X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMatches.lhs;h=12a59d766017fb1bf0da7244b66379b6426e90e7;hb=550421384b8364cdaf3135f7859c9f7d7ee1fff1;hp=484aa3c6e38ad0cfdc5bcbbd5f990d88e8d7f096;hpb=49bb45807fe94e432224601483cf3577b3f3fb7b;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMatches.lhs b/ghc/compiler/typecheck/TcMatches.lhs index 484aa3c..12a59d7 100644 --- a/ghc/compiler/typecheck/TcMatches.lhs +++ b/ghc/compiler/typecheck/TcMatches.lhs @@ -1,42 +1,56 @@ -\% +% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[TcMatches]{Typecheck some @Matches@} \begin{code} -module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda, tcStmts, tcGRHSs ) where +module TcMatches ( tcMatchesFun, tcGRHSsPat, tcMatchesCase, tcMatchLambda, + matchCtxt, + tcDoStmts, tcStmtsAndThen, tcStmts, tcThingWithSig, + tcMatchPats, + TcStmtCtxt(..), TcMatchCtxt(..) + ) where #include "HsVersions.h" -import {-# SOURCE #-} TcExpr( tcExpr ) +import {-# SOURCE #-} TcExpr( tcCheckRho, tcMonoExpr ) -import HsSyn ( HsBinds(..), Match(..), GRHSs(..), GRHS(..), - MonoBinds(..), StmtCtxt(..), Stmt(..), - pprMatch, getMatchLoc, consLetStmt, - mkMonoBind +import HsSyn ( HsExpr(..), LHsExpr, HsBindGroup(..), + Match(..), LMatch, GRHSs(..), GRHS(..), + Stmt(..), LStmt, HsMatchContext(..), HsStmtContext(..), + ReboundNames, LPat, + pprMatch, isDoExpr, + pprMatchContext, pprStmtContext, pprStmtResultContext, + collectSigTysFromPats, glueBindsOnGRHSs ) -import RnHsSyn ( RenamedMatch, RenamedGRHSs, RenamedStmt ) -import TcHsSyn ( TcMatch, TcGRHSs, TcStmt ) - -import TcMonad -import TcMonoType ( checkSigTyVars, tcHsTyVar, tcHsType, sigPatCtxt ) -import Inst ( Inst, LIE, plusLIE, emptyLIE, plusLIEs ) -import TcEnv ( tcExtendLocalValEnv, tcExtendGlobalTyVars, tcExtendTyVarEnv, tcGetGlobalTyVars ) -import TcPat ( tcPat, tcPatBndr_NoSigs, polyPatSig ) -import TcType ( TcType, newTyVarTy, newTyVarTy_OpenKind, zonkTcTyVars ) +import TcHsSyn ( ExprCoFn, TcDictBinds, isIdCoercion, (<$>), (<.>) ) + +import TcRnMonad +import TcHsType ( tcAddScopedTyVars, tcHsSigType, UserTypeCtxt(..) ) +import Inst ( tcSyntaxName, tcInstCall ) +import TcEnv ( TcId, tcLookupLocalIds, tcLookupId, tcExtendLocalValEnv, tcExtendLocalValEnv2 ) +import TcPat ( tcPat, tcMonoPatBndr ) +import TcMType ( newTyVarTy, newTyVarTys, zonkTcType ) +import TcType ( TcType, TcTyVar, TcSigmaType, TcRhoType, + tyVarsOfTypes, tidyOpenTypes, isSigmaTy, + mkFunTy, isOverloadedTy, liftedTypeKind, openTypeKind, + mkArrowKind, mkAppTy ) import TcBinds ( tcBindsAndThen ) -import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns ) -import TcUnify ( unifyFunTy, unifyTauTy ) +import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedBranches, readExpectedType, + unifyTauTy, subFunTys, unifyPArrTy, unifyListTy, unifyFunTy, + checkSigTyVarsWrt, tcSubExp, tcGen ) +import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns ) import Name ( Name ) -import TysWiredIn ( boolTy ) - +import TysWiredIn ( boolTy, mkListTy, mkPArrTy ) +import Id ( idType, mkLocalId ) +import CoreFVs ( idFreeTyVars ) import BasicTypes ( RecFlag(..) ) -import Type ( Kind, tyVarsOfType, isTauTy, mkFunTy, boxedTypeKind ) import VarSet -import Var ( Id ) -import Util import Bag +import Util ( isSingleton, notNull ) import Outputable +import SrcLoc ( Located(..), noLoc ) + import List ( nub ) \end{code} @@ -52,64 +66,97 @@ is used in error messages. It checks that all the equations have the same number of arguments before using @tcMatches@ to do the work. \begin{code} -tcMatchesFun :: [(Name,Id)] -- Bindings for the variables bound in this group - -> Name - -> TcType -- Expected type - -> [RenamedMatch] - -> TcM s ([TcMatch], LIE) +tcMatchesFun :: Name + -> [LMatch Name] + -> Expected TcRhoType -- Expected type + -> TcM [LMatch TcId] -tcMatchesFun xve fun_name expected_ty matches@(first_match:_) +tcMatchesFun fun_name matches@(first_match:_) expected_ty = -- Check that they all have the same no of arguments - -- Set the location to that of the first equation, so that + -- Location is in the monad, set the caller so that -- any inter-equation error messages get some vaguely -- sensible location. Note: we have to do this odd -- ann-grabbing, because we don't always have annotations in -- hand when we call tcMatchesFun... - tcAddSrcLoc (getMatchLoc first_match) ( - checkTc (sameNoOfArgs matches) - (varyingArgsErr fun_name matches) - ) `thenTc_` + checkTc (sameNoOfArgs matches) + (varyingArgsErr fun_name matches) `thenM_` -- ToDo: Don't use "expected" stuff if there ain't a type signature -- because inconsistency between branches -- may show up as something wrong with the (non-existent) type signature - -- No need to zonk expected_ty, because unifyFunTy does that on the fly - tcMatches xve matches expected_ty (FunRhs fun_name) + -- No need to zonk expected_ty, because subFunTys does that on the fly + tcMatches match_ctxt matches expected_ty + where + match_ctxt = MC { mc_what = FunRhs fun_name, + mc_body = tcMonoExpr } \end{code} @tcMatchesCase@ doesn't do the argument-count check because the parser guarantees that each equation has exactly one argument. \begin{code} -tcMatchesCase :: [RenamedMatch] -- The case alternatives - -> TcType -- Type of whole case expressions - -> TcM s (TcType, -- Inferred type of the scrutinee - [TcMatch], -- Translated alternatives - LIE) - -tcMatchesCase matches expr_ty - = newTyVarTy_OpenKind `thenNF_Tc` \ scrut_ty -> - tcMatches [] matches (mkFunTy scrut_ty expr_ty) CaseAlt `thenTc` \ (matches', lie) -> - returnTc (scrut_ty, matches', lie) - -tcMatchLambda :: RenamedMatch -> TcType -> TcM s (TcMatch, LIE) -tcMatchLambda match res_ty = tcMatch [] match res_ty LambdaBody +tcMatchesCase :: TcMatchCtxt -- Case context + -> [LMatch Name] -- The case alternatives + -> Expected TcRhoType -- Type of whole case expressions + -> TcM (TcRhoType, -- Inferred type of the scrutinee + [LMatch TcId]) -- Translated alternatives + +tcMatchesCase ctxt matches (Check expr_ty) + = -- This case is a bit yukky, because it prevents the + -- scrutinee being higher-ranked, which might just possible + -- matter if we were seq'ing on it. But it's awkward to fix. + newTyVarTy openTypeKind `thenM` \ scrut_ty -> + tcMatches ctxt matches (Check (mkFunTy scrut_ty expr_ty)) `thenM` \ matches' -> + returnM (scrut_ty, matches') + +tcMatchesCase ctxt matches (Infer hole) + = newHole `thenM` \ fun_hole -> + tcMatches ctxt matches (Infer fun_hole) `thenM` \ matches' -> + readMutVar fun_hole `thenM` \ fun_ty -> + -- The result of tcMatches is bound to be a function type + unifyFunTy fun_ty `thenM` \ (scrut_ty, res_ty) -> + writeMutVar hole res_ty `thenM_` + returnM (scrut_ty, matches') + + +tcMatchLambda :: LMatch Name -> Expected TcRhoType -> TcM (LMatch TcId) +tcMatchLambda match res_ty = tcMatch match_ctxt res_ty match + where + match_ctxt = MC { mc_what = LambdaExpr, + mc_body = tcMonoExpr } \end{code} +@tcGRHSsPat@ typechecks @[GRHSs]@ that occur in a @PatMonoBind@. \begin{code} -tcMatches :: [(Name,Id)] - -> [RenamedMatch] - -> TcType - -> StmtCtxt - -> TcM s ([TcMatch], LIE) - -tcMatches xve matches expected_ty fun_or_case - = mapAndUnzipTc tc_match matches `thenTc` \ (matches, lies) -> - returnTc (matches, plusLIEs lies) +tcGRHSsPat :: GRHSs Name + -> Expected TcRhoType + -> TcM (GRHSs TcId) +tcGRHSsPat grhss exp_ty = tcGRHSs match_ctxt grhss exp_ty where - tc_match match = tcMatch xve match expected_ty fun_or_case + match_ctxt = MC { mc_what = PatBindRhs, + mc_body = tcMonoExpr } +\end{code} + +\begin{code} +data TcMatchCtxt -- c.f. TcStmtCtxt, also in this module + = MC { mc_what :: HsMatchContext Name, -- What kind of thing this is + mc_body :: LHsExpr Name -- Type checker for a body of an alternative + -> Expected TcRhoType + -> TcM (LHsExpr TcId) } + +tcMatches :: TcMatchCtxt + -> [LMatch Name] + -> Expected TcRhoType + -> TcM [LMatch TcId] + +tcMatches ctxt matches exp_ty + = -- If there is more than one branch, and exp_ty is a 'hole', + -- all branches must be types, not type schemes, otherwise the + -- order in which we check them would affect the result. + zapExpectedBranches matches exp_ty `thenM` \ exp_ty' -> + mappM (tcMatch ctxt exp_ty') matches \end{code} @@ -120,116 +167,112 @@ tcMatches xve matches expected_ty fun_or_case %************************************************************************ \begin{code} -tcMatch :: [(Name,Id)] - -> RenamedMatch - -> TcType -- Expected result-type of the Match. - -- Early unification with this guy gives better error messages - -> StmtCtxt - -> TcM s (TcMatch, LIE) - -tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty ctxt - = tcAddSrcLoc (getMatchLoc match) $ - tcAddErrCtxt (matchCtxt ctxt match) $ - - if null sig_tvs then -- The common case - tc_match expected_ty `thenTc` \ (_, match_and_lie) -> - returnTc match_and_lie - - else - -- If there are sig tvs we must be careful *not* to use - -- expected_ty right away, else we'll unify with tyvars free - -- in the envt. So invent a fresh tyvar and use that instead - newTyVarTy_OpenKind `thenNF_Tc` \ tyvar_ty -> - - -- Extend the tyvar env and check the match itself - mapNF_Tc tcHsTyVar sig_tvs `thenNF_Tc` \ sig_tyvars -> - tcExtendTyVarEnv sig_tyvars ( - tc_match tyvar_ty - ) `thenTc` \ (pat_ids, match_and_lie) -> - - -- Check that the scoped type variables from the patterns - -- have not been constrained - tcAddErrCtxtM (sigPatCtxt sig_tyvars pat_ids) ( - checkSigTyVars sig_tyvars - ) `thenTc_` - - -- *Now* we're free to unify with expected_ty - unifyTauTy expected_ty tyvar_ty `thenTc_` - - returnTc match_and_lie +tcMatch :: TcMatchCtxt + -> Expected TcRhoType -- Expected result-type of the Match. + -- Early unification with this guy gives better error messages + -- We regard the Match as having type + -- (ty1 -> ... -> tyn -> result_ty) + -- where there are n patterns. + -> LMatch Name + -> TcM (LMatch TcId) + +tcMatch ctxt exp_ty match = wrapLocM (tc_match ctxt exp_ty) match + +tc_match ctxt expected_ty match@(Match pats maybe_rhs_sig grhss) + = addErrCtxt (matchCtxt (mc_what ctxt) match) $ -- I'm not sure why, so I put it back + subFunTys pats expected_ty $ \ pats_w_tys rhs_ty -> + -- This is the unique place we call subFunTys + -- The point is that if expected_y is a "hole", we want + -- to make arg_ty and rest_ty as "holes" too. + tcMatchPats pats_w_tys rhs_ty (tc_grhss rhs_ty) `thenM` \ (pats', grhss', ex_binds) -> + returnM (Match pats' Nothing (glueBindsOnGRHSs ex_binds grhss')) where - tc_match expected_ty -- Any sig tyvars are in scope by now - = -- STEP 1: Typecheck the patterns - tcMatchPats pats expected_ty `thenTc` \ (rhs_ty, pats', lie_req1, ex_tvs, pat_bndrs, lie_avail) -> - let - xve2 = bagToList pat_bndrs - pat_ids = map snd xve2 - ex_tv_list = bagToList ex_tvs - in - - -- STEP 2: Check that the remaining "expected type" is not a rank-2 type - -- If it is it'll mess up the unifier when checking the RHS - checkTc (isTauTy rhs_ty) lurkingRank2SigErr `thenTc_` - - -- STEP 3: Unify with the rhs type signature if any - (case maybe_rhs_sig of - Nothing -> returnTc () - Just sig -> tcHsType sig `thenTc` \ sig_ty -> - - -- Check that the signature isn't a polymorphic one, which - -- we don't permit (at present, anyway) - checkTc (isTauTy sig_ty) (polyPatSig sig_ty) `thenTc_` - unifyTauTy rhs_ty sig_ty - ) `thenTc_` - - -- STEP 4: Typecheck the guarded RHSs and the associated where clause - tcExtendLocalValEnv xve1 (tcExtendLocalValEnv xve2 ( - tcGRHSs grhss rhs_ty ctxt - )) `thenTc` \ (grhss', lie_req2) -> - - -- STEP 5: Check for existentially bound type variables - tcExtendGlobalTyVars (tyVarsOfType rhs_ty) ( - tcAddErrCtxtM (sigPatCtxt ex_tv_list pat_ids) $ - checkSigTyVars ex_tv_list `thenTc` \ zonked_ex_tvs -> - tcSimplifyAndCheck - (text ("the existential context of a data constructor")) - (mkVarSet zonked_ex_tvs) - lie_avail (lie_req1 `plusLIE` lie_req2) - ) `thenTc` \ (lie_req', ex_binds) -> - - -- STEP 6 In case there are any polymorpic, overloaded binders in the pattern - -- (which can happen in the case of rank-2 type signatures, or data constructors - -- with polymorphic arguments), we must do a bindInstsOfLocalFns here - bindInstsOfLocalFuns lie_req' pat_ids `thenTc` \ (lie_req'', inst_binds) -> - - -- Phew! All done. - let - grhss'' = glue_on Recursive ex_binds $ - glue_on Recursive inst_binds grhss' - in - returnTc (pat_ids, (Match [] pats' Nothing grhss'', lie_req'')) - - -- glue_on just avoids stupid dross -glue_on _ EmptyMonoBinds grhss = grhss -- The common case -glue_on is_rec mbinds (GRHSs grhss binds ty) - = GRHSs grhss (mkMonoBind mbinds [] is_rec `ThenBinds` binds) ty - -tcGRHSs :: RenamedGRHSs - -> TcType -> StmtCtxt - -> TcM s (TcGRHSs, LIE) - -tcGRHSs (GRHSs grhss binds _) expected_ty ctxt - = tcBindsAndThen glue_on binds (tc_grhss grhss) + tc_grhss rhs_ty + = case maybe_rhs_sig of -- Deal with the result signature + Nothing -> tcGRHSs ctxt grhss rhs_ty + + Just sig -> tcAddScopedTyVars [sig] $ + -- Bring into scope the type variables in the signature + tcHsSigType ResSigCtxt sig `thenM` \ sig_ty -> + tcThingWithSig sig_ty (tcGRHSs ctxt grhss . Check) rhs_ty `thenM` \ (co_fn, grhss') -> + + -- Pushes the coercion down to the right hand sides, + -- because there is no convenient place to hang it otherwise. + if isIdCoercion co_fn then + returnM grhss' + else + readExpectedType rhs_ty `thenM` \ rhs_ty' -> + returnM (lift_grhss co_fn rhs_ty' grhss') + +lift_grhss co_fn rhs_ty (GRHSs grhss binds ty) + = GRHSs (map (fmap lift_grhs) grhss) binds rhs_ty -- Change the type, since the coercion does where - tc_grhss grhss - = mapAndUnzipTc tc_grhs grhss `thenTc` \ (grhss', lies) -> - returnTc (GRHSs grhss' EmptyBinds (Just expected_ty), plusLIEs lies) - - tc_grhs (GRHS guarded locn) - = tcAddSrcLoc locn $ - tcStmts ctxt (\ty -> ty) guarded expected_ty `thenTc` \ (guarded', lie) -> - returnTc (GRHS guarded' locn, lie) + lift_grhs (GRHS stmts) = GRHS (map lift_stmt stmts) + + lift_stmt (L loc (ResultStmt e)) = L loc (ResultStmt (fmap (co_fn <$>) e)) + lift_stmt stmt = stmt + +tcGRHSs :: TcMatchCtxt -> GRHSs Name + -> Expected TcRhoType + -> TcM (GRHSs TcId) + + -- Special case when there is just one equation with a degenerate + -- guard; then we pass in the full Expected type, so that we get + -- good inference from simple things like + -- f = \(x::forall a.a->a) -> + -- This is a consequence of the fact that tcStmts takes a TcType, + -- not a Expected TcType, a decision we could revisit if necessary +tcGRHSs ctxt (GRHSs [L loc1 (GRHS [L loc2 (ResultStmt rhs)])] binds _) exp_ty + = tcBindsAndThen glueBindsOnGRHSs binds $ + mc_body ctxt rhs exp_ty `thenM` \ rhs' -> + readExpectedType exp_ty `thenM` \ exp_ty' -> + returnM (GRHSs [L loc1 (GRHS [L loc2 (ResultStmt rhs')])] [] exp_ty') + +tcGRHSs ctxt (GRHSs grhss binds _) exp_ty + = tcBindsAndThen glueBindsOnGRHSs binds $ + zapExpectedType exp_ty `thenM` \ exp_ty' -> + -- Even if there is only one guard, we zap the RHS type to + -- a monotype. Reason: it makes tcStmts much easier, + -- and even a one-armed guard has a notional second arm + let + stmt_ctxt = SC { sc_what = PatGuard (mc_what ctxt), + sc_rhs = tcCheckRho, + sc_body = sc_body, + sc_ty = exp_ty' } + sc_body body = mc_body ctxt body (Check exp_ty') + + tc_grhs (GRHS guarded) + = tcStmts stmt_ctxt guarded `thenM` \ guarded' -> + returnM (GRHS guarded') + in + mappM (wrapLocM tc_grhs) grhss `thenM` \ grhss' -> + returnM (GRHSs grhss' [] exp_ty') +\end{code} + + +\begin{code} +tcThingWithSig :: TcSigmaType -- Type signature + -> (TcRhoType -> TcM r) -- How to type check the thing inside + -> Expected TcRhoType -- Overall expected result type + -> TcM (ExprCoFn, r) +-- Used for expressions with a type signature, and for result type signatures + +tcThingWithSig sig_ty thing_inside res_ty + | not (isSigmaTy sig_ty) + = thing_inside sig_ty `thenM` \ result -> + tcSubExp res_ty sig_ty `thenM` \ co_fn -> + returnM (co_fn, result) + + | otherwise -- The signature has some outer foralls + = -- Must instantiate the outer for-alls of sig_tc_ty + -- else we risk instantiating a ? res_ty to a forall-type + -- which breaks the invariant that tcMonoExpr only returns phi-types + tcGen sig_ty emptyVarSet thing_inside `thenM` \ (gen_fn, result) -> + tcInstCall SignatureOrigin sig_ty `thenM` \ (inst_fn, inst_sig_ty) -> + tcSubExp res_ty inst_sig_ty `thenM` \ co_fn -> + returnM (co_fn <.> inst_fn <.> gen_fn, result) + -- Note that we generalise, then instantiate. Ah well. \end{code} @@ -239,123 +282,315 @@ tcGRHSs (GRHSs grhss binds _) expected_ty ctxt %* * %************************************************************************ -\begin{code} -tcMatchPats [] expected_ty - = returnTc (expected_ty, [], emptyLIE, emptyBag, emptyBag, emptyLIE) - -tcMatchPats (pat:pats) expected_ty - = unifyFunTy expected_ty `thenTc` \ (arg_ty, rest_ty) -> - tcPat tcPatBndr_NoSigs pat arg_ty `thenTc` \ (pat', lie_req, pat_tvs, pat_ids, lie_avail) -> - tcMatchPats pats rest_ty `thenTc` \ (rhs_ty, pats', lie_reqs, pats_tvs, pats_ids, lie_avails) -> - returnTc ( rhs_ty, - pat':pats', - lie_req `plusLIE` lie_reqs, - pat_tvs `unionBags` pats_tvs, - pat_ids `unionBags` pats_ids, - lie_avail `plusLIE` lie_avails +\begin{code} +tcMatchPats + :: [(LPat Name, Expected TcRhoType)] + -> Expected TcRhoType + -> TcM a + -> TcM ([LPat TcId], a, HsBindGroup TcId) +-- Typecheck the patterns, extend the environment to bind the variables, +-- do the thing inside, use any existentially-bound dictionaries to +-- discharge parts of the returning LIE, and deal with pattern type +-- signatures + +tcMatchPats pats_w_tys body_ty thing_inside + = -- STEP 1: Bring pattern-signature type variables into scope + tcAddScopedTyVars (collectSigTysFromPats (map fst pats_w_tys)) ( + + -- STEP 2: Typecheck the patterns themselves, gathering all the stuff + -- then do the thing inside + getLIE (tc_match_pats pats_w_tys thing_inside) + + ) `thenM` \ ((pats', ex_tvs, ex_ids, ex_lie, result), lie_req) -> + + -- STEP 4: Check for existentially bound type variables + -- Do this *outside* the scope of the tcAddScopedTyVars, else checkSigTyVars + -- complains that 'a' is captured by the inscope 'a'! (Test (d) in checkSigTyVars.) + -- + -- I'm a bit concerned that lie_req1 from an 'inner' pattern in the list + -- might need (via lie_req2) something made available from an 'outer' + -- pattern. But it's inconvenient to deal with, and I can't find an example + tcCheckExistentialPat ex_tvs ex_ids ex_lie lie_req + pats_w_tys body_ty `thenM` \ ex_binds -> + -- NB: we *must* pass "pats_w_tys" not just "body_ty" to tcCheckExistentialPat + -- For example, we must reject this program: + -- data C = forall a. C (a -> Int) + -- f (C g) x = g x + -- Here, result_ty will be simply Int, but expected_ty is (C -> a -> Int). + + returnM (pats', result, HsBindGroup ex_binds [] Recursive) + +tc_match_pats [] thing_inside + = thing_inside `thenM` \ answer -> + returnM ([], emptyBag, [], [], answer) + +tc_match_pats ((pat,pat_ty):pats) thing_inside + = tcPat tcMonoPatBndr pat pat_ty `thenM` \ (pat', ex_tvs, pat_bndrs, ex_lie) -> + let + xve = bagToList pat_bndrs + ex_ids = [id | (_, id) <- xve] + -- ex_ids is all the pattern-bound Ids, a superset + -- of the existential Ids used in checkExistentialPat + in + tcExtendLocalValEnv2 xve $ + tc_match_pats pats thing_inside `thenM` \ (pats', exs_tvs, exs_ids, exs_lie, answer) -> + returnM ( pat':pats', + ex_tvs `unionBags` exs_tvs, + ex_ids ++ exs_ids, + ex_lie ++ exs_lie, + answer ) + + +tcCheckExistentialPat :: Bag TcTyVar -- Existentially quantified tyvars bound by pattern + -> [TcId] -- Ids bound by this pattern; used + -- (a) by bindsInstsOfLocalFuns + -- (b) to generate helpful error messages + -> [Inst] -- and context + -> [Inst] -- Required context + -> [(pat,Expected TcRhoType)] -- Types of the patterns + -> Expected TcRhoType -- Type of the body of the match + -- Tyvars in either of these must not escape + -> TcM TcDictBinds -- LIE to float out and dict bindings +tcCheckExistentialPat ex_tvs ex_ids ex_lie lie_req pats_w_tys body_ty + | isEmptyBag ex_tvs && all not_overloaded ex_ids + -- Short cut for case when there are no existentials + -- and no polymorphic overloaded variables + -- e.g. f :: (forall a. Ord a => a -> a) -> Int -> Int + -- f op x = .... + -- Here we must discharge op Methods + = ASSERT( null ex_lie ) + extendLIEs lie_req `thenM_` + returnM emptyBag + + | otherwise + = -- Read the by-now-filled-in expected types + mapM readExpectedType (body_ty : map snd pats_w_tys) `thenM` \ tys -> + addErrCtxtM (sigPatCtxt tv_list ex_ids tys) $ + + -- In case there are any polymorpic, overloaded binders in the pattern + -- (which can happen in the case of rank-2 type signatures, or data constructors + -- with polymorphic arguments), we must do a bindInstsOfLocalFns here + getLIE (bindInstsOfLocalFuns lie_req ex_ids) `thenM` \ (inst_binds, lie) -> + + -- Deal with overloaded functions bound by the pattern + tcSimplifyCheck doc tv_list ex_lie lie `thenM` \ dict_binds -> + + -- Check for type variable escape + checkSigTyVarsWrt (tyVarsOfTypes tys) tv_list `thenM_` + + returnM (dict_binds `unionBags` inst_binds) + where + doc = text ("existential context of a data constructor") + tv_list = bagToList ex_tvs + not_overloaded id = not (isOverloadedTy (idType id)) \end{code} %************************************************************************ %* * -\subsection{tcStmts} +\subsection{@tcDoStmts@ typechecks a {\em list} of do statements} %* * %************************************************************************ - \begin{code} -tcStmts :: StmtCtxt - -> (TcType -> TcType) -- m, the relationship type of pat and rhs in pat <- rhs - -> [RenamedStmt] - -> TcType -- elt_ty, where type of the comprehension is (m elt_ty) - -> TcM s ([TcStmt], LIE) - -tcStmts do_or_lc m (stmt@(ReturnStmt exp) : stmts) elt_ty - = ASSERT( null stmts ) - tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - tcExpr exp elt_ty `thenTc` \ (exp', exp_lie) -> - returnTc ([ReturnStmt exp'], exp_lie) - - -- ExprStmt at the end -tcStmts do_or_lc m [stmt@(ExprStmt exp src_loc)] elt_ty - = tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - tcExpr exp (m elt_ty) `thenTc` \ (exp', exp_lie) -> - returnTc ([ExprStmt exp' src_loc], exp_lie) - - -- ExprStmt not at the end -tcStmts do_or_lc m (stmt@(ExprStmt exp src_loc) : stmts) elt_ty - = ASSERT( isDoStmt do_or_lc ) - tcAddSrcLoc src_loc ( - tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - -- exp has type (m tau) for some tau (doesn't matter what) - newTyVarTy_OpenKind `thenNF_Tc` \ any_ty -> - tcExpr exp (m any_ty) - ) `thenTc` \ (exp', exp_lie) -> - tcStmts do_or_lc m stmts elt_ty `thenTc` \ (stmts', stmts_lie) -> - returnTc (ExprStmt exp' src_loc : stmts', - exp_lie `plusLIE` stmts_lie) - -tcStmts do_or_lc m (stmt@(GuardStmt exp src_loc) : stmts) elt_ty - = ASSERT( not (isDoStmt do_or_lc) ) - tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( - tcAddSrcLoc src_loc $ - tcExpr exp boolTy - ) `thenTc` \ (exp', exp_lie) -> - tcStmts do_or_lc m stmts elt_ty `thenTc` \ (stmts', stmts_lie) -> - returnTc (GuardStmt exp' src_loc : stmts', - exp_lie `plusLIE` stmts_lie) - -tcStmts do_or_lc m (stmt@(BindStmt pat exp src_loc) : stmts) elt_ty - = tcAddSrcLoc src_loc ( - tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - newTyVarTy boxedTypeKind `thenNF_Tc` \ pat_ty -> - tcPat tcPatBndr_NoSigs pat pat_ty `thenTc` \ (pat', pat_lie, pat_tvs, pat_ids, avail) -> - tcExpr exp (m pat_ty) `thenTc` \ (exp', exp_lie) -> - returnTc (pat', exp', - pat_lie `plusLIE` exp_lie, - pat_tvs, pat_ids, avail) - ) `thenTc` \ (pat', exp', lie_req, pat_tvs, pat_bndrs, lie_avail) -> +tcDoStmts :: HsStmtContext Name + -> [LStmt Name] -> ReboundNames Name + -> TcRhoType -- To keep it simple, we don't have an "expected" type here + -> TcM ([LStmt TcId], ReboundNames TcId) +tcDoStmts PArrComp stmts method_names res_ty + = unifyPArrTy res_ty `thenM` \elt_ty -> + tcComprehension PArrComp mkPArrTy elt_ty stmts `thenM` \ stmts' -> + returnM (stmts', [{- unused -}]) + +tcDoStmts ListComp stmts method_names res_ty + = unifyListTy res_ty ` thenM` \ elt_ty -> + tcComprehension ListComp mkListTy elt_ty stmts `thenM` \ stmts' -> + returnM (stmts', [{- unused -}]) + +tcDoStmts do_or_mdo stmts method_names res_ty + = newTyVarTy (mkArrowKind liftedTypeKind liftedTypeKind) `thenM` \ m_ty -> + newTyVarTy liftedTypeKind `thenM` \ elt_ty -> + unifyTauTy res_ty (mkAppTy m_ty elt_ty) `thenM_` let - new_val_env = bagToList pat_bndrs - pat_ids = map snd new_val_env - pat_tv_list = bagToList pat_tvs - in + ctxt = SC { sc_what = do_or_mdo, + sc_rhs = \ rhs rhs_elt_ty -> tcCheckRho rhs (mkAppTy m_ty rhs_elt_ty), + sc_body = \ body -> tcCheckRho body res_ty, + sc_ty = res_ty } + in + tcStmts ctxt stmts `thenM` \ stmts' -> + + -- Build the then and zero methods in case we need them + -- It's important that "then" and "return" appear just once in the final LIE, + -- not only for typechecker efficiency, but also because otherwise during + -- simplification we end up with silly stuff like + -- then = case d of (t,r) -> t + -- then = then + -- where the second "then" sees that it already exists in the "available" stuff. + mapM (tcSyntaxName DoOrigin m_ty) method_names `thenM` \ methods -> + + returnM (stmts', methods) + +tcComprehension do_or_lc mk_mty elt_ty stmts + = tcStmts ctxt stmts + where + ctxt = SC { sc_what = do_or_lc, + sc_rhs = \ rhs rhs_elt_ty -> tcCheckRho rhs (mk_mty rhs_elt_ty), + sc_body = \ body -> tcCheckRho body elt_ty, -- Note: no mk_mty! + sc_ty = mk_mty elt_ty } +\end{code} - -- Do the rest; we don't need to add the pat_tvs to the envt - -- because they all appear in the pat_ids's types - tcExtendLocalValEnv new_val_env ( - tcStmts do_or_lc m stmts elt_ty - ) `thenTc` \ (stmts', stmts_lie) -> +%************************************************************************ +%* * +\subsection{tcStmts} +%* * +%************************************************************************ - -- Reinstate context for existential checks - tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - tcExtendGlobalTyVars (tyVarsOfType (m elt_ty)) $ - tcAddErrCtxtM (sigPatCtxt pat_tv_list pat_ids) $ +Typechecking statements is rendered a bit tricky by parallel list comprehensions: - checkSigTyVars pat_tv_list `thenTc` \ zonked_pat_tvs -> + [ (g x, h x) | ... ; let g v = ... + | ... ; let h v = ... ] - tcSimplifyAndCheck - (text ("the existential context of a data constructor")) - (mkVarSet zonked_pat_tvs) - lie_avail stmts_lie `thenTc` \ (final_lie, dict_binds) -> +It's possible that g,h are overloaded, so we need to feed the LIE from the +(g x, h x) up through both lots of bindings (so we get the bindInstsOfLocalFuns). +Similarly if we had an existential pattern match: - returnTc (BindStmt pat' exp' src_loc : - consLetStmt (mkMonoBind dict_binds [] Recursive) stmts', - lie_req `plusLIE` final_lie) + data T = forall a. Show a => C a -tcStmts do_or_lc m (LetStmt binds : stmts) elt_ty - = tcBindsAndThen -- No error context, but a binding group is - combine -- rather a large thing for an error context anyway - binds - (tcStmts do_or_lc m stmts elt_ty) - where - combine is_rec binds' stmts' = consLetStmt (mkMonoBind binds' [] is_rec) stmts' + [ (show x, show y) | ... ; C x <- ... + | ... ; C y <- ... ] + +Then we need the LIE from (show x, show y) to be simplified against +the bindings for x and y. +It's difficult to do this in parallel, so we rely on the renamer to +ensure that g,h and x,y don't duplicate, and simply grow the environment. +So the binders of the first parallel group will be in scope in the second +group. But that's fine; there's no shadowing to worry about. -isDoStmt DoStmt = True -isDoStmt other = False +\begin{code} +tcStmts ctxt stmts + = ASSERT( notNull stmts ) + tcStmtsAndThen (:) ctxt stmts (returnM []) + +data TcStmtCtxt + = SC { sc_what :: HsStmtContext Name, -- What kind of thing this is + sc_rhs :: LHsExpr Name -> TcType -> TcM (LHsExpr TcId), -- Type checker for RHS computations + sc_body :: LHsExpr Name -> TcM (LHsExpr TcId), -- Type checker for return computation + sc_ty :: TcType } -- Return type; used *only* to check + -- for escape in existential patterns +tcStmtsAndThen + :: (LStmt TcId -> thing -> thing) -- Combiner + -> TcStmtCtxt + -> [LStmt Name] + -> TcM thing + -> TcM thing + + -- Base case +tcStmtsAndThen combine ctxt [] thing_inside + = thing_inside + +tcStmtsAndThen combine ctxt (stmt:stmts) thing_inside + = tcStmtAndThen combine ctxt stmt $ + tcStmtsAndThen combine ctxt stmts $ + thing_inside + + -- LetStmt +tcStmtAndThen combine ctxt (L _ (LetStmt binds)) thing_inside + = tcBindsAndThen -- No error context, but a binding group is + (glue_binds combine) -- rather a large thing for an error context anyway + binds + thing_inside + + -- BindStmt +tcStmtAndThen combine ctxt (L src_loc stmt@(BindStmt pat exp)) thing_inside + = addSrcSpan src_loc $ + addErrCtxt (stmtCtxt ctxt stmt) $ + newTyVarTy liftedTypeKind `thenM` \ pat_ty -> + sc_rhs ctxt exp pat_ty `thenM` \ exp' -> + tcMatchPats [(pat, Check pat_ty)] (Check (sc_ty ctxt)) ( + popErrCtxt thing_inside + ) `thenM` \ ([pat'], thing, dict_binds) -> + returnM (combine (L src_loc (BindStmt pat' exp')) + (glue_binds combine dict_binds thing)) + + -- ExprStmt +tcStmtAndThen combine ctxt (L src_loc stmt@(ExprStmt exp _)) thing_inside + = addSrcSpan src_loc ( + addErrCtxt (stmtCtxt ctxt stmt) $ + if isDoExpr (sc_what ctxt) + then -- do or mdo; the expression is a computation + newTyVarTy openTypeKind `thenM` \ any_ty -> + sc_rhs ctxt exp any_ty `thenM` \ exp' -> + returnM (L src_loc (ExprStmt exp' any_ty)) + else -- List comprehensions, pattern guards; expression is a boolean + tcCheckRho exp boolTy `thenM` \ exp' -> + returnM (L src_loc (ExprStmt exp' boolTy)) + ) `thenM` \ stmt' -> + + thing_inside `thenM` \ thing -> + returnM (combine stmt' thing) + + + -- ParStmt +tcStmtAndThen combine ctxt (L src_loc (ParStmt bndr_stmts_s)) thing_inside + = loop bndr_stmts_s `thenM` \ (pairs', thing) -> + returnM (combine (L src_loc (ParStmt pairs')) thing) + where + loop [] = thing_inside `thenM` \ thing -> + returnM ([], thing) + + loop ((stmts, bndrs) : pairs) + = tcStmtsAndThen combine_par ctxt stmts $ + -- Notice we pass on ctxt; the result type is used only + -- to get escaping type variables for checkExistentialPat + tcLookupLocalIds bndrs `thenM` \ bndrs' -> + loop pairs `thenM` \ (pairs', thing) -> + returnM (([], bndrs') : pairs', thing) + + combine_par stmt ((stmts, bndrs) : pairs , thing) = ((stmt:stmts, bndrs) : pairs, thing) + + -- RecStmt +tcStmtAndThen combine ctxt (L src_loc (RecStmt stmts laterNames recNames _)) thing_inside + = newTyVarTys (length recNames) liftedTypeKind `thenM` \ recTys -> + let + rec_ids = zipWith mkLocalId recNames recTys + in + tcExtendLocalValEnv rec_ids $ + tcStmtsAndThen combine_rec ctxt stmts ( + mappM tc_ret (recNames `zip` recTys) `thenM` \ rec_rets -> + tcLookupLocalIds laterNames `thenM` \ later_ids -> + returnM ([], (later_ids, rec_rets)) + ) `thenM` \ (stmts', (later_ids, rec_rets)) -> + + tcExtendLocalValEnv later_ids $ + -- NB: The rec_ids for the recursive things + -- already scope over this part + thing_inside `thenM` \ thing -> + + returnM (combine (L src_loc (RecStmt stmts' later_ids rec_ids rec_rets)) thing) + where + combine_rec stmt (stmts, thing) = (stmt:stmts, thing) + + -- Unify the types of the "final" Ids with those of "knot-tied" Ids + tc_ret (rec_name, mono_ty) + = tcLookupId rec_name `thenM` \ poly_id -> + -- poly_id may have a polymorphic type + -- but mono_ty is just a monomorphic type variable + tcSubExp (Check mono_ty) (idType poly_id) `thenM` \ co_fn -> + returnM (L src_loc (co_fn <$> HsVar poly_id)) + + -- Result statements +tcStmtAndThen combine ctxt (L src_loc stmt@(ResultStmt exp)) thing_inside + = addErrCtxt (stmtCtxt ctxt stmt) (sc_body ctxt exp) `thenM` \ exp' -> + thing_inside `thenM` \ thing -> + returnM (combine (L src_loc (ResultStmt exp')) thing) + + +------------------------------ +glue_binds combine binds thing = combine (noLoc (LetStmt [binds])) thing + -- ToDo: fix the noLoc \end{code} @@ -369,47 +604,43 @@ isDoStmt other = False number of args are used in each equation. \begin{code} -sameNoOfArgs :: [RenamedMatch] -> Bool -sameNoOfArgs matches = length (nub (map args_in_match matches)) == 1 +sameNoOfArgs :: [LMatch Name] -> Bool +sameNoOfArgs matches = isSingleton (nub (map args_in_match matches)) where - args_in_match :: RenamedMatch -> Int - args_in_match (Match _ pats _ _) = length pats + args_in_match :: LMatch Name -> Int + args_in_match (L _ (Match pats _ _)) = length pats \end{code} \begin{code} -matchCtxt CaseAlt match - = hang (ptext SLIT("In a case alternative:")) - 4 (pprMatch (True,empty) {-is_case-} match) - -matchCtxt (FunRhs fun) match - = hang (hcat [ptext SLIT("In an equation for function "), quotes (ppr_fun), char ':']) - 4 (pprMatch (False, ppr_fun) {-not case-} match) - where - ppr_fun = ppr fun - -matchCtxt LambdaBody match - = hang (ptext SLIT("In the lambda expression")) - 4 (pprMatch (True, empty) match) - varyingArgsErr name matches = sep [ptext SLIT("Varying number of arguments for function"), quotes (ppr name)] -lurkingRank2SigErr - = ptext SLIT("Too few explicit arguments when defining a function with a rank-2 type") - -stmtCtxt do_or_lc stmt - = hang (ptext SLIT("In") <+> what <> colon) - 4 (ppr stmt) +matchCtxt ctxt match = hang (ptext SLIT("In") <+> pprMatchContext ctxt <> colon) + 4 (pprMatch ctxt match) + +stmtCtxt ctxt stmt = hang (ptext SLIT("In") <+> pp_ctxt (sc_what ctxt) <> colon) 4 (ppr stmt) + where + pp_ctxt = case stmt of + ResultStmt _ -> pprStmtResultContext + other -> pprStmtContext + +sigPatCtxt bound_tvs bound_ids tys tidy_env + = -- tys is (body_ty : pat_tys) + mapM zonkTcType tys `thenM` \ tys' -> + let + (env1, tidy_tys) = tidyOpenTypes tidy_env (map idType show_ids) + (_env2, tidy_body_ty : tidy_pat_tys) = tidyOpenTypes env1 tys' + in + returnM (env1, + sep [ptext SLIT("When checking an existential match that binds"), + nest 4 (vcat (zipWith ppr_id show_ids tidy_tys)), + ptext SLIT("The pattern(s) have type(s):") <+> vcat (map ppr tidy_pat_tys), + ptext SLIT("The body has type:") <+> ppr tidy_body_ty + ]) where - what = case do_or_lc of - ListComp -> ptext SLIT("a list-comprehension qualifier") - DoStmt -> ptext SLIT("a do statement") - PatBindRhs -> thing <+> ptext SLIT("a pattern binding") - FunRhs f -> thing <+> ptext SLIT("an equation for") <+> quotes (ppr f) - CaseAlt -> thing <+> ptext SLIT("a case alternative") - LambdaBody -> thing <+> ptext SLIT("a lambda abstraction") - thing = case stmt of - BindStmt _ _ _ -> ptext SLIT("a pattern guard for") - GuardStmt _ _ -> ptext SLIT("a guard for") - ExprStmt _ _ -> ptext SLIT("the right-hand side of") + show_ids = filter is_interesting bound_ids + is_interesting id = any (`elemVarSet` idFreeTyVars id) bound_tvs + + ppr_id id ty = ppr id <+> dcolon <+> ppr ty + -- Don't zonk the types so we get the separate, un-unified versions \end{code}