From 0d2346b4f52de431e6274795307759cad47f0ea8 Mon Sep 17 00:00:00 2001 From: "simonpj@microsoft.com" Date: Fri, 29 Sep 2006 12:20:10 +0000 Subject: [PATCH] Improve unification error messages (again) (push to 6.6 branch) --- compiler/typecheck/TcUnify.lhs | 102 +++++++++++++++++++++++----------------- 1 file changed, 59 insertions(+), 43 deletions(-) diff --git a/compiler/typecheck/TcUnify.lhs b/compiler/typecheck/TcUnify.lhs index 0d850de..853adef 100644 --- a/compiler/typecheck/TcUnify.lhs +++ b/compiler/typecheck/TcUnify.lhs @@ -600,18 +600,29 @@ tcSubExp :: BoxySigmaType -> BoxySigmaType -> TcM ExprCoFn -- Locally used only tcSubExp actual_ty expected_ty = -- addErrCtxtM (unifyCtxt actual_ty expected_ty) $ -- Adding the error context here leads to some very confusing error - -- messages, such as "can't match foarall a. a->a with forall a. a->a" - -- So instead I'm adding it when moving from tc_sub to u_tys + -- messages, such as "can't match forall a. a->a with forall a. a->a" + -- Example is tcfail165: + -- do var <- newEmptyMVar :: IO (MVar (forall a. Show a => a -> String)) + -- putMVar var (show :: forall a. Show a => a -> String) + -- Here the info does not flow from the 'var' arg of putMVar to its 'show' arg + -- but after zonking it looks as if it does! + -- + -- So instead I'm adding the error context when moving from tc_sub to u_tys + traceTc (text "tcSubExp" <+> ppr actual_ty <+> ppr expected_ty) >> - tc_sub Nothing actual_ty actual_ty False expected_ty expected_ty + tc_sub SubOther actual_ty actual_ty False expected_ty expected_ty tcFunResTy :: Name -> BoxySigmaType -> BoxySigmaType -> TcM ExprCoFn -- Locally used only tcFunResTy fun actual_ty expected_ty = traceTc (text "tcFunResTy" <+> ppr actual_ty <+> ppr expected_ty) >> - tc_sub (Just fun) actual_ty actual_ty False expected_ty expected_ty + tc_sub (SubFun fun) actual_ty actual_ty False expected_ty expected_ty ----------------- -tc_sub :: Maybe Name -- Just fun => we're looking at a function result type +data SubCtxt = SubDone -- Error-context already pushed + | SubFun Name -- Context is tcFunResTy + | SubOther -- Context is something else + +tc_sub :: SubCtxt -- How to add an error-context -> BoxySigmaType -- actual_ty, before expanding synonyms -> BoxySigmaType -- ..and after -> InBox -- True <=> expected_ty is inside a box @@ -625,22 +636,22 @@ tc_sub :: Maybe Name -- Just fun => we're looking at a function result type -- This invariant is needed so that we can "see" the foralls, ad -- e.g. in the SPEC rule where we just use splitSigmaTy -tc_sub mb_fun act_sty act_ty exp_ib exp_sty exp_ty - = tc_sub1 mb_fun act_sty act_ty exp_ib exp_sty exp_ty +tc_sub sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty + = tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty -- This indirection is just here to make -- it easy to insert a debug trace! -tc_sub1 mb_fun act_sty act_ty exp_ib exp_sty exp_ty - | Just exp_ty' <- tcView exp_ty = tc_sub mb_fun act_sty act_ty exp_ib exp_sty exp_ty' -tc_sub1 mb_fun act_sty act_ty exp_ib exp_sty exp_ty - | Just act_ty' <- tcView act_ty = tc_sub mb_fun act_sty act_ty' exp_ib exp_sty exp_ty +tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty + | Just exp_ty' <- tcView exp_ty = tc_sub sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty' +tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty + | Just act_ty' <- tcView act_ty = tc_sub sub_ctxt act_sty act_ty' exp_ib exp_sty exp_ty ----------------------------------- -- Rule SBOXY, plus other cases when act_ty is a type variable -- Just defer to boxy matching -- This rule takes precedence over SKOL! -tc_sub1 mb_fun act_sty (TyVarTy tv) exp_ib exp_sty exp_ty - = do { addErrCtxtM (subCtxt mb_fun act_sty exp_sty) $ +tc_sub1 sub_ctxt act_sty (TyVarTy tv) exp_ib exp_sty exp_ty + = do { addSubCtxt sub_ctxt act_sty exp_sty $ uVar True False tv exp_ib exp_sty exp_ty ; return idCoercion } @@ -655,11 +666,11 @@ tc_sub1 mb_fun act_sty (TyVarTy tv) exp_ib exp_sty exp_ty -- g :: Ord b => b->b -- Consider f g ! -tc_sub1 mb_fun act_sty act_ty exp_ib exp_sty exp_ty +tc_sub1 sub_ctxt act_sty act_ty exp_ib exp_sty exp_ty | not exp_ib, -- SKOL does not apply if exp_ty is inside a box isSigmaTy exp_ty = do { (gen_fn, co_fn) <- tcGen exp_ty act_tvs $ \ body_exp_ty -> - tc_sub mb_fun act_sty act_ty False body_exp_ty body_exp_ty + tc_sub sub_ctxt act_sty act_ty False body_exp_ty body_exp_ty ; return (gen_fn <.> co_fn) } where act_tvs = tyVarsOfType act_ty @@ -672,7 +683,7 @@ tc_sub1 mb_fun act_sty act_ty exp_ib exp_sty exp_ty -- expected_ty: Int -> Int -- co_fn e = e Int dOrdInt -tc_sub1 mb_fun act_sty actual_ty exp_ib exp_sty expected_ty +tc_sub1 sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty -- Implements the new SPEC rule in the Appendix of the paper -- "Boxy types: inference for higher rank types and impredicativity" -- (This appendix isn't in the published version.) @@ -698,7 +709,7 @@ tc_sub1 mb_fun act_sty actual_ty exp_ib exp_sty expected_ty ; traceTc (text "tc_sub_spec" <+> vcat [ppr actual_ty, ppr tyvars <+> ppr theta <+> ppr tau, ppr tau']) - ; co_fn2 <- tc_sub mb_fun tau' tau' exp_ib exp_sty expected_ty + ; co_fn2 <- tc_sub sub_ctxt tau' tau' exp_ib exp_sty expected_ty -- Deal with the dictionaries ; co_fn1 <- instCall InstSigOrigin inst_tys (substTheta subst' theta) @@ -706,33 +717,35 @@ tc_sub1 mb_fun act_sty actual_ty exp_ib exp_sty expected_ty ----------------------------------- -- Function case (rule F1) -tc_sub1 mb_fun _ (FunTy act_arg act_res) exp_ib _ (FunTy exp_arg exp_res) - = tc_sub_funs mb_fun act_arg act_res exp_ib exp_arg exp_res +tc_sub1 sub_ctxt act_sty (FunTy act_arg act_res) exp_ib exp_sty (FunTy exp_arg exp_res) + = addSubCtxt sub_ctxt act_sty exp_sty $ + tc_sub_funs act_arg act_res exp_ib exp_arg exp_res -- Function case (rule F2) -tc_sub1 mb_fun act_sty act_ty@(FunTy act_arg act_res) _ exp_sty (TyVarTy exp_tv) +tc_sub1 sub_ctxt act_sty act_ty@(FunTy act_arg act_res) _ exp_sty (TyVarTy exp_tv) | isBoxyTyVar exp_tv - = do { cts <- readMetaTyVar exp_tv + = addSubCtxt sub_ctxt act_sty exp_sty $ + do { cts <- readMetaTyVar exp_tv ; case cts of - Indirect ty -> tc_sub mb_fun act_sty act_ty True exp_sty ty + Indirect ty -> tc_sub SubDone act_sty act_ty True exp_sty ty Flexi -> do { [arg_ty,res_ty] <- withMetaTvs exp_tv fun_kinds mk_res_ty - ; tc_sub_funs mb_fun act_arg act_res True arg_ty res_ty } } + ; tc_sub_funs act_arg act_res True arg_ty res_ty } } where mk_res_ty [arg_ty', res_ty'] = mkFunTy arg_ty' res_ty' mk_res_ty other = panic "TcUnify.mk_res_ty3" fun_kinds = [argTypeKind, openTypeKind] -- Everything else: defer to boxy matching -tc_sub1 mb_fun act_sty actual_ty exp_ib exp_sty expected_ty - = do { addErrCtxtM (subCtxt mb_fun act_sty exp_sty) $ +tc_sub1 sub_ctxt act_sty actual_ty exp_ib exp_sty expected_ty + = do { addSubCtxt sub_ctxt act_sty exp_sty $ u_tys True False act_sty actual_ty exp_ib exp_sty expected_ty ; return idCoercion } ----------------------------------- -tc_sub_funs mb_fun act_arg act_res exp_ib exp_arg exp_res +tc_sub_funs act_arg act_res exp_ib exp_arg exp_res = do { uTys False act_arg exp_ib exp_arg - ; co_fn_res <- tc_sub mb_fun act_res act_res exp_ib exp_res exp_res + ; co_fn_res <- tc_sub SubDone act_res act_res exp_ib exp_res exp_res ; wrapFunResCoercion [exp_arg] co_fn_res } ----------------------------------- @@ -1477,25 +1490,28 @@ mkExpectedActualMsg act_ty exp_ty ---------------- -- If an error happens we try to figure out whether the function -- function has been given too many or too few arguments, and say so. -subCtxt mb_fun actual_res_ty expected_res_ty tidy_env - = do { exp_ty' <- zonkTcType expected_res_ty - ; act_ty' <- zonkTcType actual_res_ty - ; let - (env1, exp_ty'') = tidyOpenType tidy_env exp_ty' - (env2, act_ty'') = tidyOpenType env1 act_ty' - (exp_args, _) = tcSplitFunTys exp_ty'' - (act_args, _) = tcSplitFunTys act_ty'' +addSubCtxt SubDone actual_res_ty expected_res_ty thing_inside + = thing_inside +addSubCtxt sub_ctxt actual_res_ty expected_res_ty thing_inside + = addErrCtxtM mk_err thing_inside + where + mk_err tidy_env + = do { exp_ty' <- zonkTcType expected_res_ty + ; act_ty' <- zonkTcType actual_res_ty + ; let (env1, exp_ty'') = tidyOpenType tidy_env exp_ty' + (env2, act_ty'') = tidyOpenType env1 act_ty' + (exp_args, _) = tcSplitFunTys exp_ty'' + (act_args, _) = tcSplitFunTys act_ty'' - len_act_args = length act_args - len_exp_args = length exp_args + len_act_args = length act_args + len_exp_args = length exp_args - message = case mb_fun of - Just fun | len_exp_args < len_act_args -> wrongArgsCtxt "too few" fun - | len_exp_args > len_act_args -> wrongArgsCtxt "too many" fun - other -> mkExpectedActualMsg act_ty'' exp_ty'' - ; return (env2, message) } + message = case sub_ctxt of + SubFun fun | len_exp_args < len_act_args -> wrongArgsCtxt "too few" fun + | len_exp_args > len_act_args -> wrongArgsCtxt "too many" fun + other -> mkExpectedActualMsg act_ty'' exp_ty'' + ; return (env2, message) } - where wrongArgsCtxt too_many_or_few fun = ptext SLIT("Probable cause:") <+> quotes (ppr fun) <+> ptext SLIT("is applied to") <+> text too_many_or_few -- 1.7.10.4