X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcSimplify.lhs;h=80718b7839a0072ca5d106d6d4d5a1ec4558adff;hb=0a960884b377903e41735bb2d36bec495bf5d890;hp=47c92af1f39f61bb6ae4812d2713d7a41e821c54;hpb=041c35e5d9f3aefab6908b4c776a3fd8242720ab;p=ghc-hetmet.git diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs index 47c92af..80718b7 100644 --- a/compiler/typecheck/TcSimplify.lhs +++ b/compiler/typecheck/TcSimplify.lhs @@ -1202,9 +1202,22 @@ tcSimplifyRestricted doc top_lvl bndrs tau_tvs wanteds ; gbl_tvs' <- tcGetGlobalTyVars ; constrained_dicts' <- mappM zonkInst constrained_dicts - ; let constrained_tvs' = tyVarsOfInsts constrained_dicts' - qtvs = (tau_tvs' `minusVarSet` oclose (fdPredsOfInsts constrained_dicts) gbl_tvs') - `minusVarSet` constrained_tvs' + ; let qtvs1 = tau_tvs' `minusVarSet` oclose (fdPredsOfInsts constrained_dicts) gbl_tvs' + -- As in tcSimplifyInfer + + -- Do not quantify over constrained type variables: + -- this is the monomorphism restriction + constrained_tvs' = tyVarsOfInsts constrained_dicts' + qtvs = qtvs1 `minusVarSet` constrained_tvs' + pp_bndrs = pprWithCommas (quotes . ppr) bndrs + + -- Warn in the mono + ; warn_mono <- doptM Opt_WarnMonomorphism + ; warnTc (warn_mono && (constrained_tvs' `intersectsVarSet` qtvs1)) + (vcat[ ptext SLIT("the Monomorphism Restriction applies to the binding") + <> plural bndrs <+> ptext SLIT("for") <+> pp_bndrs, + ptext SLIT("Consider giving a type signature for") <+> pp_bndrs]) + ; traceTc (text "tcSimplifyRestricted" <+> vcat [ pprInsts wanteds, pprInsts constrained_dicts', ppr _binds, @@ -2252,17 +2265,7 @@ disambiguate interactive dflags insts ; return () } | otherwise = do { -- Figure out what default types to use - mb_defaults <- getDefaultTys - ; default_tys <- case mb_defaults of - Just tys -> return tys - Nothing -> -- No use-supplied default; - -- use [Integer, Double] - do { integer_ty <- tcMetaTy integerTyConName - ; checkWiredInTyCon doubleTyCon - ; string_ty <- tcMetaTy stringTyConName - ; if ovl_strings -- Add String if -foverloaded-strings - then return [integer_ty,doubleTy,string_ty] - else return [integer_ty,doubleTy] } + ; default_tys <- getDefaultTys extended_defaulting ovl_strings ; traceTc (text "disambigutate" <+> vcat [ppr unaries, ppr bad_tvs, ppr defaultable_groups]) ; mapM_ (disambigGroup default_tys) defaultable_groups } @@ -2325,8 +2328,43 @@ disambigGroup default_tys dicts -- After this we can't fail ; warnDefault dicts default_ty ; unifyType default_ty (mkTyVarTy tyvar) } + + +getDefaultTys :: Bool -> Bool -> TcM [Type] +getDefaultTys extended_deflts ovl_strings + = do { mb_defaults <- getDeclaredDefaultTys + ; case mb_defaults of { + Just tys -> return tys ; -- User-supplied defaults + Nothing -> do + + -- No use-supplied default + -- Use [Integer, Double], plus modifications + { integer_ty <- tcMetaTy integerTyConName + ; checkWiredInTyCon doubleTyCon + ; string_ty <- tcMetaTy stringTyConName + ; return (opt_deflt extended_deflts unitTy + -- Note [Default unitTy] + ++ + [integer_ty,doubleTy] + ++ + opt_deflt ovl_strings string_ty) } } } + where + opt_deflt True ty = [ty] + opt_deflt False ty = [] \end{code} +Note [Default unitTy] +~~~~~~~~~~~~~~~~~~~~~ +In interative mode (or with -fextended-default-rules) we add () as the first type we +try when defaulting. This has very little real impact, except in the following case. +Consider: + Text.Printf.printf "hello" +This has type (forall a. IO a); it prints "hello", and returns 'undefined'. We don't +want the GHCi repl loop to try to print that 'undefined'. The neatest thing is to +default the 'a' to (), rather than to Integer (which is what would otherwise happen; +and then GHCi doesn't attempt to print the (). So in interactive mode, we add +() to the list of defaulting types. See Trac #1200. + Note [Avoiding spurious errors] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When doing the unification for defaulting, we check for skolem @@ -2374,43 +2412,19 @@ tcSimplifyDeriv orig tyvars theta ; wanteds <- newDictBndrsO orig (substTheta tenv theta) ; (irreds, _) <- topCheckLoop doc wanteds - -- Insist that the context of a derived instance declaration - -- consists of constraints of form (C a b), where a,b are - -- type variables - -- NB: the caller will further check the tv_dicts for - -- legal instance-declaration form - ; let (tv_dicts, non_tv_dicts) = partition isTyVarDict irreds - ; addNoInstanceErrs non_tv_dicts - ; let rev_env = zipTopTvSubst tvs (mkTyVarTys tyvars) - simpl_theta = substTheta rev_env (map dictPred tv_dicts) + simpl_theta = substTheta rev_env (map dictPred irreds) -- This reverse-mapping is a pain, but the result -- should mention the original TyVars not TcTyVars + -- NB: the caller will further check the tv_dicts for + -- legal instance-declaration form + ; return simpl_theta } where doc = ptext SLIT("deriving classes for a data type") \end{code} -Note [Deriving context] -~~~~~~~~~~~~~~~~~~~~~~~ -With -fglasgow-exts, we allow things like (C Int a) in the simplified -context for a derived instance declaration, because at a use of this -instance, we might know that a=Bool, and have an instance for (C Int -Bool) - -We nevertheless insist that each predicate meets the termination -conditions. If not, the deriving mechanism generates larger and larger -constraints. Example: - data Succ a = S a - data Seq a = Cons a (Seq (Succ a)) | Nil deriving Show - -Note the lack of a Show instance for Succ. First we'll generate - instance (Show (Succ a), Show a) => Show (Seq a) -and then - instance (Show (Succ (Succ a)), Show (Succ a), Show a) => Show (Seq a) -and so on. Instead we want to complain of no instance for (Show (Succ a)). - @tcSimplifyDefault@ just checks class-type constraints, essentially; @@ -2636,6 +2650,10 @@ mkMonomorphismMsg tidy_env inst_tvs = findGlobals (mkVarSet inst_tvs) tidy_env `thenM` \ (tidy_env, docs) -> returnM (tidy_env, mk_msg docs) where + mk_msg _ | any isRuntimeUnk inst_tvs + = vcat [ptext SLIT("Cannot resolve unkonwn runtime types:") <+> + (pprWithCommas ppr inst_tvs), + ptext SLIT("Use :print or :force to determine these types")] mk_msg [] = ptext SLIT("Probable fix: add a type signature that fixes these type variable(s)") -- This happens in things like -- f x = show (read "foo") @@ -2644,6 +2662,11 @@ mkMonomorphismMsg tidy_env inst_tvs nest 2 (vcat docs), monomorphism_fix ] + +isRuntimeUnk :: TcTyVar -> Bool +isRuntimeUnk x | SkolemTv RuntimeUnkSkol <- tcTyVarDetails x = True + | otherwise = False + monomorphism_fix :: SDoc monomorphism_fix = ptext SLIT("Probable fix:") <+> (ptext SLIT("give these definition(s) an explicit type signature")