{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[TcPatSyn]{Typechecking pattern synonym declarations} -} {-# LANGUAGE CPP #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} module TcPatSyn ( tcPatSynDecl, tcPatSynBuilderBind , tcPatSynBuilderOcc, nonBidirectionalErr ) where import GhcPrelude import HsSyn import TcPat import Type( mkEmptyTCvSubst, tidyTyVarBinders, tidyTypes, tidyType ) import TcRnMonad import TcSigs( emptyPragEnv, completeSigFromId ) import TcType( mkMinimalBySCs ) import TcEnv import TcMType import TcHsSyn( zonkTyVarBindersX, zonkTcTypeToTypes , zonkTcTypeToType, emptyZonkEnv ) import TysPrim import TysWiredIn ( runtimeRepTy ) import Name import SrcLoc import PatSyn import NameSet import Panic import Outputable import FastString import Var import VarEnv( emptyTidyEnv, mkInScopeSet ) import Id import IdInfo( RecSelParent(..), setLevityInfoWithType ) import TcBinds import BasicTypes import TcSimplify import TcUnify import TcType import TcEvidence import BuildTyCl import VarSet import MkId import TcTyDecls import ConLike import FieldLabel import Bag import Util import ErrUtils import Control.Monad ( zipWithM ) import Data.List( partition ) #include "HsVersions.h" {- ************************************************************************ * * Type checking a pattern synonym * * ************************************************************************ -} tcPatSynDecl :: PatSynBind GhcRn GhcRn -> Maybe TcSigInfo -> TcM (LHsBinds GhcTc, TcGblEnv) tcPatSynDecl psb mb_sig = recoverM (recoverPSB psb) $ case mb_sig of Nothing -> tcInferPatSynDecl psb Just (TcPatSynSig tpsi) -> tcCheckPatSynDecl psb tpsi _ -> panic "tcPatSynDecl" recoverPSB :: PatSynBind GhcRn GhcRn -> TcM (LHsBinds GhcTc, TcGblEnv) -- See Note [Pattern synonym error recovery] recoverPSB (PSB { psb_id = L _ name, psb_args = details }) = do { matcher_name <- newImplicitBinder name mkMatcherOcc ; let placeholder = AConLike $ PatSynCon $ mk_placeholder matcher_name ; gbl_env <- tcExtendGlobalEnv [placeholder] getGblEnv ; return (emptyBag, gbl_env) } where (_arg_names, _rec_fields, is_infix) = collectPatSynArgInfo details mk_placeholder matcher_name = mkPatSyn name is_infix ([mkTyVarBinder Specified alphaTyVar], []) ([], []) [] -- Arg tys alphaTy (matcher_id, True) Nothing [] -- Field labels where -- The matcher_id is used only by the desugarer, so actually -- and error-thunk would probably do just as well here. matcher_id = mkLocalId matcher_name $ mkSpecForAllTys [alphaTyVar] alphaTy recoverPSB (XPatSynBind {}) = panic "recoverPSB" {- Note [Pattern synonym error recovery] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If type inference for a pattern synonym fails, we can't continue with the rest of tc_patsyn_finish, because we may get knock-on errors, or even a crash. E.g. from pattern What = True :: Maybe we get a kind error; and we must stop right away (Trac #15289). We stop if there are /any/ unsolved constraints, not just insoluble ones; because pattern synonyms are top-level things, we will never solve them later if we can't solve them now. And if we were to carry on, tc_patsyn_finish does zonkTcTypeToType, which defaults any unsolved unificatdion variables to Any, which confuses the error reporting no end (Trac #15685). So we use simplifyTop to completely solve the constraint, report any errors, throw an exception. Even in the event of such an error we can recover and carry on, just as we do for value bindings, provided we plug in placeholder for the pattern synonym: see recoverPSB. The goal of the placeholder is not to cause a raft of follow-on errors. I've used the simplest thing for now, but we might need to elaborate it a bit later. (e.g. I've given it zero args, which may cause knock-on errors if it is used in a pattern.) But it'll do for now. -} tcInferPatSynDecl :: PatSynBind GhcRn GhcRn -> TcM (LHsBinds GhcTc, TcGblEnv) tcInferPatSynDecl (PSB { psb_id = lname@(L _ name), psb_args = details , psb_def = lpat, psb_dir = dir }) = addPatSynCtxt lname $ do { traceTc "tcInferPatSynDecl {" $ ppr name ; let (arg_names, rec_fields, is_infix) = collectPatSynArgInfo details ; (tclvl, wanted, ((lpat', args), pat_ty)) <- pushLevelAndCaptureConstraints $ tcInferNoInst $ \ exp_ty -> tcPat PatSyn lpat exp_ty $ mapM tcLookupId arg_names ; let named_taus = (name, pat_ty) : map (\arg -> (getName arg, varType arg)) args ; (qtvs, req_dicts, ev_binds, residual, _) <- simplifyInfer tclvl NoRestrictions [] named_taus wanted ; top_ev_binds <- checkNoErrs (simplifyTop residual) ; addTopEvBinds top_ev_binds $ do { let (ex_tvs, prov_dicts) = tcCollectEx lpat' ex_tv_set = mkVarSet ex_tvs univ_tvs = filterOut (`elemVarSet` ex_tv_set) qtvs req_theta = map evVarPred req_dicts ; prov_dicts <- mapM zonkId prov_dicts ; let filtered_prov_dicts = mkMinimalBySCs evVarPred prov_dicts prov_theta = map evVarPred filtered_prov_dicts -- Filtering: see Note [Remove redundant provided dicts] -- Report bad universal type variables -- See Note [Type variables whose kind is captured] ; let bad_tvs = [ tv | tv <- univ_tvs , tyCoVarsOfType (tyVarKind tv) `intersectsVarSet` ex_tv_set ] ; mapM_ (badUnivTvErr ex_tvs) bad_tvs -- Report coercions that esacpe -- See Note [Coercions that escape] ; args <- mapM zonkId args ; let bad_args = [ (arg, bad_cos) | arg <- args ++ prov_dicts , let bad_cos = filterDVarSet isId $ (tyCoVarsOfTypeDSet (idType arg)) , not (isEmptyDVarSet bad_cos) ] ; mapM_ dependentArgErr bad_args ; traceTc "tcInferPatSynDecl }" $ (ppr name $$ ppr ex_tvs) ; tc_patsyn_finish lname dir is_infix lpat' (mkTyVarBinders Inferred univ_tvs , req_theta, ev_binds, req_dicts) (mkTyVarBinders Inferred ex_tvs , mkTyVarTys ex_tvs, prov_theta , map (EvExpr . evId) filtered_prov_dicts) (map nlHsVar args, map idType args) pat_ty rec_fields } } tcInferPatSynDecl (XPatSynBind _) = panic "tcInferPatSynDecl" badUnivTvErr :: [TyVar] -> TyVar -> TcM () -- See Note [Type variables whose kind is captured] badUnivTvErr ex_tvs bad_tv = addErrTc $ vcat [ text "Universal type variable" <+> quotes (ppr bad_tv) <+> text "has existentially bound kind:" , nest 2 (ppr_with_kind bad_tv) , hang (text "Existentially-bound variables:") 2 (vcat (map ppr_with_kind ex_tvs)) , text "Probable fix: give the pattern synoym a type signature" ] where ppr_with_kind tv = ppr tv <+> dcolon <+> ppr (tyVarKind tv) dependentArgErr :: (Id, DTyCoVarSet) -> TcM () -- See Note [Coercions that escape] dependentArgErr (arg, bad_cos) = addErrTc $ vcat [ text "Iceland Jack! Iceland Jack! Stop torturing me!" , hang (text "Pattern-bound variable") 2 (ppr arg <+> dcolon <+> ppr (idType arg)) , nest 2 $ hang (text "has a type that mentions pattern-bound coercion" <> plural bad_co_list <> colon) 2 (pprWithCommas ppr bad_co_list) , text "Hint: use -fprint-explicit-coercions to see the coercions" , text "Probable fix: add a pattern signature" ] where bad_co_list = dVarSetElems bad_cos {- Note [Remove redundant provided dicts] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Recall that HRefl :: forall k1 k2 (a1:k1) (a2:k2). (k1 ~ k2, a1 ~ a2) => a1 :~~: a2 (NB: technically the (k1~k2) existential dictionary is not necessary, but it's there at the moment.) Now consider (Trac #14394): pattern Foo = HRefl in a non-poly-kinded module. We don't want to get pattern Foo :: () => (* ~ *, b ~ a) => a :~~: b with that redundant (* ~ *). We'd like to remove it; hence the call to mkMinimalWithSCs. Similarly consider data S a where { MkS :: Ord a => a -> S a } pattern Bam x y <- (MkS (x::a), MkS (y::a))) The pattern (Bam x y) binds two (Ord a) dictionaries, but we only need one. Agian mkMimimalWithSCs removes the redundant one. Note [Type variables whose kind is captured] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data AST a = Sym [a] class Prj s where { prj :: [a] -> Maybe (s a) pattern P x <= Sym (prj -> Just x) Here we get a matcher with this type $mP :: forall s a. Prj s => AST a -> (s a -> r) -> r -> r No problem. But note that 's' is not fixed by the type of the pattern (AST a), nor is it existentially bound. It's really only fixed by the type of the continuation. Trac #14552 showed that this can go wrong if the kind of 's' mentions existentially bound variables. We obviously can't make a type like $mP :: forall (s::k->*) a. Prj s => AST a -> (forall k. s a -> r) -> r -> r But neither is 's' itself existentially bound, so the forall (s::k->*) can't go in the inner forall either. (What would the matcher apply the continuation to?) So we just fail in this case, with a pretty terrible error message. Maybe we could do better, but I can't see how. (It'd be possible to default 's' to (Any k), but that probably isn't what the user wanted, and it not straightforward to implement, because by the time we see the problem, simplifyInfer has already skolemised 's'.) This stuff can only happen in the presence of view patterns, with PolyKinds, so it's a bit of a corner case. Note [Coercions that escape] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Trac #14507 showed an example where the inferred type of the matcher for the pattern synonym was somethign like $mSO :: forall (r :: TYPE rep) kk (a :: k). TypeRep k a -> ((Bool ~ k) => TypeRep Bool (a |> co_a2sv) -> r) -> (Void# -> r) -> r What is that co_a2sv :: Bool ~# *?? It was bound (via a superclass selection) by the pattern being matched; and indeed it is implicit in the context (Bool ~ k). You could imagine trying to extract it like this: $mSO :: forall (r :: TYPE rep) kk (a :: k). TypeRep k a -> ( co :: ((Bool :: *) ~ (k :: *)) => let co_a2sv = sc_sel co in TypeRep Bool (a |> co_a2sv) -> r) -> (Void# -> r) -> r But we simply don't allow that in types. Maybe one day but not now. How to detect this situation? We just look for free coercion variables in the types of any of the arguments to the matcher. The error message is not very helpful, but at least we don't get a Lint error. -} tcCheckPatSynDecl :: PatSynBind GhcRn GhcRn -> TcPatSynInfo -> TcM (LHsBinds GhcTc, TcGblEnv) tcCheckPatSynDecl psb@PSB{ psb_id = lname@(L _ name), psb_args = details , psb_def = lpat, psb_dir = dir } TPSI{ patsig_implicit_bndrs = implicit_tvs , patsig_univ_bndrs = explicit_univ_tvs, patsig_prov = prov_theta , patsig_ex_bndrs = explicit_ex_tvs, patsig_req = req_theta , patsig_body_ty = sig_body_ty } = addPatSynCtxt lname $ do { let decl_arity = length arg_names (arg_names, rec_fields, is_infix) = collectPatSynArgInfo details ; traceTc "tcCheckPatSynDecl" $ vcat [ ppr implicit_tvs, ppr explicit_univ_tvs, ppr req_theta , ppr explicit_ex_tvs, ppr prov_theta, ppr sig_body_ty ] ; (arg_tys, pat_ty) <- case tcSplitFunTysN decl_arity sig_body_ty of Right stuff -> return stuff Left missing -> wrongNumberOfParmsErr name decl_arity missing -- Complain about: pattern P :: () => forall x. x -> P x -- The existential 'x' should not appear in the result type -- Can't check this until we know P's arity ; let bad_tvs = filter (`elemVarSet` tyCoVarsOfType pat_ty) explicit_ex_tvs ; checkTc (null bad_tvs) $ hang (sep [ text "The result type of the signature for" <+> quotes (ppr name) <> comma , text "namely" <+> quotes (ppr pat_ty) ]) 2 (text "mentions existential type variable" <> plural bad_tvs <+> pprQuotedList bad_tvs) -- See Note [The pattern-synonym signature splitting rule] in TcSigs ; let univ_fvs = closeOverKinds $ (tyCoVarsOfTypes (pat_ty : req_theta) `extendVarSetList` explicit_univ_tvs) (extra_univ, extra_ex) = partition ((`elemVarSet` univ_fvs) . binderVar) implicit_tvs univ_bndrs = extra_univ ++ mkTyVarBinders Specified explicit_univ_tvs ex_bndrs = extra_ex ++ mkTyVarBinders Specified explicit_ex_tvs univ_tvs = binderVars univ_bndrs ex_tvs = binderVars ex_bndrs -- Right! Let's check the pattern against the signature -- See Note [Checking against a pattern signature] ; req_dicts <- newEvVars req_theta ; (tclvl, wanted, (lpat', (ex_tvs', prov_dicts, args'))) <- ASSERT2( equalLength arg_names arg_tys, ppr name $$ ppr arg_names $$ ppr arg_tys ) pushLevelAndCaptureConstraints $ tcExtendTyVarEnv univ_tvs $ tcExtendKindEnvList [(getName (binderVar ex_tv), APromotionErr PatSynExPE) | ex_tv <- extra_ex] $ -- See Note [Pattern synonym existentials do not scope] tcPat PatSyn lpat (mkCheckExpType pat_ty) $ do { let in_scope = mkInScopeSet (mkVarSet univ_tvs) empty_subst = mkEmptyTCvSubst in_scope ; (subst, ex_tvs') <- mapAccumLM newMetaTyVarX empty_subst ex_tvs -- newMetaTyVarX: see the "Existential type variables" -- part of Note [Checking against a pattern signature] ; traceTc "tcpatsyn1" (vcat [ ppr v <+> dcolon <+> ppr (tyVarKind v) | v <- ex_tvs]) ; traceTc "tcpatsyn2" (vcat [ ppr v <+> dcolon <+> ppr (tyVarKind v) | v <- ex_tvs']) ; let prov_theta' = substTheta subst prov_theta -- Add univ_tvs to the in_scope set to -- satisfy the substitution invariant. There's no need to -- add 'ex_tvs' as they are already in the domain of the -- substitution. -- See also Note [The substitution invariant] in TyCoRep. ; prov_dicts <- mapM (emitWanted (ProvCtxtOrigin psb)) prov_theta' ; args' <- zipWithM (tc_arg subst) arg_names arg_tys ; return (ex_tvs', prov_dicts, args') } ; let skol_info = SigSkol (PatSynCtxt name) pat_ty [] -- The type here is a bit bogus, but we do not print -- the type for PatSynCtxt, so it doesn't matter -- See TcRnTypes Note [Skolem info for pattern synonyms] ; (implics, ev_binds) <- buildImplicationFor tclvl skol_info univ_tvs req_dicts wanted -- Solve the constraints now, because we are about to make a PatSyn, -- which should not contain unification variables and the like (Trac #10997) ; simplifyTopImplic implics -- ToDo: in the bidirectional case, check that the ex_tvs' are all distinct -- Otherwise we may get a type error when typechecking the builder, -- when that should be impossible ; traceTc "tcCheckPatSynDecl }" $ ppr name ; tc_patsyn_finish lname dir is_infix lpat' (univ_bndrs, req_theta, ev_binds, req_dicts) (ex_bndrs, mkTyVarTys ex_tvs', prov_theta, prov_dicts) (args', arg_tys) pat_ty rec_fields } where tc_arg :: TCvSubst -> Name -> Type -> TcM (LHsExpr GhcTcId) tc_arg subst arg_name arg_ty = do { -- Look up the variable actually bound by lpat -- and check that it has the expected type arg_id <- tcLookupId arg_name ; wrap <- tcSubType_NC GenSigCtxt (idType arg_id) (substTyUnchecked subst arg_ty) -- Why do we need tcSubType here? -- See Note [Pattern synonyms and higher rank types] ; return (mkLHsWrap wrap $ nlHsVar arg_id) } tcCheckPatSynDecl (XPatSynBind _) _ = panic "tcCheckPatSynDecl" {- [Pattern synonyms and higher rank types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider data T = MkT (forall a. a->a) pattern P :: (Int -> Int) -> T pattern P x <- MkT x This should work. But in the matcher we must match against MkT, and then instantiate its argument 'x', to get a function of type (Int -> Int). Equality is not enough! Trac #13752 was an example. Note [Pattern synonym existentials do not scope] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this (Trac #14498): pattern SS :: forall (t :: k). () => => forall (a :: kk -> k) (n :: kk). => TypeRep n -> TypeRep t pattern SS n <- (App (Typeable :: TypeRep (a::kk -> k)) n) Here 'k' is implicitly bound in the signature, but (with -XScopedTypeVariables) it does still scope over the pattern-synonym definition. But what about 'kk', which is oexistential? It too is implicitly bound in the signature; should it too scope? And if so, what type variable is it bound to? The trouble is that the type variable to which it is bound is itself only brought into scope in part the pattern, so it makes no sense for 'kk' to scope over the whole pattern. See the discussion on Trac #14498, esp comment:16ff. Here is a simpler example: data T where { MkT :: x -> (x->Int) -> T } pattern P :: () => forall x. x -> (x->Int) -> T pattern P a b = (MkT a b, True) Here it would make no sense to mention 'x' in the True pattern, like this: pattern P a b = (MkT a b, True :: x) The 'x' only makes sense "under" the MkT pattern. Conclusion: the existential type variables of a pattern-synonym signature should not scope. But it's not that easy to implement, because we don't know exactly what the existentials /are/ until we get to type checking. (See Note [The pattern-synonym signature splitting rule], and the partition of implicit_tvs in tcCheckPatSynDecl.) So we do this: - The reaner brings all the implicitly-bound kind variables into scope, without trying to distinguish universal from existential - tcCheckPatSynDecl uses tcExtendKindEnvList to bind the implicitly-bound existentials to APromotionErr PatSynExPE It's not really a promotion error, but it's a way to bind the Name (which the renamer has not complained about) to something that, when looked up, will cause a complaint (in this case TcHsType.promotionErr) Note [The pattern-synonym signature splitting rule] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Given a pattern signature, we must split the kind-generalised variables, and the implicitly-bound variables into universal and existential. The rule is this (see discussion on Trac #11224): The universal tyvars are the ones mentioned in - univ_tvs: the user-specified (forall'd) universals - req_theta - res_ty The existential tyvars are all the rest For example pattern P :: () => b -> T a pattern P x = ... Here 'a' is universal, and 'b' is existential. But there is a wrinkle: how do we split the arg_tys from req_ty? Consider pattern Q :: () => b -> S c -> T a pattern Q x = ... This is an odd example because Q has only one syntactic argument, and so presumably is defined by a view pattern matching a function. But it can happen (Trac #11977, #12108). We don't know Q's arity from the pattern signature, so we have to wait until we see the pattern declaration itself before deciding res_ty is, and hence which variables are existential and which are universal. And that in turn is why TcPatSynInfo has a separate field, patsig_implicit_bndrs, to capture the implicitly bound type variables, because we don't yet know how to split them up. It's a slight compromise, because it means we don't really know the pattern synonym's real signature until we see its declaration. So, for example, in hs-boot file, we may need to think what to do... (eg don't have any implicitly-bound variables). Note [Checking against a pattern signature] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When checking the actual supplied pattern against the pattern synonym signature, we need to be quite careful. ----- Provided constraints Example data T a where MkT :: Ord a => a -> T a pattern P :: () => Eq a => a -> [T a] pattern P x = [MkT x] We must check that the (Eq a) that P claims to bind (and to make available to matches against P), is derivable from the actual pattern. For example: f (P (x::a)) = ...here (Eq a) should be available... And yes, (Eq a) is derivable from the (Ord a) bound by P's rhs. ----- Existential type variables Unusually, we instantiate the existential tyvars of the pattern with *meta* type variables. For example data S where MkS :: Eq a => [a] -> S pattern P :: () => Eq x => x -> S pattern P x <- MkS x The pattern synonym conceals from its client the fact that MkS has a list inside it. The client just thinks it's a type 'x'. So we must unify x := [a] during type checking, and then use the instantiating type [a] (called ex_tys) when building the matcher. In this case we'll get $mP :: S -> (forall x. Ex x => x -> r) -> r -> r $mP x k = case x of MkS a (d:Eq a) (ys:[a]) -> let dl :: Eq [a] dl = $dfunEqList d in k [a] dl ys All this applies when type-checking the /matching/ side of a pattern synonym. What about the /building/ side? * For Unidirectional, there is no builder * For ExplicitBidirectional, the builder is completely separate code, typechecked in tcPatSynBuilderBind * For ImplicitBidirectional, the builder is still typechecked in tcPatSynBuilderBind, by converting the pattern to an expression and typechecking it. At one point, for ImplicitBidirectional I used SigTvs (instead of TauTvs) in tcCheckPatSynDecl. But (a) strengthening the check here is redundant since tcPatSynBuilderBind does the job, (b) it was still incomplete (SigTvs can unify with each other), and (c) it didn't even work (Trac #13441 was accepted with ExplicitBidirectional, but rejected if expressed in ImplicitBidirectional form. Conclusion: trying to be too clever is a bad idea. -} collectPatSynArgInfo :: HsPatSynDetails (Located Name) -> ([Name], [Name], Bool) collectPatSynArgInfo details = case details of PrefixCon names -> (map unLoc names, [], False) InfixCon name1 name2 -> (map unLoc [name1, name2], [], True) RecCon names -> (vars, sels, False) where (vars, sels) = unzip (map splitRecordPatSyn names) where splitRecordPatSyn :: RecordPatSynField (Located Name) -> (Name, Name) splitRecordPatSyn (RecordPatSynField { recordPatSynPatVar = L _ patVar , recordPatSynSelectorId = L _ selId }) = (patVar, selId) addPatSynCtxt :: Located Name -> TcM a -> TcM a addPatSynCtxt (L loc name) thing_inside = setSrcSpan loc $ addErrCtxt (text "In the declaration for pattern synonym" <+> quotes (ppr name)) $ thing_inside wrongNumberOfParmsErr :: Name -> Arity -> Arity -> TcM a wrongNumberOfParmsErr name decl_arity missing = failWithTc $ hang (text "Pattern synonym" <+> quotes (ppr name) <+> ptext (sLit "has") <+> speakNOf decl_arity (text "argument")) 2 (text "but its type signature has" <+> int missing <+> text "fewer arrows") ------------------------- -- Shared by both tcInferPatSyn and tcCheckPatSyn tc_patsyn_finish :: Located Name -- ^ PatSyn Name -> HsPatSynDir GhcRn -- ^ PatSyn type (Uni/Bidir/ExplicitBidir) -> Bool -- ^ Whether infix -> LPat GhcTc -- ^ Pattern of the PatSyn -> ([TcTyVarBinder], [PredType], TcEvBinds, [EvVar]) -> ([TcTyVarBinder], [TcType], [PredType], [EvTerm]) -> ([LHsExpr GhcTcId], [TcType]) -- ^ Pattern arguments and -- types -> TcType -- ^ Pattern type -> [Name] -- ^ Selector names -- ^ Whether fields, empty if not record PatSyn -> TcM (LHsBinds GhcTc, TcGblEnv) tc_patsyn_finish lname dir is_infix lpat' (univ_tvs, req_theta, req_ev_binds, req_dicts) (ex_tvs, ex_tys, prov_theta, prov_dicts) (args, arg_tys) pat_ty field_labels = do { -- Zonk everything. We are about to build a final PatSyn -- so there had better be no unification variables in there (ze, univ_tvs') <- zonkTyVarBindersX emptyZonkEnv univ_tvs ; req_theta' <- zonkTcTypeToTypes ze req_theta ; (ze, ex_tvs') <- zonkTyVarBindersX ze ex_tvs ; prov_theta' <- zonkTcTypeToTypes ze prov_theta ; pat_ty' <- zonkTcTypeToType ze pat_ty ; arg_tys' <- zonkTcTypeToTypes ze arg_tys ; let (env1, univ_tvs) = tidyTyVarBinders emptyTidyEnv univ_tvs' (env2, ex_tvs) = tidyTyVarBinders env1 ex_tvs' req_theta = tidyTypes env2 req_theta' prov_theta = tidyTypes env2 prov_theta' arg_tys = tidyTypes env2 arg_tys' pat_ty = tidyType env2 pat_ty' ; traceTc "tc_patsyn_finish {" $ ppr (unLoc lname) $$ ppr (unLoc lpat') $$ ppr (univ_tvs, req_theta, req_ev_binds, req_dicts) $$ ppr (ex_tvs, prov_theta, prov_dicts) $$ ppr args $$ ppr arg_tys $$ ppr pat_ty -- Make the 'matcher' ; (matcher_id, matcher_bind) <- tcPatSynMatcher lname lpat' (binderVars univ_tvs, req_theta, req_ev_binds, req_dicts) (binderVars ex_tvs, ex_tys, prov_theta, prov_dicts) (args, arg_tys) pat_ty -- Make the 'builder' ; builder_id <- mkPatSynBuilderId dir lname univ_tvs req_theta ex_tvs prov_theta arg_tys pat_ty -- TODO: Make this have the proper information ; let mkFieldLabel name = FieldLabel { flLabel = occNameFS (nameOccName name) , flIsOverloaded = False , flSelector = name } field_labels' = map mkFieldLabel field_labels -- Make the PatSyn itself ; let patSyn = mkPatSyn (unLoc lname) is_infix (univ_tvs, req_theta) (ex_tvs, prov_theta) arg_tys pat_ty matcher_id builder_id field_labels' -- Selectors ; let rn_rec_sel_binds = mkPatSynRecSelBinds patSyn (patSynFieldLabels patSyn) tything = AConLike (PatSynCon patSyn) ; tcg_env <- tcExtendGlobalEnv [tything] $ tcRecSelBinds rn_rec_sel_binds ; traceTc "tc_patsyn_finish }" empty ; return (matcher_bind, tcg_env) } {- ************************************************************************ * * Constructing the "matcher" Id and its binding * * ************************************************************************ -} tcPatSynMatcher :: Located Name -> LPat GhcTc -> ([TcTyVar], ThetaType, TcEvBinds, [EvVar]) -> ([TcTyVar], [TcType], ThetaType, [EvTerm]) -> ([LHsExpr GhcTcId], [TcType]) -> TcType -> TcM ((Id, Bool), LHsBinds GhcTc) -- See Note [Matchers and builders for pattern synonyms] in PatSyn tcPatSynMatcher (L loc name) lpat (univ_tvs, req_theta, req_ev_binds, req_dicts) (ex_tvs, ex_tys, prov_theta, prov_dicts) (args, arg_tys) pat_ty = do { rr_name <- newNameAt (mkTyVarOcc "rep") loc ; tv_name <- newNameAt (mkTyVarOcc "r") loc ; let rr_tv = mkTyVar rr_name runtimeRepTy rr = mkTyVarTy rr_tv res_tv = mkTyVar tv_name (tYPE rr) res_ty = mkTyVarTy res_tv is_unlifted = null args && null prov_dicts (cont_args, cont_arg_tys) | is_unlifted = ([nlHsVar voidPrimId], [voidPrimTy]) | otherwise = (args, arg_tys) cont_ty = mkInfSigmaTy ex_tvs prov_theta $ mkFunTys cont_arg_tys res_ty fail_ty = mkFunTy voidPrimTy res_ty ; matcher_name <- newImplicitBinder name mkMatcherOcc ; scrutinee <- newSysLocalId (fsLit "scrut") pat_ty ; cont <- newSysLocalId (fsLit "cont") cont_ty ; fail <- newSysLocalId (fsLit "fail") fail_ty ; let matcher_tau = mkFunTys [pat_ty, cont_ty, fail_ty] res_ty matcher_sigma = mkInfSigmaTy (rr_tv:res_tv:univ_tvs) req_theta matcher_tau matcher_id = mkExportedVanillaId matcher_name matcher_sigma -- See Note [Exported LocalIds] in Id inst_wrap = mkWpEvApps prov_dicts <.> mkWpTyApps ex_tys cont' = foldl nlHsApp (mkLHsWrap inst_wrap (nlHsVar cont)) cont_args fail' = nlHsApps fail [nlHsVar voidPrimId] args = map nlVarPat [scrutinee, cont, fail] lwpat = noLoc $ WildPat pat_ty cases = if isIrrefutableHsPat lpat then [mkHsCaseAlt lpat cont'] else [mkHsCaseAlt lpat cont', mkHsCaseAlt lwpat fail'] body = mkLHsWrap (mkWpLet req_ev_binds) $ L (getLoc lpat) $ HsCase noExt (nlHsVar scrutinee) $ MG{ mg_alts = L (getLoc lpat) cases , mg_ext = MatchGroupTc [pat_ty] res_ty , mg_origin = Generated } body' = noLoc $ HsLam noExt $ MG{ mg_alts = noLoc [mkSimpleMatch LambdaExpr args body] , mg_ext = MatchGroupTc [pat_ty, cont_ty, fail_ty] res_ty , mg_origin = Generated } match = mkMatch (mkPrefixFunRhs (L loc name)) [] (mkHsLams (rr_tv:res_tv:univ_tvs) req_dicts body') (noLoc (EmptyLocalBinds noExt)) mg :: MatchGroup GhcTc (LHsExpr GhcTc) mg = MG{ mg_alts = L (getLoc match) [match] , mg_ext = MatchGroupTc [] res_ty , mg_origin = Generated } ; let bind = FunBind{ fun_ext = emptyNameSet , fun_id = L loc matcher_id , fun_matches = mg , fun_co_fn = idHsWrapper , fun_tick = [] } matcher_bind = unitBag (noLoc bind) ; traceTc "tcPatSynMatcher" (ppr name $$ ppr (idType matcher_id)) ; traceTc "tcPatSynMatcher" (ppr matcher_bind) ; return ((matcher_id, is_unlifted), matcher_bind) } mkPatSynRecSelBinds :: PatSyn -> [FieldLabel] -- ^ Visible field labels -> [(Id, LHsBind GhcRn)] mkPatSynRecSelBinds ps fields = [ mkOneRecordSelector [PatSynCon ps] (RecSelPatSyn ps) fld_lbl | fld_lbl <- fields ] isUnidirectional :: HsPatSynDir a -> Bool isUnidirectional Unidirectional = True isUnidirectional ImplicitBidirectional = False isUnidirectional ExplicitBidirectional{} = False {- ************************************************************************ * * Constructing the "builder" Id * * ************************************************************************ -} mkPatSynBuilderId :: HsPatSynDir a -> Located Name -> [TyVarBinder] -> ThetaType -> [TyVarBinder] -> ThetaType -> [Type] -> Type -> TcM (Maybe (Id, Bool)) mkPatSynBuilderId dir (L _ name) univ_bndrs req_theta ex_bndrs prov_theta arg_tys pat_ty | isUnidirectional dir = return Nothing | otherwise = do { builder_name <- newImplicitBinder name mkBuilderOcc ; let theta = req_theta ++ prov_theta need_dummy_arg = isUnliftedType pat_ty && null arg_tys && null theta builder_sigma = add_void need_dummy_arg $ mkForAllTys univ_bndrs $ mkForAllTys ex_bndrs $ mkFunTys theta $ mkFunTys arg_tys $ pat_ty builder_id = mkExportedVanillaId builder_name builder_sigma -- See Note [Exported LocalIds] in Id builder_id' = modifyIdInfo (`setLevityInfoWithType` pat_ty) builder_id ; return (Just (builder_id', need_dummy_arg)) } where tcPatSynBuilderBind :: PatSynBind GhcRn GhcRn -> TcM (LHsBinds GhcTc) -- See Note [Matchers and builders for pattern synonyms] in PatSyn tcPatSynBuilderBind (PSB { psb_id = L loc name, psb_def = lpat , psb_dir = dir, psb_args = details }) | isUnidirectional dir = return emptyBag | Left why <- mb_match_group -- Can't invert the pattern = setSrcSpan (getLoc lpat) $ failWithTc $ vcat [ hang (text "Invalid right-hand side of bidirectional pattern synonym" <+> quotes (ppr name) <> colon) 2 why , text "RHS pattern:" <+> ppr lpat ] | Right match_group <- mb_match_group -- Bidirectional = do { patsyn <- tcLookupPatSyn name ; case patSynBuilder patsyn of { Nothing -> return emptyBag ; -- This case happens if we found a type error in the -- pattern synonym, recovered, and put a placeholder -- with patSynBuilder=Nothing in the environment Just (builder_id, need_dummy_arg) -> -- Normal case do { -- Bidirectional, so patSynBuilder returns Just let match_group' | need_dummy_arg = add_dummy_arg match_group | otherwise = match_group bind = FunBind { fun_ext = placeHolderNamesTc , fun_id = L loc (idName builder_id) , fun_matches = match_group' , fun_co_fn = idHsWrapper , fun_tick = [] } sig = completeSigFromId (PatSynCtxt name) builder_id ; traceTc "tcPatSynBuilderBind {" $ ppr patsyn $$ ppr builder_id <+> dcolon <+> ppr (idType builder_id) ; (builder_binds, _) <- tcPolyCheck emptyPragEnv sig (noLoc bind) ; traceTc "tcPatSynBuilderBind }" $ ppr builder_binds ; return builder_binds } } } | otherwise = panic "tcPatSynBuilderBind" -- Both cases dealt with where mb_match_group = case dir of ExplicitBidirectional explicit_mg -> Right explicit_mg ImplicitBidirectional -> fmap mk_mg (tcPatToExpr name args lpat) Unidirectional -> panic "tcPatSynBuilderBind" mk_mg :: LHsExpr GhcRn -> MatchGroup GhcRn (LHsExpr GhcRn) mk_mg body = mkMatchGroup Generated [builder_match] where builder_args = [L loc (VarPat noExt (L loc n)) | L loc n <- args] builder_match = mkMatch (mkPrefixFunRhs (L loc name)) builder_args body (noLoc (EmptyLocalBinds noExt)) args = case details of PrefixCon args -> args InfixCon arg1 arg2 -> [arg1, arg2] RecCon args -> map recordPatSynPatVar args add_dummy_arg :: MatchGroup GhcRn (LHsExpr GhcRn) -> MatchGroup GhcRn (LHsExpr GhcRn) add_dummy_arg mg@(MG { mg_alts = L l [L loc match@(Match { m_pats = pats })] }) = mg { mg_alts = L l [L loc (match { m_pats = nlWildPatName : pats })] } add_dummy_arg other_mg = pprPanic "add_dummy_arg" $ pprMatches other_mg tcPatSynBuilderBind (XPatSynBind _) = panic "tcPatSynBuilderBind" tcPatSynBuilderOcc :: PatSyn -> TcM (HsExpr GhcTcId, TcSigmaType) -- monadic only for failure tcPatSynBuilderOcc ps | Just (builder_id, add_void_arg) <- builder , let builder_expr = HsConLikeOut noExt (PatSynCon ps) builder_ty = idType builder_id = return $ if add_void_arg then ( builder_expr -- still just return builder_expr; the void# arg is added -- by dsConLike in the desugarer , tcFunResultTy builder_ty ) else (builder_expr, builder_ty) | otherwise -- Unidirectional = nonBidirectionalErr name where name = patSynName ps builder = patSynBuilder ps add_void :: Bool -> Type -> Type add_void need_dummy_arg ty | need_dummy_arg = mkFunTy voidPrimTy ty | otherwise = ty tcPatToExpr :: Name -> [Located Name] -> LPat GhcRn -> Either MsgDoc (LHsExpr GhcRn) -- Given a /pattern/, return an /expression/ that builds a value -- that matches the pattern. E.g. if the pattern is (Just [x]), -- the expression is (Just [x]). They look the same, but the -- input uses constructors from HsPat and the output uses constructors -- from HsExpr. -- -- Returns (Left r) if the pattern is not invertible, for reason r. -- See Note [Builder for a bidirectional pattern synonym] tcPatToExpr name args pat = go pat where lhsVars = mkNameSet (map unLoc args) -- Make a prefix con for prefix and infix patterns for simplicity mkPrefixConExpr :: Located Name -> [LPat GhcRn] -> Either MsgDoc (HsExpr GhcRn) mkPrefixConExpr lcon@(L loc _) pats = do { exprs <- mapM go pats ; return (foldl (\x y -> HsApp noExt (L loc x) y) (HsVar noExt lcon) exprs) } mkRecordConExpr :: Located Name -> HsRecFields GhcRn (LPat GhcRn) -> Either MsgDoc (HsExpr GhcRn) mkRecordConExpr con fields = do { exprFields <- mapM go fields ; return (RecordCon noExt con exprFields) } go :: LPat GhcRn -> Either MsgDoc (LHsExpr GhcRn) go (L loc p) = L loc <$> go1 p go1 :: Pat GhcRn -> Either MsgDoc (HsExpr GhcRn) go1 (ConPatIn con info) = case info of PrefixCon ps -> mkPrefixConExpr con ps InfixCon l r -> mkPrefixConExpr con [l,r] RecCon fields -> mkRecordConExpr con fields go1 (SigPat _ pat) = go1 (unLoc pat) -- See Note [Type signatures and the builder expression] go1 (VarPat _ (L l var)) | var `elemNameSet` lhsVars = return $ HsVar noExt (L l var) | otherwise = Left (quotes (ppr var) <+> text "is not bound by the LHS of the pattern synonym") go1 (ParPat _ pat) = fmap (HsPar noExt) $ go pat go1 p@(ListPat reb pats) | Nothing <- reb = do { exprs <- mapM go pats ; return $ ExplicitList noExt Nothing exprs } | otherwise = notInvertibleListPat p go1 (TuplePat _ pats box) = do { exprs <- mapM go pats ; return $ ExplicitTuple noExt (map (noLoc . (Present noExt)) exprs) box } go1 (SumPat _ pat alt arity) = do { expr <- go1 (unLoc pat) ; return $ ExplicitSum noExt alt arity (noLoc expr) } go1 (LitPat _ lit) = return $ HsLit noExt lit go1 (NPat _ (L _ n) mb_neg _) | Just neg <- mb_neg = return $ unLoc $ nlHsSyntaxApps neg [noLoc (HsOverLit noExt n)] | otherwise = return $ HsOverLit noExt n go1 (ConPatOut{}) = panic "ConPatOut in output of renamer" go1 (CoPat{}) = panic "CoPat in output of renamer" go1 (SplicePat _ (HsSpliced _ _ (HsSplicedPat pat))) = go1 pat go1 (SplicePat _ (HsSpliced{})) = panic "Invalid splice variety" -- The following patterns are not invertible. go1 p@(BangPat {}) = notInvertible p -- #14112 go1 p@(LazyPat {}) = notInvertible p go1 p@(WildPat {}) = notInvertible p go1 p@(AsPat {}) = notInvertible p go1 p@(ViewPat {}) = notInvertible p go1 p@(NPlusKPat {}) = notInvertible p go1 p@(XPat {}) = notInvertible p go1 p@(SplicePat _ (HsTypedSplice {})) = notInvertible p go1 p@(SplicePat _ (HsUntypedSplice {})) = notInvertible p go1 p@(SplicePat _ (HsQuasiQuote {})) = notInvertible p go1 p@(SplicePat _ (XSplice {})) = notInvertible p notInvertible p = Left (not_invertible_msg p) not_invertible_msg p = text "Pattern" <+> quotes (ppr p) <+> text "is not invertible" $+$ hang (text "Suggestion: instead use an explicitly bidirectional" <+> text "pattern synonym, e.g.") 2 (hang (text "pattern" <+> pp_name <+> pp_args <+> larrow <+> ppr pat <+> text "where") 2 (pp_name <+> pp_args <+> equals <+> text "...")) where pp_name = ppr name pp_args = hsep (map ppr args) -- We should really be able to invert list patterns, even when -- rebindable syntax is on, but doing so involves a bit of -- refactoring; see Trac #14380. Until then we reject with a -- helpful error message. notInvertibleListPat p = Left (vcat [ not_invertible_msg p , text "Reason: rebindable syntax is on." , text "This is fixable: add use-case to Trac #14380" ]) {- Note [Builder for a bidirectional pattern synonym] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ For a bidirectional pattern synonym we need to produce an /expression/ that matches the supplied /pattern/, given values for the arguments of the pattern synoymy. For example pattern F x y = (Just x, [y]) The 'builder' for F looks like $builderF x y = (Just x, [y]) We can't always do this: * Some patterns aren't invertible; e.g. view patterns pattern F x = (reverse -> x:_) * The RHS pattern might bind more variables than the pattern synonym, so again we can't invert it pattern F x = (x,y) * Ditto wildcards pattern F x = (x,_) Note [Redundant constraints for builder] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The builder can have redundant constraints, which are awkard to eliminate. Consider pattern P = Just 34 To match against this pattern we need (Eq a, Num a). But to build (Just 34) we need only (Num a). Fortunately instTcSigFromId sets sig_warn_redundant to False. ************************************************************************ * * Helper functions * * ************************************************************************ Note [As-patterns in pattern synonym definitions] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The rationale for rejecting as-patterns in pattern synonym definitions is that an as-pattern would introduce nonindependent pattern synonym arguments, e.g. given a pattern synonym like: pattern K x y = x@(Just y) one could write a nonsensical function like f (K Nothing x) = ... or g (K (Just True) False) = ... Note [Type signatures and the builder expression] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider pattern L x = Left x :: Either [a] [b] In tc{Infer/Check}PatSynDecl we will check that the pattern has the specified type. We check the pattern *as a pattern*, so the type signature is a pattern signature, and so brings 'a' and 'b' into scope. But we don't have a way to bind 'a, b' in the LHS, as we do 'x', say. Nevertheless, the sigature may be useful to constrain the type. When making the binding for the *builder*, though, we don't want $buildL x = Left x :: Either [a] [b] because that wil either mean (forall a b. Either [a] [b]), or we'll get a complaint that 'a' and 'b' are out of scope. (Actually the latter; Trac #9867.) No, the job of the signature is done, so when converting the pattern to an expression (for the builder RHS) we simply discard the signature. Note [Record PatSyn Desugaring] ------------------------------- It is important that prov_theta comes before req_theta as this ordering is used when desugaring record pattern synonym updates. Any change to this ordering should make sure to change deSugar/DsExpr.hs if you want to avoid difficult to decipher core lint errors! -} nonBidirectionalErr :: Outputable name => name -> TcM a nonBidirectionalErr name = failWithTc $ text "non-bidirectional pattern synonym" <+> quotes (ppr name) <+> text "used in an expression" -- Walk the whole pattern and for all ConPatOuts, collect the -- existentially-bound type variables and evidence binding variables. -- -- These are used in computing the type of a pattern synonym and also -- in generating matcher functions, since success continuations need -- to be passed these pattern-bound evidences. tcCollectEx :: LPat GhcTc -> ( [TyVar] -- Existentially-bound type variables -- in correctly-scoped order; e.g. [ k:*, x:k ] , [EvVar] ) -- and evidence variables tcCollectEx pat = go pat where go :: LPat GhcTc -> ([TyVar], [EvVar]) go = go1 . unLoc go1 :: Pat GhcTc -> ([TyVar], [EvVar]) go1 (LazyPat _ p) = go p go1 (AsPat _ _ p) = go p go1 (ParPat _ p) = go p go1 (BangPat _ p) = go p go1 (ListPat _ ps) = mergeMany . map go $ ps go1 (TuplePat _ ps _) = mergeMany . map go $ ps go1 (SumPat _ p _ _) = go p go1 (ViewPat _ _ p) = go p go1 con@ConPatOut{} = merge (pat_tvs con, pat_dicts con) $ goConDetails $ pat_args con go1 (SigPat _ p) = go p go1 (CoPat _ _ p _) = go1 p go1 (NPlusKPat _ n k _ geq subtract) = pprPanic "TODO: NPlusKPat" $ ppr n $$ ppr k $$ ppr geq $$ ppr subtract go1 _ = empty goConDetails :: HsConPatDetails GhcTc -> ([TyVar], [EvVar]) goConDetails (PrefixCon ps) = mergeMany . map go $ ps goConDetails (InfixCon p1 p2) = go p1 `merge` go p2 goConDetails (RecCon HsRecFields{ rec_flds = flds }) = mergeMany . map goRecFd $ flds goRecFd :: LHsRecField GhcTc (LPat GhcTc) -> ([TyVar], [EvVar]) goRecFd (L _ HsRecField{ hsRecFieldArg = p }) = go p merge (vs1, evs1) (vs2, evs2) = (vs1 ++ vs2, evs1 ++ evs2) mergeMany = foldr merge empty empty = ([], [])