{- (c) The University of Glasgow 2006 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 \section[TcBinds]{TcBinds} -}{-# LANGUAGE CPP, RankNTypes, ScopedTypeVariables #-}{-# LANGUAGE FlexibleContexts #-}{-# LANGUAGE TypeFamilies #-}{-# LANGUAGE ViewPatterns #-}moduleTcBinds(tcLocalBinds ,tcTopBinds ,tcValBinds ,tcHsBootSigs ,tcPolyCheck ,addTypecheckedBinds ,chooseInferredQuantifiers ,badBootDeclErr )whereimportGhcPreludeimport{-# SOURCE#-}TcMatches (tcGRHSsPat ,tcMatchesFun )import{-# SOURCE#-}TcExpr (tcMonoExpr )import{-# SOURCE#-}TcPatSyn (tcPatSynDecl ,tcPatSynBuilderBind )importCoreSyn(Tickish(..))importCostCentre(mkUserCC,CCFlavour(DeclCC))importDynFlagsimportFastStringimportHsSynimportHscTypes(isHsBootOrSig)importTcSigs importTcRnMonad importTcEnv importTcUnify importTcSimplify importTcEvidenceimportTcHsType importTcPat importTcMType importFamInstEnv(normaliseType)importFamInst (tcGetFamInstEnvs )importTyConimportTcTypeimportType(mkStrLitTy,tidyOpenType,splitTyConApp_maybe,mkCastTy)importTysPrimimportTysWiredIn(mkBoxedTupleTy)importIdimportVarimportVarSetimportVarEnv(TidyEnv)importModuleimportNameimportNameSetimportNameEnvimportSrcLocimportBagimportErrUtilsimportDigraphimportMaybesimportUtilimportBasicTypesimportOutputableimportPrelNames(ipClassName)importTcValidity (checkValidType )importUniqFMimportUniqSetimportqualifiedGHC.LanguageExtensionsasLangExtimportConLikeimportControl.Monad#include "HsVersions.h" {- ********************************************************************* * * A useful helper function * * ********************************************************************* -}addTypecheckedBinds::TcGblEnv->[LHsBindsGhcTc]->TcGblEnvaddTypecheckedBinds tcg_env binds |isHsBootOrSig(tcg_srctcg_env )=tcg_env -- Do not add the code for record-selector bindings-- when compiling hs-boot files|otherwise=tcg_env {tcg_binds=foldrunionBags(tcg_bindstcg_env )binds }{- ************************************************************************ * * \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. 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 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 -}tcTopBinds::[(RecFlag,LHsBindsGhcRn)]->[LSigGhcRn]->TcM(TcGblEnv,TcLclEnv)-- The TcGblEnv contains the new tcg_binds and tcg_spects-- The TcLclEnv has an extended type envt for the new bindingstcTopBinds binds sigs =do{-- Pattern synonym bindings populate the global environment(binds' ,(tcg_env ,tcl_env ))<-tcValBinds TopLevelbinds sigs $do{gbl <-getGblEnv ;lcl <-getLclEnv ;return(gbl ,lcl )};specs <-tcImpPrags sigs -- SPECIALISE prags for imported Ids;complete_matches <-setEnvs (tcg_env ,tcl_env )$tcCompleteSigs sigs ;traceTc "complete_matches"(pprbinds $$pprsigs );traceTc "complete_matches"(pprcomplete_matches );let{tcg_env' =tcg_env {tcg_imp_specs=specs ++tcg_imp_specstcg_env ,tcg_complete_matches=complete_matches ++tcg_complete_matchestcg_env }`addTypecheckedBinds `mapsndbinds' };return(tcg_env' ,tcl_env )}-- The top level bindings are flattened into a giant-- implicitly-mutually-recursive LHsBinds-- Note [Typechecking Complete Matches]-- Much like when a user bundled a pattern synonym, the result types of-- all the constructors in the match pragma must be consistent.---- If we allowed pragmas with inconsistent types then it would be-- impossible to ever match every constructor in the list and so-- the pragma would be useless.-- This is only used in `tcCompleteSig`. We fold over all the conlikes,-- this accumulator keeps track of the first `ConLike` with a concrete-- return type. After fixing the return type, all other constructors with-- a fixed return type must agree with this.---- The fields of `Fixed` cache the first conlike and its return type so-- that that we can compare all the other conlikes to it. The conlike is-- stored for error messages.---- `Nothing` in the case that the type is fixed by a type signaturedataCompleteSigType =AcceptAny |Fixed (MaybeConLike)TyContcCompleteSigs::[LSigGhcRn]->TcM[CompleteMatch]tcCompleteSigs sigs =letdoOne::SigGhcRn->TcM(MaybeCompleteMatch)doOne c @(CompleteMatchSig__lns mtc )=fmapJust$doaddErrCtxt (text"In"<+>pprc )$casemtc ofNothing->infer_complete_match Justtc ->check_complete_match tc wherecheckCLTypes acc =foldMcheckCLType (acc ,[])(unLoclns )infer_complete_match =do(res ,cls )<-checkCLTypes AcceptAny caseres ofAcceptAny ->failWithTc ambiguousError Fixed _tc ->return$mkMatch cls tc check_complete_match tc_name =doty_con <-tcLookupLocatedTyCon tc_name (_,cls )<-checkCLTypes (Fixed Nothingty_con )return$mkMatch cls ty_con mkMatch::[ConLike]->TyCon->CompleteMatchmkMatch cls ty_con =CompleteMatch{completeMatchConLikes=mapconLikeNamecls ,completeMatchTyCon=tyConNamety_con }doOne_=returnNothingambiguousError::SDocambiguousError =text"A type signature must be provided for a set of polymorphic"<+>text"pattern synonyms."-- See note [Typechecking Complete Matches]checkCLType::(CompleteSigType ,[ConLike])->LocatedName->TcM(CompleteSigType ,[ConLike])checkCLType (cst ,cs )n =docl <-addLocM tcLookupConLike n let(_,_,_,_,_,_,res_ty )=conLikeFullSigcl res_ty_con =fst<$>splitTyConApp_mayberes_ty case(cst ,res_ty_con )of(AcceptAny ,Nothing)->return(AcceptAny ,cl :cs )(AcceptAny ,Justtc )->return(Fixed (Justcl )tc ,cl :cs )(Fixed mfcl tc ,Nothing)->return(Fixed mfcl tc ,cl :cs )(Fixed mfcl tc ,Justtc' )->iftc ==tc' thenreturn(Fixed mfcl tc ,cl :cs )elsecasemfcl ofNothing->addErrCtxt (text"In"<+>pprcl )$failWithTc typeSigErrMsg Justcl ->failWithTc (errMsg cl )wheretypeSigErrMsg::SDoctypeSigErrMsg =text"Couldn't match expected type"<+>quotes(pprtc )<+>text"with"<+>quotes(pprtc' )errMsg::ConLike->SDocerrMsg fcl =text"Cannot form a group of complete patterns from patterns"<+>quotes(pprfcl )<+>text"and"<+>quotes(pprcl )<+>text"as they match different type constructors"<+>parens(quotes(pprtc )<+>text"resp."<+>quotes(pprtc' ))inmapMaybeM(addLocM doOne )sigs tcHsBootSigs::[(RecFlag,LHsBindsGhcRn)]->[LSigGhcRn]->TcM[Id]-- A hs-boot file has only one BindGroup, and it only has type-- signatures in it. The renamer checked all thistcHsBootSigs binds sigs =do{checkTc (nullbinds )badBootDeclErr ;concat<$>mapM(addLocM tc_boot_sig )(filterisTypeLSigsigs )}wheretc_boot_sig (TypeSig_lnames hs_ty )=mapMf lnames wheref (dL->L_name )=do{sigma_ty <-tcHsSigWcType (FunSigCtxtname False)hs_ty ;return(mkVanillaGlobalname sigma_ty )}-- Notice that we make GlobalIds, not LocalIdstc_boot_sigs =pprPanic"tcHsBootSigs/tc_boot_sig"(pprs )badBootDeclErr::MsgDocbadBootDeclErr =text"Illegal declarations in an hs-boot file"------------------------tcLocalBinds::HsLocalBindsGhcRn->TcMthing ->TcM(HsLocalBindsGhcTcId,thing )tcLocalBinds (EmptyLocalBindsx )thing_inside =do{thing <-thing_inside ;return(EmptyLocalBindsx ,thing )}tcLocalBinds(HsValBindsx (XValBindsLR(NValBindsbinds sigs )))thing_inside =do{(binds' ,thing )<-tcValBinds NotTopLevelbinds sigs thing_inside ;return(HsValBindsx (XValBindsLR(NValBindsbinds' sigs )),thing )}tcLocalBinds(HsValBinds_(ValBinds{}))_=panic"tcLocalBinds"tcLocalBinds(HsIPBindsx (IPBinds_ip_binds ))thing_inside =do{ipClass <-tcLookupClass ipClassName;(given_ips ,ip_binds' )<-mapAndUnzipM(wrapLocSndM (tc_ip_bind ipClass ))ip_binds -- If the binding binds ?x = E, we must now-- discharge any ?x constraints in expr_lie-- See Note [Implicit parameter untouchables];(ev_binds ,result )<-checkConstraints (IPSkolips )[]given_ips thing_inside ;return(HsIPBindsx (IPBindsev_binds ip_binds' ),result )}whereips =[ip |(dL->L_(IPBind_(Left(dL->L_ip ))_))<-ip_binds ]-- I wonder if we should do these one at at time-- Consider ?x = 4-- ?y = ?x + 1tc_ip_bind ipClass (IPBind_(Left(dL->L_ip ))expr )=do{ty <-newOpenFlexiTyVarTy ;letp =mkStrLitTy$hsIPNameFSip ;ip_id <-newDict ipClass [p ,ty ];expr' <-tcMonoExpr expr (mkCheckExpTypety );letd =toDict ipClass p ty `fmap`expr' ;return(ip_id ,(IPBindnoExt(Rightip_id )d ))}tc_ip_bind_(IPBind_(Right{})_)=panic"tc_ip_bind"tc_ip_bind_(XIPBind_)=panic"tc_ip_bind"-- Coerces a `t` into a dictionry for `IP "x" t`.-- co : t -> IP "x" ttoDict ipClass x ty =mkHsWrap$mkWpCastR$wrapIP$mkClassPredipClass [x ,ty ]tcLocalBinds(HsIPBinds_(XHsIPBinds_))_=panic"tcLocalBinds"tcLocalBinds(XHsLocalBindsLR_)_=panic"tcLocalBinds"{- Note [Implicit parameter untouchables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We add the type variables in the types of the implicit parameters as untouchables, not so much because we really must not unify them, but rather because we otherwise end up with constraints like this Num alpha, Implic { wanted = alpha ~ Int } The constraint solver solves alpha~Int by unification, but then doesn't float that solved constraint out (it's not an unsolved wanted). Result disaster: the (Num alpha) is again solved, this time by defaulting. No no no. However [Oct 10] this is all handled automatically by the untouchable-range idea. -}tcValBinds::TopLevelFlag->[(RecFlag,LHsBindsGhcRn)]->[LSigGhcRn]->TcMthing ->TcM([(RecFlag,LHsBindsGhcTcId)],thing )tcValBinds top_lvl binds sigs thing_inside =do{-- Typecheck the signatures-- It's easier to do so now, once for all the SCCs together-- because a single signature f,g :: <type>-- might relate to more than one SCC;(poly_ids ,sig_fn )<-tcAddPatSynPlaceholders patsyns $tcTySigs sigs -- Extend the envt right away with all the Ids-- declared with complete type signatures-- Do not extend the TcBinderStack; instead-- we extend it on a per-rhs basis in tcExtendForRhs;tcExtendSigIds top_lvl poly_ids $do{(binds' ,(extra_binds' ,thing ))<-tcBindGroups top_lvl sig_fn prag_fn binds $do{thing <-thing_inside -- See Note [Pattern synonym builders don't yield dependencies]-- in RnBinds;patsyn_builders <-mapMtcPatSynBuilderBind patsyns ;letextra_binds =[(NonRecursive,builder )|builder <-patsyn_builders ];return(extra_binds ,thing )};return(binds' ++extra_binds' ,thing )}}wherepatsyns =getPatSynBindsbinds prag_fn =mkPragEnv sigs (foldr(unionBags.snd)emptyBagbinds )------------------------tcBindGroups::TopLevelFlag->TcSigFun->TcPragEnv ->[(RecFlag,LHsBindsGhcRn)]->TcMthing ->TcM([(RecFlag,LHsBindsGhcTcId)],thing )-- Typecheck a whole lot of value bindings,-- one strongly-connected component at a time-- Here a "strongly connected component" has the strightforward-- meaning of a group of bindings that mention each other,-- ignoring type signatures (that part comes later)tcBindGroups ___[]thing_inside =do{thing <-thing_inside ;return([],thing )}tcBindGroupstop_lvl sig_fn prag_fn (group :groups )thing_inside =do{-- See Note [Closed binder groups]type_env <-getLclTypeEnv ;letclosed =isClosedBndrGroup type_env (sndgroup );(group' ,(groups' ,thing ))<-tc_group top_lvl sig_fn prag_fn group closed $tcBindGroups top_lvl sig_fn prag_fn groups thing_inside ;return(group' ++groups' ,thing )}-- Note [Closed binder groups]-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~---- A mutually recursive group is "closed" if all of the free variables of-- the bindings are closed. For example---- > h = \x -> let f = ...g...-- > g = ....f...x...-- > in ...---- Here @g@ is not closed because it mentions @x@; and hence neither is @f@-- closed.---- So we need to compute closed-ness on each strongly connected components,-- before we sub-divide it based on what type signatures it has.--------------------------tc_group::forallthing .TopLevelFlag->TcSigFun->TcPragEnv ->(RecFlag,LHsBindsGhcRn)->IsGroupClosed->TcMthing ->TcM([(RecFlag,LHsBindsGhcTcId)],thing )-- Typecheck one strongly-connected component of the original program.-- We get a list of groups back, because there may-- be specialisations etc as welltc_group top_lvl sig_fn prag_fn (NonRecursive,binds )closed thing_inside -- A single non-recursive binding-- We want to keep non-recursive things non-recursive-- so that we desugar unlifted bindings correctly=do{letbind =casebagToListbinds of[bind ]->bind []->panic"tc_group: empty list of binds"_->panic"tc_group: NonRecursive binds is not a singleton bag";(bind' ,thing )<-tc_single top_lvl sig_fn prag_fn bind closed thing_inside ;return([(NonRecursive,bind' )],thing )}tc_grouptop_lvl sig_fn prag_fn (Recursive,binds )closed thing_inside =-- To maximise polymorphism, we do a new-- strongly-connected-component analysis, this time omitting-- any references to variables with type signatures.-- (This used to be optional, but isn't now.)-- See Note [Polymorphic recursion] in HsBinds.do{traceTc "tc_group rec"(pprLHsBindsbinds );whenhasPatSyn $recursivePatSynErr binds ;(binds1 ,thing )<-go sccs ;return([(Recursive,binds1 )],thing )}-- Rec them all togetherwherehasPatSyn =anyBag(isPatSyn .unLoc)binds isPatSyn PatSynBind{}=TrueisPatSyn_=Falsesccs::[SCC(LHsBindGhcRn)]sccs =stronglyConnCompFromEdgedVerticesUniq(mkEdges sig_fn binds )go::[SCC(LHsBindGhcRn)]->TcM(LHsBindsGhcTcId,thing )go (scc :sccs )=do{(binds1 ,ids1 )<-tc_scc scc ;(binds2 ,thing )<-tcExtendLetEnv top_lvl sig_fn closed ids1 $go sccs ;return(binds1 `unionBags`binds2 ,thing )}go[]=do{thing <-thing_inside ;return(emptyBag,thing )}tc_scc (AcyclicSCCbind )=tc_sub_group NonRecursive[bind ]tc_scc(CyclicSCCbinds )=tc_sub_group Recursivebinds tc_sub_group rec_tc binds =tcPolyBinds sig_fn prag_fn Recursiverec_tc closed binds recursivePatSynErr::OutputableBndrId(GhcPassp )=>LHsBinds(GhcPassp )->TcMa recursivePatSynErr binds =failWithTc $hang(text"Recursive pattern synonym definition with following bindings:")2(vcat$mappprLBind .bagToList$binds )wherepprLoc loc =parens(text"defined at"<+>pprloc )pprLBind (dL->Lloc bind )=pprWithCommasppr(collectHsBindBindersbind )<+>pprLoc loc tc_single::forallthing .TopLevelFlag->TcSigFun->TcPragEnv ->LHsBindGhcRn->IsGroupClosed->TcMthing ->TcM(LHsBindsGhcTcId,thing )tc_single _top_lvl sig_fn _prag_fn (dL->L_(PatSynBind_psb @PSB{psb_id=(dL->L_name )}))_thing_inside =do{(aux_binds ,tcg_env )<-tcPatSynDecl psb (sig_fn name );thing <-setGblEnv tcg_env thing_inside ;return(aux_binds ,thing )}tc_singletop_lvl sig_fn prag_fn lbind closed thing_inside =do{(binds1 ,ids )<-tcPolyBinds sig_fn prag_fn NonRecursiveNonRecursiveclosed [lbind ];thing <-tcExtendLetEnv top_lvl sig_fn closed ids thing_inside ;return(binds1 ,thing )}------------------------typeBKey =Int-- Just number off the bindingsmkEdges::TcSigFun->LHsBindsGhcRn->[NodeBKey (LHsBindGhcRn)]-- See Note [Polymorphic recursion] in HsBinds.mkEdges sig_fn binds =[DigraphNodebind key [key |n <-nonDetEltsUniqSet(bind_fvs (unLocbind )),Justkey <-[lookupNameEnvkey_map n ],no_sig n ]|(bind ,key )<-keyd_binds ]-- It's OK to use nonDetEltsUFM here as stronglyConnCompFromEdgedVertices-- is still deterministic even if the edges are in nondeterministic order-- as explained in Note [Deterministic SCC] in Digraph.wherebind_fvs (FunBind{fun_ext=fvs })=fvs bind_fvs(PatBind{pat_ext=fvs })=fvs bind_fvs_=emptyNameSetno_sig::Name->Boolno_sig n =not(hasCompleteSigsig_fn n )keyd_binds =bagToListbinds `zip`[0::BKey ..]key_map::NameEnvBKey -- Which binding it comes fromkey_map =mkNameEnv[(bndr ,key )|(dL->L_bind ,key )<-keyd_binds ,bndr <-collectHsBindBindersbind ]------------------------tcPolyBinds::TcSigFun->TcPragEnv ->RecFlag-- Whether the group is really recursive->RecFlag-- Whether it's recursive after breaking-- dependencies based on type signatures->IsGroupClosed-- Whether the group is closed->[LHsBindGhcRn]-- None are PatSynBind->TcM(LHsBindsGhcTcId,[TcId])-- Typechecks a single bunch of values 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-- None of the bindings are pattern synonymstcPolyBinds sig_fn prag_fn rec_group rec_tc closed bind_list =setSrcSpan loc $recoverM (recoveryCode binder_names sig_fn )$do-- Set up main recover; take advantage of any type sigs{traceTc "------------------------------------------------"Outputable.empty;traceTc "Bindings for {"(pprbinder_names );dflags <-getDynFlags;letplan =decideGeneralisationPlan dflags bind_list closed sig_fn ;traceTc "Generalisation plan"(pprplan );result @(_,poly_ids )<-caseplan ofNoGen ->tcPolyNoGen rec_tc prag_fn sig_fn bind_list InferGen mn ->tcPolyInfer rec_tc prag_fn sig_fn mn bind_list CheckGen lbind sig ->tcPolyCheck prag_fn sig lbind ;traceTc "} End of bindings for"(vcat[pprbinder_names ,pprrec_group ,vcat[pprid <+>ppr(idTypeid )|id <-poly_ids ]]);returnresult }wherebinder_names =collectHsBindListBindersbind_list loc =foldr1combineSrcSpans(mapgetLocbind_list )-- The mbinds have been dependency analysed and-- may no longer be adjacent; so find the narrowest-- span that includes them all---------------- If typechecking the binds fails, then return with each-- signature-less binder given type (forall a.a), to minimise-- subsequent error messagesrecoveryCode::[Name]->TcSigFun->TcM(LHsBindsGhcTcId,[Id])recoveryCode binder_names sig_fn =do{traceTc "tcBindsWithSigs: error recovery"(pprbinder_names );letpoly_ids =mapmk_dummy binder_names ;return(emptyBag,poly_ids )}wheremk_dummy name |Justsig <-sig_fn name ,Justpoly_id <-completeSigPolyId_maybe sig =poly_id |otherwise=mkLocalIdname forall_a_a forall_a_a::TcType-- At one point I had (forall r (a :: TYPE r). a), but of course-- that type is ill-formed: its mentions 'r' which escapes r's scope.-- Another alternative would be (forall (a :: TYPE kappa). a), where-- kappa is a unification variable. But I don't think we need that-- complication here. I'm going to just use (forall (a::*). a).-- See #15276forall_a_a =mkSpecForAllTys[alphaTyVar]alphaTy{- ********************************************************************* * * tcPolyNoGen * * ********************************************************************* -}tcPolyNoGen-- No generalisation whatsoever::RecFlag-- Whether it's recursive after breaking-- dependencies based on type signatures->TcPragEnv ->TcSigFun->[LHsBindGhcRn]->TcM(LHsBindsGhcTcId,[TcId])tcPolyNoGen rec_tc prag_fn tc_sig_fn bind_list =do{(binds' ,mono_infos )<-tcMonoBinds rec_tc tc_sig_fn (LetGblBndr prag_fn )bind_list ;mono_ids' <-mapMtc_mono_info mono_infos ;return(binds' ,mono_ids' )}wheretc_mono_info (MBI {mbi_poly_name=name ,mbi_mono_id=mono_id })=do{_specs <-tcSpecPrags mono_id (lookupPragEnv prag_fn name );returnmono_id }-- NB: tcPrags generates error messages for-- specialisation pragmas for non-overloaded sigs-- Indeed that is why we call it here!-- So we can safely ignore _specs{- ********************************************************************* * * tcPolyCheck * * ********************************************************************* -}tcPolyCheck::TcPragEnv ->TcIdSigInfo-- Must be a complete signature->LHsBindGhcRn-- Must be a FunBind->TcM(LHsBindsGhcTcId,[TcId])-- There is just one binding,-- it is a Funbind-- it has a complete type signature,tcPolyCheck prag_fn (CompleteSig{sig_bndr=poly_id ,sig_ctxt=ctxt ,sig_loc=sig_loc })(dL->Lloc (FunBind{fun_id=(dL->Lnm_loc name ),fun_matches=matches }))=setSrcSpan sig_loc $do{traceTc "tcPolyCheck"(pprpoly_id $$pprsig_loc );(tv_prs ,theta ,tau )<-tcInstType tcInstSkolTyVars poly_id -- See Note [Instantiate sig with fresh variables];mono_name <-newNameAt (nameOccNamename )nm_loc ;ev_vars <-newEvVars theta ;letmono_id =mkLocalIdmono_name tau skol_info =SigSkolctxt (idTypepoly_id )tv_prs skol_tvs =mapsndtv_prs ;(ev_binds ,(co_fn ,matches' ))<-checkConstraints skol_info skol_tvs ev_vars $tcExtendBinderStack [TcIdBndrmono_id NotTopLevel]$tcExtendNameTyVarEnv tv_prs $setSrcSpan loc $tcMatchesFun (cLnm_loc mono_name )matches (mkCheckExpTypetau );letprag_sigs =lookupPragEnv prag_fn name ;spec_prags <-tcSpecPrags poly_id prag_sigs ;poly_id <-addInlinePrags poly_id prag_sigs ;mod <-getModule;tick <-funBindTicks nm_loc mono_id mod prag_sigs ;letbind' =FunBind{fun_id=cLnm_loc mono_id ,fun_matches=matches' ,fun_co_fn=co_fn ,fun_ext=placeHolderNamesTc,fun_tick=tick }export=ABE{abe_ext=noExt,abe_wrap=idHsWrapper,abe_poly=poly_id ,abe_mono=mono_id ,abe_prags=SpecPragsspec_prags }abs_bind =cLloc $AbsBinds{abs_ext=noExt,abs_tvs=skol_tvs ,abs_ev_vars=ev_vars ,abs_ev_binds=[ev_binds ],abs_exports=[export],abs_binds=unitBag(cLloc bind' ),abs_sig=True};return(unitBagabs_bind ,[poly_id ])}tcPolyCheck_prag_fn sig bind =pprPanic"tcPolyCheck"(pprsig $$pprbind )funBindTicks::SrcSpan->TcId->Module->[LSigGhcRn]->TcM[TickishTcId]funBindTicks loc fun_id mod sigs |(mb_cc_str :_)<-[cc_name |(dL->L_(SCCFunSig___cc_name ))<-sigs ]-- this can only be a singleton list, as duplicate pragmas are rejected-- by the renamer,letcc_str |Justcc_str <-mb_cc_str =sl_fs$unLoccc_str |otherwise=getOccFS(Var.varNamefun_id )cc_name =moduleNameFS(moduleNamemod )`appendFS`consFS'.'cc_str =doflavour <-DeclCC<$>getCCIndexM cc_name letcc =mkUserCCcc_name mod loc flavour return[ProfNotecc TrueTrue]|otherwise=return[]{- Note [Instantiate sig with fresh variables] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It's vital to instantiate a type signature with fresh variables. For example: type T = forall a. [a] -> [a] f :: T; f = g where { g :: T; g = <rhs> } We must not use the same 'a' from the defn of T at both places!! (Instantiation is only necessary because of type synonyms. Otherwise, it's all cool; each signature has distinct type variables from the renamer.) -}{- ********************************************************************* * * tcPolyInfer * * ********************************************************************* -}tcPolyInfer::RecFlag-- Whether it's recursive after breaking-- dependencies based on type signatures->TcPragEnv ->TcSigFun->Bool-- True <=> apply the monomorphism restriction->[LHsBindGhcRn]->TcM(LHsBindsGhcTcId,[TcId])tcPolyInfer rec_tc prag_fn tc_sig_fn mono bind_list =do{(tclvl ,wanted ,(binds' ,mono_infos ))<-pushLevelAndCaptureConstraints $tcMonoBinds rec_tc tc_sig_fn LetLclBndr bind_list ;letname_taus =[(mbi_poly_nameinfo ,idType(mbi_mono_idinfo ))|info <-mono_infos ]sigs =[sig |MBI {mbi_sig=Justsig }<-mono_infos ]infer_mode =ifmono thenApplyMR elseNoRestrictions ;mapM_(checkOverloadedSig mono )sigs ;traceTc "simplifyInfer call"(pprtclvl $$pprname_taus $$pprwanted );(qtvs ,givens ,ev_binds ,residual ,insoluble )<-simplifyInfer tclvl infer_mode sigs name_taus wanted ;emitConstraints residual ;letinferred_theta =mapevVarPredgivens ;exports <-checkNoErrs $mapM(mkExport prag_fn insoluble qtvs inferred_theta )mono_infos ;loc <-getSrcSpanM ;letpoly_ids =mapabe_polyexports abs_bind =cLloc $AbsBinds{abs_ext=noExt,abs_tvs=qtvs ,abs_ev_vars=givens ,abs_ev_binds=[ev_binds ],abs_exports=exports ,abs_binds=binds' ,abs_sig=False};traceTc "Binding:"(ppr(poly_ids `zip`mapidTypepoly_ids ));return(unitBagabs_bind ,poly_ids )}-- poly_ids are guaranteed zonked by mkExport--------------mkExport::TcPragEnv ->Bool-- True <=> there was an insoluble type error-- when typechecking the bindings->[TyVar]->TcThetaType-- Both already zonked->MonoBindInfo ->TcM(ABExportGhcTc)-- Only called for generalisation plan InferGen, not by CheckGen or NoGen---- mkExport generates exports with-- zonked type variables,-- zonked poly_ids-- The former is just because no further unifications will change-- the quantified type variables, so we can fix their final form-- right now.-- The latter is needed because the poly_ids are used to extend the-- type environment; see the invariant on TcEnv.tcExtendIdEnv-- Pre-condition: the qtvs and theta are already zonkedmkExport prag_fn insoluble qtvs theta mono_info @(MBI {mbi_poly_name=poly_name ,mbi_sig=mb_sig ,mbi_mono_id=mono_id })=do{mono_ty <-zonkTcType (idTypemono_id );poly_id <-mkInferredPolyId insoluble qtvs theta poly_name mb_sig mono_ty -- NB: poly_id has a zonked type;poly_id <-addInlinePrags poly_id prag_sigs ;spec_prags <-tcSpecPrags poly_id prag_sigs -- tcPrags requires a zonked poly_id-- See Note [Impedance matching]-- NB: we have already done checkValidType, including an ambiguity check,-- on the type; either when we checked the sig or in mkInferredPolyId;letpoly_ty =idTypepoly_id sel_poly_ty =mkInfSigmaTyqtvs theta mono_ty -- This type is just going into tcSubType,-- so Inferred vs. Specified doesn't matter;wrap <-ifsel_poly_ty `eqType`poly_ty -- NB: eqType ignores visibilitythenreturnidHsWrapper-- Fast path; also avoids complaint when we infer-- an ambiguous type and have AllowAmbiguousType-- e..g infer x :: forall a. F a -> IntelseaddErrCtxtM (mk_impedance_match_msg mono_info sel_poly_ty poly_ty )$tcSubType_NC sig_ctxt sel_poly_ty poly_ty ;warn_missing_sigs <-woptM Opt_WarnMissingLocalSignatures;whenwarn_missing_sigs $localSigWarn Opt_WarnMissingLocalSignaturespoly_id mb_sig ;return(ABE{abe_ext=noExt,abe_wrap=wrap -- abe_wrap :: idType poly_id ~ (forall qtvs. theta => mono_ty),abe_poly=poly_id ,abe_mono=mono_id ,abe_prags=SpecPragsspec_prags })}whereprag_sigs =lookupPragEnv prag_fn poly_name sig_ctxt =InfSigCtxtpoly_name mkInferredPolyId::Bool-- True <=> there was an insoluble error when-- checking the binding group for this Id->[TyVar]->TcThetaType->Name->MaybeTcIdSigInst->TcType->TcMTcIdmkInferredPolyId insoluble qtvs inferred_theta poly_name mb_sig_inst mono_ty |Just(TISI{sig_inst_sig=sig })<-mb_sig_inst ,CompleteSig{sig_bndr=poly_id }<-sig =returnpoly_id |otherwise-- Either no type sig or partial type sig=checkNoErrs $-- The checkNoErrs ensures that if the type is ambiguous-- we don't carry on to the impedance matching, and generate-- a duplicate ambiguity error. There is a similar-- checkNoErrs for complete type signatures too.do{fam_envs <-tcGetFamInstEnvs ;let(_co ,mono_ty' )=normaliseTypefam_envs Nominalmono_ty -- Unification may not have normalised the type,-- (see Note [Lazy flattening] in TcFlatten) so do it-- here to make it as uncomplicated as possible.-- Example: f :: [F Int] -> Bool-- should be rewritten to f :: [Char] -> Bool, if possible---- We can discard the coercion _co, because we'll reconstruct-- it in the call to tcSubType below;(binders ,theta' )<-chooseInferredQuantifiers inferred_theta (tyCoVarsOfTypemono_ty' )qtvs mb_sig_inst ;letinferred_poly_ty =mkForAllTysbinders (mkPhiTytheta' mono_ty' );traceTc "mkInferredPolyId"(vcat[pprpoly_name ,pprqtvs ,pprtheta' ,pprinferred_poly_ty ]);unlessinsoluble $addErrCtxtM (mk_inf_msg poly_name inferred_poly_ty )$checkValidType (InfSigCtxtpoly_name )inferred_poly_ty -- See Note [Validity of inferred types]-- If we found an insoluble error in the function definition, don't-- do this check; otherwise (#14000) we may report an ambiguity-- error for a rather bogus type.;return(mkLocalIdOrCoVarpoly_name inferred_poly_ty )}chooseInferredQuantifiers::TcThetaType-- inferred->TcTyVarSet-- tvs free in tau type->[TcTyVar]-- inferred quantified tvs->MaybeTcIdSigInst->TcM([TyVarBinder],TcThetaType)chooseInferredQuantifiers inferred_theta tau_tvs qtvs Nothing=-- No type signature (partial or complete) for this binder,do{letfree_tvs =closeOverKinds(growThetaTyVars inferred_theta tau_tvs )-- Include kind variables! #7916my_theta =pickCapturedPredsfree_tvs inferred_theta binders =[mkTyVarBinderInferredtv |tv <-qtvs ,tv `elemVarSet`free_tvs ];return(binders ,my_theta )}chooseInferredQuantifiersinferred_theta tau_tvs qtvs (Just(TISI{sig_inst_sig=sig -- Always PartialSig,sig_inst_wcx=wcx ,sig_inst_theta=annotated_theta ,sig_inst_skols=annotated_tvs }))=-- Choose quantifiers for a partial type signaturedo{psig_qtv_prs <-zonkTyVarTyVarPairs annotated_tvs -- Check whether the quantified variables of the-- partial signature have been unified together-- See Note [Quantified variables in partial type signatures];mapM_report_dup_tyvar_tv_err (findDupTyVarTvspsig_qtv_prs )-- Check whether a quantified variable of the partial type-- signature is not actually quantified. How can that happen?-- See Note [Quantification and partial signatures] Wrinkle 4-- in TcSimplify;mapM_report_mono_sig_tv_err [n |(n ,tv )<-psig_qtv_prs ,not(tv `elem`qtvs )];letpsig_qtvs =mkVarSet(mapsndpsig_qtv_prs );annotated_theta <-zonkTcTypes annotated_theta ;(free_tvs ,my_theta )<-choose_psig_context psig_qtvs annotated_theta wcx ;letkeep_me =free_tvs `unionVarSet`psig_qtvs final_qtvs =[mkTyVarBindervis tv |tv <-qtvs -- Pulling from qtvs maintains original order,tv `elemVarSet`keep_me ,letvis |tv `elemVarSet`psig_qtvs =Specified|otherwise=Inferred];return(final_qtvs ,my_theta )}wherereport_dup_tyvar_tv_err (n1 ,n2 )|PartialSig{psig_name=fn_name ,psig_hs_ty=hs_ty }<-sig =addErrTc (hang(text"Couldn't match"<+>quotes(pprn1 )<+>text"with"<+>quotes(pprn2 ))2(hang(text"both bound by the partial type signature:")2(pprfn_name <+>dcolon<+>pprhs_ty )))|otherwise-- Can't happen; by now we know it's a partial sig=pprPanic"report_tyvar_tv_err"(pprsig )report_mono_sig_tv_err n |PartialSig{psig_name=fn_name ,psig_hs_ty=hs_ty }<-sig =addErrTc (hang(text"Can't quantify over"<+>quotes(pprn ))2(hang(text"bound by the partial type signature:")2(pprfn_name <+>dcolon<+>pprhs_ty )))|otherwise-- Can't happen; by now we know it's a partial sig=pprPanic"report_mono_sig_tv_err"(pprsig )choose_psig_context::VarSet->TcThetaType->MaybeTcType->TcM(VarSet,TcThetaType)choose_psig_context _annotated_theta Nothing=do{letfree_tvs =closeOverKinds(tyCoVarsOfTypesannotated_theta `unionVarSet`tau_tvs );return(free_tvs ,annotated_theta )}choose_psig_contextpsig_qtvs annotated_theta (Justwc_var_ty )=do{letfree_tvs =closeOverKinds(growThetaTyVars inferred_theta seed_tvs )-- growThetaVars just like the no-type-sig case-- Omitting this caused #12844seed_tvs =tyCoVarsOfTypesannotated_theta -- These are put there`unionVarSet`tau_tvs -- by the user;letkeep_me =psig_qtvs `unionVarSet`free_tvs my_theta =pickCapturedPredskeep_me inferred_theta -- Fill in the extra-constraints wildcard hole with inferred_theta,-- so that the Hole constraint we have already emitted-- (in tcHsPartialSigType) can report what filled it in.-- NB: my_theta already includes all the annotated constraints;letinferred_diff =[pred |pred <-my_theta ,all(not.(`eqType`pred ))annotated_theta ];ctuple <-mk_ctuple inferred_diff ;casetcGetCastedTyVar_maybewc_var_ty of-- We know that wc_co must have type kind(wc_var) ~ Constraint, as it-- comes from the checkExpectedKind in TcHsType.tcWildCardOcc. So, to-- make the kinds work out, we reverse the cast here.Just(wc_var ,wc_co )->writeMetaTyVar wc_var (ctuple `mkCastTy`mkTcSymCowc_co )Nothing->pprPanic"chooseInferredQuantifiers 1"(pprwc_var_ty );traceTc "completeTheta"$vcat[pprsig ,pprannotated_theta ,pprinferred_theta ,pprinferred_diff ];return(free_tvs ,my_theta )}mk_ctuple preds =return(mkBoxedTupleTypreds )-- Hack alert! See TcHsType:-- Note [Extra-constraint holes in partial type signatures]mk_impedance_match_msg::MonoBindInfo ->TcType->TcType->TidyEnv->TcM(TidyEnv,SDoc)-- This is a rare but rather awkward error messagesmk_impedance_match_msg (MBI {mbi_poly_name=name ,mbi_sig=mb_sig })inf_ty sig_ty tidy_env =do{(tidy_env1 ,inf_ty )<-zonkTidyTcType tidy_env inf_ty ;(tidy_env2 ,sig_ty )<-zonkTidyTcType tidy_env1 sig_ty ;letmsg =vcat[text"When checking that the inferred type",nest2$pprname <+>dcolon<+>pprinf_ty ,text"is as general as its"<+>what <+>text"signature",nest2$pprname <+>dcolon<+>pprsig_ty ];return(tidy_env2 ,msg )}wherewhat =casemb_sig ofNothing->text"inferred"Justsig |isPartialSigsig ->text"(partial)"|otherwise->emptymk_inf_msg::Name->TcType->TidyEnv->TcM(TidyEnv,SDoc)mk_inf_msg poly_name poly_ty tidy_env =do{(tidy_env1 ,poly_ty )<-zonkTidyTcType tidy_env poly_ty ;letmsg =vcat[text"When checking the inferred type",nest2$pprpoly_name <+>dcolon<+>pprpoly_ty ];return(tidy_env1 ,msg )}-- | Warn the user about polymorphic local binders that lack type signatures.localSigWarn::WarningFlag->Id->MaybeTcIdSigInst->TcM()localSigWarn flag id mb_sig |Just_<-mb_sig =return()|not(isSigmaTy(idTypeid ))=return()|otherwise=warnMissingSignatures flag msg id wheremsg =text"Polymorphic local binding with no type signature:"warnMissingSignatures::WarningFlag->SDoc->Id->TcM()warnMissingSignatures flag msg id =do{env0 <-tcInitTidyEnv ;let(env1 ,tidy_ty )=tidyOpenTypeenv0 (idTypeid );addWarnTcM (Reasonflag )(env1 ,mk_msg tidy_ty )}wheremk_msg ty =sep[msg ,nest2$pprPrefixName(idNameid )<+>dcolon<+>pprty ]checkOverloadedSig::Bool->TcIdSigInst->TcM()-- Example:-- f :: Eq a => a -> a-- K f = e-- The MR applies, but the signature is overloaded, and it's-- best to complain about this directly-- c.f #11339checkOverloadedSig monomorphism_restriction_applies sig |not(null(sig_inst_thetasig )),monomorphism_restriction_applies ,letorig_sig =sig_inst_sigsig =setSrcSpan (sig_locorig_sig )$failWith $hang(text"Overloaded signature conflicts with monomorphism restriction")2(pprorig_sig )|otherwise=return(){- Note [Partial type signatures and generalisation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ If /any/ of the signatures in the gropu is a partial type signature f :: _ -> Int then we *always* use the InferGen plan, and hence tcPolyInfer. We do this even for a local binding with -XMonoLocalBinds, when we normally use NoGen. Reasons: * The TcSigInfo for 'f' has a unification variable for the '_', whose TcLevel is one level deeper than the current level. (See pushTcLevelM in tcTySig.) But NoGen doesn't increase the TcLevel like InferGen, so we lose the level invariant. * The signature might be f :: forall a. _ -> a so it really is polymorphic. It's not clear what it would mean to use NoGen on this, and indeed the ASSERT in tcLhs, in the (Just sig) case, checks that if there is a signature then we are using LetLclBndr, and hence a nested AbsBinds with increased TcLevel It might be possible to fix these difficulties somehow, but there doesn't seem much point. Indeed, adding a partial type signature is a way to get per-binding inferred generalisation. We apply the MR if /all/ of the partial signatures lack a context. In particular (#11016): f2 :: (?loc :: Int) => _ f2 = ?loc It's stupid to apply the MR here. This test includes an extra-constraints wildcard; that is, we don't apply the MR if you write f3 :: _ => blah Note [Quantified variables in partial type signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f :: forall a. a -> a -> _ f x y = g x y g :: forall b. b -> b -> _ g x y = [x, y] Here, 'f' and 'g' are mutually recursive, and we end up unifying 'a' and 'b' together, which is fine. So we bind 'a' and 'b' to TyVarTvs, which can then unify with each other. But now consider: f :: forall a b. a -> b -> _ f x y = [x, y] We want to get an error from this, because 'a' and 'b' get unified. So we make a test, one per parital signature, to check that the explicitly-quantified type variables have not been unified together. #14449 showed this up. Note [Validity of inferred types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We need to check inferred type for validity, in case it uses language extensions that are not turned on. The principle is that if the user simply adds the inferred type to the program source, it'll compile fine. See #8883. Examples that might fail: - the type might be ambiguous - an inferred theta that requires type equalities e.g. (F a ~ G b) or multi-parameter type classes - an inferred type that includes unboxed tuples Note [Impedance matching] ~~~~~~~~~~~~~~~~~~~~~~~~~ Consider f 0 x = x f n x = g [] (not x) g [] y = f 10 y g _ y = f 9 y After typechecking we'll get f_mono_ty :: a -> Bool -> Bool g_mono_ty :: [b] -> Bool -> Bool with constraints (Eq a, Num a) Note that f is polymorphic in 'a' and g in 'b'; and these are not linked. The types we really want for f and g are f :: forall a. (Eq a, Num a) => a -> Bool -> Bool g :: forall b. [b] -> Bool -> Bool We can get these by "impedance matching": tuple :: forall a b. (Eq a, Num a) => (a -> Bool -> Bool, [b] -> Bool -> Bool) tuple a b d1 d1 = let ...bind f_mono, g_mono in (f_mono, g_mono) f a d1 d2 = case tuple a Any d1 d2 of (f, g) -> f g b = case tuple Integer b dEqInteger dNumInteger of (f,g) -> g Suppose the shared quantified tyvars are qtvs and constraints theta. Then we want to check that forall qtvs. theta => f_mono_ty is more polymorphic than f's polytype and the proof is the impedance matcher. Notice that the impedance matcher may do defaulting. See #7173. It also cleverly does an ambiguity check; for example, rejecting f :: F a -> F a where F is a non-injective type function. -}{- Note [SPECIALISE pragmas] ~~~~~~~~~~~~~~~~~~~~~~~~~ There is no point in a SPECIALISE pragma for a non-overloaded function: reverse :: [a] -> [a] {-# SPECIALISE reverse :: [Int] -> [Int] #-} But SPECIALISE INLINE *can* make sense for GADTS: data Arr e where ArrInt :: !Int -> ByteArray# -> Arr Int ArrPair :: !Int -> Arr e1 -> Arr e2 -> Arr (e1, e2) (!:) :: Arr e -> Int -> e {-# SPECIALISE INLINE (!:) :: Arr Int -> Int -> Int #-} {-# SPECIALISE INLINE (!:) :: Arr (a, b) -> Int -> (a, b) #-} (ArrInt _ ba) !: (I# i) = I# (indexIntArray# ba i) (ArrPair _ a1 a2) !: i = (a1 !: i, a2 !: i) When (!:) is specialised it becomes non-recursive, and can usefully be inlined. Scary! So we only warn for SPECIALISE *without* INLINE for a non-overloaded function. ************************************************************************ * * tcMonoBinds * * ************************************************************************ @tcMonoBinds@ deals with a perhaps-recursive group of HsBinds. The signatures have been dealt with already. -}dataMonoBindInfo =MBI {mbi_poly_name ::Name,mbi_sig ::MaybeTcIdSigInst,mbi_mono_id ::TcId}tcMonoBinds::RecFlag-- Whether the binding is recursive for typechecking purposes-- i.e. the binders are mentioned in their RHSs, and-- we are not rescued by a type signature->TcSigFun->LetBndrSpec ->[LHsBindGhcRn]->TcM(LHsBindsGhcTcId,[MonoBindInfo ])tcMonoBinds is_rec sig_fn no_gen [dL->Lb_loc (FunBind{fun_id=(dL->Lnm_loc name ),fun_matches=matches ,fun_ext=fvs })]-- Single function binding,|NonRecursive<-is_rec -- ...binder isn't mentioned in RHS,Nothing<-sig_fn name -- ...with no type signature=-- Note [Single function non-recursive binding special-case]-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-- 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) -> <body>-- We want to infer a higher-rank type for fsetSrcSpan b_loc $do{((co_fn ,matches' ),rhs_ty )<-tcInferInst $\exp_ty ->-- tcInferInst: see TcUnify,-- Note [Deep instantiation of InferResult] in TcUnifytcExtendBinderStack [TcIdBndr_ExpTypename exp_ty NotTopLevel]$-- We extend the error context even for a non-recursive-- function so that in type error messages we show the-- type of the thing whose rhs we are type checkingtcMatchesFun (cLnm_loc name )matches exp_ty ;mono_id <-newLetBndr no_gen name rhs_ty ;return(unitBag$cLb_loc $FunBind{fun_id=cLnm_loc mono_id ,fun_matches=matches' ,fun_ext=fvs ,fun_co_fn=co_fn ,fun_tick=[]},[MBI {mbi_poly_name=name ,mbi_sig=Nothing,mbi_mono_id=mono_id }])}tcMonoBinds_sig_fn no_gen binds =do{tc_binds <-mapM(wrapLocM (tcLhs sig_fn no_gen ))binds -- Bring the monomorphic Ids, into scope for the RHSs;letmono_infos =getMonoBindInfo tc_binds rhs_id_env =[(name ,mono_id )|MBI {mbi_poly_name=name ,mbi_sig=mb_sig ,mbi_mono_id=mono_id }<-mono_infos ,casemb_sig ofJustsig ->isPartialSigsig Nothing->True]-- A monomorphic binding for each term variable that lacks-- a complete type sig. (Ones with a sig are already in scope.);traceTc "tcMonoBinds"$vcat[pprn <+>pprid <+>ppr(idTypeid )|(n ,id )<-rhs_id_env ];binds' <-tcExtendRecIds rhs_id_env $mapM(wrapLocM tcRhs )tc_binds ;return(listToBagbinds' ,mono_infos )}-------------------------- 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'tdataTcMonoBind -- Half completed; LHS done, RHS not done=TcFunBind MonoBindInfo SrcSpan(MatchGroupGhcRn(LHsExprGhcRn))|TcPatBind [MonoBindInfo ](LPatGhcTcId)(GRHSsGhcRn(LHsExprGhcRn))TcSigmaTypetcLhs::TcSigFun->LetBndrSpec ->HsBindGhcRn->TcMTcMonoBind -- Only called with plan InferGen (LetBndrSpec = LetLclBndr)-- or NoGen (LetBndrSpec = LetGblBndr)-- CheckGen is used only for functions with a complete type signature,-- and tcPolyCheck doesn't use tcMonoBinds at alltcLhs sig_fn no_gen (FunBind{fun_id=(dL->Lnm_loc name ),fun_matches=matches })|Just(TcIdSigsig )<-sig_fn name =-- There is a type signature.-- It must be partial; if complete we'd be in tcPolyCheck!-- e.g. f :: _ -> _-- f x = ...g...-- Just g = ...f...-- Hence always typechecked with InferGendo{mono_info <-tcLhsSigId no_gen (name ,sig );return(TcFunBind mono_info nm_loc matches )}|otherwise-- No type signature=do{mono_ty <-newOpenFlexiTyVarTy ;mono_id <-newLetBndr no_gen name mono_ty ;letmono_info =MBI {mbi_poly_name=name ,mbi_sig=Nothing,mbi_mono_id=mono_id };return(TcFunBind mono_info nm_loc matches )}tcLhssig_fn no_gen (PatBind{pat_lhs=pat ,pat_rhs=grhss })=-- See Note [Typechecking pattern bindings]do{sig_mbis <-mapM(tcLhsSigId no_gen )sig_names ;letinst_sig_fun =lookupNameEnv$mkNameEnv$[(mbi_poly_namembi ,mbi_mono_idmbi )|mbi <-sig_mbis ]-- See Note [Existentials in pattern bindings];((pat' ,nosig_mbis ),pat_ty )<-addErrCtxt (patMonoBindsCtxt pat grhss )$tcInferNoInst $\exp_ty ->tcLetPat inst_sig_fun no_gen pat exp_ty $mapMlookup_info nosig_names ;letmbis =sig_mbis ++nosig_mbis ;traceTc "tcLhs"(vcat[pprid <+>dcolon<+>ppr(idTypeid )|mbi <-mbis ,letid =mbi_mono_idmbi ]$$pprno_gen );return(TcPatBind mbis pat' grhss pat_ty )}wherebndr_names =collectPatBinderspat (nosig_names ,sig_names )=partitionWithfind_sig bndr_names find_sig::Name->EitherName(Name,TcIdSigInfo)find_sig name =casesig_fn name ofJust(TcIdSigsig )->Right(name ,sig )_->Leftname -- After typechecking the pattern, look up the binder-- names that lack a signature, which the pattern has brought-- into scope.lookup_info::Name->TcMMonoBindInfo lookup_info name =do{mono_id <-tcLookupId name ;return(MBI {mbi_poly_name=name ,mbi_sig=Nothing,mbi_mono_id=mono_id })}tcLhs__other_bind =pprPanic"tcLhs"(pprother_bind )-- AbsBind, VarBind impossible-------------------tcLhsSigId::LetBndrSpec ->(Name,TcIdSigInfo)->TcMMonoBindInfo tcLhsSigId no_gen (name ,sig )=do{inst_sig <-tcInstSig sig ;mono_id <-newSigLetBndr no_gen name inst_sig ;return(MBI {mbi_poly_name=name ,mbi_sig=Justinst_sig ,mbi_mono_id=mono_id })}------------newSigLetBndr::LetBndrSpec ->Name->TcIdSigInst->TcMTcIdnewSigLetBndr (LetGblBndr prags )name (TISI{sig_inst_sig=id_sig })|CompleteSig{sig_bndr=poly_id }<-id_sig =addInlinePrags poly_id (lookupPragEnv prags name )newSigLetBndrno_gen name (TISI{sig_inst_tau=tau })=newLetBndr no_gen name tau -------------------tcRhs::TcMonoBind ->TcM(HsBindGhcTcId)tcRhs (TcFunBind info @(MBI {mbi_sig=mb_sig ,mbi_mono_id=mono_id })loc matches )=tcExtendIdBinderStackForRhs [info ]$tcExtendTyVarEnvForRhs mb_sig $do{traceTc "tcRhs: fun bind"(pprmono_id $$ppr(idTypemono_id ));(co_fn ,matches' )<-tcMatchesFun (cLloc (idNamemono_id ))matches (mkCheckExpType$idTypemono_id );return(FunBind{fun_id=cLloc mono_id ,fun_matches=matches' ,fun_co_fn=co_fn ,fun_ext=placeHolderNamesTc,fun_tick=[]})}tcRhs(TcPatBind infos pat' grhss pat_ty )=-- When we are doing pattern bindings we *don't* bring any scoped-- type variables into scope unlike function bindings-- Wny not? They are not completely rigid.-- That's why we have the special case for a single FunBind in tcMonoBindstcExtendIdBinderStackForRhs infos $do{traceTc "tcRhs: pat bind"(pprpat' $$pprpat_ty );grhss' <-addErrCtxt (patMonoBindsCtxt pat' grhss )$tcGRHSsPat grhss pat_ty ;return(PatBind{pat_lhs=pat' ,pat_rhs=grhss' ,pat_ext=NPatBindTcplaceHolderNamesTcpat_ty ,pat_ticks=([],[])})}tcExtendTyVarEnvForRhs::MaybeTcIdSigInst->TcMa ->TcMa tcExtendTyVarEnvForRhs Nothingthing_inside =thing_inside tcExtendTyVarEnvForRhs(Justsig )thing_inside =tcExtendTyVarEnvFromSig sig thing_inside tcExtendTyVarEnvFromSig::TcIdSigInst->TcMa ->TcMa tcExtendTyVarEnvFromSig sig_inst thing_inside |TISI{sig_inst_skols=skol_prs ,sig_inst_wcs=wcs }<-sig_inst =tcExtendNameTyVarEnv wcs $tcExtendNameTyVarEnv skol_prs $thing_inside tcExtendIdBinderStackForRhs::[MonoBindInfo ]->TcMa ->TcMa -- Extend the TcBinderStack for the RHS of the binding, with-- the monomorphic Id. That way, if we have, say-- f = \x -> blah-- and something goes wrong in 'blah', we get a "relevant binding"-- looking like f :: alpha -> beta-- This applies if 'f' has a type signature too:-- f :: forall a. [a] -> [a]-- f x = True-- We can't unify True with [a], and a relevant binding is f :: [a] -> [a]-- If we had the *polymorphic* version of f in the TcBinderStack, it-- would not be reported as relevant, because its type is closedtcExtendIdBinderStackForRhs infos thing_inside =tcExtendBinderStack [TcIdBndrmono_id NotTopLevel|MBI {mbi_mono_id=mono_id }<-infos ]thing_inside -- NotTopLevel: it's a monomorphic binding---------------------getMonoBindInfo::[LocatedTcMonoBind ]->[MonoBindInfo ]getMonoBindInfo tc_binds =foldr(get_info .unLoc)[]tc_binds whereget_info (TcFunBind info __)rest =info :rest get_info(TcPatBind infos ___)rest =infos ++rest {- Note [Typechecking pattern bindings] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Look at: - typecheck/should_compile/ExPat - #12427, typecheck/should_compile/T12427{a,b} data T where MkT :: Integral a => a -> Int -> T and suppose t :: T. Which of these pattern bindings are ok? E1. let { MkT p _ = t } in <body> E2. let { MkT _ q = t } in <body> E3. let { MkT (toInteger -> r) _ = t } in <body> * (E1) is clearly wrong because the existential 'a' escapes. What type could 'p' possibly have? * (E2) is fine, despite the existential pattern, because q::Int, and nothing escapes. * Even (E3) is fine. The existential pattern binds a dictionary for (Integral a) which the view pattern can use to convert the a-valued field to an Integer, so r :: Integer. An easy way to see all three is to imagine the desugaring. For (E2) it would look like let q = case t of MkT _ q' -> q' in <body> We typecheck pattern bindings as follows. First tcLhs does this: 1. Take each type signature q :: ty, partial or complete, and instantiate it (with tcLhsSigId) to get a MonoBindInfo. This gives us a fresh "mono_id" qm :: instantiate(ty), where qm has a fresh name. Any fresh unification variables in instantiate(ty) born here, not deep under implications as would happen if we allocated them when we encountered q during tcPat. 2. Build a little environment mapping "q" -> "qm" for those Ids with signatures (inst_sig_fun) 3. Invoke tcLetPat to typecheck the pattern. - We pass in the current TcLevel. This is captured by TcPat.tcLetPat, and put into the pc_lvl field of PatCtxt, in PatEnv. - When tcPat finds an existential constructor, it binds fresh type variables and dictionaries as usual, increments the TcLevel, and emits an implication constraint. - When we come to a binder (TcPat.tcPatBndr), it looks it up in the little environment (the pc_sig_fn field of PatCtxt). Success => There was a type signature, so just use it, checking compatibility with the expected type. Failure => No type sigature. Infer case: (happens only outside any constructor pattern) use a unification variable at the outer level pc_lvl Check case: use promoteTcType to promote the type to the outer level pc_lvl. This is the place where we emit a constraint that'll blow up if existential capture takes place Result: the type of the binder is always at pc_lvl. This is crucial. 4. Throughout, when we are making up an Id for the pattern-bound variables (newLetBndr), we have two cases: - If we are generalising (generalisation plan is InferGen or CheckGen), then the let_bndr_spec will be LetLclBndr. In that case we want to bind a cloned, local version of the variable, with the type given by the pattern context, *not* by the signature (even if there is one; see #7268). The mkExport part of the generalisation step will do the checking and impedance matching against the signature. - If for some some reason we are not generalising (plan = NoGen), the LetBndrSpec will be LetGblBndr. In that case we must bind the global version of the Id, and do so with precisely the type given in the signature. (Then we unify with the type from the pattern context type.) And that's it! The implication constraints check for the skolem escape. It's quite simple and neat, and more expressive than before e.g. GHC 8.0 rejects (E2) and (E3). Example for (E1), starting at level 1. We generate p :: beta:1, with constraints (forall:3 a. Integral a => a ~ beta) The (a~beta) can't float (because of the 'a'), nor be solved (because beta is untouchable.) Example for (E2), we generate q :: beta:1, with constraint (forall:3 a. Integral a => Int ~ beta) The beta is untouchable, but floats out of the constraint and can be solved absolutely fine. ************************************************************************ * * Generalisation * * ********************************************************************* -}dataGeneralisationPlan =NoGen -- No generalisation, no AbsBinds|InferGen -- Implicit generalisation; there is an AbsBindsBool-- True <=> apply the MR; generalise only unconstrained type vars|CheckGen (LHsBindGhcRn)TcIdSigInfo-- One FunBind with a signature-- Explicit generalisation-- A consequence of the no-AbsBinds choice (NoGen) is that there is-- no "polymorphic Id" and "monmomorphic Id"; there is just the oneinstanceOutputableGeneralisationPlan whereppr NoGen =text"NoGen"ppr(InferGen b )=text"InferGen"<+>pprb ppr(CheckGen _s )=text"CheckGen"<+>pprs decideGeneralisationPlan::DynFlags->[LHsBindGhcRn]->IsGroupClosed->TcSigFun->GeneralisationPlan decideGeneralisationPlan dflags lbinds closed sig_fn |has_partial_sigs =InferGen (andpartial_sig_mrs )|Just(bind ,sig )<-one_funbind_with_sig =CheckGen bind sig |do_not_generalise closed =NoGen |otherwise=InferGen mono_restriction wherebinds =mapunLoclbinds partial_sig_mrs::[Bool]-- One for each partial signature (so empty => no partial sigs)-- The Bool is True if the signature has no constraint context-- so we should apply the MR-- See Note [Partial type signatures and generalisation]partial_sig_mrs =[nulltheta |TcIdSig(PartialSig{psig_hs_ty=hs_ty })<-mapMaybesig_fn (collectHsBindListBinderslbinds ),let(_,dL->L_theta ,_)=splitLHsSigmaTy(hsSigWcTypehs_ty )]has_partial_sigs =not(nullpartial_sig_mrs )mono_restriction =xoptLangExt.MonomorphismRestrictiondflags &&anyrestricted binds do_not_generalise (IsGroupClosed_True)=False-- The 'True' means that all of the group's-- free vars have ClosedTypeId=True; so we can ignore-- -XMonoLocalBinds, and generalise anywaydo_not_generalise_=xoptLangExt.MonoLocalBindsdflags -- With OutsideIn, all nested bindings are monomorphic-- except a single function binding with a signatureone_funbind_with_sig |[lbind @(dL->L_(FunBind{fun_id=v }))]<-lbinds ,Just(TcIdSigsig )<-sig_fn (unLocv )=Just(lbind ,sig )|otherwise=Nothing-- The Haskell 98 monomorphism restrictionrestricted (PatBind{})=Truerestricted(VarBind{var_id=v })=no_sig v restricted(FunBind{fun_id=v ,fun_matches=m })=restricted_match m &&no_sig (unLocv )restrictedb =pprPanic"isRestrictedGroup/unrestricted"(pprb )restricted_match mg =matchGroupAritymg ==0-- No args => like a pattern binding-- Some args => a function bindingno_sig n =not(hasCompleteSigsig_fn n )isClosedBndrGroup::TcTypeEnv->Bag(LHsBindGhcRn)->IsGroupClosedisClosedBndrGroup type_env binds =IsGroupClosedfv_env type_closed wheretype_closed =allUFM(nameSetAllis_closed_type_id )fv_env fv_env::NameEnvNameSetfv_env =mkNameEnv$concatMap(bindFvs .unLoc)binds bindFvs::HsBindLRGhcRnGhcRn->[(Name,NameSet)]bindFvs (FunBind{fun_id=(dL->L_f ),fun_ext=fvs })=letopen_fvs =get_open_fvs fvs in[(f ,open_fvs )]bindFvs(PatBind{pat_lhs=pat ,pat_ext=fvs })=letopen_fvs =get_open_fvs fvs in[(b ,open_fvs )|b <-collectPatBinderspat ]bindFvs_=[]get_open_fvs fvs =filterNameSet(not.is_closed )fvs is_closed::Name->ClosedTypeIdis_closed name |Justthing <-lookupNameEnvtype_env name =casething ofAGlobal{}->TrueATcId{tct_info=ClosedLet}->True_->False|otherwise=True-- The free-var set for a top level binding mentionsis_closed_type_id::Name->Bool-- We're already removed Global and ClosedLet Idsis_closed_type_id name |Justthing <-lookupNameEnvtype_env name =casething ofATcId{tct_info=NonClosedLet_cl }->cl ATcId{tct_info=NotLetBound}->FalseATyVar{}->False-- In-scope type variables are not closed!_->pprPanic"is_closed_id"(pprname )|otherwise=True-- The free-var set for a top level binding mentions-- imported things too, so that we can report unused imports-- These won't be in the local type env.-- Ditto class method etc from the current module{- ********************************************************************* * * Error contexts and messages * * ********************************************************************* -}-- This one is called on LHS, when pat and grhss are both Name-- and on RHS, when pat is TcId and grhss is still NamepatMonoBindsCtxt::(OutputableBndrId(GhcPassp ),Outputablebody )=>LPat(GhcPassp )->GRHSsGhcRnbody ->SDocpatMonoBindsCtxt pat grhss =hang(text"In a pattern binding:")2(pprPatBindpat grhss )