% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[TcBinds]{TcBinds} \begin{code} module TcBinds ( tcLocalBinds, tcTopBinds, tcHsBootSigs, tcMonoBinds, TcPragFun, tcSpecPrag, tcPrags, mkPragFun, TcSigInfo(..), badBootDeclErr ) where #include "HsVersions.h" import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun ) import {-# SOURCE #-} TcExpr ( tcMonoExpr ) import DynFlags ( DynFlag(Opt_MonomorphismRestriction, Opt_GlasgowExts) ) import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..), HsLocalBinds(..), HsValBinds(..), HsIPBinds(..), LSig, Match(..), IPBind(..), Prag(..), HsType(..), LHsType, HsExplicitForAll(..), hsLTyVarNames, isVanillaLSig, sigName, placeHolderNames, isPragLSig, LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsCoerce, collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind ) import TcHsSyn ( zonkId ) import TcRnMonad import Inst ( newDictsAtLoc, newIPDict, instToId ) import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2, pprBinders, tcLookupLocalId_maybe, tcLookupId, tcGetGlobalTyVars ) import TcUnify ( tcInfer, tcSubExp, unifyTheta, bleatEscapedTvs, sigCtxt ) import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyIPs ) import TcHsType ( tcHsSigType, UserTypeCtxt(..) ) import TcPat ( tcPat, PatCtxt(..) ) import TcSimplify ( bindInstsOfLocalFuns ) import TcMType ( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar, tcInstSigTyVars, tcInstSkolTyVars, tcInstType, zonkTcType, zonkTcTypes, zonkTcTyVars ) import TcType ( TcType, TcTyVar, TcThetaType, SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt), TcTauType, TcSigmaType, isUnboxedTupleType, mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType, mkForAllTy, isUnLiftedType, tcGetTyVar, mkTyVarTys, tidyOpenTyVar ) import Kind ( argTypeKind ) import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv ) import TysWiredIn ( unitTy ) import TysPrim ( alphaTyVar ) import Id ( Id, mkLocalId, mkVanillaGlobal ) import IdInfo ( vanillaIdInfo ) import Var ( TyVar, idType, idName ) import Name ( Name ) import NameSet import NameEnv import VarSet import SrcLoc ( Located(..), unLoc, getLoc ) import Bag import ErrUtils ( Message ) import Digraph ( SCC(..), stronglyConnComp ) import Maybes ( expectJust, isJust, isNothing, orElse ) import Util ( singleton ) import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel, RecFlag(..), isNonRec, InlineSpec, defaultInlineSpec ) import Outputable \end{code} %************************************************************************ %* * \subsection{Type-checking bindings} %* * %************************************************************************ @tcBindsAndThen@ typechecks a @HsBinds@. The "and then" part is because it needs to know something about the {\em usage} of the things bound, so that it can create specialisations of them. So @tcBindsAndThen@ takes a function which, given an extended environment, E, typechecks the scope of the bindings returning a typechecked thing and (most important) an LIE. It is this LIE which is then used as the basis for specialising the things bound. @tcBindsAndThen@ also takes a "combiner" which glues together the bindings and the "thing" to make a new "thing". The real work is done by @tcBindWithSigsAndThen@. Recursive and non-recursive binds are handled in essentially the same way: because of uniques there are no scoping issues left. The only difference is that non-recursive bindings can bind primitive values. Even for non-recursive binding groups we add typings for each binder to the LVE for the following reason. When each individual binding is checked the type of its LHS is unified with that of its RHS; and type-checking the LHS of course requires that the binder is in scope. At the top-level the LIE is sure to contain nothing but constant dictionaries, which we resolve at the module level. \begin{code} tcTopBinds :: HsValBinds Name -> TcM (LHsBinds TcId, TcLclEnv) -- Note: returning the TcLclEnv is more than we really -- want. The bit we care about is the local bindings -- and the free type variables thereof tcTopBinds binds = do { (ValBindsOut prs _, env) <- tcValBinds TopLevel binds getLclEnv ; return (foldr (unionBags . snd) emptyBag prs, env) } -- The top level bindings are flattened into a giant -- implicitly-mutually-recursive LHsBinds tcHsBootSigs :: HsValBinds Name -> TcM [Id] -- A hs-boot file has only one BindGroup, and it only has type -- signatures in it. The renamer checked all this tcHsBootSigs (ValBindsOut binds sigs) = do { checkTc (null binds) badBootDeclErr ; mapM (addLocM tc_boot_sig) (filter isVanillaLSig sigs) } where tc_boot_sig (TypeSig (L _ name) ty) = do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty ; return (mkVanillaGlobal name sigma_ty vanillaIdInfo) } -- Notice that we make GlobalIds, not LocalIds tcHsBootSigs groups = pprPanic "tcHsBootSigs" (ppr groups) badBootDeclErr :: Message badBootDeclErr = ptext SLIT("Illegal declarations in an hs-boot file") ------------------------ tcLocalBinds :: HsLocalBinds Name -> TcM thing -> TcM (HsLocalBinds TcId, thing) tcLocalBinds EmptyLocalBinds thing_inside = do { thing <- thing_inside ; return (EmptyLocalBinds, thing) } tcLocalBinds (HsValBinds binds) thing_inside = do { (binds', thing) <- tcValBinds NotTopLevel binds thing_inside ; return (HsValBinds binds', thing) } tcLocalBinds (HsIPBinds (IPBinds ip_binds _)) thing_inside = do { (thing, lie) <- getLIE thing_inside ; (avail_ips, ip_binds') <- mapAndUnzipM (wrapLocSndM tc_ip_bind) ip_binds -- If the binding binds ?x = E, we must now -- discharge any ?x constraints in expr_lie ; dict_binds <- tcSimplifyIPs avail_ips lie ; return (HsIPBinds (IPBinds ip_binds' dict_binds), thing) } where -- I wonder if we should do these one at at time -- Consider ?x = 4 -- ?y = ?x + 1 tc_ip_bind (IPBind ip expr) = newFlexiTyVarTy argTypeKind `thenM` \ ty -> newIPDict (IPBindOrigin ip) ip ty `thenM` \ (ip', ip_inst) -> tcMonoExpr expr ty `thenM` \ expr' -> returnM (ip_inst, (IPBind ip' expr')) ------------------------ tcValBinds :: TopLevelFlag -> HsValBinds Name -> TcM thing -> TcM (HsValBinds TcId, thing) tcValBinds top_lvl (ValBindsIn binds sigs) thing_inside = pprPanic "tcValBinds" (ppr binds) tcValBinds top_lvl (ValBindsOut binds sigs) thing_inside = do { -- Typecheck the signature ; let { prag_fn = mkPragFun sigs ; ty_sigs = filter isVanillaLSig sigs ; sig_fn = mkSigFun ty_sigs } ; poly_ids <- mapM tcTySig ty_sigs -- Extend the envt right away with all -- the Ids declared with type signatures ; (binds', thing) <- tcExtendIdEnv poly_ids $ tc_val_binds top_lvl sig_fn prag_fn binds thing_inside ; return (ValBindsOut binds' sigs, thing) } ------------------------ tc_val_binds :: TopLevelFlag -> TcSigFun -> TcPragFun -> [(RecFlag, LHsBinds Name)] -> TcM thing -> TcM ([(RecFlag, LHsBinds TcId)], thing) -- Typecheck a whole lot of value bindings, -- one strongly-connected component at a time tc_val_binds top_lvl sig_fn prag_fn [] thing_inside = do { thing <- thing_inside ; return ([], thing) } tc_val_binds top_lvl sig_fn prag_fn (group : groups) thing_inside = do { (group', (groups', thing)) <- tc_group top_lvl sig_fn prag_fn group $ tc_val_binds top_lvl sig_fn prag_fn groups thing_inside ; return (group' ++ groups', thing) } ------------------------ tc_group :: TopLevelFlag -> TcSigFun -> TcPragFun -> (RecFlag, LHsBinds Name) -> TcM thing -> TcM ([(RecFlag, LHsBinds TcId)], thing) -- Typecheck one strongly-connected component of the original program. -- We get a list of groups back, because there may -- be specialisations etc as well tc_group top_lvl sig_fn prag_fn (NonRecursive, binds) thing_inside = -- A single non-recursive binding -- We want to keep non-recursive things non-recursive -- so that we desugar unlifted bindings correctly do { (binds, thing) <- tcPolyBinds top_lvl NonRecursive NonRecursive sig_fn prag_fn binds thing_inside ; return ([(NonRecursive, b) | b <- binds], thing) } tc_group top_lvl sig_fn prag_fn (Recursive, binds) thing_inside = -- A recursive strongly-connected component -- To maximise polymorphism (with -fglasgow-exts), we do a new -- strongly-connected-component analysis, this time omitting -- any references to variables with type signatures. -- -- Then we bring into scope all the variables with type signatures do { traceTc (text "tc_group rec" <+> pprLHsBinds binds) ; gla_exts <- doptM Opt_GlasgowExts ; (binds,thing) <- if gla_exts then go new_sccs else tc_binds Recursive binds thing_inside ; return ([(Recursive, unionManyBags binds)], thing) } -- Rec them all together where new_sccs :: [SCC (LHsBind Name)] new_sccs = stronglyConnComp (mkEdges sig_fn binds) -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], thing) go (scc:sccs) = do { (binds1, (binds2, thing)) <- go1 scc (go sccs) ; return (binds1 ++ binds2, thing) } go [] = do { thing <- thing_inside; return ([], thing) } go1 (AcyclicSCC bind) = tc_binds NonRecursive (unitBag bind) go1 (CyclicSCC binds) = tc_binds Recursive (listToBag binds) tc_binds rec_tc binds = tcPolyBinds top_lvl Recursive rec_tc sig_fn prag_fn binds ------------------------ mkEdges :: TcSigFun -> LHsBinds Name -> [(LHsBind Name, BKey, [BKey])] type BKey = Int -- Just number off the bindings mkEdges sig_fn binds = [ (bind, key, [key | n <- nameSetToList (bind_fvs (unLoc bind)), Just key <- [lookupNameEnv key_map n], no_sig n ]) | (bind, key) <- keyd_binds ] where no_sig :: Name -> Bool no_sig n = isNothing (sig_fn n) keyd_binds = bagToList binds `zip` [0::BKey ..] key_map :: NameEnv BKey -- Which binding it comes from key_map = mkNameEnv [(bndr, key) | (L _ bind, key) <- keyd_binds , bndr <- bindersOfHsBind bind ] bindersOfHsBind :: HsBind Name -> [Name] bindersOfHsBind (PatBind { pat_lhs = pat }) = collectPatBinders pat bindersOfHsBind (FunBind { fun_id = L _ f }) = [f] ------------------------ tcPolyBinds :: TopLevelFlag -> RecFlag -- Whether the group is really recursive -> RecFlag -- Whether it's recursive for typechecking purposes -> TcSigFun -> TcPragFun -> LHsBinds Name -> TcM thing -> TcM ([LHsBinds TcId], thing) -- Typechecks a single bunch of bindings all together, -- and generalises them. The bunch may be only part of a recursive -- group, because we use type signatures to maximise polymorphism -- -- Deals with the bindInstsOfLocalFuns thing too -- -- Returns a list because the input may be a single non-recursive binding, -- in which case the dependency order of the resulting bindings is -- important. tcPolyBinds top_lvl rec_group rec_tc sig_fn prag_fn scc thing_inside = -- NB: polymorphic recursion means that a function -- may use an instance of itself, we must look at the LIE arising -- from the function's own right hand side. Hence the getLIE -- encloses the tc_poly_binds. do { traceTc (text "tcPolyBinds" <+> ppr scc) ; ((binds1, poly_ids, thing), lie) <- getLIE $ do { (binds1, poly_ids) <- tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn scc ; thing <- tcExtendIdEnv poly_ids thing_inside ; return (binds1, poly_ids, thing) } ; if isTopLevel top_lvl then -- For the top level don't bother will all this -- bindInstsOfLocalFuns stuff. All the top level -- things are rec'd together anyway, so it's fine to -- leave them to the tcSimplifyTop, -- and quite a bit faster too do { extendLIEs lie; return (binds1, thing) } else do -- Nested case { lie_binds <- bindInstsOfLocalFuns lie poly_ids ; return (binds1 ++ [lie_binds], thing) }} ------------------------ tc_poly_binds :: TopLevelFlag -- See comments on tcPolyBinds -> RecFlag -> RecFlag -> TcSigFun -> TcPragFun -> LHsBinds Name -> TcM ([LHsBinds TcId], [TcId]) -- Typechecks the bindings themselves -- Knows nothing about the scope of the bindings tc_poly_binds top_lvl rec_group rec_tc sig_fn prag_fn binds = let binder_names = collectHsBindBinders binds bind_list = bagToList binds loc = getLoc (head bind_list) -- TODO: location a bit awkward, but the mbinds have been -- dependency analysed and may no longer be adjacent in -- SET UP THE MAIN RECOVERY; take advantage of any type sigs setSrcSpan loc $ recoverM (recoveryCode binder_names) $ do { traceTc (ptext SLIT("------------------------------------------------")) ; traceTc (ptext SLIT("Bindings for") <+> ppr binder_names) -- TYPECHECK THE BINDINGS ; ((binds', mono_bind_infos), lie_req) <- getLIE (tcMonoBinds bind_list sig_fn rec_tc) -- CHECK FOR UNLIFTED BINDINGS -- These must be non-recursive etc, and are not generalised -- They desugar to a case expression in the end ; zonked_mono_tys <- zonkTcTypes (map getMonoType mono_bind_infos) ; is_strict <- checkStrictBinds top_lvl rec_group binds' zonked_mono_tys mono_bind_infos ; if is_strict then do { extendLIEs lie_req ; let exports = zipWith mk_export mono_bind_infos zonked_mono_tys mk_export (name, Nothing, mono_id) mono_ty = ([], mkLocalId name mono_ty, mono_id, []) mk_export (name, Just sig, mono_id) mono_ty = ([], sig_id sig, mono_id, []) -- ToDo: prags for unlifted bindings ; return ( [unitBag $ L loc $ AbsBinds [] [] exports binds'], [poly_id | (_, poly_id, _, _) <- exports]) } -- Guaranteed zonked else do -- The normal lifted case: GENERALISE { is_unres <- isUnRestrictedGroup bind_list sig_fn ; (tyvars_to_gen, dict_binds, dict_ids) <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $ generalise top_lvl is_unres mono_bind_infos lie_req -- FINALISE THE QUANTIFIED TYPE VARIABLES -- The quantified type variables often include meta type variables -- we want to freeze them into ordinary type variables, and -- default their kind (e.g. from OpenTypeKind to TypeKind) ; tyvars_to_gen' <- mappM zonkQuantifiedTyVar tyvars_to_gen -- BUILD THE POLYMORPHIC RESULT IDs ; exports <- mapM (mkExport prag_fn tyvars_to_gen' (map idType dict_ids)) mono_bind_infos -- ZONK THE poly_ids, because they are used to extend the type -- environment; see the invariant on TcEnv.tcExtendIdEnv ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports] ; zonked_poly_ids <- mappM zonkId poly_ids ; traceTc (text "binding:" <+> ppr (zonked_poly_ids `zip` map idType zonked_poly_ids)) ; let abs_bind = L loc $ AbsBinds tyvars_to_gen' dict_ids exports (dict_binds `unionBags` binds') ; return ([unitBag abs_bind], zonked_poly_ids) } } -------------- mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo -> TcM ([TyVar], Id, Id, [Prag]) mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id) = case mb_sig of Nothing -> do { prags <- tcPrags poly_id (prag_fn poly_name) ; return (inferred_tvs, poly_id, mono_id, prags) } where poly_id = mkLocalId poly_name poly_ty poly_ty = mkForAllTys inferred_tvs $ mkFunTys dict_tys $ idType mono_id Just sig -> do { let poly_id = sig_id sig ; prags <- tcPrags poly_id (prag_fn poly_name) ; sig_tys <- zonkTcTyVars (sig_tvs sig) ; let sig_tvs' = map (tcGetTyVar "mkExport") sig_tys ; return (sig_tvs', poly_id, mono_id, prags) } -- We zonk the sig_tvs here so that the export triple -- always has zonked type variables; -- a convenient invariant ------------------------ type TcPragFun = Name -> [LSig Name] mkPragFun :: [LSig Name] -> TcPragFun mkPragFun sigs = \n -> lookupNameEnv env n `orElse` [] where prs = [(expectJust "mkPragFun" (sigName sig), sig) | sig <- sigs, isPragLSig sig] env = foldl add emptyNameEnv prs add env (n,p) = extendNameEnv_Acc (:) singleton env n p tcPrags :: Id -> [LSig Name] -> TcM [Prag] tcPrags poly_id prags = mapM tc_prag prags where tc_prag (L loc prag) = setSrcSpan loc $ addErrCtxt (pragSigCtxt prag) $ tcPrag poly_id prag pragSigCtxt prag = hang (ptext SLIT("In the pragma")) 2 (ppr prag) tcPrag :: TcId -> Sig Name -> TcM Prag tcPrag poly_id (SpecSig orig_name hs_ty inl) = tcSpecPrag poly_id hs_ty inl tcPrag poly_id (SpecInstSig hs_ty) = tcSpecPrag poly_id hs_ty defaultInlineSpec tcPrag poly_id (InlineSig v inl) = return (InlinePrag inl) tcSpecPrag :: TcId -> LHsType Name -> InlineSpec -> TcM Prag tcSpecPrag poly_id hs_ty inl = do { spec_ty <- tcHsSigType (FunSigCtxt (idName poly_id)) hs_ty ; (co_fn, lie) <- getLIE (tcSubExp (idType poly_id) spec_ty) ; extendLIEs lie ; let const_dicts = map instToId lie ; return (SpecPrag (mkHsCoerce co_fn (HsVar poly_id)) spec_ty const_dicts inl) } -------------- -- If typechecking the binds fails, then return with each -- signature-less binder given type (forall a.a), to minimise -- subsequent error messages recoveryCode binder_names = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names) ; poly_ids <- mapM mk_dummy binder_names ; return ([], poly_ids) } where mk_dummy name = do { mb_id <- tcLookupLocalId_maybe name ; case mb_id of Just id -> return id -- Had signature, was in envt Nothing -> return (mkLocalId name forall_a_a) } -- No signature forall_a_a :: TcType forall_a_a = mkForAllTy alphaTyVar (mkTyVarTy alphaTyVar) -- Check that non-overloaded unlifted bindings are -- a) non-recursive, -- b) not top level, -- c) not a multiple-binding group (more or less implied by (a)) checkStrictBinds :: TopLevelFlag -> RecFlag -> LHsBinds TcId -> [TcType] -> [MonoBindInfo] -> TcM Bool checkStrictBinds top_lvl rec_group mbind mono_tys infos | unlifted || bang_pat = do { checkTc (isNotTopLevel top_lvl) (strictBindErr "Top-level" unlifted mbind) ; checkTc (isNonRec rec_group) (strictBindErr "Recursive" unlifted mbind) ; checkTc (isSingletonBag mbind) (strictBindErr "Multiple" unlifted mbind) ; mapM_ check_sig infos ; return True } | otherwise = return False where unlifted = any isUnLiftedType mono_tys bang_pat = anyBag (isBangHsBind . unLoc) mbind check_sig (_, Just sig, _) = checkTc (null (sig_tvs sig) && null (sig_theta sig)) (badStrictSig unlifted sig) check_sig other = return () strictBindErr flavour unlifted mbind = hang (text flavour <+> msg <+> ptext SLIT("aren't allowed:")) 4 (ppr mbind) where msg | unlifted = ptext SLIT("bindings for unlifted types") | otherwise = ptext SLIT("bang-pattern bindings") badStrictSig unlifted sig = hang (ptext SLIT("Illegal polymorphic signature in") <+> msg) 4 (ppr sig) where msg | unlifted = ptext SLIT("an unlifted binding") | otherwise = ptext SLIT("a bang-pattern binding") \end{code} %************************************************************************ %* * \subsection{tcMonoBind} %* * %************************************************************************ @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds. The signatures have been dealt with already. \begin{code} tcMonoBinds :: [LHsBind Name] -> TcSigFun -> RecFlag -- Whether the binding is recursive for typechecking purposes -- i.e. the binders are mentioned in their RHSs, and -- we are not resuced by a type signature -> TcM (LHsBinds TcId, [MonoBindInfo]) tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches, bind_fvs = fvs })] sig_fn -- Single function binding, NonRecursive -- binder isn't mentioned in RHS, | Nothing <- sig_fn name -- ...with no type signature = -- In this very special case we infer the type of the -- right hand side first (it may have a higher-rank type) -- and *then* make the monomorphic Id for the LHS -- e.g. f = \(x::forall a. a->a) ->
-- We want to infer a higher-rank type for f setSrcSpan b_loc $ do { ((co_fn, matches'), rhs_ty) <- tcInfer (tcMatchesFun name matches) -- Check for an unboxed tuple type -- f = (# True, False #) -- Zonk first just in case it's hidden inside a meta type variable -- (This shows up as a (more obscure) kind error -- in the 'otherwise' case of tcMonoBinds.) ; zonked_rhs_ty <- zonkTcType rhs_ty ; checkTc (not (isUnboxedTupleType zonked_rhs_ty)) (unboxedTupleErr name zonked_rhs_ty) ; mono_name <- newLocalName name ; let mono_id = mkLocalId mono_name zonked_rhs_ty ; return (unitBag (L b_loc (FunBind { fun_id = L nm_loc mono_id, fun_infix = inf, fun_matches = matches', bind_fvs = fvs, fun_co_fn = co_fn })), [(name, Nothing, mono_id)]) } tcMonoBinds [L b_loc (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches, bind_fvs = fvs })] sig_fn -- Single function binding non_rec | Just sig <- sig_fn name -- ...with a type signature = -- When we have a single function binding, with a type signature -- we can (a) use genuine, rigid skolem constants for the type variables -- (b) bring (rigid) scoped type variables into scope setSrcSpan b_loc $ do { tc_sig <- tcInstSig True sig ; mono_name <- newLocalName name ; let mono_ty = sig_tau tc_sig mono_id = mkLocalId mono_name mono_ty rhs_tvs = [ (name, mkTyVarTy tv) | (name, tv) <- sig_scoped tc_sig `zip` sig_tvs tc_sig ] ; (co_fn, matches') <- tcExtendTyVarEnv2 rhs_tvs $ tcMatchesFun mono_name matches mono_ty ; let fun_bind' = FunBind { fun_id = L nm_loc mono_id, fun_infix = inf, fun_matches = matches', bind_fvs = placeHolderNames, fun_co_fn = co_fn } ; return (unitBag (L b_loc fun_bind'), [(name, Just tc_sig, mono_id)]) } tcMonoBinds binds sig_fn non_rec = do { tc_binds <- mapM (wrapLocM (tcLhs sig_fn)) binds -- Bring the monomorphic Ids, into scope for the RHSs ; let mono_info = getMonoBindInfo tc_binds rhs_id_env = [(name,mono_id) | (name, Nothing, mono_id) <- mono_info] -- A monomorphic binding for each term variable that lacks -- a type sig. (Ones with a sig are already in scope.) ; binds' <- tcExtendIdEnv2 rhs_id_env $ traceTc (text "tcMonoBinds" <+> vcat [ ppr n <+> ppr id <+> ppr (idType id) | (n,id) <- rhs_id_env]) `thenM_` mapM (wrapLocM tcRhs) tc_binds ; return (listToBag binds', mono_info) } ------------------------ -- tcLhs typechecks the LHS of the bindings, to construct the environment in which -- we typecheck the RHSs. Basically what we are doing is this: for each binder: -- if there's a signature for it, use the instantiated signature type -- otherwise invent a type variable -- You see that quite directly in the FunBind case. -- -- But there's a complication for pattern bindings: -- data T = MkT (forall a. a->a) -- MkT f = e -- Here we can guess a type variable for the entire LHS (which will be refined to T) -- but we want to get (f::forall a. a->a) as the RHS environment. -- The simplest way to do this is to typecheck the pattern, and then look up the -- bound mono-ids. Then we want to retain the typechecked pattern to avoid re-doing -- it; hence the TcMonoBind data type in which the LHS is done but the RHS isn't data TcMonoBind -- Half completed; LHS done, RHS not done = TcFunBind MonoBindInfo (Located TcId) Bool (MatchGroup Name) | TcPatBind [MonoBindInfo] (LPat TcId) (GRHSs Name) TcSigmaType type MonoBindInfo = (Name, Maybe TcSigInfo, TcId) -- Type signature (if any), and -- the monomorphic bound things bndrNames :: [MonoBindInfo] -> [Name] bndrNames mbi = [n | (n,_,_) <- mbi] getMonoType :: MonoBindInfo -> TcTauType getMonoType (_,_,mono_id) = idType mono_id tcLhs :: TcSigFun -> HsBind Name -> TcM TcMonoBind tcLhs sig_fn (FunBind { fun_id = L nm_loc name, fun_infix = inf, fun_matches = matches }) = do { mb_sig <- tcInstSig_maybe (sig_fn name) ; mono_name <- newLocalName name ; mono_ty <- mk_mono_ty mb_sig ; let mono_id = mkLocalId mono_name mono_ty ; return (TcFunBind (name, mb_sig, mono_id) (L nm_loc mono_id) inf matches) } where mk_mono_ty (Just sig) = return (sig_tau sig) mk_mono_ty Nothing = newFlexiTyVarTy argTypeKind tcLhs sig_fn bind@(PatBind { pat_lhs = pat, pat_rhs = grhss }) = do { mb_sigs <- mapM (tcInstSig_maybe . sig_fn) names ; let nm_sig_prs = names `zip` mb_sigs tau_sig_env = mkNameEnv [ (name, sig_tau sig) | (name, Just sig) <- nm_sig_prs] sig_tau_fn = lookupNameEnv tau_sig_env tc_pat exp_ty = tcPat (LetPat sig_tau_fn) pat exp_ty unitTy $ \ _ -> mapM lookup_info nm_sig_prs -- The unitTy is a bit bogus; it's the "result type" for lookup_info. -- After typechecking the pattern, look up the binder -- names, which the pattern has brought into scope. lookup_info :: (Name, Maybe TcSigInfo) -> TcM MonoBindInfo lookup_info (name, mb_sig) = do { mono_id <- tcLookupId name ; return (name, mb_sig, mono_id) } ; ((pat', infos), pat_ty) <- addErrCtxt (patMonoBindsCtxt pat grhss) $ tcInfer tc_pat ; return (TcPatBind infos pat' grhss pat_ty) } where names = collectPatBinders pat tcLhs sig_fn other_bind = pprPanic "tcLhs" (ppr other_bind) -- AbsBind, VarBind impossible ------------------- tcRhs :: TcMonoBind -> TcM (HsBind TcId) tcRhs (TcFunBind info fun'@(L _ mono_id) inf matches) = do { (co_fn, matches') <- tcMatchesFun (idName mono_id) matches (idType mono_id) ; return (FunBind { fun_id = fun', fun_infix = inf, fun_matches = matches', bind_fvs = placeHolderNames, fun_co_fn = co_fn }) } tcRhs bind@(TcPatBind _ pat' grhss pat_ty) = do { grhss' <- addErrCtxt (patMonoBindsCtxt pat' grhss) $ tcGRHSsPat grhss pat_ty ; return (PatBind { pat_lhs = pat', pat_rhs = grhss', pat_rhs_ty = pat_ty, bind_fvs = placeHolderNames }) } --------------------- getMonoBindInfo :: [Located TcMonoBind] -> [MonoBindInfo] getMonoBindInfo tc_binds = foldr (get_info . unLoc) [] tc_binds where get_info (TcFunBind info _ _ _) rest = info : rest get_info (TcPatBind infos _ _ _) rest = infos ++ rest \end{code} %************************************************************************ %* * Generalisation %* * %************************************************************************ \begin{code} generalise :: TopLevelFlag -> Bool -> [MonoBindInfo] -> [Inst] -> TcM ([TcTyVar], TcDictBinds, [TcId]) generalise top_lvl is_unrestricted mono_infos lie_req | not is_unrestricted -- RESTRICTED CASE = -- Check signature contexts are empty do { checkTc (all is_mono_sig sigs) (restrictedBindCtxtErr bndrs) -- Now simplify with exactly that set of tyvars -- We have to squash those Methods ; (qtvs, binds) <- tcSimplifyRestricted doc top_lvl bndrs tau_tvs lie_req -- Check that signature type variables are OK ; final_qtvs <- checkSigsTyVars qtvs sigs ; return (final_qtvs, binds, []) } | null sigs -- UNRESTRICTED CASE, NO TYPE SIGS = tcSimplifyInfer doc tau_tvs lie_req | otherwise -- UNRESTRICTED CASE, WITH TYPE SIGS = do { sig_lie <- unifyCtxts sigs -- sigs is non-empty ; let -- The "sig_avails" is the stuff available. We get that from -- the context of the type signature, BUT ALSO the lie_avail -- so that polymorphic recursion works right (see Note [Polymorphic recursion]) local_meths = [mkMethInst sig mono_id | (_, Just sig, mono_id) <- mono_infos] sig_avails = sig_lie ++ local_meths -- Check that the needed dicts can be -- expressed in terms of the signature ones ; (forall_tvs, dict_binds) <- tcSimplifyInferCheck doc tau_tvs sig_avails lie_req -- Check that signature type variables are OK ; final_qtvs <- checkSigsTyVars forall_tvs sigs ; returnM (final_qtvs, dict_binds, map instToId sig_lie) } where bndrs = bndrNames mono_infos sigs = [sig | (_, Just sig, _) <- mono_infos] tau_tvs = foldr (unionVarSet . exactTyVarsOfType . getMonoType) emptyVarSet mono_infos -- NB: exactTyVarsOfType; see Note [Silly type synonym] -- near defn of TcType.exactTyVarsOfType is_mono_sig sig = null (sig_theta sig) doc = ptext SLIT("type signature(s) for") <+> pprBinders bndrs mkMethInst (TcSigInfo { sig_id = poly_id, sig_tvs = tvs, sig_theta = theta, sig_loc = loc }) mono_id = Method mono_id poly_id (mkTyVarTys tvs) theta loc \end{code} unifyCtxts checks that all the signature contexts are the same The type signatures on a mutually-recursive group of definitions must all have the same context (or none). The trick here is that all the signatures should have the same context, and we want to share type variables for that context, so that all the right hand sides agree a common vocabulary for their type constraints We unify them because, with polymorphic recursion, their types might not otherwise be related. This is a rather subtle issue. \begin{code} unifyCtxts :: [TcSigInfo] -> TcM [Inst] unifyCtxts (sig1 : sigs) -- Argument is always non-empty = do { mapM unify_ctxt sigs ; newDictsAtLoc (sig_loc sig1) (sig_theta sig1) } where theta1 = sig_theta sig1 unify_ctxt :: TcSigInfo -> TcM () unify_ctxt sig@(TcSigInfo { sig_theta = theta }) = setSrcSpan (instLocSrcSpan (sig_loc sig)) $ addErrCtxt (sigContextsCtxt sig1 sig) $ unifyTheta theta1 theta checkSigsTyVars :: [TcTyVar] -> [TcSigInfo] -> TcM [TcTyVar] checkSigsTyVars qtvs sigs = do { gbl_tvs <- tcGetGlobalTyVars ; sig_tvs_s <- mappM (check_sig gbl_tvs) sigs ; let -- Sigh. Make sure that all the tyvars in the type sigs -- appear in the returned ty var list, which is what we are -- going to generalise over. Reason: we occasionally get -- silly types like -- type T a = () -> () -- f :: T a -- f () = () -- Here, 'a' won't appear in qtvs, so we have to add it sig_tvs = foldl extendVarSetList emptyVarSet sig_tvs_s all_tvs = varSetElems (extendVarSetList sig_tvs qtvs) ; returnM all_tvs } where check_sig gbl_tvs (TcSigInfo {sig_id = id, sig_tvs = tvs, sig_theta = theta, sig_tau = tau}) = addErrCtxt (ptext SLIT("In the type signature for") <+> quotes (ppr id)) $ addErrCtxtM (sigCtxt id tvs theta tau) $ do { tvs' <- checkDistinctTyVars tvs ; ifM (any (`elemVarSet` gbl_tvs) tvs') (bleatEscapedTvs gbl_tvs tvs tvs') ; return tvs' } checkDistinctTyVars :: [TcTyVar] -> TcM [TcTyVar] -- (checkDistinctTyVars tvs) checks that the tvs from one type signature -- are still all type variables, and all distinct from each other. -- It returns a zonked set of type variables. -- For example, if the type sig is -- f :: forall a b. a -> b -> b -- we want to check that 'a' and 'b' haven't -- (a) been unified with a non-tyvar type -- (b) been unified with each other (all distinct) checkDistinctTyVars sig_tvs = do { zonked_tvs <- mapM zonkSigTyVar sig_tvs ; foldlM check_dup emptyVarEnv (sig_tvs `zip` zonked_tvs) ; return zonked_tvs } where check_dup :: TyVarEnv TcTyVar -> (TcTyVar, TcTyVar) -> TcM (TyVarEnv TcTyVar) -- The TyVarEnv maps each zonked type variable back to its -- corresponding user-written signature type variable check_dup acc (sig_tv, zonked_tv) = case lookupVarEnv acc zonked_tv of Just sig_tv' -> bomb_out sig_tv sig_tv' Nothing -> return (extendVarEnv acc zonked_tv sig_tv) bomb_out sig_tv1 sig_tv2 = do { env0 <- tcInitTidyEnv ; let (env1, tidy_tv1) = tidyOpenTyVar env0 sig_tv1 (env2, tidy_tv2) = tidyOpenTyVar env1 sig_tv2 msg = ptext SLIT("Quantified type variable") <+> quotes (ppr tidy_tv1) <+> ptext SLIT("is unified with another quantified type variable") <+> quotes (ppr tidy_tv2) ; failWithTcM (env2, msg) } where \end{code} @getTyVarsToGen@ decides what type variables to generalise over. For a "restricted group" -- see the monomorphism restriction for a definition -- we bind no dictionaries, and remove from tyvars_to_gen any constrained type variables *Don't* simplify dicts at this point, because we aren't going to generalise over these dicts. By the time we do simplify them we may well know more. For example (this actually came up) f :: Array Int Int f x = array ... xs where xs = [1,2,3,4,5] We don't want to generate lots of (fromInt Int 1), (fromInt Int 2) stuff. If we simplify only at the f-binding (not the xs-binding) we'll know that the literals are all Ints, and we can just produce Int literals! Find all the type variables involved in overloading, the "constrained_tyvars". These are the ones we *aren't* going to generalise. We must be careful about doing this: (a) If we fail to generalise a tyvar which is not actually constrained, then it will never, ever get bound, and lands up printed out in interface files! Notorious example: instance Eq a => Eq (Foo a b) where .. Here, b is not constrained, even though it looks as if it is. Another, more common, example is when there's a Method inst in the LIE, whose type might very well involve non-overloaded type variables. [NOTE: Jan 2001: I don't understand the problem here so I'm doing the simple thing instead] (b) On the other hand, we mustn't generalise tyvars which are constrained, because we are going to pass on out the unmodified LIE, with those tyvars in it. They won't be in scope if we've generalised them. So we are careful, and do a complete simplification just to find the constrained tyvars. We don't use any of the results, except to find which tyvars are constrained. Note [Polymorphic recursion] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The game plan for polymorphic recursion in the code above is * Bind any variable for which we have a type signature to an Id with a polymorphic type. Then when type-checking the RHSs we'll make a full polymorphic call. This fine, but if you aren't a bit careful you end up with a horrendous amount of partial application and (worse) a huge space leak. For example: f :: Eq a => [a] -> [a] f xs = ...f... If we don't take care, after typechecking we get f = /\a -> \d::Eq a -> let f' = f a d in \ys:[a] -> ...f'... Notice the the stupid construction of (f a d), which is of course identical to the function we're executing. In this case, the polymorphic recursion isn't being used (but that's a very common case). This can lead to a massive space leak, from the following top-level defn (post-typechecking) ff :: [Int] -> [Int] ff = f Int dEqInt Now (f dEqInt) evaluates to a lambda that has f' as a free variable; but f' is another thunk which evaluates to the same thing... and you end up with a chain of identical values all hung onto by the CAF ff. ff = f Int dEqInt = let f' = f Int dEqInt in \ys. ...f'... = let f' = let f' = f Int dEqInt in \ys. ...f'... in \ys. ...f'... Etc. NOTE: a bit of arity anaysis would push the (f a d) inside the (\ys...), which would make the space leak go away in this case Solution: when typechecking the RHSs we always have in hand the *monomorphic* Ids for each binding. So we just need to make sure that if (Method f a d) shows up in the constraints emerging from (...f...) we just use the monomorphic Id. We achieve this by adding monomorphic Ids to the "givens" when simplifying constraints. That's what the "lies_avail" is doing. Then we get f = /\a -> \d::Eq a -> letrec fm = \ys:[a] -> ...fm... in fm %************************************************************************ %* * Signatures %* * %************************************************************************ Type signatures are tricky. See Note [Signature skolems] in TcType @tcSigs@ checks the signatures for validity, and returns a list of {\em freshly-instantiated} signatures. That is, the types are already split up, and have fresh type variables installed. All non-type-signature "RenamedSigs" are ignored. The @TcSigInfo@ contains @TcTypes@ because they are unified with the variable's type, and after that checked to see whether they've been instantiated. \begin{code} type TcSigFun = Name -> Maybe (LSig Name) mkSigFun :: [LSig Name] -> TcSigFun -- Search for a particular type signature -- Precondition: the sigs are all type sigs -- Precondition: no duplicates mkSigFun sigs = lookupNameEnv env where env = mkNameEnv [(expectJust "mkSigFun" (sigName sig), sig) | sig <- sigs] --------------- data TcSigInfo = TcSigInfo { sig_id :: TcId, -- *Polymorphic* binder for this value... sig_scoped :: [Name], -- Names for any scoped type variables -- Invariant: correspond 1-1 with an initial -- segment of sig_tvs (see Note [Scoped]) sig_tvs :: [TcTyVar], -- Instantiated type variables -- See Note [Instantiate sig] sig_theta :: TcThetaType, -- Instantiated theta sig_tau :: TcTauType, -- Instantiated tau sig_loc :: InstLoc -- The location of the signature } -- Note [Scoped] -- There may be more instantiated type variables than scoped -- ones. For example: -- type T a = forall b. b -> (a,b) -- f :: forall c. T c -- Here, the signature for f will have one scoped type variable, c, -- but two instantiated type variables, c' and b'. -- -- We assume that the scoped ones are at the *front* of sig_tvs, -- and remember the names from the original HsForAllTy in sig_scoped -- Note [Instantiate sig] -- It's vital to instantiate a type signature with fresh variable. -- For example: -- type S = forall a. a->a -- f,g :: S -- f = ... -- g = ... -- Here, we must use distinct type variables when checking f,g's right hand sides. -- (Instantiation is only necessary because of type synonyms. Otherwise, -- it's all cool; each signature has distinct type variables from the renamer.) instance Outputable TcSigInfo where ppr (TcSigInfo { sig_id = id, sig_tvs = tyvars, sig_theta = theta, sig_tau = tau}) = ppr id <+> ptext SLIT("::") <+> ppr tyvars <+> ppr theta <+> ptext SLIT("=>") <+> ppr tau \end{code} \begin{code} tcTySig :: LSig Name -> TcM TcId tcTySig (L span (TypeSig (L _ name) ty)) = setSrcSpan span $ do { sigma_ty <- tcHsSigType (FunSigCtxt name) ty ; return (mkLocalId name sigma_ty) } ------------------- tcInstSig_maybe :: Maybe (LSig Name) -> TcM (Maybe TcSigInfo) -- Instantiate with *meta* type variables; -- this signature is part of a multi-signature group tcInstSig_maybe Nothing = return Nothing tcInstSig_maybe (Just sig) = do { tc_sig <- tcInstSig False sig ; return (Just tc_sig) } tcInstSig :: Bool -> LSig Name -> TcM TcSigInfo -- Instantiate the signature, with either skolems or meta-type variables -- depending on the use_skols boolean -- -- We always instantiate with freshs uniques, -- although we keep the same print-name -- -- type T = forall a. [a] -> [a] -- f :: T; -- f = g where { g :: T; g =