)", decompRule) - , ("(TOP)", topRule) - , ("(UNIFY)", unifyMetaRule) -- incl. occurs check - , ("(SUBST)", substRule) -- incl. occurs check - ] insts - ; traceTc (text "normaliseWantedEqs ->" <+> ppr result) - ; return result +tcReduceEqs :: [Inst] -- locals + -> [Inst] -- wanteds + -> TcM ([Inst], -- normalised locals (w/o equalities) + [Inst], -- normalised wanteds (including equalities) + TcDictBinds, -- bindings for all simplified dictionaries + Bool) -- whether any flexibles where instantiated +tcReduceEqs locals wanteds + = do { let (local_eqs , local_dicts) = partition isEqInst locals + (wanteds_eqs, wanteds_dicts) = partition isEqInst wanteds + ; eqCfg1 <- normaliseEqs (local_eqs ++ wanteds_eqs) + ; eqCfg2 <- normaliseDicts False local_dicts + ; eqCfg3 <- normaliseDicts True wanteds_dicts + ; eqCfg <- propagateEqs (eqCfg1 `unionEqConfig` eqCfg2 + `unionEqConfig` eqCfg3) + ; finaliseEqsAndDicts eqCfg } \end{code} %************************************************************************ %* * -\section{Solving of wanted constraints with respect to a given set} + Equality Configurations %* * %************************************************************************ -The set of given equalities must have been normalised already. +We maintain normalised equalities together with the skolems introduced as +intermediates during flattening of equalities as well as + +!!!TODO: We probably now can do without the skolem set. It's not used during +finalisation in the current code. \begin{code} -solveWantedEqs :: [Inst] -- givens - -> [Inst] -- wanteds - -> TcM [Inst] -- irreducible wanteds -solveWantedEqs givens wanteds - = do { traceTc $ text "solveWantedEqs <-" <+> ppr wanteds <+> text "with" <+> - ppr givens - ; result <- liftM fst $ rewriteToFixedPoint Nothing - [ ("(ZONK)", dontRerun $ zonkInsts) - , ("(TRIVIAL)", dontRerun $ trivialRule) - , ("(DECOMP)", decompRule) - , ("(TOP)", topRule) - , ("(GIVEN)", substGivens givens) -- incl. occurs check - , ("(UNIFY)", unifyMetaRule) -- incl. occurs check - ] wanteds - ; traceTc (text "solveWantedEqs ->" <+> ppr result) - ; return result - } - where - -- Use `substInst' with every given on all the wanteds. - substGivens :: [Inst] -> [Inst] -> TcM ([Inst], Bool) - substGivens [] wanteds = return (wanteds, False) - substGivens (g:gs) wanteds - = do { (wanteds1, changed1) <- substGivens gs wanteds - ; (wanteds2, changed2) <- substInst g wanteds1 - ; return (wanteds2, changed1 || changed2) - } +-- |Configuration of normalised equalities used during solving. +-- +data EqConfig = EqConfig { eqs :: [RewriteInst] -- all equalities + , locals :: [Inst] -- given dicts + , wanteds :: [Inst] -- wanted dicts + , binds :: TcDictBinds -- bindings + , skolems :: TyVarSet -- flattening skolems + } + +addSkolems :: EqConfig -> TyVarSet -> EqConfig +addSkolems eqCfg newSkolems + = eqCfg {skolems = skolems eqCfg `unionVarSet` newSkolems} + +addEq :: EqConfig -> RewriteInst -> EqConfig +addEq eqCfg eq = eqCfg {eqs = eq : eqs eqCfg} + +unionEqConfig :: EqConfig -> EqConfig -> EqConfig +unionEqConfig eqc1 eqc2 = EqConfig + { eqs = eqs eqc1 ++ eqs eqc2 + , locals = locals eqc1 ++ locals eqc2 + , wanteds = wanteds eqc1 ++ wanteds eqc2 + , binds = binds eqc1 `unionBags` binds eqc2 + , skolems = skolems eqc1 `unionVarSet` skolems eqc2 + } + +emptyEqConfig :: EqConfig +emptyEqConfig = EqConfig + { eqs = [] + , locals = [] + , wanteds = [] + , binds = emptyBag + , skolems = emptyVarSet + } + +instance Outputable EqConfig where + ppr (EqConfig {eqs = eqs, locals = locals, wanteds = wanteds, binds = binds}) + = vcat [ppr eqs, ppr locals, ppr wanteds, ppr binds] \end{code} - -%************************************************************************ -%* * -\section{Normalisation of non-equality dictionaries} -%* * -%************************************************************************ +The set of operations on an equality configuration. We obtain the initialise +configuration by normalisation ('normaliseEqs'), solve the equalities by +propagation ('propagateEqs'), and eventually finalise the configuration when +no further propoagation is possible. \begin{code} -normaliseGivenDicts, normaliseWantedDicts - :: [Inst] -- given equations - -> [Inst] -- dictionaries - -> TcM ([Inst],TcDictBinds) - -normaliseGivenDicts eqs dicts = normalise_dicts eqs dicts False -normaliseWantedDicts eqs dicts = normalise_dicts eqs dicts True - -normalise_dicts - :: [Inst] -- given equations - -> [Inst] -- dictionaries - -> Bool -- True <=> the dicts are wanted - -- Fals <=> they are given - -> TcM ([Inst],TcDictBinds) -normalise_dicts given_eqs dicts is_wanted - = do { traceTc $ let name | is_wanted = "normaliseWantedDicts <-" - | otherwise = "normaliseGivenDicts <-" - in - text name <+> ppr dicts <+> - text "with" <+> ppr given_eqs - ; (dicts0, binds0) <- normaliseInsts is_wanted dicts - ; (dicts1, binds1) <- substEqInDictInsts is_wanted given_eqs dicts0 - ; let binds01 = binds0 `unionBags` binds1 - ; if isEmptyBag binds1 - then return (dicts1, binds01) - else do { (dicts2, binds2) <- - normalise_dicts given_eqs dicts1 is_wanted - ; return (dicts2, binds01 `unionBags` binds2) } } +-- |Turn a set of equalities into an equality configuration for solving. +-- +-- Precondition: The Insts are zonked. +-- +normaliseEqs :: [Inst] -> TcM EqConfig +normaliseEqs eqs + = do { ASSERTM2( allM isValidWantedEqInst eqs, ppr eqs ) + ; traceTc $ ptext (sLit "Entering normaliseEqs") + + ; (eqss, skolemss) <- mapAndUnzipM normEqInst eqs + ; return $ emptyEqConfig { eqs = concat eqss + , skolems = unionVarSets skolemss + } + } + +-- |Flatten the type arguments of all dictionaries, returning the result as a +-- equality configuration. The dictionaries go into the 'wanted' component if +-- the second argument is 'True'. +-- +-- Precondition: The Insts are zonked. +-- +normaliseDicts :: Bool -> [Inst] -> TcM EqConfig +normaliseDicts isWanted insts + = do { traceTc $ ptext (sLit "Entering normaliseDicts") <+> + ptext (if isWanted then sLit "[Wanted]" else sLit "[Local]") + ; (insts', eqss, bindss, skolemss) <- mapAndUnzip4M (normDict isWanted) + insts + ; return $ emptyEqConfig { eqs = concat eqss + , locals = if isWanted then [] else insts' + , wanteds = if isWanted then insts' else [] + , binds = unionManyBags bindss + , skolems = unionVarSets skolemss + } + } + +-- |Solves the equalities as far as possible by applying propagation rules. +-- +propagateEqs :: EqConfig -> TcM EqConfig +propagateEqs eqCfg@(EqConfig {eqs = todoEqs}) + = do { traceTc $ hang (ptext (sLit "Entering propagateEqs:")) + 4 (ppr eqCfg) + + ; propagate todoEqs (eqCfg {eqs = []}) + } + +-- |Finalise a set of equalities and associated dictionaries after +-- propagation. The returned Boolean value is `True' iff any flexible +-- variables, except those introduced by flattening (i.e., those in the +-- `skolems' component of the argument) where instantiated. The first returned +-- set of instances are the locals (without equalities) and the second set are +-- all residual wanteds, including equalities. +-- +-- Remove all identity dictinary bindings (i.e., those whose source and target +-- dictionary are the same). This is important for termination, as +-- TcSimplify.reduceContext takes the presence of dictionary bindings as an +-- indicator that there was some improvement. +-- +finaliseEqsAndDicts :: EqConfig + -> TcM ([Inst], [Inst], TcDictBinds, Bool) +finaliseEqsAndDicts (EqConfig { eqs = eqs + , locals = locals + , wanteds = wanteds + , binds = binds + }) + = do { traceTc $ ptext (sLit "finaliseEqsAndDicts") + ; (eqs', subst_binds, locals', wanteds') <- substitute eqs locals wanteds + ; (eqs'', improved) <- instantiateAndExtract eqs' (null locals) + ; final_binds <- filterM nonTrivialDictBind $ + bagToList (subst_binds `unionBags` binds) + + ; ASSERTM2( allM isValidWantedEqInst eqs'', ppr eqs'' ) + ; return (locals', eqs'' ++ wanteds', listToBag final_binds, improved) + } + where + nonTrivialDictBind (L _ (VarBind { var_id = ide1 + , var_rhs = L _ (HsWrap _ (HsVar ide2))})) + = do { ty1 <- zonkTcType (idType ide1) + ; ty2 <- zonkTcType (idType ide2) + ; return $ not (ty1 `tcEqType` ty2) + } + nonTrivialDictBind _ = return True \end{code} %************************************************************************ %* * -\section{Normalisation rules and iterative rule application} + Normalisation of equalities %* * %************************************************************************ -We have three kinds of normalising rewrite rules: +A normal equality is a properly oriented equality with associated coercion +that contains at most one family equality (in its left-hand side) is oriented +such that it may be used as a reqrite rule. It has one of the following two +forms: -(1) Normalisation rules that rewrite a set of insts and return a flag indicating - whether any changes occurred during rewriting that necessitate re-running - the current rule set. +(1) co :: F t1..tn ~ t (family equalities) +(2) co :: x ~ t (variable equalities) -(2) Precondition rules that rewrite a set of insts and return a monadic action - that reverts the effect of preconditioning. +Variable equalities fall again in two classes: -(3) Idempotent normalisation rules that never require re-running the rule set. +(2a) co :: x ~ t, where t is *not* a variable, or +(2b) co :: x ~ y, where x > y. -\begin{code} -type RewriteRule = [Inst] -> TcM ([Inst], Bool) -- rewrite, maybe re-run -type PrecondRule = [Inst] -> TcM ([Inst], TcM ()) -- rewrite, revertable -type IdemRewriteRule = [Inst] -> TcM [Inst] -- rewrite, don't re-run - -type NamedRule = (String, RewriteRule) -- rule with description -type NamedPreRule = (String, PrecondRule) -- precond with desc -\end{code} +The types t, t1, ..., tn may not contain any occurrences of synonym +families. Moreover, in Forms (2) & (3), the left-hand side may not occur in +the right-hand side, and the relation x > y is an arbitrary, but total order +on type variables -Template lifting idempotent rules to full rules (which can be put into a rule -set). +!!!TODO: We may need to keep track of swapping for error messages (and to +re-orient on finilisation). \begin{code} -dontRerun :: IdemRewriteRule -> RewriteRule -dontRerun rule insts = liftM addFalse $ rule insts +data RewriteInst + = RewriteVar -- Form (2) above + { rwi_var :: TyVar -- may be rigid or flexible + , rwi_right :: TcType -- contains no synonym family applications + , rwi_co :: EqInstCo -- the wanted or given coercion + , rwi_loc :: InstLoc + , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst) + , rwi_swapped :: Bool -- swapped orientation of original EqInst + } + | RewriteFam -- Forms (1) above + { rwi_fam :: TyCon -- synonym family tycon + , rwi_args :: [Type] -- contain no synonym family applications + , rwi_right :: TcType -- contains no synonym family applications + , rwi_co :: EqInstCo -- the wanted or given coercion + , rwi_loc :: InstLoc + , rwi_name :: Name -- no semantic significance (cf. TcRnTypes.EqInst) + , rwi_swapped :: Bool -- swapped orientation of original EqInst + } + +isWantedRewriteInst :: RewriteInst -> Bool +isWantedRewriteInst = isWantedCo . rwi_co + +rewriteInstToInst :: RewriteInst -> TcM Inst +rewriteInstToInst eq@(RewriteVar {rwi_var = tv}) + = deriveEqInst eq (mkTyVarTy tv) (rwi_right eq) (rwi_co eq) +rewriteInstToInst eq@(RewriteFam {rwi_fam = fam, rwi_args = args}) + = deriveEqInst eq (mkTyConApp fam args) (rwi_right eq) (rwi_co eq) + +-- Derive an EqInst based from a RewriteInst, possibly swapping the types +-- around. +-- +deriveEqInst :: RewriteInst -> TcType -> TcType -> EqInstCo -> TcM Inst +deriveEqInst rewrite ty1 ty2 co + = do { co_adjusted <- if not swapped then return co + else mkSymEqInstCo co (ty2, ty1) + ; return $ EqInst + { tci_left = left + , tci_right = right + , tci_co = co_adjusted + , tci_loc = rwi_loc rewrite + , tci_name = rwi_name rewrite + } + } where - addFalse x = (x, False) + swapped = rwi_swapped rewrite + (left, right) = if not swapped then (ty1, ty2) else (ty2, ty1) + +instance Outputable RewriteInst where + ppr (RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = rhs, rwi_co =co}) + = hsep [ pprEqInstCo co <+> text "::" + , ppr (mkTyConApp fam args) + , text "~>" + , ppr rhs + ] + ppr (RewriteVar {rwi_var = tv, rwi_right = rhs, rwi_co =co}) + = hsep [ pprEqInstCo co <+> text "::" + , ppr tv + , text "~>" + , ppr rhs + ] + +pprEqInstCo :: EqInstCo -> SDoc +pprEqInstCo (Left cotv) = ptext (sLit "Wanted") <+> ppr cotv +pprEqInstCo (Right co) = ptext (sLit "Local") <+> ppr co \end{code} -The following function applies a set of rewrite rules until a fixed point is -reached; i.e., none of the `RewriteRule's require re-running the rule set. -Optionally, there may be a pre-conditing rule that is applied before any other -rules are applied and before the rule set is re-run. +The following functions turn an arbitrary equality into a set of normal +equalities. This implements the WFlat and LFlat rules of the paper in one +sweep. However, we use flexible variables for both locals and wanteds, and +avoid to carry around the unflattening substitution \Sigma (for locals) by +already updating the skolems for locals with the family application that they +represent - i.e., they will turn into that family application on the next +zonking (which only happens after finalisation). -The result is the set of rewritten (i.e., normalised) insts and, in case of a -pre-conditing rule, a monadic action that reverts the effects of -pre-conditioning - specifically, this is removing introduced skolems. +In a corresponding manner, normDict normalises class dictionaries by +extracting any synonym family applications and generation appropriate normal +equalities. + +Whenever we encounter a loopy equality (of the form a ~ T .. (F ...a...) ...), +we drop that equality and raise an error if it is a wanted or a warning if it +is a local. \begin{code} -rewriteToFixedPoint :: Maybe NamedPreRule -- optional preconditioning rule - -> [NamedRule] -- rule set - -> [Inst] -- insts to rewrite - -> TcM ([Inst], TcM ()) -rewriteToFixedPoint precondRule rules insts - = completeRewrite (return ()) precondRule insts +normEqInst :: Inst -> TcM ([RewriteInst], TyVarSet) +-- Normalise one equality. +normEqInst inst + = ASSERT( isEqInst inst ) + go ty1 ty2 (eqInstCoercion inst) where - completeRewrite :: TcM () -> Maybe NamedPreRule -> [Inst] - -> TcM ([Inst], TcM ()) - completeRewrite dePrecond (Just (precondName, precond)) insts - = do { traceTc $ text precondName <+> text " <- " <+> ppr insts - ; (insts', dePrecond') <- precond insts - ; traceTc $ text precondName <+> text " -> " <+> ppr insts' - ; tryRules (dePrecond >> dePrecond') rules insts' - } - completeRewrite dePrecond Nothing insts - = tryRules dePrecond rules insts - - tryRules dePrecond _ [] = return ([] , dePrecond) - tryRules dePrecond [] insts = return (insts, dePrecond) - tryRules dePrecond ((name, rule):rules) insts - = do { traceTc $ text name <+> text " <- " <+> ppr insts - ; (insts', rerun) <- rule insts - ; traceTc $ text name <+> text " -> " <+> ppr insts' - ; if rerun then completeRewrite dePrecond precondRule insts' - else tryRules dePrecond rules insts' - } -\end{code} - - -%************************************************************************ -%* * -\section{Different forms of Inst rewrite rules} -%* * -%************************************************************************ + (ty1, ty2) = eqInstTys inst -Splitting of non-terminating given constraints: skolemOccurs -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -This is a preconditioning rule exclusively applied to given constraints. -Moreover, its rewriting is only temporary, as it is undone by way of -side-effecting mutable type variables after simplification and constraint -entailment has been completed. - -This version is an (attempt at, yet unproven, an) *unflattened* version of -the SubstL-Ev completion rule. - -The above rule is essential to catch non-terminating rules that cannot be -oriented properly, like - - F a ~ [G (F a)] - or even - a ~ [G a] , where a is a skolem tyvar - -The left-to-right orientiation is not suitable because it does not -terminate. The right-to-left orientation is not suitable because it -does not have a type-function on the left. This is undesirable because -it would hide information. E.g. assume - - instance C [x] - -then rewriting C [G (F a)] to C (F a) is bad because we cannot now -see that the C [x] instance applies. + -- look through synonyms + go ty1 ty2 co | Just ty1' <- tcView ty1 = go ty1' ty2 co + go ty1 ty2 co | Just ty2' <- tcView ty2 = go ty1 ty2' co -The rule also caters for badly-oriented rules of the form: + -- left-to-right rule with type family head + go (TyConApp con args) ty2 co + | isOpenSynTyCon con + = mkRewriteFam False con args ty2 co - F a ~ G (F a) + -- right-to-left rule with type family head + go ty1 ty2@(TyConApp con args) co + | isOpenSynTyCon con + = do { co' <- mkSymEqInstCo co (ty2, ty1) + ; mkRewriteFam True con args ty1 co' + } -for which other solutions are possible, but this one will do too. + -- no outermost family + go ty1 ty2 co + = do { (ty1', co1, ty1_eqs, ty1_skolems) <- flattenType inst ty1 + ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2 + ; let ty12_eqs = ty1_eqs ++ ty2_eqs + sym_co2 = mkSymCoercion co2 + eqTys = (ty1', ty2') + ; (co', ty12_eqs') <- adjustCoercions co co1 sym_co2 eqTys ty12_eqs + ; eqs <- checkOrientation ty1' ty2' co' inst + ; if isLoopyEquality eqs ty12_eqs' + then do { if isWantedCo (tci_co inst) + then + addErrCtxt (ptext (sLit "Rejecting loopy equality")) $ + eqInstMisMatch inst + else + warnDroppingLoopyEquality ty1 ty2 + ; return ([], emptyVarSet) -- drop the equality + } + else + return (eqs ++ ty12_eqs', + ty1_skolems `unionVarSet` ty2_skolems) + } -It's behavior is: + mkRewriteFam swapped con args ty2 co + = do { (args', cargs, args_eqss, args_skolemss) + <- mapAndUnzip4M (flattenType inst) args + ; (ty2', co2, ty2_eqs, ty2_skolems) <- flattenType inst ty2 + ; let co1 = mkTyConApp con cargs + sym_co2 = mkSymCoercion co2 + all_eqs = concat args_eqss ++ ty2_eqs + eqTys = (mkTyConApp con args', ty2') + ; (co', all_eqs') <- adjustCoercions co co1 sym_co2 eqTys all_eqs + ; let thisRewriteFam = RewriteFam + { rwi_fam = con + , rwi_args = args' + , rwi_right = ty2' + , rwi_co = co' + , rwi_loc = tci_loc inst + , rwi_name = tci_name inst + , rwi_swapped = swapped + } + ; return $ (thisRewriteFam : all_eqs', + unionVarSets (ty2_skolems:args_skolemss)) + } - co : ty1 ~ ty2{F ty1} - >--> - co : ty1 ~ ty2{b} - sym (F co) : F ty2{b} ~ b - where b is a fresh skolem variable + -- If the original equality has the form a ~ T .. (F ...a...) ..., we will + -- have a variable equality with 'a' on the lhs as the first equality. + -- Then, check whether 'a' occurs in the lhs of any family equality + -- generated by flattening. + isLoopyEquality (RewriteVar {rwi_var = tv}:_) eqs + = any inRewriteFam eqs + where + inRewriteFam (RewriteFam {rwi_args = args}) + = tv `elemVarSet` tyVarsOfTypes args + inRewriteFam _ = False + isLoopyEquality _ _ = False + +normDict :: Bool -> Inst -> TcM (Inst, [RewriteInst], TcDictBinds, TyVarSet) +-- Normalise one dictionary or IP constraint. +normDict isWanted inst@(Dict {tci_pred = ClassP clas args}) + = do { (args', cargs, args_eqss, args_skolemss) + <- mapAndUnzip4M (flattenType inst) args + ; let rewriteCo = PredTy $ ClassP clas cargs + eqs = concat args_eqss + pred' = ClassP clas args' + ; if null eqs + then -- don't generate a binding if there is nothing to flatten + return (inst, [], emptyBag, emptyVarSet) + else do { + ; (inst', bind) <- mkDictBind inst isWanted rewriteCo pred' + ; eqs' <- if isWanted then return eqs else mapM wantedToLocal eqs + ; return (inst', eqs', bind, unionVarSets args_skolemss) + }} +normDict _isWanted inst + = return (inst, [], emptyBag, emptyVarSet) +-- !!!TODO: Still need to normalise IP constraints. + +checkOrientation :: Type -> Type -> EqInstCo -> Inst -> TcM [RewriteInst] +-- Performs the occurs check, decomposition, and proper orientation +-- (returns a singleton, or an empty list in case of a trivial equality) +-- NB: We cannot assume that the two types already have outermost type +-- synonyms expanded due to the recursion in the case of type applications. +checkOrientation ty1 ty2 co inst + = do { traceTc $ ptext (sLit "checkOrientation of ") <+> + pprEqInstCo co <+> text "::" <+> + ppr ty1 <+> text "~" <+> ppr ty2 + ; eqs <- go ty1 ty2 + ; traceTc $ ptext (sLit "checkOrientation returns") <+> ppr eqs + ; return eqs + } + where + -- look through synonyms + go ty1 ty2 | Just ty1' <- tcView ty1 = go ty1' ty2 + go ty1 ty2 | Just ty2' <- tcView ty2 = go ty1 ty2' + + -- identical types => trivial + go ty1 ty2 + | ty1 `tcEqType` ty2 + = do { mkIdEqInstCo co ty1 + ; return [] + } -We also cater for the symmetric situation *if* the rule cannot be used as a -left-to-right rewrite rule. + -- two tvs, left greater => unchanged + go ty1@(TyVarTy tv1) ty2@(TyVarTy tv2) + | tv1 > tv2 + = mkRewriteVar False tv1 ty2 co -We also return an action (b := ty1) which is used to eliminate b -after the dust of normalisation with the completed rewrite system -has settled. + -- two tvs, right greater => swap + | otherwise + = do { co' <- mkSymEqInstCo co (ty2, ty1) + ; mkRewriteVar True tv2 ty1 co' + } -A subtle point of this transformation is that both coercions in the results -are strictly speaking incorrect. However, they are correct again after the -action {B := ty1} has removed the skolem again. This happens immediately -after constraint entailment has been checked; ie, code outside of the -simplification and entailment checking framework will never see these -temporarily incorrect coercions. + -- only lhs is a tv => unchanged + go ty1@(TyVarTy tv1) ty2 + | ty1 `tcPartOfType` ty2 -- occurs check! + = occurCheckErr ty1 ty2 + | otherwise + = mkRewriteVar False tv1 ty2 co + + -- only rhs is a tv => swap + go ty1 ty2@(TyVarTy tv2) + | ty2 `tcPartOfType` ty1 -- occurs check! + = occurCheckErr ty2 ty1 + | otherwise + = do { co' <- mkSymEqInstCo co (ty2, ty1) + ; mkRewriteVar True tv2 ty1 co' + } -NB: We perform this transformation for multiple occurences of ty1 under one - or multiple family applications on the left-hand side at once (ie, the - rule doesn't need to be applied multiple times at a single inst). As a - result we can get two or more insts back. + -- type applications => decompose + go ty1 ty2 + | Just (ty1_l, ty1_r) <- repSplitAppTy_maybe ty1 -- won't split fam apps + , Just (ty2_l, ty2_r) <- repSplitAppTy_maybe ty2 + = do { (co_l, co_r) <- mkAppEqInstCo co (ty1_l, ty2_l) (ty1_r, ty2_r) + ; eqs_l <- checkOrientation ty1_l ty2_l co_l inst + ; eqs_r <- checkOrientation ty1_r ty2_r co_r inst + ; return $ eqs_l ++ eqs_r + } +-- !!!TODO: would be more efficient to handle the FunApp and the data +-- constructor application explicitly. + + -- inconsistency => type error + go ty1 ty2 + = ASSERT( (not . isForAllTy $ ty1) && (not . isForAllTy $ ty2) ) + eqInstMisMatch inst + + mkRewriteVar swapped tv ty co = return [RewriteVar + { rwi_var = tv + , rwi_right = ty + , rwi_co = co + , rwi_loc = tci_loc inst + , rwi_name = tci_name inst + , rwi_swapped = swapped + }] + +flattenType :: Inst -- context to get location & name + -> Type -- the type to flatten + -> TcM (Type, -- the flattened type + Coercion, -- coercion witness of flattening wanteds + [RewriteInst], -- extra equalities + TyVarSet) -- new intermediate skolems +-- Removes all family synonyms from a type by moving them into extra equalities +flattenType inst ty + = go ty + where + -- look through synonyms + go ty | Just ty' <- tcView ty + = do { (ty_flat, co, eqs, skolems) <- go ty' + ; if null eqs + then -- unchanged, keep the old type with folded synonyms + return (ty, ty, [], emptyVarSet) + else + return (ty_flat, co, eqs, skolems) + } -Note [skolemOccurs loop] -~~~~~~~~~~~~~~~~~~~~~~~~ -You might think that under + -- type variable => nothing to do + go ty@(TyVarTy _) + = return (ty, ty, [] , emptyVarSet) - type family F a - type instance F [a] = [F a] + -- type family application + -- => flatten to "gamma :: F t1'..tn' ~ alpha" (alpha & gamma fresh) + go ty@(TyConApp con args) + | isOpenSynTyCon con + = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args + ; alpha <- newFlexiTyVar (typeKind ty) + ; let alphaTy = mkTyVarTy alpha + ; cotv <- newMetaCoVar (mkTyConApp con args') alphaTy + ; let thisRewriteFam = RewriteFam + { rwi_fam = con + , rwi_args = args' + , rwi_right = alphaTy + , rwi_co = mkWantedCo cotv + , rwi_loc = tci_loc inst + , rwi_name = tci_name inst + , rwi_swapped = True + } + ; return (alphaTy, + mkTyConApp con cargs `mkTransCoercion` mkTyVarTy cotv, + thisRewriteFam : concat args_eqss, + unionVarSets args_skolemss `extendVarSet` alpha) + } -- adding new unflatten var inst + + -- data constructor application => flatten subtypes + -- NB: Special cased for efficiency - could be handled as type application + go ty@(TyConApp con args) + = do { (args', cargs, args_eqss, args_skolemss) <- mapAndUnzip4M go args + ; if null args_eqss + then -- unchanged, keep the old type with folded synonyms + return (ty, ty, [], emptyVarSet) + else + return (mkTyConApp con args', + mkTyConApp con cargs, + concat args_eqss, + unionVarSets args_skolemss) + } -a signature such as + -- function type => flatten subtypes + -- NB: Special cased for efficiency - could be handled as type application + go ty@(FunTy ty_l ty_r) + = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l + ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r + ; if null eqs_l && null eqs_r + then -- unchanged, keep the old type with folded synonyms + return (ty, ty, [], emptyVarSet) + else + return (mkFunTy ty_l' ty_r', + mkFunTy co_l co_r, + eqs_l ++ eqs_r, + skolems_l `unionVarSet` skolems_r) + } - foo :: (F [a] ~ a) => a + -- type application => flatten subtypes + go ty@(AppTy ty_l ty_r) + = do { (ty_l', co_l, eqs_l, skolems_l) <- go ty_l + ; (ty_r', co_r, eqs_r, skolems_r) <- go ty_r + ; if null eqs_l && null eqs_r + then -- unchanged, keep the old type with folded synonyms + return (ty, ty, [], emptyVarSet) + else + return (mkAppTy ty_l' ty_r', + mkAppTy co_l co_r, + eqs_l ++ eqs_r, + skolems_l `unionVarSet` skolems_r) + } -will get us into a loop. However, this is *not* the case. Here is why: + -- forall type => panic if the body contains a type family + -- !!!TODO: As long as the family does not contain a quantified variable + -- we might pull it out, but what if it does contain a quantified + -- variable??? + go ty@(ForAllTy _ body) + | null (tyFamInsts body) + = return (ty, ty, [] , emptyVarSet) + | otherwise + = panic "TcTyFuns.flattenType: synonym family in a rank-n type" + + -- we should never see a predicate type + go (PredTy _) + = panic "TcTyFuns.flattenType: unexpected PredType" + +adjustCoercions :: EqInstCo -- coercion of original equality + -> Coercion -- coercion witnessing the left rewrite + -> Coercion -- coercion witnessing the right rewrite + -> (Type, Type) -- types of flattened equality + -> [RewriteInst] -- equalities from flattening + -> TcM (EqInstCo, -- coercion for flattened equality + [RewriteInst]) -- final equalities from flattening +-- Depending on whether we flattened a local or wanted equality, that equality's +-- coercion and that of the new equalities produced during flattening are +-- adjusted . +adjustCoercions (Left cotv) co1 co2 (ty_l, ty_r) all_eqs + -- wanted => generate a fresh coercion variable for the flattened equality + = do { cotv' <- newMetaCoVar ty_l ty_r + ; writeMetaTyVar cotv $ + (co1 `mkTransCoercion` TyVarTy cotv' `mkTransCoercion` co2) + ; return (Left cotv', all_eqs) + } - F [a] ~ a +adjustCoercions co@(Right _) _co1 _co2 _eqTys all_eqs + -- local => turn all new equalities into locals and update (but not zonk) + -- the skolem + = do { all_eqs' <- mapM wantedToLocal all_eqs + ; return (co, all_eqs') + } - -->(TOP) +mkDictBind :: Inst -- original instance + -> Bool -- is this a wanted contraint? + -> Coercion -- coercion witnessing the rewrite + -> PredType -- coerced predicate + -> TcM (Inst, -- new inst + TcDictBinds) -- binding for coerced dictionary +mkDictBind dict isWanted rewriteCo pred + = do { dict' <- newDictBndr loc pred + -- relate the old inst to the new one + -- target_dict = source_dict `cast` st_co + ; let (target_dict, source_dict, st_co) + | isWanted = (dict, dict', mkSymCoercion rewriteCo) + | otherwise = (dict', dict, rewriteCo) + -- we have + -- co :: dict ~ dict' + -- hence, if isWanted + -- dict = dict' `cast` sym co + -- else + -- dict' = dict `cast` co + expr = HsVar $ instToId source_dict + cast_expr = HsWrap (WpCast st_co) expr + rhs = L (instLocSpan loc) cast_expr + binds = instToDictBind target_dict rhs + ; return (dict', binds) + } + where + loc = tci_loc dict + +-- gamma :: Fam args ~ alpha +-- => alpha :: Fam args ~ alpha, with alpha := Fam args +-- (the update of alpha will not be apparent during propagation, as we +-- never follow the indirections of meta variables; it will be revealed +-- when the equality is zonked) +wantedToLocal :: RewriteInst -> TcM RewriteInst +wantedToLocal eq@(RewriteFam {rwi_fam = fam, + rwi_args = args, + rwi_right = alphaTy@(TyVarTy alpha)}) + = do { writeMetaTyVar alpha (mkTyConApp fam args) + ; return $ eq {rwi_co = mkGivenCo alphaTy} + } +wantedToLocal _ = panic "TcTyFuns.wantedToLocal" +\end{code} - [F a] ~ a - -->(SkolemOccurs) +%************************************************************************ +%* * + Propagation of equalities +%* * +%************************************************************************ - [b] ~ a - F [b] ~ b , with b := F a +Apply the propagation rules exhaustively. - -->(TOP) +\begin{code} +propagate :: [RewriteInst] -> EqConfig -> TcM EqConfig +propagate [] eqCfg = return eqCfg +propagate (eq:eqs) eqCfg + = do { optEqs <- applyTop eq + ; case optEqs of + + -- Top applied to 'eq' => retry with new equalities + Just (eqs2, skolems2) + -> propagate (eqs2 ++ eqs) (eqCfg `addSkolems` skolems2) + + -- Top doesn't apply => try subst rules with all other + -- equalities, after that 'eq' can go into the residual list + Nothing + -> do { (eqs', eqCfg') <- applySubstRules eq eqs eqCfg + ; propagate eqs' (eqCfg' `addEq` eq) + } + } + +applySubstRules :: RewriteInst -- currently considered eq + -> [RewriteInst] -- todo eqs list + -> EqConfig -- residual + -> TcM ([RewriteInst], EqConfig) -- new todo & residual +applySubstRules eq todoEqs (eqConfig@EqConfig {eqs = resEqs}) + = do { (newEqs_t, unchangedEqs_t, skolems_t) <- mapSubstRules eq todoEqs + ; (newEqs_r, unchangedEqs_r, skolems_r) <- mapSubstRules eq resEqs + ; return (newEqs_t ++ newEqs_r ++ unchangedEqs_t, + eqConfig {eqs = unchangedEqs_r} + `addSkolems` (skolems_t `unionVarSet` skolems_r)) + } - [b] ~ a - [F b] ~ b , with b := F a +mapSubstRules :: RewriteInst -- try substituting this equality + -> [RewriteInst] -- into these equalities + -> TcM ([RewriteInst], [RewriteInst], TyVarSet) +mapSubstRules eq eqs + = do { (newEqss, unchangedEqss, skolemss) <- mapAndUnzip3M (substRules eq) eqs + ; return (concat newEqss, concat unchangedEqss, unionVarSets skolemss) + } + where + substRules eq1 eq2 + = do { -- try the SubstFam rule + optEqs <- applySubstFam eq1 eq2 + ; case optEqs of + Just (eqs, skolems) -> return (eqs, [], skolems) + Nothing -> do + { -- try the SubstVarVar rule + optEqs <- applySubstVarVar eq1 eq2 + ; case optEqs of + Just (eqs, skolems) -> return (eqs, [], skolems) + Nothing -> do + { -- try the SubstVarFam rule + optEqs <- applySubstVarFam eq1 eq2 + ; case optEqs of + Just eq -> return ([eq], [], emptyVarSet) + Nothing -> return ([], [eq2], emptyVarSet) + -- if no rule matches, we return the equlity we tried to + -- substitute into unchanged + }}} +\end{code} -At this point (SkolemOccurs) does *not* apply anymore, as +Attempt to apply the Top rule. The rule is - [F b] ~ b + co :: F t1..tn ~ t + =(Top)=> + co' :: [s1/x1, .., sm/xm]s ~ t with co = g s1..sm |> co' -is not used as a rewrite rule. The variable b is not a skolem (cf -eqInstToRewrite). +where g :: forall x1..xm. F u1..um ~ s and [s1/x1, .., sm/xm]u1 == t1. -(The regression test indexed-types/should_compile/Simple20 checks that the -described property of the system does not change.) +Returns Nothing if the rule could not be applied. Otherwise, the resulting +equality is normalised and a list of the normal equalities is returned. \begin{code} -skolemOccurs :: PrecondRule -skolemOccurs insts - = do { (instss, undoSkolems) <- mapAndUnzipM oneSkolemOccurs insts - ; return (concat instss, sequence_ undoSkolems) +applyTop :: RewriteInst -> TcM (Maybe ([RewriteInst], TyVarSet)) + +applyTop eq@(RewriteFam {rwi_fam = fam, rwi_args = args}) + = do { optTyCo <- tcUnfoldSynFamInst (TyConApp fam args) + ; case optTyCo of + Nothing -> return Nothing + Just (lhs, rewrite_co) + -> do { co' <- mkRightTransEqInstCo co rewrite_co (lhs, rhs) + ; eq' <- deriveEqInst eq lhs rhs co' + ; liftM Just $ normEqInst eq' + } } where - oneSkolemOccurs inst - = ASSERT( isEqInst inst ) - case eqInstToRewrite inst of - Just (rewrite, swapped) -> breakRecursion rewrite swapped - Nothing -> return ([inst], return ()) - where - -- inst is an elementary rewrite rule, check whether we need to break - -- it up - breakRecursion (Rewrite pat body _) swapped - - -- skolemOccurs does not apply, leave as is - | null tysToLiftOut - = do { traceTc $ text "oneSkolemOccurs: no tys to lift out" - ; return ([inst], return ()) - } + co = rwi_co eq + rhs = rwi_right eq - -- recursive occurence of pat in body under a type family application - | otherwise - = do { traceTc $ text "oneSkolemOccurs[TLO]:" <+> ppr tysToLiftOut - ; skTvs <- mapM (newMetaTyVar TauTv . typeKind) tysToLiftOut - ; let skTvs_tysTLO = zip skTvs tysToLiftOut - insertSkolems = return . replace skTvs_tysTLO - ; (_, body') <- tcGenericNormaliseFamInst insertSkolems body - ; inst' <- if swapped then mkEqInst (EqPred body' pat) co - else mkEqInst (EqPred pat body') co - -- ensure to reconstruct the inst in the - -- original orientation - ; traceTc $ text "oneSkolemOccurs[inst']:" <+> ppr inst' - ; (insts, undoSk) <- mapAndUnzipM (mkSkolemInst inst') - skTvs_tysTLO - ; return (inst':insts, sequence_ undoSk) - } - where - co = eqInstCoercion inst - - -- all subtypes that are (1) type family instances and (2) contain - -- the lhs type as part of the type arguments of the type family - -- constructor - tysToLiftOut = [mkTyConApp tc tys | (tc, tys) <- tyFamInsts body - , any (pat `tcPartOfType`) tys] - - replace :: [(TcTyVar, Type)] -> Type -> Maybe (Type, Coercion) - replace [] _ = Nothing - replace ((skTv, tyTLO):rest) ty - | tyTLO `tcEqType` ty = Just (mkTyVarTy skTv, undefined) - | otherwise = replace rest ty - - -- create the EqInst for the equality determining the skolem and a - -- TcM action undoing the skolem introduction - mkSkolemInst inst' (skTv, tyTLO) - = do { (co, tyLiftedOut) <- tcEqInstNormaliseFamInst inst' tyTLO - ; inst <- mkEqInst (EqPred tyLiftedOut (mkTyVarTy skTv)) - (mkGivenCo $ mkSymCoercion (fromACo co)) - -- co /= IdCo due to construction of inst' - ; return (inst, writeMetaTyVar skTv tyTLO) - } +applyTop _ = return Nothing \end{code} +Attempt to apply the SubstFam rule. The rule is -Removal of trivial equalities: trivialRule -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -The following rules exploits the reflexivity of equality: + co1 :: F t1..tn ~ t & co2 :: F t1..tn ~ s + =(SubstFam)=> + co1 :: F t1..tn ~ t & co2' :: t ~ s with co2 = co1 |> co2' - (Trivial) - g1 : t ~ t - >--> - g1 := t +where co1 may be a wanted only if co2 is a wanted, too. + +Returns Nothing if the rule could not be applied. Otherwise, the equality +co2' is normalised and a list of the normal equalities is returned. (The +equality co1 is not returned as it remain unaltered.) \begin{code} -trivialRule :: IdemRewriteRule -trivialRule insts - = liftM catMaybes $ mapM trivial insts +applySubstFam :: RewriteInst + -> RewriteInst + -> TcM (Maybe ([RewriteInst], TyVarSet)) +applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1}) + eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2}) + | fam1 == fam2 && tcEqTypes args1 args2 && + (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1)) +-- !!!TODO: tcEqTypes is insufficient as it does not look through type synonyms +-- !!!Check whether anything breaks by making tcEqTypes look through synonyms. +-- !!!Should be ok and we don't want three type equalities. + = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs) + ; eq2' <- deriveEqInst eq2 lhs rhs co2' + ; liftM Just $ normEqInst eq2' + } where - trivial inst - | ASSERT( isEqInst inst ) - ty1 `tcEqType` ty2 - = do { eitherEqInst inst - (\cotv -> writeMetaTyVar cotv ty1) - (\_ -> return ()) - ; return Nothing - } - | otherwise - = return $ Just inst - where - (ty1,ty2) = eqInstTys inst + lhs = rwi_right eq1 + rhs = rwi_right eq2 + co1 = eqInstCoType (rwi_co eq1) + co2 = rwi_co eq2 +applySubstFam _ _ = return Nothing \end{code} +Attempt to apply the SubstVarVar rule. The rule is -Decomposition of data type constructors: decompRule -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Whenever, the same *data* constructors occurs on both sides of an equality, we -can decompose as in standard unification. - - (Decomp) - g1 : T cs ~ T ds - >--> - g21 : c1 ~ d1, ..., g2n : cn ~ dn - g1 := T g2s + co1 :: x ~ t & co2 :: x ~ s + =(SubstVarVar)=> + co1 :: x ~ t & co2' :: t ~ s with co2 = co1 |> co2' -Works also for the case where T is actually an application of a type family -constructor to a set of types, provided the applications on both sides of the -~ are identical; see also Note [OpenSynTyCon app] in TcUnify. +where co1 may be a wanted only if co2 is a wanted, too. -We guarantee to raise an error for any inconsistent equalities; -cf Note [Inconsistencies in equality constraints]. +Returns Nothing if the rule could not be applied. Otherwise, the equality +co2' is normalised and a list of the normal equalities is returned. (The +equality co1 is not returned as it remain unaltered.) \begin{code} -decompRule :: RewriteRule -decompRule insts - = do { (insts, changed) <- mapAndUnzipM decomp insts - ; return (concat insts, or changed) +applySubstVarVar :: RewriteInst + -> RewriteInst + -> TcM (Maybe ([RewriteInst], TyVarSet)) +applySubstVarVar eq1@(RewriteVar {rwi_var = tv1}) + eq2@(RewriteVar {rwi_var = tv2}) + | tv1 == tv2 && + (isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1)) + = do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs) + ; eq2' <- deriveEqInst eq2 lhs rhs co2' + ; liftM Just $ normEqInst eq2' } where - decomp inst - = ASSERT( isEqInst inst ) - go ty1 ty2 - where - (ty1,ty2) = eqInstTys inst - go ty1 ty2 - | Just ty1' <- tcView ty1 = go ty1' ty2 - | Just ty2' <- tcView ty2 = go ty1 ty2' - - go (TyConApp con1 tys1) (TyConApp con2 tys2) - | con1 == con2 && identicalHead - = mkArgInsts (mkTyConApp con1) tys1 tys2 - - | con1 /= con2 && not (isOpenSynTyCon con1 || isOpenSynTyCon con2) - -- not matching data constructors (of any flavour) are bad news - = eqInstMisMatch inst - where - n = tyConArity con1 - (idxTys1, _) = splitAt n tys1 - (idxTys2, _) = splitAt n tys2 - identicalHead = not (isOpenSynTyCon con1) || - idxTys1 `tcEqTypes` idxTys2 - - go (FunTy fun1 arg1) (FunTy fun2 arg2) - = mkArgInsts (\[funCo, argCo] -> mkFunTy funCo argCo) [fun1, arg1] - [fun2, arg2] - - -- Applications need a bit of care! - -- They can match FunTy and TyConApp, so use splitAppTy_maybe - go (AppTy s1 t1) ty2 - | Just (s2, t2) <- tcSplitAppTy_maybe ty2 - = mkArgInsts (\[s, t] -> mkAppTy s t) [s1, t1] [s2, t2] - - -- Symmetric case - go ty1 (AppTy s2 t2) - | Just (s1, t1) <- tcSplitAppTy_maybe ty1 - = mkArgInsts (\[s, t] -> mkAppTy s t) [s1, t1] [s2, t2] - - -- We already covered all the consistent cases of rigid types on both - -- sides; so, if we see two rigid types here, we discovered an - -- inconsistency. - go ty1 ty2 - | isRigid ty1 && isRigid ty2 - = eqInstMisMatch inst - - -- We can neither assert consistency nor inconsistency => defer - go _ _ = return ([inst], False) - - isRigid (TyConApp con _) = not (isOpenSynTyCon con) - isRigid (FunTy _ _) = True - isRigid (AppTy _ _) = True - isRigid _ = False - - -- Create insts for matching argument positions (ie, the bit after - -- '>-->' in the rule description above) - mkArgInsts con tys1 tys2 - = do { cos <- eitherEqInst inst - -- old_co := Con1 cos - (\old_covar -> - do { cotvs <- zipWithM newMetaCoVar tys1 tys2 - ; let cos = map mkTyVarTy cotvs - ; writeMetaTyVar old_covar (con cos) - ; return $ map mkWantedCo cotvs - }) - -- co_i := Con_i old_co - (\old_co -> - return $ map mkGivenCo $ - mkRightCoercions (length tys1) old_co) - ; insts <- zipWithM mkEqInst (zipWith EqPred tys1 tys2) cos - ; traceTc (text "decomp identicalHead" <+> ppr insts) - ; return (insts, not $ null insts) - } + lhs = rwi_right eq1 + rhs = rwi_right eq2 + co1 = eqInstCoType (rwi_co eq1) + co2 = rwi_co eq2 +applySubstVarVar _ _ = return Nothing \end{code} +Attempt to apply the SubstVarFam rule. The rule is -Rewriting with type instances: topRule -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We use (toplevel) type instances to normalise both sides of equalities. + co1 :: x ~ t & co2 :: F s1..sn ~ s + =(SubstVarFam)=> + co1 :: x ~ t & co2' :: [t/x](F s1..sn) ~ s + with co2 = [co1/x](F s1..sn) |> co2' - (Top) - g1 : t ~ s - >--> co1 :: t ~ t' / co2 :: s ~ s' - g2 : t' ~ s' - g1 := co1 * g2 * sym co2 +where x occurs in F s1..sn. (co1 may be local or wanted.) + +Returns Nothing if the rule could not be applied. Otherwise, the equality +co2' is returned. (The equality co1 is not returned as it remain unaltered.) \begin{code} -topRule :: RewriteRule -topRule insts - = do { (insts, changed) <- mapAndUnzipM top insts - ; return (insts, or changed) - } +applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst) +applySubstVarFam eq1@(RewriteVar {rwi_var = tv1}) + eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2}) + | tv1 `elemVarSet` tyVarsOfTypes args2 + = do { let co1Subst = substTyWith [tv1] [co1] (mkTyConApp fam2 args2) + args2' = substTysWith [tv1] [rhs1] args2 + lhs2 = mkTyConApp fam2 args2' + ; co2' <- mkRightTransEqInstCo co2 co1Subst (lhs2, rhs2) + ; return $ Just (eq2 {rwi_args = args2', rwi_co = co2'}) + } where - top inst - = ASSERT( isEqInst inst ) - do { (coi1, ty1') <- tcNormaliseFamInst ty1 - ; (coi2, ty2') <- tcNormaliseFamInst ty2 - ; case (coi1, coi2) of - (IdCo, IdCo) -> return (inst, False) - _ -> - do { wg_co <- - eitherEqInst inst - -- old_co = co1 * new_co * sym co2 - (\old_covar -> - do { new_cotv <- newMetaCoVar ty1' ty2' - ; let new_co = mkTyVarTy new_cotv - old_coi = coi1 `mkTransCoI` - ACo new_co `mkTransCoI` - (mkSymCoI coi2) - ; writeMetaTyVar old_covar (fromACo old_coi) - ; return $ mkWantedCo new_cotv - }) - -- new_co = sym co1 * old_co * co2 - (\old_co -> - return $ - mkGivenCo $ - fromACo $ - mkSymCoI coi1 `mkTransCoI` - ACo old_co `mkTransCoI` coi2) - ; new_inst <- mkEqInst (EqPred ty1' ty2') wg_co - ; return (new_inst, True) - } - } - where - (ty1,ty2) = eqInstTys inst + rhs1 = rwi_right eq1 + rhs2 = rwi_right eq2 + co1 = eqInstCoType (rwi_co eq1) + co2 = rwi_co eq2 +applySubstVarFam _ _ = return Nothing \end{code} -Rewriting with equalities: substRule -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -From a set of insts, use all insts that can be read as rewrite rules to -rewrite the types in all other insts. - - (Subst) - g : F c ~ t, - forall g1 : s1{F c} ~ s2{F c} - >--> - g2 : s1{t} ~ s2{t} - g1 := s1{g} * g2 * sym s2{g} <=> g2 := sym s1{g} * g1 * s2{g} +%************************************************************************ +%* * + Finalisation of equalities +%* * +%************************************************************************ -Alternatively, the rewrite rule may have the form (g : a ~ t). +Exhaustive substitution of all variable equalities of the form co :: x ~ t +(both local and wanted) into the left-hand sides of all other equalities. This +may lead to recursive equalities; i.e., (1) we need to apply the substitution +implied by one variable equality exhaustively before turning to the next and +(2) we need an occurs check. -To avoid having to swap rules of the form (g : t ~ F c) and (g : t ~ a), -where t is neither a variable nor a type family application, we use them for -rewriting from right-to-left. However, it is crucial to only apply rules -from right-to-left if they cannot be used left-to-right. +We also apply the same substitutions to the local and wanted class and IP +dictionaries. -The workhorse is substInst, which performs an occurs check before actually -using an equality for rewriting. If the type pattern occurs in the type we -substitute for the pattern, normalisation would diverge. +NB: Given that we apply the substitution corresponding to a single equality +exhaustively, before turning to the next, and because we eliminate recursive +equalities, all opportunities for subtitution will have been exhausted after +we have considered each equality once. \begin{code} -substRule :: RewriteRule -substRule insts = tryAllInsts insts [] +substitute :: [RewriteInst] -- equalities + -> [Inst] -- local class dictionaries + -> [Inst] -- wanted class dictionaries + -> TcM ([RewriteInst], -- equalities after substitution + TcDictBinds, -- all newly generated dictionary bindings + [Inst], -- local dictionaries after substitution + [Inst]) -- wanted dictionaries after substitution +substitute eqs locals wanteds = subst eqs [] emptyBag locals wanteds where - -- for every inst check whether it can be used to rewrite the others - -- (we make an effort to keep the insts in order; it makes debugging - -- easier) - tryAllInsts [] triedInsts = return (reverse triedInsts, False) - tryAllInsts (inst:insts) triedInsts - = do { (insts', changed) <- substInst inst (reverse triedInsts ++ insts) - ; if changed then return (insertAt (length triedInsts) inst insts', - True) - else tryAllInsts insts (inst:triedInsts) + subst [] res binds locals wanteds + = return (res, binds, locals, wanteds) + subst (eq@(RewriteVar {rwi_var = tv, rwi_right = ty, rwi_co = co}):eqs) + res binds locals wanteds + = do { traceTc $ ptext (sLit "TcTyFuns.substitute:") <+> ppr eq + ; let coSubst = zipOpenTvSubst [tv] [eqInstCoType co] + tySubst = zipOpenTvSubst [tv] [ty] + ; eqs' <- mapM (substEq eq coSubst tySubst) eqs + ; res' <- mapM (substEq eq coSubst tySubst) res + ; (lbinds, locals') <- mapAndUnzipM + (substDict eq coSubst tySubst False) + locals + ; (wbinds, wanteds') <- mapAndUnzipM + (substDict eq coSubst tySubst True) + wanteds + ; let binds' = unionManyBags $ binds : lbinds ++ wbinds + ; subst eqs' (eq:res') binds' locals' wanteds' } - where - insertAt n x xs = let (xs1, xs2) = splitAt n xs - in xs1 ++ [x] ++ xs2 - --- Use the given inst as a rewrite rule to normalise the insts in the second --- argument. Don't do anything if the inst cannot be used as a rewrite rule, --- but do apply it right-to-left, if possible, and if it cannot be used --- left-to-right. --- -substInst :: Inst -> [Inst] -> TcM ([Inst], Bool) -substInst inst insts - = case eqInstToRewrite inst of - Just (rewrite, _) -> substEquality rewrite insts - Nothing -> return (insts, False) - where - substEquality :: Rewrite -- elementary rewrite - -> [Inst] -- insts to rewrite - -> TcM ([Inst], Bool) - substEquality eqRule@(Rewrite pat rhs _) insts - | pat `tcPartOfType` rhs -- occurs check! - = occurCheckErr pat rhs - | otherwise - = do { (insts', changed) <- mapAndUnzipM substOne insts - ; return (insts', or changed) + subst (eq:eqs) res binds locals wanteds + = subst eqs (eq:res) binds locals wanteds + + -- We have, co :: tv ~ ty + -- => apply [ty/tv] to right-hand side of eq2 + -- (but only if tv actually occurs in the right-hand side of eq2) + substEq (RewriteVar {rwi_var = tv, rwi_right = ty}) + coSubst tySubst eq2 + | tv `elemVarSet` tyVarsOfType (rwi_right eq2) + = do { let co1Subst = mkSymCoercion $ substTy coSubst (rwi_right eq2) + right2' = substTy tySubst (rwi_right eq2) + left2 = case eq2 of + RewriteVar {rwi_var = tv2} -> mkTyVarTy tv2 + RewriteFam {rwi_fam = fam, + rwi_args = args} ->mkTyConApp fam args + ; co2' <- mkLeftTransEqInstCo (rwi_co eq2) co1Subst (left2, right2') + ; case eq2 of + RewriteVar {rwi_var = tv2} | tv2 `elemVarSet` tyVarsOfType ty + -> occurCheckErr left2 right2' + _ -> return $ eq2 {rwi_right = right2', rwi_co = co2'} } - where - substOne inst - = ASSERT( isEqInst inst ) - do { (coi1, ty1') <- tcEqRuleNormaliseFamInst eqRule ty1 - ; (coi2, ty2') <- tcEqRuleNormaliseFamInst eqRule ty2 - ; case (coi1, coi2) of - (IdCo, IdCo) -> return (inst, False) - _ -> - do { gw_co <- - eitherEqInst inst - -- old_co := co1 * new_co * sym co2 - (\old_covar -> - do { new_cotv <- newMetaCoVar ty1' ty2' - ; let new_co = mkTyVarTy new_cotv - old_coi = coi1 `mkTransCoI` - ACo new_co `mkTransCoI` - (mkSymCoI coi2) - ; writeMetaTyVar old_covar (fromACo old_coi) - ; return $ mkWantedCo new_cotv - }) - -- new_co := sym co1 * old_co * co2 - (\old_co -> - return $ - mkGivenCo $ - fromACo $ - mkSymCoI coi1 `mkTransCoI` - ACo old_co `mkTransCoI` coi2) - ; new_inst <- mkEqInst (EqPred ty1' ty2') gw_co - ; return (new_inst, True) - } - } - where - (ty1,ty2) = eqInstTys inst -\end{code} - - -Instantiate meta variables: unifyMetaRule -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -If an equality equates a meta type variable with a type, we simply instantiate -the meta variable. - (UnifyMeta) - g : alpha ~ t - >--> - alpha := t - g := t + -- unchanged + substEq _ _ _ eq2 + = return eq2 + + -- We have, co :: tv ~ ty + -- => apply [ty/tv] to dictionary predicate + -- (but only if tv actually occurs in the predicate) + substDict (RewriteVar {rwi_var = tv}) + coSubst tySubst isWanted dict + | isClassDict dict + , tv `elemVarSet` tyVarsOfPred (tci_pred dict) + = do { let co1Subst = PredTy (substPred coSubst (tci_pred dict)) + pred' = substPred tySubst (tci_pred dict) + ; (dict', binds) <- mkDictBind dict isWanted co1Subst pred' + ; return (binds, dict') + } -Meta variables can only appear in wanted constraints, and this rule should -only be applied to wanted constraints. We also know that t definitely is -distinct from alpha (as the trivialRule) has been run on the insts beforehand. + -- unchanged + substDict _ _ _ _ dict + = return (emptyBag, dict) +-- !!!TODO: Still need to substitute into IP constraints. +\end{code} -NB: We cannot assume that meta tyvars are empty. They may have been updated -by another inst in the currently processed wanted list. We need to be very -careful when updateing type variables (see TcUnify.uUnfilledVar), but at least -we know that we have no boxes. It's unclear that it would be an advantage to -common up the code in TcUnify and the code below. Firstly, we don't want -calls to TcUnify.defer_unification here, and secondly, TcUnify import the -current module, so we would have to move everything here (Yuk!) or to -TcMType. Besides, the code here is much simpler due to the lack of boxes. +For any *wanted* variable equality of the form co :: alpha ~ t or co :: a ~ +alpha, we instantiate alpha with t or a, respectively, and set co := id. +Return all remaining wanted equalities. The Boolean result component is True +if at least one instantiation of a flexible was performed. \begin{code} -unifyMetaRule :: RewriteRule -unifyMetaRule insts - = do { (insts', changed) <- mapAndUnzipM unifyMeta insts - ; return (concat insts', or changed) +instantiateAndExtract :: [RewriteInst] -> Bool -> TcM ([Inst], Bool) +instantiateAndExtract eqs localsEmpty + = do { wanteds' <- mapM inst wanteds + ; let residuals = catMaybes wanteds' + improved = length wanteds /= length residuals + ; residuals' <- mapM rewriteInstToInst residuals + ; return (residuals', improved) } where - unifyMeta inst - = ASSERT( isEqInst inst ) - go ty1 ty2 - (fromWantedCo "unifyMetaRule" $ eqInstCoercion inst) + wanteds = filter (isWantedCo . rwi_co) eqs + checkingMode = length eqs > length wanteds || not localsEmpty + -- no local equalities or dicts => checking mode + + inst eq@(RewriteVar {rwi_var = tv1, rwi_right = ty2, rwi_co = co}) + + -- co :: alpha ~ t + | isMetaTyVar tv1 + = doInst (rwi_swapped eq) tv1 ty2 co eq + + -- co :: a ~ alpha + | Just tv2 <- tcGetTyVar_maybe ty2 + , isMetaTyVar tv2 + = doInst (not $ rwi_swapped eq) tv2 (mkTyVarTy tv1) co eq + + -- co :: F args ~ alpha, and we are in checking mode (ie, no locals) + inst eq@(RewriteFam {rwi_fam = fam, rwi_args = args, rwi_right = ty2, + rwi_co = co}) + | checkingMode + , Just tv2 <- tcGetTyVar_maybe ty2 + , isMetaTyVar tv2 + = doInst (not $ rwi_swapped eq) tv2 (mkTyConApp fam args) co eq + + inst eq = return $ Just eq + + doInst _swapped _tv _ty (Right ty) _eq + = pprPanic "TcTyFuns.doInst: local eq: " (ppr ty) + doInst swapped tv ty (Left cotv) eq + = do { lookupTV <- lookupTcTyVar tv + ; uMeta swapped tv lookupTV ty cotv + } where - (ty1,ty2) = eqInstTys inst - go ty1 ty2 cotv - | Just ty1' <- tcView ty1 = go ty1' ty2 cotv - | Just ty2' <- tcView ty2 = go ty1 ty2' cotv - - | TyVarTy tv1 <- ty1 - , isMetaTyVar tv1 = do { lookupTV <- lookupTcTyVar tv1 - ; uMeta False tv1 lookupTV ty2 cotv - } - | TyVarTy tv2 <- ty2 - , isMetaTyVar tv2 = do { lookupTV <- lookupTcTyVar tv2 - ; uMeta True tv2 lookupTV ty1 cotv - } - | otherwise = return ([inst], False) - -- meta variable has been filled already - -- => ignore this inst (we'll come around again, after zonking) + -- => ignore (must be a skolem that was introduced by flattening locals) uMeta _swapped _tv (IndirectTv _) _ty _cotv - = return ([inst], False) - - -- signature skolem meets non-variable type - -- => cannot update! - uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) ty _cotv - | not $ isTyVarTy ty - = return ([inst], False) + = return Nothing -- type variable meets type variable -- => check that tv2 hasn't been updated yet and choose which to update - uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv - = do { lookupTV2 <- lookupTcTyVar tv2 + uMeta swapped tv1 (DoneTv details1) (TyVarTy tv2) cotv + | tv1 == tv2 + = panic "TcTyFuns.uMeta: normalisation shouldn't allow x ~ x" + + | otherwise + = do { lookupTV2 <- lookupTcTyVar tv2 ; case lookupTV2 of - IndirectTv ty -> uMeta swapped tv1 (DoneTv details1) ty cotv + IndirectTv ty -> + uMeta swapped tv1 (DoneTv details1) ty cotv DoneTv details2 -> uMetaVar swapped tv1 details1 tv2 details2 cotv - } + } + + ------ Beyond this point we know that ty2 is not a type variable + + -- signature skolem meets non-variable type + -- => cannot update (retain the equality)! + uMeta _swapped _tv (DoneTv (MetaTv (SigTv _) _)) _non_tv_ty _cotv + = return $ Just eq -- updatable meta variable meets non-variable type -- => occurs check, monotype check, and kinds match check, then update - uMeta swapped tv (DoneTv (MetaTv _ ref)) ty cotv - = do { mb_ty' <- checkTauTvUpdate tv ty -- occurs + monotype check + uMeta swapped tv (DoneTv (MetaTv _ ref)) non_tv_ty cotv + = do { -- occurs + monotype check + ; mb_ty' <- checkTauTvUpdate tv non_tv_ty + ; case mb_ty' of - Nothing -> return ([inst], False) -- tv occurs in faminst + Nothing -> + -- normalisation shouldn't leave families in non_tv_ty + panic "TcTyFuns.uMeta: unexpected synonym family" Just ty' -> do { checkUpdateMeta swapped tv ref ty' -- update meta var - ; writeMetaTyVar cotv ty' -- update co var - ; return ([], True) + ; writeMetaTyVar cotv ty' -- update co var + ; return Nothing } - } + } - uMeta _ _ _ _ _ = panic "uMeta" + uMeta _ _ _ _ _ = panic "TcTyFuns.uMeta" + -- uMetaVar: unify two type variables -- meta variable meets skolem -- => just update uMetaVar swapped tv1 (MetaTv _ ref) tv2 (SkolemTv _) cotv = do { checkUpdateMeta swapped tv1 ref (mkTyVarTy tv2) - ; writeMetaTyVar cotv (mkTyVarTy tv2) - ; return ([], True) - } + ; writeMetaTyVar cotv (mkTyVarTy tv2) + ; return Nothing + } -- meta variable meets meta variable -- => be clever about which of the two to update @@ -1044,8 +1240,8 @@ unifyMetaRule insts -- The "nicer to" part only applies if the two kinds are the same, -- so we can choose which to do. - ; writeMetaTyVar cotv (mkTyVarTy tv2) - ; return ([], True) + ; writeMetaTyVar cotv (mkTyVarTy tv2) + ; return Nothing } where -- Kinds should be guaranteed ok at this point @@ -1071,139 +1267,6 @@ unifyMetaRule insts %************************************************************************ %* * -\section{Normalisation of Insts} -%* * -%************************************************************************ - -Normalises a set of dictionaries relative to a set of given equalities (which -are interpreted as rewrite rules). We only consider given equalities of the -form - - F ts ~ t or a ~ t - -where F is a type family. - -\begin{code} -substEqInDictInsts :: Bool -- whether the *dictionaries* are wanted/given - -> [Inst] -- given equalities (used as rewrite rules) - -> [Inst] -- dictinaries to be normalised - -> TcM ([Inst], TcDictBinds) -substEqInDictInsts isWanted eqInsts dictInsts - = do { traceTc (text "substEqInDictInst <-" <+> ppr dictInsts) - ; dictInsts' <- - foldlM rewriteWithOneEquality (dictInsts, emptyBag) eqInsts - ; traceTc (text "substEqInDictInst ->" <+> ppr dictInsts') - ; return dictInsts' - } - where - -- (1) Given equality of form 'F ts ~ t' or 'a ~ t': use for rewriting - rewriteWithOneEquality (dictInsts, dictBinds) - eqInst@(EqInst {tci_left = pattern, - tci_right = target}) - | isOpenSynTyConApp pattern || isTyVarTy pattern - = do { (dictInsts', moreDictBinds) <- - genericNormaliseInsts isWanted applyThisEq dictInsts - ; return (dictInsts', dictBinds `unionBags` moreDictBinds) - } - where - applyThisEq = tcGenericNormaliseFamInstPred (return . matchResult) - - -- rewrite in case of an exact match - matchResult ty | tcEqType pattern ty = Just (target, eqInstType eqInst) - | otherwise = Nothing - - -- (2) Given equality has the wrong form: ignore - rewriteWithOneEquality (dictInsts, dictBinds) _not_a_rewrite_rule - = return (dictInsts, dictBinds) -\end{code} - - -Take a bunch of Insts (not EqInsts), and normalise them wrt the top-level -type-function equations, where - - (norm_insts, binds) = normaliseInsts is_wanted insts - -If 'is_wanted' - = True, (binds + norm_insts) defines insts (wanteds) - = False, (binds + insts) defines norm_insts (givens) - -Ie, in the case of normalising wanted dictionaries, we use the normalised -dictionaries to define the originally wanted ones. However, in the case of -given dictionaries, we use the originally given ones to define the normalised -ones. - -\begin{code} -normaliseInsts :: Bool -- True <=> wanted insts - -> [Inst] -- wanted or given insts - -> TcM ([Inst], TcDictBinds) -- normalised insts and bindings -normaliseInsts isWanted insts - = genericNormaliseInsts isWanted tcNormaliseFamInstPred insts - -genericNormaliseInsts :: Bool -- True <=> wanted insts - -> (TcPredType -> TcM (CoercionI, TcPredType)) - -- how to normalise - -> [Inst] -- wanted or given insts - -> TcM ([Inst], TcDictBinds) -- normalised insts & binds -genericNormaliseInsts isWanted fun insts - = do { (insts', binds) <- mapAndUnzipM (normaliseOneInst isWanted fun) insts - ; return (insts', unionManyBags binds) - } - where - normaliseOneInst isWanted fun - dict@(Dict {tci_pred = pred, - tci_loc = loc}) - = do { traceTc $ text "genericNormaliseInst <-" <+> ppr dict - ; (coi, pred') <- fun pred - - ; case coi of - IdCo -> - do { traceTc $ text "genericNormaliseInst ->" <+> ppr dict - ; return (dict, emptyBag) - } - -- don't use pred' in this case; otherwise, we get - -- more unfolded closed type synonyms in error messages - ACo co -> - do { -- an inst for the new pred - ; dict' <- newDictBndr loc pred' - -- relate the old inst to the new one - -- target_dict = source_dict `cast` st_co - ; let (target_dict, source_dict, st_co) - | isWanted = (dict, dict', mkSymCoercion co) - | otherwise = (dict', dict, co) - -- we have - -- co :: dict ~ dict' - -- hence, if isWanted - -- dict = dict' `cast` sym co - -- else - -- dict' = dict `cast` co - expr = HsVar $ instToId source_dict - cast_expr = HsWrap (WpCo st_co) expr - rhs = L (instLocSpan loc) cast_expr - binds = instToDictBind target_dict rhs - -- return the new inst - ; traceTc $ let name | isWanted - = "genericNormaliseInst (wanted) ->" - | otherwise - = "genericNormaliseInst (given) ->" - in - text name <+> ppr dict' <+> - text "with" <+> ppr binds - ; return (dict', binds) - } - } - - -- TOMDO: What do we have to do about ImplicInst, Method, and LitInst?? - normaliseOneInst _isWanted _fun inst - = do { inst' <- zonkInst inst - ; traceTc $ text "*** TcTyFuns.normaliseOneInst: Skipping" <+> - ppr inst - ; return (inst', emptyBag) - } -\end{code} - - -%************************************************************************ -%* * \section{Errors} %* * %************************************************************************ @@ -1236,9 +1299,9 @@ misMatchMsg :: TidyEnv -> (TcType, TcType) -> (TidyEnv, SDoc) misMatchMsg env0 (ty_act, ty_exp) = let (env1, pp_exp, extra_exp) = ppr_ty env0 ty_exp (env2, pp_act, extra_act) = ppr_ty env1 ty_act - msg = sep [sep [ptext SLIT("Couldn't match expected type") <+> pp_exp, + msg = sep [sep [ptext (sLit "Couldn't match expected type") <+> pp_exp, nest 7 $ - ptext SLIT("against inferred type") <+> pp_act], + ptext (sLit "against inferred type") <+> pp_act], nest 2 (extra_exp $$ extra_act)] in (env2, msg) @@ -1261,3 +1324,18 @@ misMatchMsg env0 (ty_act, ty_exp) ppr_extra env _ty = (env, empty) -- Normal case \end{code} + +Warn of loopy local equalities that were dropped. + +\begin{code} +warnDroppingLoopyEquality :: TcType -> TcType -> TcM () +warnDroppingLoopyEquality ty1 ty2 + = do { env0 <- tcInitTidyEnv + ; ty1 <- zonkTcType ty1 + ; ty2 <- zonkTcType ty2 + ; let (env1 , tidy_ty1) = tidyOpenType env0 ty1 + (_env2, tidy_ty2) = tidyOpenType env1 ty2 + ; addWarnTc $ hang (ptext (sLit "Dropping loopy given equality")) + 2 (quotes (ppr tidy_ty1 <+> text "~" <+> ppr tidy_ty2)) + } +\end{code}