% % (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(..), TcSigFun, mkTcSigFun, badBootDeclErr ) where #include "HsVersions.h" import {-# SOURCE #-} TcMatches ( tcGRHSsPat, tcMatchesFun ) import {-# SOURCE #-} TcExpr ( tcMonoExpr ) import DynFlags ( dopt, DynFlags, DynFlag(Opt_MonomorphismRestriction, Opt_MonoPatBinds, Opt_GlasgowExts) ) import HsSyn ( HsExpr(..), HsBind(..), LHsBinds, LHsBind, Sig(..), HsLocalBinds(..), HsValBinds(..), HsIPBinds(..), LSig, Match(..), IPBind(..), Prag(..), LHsType, isVanillaLSig, sigName, placeHolderNames, isPragLSig, LPat, GRHSs, MatchGroup(..), pprLHsBinds, mkHsWrap, hsExplicitTvs, collectHsBindBinders, collectPatBinders, pprPatBind, isBangHsBind ) import TcHsSyn ( zonkId ) import TcRnMonad import Inst ( newDictBndrs, newIPDict, instToId ) import TcEnv ( tcExtendIdEnv, tcExtendIdEnv2, tcExtendTyVarEnv2, pprBinders, tcLookupId, tcGetGlobalTyVars ) import TcUnify ( tcInfer, tcSubExp, unifyTheta, bleatEscapedTvs, sigCtxt ) import TcSimplify ( tcSimplifyInfer, tcSimplifyInferCheck, tcSimplifyRestricted, tcSimplifyIPs ) import TcHsType ( tcHsSigType, UserTypeCtxt(..) ) import TcPat ( tcLetPat ) import TcSimplify ( bindInstsOfLocalFuns ) import TcMType ( newFlexiTyVarTy, zonkQuantifiedTyVar, zonkSigTyVar, tcInstSigTyVars, tcInstSkolTyVars, tcInstType, zonkTcType, zonkTcTypes, zonkTcTyVar ) import TcType ( TcType, TcTyVar, TcThetaType, SkolemInfo(SigSkol), UserTypeCtxt(FunSigCtxt), TcTauType, TcSigmaType, isUnboxedTupleType, mkTyVarTy, mkForAllTys, mkFunTys, exactTyVarsOfType, mkForAllTy, isUnLiftedType, tcGetTyVar, mkTyVarTys, tidyOpenTyVar ) import {- Kind parts of -} Type ( argTypeKind ) import VarEnv ( TyVarEnv, emptyVarEnv, lookupVarEnv, extendVarEnv ) 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 = mkTcSigFun ty_sigs } ; poly_ids <- mapM tcTySig ty_sigs -- No recovery from bad signatures, because the type sigs -- may bind type variables, so proceeding without them -- can lead to a cascade of errors -- ToDo: this means we fall over immediately if any type sig -- is wrong, which is over-conservative, see Trac bug #745 -- Extend the envt right away with all -- the Ids declared with type signatures ; gla_exts <- doptM Opt_GlasgowExts ; (binds', thing) <- tcExtendIdEnv poly_ids $ tc_val_binds gla_exts top_lvl sig_fn prag_fn binds thing_inside ; return (ValBindsOut binds' sigs, thing) } ------------------------ tc_val_binds :: Bool -> 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 gla_exts top_lvl sig_fn prag_fn [] thing_inside = do { thing <- thing_inside ; return ([], thing) } tc_val_binds gla_exts top_lvl sig_fn prag_fn (group : groups) thing_inside = do { (group', (groups', thing)) <- tc_group gla_exts top_lvl sig_fn prag_fn group $ tc_val_binds gla_exts top_lvl sig_fn prag_fn groups thing_inside ; return (group' ++ groups', thing) } ------------------------ tc_group :: Bool -> 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 gla_exts 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) <- tc_haskell98 top_lvl sig_fn prag_fn NonRecursive binds thing_inside ; return ([(NonRecursive, b) | b <- binds], thing) } tc_group gla_exts top_lvl sig_fn prag_fn (Recursive, binds) thing_inside | not gla_exts -- Recursive group, normal Haskell 98 route = do { (binds1, thing) <- tc_haskell98 top_lvl sig_fn prag_fn Recursive binds thing_inside ; return ([(Recursive, unionManyBags binds1)], thing) } | otherwise -- Recursive group, with gla-exts = -- To maximise polymorphism (with -fglasgow-exts), we do a new -- strongly-connected-component analysis, this time omitting -- any references to variables with type signatures. -- -- Notice that the bindInsts thing covers *all* the bindings in the original -- group at once; an earlier one may use a later one! do { traceTc (text "tc_group rec" <+> pprLHsBinds binds) ; (binds1,thing) <- bindLocalInsts top_lvl $ go (stronglyConnComp (mkEdges sig_fn binds)) ; return ([(Recursive, unionManyBags binds1)], thing) } -- Rec them all together where -- go :: SCC (LHsBind Name) -> TcM ([LHsBind TcId], [TcId], thing) go (scc:sccs) = do { (binds1, ids1) <- tc_scc scc ; (binds2, ids2, thing) <- tcExtendIdEnv ids1 $ go sccs ; return (binds1 ++ binds2, ids1 ++ ids2, thing) } go [] = do { thing <- thing_inside; return ([], [], thing) } tc_scc (AcyclicSCC bind) = tc_sub_group NonRecursive (unitBag bind) tc_scc (CyclicSCC binds) = tc_sub_group Recursive (listToBag binds) tc_sub_group = tcPolyBinds top_lvl sig_fn prag_fn Recursive tc_haskell98 top_lvl sig_fn prag_fn rec_flag binds thing_inside = bindLocalInsts top_lvl $ do { (binds1, ids) <- tcPolyBinds top_lvl sig_fn prag_fn rec_flag rec_flag binds ; thing <- tcExtendIdEnv ids thing_inside ; return (binds1, ids, thing) } ------------------------ bindLocalInsts :: TopLevelFlag -> TcM ([LHsBinds TcId], [TcId], a) -> TcM ([LHsBinds TcId], a) bindLocalInsts top_lvl thing_inside | isTopLevel top_lvl = do { (binds, ids, thing) <- thing_inside; return (binds, thing) } -- 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 | otherwise -- Nested case = do { ((binds, ids, thing), lie) <- getLIE thing_inside ; lie_binds <- bindInstsOfLocalFuns lie ids ; return (binds ++ [lie_binds], thing) } ------------------------ 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 -> TcSigFun -> TcPragFun -> RecFlag -- Whether the group is really recursive -> RecFlag -- Whether it's recursive after breaking -- dependencies based on type signatures -> LHsBinds Name -> TcM ([LHsBinds TcId], [TcId]) -- 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 -- -- 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. -- -- Knows nothing about the scope of the bindings tcPolyBinds top_lvl sig_fn prag_fn rec_group rec_tc binds = let bind_list = bagToList binds binder_names = collectHsBindBinders 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 sig_fn) $ 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 { dflags <- getDOpts ; (tyvars_to_gen, dict_binds, dict_ids) <- addErrCtxt (genCtxt (bndrNames mono_bind_infos)) $ generalise dflags top_lvl bind_list sig_fn 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 ; let poly_ids = [poly_id | (_, poly_id, _, _) <- exports] ; traceTc (text "binding:" <+> ppr (poly_ids `zip` map idType poly_ids)) ; let abs_bind = L loc $ AbsBinds tyvars_to_gen' dict_ids exports (dict_binds `unionBags` binds') ; return ([unitBag abs_bind], poly_ids) -- poly_ids are guaranteed zonked by mkExport } } -------------- mkExport :: TcPragFun -> [TyVar] -> [TcType] -> MonoBindInfo -> TcM ([TyVar], Id, Id, [Prag]) -- mkExport generates exports with -- zonked type variables, -- zonked poly_ids -- The former is just because no further unifications will change -- the quantified type variables, so we can fix their final form -- right now. -- The latter is needed because the poly_ids are used to extend the -- type environment; see the invariant on TcEnv.tcExtendIdEnv -- Pre-condition: the inferred_tvs are already zonked mkExport prag_fn inferred_tvs dict_tys (poly_name, mb_sig, mono_id) = do { (tvs, poly_id) <- mk_poly_id mb_sig ; poly_id' <- zonkId poly_id ; prags <- tcPrags poly_id' (prag_fn poly_name) -- tcPrags requires a zonked poly_id ; return (tvs, poly_id', mono_id, prags) } where poly_ty = mkForAllTys inferred_tvs (mkFunTys dict_tys (idType mono_id)) mk_poly_id Nothing = return (inferred_tvs, mkLocalId poly_name poly_ty) mk_poly_id (Just sig) = do { tvs <- mapM zonk_tv (sig_tvs sig) ; return (tvs, sig_id sig) } zonk_tv tv = do { ty <- zonkTcTyVar tv; return (tcGetTyVar "mkExport" ty) } ------------------------ 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 -- Pre-condition: the poly_id is zonked -- Reason: required by tcSubExp 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 (mkHsWrap co_fn (HsVar poly_id)) spec_ty const_dicts inl) } -- Most of the work of specialisation is done by -- the desugarer, guided by the SpecPrag -------------- -- 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 sig_fn = do { traceTc (text "tcBindsWithSigs: error recovery" <+> ppr binder_names) ; poly_ids <- mapM mk_dummy binder_names ; return ([], poly_ids) } where mk_dummy name | isJust (sig_fn name) = tcLookupId name -- Had signature; look it up | otherwise = 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 (pprLHsBinds 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 scoped_tvs <- 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 name scoped_tvs ; 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 ; mono_pat_binds <- doptM Opt_MonoPatBinds -- With -fmono-pat-binds, we do no generalisation of pattern bindings -- But the signature can still be polymoprhic! -- data T = MkT (forall a. a->a) -- x :: forall a. a->a -- MkT x =