X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2Ftypecheck%2FTcMatches.lhs;h=269abdef4929f6a8aeeb74d654c6562369d79533;hb=3a223cd2811d46295048b3a2dab11403ca291b20;hp=9185d6054f2ad043bb4f8da999c8aff168020cd1;hpb=8e3bfa9b311ee374bd904604216a01d727e78fa1;p=ghc-hetmet.git diff --git a/ghc/compiler/typecheck/TcMatches.lhs b/ghc/compiler/typecheck/TcMatches.lhs index 9185d60..269abde 100644 --- a/ghc/compiler/typecheck/TcMatches.lhs +++ b/ghc/compiler/typecheck/TcMatches.lhs @@ -1,39 +1,68 @@ % -% (c) The GRASP/AQUA Project, Glasgow University, 1992-1994 +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[TcMatches]{Typecheck some @Matches@} \begin{code} -module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchExpected ) where +module TcMatches ( tcMatchesFun, tcMatchesCase, tcMatchLambda, matchCtxt, + tcDoStmts, tcStmtsAndThen, tcStmts, tcGRHSs, tcThingWithSig, + tcMatchPats, + TcStmtCtxt(..) + ) where #include "HsVersions.h" -import {-# SOURCE #-} TcGRHSs ( tcGRHSsAndBinds ) +import {-# SOURCE #-} TcExpr( tcCheckRho, tcMonoExpr ) -import HsSyn ( HsBinds(..), Match(..), GRHSsAndBinds(..), GRHS(..), - HsExpr(..), MonoBinds(..), - collectPatBinders, pprMatch, getMatchLoc +import HsSyn ( HsExpr(..), HsBinds(..), Match(..), GRHSs(..), GRHS(..), + MonoBinds(..), Stmt(..), HsMatchContext(..), HsStmtContext(..), + ReboundNames, + pprMatch, getMatchLoc, isDoExpr, + pprMatchContext, pprStmtContext, pprStmtResultContext, + mkMonoBind, collectSigTysFromPats, andMonoBindList, glueBindsOnGRHSs ) -import RnHsSyn ( RenamedMatch ) -import TcHsSyn ( TcIdBndr, TcMatch ) - -import TcMonad -import Inst ( Inst, LIE, plusLIE ) -import TcEnv ( TcIdOcc(..), newMonoIds ) -import TcPat ( tcPat ) -import TcType ( TcType, TcMaybe, zonkTcType, newTyVarTy ) -import TcSimplify ( bindInstsOfLocalFuns ) -import Unify ( unifyTauTy, unifyTauTyList, unifyFunTy ) -import Name ( Name {- instance Outputable -} ) - -import Kind ( Kind, mkTypeKind ) +import RnHsSyn ( RenamedMatch, RenamedGRHSs, RenamedStmt, RenamedHsExpr, + RenamedPat, RenamedMatchContext ) +import TcHsSyn ( TcMatch, TcGRHSs, TcStmt, TcDictBinds, TcHsBinds, TcExpr, + TcMonoBinds, TcPat, TcStmt, ExprCoFn, + isIdCoercion, (<$>), (<.>) ) + +import TcRnMonad +import TcMonoType ( 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, tidyOpenType, isSigmaTy, + mkFunTy, isOverloadedTy, liftedTypeKind, openTypeKind, + mkArrowKind, mkAppTy ) +import TcBinds ( tcBindsAndThen ) +import TcUnify ( Expected(..), newHole, zapExpectedType, zapExpectedBranches, readExpectedType, + unifyTauTy, subFunTys, unifyPArrTy, unifyListTy, unifyFunTy, + checkSigTyVarsWrt, tcSubExp, tcGen ) +import TcSimplify ( tcSimplifyCheck, bindInstsOfLocalFuns ) +import Name ( Name ) +import PrelNames ( monadNames, mfixName ) +import TysWiredIn ( boolTy, mkListTy, mkPArrTy ) +import Id ( idType, mkSysLocal, mkLocalId ) +import CoreFVs ( idFreeTyVars ) import BasicTypes ( RecFlag(..) ) -import Type ( isTyVarTy, isTauTy, mkFunTy, splitFunTy_maybe ) -import Util +import VarSet +import Var ( Id ) +import Bag +import Util ( isSingleton, notNull, zipEqual ) import Outputable -import SrcLoc (SrcLoc) + +import List ( nub ) \end{code} +%************************************************************************ +%* * +\subsection{tcMatchesFun, tcMatchesCase} +%* * +%************************************************************************ + @tcMatchesFun@ typechecks a @[Match]@ list which occurs in a @FunMonoBind@. The second argument is the name of the function, which is used in error messages. It checks that all the equations have the @@ -41,159 +70,559 @@ same number of arguments before using @tcMatches@ to do the work. \begin{code} tcMatchesFun :: Name - -> TcType s -- Expected type -> [RenamedMatch] - -> TcM s ([TcMatch s], LIE s) + -> Expected TcRhoType -- Expected type + -> TcM [TcMatch] -tcMatchesFun fun_name expected_ty matches@(first_match:_) - = -- Set the location to that of the first equation, so that +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 -- 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) ( - - -- Check that they all have the same no of arguments - checkTc (all_same (noOfArgs matches)) - (varyingArgsErr fun_name matches) `thenTc_` + addSrcLoc (getMatchLoc first_match) ( + 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 - -- We need to substitute so that we can see as much about the type as possible - zonkTcType expected_ty `thenNF_Tc` \ expected_ty' -> - tcMatchesExpected expected_ty' (MFun fun_name) matches - - ) - where - all_same :: [Int] -> Bool - all_same [] = True -- Should never happen (ToDo: panic?) - all_same [x] = True - all_same (x:xs) = all ((==) x) xs + -- No need to zonk expected_ty, because subFunTys does that on the fly + tcMatches (FunRhs fun_name) matches expected_ty \end{code} @tcMatchesCase@ doesn't do the argument-count check because the parser guarantees that each equation has exactly one argument. \begin{code} -tcMatchesCase :: TcType s -- Type of whole case expressions - -> [RenamedMatch] -- The case alternatives - -> TcM s (TcType s, -- Inferred type of the scrutinee - [TcMatch s], -- Translated alternatives - LIE s) - -tcMatchesCase expr_ty matches - = newTyVarTy mkTypeKind `thenNF_Tc` \ scrut_ty -> - tcMatchesExpected (mkFunTy scrut_ty expr_ty) MCase matches `thenTc` \ (matches', lie) -> - returnTc (scrut_ty, matches', lie) +tcMatchesCase :: [RenamedMatch] -- The case alternatives + -> Expected TcRhoType -- Type of whole case expressions + -> TcM (TcRhoType, -- Inferred type of the scrutinee + [TcMatch]) -- Translated alternatives + +tcMatchesCase 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 CaseAlt matches (Check (mkFunTy scrut_ty expr_ty)) `thenM` \ matches' -> + returnM (scrut_ty, matches') + +tcMatchesCase matches (Infer hole) + = newHole `thenM` \ fun_hole -> + tcMatches CaseAlt 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 :: RenamedMatch -> Expected TcRhoType -> TcM TcMatch +tcMatchLambda match res_ty = tcMatch LambdaExpr match res_ty \end{code} \begin{code} -data FunOrCase = MCase | MFun Name -- Records whether doing fun or case rhss; - -- used to produced better error messages - -tcMatchesExpected :: TcType s - -> FunOrCase - -> [RenamedMatch] - -> TcM s ([TcMatch s], LIE s) - -tcMatchesExpected expected_ty fun_or_case [match] - = tcAddSrcLoc (getMatchLoc match) $ - tcAddErrCtxt (matchCtxt fun_or_case match) $ - tcMatchExpected [] expected_ty match `thenTc` \ (match', lie) -> - returnTc ([match'], lie) - -tcMatchesExpected expected_ty fun_or_case (match1 : matches) - = tcAddSrcLoc (getMatchLoc match1) ( - tcAddErrCtxt (matchCtxt fun_or_case match1) $ - tcMatchExpected [] expected_ty match1 - ) `thenTc` \ (match1', lie1) -> - tcMatchesExpected expected_ty fun_or_case matches `thenTc` \ (matches', lie2) -> - returnTc (match1' : matches', plusLIE lie1 lie2) +tcMatches :: RenamedMatchContext + -> [RenamedMatch] + -> Expected TcRhoType + -> TcM [TcMatch] + +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 (tc_match exp_ty') matches + where + tc_match exp_ty match = tcMatch ctxt match exp_ty \end{code} + +%************************************************************************ +%* * +\subsection{tcMatch} +%* * +%************************************************************************ + \begin{code} -tcMatchExpected - :: [TcIdBndr s] -- Ids bound by enclosing matches - -> TcType s -- This gives the expected - -- result-type of the Match. Early unification - -- with this guy gives better error messages +tcMatch :: RenamedMatchContext -> RenamedMatch - -> TcM s (TcMatch s,LIE s) -- NB No type returned, because it was passed - -- in instead! - -tcMatchExpected matched_ids expected_ty the_match@(PatMatch pat match) - = unifyFunTy expected_ty `thenTc` \ (arg_ty, rest_ty) -> + -> 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. + -> TcM TcMatch + +tcMatch ctxt match@(Match pats maybe_rhs_sig grhss) expected_ty + = addSrcLoc (getMatchLoc match) $ -- At one stage I removed this; + addErrCtxt (matchCtxt 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')) - let binders = collectPatBinders pat + where + 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 lift_grhs grhss) binds rhs_ty -- Change the type, since the coercion does + where + lift_grhs (GRHS stmts loc) = GRHS (map lift_stmt stmts) loc + + lift_stmt (ResultStmt e l) = ResultStmt (co_fn <$> e) l + lift_stmt stmt = stmt + +tcGRHSs :: RenamedMatchContext -> RenamedGRHSs + -> Expected TcRhoType + -> TcM TcGRHSs + + -- 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 [GRHS [ResultStmt rhs loc1] loc2] binds _) exp_ty + = tcBindsAndThen glueBindsOnGRHSs binds $ + tcMonoExpr rhs exp_ty `thenM` \ rhs' -> + readExpectedType exp_ty `thenM` \ exp_ty' -> + returnM (GRHSs [GRHS [ResultStmt rhs' loc1] loc2] EmptyBinds 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 ctxt, + sc_rhs = tcCheckRho, + sc_body = \ body -> tcCheckRho body exp_ty', + sc_ty = exp_ty' } + + tc_grhs (GRHS guarded locn) + = addSrcLoc locn $ + tcStmts stmt_ctxt guarded `thenM` \ guarded' -> + returnM (GRHS guarded' locn) in - newMonoIds binders mkTypeKind (\ mono_ids -> - tcPat pat `thenTc` \ (pat', lie_pat, pat_ty) -> - unifyTauTy pat_ty arg_ty `thenTc_` + mappM tc_grhs grhss `thenM` \ grhss' -> + returnM (GRHSs grhss' EmptyBinds exp_ty') +\end{code} + - tcMatchExpected (mono_ids ++ matched_ids) - rest_ty match `thenTc` \ (match', lie_match) -> +\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} - returnTc (PatMatch pat' match', - plusLIE lie_pat lie_match) + +%************************************************************************ +%* * +\subsection{tcMatchPats} +%* * +%************************************************************************ + +\begin{code} +tcMatchPats + :: [(RenamedPat, Expected TcRhoType)] + -> Expected TcRhoType + -> TcM a + -> TcM ([TcPat], a, TcHsBinds) +-- 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, mkMonoBind Recursive ex_binds) + +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 ) -tcMatchExpected matched_ids expected_ty (GRHSMatch grhss_and_binds) - = -- 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 expected_ty) - lurkingRank2SigErr `thenTc_` - tcGRHSsAndBinds expected_ty grhss_and_binds `thenTc` \ (GRHSsAndBindsOut grhss binds ty, lie) -> +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 EmptyMonoBinds + + | 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 - bindInstsOfLocalFuns lie matched_ids `thenTc` \ (lie', inst_mbinds) -> - let - binds' = case inst_mbinds of - EmptyMonoBinds -> binds -- The common case - other -> MonoBind inst_mbinds [] Recursive `ThenBinds` binds - in - returnTc (GRHSMatch (GRHSsAndBindsOut grhss binds' ty), lie') + 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 `AndMonoBinds` 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} -@noOfArgs@ takes a @[RenamedMatch]@ and returns a list telling how -many arguments were used in each of the equations. This is used to -report a sensible error message when different equations have -different numbers of arguments. +%************************************************************************ +%* * +\subsection{@tcDoStmts@ typechecks a {\em list} of do statements} +%* * +%************************************************************************ \begin{code} -noOfArgs :: [RenamedMatch] -> [Int] - -noOfArgs ms = map args_in_match ms +tcDoStmts :: HsStmtContext Name + -> [RenamedStmt] -> ReboundNames Name + -> TcRhoType -- To keep it simple, we don't have an "expected" type here + -> TcM ([TcStmt], 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 + 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 - args_in_match :: RenamedMatch -> Int - args_in_match (GRHSMatch _) = 0 - args_in_match (PatMatch _ match) = 1 + args_in_match match + 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} -Errors and contexts -~~~~~~~~~~~~~~~~~~~ -\begin{code} -matchCtxt MCase match - = hang (ptext SLIT("In a \"case\" branch:")) - 4 (pprMatch True{-is_case-} match) -matchCtxt (MFun fun) match - = hang (hcat [ptext SLIT("In an equation for function "), quotes (ppr fun), char ':']) - 4 (hcat [ppr fun, space, pprMatch False{-not case-} match]) +%************************************************************************ +%* * +\subsection{tcStmts} +%* * +%************************************************************************ + +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 ctxt stmts + = ASSERT( notNull stmts ) + tcStmtsAndThen (:) ctxt stmts (returnM []) + +data TcStmtCtxt + = SC { sc_what :: HsStmtContext Name, -- What kind of thing this is + sc_rhs :: RenamedHsExpr -> TcType -> TcM TcExpr, -- Type checker for RHS computations + sc_body :: RenamedHsExpr -> TcM TcExpr, -- Type checker for return computation + sc_ty :: TcType } -- Return type; used *only* to check + -- for escape in existential patterns +tcStmtsAndThen + :: (TcStmt -> thing -> thing) -- Combiner + -> TcStmtCtxt + -> [RenamedStmt] + -> 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 (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 stmt@(BindStmt pat exp src_loc) thing_inside + = addSrcLoc 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 (BindStmt pat' exp' src_loc) + (glue_binds combine dict_binds thing)) + + -- ExprStmt +tcStmtAndThen combine ctxt stmt@(ExprStmt exp _ src_loc) thing_inside + = addSrcLoc 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 (ExprStmt exp' any_ty src_loc) + else -- List comprehensions, pattern guards; expression is a boolean + tcCheckRho exp boolTy `thenM` \ exp' -> + returnM (ExprStmt exp' boolTy src_loc) + ) `thenM` \ stmt' -> + + thing_inside `thenM` \ thing -> + returnM (combine stmt' thing) + + + -- ParStmt +tcStmtAndThen combine ctxt (ParStmt bndr_stmts_s) thing_inside + = loop bndr_stmts_s `thenM` \ (pairs', thing) -> + returnM (combine (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 (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 (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 (co_fn <$> HsVar poly_id) + + -- Result statements +tcStmtAndThen combine ctxt stmt@(ResultStmt exp locn) thing_inside + = addErrCtxt (stmtCtxt ctxt stmt) (sc_body ctxt exp) `thenM` \ exp' -> + thing_inside `thenM` \ thing -> + returnM (combine (ResultStmt exp' locn) thing) + + +------------------------------ +glue_binds combine EmptyBinds thing = thing +glue_binds combine other_binds thing = combine (LetStmt other_binds) thing \end{code} +%************************************************************************ +%* * +\subsection{Errors and contexts} +%* * +%************************************************************************ + +@sameNoOfArgs@ takes a @[RenamedMatch]@ and decides whether the same +number of args are used in each equation. + +\begin{code} +sameNoOfArgs :: [RenamedMatch] -> Bool +sameNoOfArgs matches = isSingleton (nub (map args_in_match matches)) + where + args_in_match :: RenamedMatch -> Int + args_in_match (Match pats _ _) = length pats +\end{code} + \begin{code} 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") +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 + 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}