\section[TcMonoType]{Typechecking user-specified @MonoTypes@}
\begin{code}
-module TcMonoType ( tcHsType, tcHsSigType, tcHsBoxedSigType,
- tcContext, tcClassContext,
+module TcMonoType ( tcHsType, tcHsRecType, tcIfaceType,
+ tcHsSigType, tcHsLiftedSigType,
+ tcRecTheta, checkAmbiguity,
-- Kind checking
kcHsTyVar, kcHsTyVars, mkTyClTyVars,
- kcHsType, kcHsSigType, kcHsBoxedSigType, kcHsContext,
- tcTyVars, tcHsTyVars, mkImmutTyVars,
+ kcHsType, kcHsSigType, kcHsSigTypes,
+ kcHsLiftedSigType, kcHsContext,
+ tcScopedTyVars, tcHsTyVars, mkImmutTyVars,
TcSigInfo(..), tcTySig, mkTcSig, maybeSig,
checkSigTyVars, sigCtxt, sigPatCtxt
import TcHsSyn ( TcId )
import TcMonad
-import TcEnv ( tcExtendTyVarEnv, tcExtendKindEnv,
- tcLookupGlobal, tcLookup,
- tcEnvTcIds, tcEnvTyVars,
- tcGetGlobalTyVars,
- TyThing(..), TcTyThing(..)
+import TcEnv ( tcExtendTyVarEnv, tcLookup, tcLookupGlobal,
+ tcGetGlobalTyVars, tcEnvTcIds, tcEnvTyVars,
+ TyThing(..), TcTyThing(..), tcExtendKindEnv
)
-import TcType ( TcType, TcKind, TcTyVar, TcThetaType, TcTauType,
- newKindVar, tcInstSigVar,
- zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar
+import TcMType ( newKindVar, tcInstSigVars,
+ zonkKindEnv, zonkTcType, zonkTcTyVars, zonkTcTyVar,
+ unifyKind, unifyOpenTypeKind
)
-import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToIdBndr,
- instFunDeps, instFunDepsOfTheta )
-import FunDeps ( tyVarFunDep, oclose )
-import TcUnify ( unifyKind, unifyOpenTypeKind )
-import Type ( Type, Kind, PredType(..), ThetaType,
+import TcType ( Type, Kind, SourceType(..), ThetaType, SigmaType, TauType,
mkTyVarTy, mkTyVarTys, mkFunTy, mkSynTy,
- zipFunTys, hoistForAllTys,
+ tcSplitForAllTys, tcSplitRhoTy,
+ hoistForAllTys, allDistinctTyVars,
+ zipFunTys,
mkSigmaTy, mkPredTy, mkTyConApp,
- mkAppTys, splitForAllTys, splitRhoTy, mkRhoTy,
- boxedTypeKind, unboxedTypeKind, mkArrowKind,
- mkArrowKinds, getTyVar_maybe, getTyVar, splitFunTy_maybe,
+ mkAppTys, mkRhoTy,
+ liftedTypeKind, unliftedTypeKind, mkArrowKind,
+ mkArrowKinds, tcGetTyVar_maybe, tcGetTyVar, tcSplitFunTy_maybe,
tidyOpenType, tidyOpenTypes, tidyTyVar, tidyTyVars,
tyVarsOfType, tyVarsOfPred, mkForAllTys,
- classesOfPreds,
+ isUnboxedTupleType, tcIsForAllTy, isIPPred
)
-import PprType ( pprType, pprPred )
+import Inst ( Inst, InstOrigin(..), newMethodWithGivenTy, instToId )
+import FunDeps ( grow )
+import PprType ( pprType, pprTheta, pprPred )
import Subst ( mkTopTyVarSubst, substTy )
-import Id ( Id, mkVanillaId, idName, idType, idFreeTyVars )
-import Var ( Var, TyVar, mkTyVar, tyVarKind )
+import CoreFVs ( idFreeTyVars )
+import Id ( mkLocalId, idName, idType )
+import Var ( Id, Var, TyVar, mkTyVar, tyVarKind )
import VarEnv
import VarSet
import ErrUtils ( Message )
import TyCon ( TyCon, isSynTyCon, tyConArity, tyConKind )
-import Class ( ClassContext, classArity, classTyCon )
+import Class ( classArity, classTyCon )
import Name ( Name )
import TysWiredIn ( mkListTy, mkTupleTy, genUnitTyCon )
-import UniqFM ( elemUFM )
-import BasicTypes ( Boxity(..) )
+import BasicTypes ( Boxity(..), RecFlag(..), isRec )
import SrcLoc ( SrcLoc )
import Util ( mapAccumL, isSingleton )
import Outputable
-import HscTypes ( TyThing(..) )
+
\end{code}
a::(*->*)-> *, b::*->*
\begin{code}
+-- tcHsTyVars is used for type variables in type signatures
+-- e.g. forall a. a->a
+-- They are immutable, because they scope only over the signature
+-- They may or may not be explicitly-kinded
tcHsTyVars :: [HsTyVarBndr Name]
-> TcM a -- The kind checker
-> ([TyVar] -> TcM b)
in
tcExtendTyVarEnv tyvars (thing_inside tyvars)
-tcTyVars :: [Name]
- -> TcM a -- The kind checker
- -> TcM [TyVar]
-tcTyVars [] kind_check = returnTc []
-
-tcTyVars tv_names kind_check
+-- tcScopedTyVars is used for scoped type variables
+-- e.g. \ (x::a) (y::a) -> x+y
+-- They never have explicit kinds (because this is source-code only)
+-- They are mutable (because they can get bound to a more specific type)
+tcScopedTyVars :: [Name]
+ -> TcM a -- The kind checker
+ -> TcM b
+ -> TcM b
+tcScopedTyVars [] kind_check thing_inside = thing_inside
+
+tcScopedTyVars tv_names kind_check thing_inside
= mapNF_Tc newNamedKindVar tv_names `thenTc` \ kind_env ->
tcExtendKindEnv kind_env kind_check `thenTc_`
zonkKindEnv kind_env `thenNF_Tc` \ tvs_w_kinds ->
- listNF_Tc [tcNewSigTyVar name kind | (name,kind) <- tvs_w_kinds]
+ listTc [tcNewMutTyVar name kind | (name, kind) <- tvs_w_kinds] `thenNF_Tc` \ tyvars ->
+ tcExtendTyVarEnv tyvars thing_inside
\end{code}
returnNF_Tc (name, kind)
---------------------------
-kcBoxedType :: RenamedHsType -> TcM ()
- -- The type ty must be a *boxed* *type*
-kcBoxedType ty
+kcLiftedType :: RenamedHsType -> TcM ()
+ -- The type ty must be a *lifted* *type*
+kcLiftedType ty
= kcHsType ty `thenTc` \ kind ->
tcAddErrCtxt (typeKindCtxt ty) $
- unifyKind boxedTypeKind kind
+ unifyKind liftedTypeKind kind
---------------------------
kcTypeType :: RenamedHsType -> TcM ()
- -- The type ty must be a *type*, but it can be boxed or unboxed.
+ -- The type ty must be a *type*, but it can be lifted or unlifted.
kcTypeType ty
= kcHsType ty `thenTc` \ kind ->
tcAddErrCtxt (typeKindCtxt ty) $
unifyOpenTypeKind kind
---------------------------
-kcHsSigType, kcHsBoxedSigType :: RenamedHsType -> TcM ()
+kcHsSigType, kcHsLiftedSigType :: RenamedHsType -> TcM ()
-- Used for type signatures
-kcHsSigType = kcTypeType
-kcHsBoxedSigType = kcBoxedType
+kcHsSigType = kcTypeType
+kcHsSigTypes tys = mapTc_ kcHsSigType tys
+kcHsLiftedSigType = kcLiftedType
---------------------------
kcHsType :: RenamedHsType -> TcM TcKind
kcHsType (HsTyVar name) = kcTyVar name
-kcHsType (HsUsgTy _ ty) = kcHsType ty
-kcHsType (HsUsgForAllTy _ ty) = kcHsType ty
kcHsType (HsListTy ty)
- = kcBoxedType ty `thenTc` \ tau_ty ->
- returnTc boxedTypeKind
-
-kcHsType (HsTupleTy (HsTupCon _ Boxed) tys)
- = mapTc kcBoxedType tys `thenTc_`
- returnTc boxedTypeKind
+ = kcLiftedType ty `thenTc` \ tau_ty ->
+ returnTc liftedTypeKind
-kcHsType ty@(HsTupleTy (HsTupCon _ Unboxed) tys)
- = failWithTc (unboxedTupleErr ty)
- -- Unboxed tuples are illegal everywhere except
- -- just after a function arrow (see kcFunResType)
+kcHsType (HsTupleTy (HsTupCon _ boxity _) tys)
+ = mapTc kcTypeType tys `thenTc_`
+ returnTc (case boxity of
+ Boxed -> liftedTypeKind
+ Unboxed -> unliftedTypeKind)
kcHsType (HsFunTy ty1 ty2)
= kcTypeType ty1 `thenTc_`
- kcFunResType ty2 `thenTc_`
- returnTc boxedTypeKind
+ kcTypeType ty2 `thenTc_`
+ returnTc liftedTypeKind
+
+kcHsType (HsNumTy _) -- The unit type for generics
+ = returnTc liftedTypeKind
kcHsType ty@(HsOpTy ty1 op ty2)
= kcTyVar op `thenTc` \ op_kind ->
kcHsType (HsPredTy pred)
= kcHsPred pred `thenTc_`
- returnTc boxedTypeKind
+ returnTc liftedTypeKind
kcHsType ty@(HsAppTy ty1 ty2)
= kcHsType ty1 `thenTc` \ tc_kind ->
= kcHsTyVars tv_names `thenNF_Tc` \ kind_env ->
tcExtendKindEnv kind_env $
kcHsContext context `thenTc_`
-
- -- 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 context then
- kcHsType ty
- else
- kcFunResType ty `thenTc_`
- returnTc boxedTypeKind
-
----------------------------
-kcFunResType :: RenamedHsType -> TcM TcKind
--- The only place an unboxed tuple type is allowed
--- is at the right hand end of an arrow
-kcFunResType (HsTupleTy (HsTupCon _ Unboxed) tys)
- = mapTc kcTypeType tys `thenTc_`
- returnTc unboxedTypeKind
-
-kcFunResType ty = kcHsType ty
+ kcHsType ty `thenTc_`
+ returnTc liftedTypeKind
---------------------------
kcAppKind fun_kind arg_kind
- = case splitFunTy_maybe fun_kind of
+ = case tcSplitFunTy_maybe fun_kind of
Just (arg_kind', res_kind)
-> unifyKind arg_kind arg_kind' `thenTc_`
returnTc res_kind
kcHsContext ctxt = mapTc_ kcHsPred ctxt
kcHsPred :: RenamedHsPred -> TcM ()
-kcHsPred pred@(HsPIParam name ty)
+kcHsPred pred@(HsIParam name ty)
= tcAddErrCtxt (appKindCtxt (ppr pred)) $
- kcBoxedType ty
+ kcLiftedType ty
-kcHsPred pred@(HsPClass cls tys)
+kcHsPred pred@(HsClassP cls tys)
= tcAddErrCtxt (appKindCtxt (ppr pred)) $
kcClass cls `thenTc` \ kind ->
mapTc kcHsType tys `thenTc` \ arg_kinds ->
- unifyKind kind (mkArrowKinds arg_kinds boxedTypeKind)
+ unifyKind kind (mkArrowKinds arg_kinds liftedTypeKind)
----------------------------
+ ---------------------------
kcTyVar name -- Could be a tyvar or a tycon
= tcLookup name `thenTc` \ thing ->
case thing of
%* *
%************************************************************************
-tcHsSigType and tcHsBoxedSigType
+tcHsSigType and tcHsLiftedSigType
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-tcHsSigType and tcHsBoxedSigType are used for type signatures written by the programmer
+tcHsSigType and tcHsLiftedSigType are used for type signatures written by the programmer
* We hoist any inner for-alls to the top
so the kind returned is indeed a Kind not a TcKind
\begin{code}
-tcHsSigType :: RenamedHsType -> TcM TcType
-tcHsSigType ty
- = kcTypeType ty `thenTc_`
- tcHsType ty `thenTc` \ ty' ->
- returnTc (hoistForAllTys ty')
-
-tcHsBoxedSigType :: RenamedHsType -> TcM Type
-tcHsBoxedSigType ty
- = kcBoxedType ty `thenTc_`
- tcHsType ty `thenTc` \ ty' ->
- returnTc (hoistForAllTys ty')
+tcHsSigType, tcHsLiftedSigType :: RenamedHsType -> TcM Type
+ -- Do kind checking, and hoist for-alls to the top
+tcHsSigType ty = traceTc (text "tcHsSig1:" <+> ppr ty) `thenTc_`
+ kcTypeType ty `thenTc_`
+ traceTc (text "tcHsSig2:" <+> ppr ty) `thenTc_`
+ tcHsType ty `thenTc` \ sig_ty ->
+ traceTc (text "tcHsSig3:" <+> ppr sig_ty) `thenTc_`
+ returnTc sig_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}
-tcHsType, the main work horse
+%************************************************************************
+%* *
+\subsection{tc_type}
+%* *
+%************************************************************************
+
+tc_type, the main work horse
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ -------------------
+ *** BIG WARNING ***
+ -------------------
+
+tc_type is used to typecheck the types in the RHS of data
+constructors. In the case of recursive data types, that means that
+the type constructors themselves are (partly) black holes. e.g.
+
+ data T a = MkT a [T a]
+
+While typechecking the [T a] on the RHS, T itself is not yet fully
+defined. That in turn places restrictions on what you can check in
+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.
+
+ --------------------------
+ *** END OF BIG WARNING ***
+ --------------------------
+
+
\begin{code}
-tcHsType :: RenamedHsType -> TcM Type
-tcHsType ty@(HsTyVar name)
- = tc_app ty []
+tc_type :: RecFlag -> RenamedHsType -> TcM Type
-tcHsType (HsListTy ty)
- = tcHsType ty `thenTc` \ tau_ty ->
- returnTc (mkListTy tau_ty)
+tc_type wimp_out ty@(HsTyVar name)
+ = tc_app wimp_out ty []
-tcHsType (HsTupleTy (HsTupCon _ boxity) tys)
- = mapTc tcHsType tys `thenTc` \ tau_tys ->
- returnTc (mkTupleTy boxity (length tys) tau_tys)
+tc_type wimp_out (HsListTy ty)
+ = tc_arg_type wimp_out ty `thenTc` \ tau_ty ->
+ returnTc (mkListTy tau_ty)
-tcHsType (HsFunTy ty1 ty2)
- = tcHsType ty1 `thenTc` \ tau_ty1 ->
- tcHsType ty2 `thenTc` \ tau_ty2 ->
+tc_type wimp_out (HsTupleTy (HsTupCon _ boxity arity) tys)
+ = ASSERT( arity == length tys )
+ mapTc tc_tup_arg 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 ->
returnTc (mkFunTy tau_ty1 tau_ty2)
-tcHsType (HsNumTy n)
+tc_type wimp_out (HsNumTy n)
= ASSERT(n== 1)
returnTc (mkTyConApp genUnitTyCon [])
-tcHsType (HsOpTy ty1 op ty2) =
- tcHsType ty1 `thenTc` \ tau_ty1 ->
- tcHsType ty2 `thenTc` \ tau_ty2 ->
+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]
-tcHsType (HsAppTy ty1 ty2)
- = tc_app ty1 [ty2]
+tc_type wimp_out (HsAppTy ty1 ty2)
+ = tc_app wimp_out ty1 [ty2]
-tcHsType (HsPredTy pred)
- = tcClassAssertion True pred `thenTc` \ pred' ->
+tc_type wimp_out (HsPredTy pred)
+ = tc_pred wimp_out pred `thenTc` \ pred' ->
returnTc (mkPredTy pred')
-tcHsType full_ty@(HsForAllTy (Just tv_names) ctxt ty)
+tc_type wimp_out full_ty@(HsForAllTy (Just tv_names) ctxt ty)
= let
- kind_check = kcHsContext ctxt `thenTc_` kcFunResType ty
+ kind_check = kcHsContext ctxt `thenTc_` kcHsType ty
in
- tcHsTyVars tv_names kind_check $ \ tyvars ->
- tcContext ctxt `thenTc` \ theta ->
- tcHsType ty `thenTc` \ tau ->
- checkAmbiguity full_ty tyvars theta tau `thenTc_`
- returnTc (mkSigmaTy tyvars theta tau)
-
- -- 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
+ 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:
--
- -- 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
+ -- instance Ord a => Ord (forall s. T s a)
+ -- and
+ -- g :: T s (forall b.b)
--
- -- 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.
-
-checkAmbiguity full_ty forall_tyvars theta tau
- = mapTc check_pred theta
- where
- tau_vars = tyVarsOfType tau
- fds = instFunDepsOfTheta theta
- tvFundep = tyVarFunDep fds
- extended_tau_vars = oclose tvFundep tau_vars
+ -- Other unboxed types are very occasionally allowed as type
+ -- arguments depending on the kind of the type constructor
- is_ambig ct_var = (ct_var `elem` forall_tyvars) &&
- not (ct_var `elemUFM` extended_tau_vars)
- is_free ct_var = not (ct_var `elem` forall_tyvars)
-
- check_pred pred = checkTc (not any_ambig) (ambigErr pred full_ty) `thenTc_`
- checkTc (not all_free) (freeErr pred full_ty)
- where
- ct_vars = varSetElems (tyVarsOfPred pred)
- all_free = all is_free ct_vars
- any_ambig = is_source_polytype && any is_ambig ct_vars
-
- -- 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).
- is_source_polytype
- = case full_ty of
- HsForAllTy (Just (UserTyVar _ : _)) _ _ -> True
- other -> False
+tc_arg_type wimp_out arg_ty
+ | isRec wimp_out
+ = tc_type wimp_out arg_ty
+
+ | 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
\end{code}
Help functions for type applications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin{code}
-tc_app :: RenamedHsType -> [RenamedHsType] -> TcM Type
-tc_app (HsAppTy ty1 ty2) tys
- = tc_app ty1 (ty2:tys)
+tc_app :: RecFlag -> RenamedHsType -> [RenamedHsType] -> TcM Type
+tc_app wimp_out (HsAppTy ty1 ty2) tys
+ = tc_app wimp_out ty1 (ty2:tys)
-tc_app ty tys
+tc_app wimp_out ty tys
= tcAddErrCtxt (appKindCtxt pp_app) $
- mapTc tcHsType tys `thenTc` \ arg_tys ->
+ tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
case ty of
HsTyVar fun -> tc_fun_type fun arg_tys
- other -> tcHsType ty `thenTc` \ fun_ty ->
+ other -> tc_type wimp_out ty `thenTc` \ fun_ty ->
returnNF_Tc (mkAppTys fun_ty arg_tys)
where
pp_app = ppr ty <+> sep (map pprParendHsType tys)
AGlobal (ATyCon tc)
| isSynTyCon tc -> checkTc arity_ok err_msg `thenTc_`
returnTc (mkAppTys (mkSynTy tc (take arity arg_tys))
- (drop arity arg_tys))
+ (drop arity arg_tys))
- | otherwise -> returnTc (mkTyConApp tc arg_tys)
+ | otherwise -> returnTc (mkTyConApp tc arg_tys)
where
arity_ok = arity <= n_args
Contexts
~~~~~~~~
\begin{code}
-tcClassContext :: RenamedContext -> TcM ClassContext
+tcRecTheta :: RecFlag -> RenamedContext -> TcM ThetaType
-- Used when we are expecting a ClassContext (i.e. no implicit params)
-tcClassContext context
- = tcContext context `thenTc` \ theta ->
- returnTc (classesOfPreds theta)
+tcRecTheta wimp_out context = mapTc (tc_pred wimp_out) context
-tcContext :: RenamedContext -> TcM ThetaType
-tcContext context = mapTc (tcClassAssertion False) context
-
-tcClassAssertion ccall_ok assn@(HsPClass class_name tys)
+tc_pred wimp_out assn@(HsClassP class_name tys)
= tcAddErrCtxt (appKindCtxt (ppr assn)) $
- mapTc tcHsType tys `thenTc` \ arg_tys ->
+ tc_arg_types wimp_out tys `thenTc` \ arg_tys ->
tcLookupGlobal class_name `thenTc` \ thing ->
case thing of
- AClass clas -> checkTc (arity == n_tys) err `thenTc_`
- returnTc (Class clas arg_tys)
+ AClass clas -> checkTc (arity == n_tys) err `thenTc_`
+ returnTc (ClassP clas arg_tys)
where
arity = classArity clas
n_tys = length tys
other -> failWithTc (wrongThingErr "class" (AGlobal thing) class_name)
-tcClassAssertion ccall_ok assn@(HsPIParam name ty)
+tc_pred wimp_out assn@(HsIParam name ty)
= tcAddErrCtxt (appKindCtxt (ppr assn)) $
- tcHsType ty `thenTc` \ arg_ty ->
+ tc_arg_type wimp_out 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}
+
%************************************************************************
%* *
\subsection{Type variables, with knot tying!}
= tcAddSrcLoc src_loc $
tcAddErrCtxt (tcsigCtxt v) $
tcHsSigType ty `thenTc` \ sigma_tc_ty ->
- mkTcSig (mkVanillaId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
+ mkTcSig (mkLocalId v sigma_tc_ty) src_loc `thenNF_Tc` \ sig ->
returnTc sig
mkTcSig :: TcId -> SrcLoc -> NF_TcM TcSigInfo
-- typechecking the rest of the program with the function bound
-- to a pristine type, namely sigma_tc_ty
let
- (tyvars, rho) = splitForAllTys (idType poly_id)
+ (tyvars, rho) = tcSplitForAllTys (idType poly_id)
in
- mapNF_Tc tcInstSigVar tyvars `thenNF_Tc` \ tyvars' ->
+ tcInstSigVars tyvars `thenNF_Tc` \ tyvars' ->
-- Make *signature* type variables
let
tyvar_tys' = mkTyVarTys tyvars'
rho' = substTy (mkTopTyVarSubst tyvars tyvar_tys') rho
-- mkTopTyVarSubst because the tyvars' are fresh
- (theta', tau') = splitRhoTy rho'
+
+ (theta', tau') = tcSplitRhoTy rho'
-- This splitRhoTy tries hard to make sure that tau' is a type synonym
-- wherever possible, which can improve interface files.
in
tyvar_tys'
theta' tau' `thenNF_Tc` \ inst ->
-- We make a Method even if it's not overloaded; no harm
- instFunDeps SignatureOrigin theta' `thenNF_Tc` \ fds ->
- returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToIdBndr inst) (inst : fds) src_loc)
+ returnNF_Tc (TySigInfo name poly_id tyvars' theta' tau' (instToId inst) [inst] src_loc)
where
name = idName poly_id
\end{code}
\begin{code}
checkSigTyVars :: [TcTyVar] -- Universally-quantified type variables in the signature
-> TcTyVarSet -- Tyvars that are free in the type signature
- -- These should *already* be in the global-var set, and are
- -- used here only to improve the error message
- -> TcM [TcTyVar] -- Zonked signature type variables
+ -- Not necessarily zonked
+ -- These should *already* be in the free-in-env set,
+ -- and are used here only to improve the error message
+ -> TcM [TcTyVar] -- Zonked signature type variables
checkSigTyVars [] free = returnTc []
-
checkSigTyVars sig_tyvars free_tyvars
= zonkTcTyVars sig_tyvars `thenNF_Tc` \ sig_tys ->
tcGetGlobalTyVars `thenNF_Tc` \ globals ->
- checkTcM (all_ok sig_tys globals)
+ checkTcM (allDistinctTyVars sig_tys globals)
(complain sig_tys globals) `thenTc_`
- returnTc (map (getTyVar "checkSigTyVars") sig_tys)
+ returnTc (map (tcGetTyVar "checkSigTyVars") sig_tys)
where
- all_ok [] acc = True
- all_ok (ty:tys) acc = case getTyVar_maybe ty of
- Nothing -> False -- Point (a)
- Just tv | tv `elemVarSet` acc -> False -- Point (b) or (c)
- | otherwise -> all_ok tys (acc `extendVarSet` tv)
-
-
complain sig_tys globals
= -- For the in-scope ones, zonk them and construct a map
-- from the zonked tyvar to the in-scope one
-- If any of the in-scope tyvars zonk to a type, then ignore them;
-- that'll be caught later when we back up to their type sig
- tcGetEnv `thenNF_Tc` \ env ->
- let
- in_scope_tvs = tcEnvTyVars env
- in
+ tcGetEnv `thenNF_Tc` \ env ->
+ let
+ in_scope_tvs = tcEnvTyVars env
+ in
zonkTcTyVars in_scope_tvs `thenNF_Tc` \ in_scope_tys ->
let
in_scope_assoc = [ (zonked_tv, in_scope_tv)
| (z_ty, in_scope_tv) <- in_scope_tys `zip` in_scope_tvs,
- Just zonked_tv <- [getTyVar_maybe z_ty]
+ Just zonked_tv <- [tcGetTyVar_maybe z_ty]
]
in_scope_env = mkVarEnv in_scope_assoc
in
-- ty is what you get if you zonk sig_tyvar and then tidy it
--
-- acc maps a zonked type variable back to a signature type variable
- = case getTyVar_maybe ty of {
+ = case tcGetTyVar_maybe ty of {
Nothing -> -- Error (a)!
- returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr ty) : msgs) ;
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (quotes (ppr ty)) : msgs) ;
Just tv ->
case lookupVarEnv acc tv of {
Just sig_tyvar' -> -- Error (b) or (d)!
- returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar (ppr sig_tyvar') : msgs) ;
+ returnNF_Tc (tidy_env, acc, unify_msg sig_tyvar thing : msgs)
+ where
+ thing = ptext SLIT("another quantified type variable") <+> quotes (ppr sig_tyvar')
- Nothing ->
+ ; Nothing ->
if tv `elemVarSet` globals -- Error (c)! Type variable escapes
-- The least comprehensible, so put it last
-- a) get the local TcIds from the environment,
-- and pass them to find_globals (they might have tv free)
-- b) similarly, find any free_tyvars that mention tv
- then tcGetEnv `thenNF_Tc` \ tc_env ->
- find_globals tv tidy_env [] (tcEnvTcIds tc_env) `thenNF_Tc` \ (tidy_env1, globs) ->
+ then tcGetEnv `thenNF_Tc` \ ve ->
+ find_globals tv tidy_env [] (tcEnvTcIds ve) `thenNF_Tc` \ (tidy_env1, globs) ->
find_frees tv tidy_env1 [] (varSetElems free_tyvars) `thenNF_Tc` \ (tidy_env2, frees) ->
returnNF_Tc (tidy_env2, acc, escape_msg sig_tyvar tv globs frees : msgs)
vcat_first 0 (x:xs) = text "...others omitted..."
vcat_first n (x:xs) = x $$ vcat_first (n-1) xs
-unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> quotes thing
+unify_msg tv thing = mk_msg tv <+> ptext SLIT("is unified with") <+> thing
mk_msg tv = ptext SLIT("Quantified type variable") <+> quotes (ppr tv)
\end{code}
pp_thing (ATcId _) = ptext SLIT("Local identifier")
pp_thing (AThing _) = ptext SLIT("Utterly bogus")
-ambigErr pred ty
+ambigErr pred ppr_ty
= sep [ptext SLIT("Ambiguous constraint") <+> quotes (pprPred pred),
- nest 4 (ptext SLIT("for the type:") <+> ppr ty),
- nest 4 (ptext SLIT("Each forall'd type variable mentioned by the constraint must appear after the =>"))]
-
-freeErr pred ty
- = sep [ptext SLIT("The constraint") <+> quotes (pprPred pred) <+>
- ptext SLIT("does not mention any of the universally quantified type variables"),
- nest 4 (ptext SLIT("in the type") <+> quotes (ppr ty))
+ nest 4 (ptext SLIT("for the type:") <+> ppr_ty),
+ nest 4 (ptext SLIT("At least one of the forall'd type variables mentioned by the constraint") $$
+ 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
]
-unboxedTupleErr ty
- = sep [ptext (SLIT("Illegal unboxed tuple as a function or contructor argument:")), nest 4 (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}
projects / ghc-hetmet.git / blobdiff