X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcUnify.lhs;h=d5323d82b9785fe4296daf467cf6506b019027e8;hb=16e4ce4c0c02650082f2e11982017c903c549ad5;hp=8ee07bc1f21021596f6c3426a0738f6bbcb5fd5a;hpb=20f50b2a3651ce7dacdcb86a83afb5c5d444cb0b;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcUnify.lhs b/ghc/compiler/typecheck/TcUnify.lhs index 8ee07bc..d5323d8 100644 --- a/ghc/compiler/typecheck/TcUnify.lhs +++ b/ghc/compiler/typecheck/TcUnify.lhs @@ -6,18 +6,21 @@ \begin{code} module TcUnify ( -- Full-blown subsumption - tcSub, tcGen, subFunTy, - checkSigTyVars, sigCtxt, sigPatCtxt, + tcSubOff, tcSubExp, tcGen, + checkSigTyVars, checkSigTyVarsWrt, sigCtxt, findGlobals, -- Various unifications unifyTauTy, unifyTauTyList, unifyTauTyLists, - unifyFunTy, unifyListTy, unifyTupleTy, - unifyKind, unifyKinds, unifyOpenTypeKind, + unifyKind, unifyKinds, unifyOpenTypeKind, unifyFunKind, - -- Coercions - Coercion, ExprCoFn, PatCoFn, - (<$>), (<.>), mkCoercion, - idCoercion, isIdCoercion + -------------------------------- + -- Holes + Expected(..), newHole, readExpectedType, + zapExpectedType, zapExpectedTo, zapExpectedBranches, + subFunTys, unifyFunTy, + zapToListTy, unifyListTy, + zapToPArrTy, unifyPArrTy, + zapToTupleTy, unifyTupleTy ) where @@ -25,78 +28,308 @@ module TcUnify ( import HsSyn ( HsExpr(..) ) -import TcHsSyn ( TypecheckedHsExpr, TcPat, - mkHsDictApp, mkHsTyApp, mkHsLet ) -import TypeRep ( Type(..), SourceType(..), - openKindCon, typeCon ) - -import TcMonad -- TcType, amongst others -import TcType ( TcKind, TcType, TcSigmaType, TcPhiType, TcTyVar, TcTauType, - TcTyVarSet, TcThetaType, - isTauTy, isSigmaTy, +import TcHsSyn ( mkHsLet, + ExprCoFn, idCoercion, isIdCoercion, mkCoercion, (<.>), (<$>) ) +import TypeRep ( Type(..), SourceType(..), TyNote(..), openKindCon ) + +import TcRnMonad -- TcType, amongst others +import TcType ( TcKind, TcType, TcSigmaType, TcRhoType, TcTyVar, TcTauType, + TcTyVarSet, TcThetaType, TyVarDetails(SigTv), + isTauTy, isSigmaTy, mkFunTys, tcSplitAppTy_maybe, tcSplitTyConApp_maybe, tcGetTyVar_maybe, tcGetTyVar, - mkTyConApp, mkTyVarTys, mkFunTy, tyVarsOfType, mkRhoTy, + mkFunTy, tyVarsOfType, mkPhiTy, typeKind, tcSplitFunTy_maybe, mkForAllTys, - isHoleTyVar, isSkolemTyVar, isUserTyVar, allDistinctTyVars, + isSkolemTyVar, isUserTyVar, tidyOpenType, tidyOpenTypes, tidyOpenTyVar, tidyOpenTyVars, - eqKind, openTypeKind, liftedTypeKind, unliftedTypeKind, isTypeKind, - hasMoreBoxityInfo, tyVarBindingInfo + eqKind, openTypeKind, liftedTypeKind, isTypeKind, mkArrowKind, + hasMoreBoxityInfo, allDistinctTyVars ) -import qualified Type ( getTyVar_maybe ) -import Inst ( LIE, emptyLIE, plusLIE, mkLIE, - newDicts, instToId - ) -import TcMType ( getTcTyVar, putTcTyVar, tcInstType, - newTyVarTy, newTyVarTys, newBoxityVar, newHoleTyVarTy, - zonkTcType, zonkTcTyVars, zonkTcTyVar ) +import Inst ( newDicts, instToId, tcInstCall ) +import TcMType ( getTcTyVar, putTcTyVar, tcInstType, newKindVar, + newTyVarTy, newTyVarTys, newOpenTypeKind, + zonkTcType, zonkTcTyVars, zonkTcTyVarsAndFV ) import TcSimplify ( tcSimplifyCheck ) -import TysWiredIn ( listTyCon, mkListTy, mkTupleTy ) -import TcEnv ( TcTyThing(..), tcExtendGlobalTyVars, tcGetGlobalTyVars, tcLEnvElts ) +import TysWiredIn ( listTyCon, parrTyCon, mkListTy, mkPArrTy, mkTupleTy ) +import TcEnv ( tcGetGlobalTyVars, findGlobals ) import TyCon ( tyConArity, isTupleTyCon, tupleTyConBoxity ) import PprType ( pprType ) -import CoreFVs ( idFreeTyVars ) -import Id ( mkSysLocal, idType ) +import Id ( Id, mkSysLocal ) import Var ( Var, varName, tyVarKind ) -import VarSet ( elemVarSet, varSetElems ) +import VarSet ( emptyVarSet, unitVarSet, unionVarSet, elemVarSet, varSetElems ) import VarEnv -import Name ( isSystemName, getSrcLoc ) +import Name ( isSystemName ) import ErrUtils ( Message ) import BasicTypes ( Boxity, Arity, isBoxed ) -import Util ( isSingleton, equalLength ) -import Maybe ( isNothing ) +import Util ( equalLength, lengthExceeds, notNull ) import Outputable \end{code} +Notes on holes +~~~~~~~~~~~~~~ +* A hole is always filled in with an ordinary type, not another hole. %************************************************************************ %* * -\subsection{Subsumption} +\subsection{'hole' type variables} %* * %************************************************************************ \begin{code} -tcSub :: TcSigmaType -- expected_ty; can be a type scheme; - -- can be a "hole" type variable - -> TcSigmaType -- actual_ty; can be a type scheme - -> TcM (ExprCoFn, LIE) +data Expected ty = Infer (TcRef ty) -- The hole to fill in for type inference + | Check ty -- The type to check during type checking + +newHole :: TcM (TcRef ty) +newHole = newMutVar (error "Empty hole in typechecker") + +readExpectedType :: Expected ty -> TcM ty +readExpectedType (Infer hole) = readMutVar hole +readExpectedType (Check ty) = returnM ty + +zapExpectedType :: Expected TcType -> TcM TcTauType +-- In the inference case, ensure we have a monotype +zapExpectedType (Infer hole) + = do { ty <- newTyVarTy openTypeKind ; + writeMutVar hole ty ; + return ty } + +zapExpectedType (Check ty) = return ty + +zapExpectedTo :: Expected TcType -> TcTauType -> TcM () +zapExpectedTo (Infer hole) ty2 = writeMutVar hole ty2 +zapExpectedTo (Check ty1) ty2 = unifyTauTy ty1 ty2 + +zapExpectedBranches :: [a] -> Expected TcType -> TcM (Expected TcType) +-- Zap the expected type to a monotype if there is more than one branch +zapExpectedBranches branches exp_ty + | lengthExceeds branches 1 = zapExpectedType exp_ty `thenM` \ exp_ty' -> + return (Check exp_ty') + | otherwise = returnM exp_ty + +instance Outputable ty => Outputable (Expected ty) where + ppr (Check ty) = ptext SLIT("Expected type") <+> ppr ty + ppr (Infer hole) = ptext SLIT("Inferring type") +\end{code} + + +%************************************************************************ +%* * +\subsection[Unify-fun]{@unifyFunTy@} +%* * +%************************************************************************ + +@subFunTy@ and @unifyFunTy@ is used to avoid the fruitless +creation of type variables. + +* subFunTy is used when we might be faced with a "hole" type variable, + in which case we should create two new holes. + +* unifyFunTy is used when we expect to encounter only "ordinary" + type variables, so we should create new ordinary type variables + +\begin{code} +subFunTys :: [pat] + -> Expected TcRhoType -- Fail if ty isn't a function type + -> ([(pat, Expected TcRhoType)] -> Expected TcRhoType -> TcM a) + -> TcM a + +subFunTys pats (Infer hole) thing_inside + = -- This is the interesting case + mapM new_pat_hole pats `thenM` \ pats_w_holes -> + newHole `thenM` \ res_hole -> + + -- Do the business + thing_inside pats_w_holes (Infer res_hole) `thenM` \ answer -> + + -- Extract the answers + mapM read_pat_hole pats_w_holes `thenM` \ arg_tys -> + readMutVar res_hole `thenM` \ res_ty -> + + -- Write the answer into the incoming hole + writeMutVar hole (mkFunTys arg_tys res_ty) `thenM_` + + -- And return the answer + returnM answer + where + new_pat_hole pat = newHole `thenM` \ hole -> return (pat, Infer hole) + read_pat_hole (pat, Infer hole) = readMutVar hole + +subFunTys pats (Check ty) thing_inside + = go pats ty `thenM` \ (pats_w_tys, res_ty) -> + thing_inside pats_w_tys res_ty + where + go [] ty = return ([], Check ty) + go (pat:pats) ty = unifyFunTy ty `thenM` \ (arg,res) -> + go pats res `thenM` \ (pats_w_tys, final_res) -> + return ((pat, Check arg) : pats_w_tys, final_res) + +unifyFunTy :: TcRhoType -- Fail if ty isn't a function type + -> TcM (TcType, TcType) -- otherwise return arg and result types + +unifyFunTy ty@(TyVarTy tyvar) + = getTcTyVar tyvar `thenM` \ maybe_ty -> + case maybe_ty of + Just ty' -> unifyFunTy ty' + Nothing -> unify_fun_ty_help ty + +unifyFunTy ty + = case tcSplitFunTy_maybe ty of + Just arg_and_res -> returnM arg_and_res + Nothing -> unify_fun_ty_help ty + +unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification + = newTyVarTy openTypeKind `thenM` \ arg -> + newTyVarTy openTypeKind `thenM` \ res -> + unifyTauTy ty (mkFunTy arg res) `thenM_` + returnM (arg,res) +\end{code} + +\begin{code} +zapToListTy :: Expected TcType -- expected list type + -> TcM TcType -- list element type + +zapToListTy (Check ty) = unifyListTy ty +zapToListTy (Infer hole) = do { elt_ty <- newTyVarTy liftedTypeKind ; + writeMutVar hole (mkListTy elt_ty) ; + return elt_ty } + +unifyListTy :: TcType -> TcM TcType +unifyListTy ty@(TyVarTy tyvar) + = getTcTyVar tyvar `thenM` \ maybe_ty -> + case maybe_ty of + Just ty' -> unifyListTy ty' + other -> unify_list_ty_help ty + +unifyListTy ty + = case tcSplitTyConApp_maybe ty of + Just (tycon, [arg_ty]) | tycon == listTyCon -> returnM arg_ty + other -> unify_list_ty_help ty + +unify_list_ty_help ty -- Revert to ordinary unification + = newTyVarTy liftedTypeKind `thenM` \ elt_ty -> + unifyTauTy ty (mkListTy elt_ty) `thenM_` + returnM elt_ty + +-- variant for parallel arrays +-- +zapToPArrTy :: Expected TcType -- Expected list type + -> TcM TcType -- List element type + +zapToPArrTy (Check ty) = unifyPArrTy ty +zapToPArrTy (Infer hole) = do { elt_ty <- newTyVarTy liftedTypeKind ; + writeMutVar hole (mkPArrTy elt_ty) ; + return elt_ty } + +unifyPArrTy :: TcType -> TcM TcType + +unifyPArrTy ty@(TyVarTy tyvar) + = getTcTyVar tyvar `thenM` \ maybe_ty -> + case maybe_ty of + Just ty' -> unifyPArrTy ty' + _ -> unify_parr_ty_help ty +unifyPArrTy ty + = case tcSplitTyConApp_maybe ty of + Just (tycon, [arg_ty]) | tycon == parrTyCon -> returnM arg_ty + _ -> unify_parr_ty_help ty + +unify_parr_ty_help ty -- Revert to ordinary unification + = newTyVarTy liftedTypeKind `thenM` \ elt_ty -> + unifyTauTy ty (mkPArrTy elt_ty) `thenM_` + returnM elt_ty +\end{code} + +\begin{code} +zapToTupleTy :: Boxity -> Arity -> Expected TcType -> TcM [TcType] +zapToTupleTy boxity arity (Check ty) = unifyTupleTy boxity arity ty +zapToTupleTy boxity arity (Infer hole) = do { (tup_ty, arg_tys) <- new_tuple_ty boxity arity ; + writeMutVar hole tup_ty ; + return arg_tys } + +unifyTupleTy boxity arity ty@(TyVarTy tyvar) + = getTcTyVar tyvar `thenM` \ maybe_ty -> + case maybe_ty of + Just ty' -> unifyTupleTy boxity arity ty' + other -> unify_tuple_ty_help boxity arity ty + +unifyTupleTy boxity arity ty + = case tcSplitTyConApp_maybe ty of + Just (tycon, arg_tys) + | isTupleTyCon tycon + && tyConArity tycon == arity + && tupleTyConBoxity tycon == boxity + -> returnM arg_tys + other -> unify_tuple_ty_help boxity arity ty + +unify_tuple_ty_help boxity arity ty + = new_tuple_ty boxity arity `thenM` \ (tup_ty, arg_tys) -> + unifyTauTy ty tup_ty `thenM_` + returnM arg_tys + +new_tuple_ty boxity arity + = newTyVarTys arity kind `thenM` \ arg_tys -> + return (mkTupleTy boxity arity arg_tys, arg_tys) + where + kind | isBoxed boxity = liftedTypeKind + | otherwise = openTypeKind \end{code} -(tcSub expected_ty actual_ty) checks that - actual_ty <= expected_ty -That is, that a value of type actual_ty is acceptable in + +%************************************************************************ +%* * +\subsection{Subsumption} +%* * +%************************************************************************ + +All the tcSub calls have the form + + tcSub expected_ty offered_ty +which checks + offered_ty <= expected_ty + +That is, that a value of type offered_ty is acceptable in a place expecting a value of type expected_ty. It returns a coercion function - co_fn :: actual_ty -> expected_ty -which takes an HsExpr of type actual_ty into one of type + co_fn :: offered_ty -> expected_ty +which takes an HsExpr of type offered_ty into one of type expected_ty. \begin{code} +tcSubExp :: Expected TcRhoType -> TcRhoType -> TcM ExprCoFn +tcSubOff :: TcSigmaType -> Expected TcSigmaType -> TcM ExprCoFn +\end{code} + +These two check for holes + +\begin{code} +tcSubExp expected_ty offered_ty + = traceTc (text "tcSubExp" <+> (ppr expected_ty $$ ppr offered_ty)) `thenM_` + checkHole expected_ty offered_ty tcSub + +tcSubOff expected_ty offered_ty + = checkHole offered_ty expected_ty (\ off exp -> tcSub exp off) + +-- checkHole looks for a hole in its first arg; +-- If so, and it is uninstantiated, it fills in the hole +-- with its second arg +-- Otherwise it calls thing_inside, passing the two args, looking +-- through any instantiated hole + +checkHole (Infer hole) other_ty thing_inside + = do { writeMutVar hole other_ty; return idCoercion } + +checkHole (Check ty) other_ty thing_inside + = thing_inside ty other_ty +\end{code} + +No holes expected now. Add some error-check context info. + +\begin{code} +tcSub :: TcSigmaType -> TcSigmaType -> TcM ExprCoFn -- Locally used only tcSub expected_ty actual_ty - = traceTc (text "tcSub" <+> details) `thenNF_Tc_` - tcAddErrCtxtM (unifyCtxt "type" expected_ty actual_ty) - (tc_sub expected_ty expected_ty actual_ty actual_ty) + = traceTc (text "tcSub" <+> details) `thenM_` + addErrCtxtM (unifyCtxt "type" expected_ty actual_ty) + (tc_sub expected_ty expected_ty actual_ty actual_ty) where details = vcat [text "Expected:" <+> ppr expected_ty, text "Actual: " <+> ppr actual_ty] @@ -109,7 +342,7 @@ tc_sub :: TcSigmaType -- expected_ty, before expanding synonyms -> TcSigmaType -- ..and after -> TcSigmaType -- actual_ty, before -> TcSigmaType -- ..and after - -> TcM (ExprCoFn, LIE) + -> TcM ExprCoFn ----------------------------------- -- Expand synonyms @@ -117,24 +350,6 @@ tc_sub exp_sty (NoteTy _ exp_ty) act_sty act_ty = tc_sub exp_sty exp_ty act_sty tc_sub exp_sty exp_ty act_sty (NoteTy _ act_ty) = tc_sub exp_sty exp_ty act_sty act_ty ----------------------------------- --- "Hole type variable" case --- Do this case before unwrapping for-alls in the actual_ty - -tc_sub _ (TyVarTy tv) act_sty act_ty - | isHoleTyVar tv - = -- It's a "hole" type variable - getTcTyVar tv `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - - Just ty -> -- Already been assigned - tc_sub ty ty act_sty act_ty ; - - Nothing -> -- Assign it - putTcTyVar tv act_sty `thenNF_Tc_` - returnTc (idCoercion, emptyLIE) - - ------------------------------------ -- Generalisation case -- actual_ty: d:Eq b => b->b -- expected_ty: forall a. Ord a => a->a @@ -147,10 +362,12 @@ tc_sub _ (TyVarTy tv) act_sty act_ty tc_sub exp_sty expected_ty act_sty actual_ty | isSigmaTy expected_ty - = tcGen expected_ty ( + = tcGen expected_ty (tyVarsOfType actual_ty) ( + -- It's really important to check for escape wrt the free vars of + -- both expected_ty *and* actual_ty \ body_exp_ty -> tc_sub body_exp_ty body_exp_ty act_sty actual_ty - ) `thenTc` \ (gen_fn, co_fn, lie) -> - returnTc (gen_fn <.> co_fn, lie) + ) `thenM` \ (gen_fn, co_fn) -> + returnM (gen_fn <.> co_fn) ----------------------------------- -- Specialisation case: @@ -160,16 +377,9 @@ tc_sub exp_sty expected_ty act_sty actual_ty tc_sub exp_sty expected_ty act_sty actual_ty | isSigmaTy actual_ty - = tcInstType actual_ty `thenNF_Tc` \ (tvs, theta, body_ty) -> - newDicts orig theta `thenNF_Tc` \ dicts -> - let - inst_fn e = mkHsDictApp (mkHsTyApp e (mkTyVarTys tvs)) - (map instToId dicts) - in - tc_sub exp_sty expected_ty body_ty body_ty `thenTc` \ (co_fn, lie) -> - returnTc (co_fn <.> mkCoercion inst_fn, lie `plusLIE` mkLIE dicts) - where - orig = Rank2Origin + = tcInstCall Rank2Origin actual_ty `thenM` \ (inst_fn, body_ty) -> + tc_sub exp_sty expected_ty body_ty body_ty `thenM` \ co_fn -> + returnM (co_fn <.> inst_fn) ----------------------------------- -- Function case @@ -189,28 +399,40 @@ tc_sub _ (FunTy exp_arg exp_res) _ (FunTy act_arg act_res) -- when the arg/res is not a tau-type? -- NO! e.g. f :: ((forall a. a->a) -> Int) -> Int -- then x = (f,f) --- is perfectly fine! +-- is perfectly fine, because we can instantiat f's type to a monotype +-- +-- However, we get can get jolly unhelpful error messages. +-- e.g. foo = id runST +-- +-- Inferred type is less polymorphic than expected +-- Quantified type variable `s' escapes +-- Expected type: ST s a -> t +-- Inferred type: (forall s1. ST s1 a) -> a +-- In the first argument of `id', namely `runST' +-- In a right-hand side of function `foo': id runST +-- +-- I'm not quite sure what to do about this! tc_sub exp_sty exp_ty@(FunTy exp_arg exp_res) _ (TyVarTy tv) - = getTcTyVar tv `thenNF_Tc` \ maybe_ty -> + = getTcTyVar tv `thenM` \ maybe_ty -> case maybe_ty of Just ty -> tc_sub exp_sty exp_ty ty ty - Nothing -> imitateFun tv exp_sty `thenNF_Tc` \ (act_arg, act_res) -> + Nothing -> imitateFun tv exp_sty `thenM` \ (act_arg, act_res) -> tcSub_fun exp_arg exp_res act_arg act_res tc_sub _ (TyVarTy tv) act_sty act_ty@(FunTy act_arg act_res) - = getTcTyVar tv `thenNF_Tc` \ maybe_ty -> + = getTcTyVar tv `thenM` \ maybe_ty -> case maybe_ty of Just ty -> tc_sub ty ty act_sty act_ty - Nothing -> imitateFun tv act_sty `thenNF_Tc` \ (exp_arg, exp_res) -> + Nothing -> imitateFun tv act_sty `thenM` \ (exp_arg, exp_res) -> tcSub_fun exp_arg exp_res act_arg act_res ----------------------------------- -- Unification case -- If none of the above match, we revert to the plain unifier tc_sub exp_sty expected_ty act_sty actual_ty - = uTys exp_sty expected_ty act_sty actual_ty `thenTc_` - returnTc (idCoercion, emptyLIE) + = uTys exp_sty expected_ty act_sty actual_ty `thenM_` + returnM idCoercion \end{code} %************************************************************************ @@ -221,14 +443,14 @@ tc_sub exp_sty expected_ty act_sty actual_ty \begin{code} tcSub_fun exp_arg exp_res act_arg act_res - = tcSub act_arg exp_arg `thenTc` \ (co_fn_arg, lie1) -> - tcSub exp_res act_res `thenTc` \ (co_fn_res, lie2) -> - tcGetUnique `thenNF_Tc` \ uniq -> + = tc_sub act_arg act_arg exp_arg exp_arg `thenM` \ co_fn_arg -> + tc_sub exp_res exp_res act_res act_res `thenM` \ co_fn_res -> + newUnique `thenM` \ uniq -> let -- co_fn_arg :: HsExpr exp_arg -> HsExpr act_arg -- co_fn_res :: HsExpr act_res -> HsExpr exp_res -- co_fn :: HsExpr (act_arg -> act_res) -> HsExpr (exp_arg -> exp_res) - arg_id = mkSysLocal SLIT("sub") uniq exp_arg + arg_id = mkSysLocal FSLIT("sub") uniq exp_arg coercion | isIdCoercion co_fn_arg, isIdCoercion co_fn_res = idCoercion | otherwise = mkCoercion co_fn @@ -241,23 +463,22 @@ tcSub_fun exp_arg exp_res act_arg act_res -- HsApp e $it :: HsExpr act_res -- co_fn_res $it :: HsExpr exp_res in - returnTc (coercion, lie1 `plusLIE` lie2) + returnM coercion -imitateFun :: TcTyVar -> TcType -> NF_TcM (TcType, TcType) +imitateFun :: TcTyVar -> TcType -> TcM (TcType, TcType) imitateFun tv ty - = ASSERT( not (isHoleTyVar tv) ) - -- NB: tv is an *ordinary* tyvar and so are the new ones + = -- NB: tv is an *ordinary* tyvar and so are the new ones -- Check that tv isn't a type-signature type variable -- (This would be found later in checkSigTyVars, but -- we get a better error message if we do it here.) - checkTcM (not (isSkolemTyVar tv)) - (failWithTcM (unifyWithSigErr tv ty)) `thenTc_` + checkM (not (isSkolemTyVar tv)) + (failWithTcM (unifyWithSigErr tv ty)) `thenM_` - newTyVarTy openTypeKind `thenNF_Tc` \ arg -> - newTyVarTy openTypeKind `thenNF_Tc` \ res -> - putTcTyVar tv (mkFunTy arg res) `thenNF_Tc_` - returnNF_Tc (arg,res) + newTyVarTy openTypeKind `thenM` \ arg -> + newTyVarTy openTypeKind `thenM` \ res -> + putTcTyVar tv (mkFunTy arg res) `thenM_` + returnM (arg,res) \end{code} @@ -269,16 +490,19 @@ imitateFun tv ty \begin{code} tcGen :: TcSigmaType -- expected_ty - -> (TcPhiType -> TcM (result, LIE)) -- spec_ty - -> TcM (ExprCoFn, result, LIE) + -> TcTyVarSet -- Extra tyvars that the universally + -- quantified tyvars of expected_ty + -- must not be unified + -> (TcRhoType -> TcM result) -- spec_ty + -> TcM (ExprCoFn, result) -- The expression has type: spec_ty -> expected_ty -tcGen expected_ty thing_inside -- We expect expected_ty to be a forall-type - -- If not, the call is a no-op - = tcInstType expected_ty `thenNF_Tc` \ (forall_tvs, theta, phi_ty) -> +tcGen expected_ty extra_tvs thing_inside -- We expect expected_ty to be a forall-type + -- If not, the call is a no-op + = tcInstType SigTv expected_ty `thenM` \ (forall_tvs, theta, phi_ty) -> -- Type-check the arg and unify with poly type - thing_inside phi_ty `thenTc` \ (result, lie) -> + getLIE (thing_inside phi_ty) `thenM` \ (result, lie) -> -- Check that the "forall_tvs" havn't been constrained -- The interesting bit here is that we must include the free variables @@ -291,12 +515,21 @@ tcGen expected_ty thing_inside -- We expect expected_ty to be a forall-type -- Conclusion: include the free vars of the expected_ty in the -- list of "free vars" for the signature check. - tcExtendGlobalTyVars free_tvs $ - tcAddErrCtxtM (sigCtxt forall_tvs theta phi_ty) $ + newDicts SignatureOrigin theta `thenM` \ dicts -> + tcSimplifyCheck sig_msg forall_tvs dicts lie `thenM` \ inst_binds -> + +#ifdef DEBUG + zonkTcTyVars forall_tvs `thenM` \ forall_tys -> + traceTc (text "tcGen" <+> vcat [text "extra_tvs" <+> ppr extra_tvs, + text "expected_ty" <+> ppr expected_ty, + text "inst ty" <+> ppr forall_tvs <+> ppr theta <+> ppr phi_ty, + text "free_tvs" <+> ppr free_tvs, + text "forall_tys" <+> ppr forall_tys]) `thenM_` +#endif + + checkSigTyVarsWrt free_tvs forall_tvs `thenM` \ zonked_tvs -> - newDicts SignatureOrigin theta `thenNF_Tc` \ dicts -> - tcSimplifyCheck sig_msg forall_tvs dicts lie `thenTc` \ (free_lie, inst_binds) -> - checkSigTyVars forall_tvs free_tvs `thenTc` \ zonked_tvs -> + traceTc (text "tcGen:done") `thenM_` let -- This HsLet binds any Insts which came out of the simplification. @@ -305,49 +538,16 @@ tcGen expected_ty thing_inside -- We expect expected_ty to be a forall-type dict_ids = map instToId dicts co_fn e = TyLam zonked_tvs (DictLam dict_ids (mkHsLet inst_binds e)) in - returnTc (mkCoercion co_fn, result, free_lie) + returnM (mkCoercion co_fn, result) where - free_tvs = tyVarsOfType expected_ty - sig_msg = ptext SLIT("When generalising the type of an expression") + free_tvs = tyVarsOfType expected_ty `unionVarSet` extra_tvs + sig_msg = ptext SLIT("expected type of an expression") \end{code} %************************************************************************ %* * -\subsection{Coercion functions} -%* * -%************************************************************************ - -\begin{code} -type Coercion a = Maybe (a -> a) - -- Nothing => identity fn - -type ExprCoFn = Coercion TypecheckedHsExpr -type PatCoFn = Coercion TcPat - -(<.>) :: Coercion a -> Coercion a -> Coercion a -- Composition -Nothing <.> Nothing = Nothing -Nothing <.> Just f = Just f -Just f <.> Nothing = Just f -Just f1 <.> Just f2 = Just (f1 . f2) - -(<$>) :: Coercion a -> a -> a -Just f <$> e = f e -Nothing <$> e = e - -mkCoercion :: (a -> a) -> Coercion a -mkCoercion f = Just f - -idCoercion :: Coercion a -idCoercion = Nothing - -isIdCoercion :: Coercion a -> Bool -isIdCoercion = isNothing -\end{code} - -%************************************************************************ -%* * \subsection[Unify-exported]{Exported unification functions} %* * %************************************************************************ @@ -364,7 +564,7 @@ unifyTauTy ty1 ty2 -- ty1 expected, ty2 inferred -- (no quantification whatsoever) ASSERT2( isTauTy ty1, ppr ty1 ) ASSERT2( isTauTy ty2, ppr ty2 ) - tcAddErrCtxtM (unifyCtxt "type" ty1 ty2) $ + addErrCtxtM (unifyCtxt "type" ty1 ty2) $ uTys ty1 ty1 ty2 ty2 \end{code} @@ -375,8 +575,8 @@ complain if their lengths differ. \begin{code} unifyTauTyLists :: [TcTauType] -> [TcTauType] -> TcM () -unifyTauTyLists [] [] = returnTc () -unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenTc_` +unifyTauTyLists [] [] = returnM () +unifyTauTyLists (ty1:tys1) (ty2:tys2) = uTys ty1 ty1 ty2 ty2 `thenM_` unifyTauTyLists tys1 tys2 unifyTauTyLists ty1s ty2s = panic "Unify.unifyTauTyLists: mismatched type lists!" \end{code} @@ -387,9 +587,9 @@ lists, when all the elts should be of the same type. \begin{code} unifyTauTyList :: [TcTauType] -> TcM () -unifyTauTyList [] = returnTc () -unifyTauTyList [ty] = returnTc () -unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenTc_` +unifyTauTyList [] = returnM () +unifyTauTyList [ty] = returnM () +unifyTauTyList (ty1:tys@(ty2:_)) = unifyTauTy ty1 ty2 `thenM_` unifyTauTyList tys \end{code} @@ -435,7 +635,7 @@ uTys _ (SourceTy (NType tc1 tys1)) _ (SourceTy (NType tc2 tys2)) -- Functions; just check the two parts uTys _ (FunTy fun1 arg1) _ (FunTy fun2 arg2) - = uTys fun1 fun1 fun2 fun2 `thenTc_` uTys arg1 arg1 arg2 arg2 + = uTys fun1 fun1 fun2 fun2 `thenM_` uTys arg1 arg1 arg2 arg2 -- Type constructors must match uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2) @@ -454,14 +654,14 @@ uTys ps_ty1 (TyConApp con1 tys1) ps_ty2 (TyConApp con2 tys2) -- so if one type is an App the other one jolly well better be too uTys ps_ty1 (AppTy s1 t1) ps_ty2 ty2 = case tcSplitAppTy_maybe ty2 of - Just (s2,t2) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2 + Just (s2,t2) -> uTys s1 s1 s2 s2 `thenM_` uTys t1 t1 t2 t2 Nothing -> unifyMisMatch ps_ty1 ps_ty2 -- Now the same, but the other way round -- Don't swap the types, because the error messages get worse uTys ps_ty1 ty1 ps_ty2 (AppTy s2 t2) = case tcSplitAppTy_maybe ty1 of - Just (s1,t1) -> uTys s1 s1 s2 s2 `thenTc_` uTys t1 t1 t2 t2 + Just (s1,t1) -> uTys s1 s1 s2 s2 `thenM_` uTys t1 t1 t2 t2 Nothing -> unifyMisMatch ps_ty1 ps_ty2 -- Not expecting for-alls in unification @@ -544,8 +744,8 @@ uVar :: Bool -- False => tyvar is the "expected" -> TcM () uVar swapped tv1 ps_ty2 ty2 - = traceTc (text "uVar" <+> ppr swapped <+> ppr tv1 <+> (ppr ps_ty2 $$ ppr ty2)) `thenNF_Tc_` - getTcTyVar tv1 `thenNF_Tc` \ maybe_ty1 -> + = traceTc (text "uVar" <+> ppr swapped <+> ppr tv1 <+> (ppr ps_ty2 $$ ppr ty2)) `thenM_` + getTcTyVar tv1 `thenM` \ maybe_ty1 -> case maybe_ty1 of Just ty1 | swapped -> uTys ps_ty2 ty2 ty1 ty1 -- Swap back | otherwise -> uTys ty1 ty1 ps_ty2 ty2 -- Same order @@ -561,25 +761,25 @@ uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2) -- Same type variable => no-op | tv1 == tv2 - = returnTc () + = returnM () -- Distinct type variables -- ASSERT maybe_ty1 /= Just | otherwise - = getTcTyVar tv2 `thenNF_Tc` \ maybe_ty2 -> + = getTcTyVar tv2 `thenM` \ maybe_ty2 -> case maybe_ty2 of Just ty2' -> uUnboundVar swapped tv1 maybe_ty1 ty2' ty2' Nothing | update_tv2 -> WARN( not (k1 `hasMoreBoxityInfo` k2), (ppr tv1 <+> ppr k1) $$ (ppr tv2 <+> ppr k2) ) - putTcTyVar tv2 (TyVarTy tv1) `thenNF_Tc_` - returnTc () + putTcTyVar tv2 (TyVarTy tv1) `thenM_` + returnM () | otherwise -> WARN( not (k2 `hasMoreBoxityInfo` k1), (ppr tv2 <+> ppr k2) $$ (ppr tv1 <+> ppr k1) ) - putTcTyVar tv1 ps_ty2 `thenNF_Tc_` - returnTc () + putTcTyVar tv1 ps_ty2 `thenM_` + returnM () where k1 = tyVarKind tv1 k2 = tyVarKind tv2 @@ -594,59 +794,35 @@ uUnboundVar swapped tv1 maybe_ty1 ps_ty2 ty2@(TyVarTy tv2) -- Second one isn't a type variable uUnboundVar swapped tv1 maybe_ty1 ps_ty2 non_var_ty2 = -- Check that tv1 isn't a type-signature type variable - checkTcM (not (isSkolemTyVar tv1)) - (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenTc_` + checkM (not (isSkolemTyVar tv1)) + (failWithTcM (unifyWithSigErr tv1 ps_ty2)) `thenM_` + + -- Do the occurs check, and check that we are not + -- unifying a type variable with a polytype + -- Returns a zonked type ready for the update + checkValue tv1 ps_ty2 non_var_ty2 `thenM` \ ty2 -> -- Check that the kinds match - zonkTcType ps_ty2 `thenNF_Tc` \ ps_ty2' -> - checkKinds swapped tv1 ps_ty2' `thenTc_` - - -- Occurs check - -- Basically we want to update tv1 := ps_ty2 - -- because ps_ty2 has type-synonym info, which improves later error messages - -- - -- But consider - -- type A a = () - -- - -- f :: (A a -> a -> ()) -> () - -- f = \ _ -> () - -- - -- x :: () - -- x = f (\ x p -> p x) - -- - -- In the application (p x), we try to match "t" with "A t". If we go - -- ahead and bind t to A t (= ps_ty2), we'll lead the type checker into - -- an infinite loop later. - -- But we should not reject the program, because A t = (). - -- Rather, we should bind t to () (= non_var_ty2). - -- - -- That's why we have this two-state occurs-check - if not (tv1 `elemVarSet` tyVarsOfType ps_ty2') then - putTcTyVar tv1 ps_ty2' `thenNF_Tc_` - returnTc () - else - zonkTcType non_var_ty2 `thenNF_Tc` \ non_var_ty2' -> - if not (tv1 `elemVarSet` tyVarsOfType non_var_ty2') then - -- This branch rarely succeeds, except in strange cases - -- like that in the example above - putTcTyVar tv1 non_var_ty2' `thenNF_Tc_` - returnTc () - else - failWithTcM (unifyOccurCheck tv1 ps_ty2') + checkKinds swapped tv1 ty2 `thenM_` + -- Perform the update + putTcTyVar tv1 ty2 `thenM_` + returnM () +\end{code} +\begin{code} checkKinds swapped tv1 ty2 -- We're about to unify a type variable tv1 with a non-tyvar-type ty2. --- ty2 has been zonked at this stage. - - | tk2 `hasMoreBoxityInfo` tk1 = returnTc () +-- ty2 has been zonked at this stage, which ensures that +-- its kind has as much boxity information visible as possible. + | tk2 `hasMoreBoxityInfo` tk1 = returnM () | otherwise -- Either the kinds aren't compatible -- (can happen if we unify (a b) with (c d)) -- or we are unifying a lifted type variable with an -- unlifted type: e.g. (id 3#) is illegal - = tcAddErrCtxtM (unifyKindCtxt swapped tv1 ty2) $ + = addErrCtxtM (unifyKindCtxt swapped tv1 ty2) $ unifyMisMatch k1 k2 where @@ -656,113 +832,78 @@ checkKinds swapped tv1 ty2 tk2 = typeKind ty2 \end{code} - -%************************************************************************ -%* * -\subsection[Unify-fun]{@unifyFunTy@} -%* * -%************************************************************************ - -@subFunTy@ and @unifyFunTy@ is used to avoid the fruitless -creation of type variables. - -* subFunTy is used when we might be faced with a "hole" type variable, - in which case we should create two new holes. - -* unifyFunTy is used when we expect to encounter only "ordinary" - type variables, so we should create new ordinary type variables - -\begin{code} -subFunTy :: TcSigmaType -- Fail if ty isn't a function type - -> TcM (TcType, TcType) -- otherwise return arg and result types -subFunTy ty@(TyVarTy tyvar) - - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty -> subFunTy ty - Nothing | isHoleTyVar tyvar - -> newHoleTyVarTy `thenNF_Tc` \ arg -> - newHoleTyVarTy `thenNF_Tc` \ res -> - putTcTyVar tyvar (mkFunTy arg res) `thenNF_Tc_` - returnTc (arg,res) - | otherwise - -> unify_fun_ty_help ty - -subFunTy ty - = case tcSplitFunTy_maybe ty of - Just arg_and_res -> returnTc arg_and_res - Nothing -> unify_fun_ty_help ty - - -unifyFunTy :: TcPhiType -- Fail if ty isn't a function type - -> TcM (TcType, TcType) -- otherwise return arg and result types - -unifyFunTy ty@(TyVarTy tyvar) - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyFunTy ty' - Nothing -> unify_fun_ty_help ty - -unifyFunTy ty - = case tcSplitFunTy_maybe ty of - Just arg_and_res -> returnTc arg_and_res - Nothing -> unify_fun_ty_help ty - -unify_fun_ty_help ty -- Special cases failed, so revert to ordinary unification - = newTyVarTy openTypeKind `thenNF_Tc` \ arg -> - newTyVarTy openTypeKind `thenNF_Tc` \ res -> - unifyTauTy ty (mkFunTy arg res) `thenTc_` - returnTc (arg,res) -\end{code} - -\begin{code} -unifyListTy :: TcType -- expected list type - -> TcM TcType -- list element type - -unifyListTy ty@(TyVarTy tyvar) - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyListTy ty' - other -> unify_list_ty_help ty - -unifyListTy ty - = case tcSplitTyConApp_maybe ty of - Just (tycon, [arg_ty]) | tycon == listTyCon -> returnTc arg_ty - other -> unify_list_ty_help ty - -unify_list_ty_help ty -- Revert to ordinary unification - = newTyVarTy liftedTypeKind `thenNF_Tc` \ elt_ty -> - unifyTauTy ty (mkListTy elt_ty) `thenTc_` - returnTc elt_ty -\end{code} - \begin{code} -unifyTupleTy :: Boxity -> Arity -> TcType -> TcM [TcType] -unifyTupleTy boxity arity ty@(TyVarTy tyvar) - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> - case maybe_ty of - Just ty' -> unifyTupleTy boxity arity ty' - other -> unify_tuple_ty_help boxity arity ty - -unifyTupleTy boxity arity ty - = case tcSplitTyConApp_maybe ty of - Just (tycon, arg_tys) - | isTupleTyCon tycon - && tyConArity tycon == arity - && tupleTyConBoxity tycon == boxity - -> returnTc arg_tys - other -> unify_tuple_ty_help boxity arity ty - -unify_tuple_ty_help boxity arity ty - = newTyVarTys arity kind `thenNF_Tc` \ arg_tys -> - unifyTauTy ty (mkTupleTy boxity arity arg_tys) `thenTc_` - returnTc arg_tys +checkValue tv1 ps_ty2 non_var_ty2 +-- Do the occurs check, and check that we are not +-- unifying a type variable with a polytype +-- Return the type to update the type variable with, or fail + +-- Basically we want to update tv1 := ps_ty2 +-- because ps_ty2 has type-synonym info, which improves later error messages +-- +-- But consider +-- type A a = () +-- +-- f :: (A a -> a -> ()) -> () +-- f = \ _ -> () +-- +-- x :: () +-- x = f (\ x p -> p x) +-- +-- In the application (p x), we try to match "t" with "A t". If we go +-- ahead and bind t to A t (= ps_ty2), we'll lead the type checker into +-- an infinite loop later. +-- But we should not reject the program, because A t = (). +-- Rather, we should bind t to () (= non_var_ty2). +-- +-- That's why we have this two-state occurs-check + = zonkTcType ps_ty2 `thenM` \ ps_ty2' -> + case okToUnifyWith tv1 ps_ty2' of { + Nothing -> returnM ps_ty2' ; -- Success + other -> + + zonkTcType non_var_ty2 `thenM` \ non_var_ty2' -> + case okToUnifyWith tv1 non_var_ty2' of + Nothing -> -- This branch rarely succeeds, except in strange cases + -- like that in the example above + returnM non_var_ty2' + + Just problem -> failWithTcM (unifyCheck problem tv1 ps_ty2') + } + +data Problem = OccurCheck | NotMonoType + +okToUnifyWith :: TcTyVar -> TcType -> Maybe Problem +-- (okToUnifyWith tv ty) checks whether it's ok to unify +-- tv :=: ty +-- Nothing => ok +-- Just p => not ok, problem p + +okToUnifyWith tv ty + = ok ty where - kind | isBoxed boxity = liftedTypeKind - | otherwise = openTypeKind + ok (TyVarTy tv') | tv == tv' = Just OccurCheck + | otherwise = Nothing + ok (AppTy t1 t2) = ok t1 `and` ok t2 + ok (FunTy t1 t2) = ok t1 `and` ok t2 + ok (TyConApp _ ts) = oks ts + ok (ForAllTy _ _) = Just NotMonoType + ok (SourceTy st) = ok_st st + ok (NoteTy (FTVNote _) t) = ok t + ok (NoteTy (SynNote t1) t2) = ok t1 `and` ok t2 + -- Type variables may be free in t1 but not t2 + -- A forall may be in t2 but not t1 + + oks ts = foldr (and . ok) Nothing ts + + ok_st (ClassP _ ts) = oks ts + ok_st (IParam _ t) = ok t + ok_st (NType _ ts) = oks ts + + Nothing `and` m = m + Just p `and` m = Just p \end{code} - %************************************************************************ %* * \subsection{Kind unification} @@ -773,13 +914,11 @@ unify_tuple_ty_help boxity arity ty unifyKind :: TcKind -- Expected -> TcKind -- Actual -> TcM () -unifyKind k1 k2 - = tcAddErrCtxtM (unifyCtxt "kind" k1 k2) $ - uTys k1 k1 k2 k2 +unifyKind k1 k2 = uTys k1 k1 k2 k2 unifyKinds :: [TcKind] -> [TcKind] -> TcM () -unifyKinds [] [] = returnTc () -unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenTc_` +unifyKinds [] [] = returnM () +unifyKinds (k1:ks1) (k2:ks2) = unifyKind k1 k2 `thenM_` unifyKinds ks1 ks2 unifyKinds _ _ = panic "unifyKinds: length mis-match" \end{code} @@ -790,20 +929,37 @@ unifyOpenTypeKind :: TcKind -> TcM () -- for some boxity bx unifyOpenTypeKind ty@(TyVarTy tyvar) - = getTcTyVar tyvar `thenNF_Tc` \ maybe_ty -> + = getTcTyVar tyvar `thenM` \ maybe_ty -> case maybe_ty of Just ty' -> unifyOpenTypeKind ty' other -> unify_open_kind_help ty unifyOpenTypeKind ty - | isTypeKind ty = returnTc () + | isTypeKind ty = returnM () | otherwise = unify_open_kind_help ty unify_open_kind_help ty -- Revert to ordinary unification - = newBoxityVar `thenNF_Tc` \ boxity -> - unifyKind ty (mkTyConApp typeCon [boxity]) + = newOpenTypeKind `thenM` \ open_kind -> + unifyKind ty open_kind \end{code} +\begin{code} +unifyFunKind :: TcKind -> TcM (Maybe (TcKind, TcKind)) +-- Like unifyFunTy, but does not fail; instead just returns Nothing + +unifyFunKind (TyVarTy tyvar) + = getTcTyVar tyvar `thenM` \ maybe_ty -> + case maybe_ty of + Just fun_kind -> unifyFunKind fun_kind + Nothing -> newKindVar `thenM` \ arg_kind -> + newKindVar `thenM` \ res_kind -> + putTcTyVar tyvar (mkArrowKind arg_kind res_kind) `thenM_` + returnM (Just (arg_kind,res_kind)) + +unifyFunKind (FunTy arg_kind res_kind) = returnM (Just (arg_kind,res_kind)) +unifyFunKind (NoteTy _ ty) = unifyFunKind ty +unifyFunKind other = returnM Nothing +\end{code} %************************************************************************ %* * @@ -816,9 +972,9 @@ Errors \begin{code} unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred - = zonkTcType ty1 `thenNF_Tc` \ ty1' -> - zonkTcType ty2 `thenNF_Tc` \ ty2' -> - returnNF_Tc (err ty1' ty2') + = zonkTcType ty1 `thenM` \ ty1' -> + zonkTcType ty2 `thenM` \ ty2' -> + returnM (err ty1' ty2') where err ty1 ty2 = (env1, nest 4 @@ -831,8 +987,8 @@ unifyCtxt s ty1 ty2 tidy_env -- ty1 expected, ty2 inferred unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 inferred -- tv1 is zonked already - = zonkTcType ty2 `thenNF_Tc` \ ty2' -> - returnNF_Tc (err ty2') + = zonkTcType ty2 `thenM` \ ty2' -> + returnM (err ty2') where err ty2 = (env2, ptext SLIT("When matching types") <+> sep [quotes pp_expected, ptext SLIT("and"), quotes pp_actual]) @@ -845,8 +1001,8 @@ unifyKindCtxt swapped tv1 ty2 tidy_env -- not swapped => tv1 expected, ty2 infer pp2 = ppr ty2' unifyMisMatch ty1 ty2 - = zonkTcType ty1 `thenNF_Tc` \ ty1' -> - zonkTcType ty2 `thenNF_Tc` \ ty2' -> + = zonkTcType ty1 `thenM` \ ty1' -> + zonkTcType ty2 `thenM` \ ty2' -> let (env, [tidy_ty1, tidy_ty2]) = tidyOpenTypes emptyTidyEnv [ty1',ty2'] msg = hang (ptext SLIT("Couldn't match")) @@ -863,12 +1019,16 @@ unifyWithSigErr tyvar ty (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar (env2, tidy_ty) = tidyOpenType env1 ty -unifyOccurCheck tyvar ty - = (env2, hang (ptext SLIT("Occurs check: cannot construct the infinite type:")) +unifyCheck problem tyvar ty + = (env2, hang msg 4 (sep [ppr tidy_tyvar, char '=', ppr tidy_ty])) where (env1, tidy_tyvar) = tidyOpenTyVar emptyTidyEnv tyvar (env2, tidy_ty) = tidyOpenType env1 ty + + msg = case problem of + OccurCheck -> ptext SLIT("Occurs check: cannot construct the infinite type:") + NotMonoType -> ptext SLIT("Cannot unify a type variable with a type scheme:") \end{code} @@ -936,33 +1096,49 @@ So we revert to ordinary type variables for signatures, and try to give a helpful message in checkSigTyVars. \begin{code} -checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature - -> TcTyVarSet -- Tyvars that are free in the type signature - -- Not necessarily zonked - -- These should *already* be in the free-in-env set, - -- and are used here only to improve the error message - -> TcM [TcTyVar] -- Zonked signature type variables - -checkSigTyVars [] free = returnTc [] -checkSigTyVars sig_tyvars free_tyvars - = zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys -> - tcGetGlobalTyVars `thenNF_Tc` \ globals -> +checkSigTyVars :: [TcTyVar] -> TcM [TcTyVar] +checkSigTyVars sig_tvs = check_sig_tyvars emptyVarSet sig_tvs + +checkSigTyVarsWrt :: TcTyVarSet -> [TcTyVar] -> TcM [TcTyVar] +checkSigTyVarsWrt extra_tvs sig_tvs + = zonkTcTyVarsAndFV (varSetElems extra_tvs) `thenM` \ extra_tvs' -> + check_sig_tyvars extra_tvs' sig_tvs + +check_sig_tyvars + :: TcTyVarSet -- Global type variables. The universally quantified + -- tyvars should not mention any of these + -- Guaranteed already zonked. + -> [TcTyVar] -- Universally-quantified type variables in the signature + -- Not guaranteed zonked. + -> TcM [TcTyVar] -- Zonked signature type variables + +check_sig_tyvars extra_tvs [] + = returnM [] +check_sig_tyvars extra_tvs sig_tvs + = zonkTcTyVars sig_tvs `thenM` \ sig_tys -> + tcGetGlobalTyVars `thenM` \ gbl_tvs -> + let + env_tvs = gbl_tvs `unionVarSet` extra_tvs + in + traceTc (text "check_sig_tyvars" <+> (vcat [text "sig_tys" <+> ppr sig_tys, + text "gbl_tvs" <+> ppr gbl_tvs, + text "extra_tvs" <+> ppr extra_tvs])) `thenM_` - checkTcM (allDistinctTyVars sig_tys globals) - (complain sig_tys globals) `thenTc_` + checkM (allDistinctTyVars sig_tys env_tvs) + (complain sig_tys env_tvs) `thenM_` - returnTc (map (tcGetTyVar "checkSigTyVars") sig_tys) + returnM (map (tcGetTyVar "checkSigTyVars") sig_tys) where complain sig_tys globals = -- "check" checks each sig tyvar in turn - foldlNF_Tc check - (env2, emptyVarEnv, []) - (tidy_tvs `zip` tidy_tys) `thenNF_Tc` \ (env3, _, msgs) -> + foldlM check + (env2, emptyVarEnv, []) + (tidy_tvs `zip` tidy_tys) `thenM` \ (env3, _, msgs) -> - failWithTcM (env3, main_msg $$ vcat msgs) + failWithTcM (env3, main_msg $$ nest 4 (vcat msgs)) where - (env1, tidy_tvs) = tidyOpenTyVars emptyTidyEnv sig_tyvars + (env1, tidy_tvs) = tidyOpenTyVars emptyTidyEnv sig_tvs (env2, tidy_tys) = tidyOpenTypes env1 sig_tys main_msg = ptext SLIT("Inferred type is less polymorphic than expected") @@ -974,13 +1150,13 @@ checkSigTyVars sig_tyvars free_tyvars -- acc maps a zonked type variable back to a signature type variable = case tcGetTyVar_maybe ty of { Nothing -> -- Error (a)! - returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ; + returnM (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ; Just tv -> case lookupVarEnv acc tv of { Just sig_tyvar' -> -- Error (b)! - returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar thing : msgs) + returnM (tidy_env, acc, unify_msg sig_tyvar thing : msgs) where thing = ptext SLIT("another quantified type variable") <+> quotes (ppr sig_tyvar') @@ -989,108 +1165,32 @@ checkSigTyVars sig_tyvars free_tyvars if tv `elemVarSet` globals -- Error (c) or (d)! Type variable escapes -- The least comprehensible, so put it last -- Game plan: - -- a) get the local TcIds and TyVars from the environment, + -- get the local TcIds and TyVars from the environment, -- and pass them to find_globals (they might have tv free) - -- b) similarly, find any free_tyvars that mention tv - then tcGetEnv `thenNF_Tc` \ ve -> - find_globals tv tidy_env (tcLEnvElts ve) `thenNF_Tc` \ (tidy_env1, globs) -> - find_frees tv tidy_env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (tidy_env2, frees) -> - returnNF_Tc (tidy_env2, acc, escape_msg sig_tyvar tv globs frees : msgs) + then findGlobals (unitVarSet tv) tidy_env `thenM` \ (tidy_env1, globs) -> + returnM (tidy_env1, acc, escape_msg sig_tyvar tv globs : msgs) else -- All OK - returnNF_Tc (tidy_env, extendVarEnv acc tv sig_tyvar, msgs) + returnM (tidy_env, extendVarEnv acc tv sig_tyvar, msgs) }} +\end{code} ------------------------ --- find_globals looks at the value environment and finds values --- whose types mention the offending type variable. It has to be --- careful to zonk the Id's type first, so it has to be in the monad. --- We must be careful to pass it a zonked type variable, too. - -find_globals :: Var - -> TidyEnv - -> [TcTyThing] - -> NF_TcM (TidyEnv, [SDoc]) - -find_globals tv tidy_env things - = go tidy_env [] things - where - go tidy_env acc [] = returnNF_Tc (tidy_env, acc) - go tidy_env acc (thing : things) - = find_thing ignore_it tidy_env thing `thenNF_Tc` \ (tidy_env1, maybe_doc) -> - case maybe_doc of - Just d -> go tidy_env1 (d:acc) things - Nothing -> go tidy_env1 acc things - - ignore_it ty = not (tv `elemVarSet` tyVarsOfType ty) - ------------------------ -find_thing ignore_it tidy_env (ATcId id) - = zonkTcType (idType id) `thenNF_Tc` \ id_ty -> - if ignore_it id_ty then - returnNF_Tc (tidy_env, Nothing) - else let - (tidy_env', tidy_ty) = tidyOpenType tidy_env id_ty - msg = sep [ppr id <+> dcolon <+> ppr tidy_ty, - nest 2 (parens (ptext SLIT("bound at") <+> - ppr (getSrcLoc id)))] - in - returnNF_Tc (tidy_env', Just msg) - -find_thing ignore_it tidy_env (ATyVar tv) - = zonkTcTyVar tv `thenNF_Tc` \ tv_ty -> - if ignore_it tv_ty then - returnNF_Tc (tidy_env, Nothing) - else let - (tidy_env1, tv1) = tidyOpenTyVar tidy_env tv - (tidy_env2, tidy_ty) = tidyOpenType tidy_env1 tv_ty - msg = sep [ptext SLIT("Type variable") <+> quotes (ppr tv1) <+> eq_stuff, nest 2 bound_at] - - eq_stuff | Just tv' <- Type.getTyVar_maybe tv_ty, tv == tv' = empty - | otherwise = equals <+> ppr tv_ty - -- It's ok to use Type.getTyVar_maybe because ty is zonked by now - - bound_at = tyVarBindingInfo tv - in - returnNF_Tc (tidy_env2, Just msg) +\begin{code} ----------------------- -find_frees tv tidy_env acc [] - = returnNF_Tc (tidy_env, acc) -find_frees tv tidy_env acc (ftv:ftvs) - = zonkTcTyVar ftv `thenNF_Tc` \ ty -> - if tv `elemVarSet` tyVarsOfType ty then - let - (tidy_env', ftv') = tidyOpenTyVar tidy_env ftv - in - find_frees tv tidy_env' (ftv':acc) ftvs - else - find_frees tv tidy_env acc ftvs - - -escape_msg sig_tv tv globs frees +escape_msg sig_tv tv globs = mk_msg sig_tv <+> ptext SLIT("escapes") $$ - if not (null globs) then + if notNull globs then vcat [pp_it <+> ptext SLIT("is mentioned in the environment:"), nest 2 (vcat globs)] - else if not (null frees) then - vcat [ptext SLIT("It is reachable from the type variable(s)") <+> pprQuotedList frees, - nest 2 (ptext SLIT("which") <+> is_are <+> ptext SLIT("free in the signature")) - ] else empty -- Sigh. It's really hard to give a good error message - -- all the time. One bad case is an existential pattern match + -- all the time. One bad case is an existential pattern match. + -- We rely on the "When..." context to help. where - is_are | isSingleton frees = ptext SLIT("is") - | otherwise = ptext SLIT("are") pp_it | sig_tv /= tv = ptext SLIT("It unifies with") <+> quotes (ppr tv) <> comma <+> ptext SLIT("which") | otherwise = ptext SLIT("It") - vcat_first :: Int -> [SDoc] -> SDoc - vcat_first n [] = empty - vcat_first 0 (x:xs) = text "...others omitted..." - vcat_first n (x:xs) = x $$ vcat_first (n-1) xs - unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> thing mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv) @@ -1099,31 +1199,19 @@ mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv) These two context are used with checkSigTyVars \begin{code} -sigCtxt :: [TcTyVar] -> TcThetaType -> TcTauType - -> TidyEnv -> NF_TcM (TidyEnv, Message) -sigCtxt sig_tyvars sig_theta sig_tau tidy_env - = zonkTcType sig_tau `thenNF_Tc` \ actual_tau -> +sigCtxt :: Id -> [TcTyVar] -> TcThetaType -> TcTauType + -> TidyEnv -> TcM (TidyEnv, Message) +sigCtxt id sig_tvs sig_theta sig_tau tidy_env + = zonkTcType sig_tau `thenM` \ actual_tau -> let - (env1, tidy_sig_tyvars) = tidyOpenTyVars tidy_env sig_tyvars - (env2, tidy_sig_rho) = tidyOpenType env1 (mkRhoTy sig_theta sig_tau) - (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau - msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tyvars tidy_sig_rho), - ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau + (env1, tidy_sig_tvs) = tidyOpenTyVars tidy_env sig_tvs + (env2, tidy_sig_rho) = tidyOpenType env1 (mkPhiTy sig_theta sig_tau) + (env3, tidy_actual_tau) = tidyOpenType env2 actual_tau + sub_msg = vcat [ptext SLIT("Signature type: ") <+> pprType (mkForAllTys tidy_sig_tvs tidy_sig_rho), + ptext SLIT("Type to generalise:") <+> pprType tidy_actual_tau ] + msg = vcat [ptext SLIT("When trying to generalise the type inferred for") <+> quotes (ppr id), + nest 4 sub_msg] in - returnNF_Tc (env3, msg) - -sigPatCtxt bound_tvs bound_ids tidy_env - = returnNF_Tc (env1, - sep [ptext SLIT("When checking a pattern that binds"), - nest 4 (vcat (zipWith ppr_id show_ids tidy_tys))]) - where - show_ids = filter is_interesting bound_ids - is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs - - (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids) - ppr_id id ty = ppr id <+> dcolon <+> ppr ty - -- Don't zonk the types so we get the separate, un-unified versions + returnM (env3, msg) \end{code} - -