\section[TcMonoType]{Typechecking user-specified @MonoTypes@}
\begin{code}
-module TcMonoType ( tcHsType, tcHsRecType, tcIfaceType,
- tcHsSigType, tcHsLiftedSigType,
- tcRecTheta, checkAmbiguity,
+module TcMonoType ( tcHsSigType, tcHsType, tcIfaceType, tcHsTheta,
+ UserTypeCtxt(..),
-- Kind checking
kcHsTyVar, kcHsTyVars, mkTyClTyVars,
)
import TcMType ( newKindVar, tcInstSigVars,
zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar,
- unifyKind, unifyOpenTypeKind
+ unifyKind, unifyOpenTypeKind,
+ checkValidType, UserTypeCtxt(..), pprUserTypeCtxt
)
-import TcType ( Type, Kind, SourceType(..), ThetaType, SigmaType, TauType,
+import TcType ( Type, Kind, SourceType(..), ThetaType,
mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy,
tcSplitForAllTys, tcSplitRhoTy,
hoistForAllTys, allDistinctTyVars,
liftedTypeKind, unliftedTypeKind, mkArrowKind,
mkArrowKinds, tcGetTyVar_maybe, tcGetTyVar, tcSplitFunTy_maybe,
tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars,
- tyVarsOfType, tyVarsOfPred, mkForAllTys,
- isUnboxedTupleType, tcIsForAllTy, isIPPred
+ tyVarsOfType, mkForAllTys
)
import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId )
-import FunDeps ( grow )
-import PprType ( pprType, pprTheta, pprPred )
+import PprType ( pprType )
import Subst ( mkTopTyVarSubst, substTy )
import CoreFVs ( idFreeTyVars )
import Id ( mkLocalId, idName, idType )
import VarSet
import ErrUtils ( Message )
import TyCon ( TyCon, isSynTyCon, tyConArity, tyConKind )
-import Class ( classArity, classTyCon )
+import Class ( classTyCon )
import Name ( Name )
import TysWiredIn ( mkListTy, mkTupleTy, genUnitTyCon )
-import BasicTypes ( Boxity(..), RecFlag(..), isRec )
+import BasicTypes ( Boxity(..) )
import SrcLoc ( SrcLoc )
import Util ( mapAccumL, isSingleton )
import Outputable
%************************************************************************
%* *
+\subsection{Checking types}
+%* *
+%************************************************************************
+
+Generally speaking we now type-check types in three phases
+
+ 1. Kind check the HsType [kcHsType]
+ 2. Convert from HsType to Type, and hoist the foralls [tcHsType]
+ 3. Check the validity of the resultint type [checkValidType]
+
+Often these steps are done one after the othe (tcHsSigType).
+But in mutually recursive groups of type and class decls we do
+ 1 kind-check the whole group
+ 2 build TyCons/Classes in a knot-tied wa
+ 3 check the validity of types in the now-unknotted TyCons/Classes
+
+\begin{code}
+tcHsSigType :: UserTypeCtxt -> RenamedHsType -> TcM Type
+ -- Do kind checking, and hoist for-alls to the top
+tcHsSigType ctxt ty = tcAddErrCtxt (checkTypeCtxt ctxt ty) (
+ kcTypeType ty `thenTc_`
+ tcHsType ty
+ ) `thenTc` \ ty' ->
+ checkValidType ctxt ty' `thenTc_`
+ returnTc ty'
+
+checkTypeCtxt ctxt ty
+ = vcat [ptext SLIT("In the type:") <+> ppr ty,
+ ptext SLIT("While checking") <+> pprUserTypeCtxt ctxt ]
+
+tcHsType :: RenamedHsType -> TcM Type
+ -- Don't do kind checking, nor validity checking,
+ -- but do hoist for-alls to the top
+ -- This is used in type and class decls, where kinding is
+ -- done in advance, and validity checking is done later
+ -- [Validity checking done later because of knot-tying issues.]
+tcHsType ty = tc_type ty `thenTc` \ ty' ->
+ returnTc (hoistForAllTys ty')
+
+tcHsTheta :: RenamedContext -> TcM ThetaType
+-- Used when we are expecting a ClassContext (i.e. no implicit params)
+-- Does not do validity checking, like tcHsType
+tcHsTheta hs_theta = mapTc tc_pred hs_theta
+
+-- In interface files the type is already kinded,
+-- and we definitely don't want to hoist for-alls.
+-- Otherwise we'll change
+-- dmfail :: forall m:(*->*) Monad m => forall a:* => String -> m a
+-- into
+-- dmfail :: forall m:(*->*) a:* Monad m => String -> m a
+-- which definitely isn't right!
+tcIfaceType ty = tc_type ty
+\end{code}
+
+
+%************************************************************************
+%* *
\subsection{Kind checking}
%* *
%************************************************************************
%************************************************************************
%* *
-\subsection{Checking types}
-%* *
-%************************************************************************
-
-tcHsSigType and tcHsLiftedSigType
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-tcHsSigType and tcHsLiftedSigType are used for type signatures written by the programmer
-
- * We hoist any inner for-alls to the top
-
- * Notice that we kind-check first, because the type-check assumes
- that the kinds are already checked.
-
- * They are only called when there are no kind vars in the environment
- so the kind returned is indeed a Kind not a TcKind
-
-\begin{code}
-tcHsSigType, tcHsLiftedSigType :: RenamedHsType -> TcM Type
- -- Do kind checking, and hoist for-alls to the top
-tcHsSigType ty = kcTypeType ty `thenTc_` tcHsType ty
-tcHsLiftedSigType ty = kcLiftedType ty `thenTc_` tcHsType ty
-
-tcHsType :: RenamedHsType -> TcM Type
-tcHsRecType :: RecFlag -> RenamedHsType -> TcM Type
- -- Don't do kind checking, but do hoist for-alls to the top
- -- These are used in type and class decls, where kinding is
- -- done in advance
-tcHsType ty = tc_type NonRecursive ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty')
-tcHsRecType wimp_out ty = tc_type wimp_out ty `thenTc` \ ty' -> returnTc (hoistForAllTys ty')
-
--- In interface files the type is already kinded,
--- and we definitely don't want to hoist for-alls.
--- Otherwise we'll change
--- dmfail :: forall m:(*->*) Monad m => forall a:* => String -> m a
--- into
--- dmfail :: forall m:(*->*) a:* Monad m => String -> m a
--- which definitely isn't right!
-tcIfaceType ty = tc_type NonRecursive ty
-\end{code}
-
-
-%************************************************************************
-%* *
\subsection{tc_type}
%* *
%************************************************************************
tcHsType; if you poke on too much you get a black hole. I keep
forgetting this, hence this warning!
-The wimp_out argument tells when we are in a mutually-recursive
-group of type declarations, so omit various checks else we
-get a black hole. They'll be done again later, in TcTyClDecls.tcGroup.
+So tc_type does no validity-checking. Instead that's all done
+by TcMType.checkValidType
--------------------------
*** END OF BIG WARNING ***
\begin{code}
-tc_type :: RecFlag -> RenamedHsType -> TcM Type
+tc_type :: RenamedHsType -> TcM Type
-tc_type wimp_out ty@(HsTyVar name)
- = tc_app wimp_out ty []
+tc_type ty@(HsTyVar name)
+ = tc_app ty []
-tc_type wimp_out (HsListTy ty)
- = tc_arg_type wimp_out ty `thenTc` \ tau_ty ->
+tc_type (HsListTy ty)
+ = tc_type ty `thenTc` \ tau_ty ->
returnTc (mkListTy tau_ty)
-tc_type wimp_out (HsTupleTy (HsTupCon _ boxity arity) tys)
+tc_type (HsTupleTy (HsTupCon _ boxity arity) tys)
= ASSERT( arity == length tys )
- mapTc tc_tup_arg tys `thenTc` \ tau_tys ->
+ tc_types tys `thenTc` \ tau_tys ->
returnTc (mkTupleTy boxity arity tau_tys)
- where
- tc_tup_arg = case boxity of
- Boxed -> tc_arg_type wimp_out
- Unboxed -> tc_type wimp_out
- -- Unboxed tuples can have polymorphic or unboxed args.
- -- This happens in the workers for functions returning
- -- product types with polymorphic components
-
-tc_type wimp_out (HsFunTy ty1 ty2)
- = tc_type wimp_out ty1 `thenTc` \ tau_ty1 ->
- -- Function argument can be polymorphic, but
- -- must not be an unboxed tuple
- --
- -- In a recursive loop we can't ask whether the thing is
- -- unboxed -- might be a synonym inside a synonym inside a group
- checkTc (isRec wimp_out || not (isUnboxedTupleType tau_ty1))
- (ubxArgTyErr ty1) `thenTc_`
- tc_type wimp_out ty2 `thenTc` \ tau_ty2 ->
+
+tc_type (HsFunTy ty1 ty2)
+ = tc_type ty1 `thenTc` \ tau_ty1 ->
+ tc_type ty2 `thenTc` \ tau_ty2 ->
returnTc (mkFunTy tau_ty1 tau_ty2)
-tc_type wimp_out (HsNumTy n)
+tc_type (HsNumTy n)
= ASSERT(n== 1)
returnTc (mkTyConApp genUnitTyCon [])
-tc_type wimp_out (HsOpTy ty1 op ty2) =
- tc_arg_type wimp_out ty1 `thenTc` \ tau_ty1 ->
- tc_arg_type wimp_out ty2 `thenTc` \ tau_ty2 ->
- tc_fun_type op [tau_ty1,tau_ty2]
+tc_type (HsOpTy ty1 op ty2)
+ = tc_type ty1 `thenTc` \ tau_ty1 ->
+ tc_type ty2 `thenTc` \ tau_ty2 ->
+ tc_fun_type op [tau_ty1,tau_ty2]
-tc_type wimp_out (HsAppTy ty1 ty2)
- = tc_app wimp_out ty1 [ty2]
+tc_type (HsAppTy ty1 ty2) = tc_app ty1 [ty2]
-tc_type wimp_out (HsPredTy pred)
- = tc_pred wimp_out pred `thenTc` \ pred' ->
+tc_type (HsPredTy pred)
+ = tc_pred pred `thenTc` \ pred' ->
returnTc (mkPredTy pred')
-tc_type wimp_out full_ty@(HsForAllTy (Just tv_names) ctxt ty)
+tc_type full_ty@(HsForAllTy (Just tv_names) ctxt ty)
= let
kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
in
- tcHsTyVars tv_names kind_check $ \ tyvars ->
- tcRecTheta wimp_out ctxt `thenTc` \ theta ->
-
- -- Context behaves like a function type
- -- This matters. Return-unboxed-tuple analysis can
- -- give overloaded functions like
- -- f :: forall a. Num a => (# a->a, a->a #)
- -- And we want these to get through the type checker
- (if null theta then
- tc_arg_type wimp_out ty
- else
- tc_type wimp_out ty
- ) `thenTc` \ tau ->
-
- checkAmbiguity wimp_out is_source tyvars theta tau
- where
- is_source = case tv_names of
- (UserTyVar _ : _) -> True
- other -> False
-
-
- -- tc_arg_type checks that the argument of a
- -- type appplication isn't a for-all type or an unboxed tuple type
- -- For example, we want to reject things like:
- --
- -- instance Ord a => Ord (forall s. T s a)
- -- and
- -- g :: T s (forall b.b)
- --
- -- Other unboxed types are very occasionally allowed as type
- -- arguments depending on the kind of the type constructor
-
-tc_arg_type wimp_out arg_ty
- | isRec wimp_out
- = tc_type wimp_out arg_ty
+ tcHsTyVars tv_names kind_check $ \ tyvars ->
+ mapTc tc_pred ctxt `thenTc` \ theta ->
+ tc_type ty `thenTc` \ tau ->
+ returnTc (mkSigmaTy tyvars theta tau)
- | otherwise
- = tc_type wimp_out arg_ty `thenTc` \ arg_ty' ->
- checkTc (isRec wimp_out || not (tcIsForAllTy arg_ty')) (polyArgTyErr arg_ty) `thenTc_`
- checkTc (isRec wimp_out || not (isUnboxedTupleType arg_ty')) (ubxArgTyErr arg_ty) `thenTc_`
- returnTc arg_ty'
-
-tc_arg_types wimp_out arg_tys = mapTc (tc_arg_type wimp_out) arg_tys
+tc_types arg_tys = mapTc tc_type arg_tys
\end{code}
Help functions for type applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
-tc_app :: RecFlag -> RenamedHsType -> [RenamedHsType] -> TcM Type
-tc_app wimp_out (HsAppTy ty1 ty2) tys
- = tc_app wimp_out ty1 (ty2:tys)
+tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
+tc_app (HsAppTy ty1 ty2) tys
+ = tc_app ty1 (ty2:tys)
-tc_app wimp_out ty tys
+tc_app ty tys
= tcAddErrCtxt (appKindCtxt pp_app) $
- tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
+ tc_types tys `thenTc` \ arg_tys ->
case ty of
HsTyVar fun -> tc_fun_type fun arg_tys
- other -> tc_type wimp_out ty `thenTc` \ fun_ty ->
+ other -> tc_type ty `thenTc` \ fun_ty ->
returnNF_Tc (mkAppTys fun_ty arg_tys)
where
pp_app = ppr ty <+> sep (map pprParendHsType tys)
ATyVar tv -> returnTc (mkAppTys (mkTyVarTy tv) arg_tys)
AGlobal (ATyCon tc)
- | isSynTyCon tc -> checkTc arity_ok err_msg `thenTc_`
- returnTc (mkAppTys (mkSynTy tc (take arity arg_tys))
+ | isSynTyCon tc -> returnTc (mkAppTys (mkSynTy tc (take arity arg_tys))
(drop arity arg_tys))
-
- | otherwise -> returnTc (mkTyConApp tc arg_tys)
+ | otherwise -> returnTc (mkTyConApp tc arg_tys)
where
+ arity = tyConArity tc
- arity_ok = arity <= n_args
- arity = tyConArity tc
- -- It's OK to have an *over-applied* type synonym
- -- data Tree a b = ...
- -- type Foo a = Tree [a]
- -- f :: Foo a b -> ...
- err_msg = arityErr "Type synonym" name arity n_args
- n_args = length arg_tys
other -> failWithTc (wrongThingErr "type constructor" thing name)
\end{code}
Contexts
~~~~~~~~
\begin{code}
-tcRecTheta :: RecFlag -> RenamedContext -> TcM ThetaType
- -- Used when we are expecting a ClassContext (i.e. no implicit params)
-tcRecTheta wimp_out context = mapTc (tc_pred wimp_out) context
-
-tc_pred wimp_out assn@(HsClassP class_name tys)
+tc_pred assn@(HsClassP class_name tys)
= tcAddErrCtxt (appKindCtxt (ppr assn)) $
- tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
+ tc_types tys `thenTc` \ arg_tys ->
tcLookupGlobal class_name `thenTc` \ thing ->
case thing of
- AClass clas -> checkTc (arity == n_tys) err `thenTc_`
- returnTc (ClassP clas arg_tys)
- where
- arity = classArity clas
- n_tys = length tys
- err = arityErr "Class" class_name arity n_tys
+ AClass clas -> returnTc (ClassP clas arg_tys)
+ other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
- other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
-
-tc_pred wimp_out assn@(HsIParam name ty)
+tc_pred assn@(HsIParam name ty)
= tcAddErrCtxt (appKindCtxt (ppr assn)) $
- tc_arg_type wimp_out ty `thenTc` \ arg_ty ->
+ tc_type ty `thenTc` \ arg_ty ->
returnTc (IParam name arg_ty)
\end{code}
-Check for ambiguity
-~~~~~~~~~~~~~~~~~~~
- forall V. P => tau
-is ambiguous if P contains generic variables
-(i.e. one of the Vs) that are not mentioned in tau
-
-However, we need to take account of functional dependencies
-when we speak of 'mentioned in tau'. Example:
- class C a b | a -> b where ...
-Then the type
- forall x y. (C x y) => x
-is not ambiguous because x is mentioned and x determines y
-
-NOTE: In addition, GHC insists that at least one type variable
-in each constraint is in V. So we disallow a type like
- forall a. Eq b => b -> b
-even in a scope where b is in scope.
-This is the is_free test below.
-
-Notes on the 'is_source_polytype' test above
-Check ambiguity only for source-program types, not
-for types coming from inteface files. The latter can
-legitimately have ambiguous types. Example
- class S a where s :: a -> (Int,Int)
- instance S Char where s _ = (1,1)
- f:: S a => [a] -> Int -> (Int,Int)
- f (_::[a]) x = (a*x,b)
- where (a,b) = s (undefined::a)
-Here the worker for f gets the type
- fw :: forall a. S a => Int -> (# Int, Int #)
-
-If the list of tv_names is empty, we have a monotype,
-and then we don't need to check for ambiguity either,
-because the test can't fail (see is_ambig).
-
-\begin{code}
-checkAmbiguity :: RecFlag -> Bool
- -> [TyVar] -> ThetaType -> TauType
- -> TcM SigmaType
-checkAmbiguity wimp_out is_source_polytype forall_tyvars theta tau
- | isRec wimp_out = returnTc sigma_ty
- | otherwise = mapTc_ check_pred theta `thenTc_`
- returnTc sigma_ty
- where
- sigma_ty = mkSigmaTy forall_tyvars theta tau
- tau_vars = tyVarsOfType tau
- extended_tau_vars = grow theta tau_vars
-
- -- Hack alert. If there are no tyvars, (ppr sigma_ty) will print
- -- something strange like {Eq k} -> k -> k, because there is no
- -- ForAll at the top of the type. Since this is going to the user
- -- we want it to look like a proper Haskell type even then; hence the hack
- --
- -- This shows up in the complaint about
- -- case C a where
- -- op :: Eq a => a -> a
- ppr_sigma | null forall_tyvars = pprTheta theta <+> ptext SLIT("=>") <+> ppr tau
- | otherwise = ppr sigma_ty
-
- is_ambig ct_var = (ct_var `elem` forall_tyvars) &&
- not (ct_var `elemVarSet` extended_tau_vars)
- is_free ct_var = not (ct_var `elem` forall_tyvars)
-
- check_pred pred = checkTc (not any_ambig) (ambigErr pred ppr_sigma) `thenTc_`
- checkTc (isIPPred pred || not all_free) (freeErr pred ppr_sigma)
- where
- ct_vars = varSetElems (tyVarsOfPred pred)
- all_free = all is_free ct_vars
- any_ambig = is_source_polytype && any is_ambig ct_vars
-\end{code}
%************************************************************************
%* *
tcTySig (Sig v ty src_loc)
= tcAddSrcLoc src_loc $
- tcAddErrCtxt (tcsigCtxt v) $
- tcHsSigType ty `thenTc` \ sigma_tc_ty ->
+ tcHsSigType (FunSigCtxt v) ty `thenTc` \ sigma_tc_ty ->
mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
returnTc sig
%************************************************************************
\begin{code}
-tcsigCtxt v = ptext SLIT("In a type signature for") <+> quotes (ppr v)
-
typeKindCtxt :: RenamedHsType -> Message
typeKindCtxt ty = sep [ptext SLIT("When checking that"),
nest 2 (quotes (ppr ty)),
pp_thing (ATyVar _) = ptext SLIT("Type variable")
pp_thing (ATcId _) = ptext SLIT("Local identifier")
pp_thing (AThing _) = ptext SLIT("Utterly bogus")
-
-ambigErr pred ppr_ty
- = sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
- nest 4 (ptext SLIT("for the type:") <+> ppr_ty),
- nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
- ptext SLIT("must be reachable from the type after the =>"))]
-
-freeErr pred ppr_ty
- = sep [ptext SLIT("All of the type variables in the constraint") <+> quotes (pprPred pred) <+>
- ptext SLIT("are already in scope"),
- nest 4 (ptext SLIT("At least one must be universally quantified here")),
- ptext SLIT("In the type") <+> quotes ppr_ty
- ]
-
-polyArgTyErr ty = ptext SLIT("Illegal polymorphic type as argument:") <+> ppr ty
-ubxArgTyErr ty = ptext SLIT("Illegal unboxed tuple type as argument:") <+> ppr ty
\end{code}
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