X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMatches.lhs;h=32fd91e821374a7e84d822759b98e8ffc6da2290;hb=1c62b517711ac232a8024d91fd4b317a6804d28e;hp=4d73dbe36bc00ba61c9293b9be1d55be0e6569e6;hpb=ff755dd9a0a0ad2f106c323852553ea247f16141;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMatches.lhs b/ghc/compiler/typecheck/TcMatches.lhs index 4d73dbe..32fd91e 100644 --- a/ghc/compiler/typecheck/TcMatches.lhs +++ b/ghc/compiler/typecheck/TcMatches.lhs @@ -4,34 +4,37 @@ \section[TcMatches]{Typecheck some @Matches@} \begin{code} -module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda, tcStmts, tcGRHSs ) where +module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda, + tcStmts, tcStmtsAndThen, tcGRHSs + ) where #include "HsVersions.h" import {-# SOURCE #-} TcExpr( tcExpr ) import HsSyn ( HsBinds(..), Match(..), GRHSs(..), GRHS(..), - MonoBinds(..), StmtCtxt(..), Stmt(..), - pprMatch, getMatchLoc, consLetStmt, - mkMonoBind + MonoBinds(..), Stmt(..), HsMatchContext(..), + pprMatch, getMatchLoc, pprMatchContext, isDoExpr, + mkMonoBind, nullMonoBinds, collectSigTysFromPats ) import RnHsSyn ( RenamedMatch, RenamedGRHSs, RenamedStmt ) -import TcHsSyn ( TcMatch, TcGRHSs, TcStmt ) +import TcHsSyn ( TcMatch, TcGRHSs, TcStmt, TcDictBinds ) import TcMonad -import TcMonoType ( checkSigTyVars, tcHsTyVar, tcHsSigType, 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 TcMonoType ( kcHsSigType, tcTyVars, checkSigTyVars, tcHsSigType, sigPatCtxt ) +import Inst ( LIE, isEmptyLIE, plusLIE, emptyLIE, plusLIEs, lieToList ) +import TcEnv ( TcId, tcLookupLocalIds, tcExtendTyVarEnv, tcExtendLocalValEnv, tcExtendGlobalTyVars ) +import TcPat ( tcPat, tcMonoPatBndr, polyPatSig ) +import TcType ( TcType, newTyVarTy ) import TcBinds ( tcBindsAndThen ) -import TcSimplify ( tcSimplifyAndCheck, bindInstsOfLocalFuns ) +import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns ) import TcUnify ( unifyFunTy, unifyTauTy ) import Name ( Name ) -import TysWiredIn ( boolTy ) - +import TysWiredIn ( boolTy, mkListTy ) +import Id ( idType ) import BasicTypes ( RecFlag(..) ) -import Type ( Kind, tyVarsOfType, isTauTy, mkFunTy, boxedTypeKind ) +import Type ( tyVarsOfType, isTauTy, mkFunTy, + liftedTypeKind, openTypeKind, splitSigmaTy ) import VarSet import Var ( Id ) import Bag @@ -55,7 +58,7 @@ tcMatchesFun :: [(Name,Id)] -- Bindings for the variables bound in this group -> Name -> TcType -- Expected type -> [RenamedMatch] - -> TcM s ([TcMatch], LIE) + -> TcM ([TcMatch], LIE) tcMatchesFun xve fun_name expected_ty matches@(first_match:_) = -- Check that they all have the same no of arguments @@ -83,17 +86,17 @@ 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 + -> TcM (TcType, -- Inferred type of the scrutinee [TcMatch], -- Translated alternatives LIE) tcMatchesCase matches expr_ty - = newTyVarTy_OpenKind `thenNF_Tc` \ scrut_ty -> + = newTyVarTy openTypeKind `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 +tcMatchLambda :: RenamedMatch -> TcType -> TcM (TcMatch, LIE) +tcMatchLambda match res_ty = tcMatch [] match res_ty LambdaExpr \end{code} @@ -101,8 +104,8 @@ tcMatchLambda match res_ty = tcMatch [] match res_ty LambdaBody tcMatches :: [(Name,Id)] -> [RenamedMatch] -> TcType - -> StmtCtxt - -> TcM s ([TcMatch], LIE) + -> HsMatchContext + -> TcM ([TcMatch], LIE) tcMatches xve matches expected_ty fun_or_case = mapAndUnzipTc tc_match matches `thenTc` \ (matches, lies) -> @@ -123,8 +126,8 @@ 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) + -> HsMatchContext + -> TcM (TcMatch, LIE) tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty ctxt = tcAddSrcLoc (getMatchLoc match) $ @@ -138,13 +141,11 @@ tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty ctxt -- 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 -> + newTyVarTy openTypeKind `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) -> + tcTyVars sig_tvs (mapTc_ kcHsSigType sig_tys) `thenTc` \ 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 @@ -158,13 +159,15 @@ tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty ctxt returnTc match_and_lie where + sig_tys = case maybe_rhs_sig of { Just t -> [t]; Nothing -> [] } + ++ collectSigTysFromPats pats + 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 @@ -174,7 +177,7 @@ tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_ty ctxt -- STEP 3: Unify with the rhs type signature if any (case maybe_rhs_sig of Nothing -> returnTc () - Just sig -> tcHsSigType sig `thenTc` \ sig_ty -> + Just sig -> tcHsSigType sig `thenTc` \ sig_ty -> -- Check that the signature isn't a polymorphic one, which -- we don't permit (at present, anyway) @@ -188,26 +191,15 @@ tcMatch xve1 match@(Match sig_tvs pats maybe_rhs_sig grhss) expected_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 emptyVarSet `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) -> + tcCheckExistentialPat pat_ids ex_tvs lie_avail + (lie_req1 `plusLIE` lie_req2) + rhs_ty `thenTc` \ (lie_req', ex_binds) -> -- Phew! All done. let - grhss'' = glue_on Recursive ex_binds $ - glue_on Recursive inst_binds grhss' + match' = Match [] pats' Nothing (glue_on Recursive ex_binds grhss') in - returnTc (pat_ids, (Match [] pats' Nothing grhss'', lie_req'')) + returnTc (pat_ids, (match', lie_req')) -- glue_on just avoids stupid dross glue_on _ EmptyMonoBinds grhss = grhss -- The common case @@ -215,20 +207,58 @@ 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) + -> TcType -> HsMatchContext + -> TcM (TcGRHSs, LIE) tcGRHSs (GRHSs grhss binds _) expected_ty ctxt = tcBindsAndThen glue_on binds (tc_grhss grhss) where tc_grhss grhss - = mapAndUnzipTc tc_grhs grhss `thenTc` \ (grhss', lies) -> + = 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) -> + = tcAddSrcLoc locn $ + tcStmts ctxt (\ty -> ty, expected_ty) guarded `thenTc` \ (guarded', lie) -> returnTc (GRHS guarded' locn, lie) + + +tcCheckExistentialPat :: [TcId] -- Ids bound by this pattern + -> Bag TcTyVar -- Existentially quantified tyvars bound by pattern + -> LIE -- and context + -> LIE -- Required context + -> TcType -- and result type; vars in here must not escape + -> TcM (LIE, TcDictBinds) -- LIE to float out and dict bindings +tcCheckExistentialPat ids ex_tvs lie_avail lie_req result_ty + | isEmptyBag ex_tvs && all not_overloaded 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( isEmptyLIE lie_avail ) + returnTc (lie_req, EmptyMonoBinds) + + | otherwise + = tcExtendGlobalTyVars (tyVarsOfType result_ty) $ + tcAddErrCtxtM (sigPatCtxt tv_list ids) $ + + -- 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 ids `thenTc` \ (lie1, inst_binds) -> + + -- Deal with overloaded functions bound by the pattern + tcSimplifyCheck doc tv_list + (lieToList lie_avail) lie1 `thenTc` \ (lie2, dict_binds) -> + checkSigTyVars tv_list emptyVarSet `thenTc_` + + returnTc (lie2, dict_binds `AndMonoBinds` inst_binds) + where + doc = text ("the existential context of a data constructor") + tv_list = bagToList ex_tvs + not_overloaded id = case splitSigmaTy (idType id) of + (_, theta, _) -> null theta \end{code} @@ -244,7 +274,7 @@ tcMatchPats [] expected_ty 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) -> + tcPat tcMonoPatBndr 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', @@ -262,55 +292,59 @@ tcMatchPats (pat:pats) expected_ty %* * %************************************************************************ +Typechecking statements is rendered a bit tricky by parallel list comprehensions: + + [ (g x, h x) | ... ; let g v = ... + | ... ; let h v = ... ] + +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: + + data T = forall a. Show a => C a + + [ (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. \begin{code} -tcStmts :: StmtCtxt - -> (TcType -> TcType) -- m, the relationship type of pat and rhs in pat <- rhs +tcStmts do_or_lc m_ty stmts + = tcStmtsAndThen (:) do_or_lc m_ty stmts (returnTc ([], emptyLIE)) + +tcStmtsAndThen + :: (TcStmt -> thing -> thing) -- Combiner + -> HsMatchContext + -> (TcType -> TcType, TcType) -- m, the relationship type of pat and rhs in pat <- rhs + -- elt_ty, where type of the comprehension is (m elt_ty) -> [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 + -> TcM (thing, LIE) + -> TcM (thing, LIE) + + -- Base case +tcStmtsAndThen combine do_or_lc m_ty [] do_next + = do_next + + -- LetStmt +tcStmtsAndThen combine do_or_lc m_ty (LetStmt binds : stmts) do_next + = tcBindsAndThen -- No error context, but a binding group is + (glue_binds combine) -- rather a large thing for an error context anyway + binds + (tcStmtsAndThen combine do_or_lc m_ty stmts do_next) + + -- BindStmt +tcStmtsAndThen combine do_or_lc m_ty@(m,elt_ty) (stmt@(BindStmt pat exp src_loc) : stmts) do_next = 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) -> + newTyVarTy liftedTypeKind `thenNF_Tc` \ pat_ty -> + tcPat tcMonoPatBndr 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) @@ -318,43 +352,80 @@ tcStmts do_or_lc m (stmt@(BindStmt pat exp src_loc) : stmts) elt_ty let new_val_env = bagToList pat_bndrs pat_ids = map snd new_val_env - pat_tv_list = bagToList pat_tvs in -- 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) -> - + tcStmtsAndThen combine do_or_lc m_ty stmts do_next + ) `thenTc` \ (thing, stmts_lie) -> -- Reinstate context for existential checks - tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ - tcExtendGlobalTyVars (tyVarsOfType (m elt_ty)) $ - tcAddErrCtxtM (sigPatCtxt pat_tv_list pat_ids) $ + tcSetErrCtxt (stmtCtxt do_or_lc stmt) $ + tcCheckExistentialPat pat_ids pat_tvs lie_avail + stmts_lie (m elt_ty) `thenTc` \ (final_lie, dict_binds) -> - checkSigTyVars pat_tv_list emptyVarSet `thenTc` \ zonked_pat_tvs -> + returnTc (combine (BindStmt pat' exp' src_loc) + (glue_binds combine Recursive dict_binds thing), + lie_req `plusLIE` final_lie) - tcSimplifyAndCheck - (text ("the existential context of a data constructor")) - (mkVarSet zonked_pat_tvs) - lie_avail stmts_lie `thenTc` \ (final_lie, dict_binds) -> - returnTc (BindStmt pat' exp' src_loc : - consLetStmt (mkMonoBind dict_binds [] Recursive) stmts', - lie_req `plusLIE` final_lie) + -- ParStmt +tcStmtsAndThen combine do_or_lc m_ty (ParStmtOut bndr_stmts_s : stmts) do_next + = loop bndr_stmts_s `thenTc` \ ((pairs', thing), lie) -> + returnTc (combine (ParStmtOut pairs') thing, lie) + where + loop [] + = tcStmtsAndThen combine do_or_lc m_ty stmts do_next `thenTc` \ (thing, stmts_lie) -> + returnTc (([], thing), stmts_lie) -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' + loop ((bndrs,stmts) : pairs) + = tcStmtsAndThen + combine_par ListComp (mkListTy, not_required) stmts + (tcLookupLocalIds bndrs `thenNF_Tc` \ bndrs' -> + loop pairs `thenTc` \ ((pairs', thing), lie) -> + returnTc (([], (bndrs', pairs', thing)), lie)) `thenTc` \ ((stmts', (bndrs', pairs', thing)), lie) -> + returnTc ( ((bndrs',stmts') : pairs', thing), lie) -isDoStmt DoStmt = True -isDoStmt other = False + combine_par stmt (stmts, thing) = (stmt:stmts, thing) + not_required = panic "tcStmtsAndThen: elt_ty" + + -- The simple-statment case +tcStmtsAndThen combine do_or_lc m_ty (stmt@(ExprStmt exp locn):stmts) do_next + = tcSetErrCtxt (stmtCtxt do_or_lc stmt) ( + tcExprStmt do_or_lc m_ty exp (null stmts) + ) `thenTc` \ (exp', stmt_lie) -> + + tcStmtsAndThen combine do_or_lc m_ty stmts do_next `thenTc` \ (thing, stmts_lie) -> + + returnTc (combine (ExprStmt exp' locn) thing, + stmt_lie `plusLIE` stmts_lie) + + +------------------------------ + -- ExprStmt; see comments with HsExpr.HsStmt + -- for meaning of ExprStmt +tcExprStmt do_or_lc (m, res_elt_ty) exp is_last_stmt + = compute_expr_ty `thenNF_Tc` \ expr_ty -> + tcExpr exp expr_ty + where + compute_expr_ty + | is_last_stmt = if isDoExpr do_or_lc then + returnNF_Tc (m res_elt_ty) + else + returnNF_Tc res_elt_ty + + | otherwise = if isDoExpr do_or_lc then + newTyVarTy openTypeKind `thenNF_Tc` \ any_ty -> + returnNF_Tc (m any_ty) + else + returnNF_Tc boolTy + +------------------------------ +glue_binds combine is_rec binds thing + | nullMonoBinds binds = thing + | otherwise = combine (LetStmt (mkMonoBind binds [] is_rec)) thing \end{code} @@ -386,7 +457,7 @@ matchCtxt (FunRhs fun) match where ppr_fun = ppr fun -matchCtxt LambdaBody match +matchCtxt LambdaExpr match = hang (ptext SLIT("In the lambda expression")) 4 (pprMatch (True, empty) match) @@ -396,19 +467,5 @@ varyingArgsErr name matches 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) - 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") +stmtCtxt do_or_lc stmt = hang (pprMatchContext do_or_lc <> colon) 4 (ppr stmt) \end{code}